7
Disposal of Waste

   

7.A INTRODUCTION

 

141

   

7.B CHEMICALLY HAZARDOUS WASTE

 

141

   

7.B.1 Characterization of Waste

 

141

   

7.B.2 Regulated Chemically Hazardous Waste

 

143

   

7.B.2.1 Definition of Characteristic Waste

 

144

   

7.B.2.2 Definition of Listed Waste

 

144

   

7.B.2.3 Determining the Status of a Waste

 

145

   

7.B.3 Collection and Storage of Waste

 

145

   

7.B.3.1 At the Location of Generation

 

145

   

7.B.3.2 At a Central Accumulation Area

 

145

   

7.B.4 Records

 

146

   

7.B.5 Hazard Reduction

 

146

   

7.B.6 Disposal Options

 

147

   

7.B.6.1 Incineration

 

147

   

7.B.6.2 Disposal in the Normal Trash

 

148

   

7.B.6.3 Disposal in the Sanitary Sewer

 

148

   

7.B.6.4 Release to the Atmosphere

 

148

   

7.B.7 Disposal of Nonhazardous and Nonregulated Waste

 

148

   

7.B.8 Disposal of Spills

 

149

   

7.B.9 Monitoring of Off-site Waste Disposal

 

149

   

7.B.9.1 Preparation for Off-site Disposal

 

150

   

7.B.9.2 Choice of Transporter and Disposal Facility

 

150

   

7.C MULTIHAZARDOUS WASTE

 

150

   

7.C.1 Chemical-Radioactive (Mixed) Waste

 

152

   

7.C.1.1 Minimization of Mixed Waste

 

153

   

7.C.1.2 Safe Storage of Mixed Waste

 

154

   

7.C.1.3 Hazard Reduction of Mixed Waste

 

154

   

7.C.1.4 Commercial Disposal Services for Mixed Waste

 

155

   

7.C.2 Chemical-Biological Waste

 

155

   

7.C.2.1 Disposal of Chemically Contaminated Animal Tissue

 

156

   

7.C.2.2 Sewer Disposal of Chemical-Biological Liquids

 

156

   

7.C.2.3 Disinfection and Autoclaving of Contaminated Labware

 

156

   

7.C.2.4 Disposal of Chemically Contaminated Medical Waste and Sharps

 

157

   

7.C.2.5 Minimization Methods for Chemical-Biological Waste

 

157

   

7.C.3 Radioactive-Biological Waste

 

157

   

7.C.3.1 On-site Incineration of Low-level Radioactive Waste

 

158

   

7.C.3.2 Off-site Management of Low-level Radioactive Waste

 

158

   

7.C.3.3 Disposal of Radioactive Animal Carcasses and Tissue

 

158

   

7.C.3.4 Disposal of Radioactive-Biological Contaminated Labware

 

158

   

7.C.3.5 Sewer Disposal of Radioactive-Biological Liquids

 

159



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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 7 Disposal of Waste     7.A INTRODUCTION   141     7.B CHEMICALLY HAZARDOUS WASTE   141     7.B.1 Characterization of Waste   141     7.B.2 Regulated Chemically Hazardous Waste   143     7.B.2.1 Definition of Characteristic Waste   144     7.B.2.2 Definition of Listed Waste   144     7.B.2.3 Determining the Status of a Waste   145     7.B.3 Collection and Storage of Waste   145     7.B.3.1 At the Location of Generation   145     7.B.3.2 At a Central Accumulation Area   145     7.B.4 Records   146     7.B.5 Hazard Reduction   146     7.B.6 Disposal Options   147     7.B.6.1 Incineration   147     7.B.6.2 Disposal in the Normal Trash   148     7.B.6.3 Disposal in the Sanitary Sewer   148     7.B.6.4 Release to the Atmosphere   148     7.B.7 Disposal of Nonhazardous and Nonregulated Waste   148     7.B.8 Disposal of Spills   149     7.B.9 Monitoring of Off-site Waste Disposal   149     7.B.9.1 Preparation for Off-site Disposal   150     7.B.9.2 Choice of Transporter and Disposal Facility   150     7.C MULTIHAZARDOUS WASTE   150     7.C.1 Chemical-Radioactive (Mixed) Waste   152     7.C.1.1 Minimization of Mixed Waste   153     7.C.1.2 Safe Storage of Mixed Waste   154     7.C.1.3 Hazard Reduction of Mixed Waste   154     7.C.1.4 Commercial Disposal Services for Mixed Waste   155     7.C.2 Chemical-Biological Waste   155     7.C.2.1 Disposal of Chemically Contaminated Animal Tissue   156     7.C.2.2 Sewer Disposal of Chemical-Biological Liquids   156     7.C.2.3 Disinfection and Autoclaving of Contaminated Labware   156     7.C.2.4 Disposal of Chemically Contaminated Medical Waste and Sharps   157     7.C.2.5 Minimization Methods for Chemical-Biological Waste   157     7.C.3 Radioactive-Biological Waste   157     7.C.3.1 On-site Incineration of Low-level Radioactive Waste   158     7.C.3.2 Off-site Management of Low-level Radioactive Waste   158     7.C.3.3 Disposal of Radioactive Animal Carcasses and Tissue   158     7.C.3.4 Disposal of Radioactive-Biological Contaminated Labware   158     7.C.3.5 Sewer Disposal of Radioactive-Biological Liquids   159

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals     7.C.4 Chemical-Radioactive-Biological Waste   159     7.C.5 Future Trends in Management of Multihazardous Waste   159     7.D PROCEDURES FOR THE LABORATORY-SCALE TREATMENT OF SURPLUS AND WASTE CHEMICALS   160     7.D.1 Acids and Bases   160     7.D.2 Organic Chemicals   161     7.D.2.1 Thiols and Sulfides   161     7.D.2.2 Acyl Halides and Anhydrides   161     7.D.2.3 Aldehydes   162     7.D.2.4 Amines   162     7.D.2.5 Organic Peroxides and Hydroperoxides   162     7.D.3 Inorganic Chemicals   163     7.D.3.1 Metal Hydrides   163     7.D.3.2 Inorganic Cyanides   164     7.D.3.3 Metal Azides   165     7.D.3.4 Alkali Metals   165     7.D.3.5 Metal Catalysts   165     7.D.3.6 Water-Reactive Metal Halides   165     7.D.3.7 Halides and Acid Halides of Nonmetals   166     7.D.3.8 Inorganic Ions   166     7.D.3.8.1 Chemicals in Which Neither the Cation Nor the Anion Presents a Significant Hazard   166     7.D.3.8.2 Precipitation of Cations as Their Hydroxides   166     7.D.3.8.3 Chemicals in Which the Cation Presents a Relatively High Hazard from Toxicity   167     7.D.3.8.4 Chemicals in Which an Anion Presents a Relatively High Hazard   170     7.D.3.8.5 Procedure for Reduction of Oxidizing Salts   170

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals 7.A INTRODUCTION Within the broad theme of pollution prevention, earlier chapters of this book consider various management strategies to reduce the formation of waste during laboratory operations. These include reducing the scale of laboratory operations, cataloging and reusing excess materials, and recycling chemicals that can be recovered safely. Clearly, the best approach to laboratory waste is to not generate it. However, this ideal situation is seldom attained in the laboratory. Therefore, this chapter considers methods for dealing with the waste that is generated during laboratory operations and for accomplishing its ultimate disposal. The earlier chapters are directed primarily at enhancing the safety of laboratory workers and visitors and focus on the laboratory environment. However, discussing prudent practices for disposal of waste requires a broader perspective. When waste is eventually removed from the laboratory, it affects individuals other than those who acquired or generated it, and, ultimately, society as a whole. Waste is disposed of by three routes: (1) into the atmosphere, either through evaporation or through the volatile effluent from incineration; (2) into rivers and oceans via the sewer system and wastewater treatment facilities; and (3) into landfills. Occasionally, waste has to be held indefinitely at the laboratory site or elsewhere until acceptable modes of disposal are developed. The laboratory worker who generates waste has an obligation to consider the ultimate fate of the materials resulting from his or her work. The high cost of disposal of many materials, the potential hazards to people outside the laboratory, and the impact on the environment are all important factors to be considered. Because of the potential adverse impact on the public through pollution of the air, water, or land, society invariably regulates waste disposal. Disposal of household waste is usually regulated by municipalities, while hazardous waste disposal is regulated at the federal level and often also by states and municipalities. The focus in this chapter is on the disposal of waste that may present chemical hazards, as well as those multihazardous wastes that contain some combination of chemical, radioactive, and biological hazards. Many of the disposal solutions outlined in this chapter have been designed to take advantage of the fact that there is a normal stream of nonhazardous waste generated in the laboratory and other parts of the institution. In some instances, waste that is classified as hazardous can be modified to permit disposal as nonhazardous waste, which is usually a less expensive and less cumbersome undertaking. The scientist who generates hazardous waste must make decisions consistent with the institutional framework for handling such materials. Generally, waste is defined as surplus, unneeded, or unwanted material. It is usually the laboratory worker or supervisor who decides whether to declare a given laboratory material a waste. However, specific regulatory definitions must be taken into account as well. Even the question of when an unwanted or excess material becomes a waste involves some regulatory considerations. Whereas some institutions have created glossaries of terms to label waste materials as co-products or surplus reagents, regulations state that a material may be declared a waste if it is ''abandoned" or is considered "inherently wastelike." Spilled materials, for example, often fall into these latter categories. Therefore, it is not necessarily up to the generator to decide whether or not a material is a waste. Once material becomes a waste by a generator's decision or by regulatory definition, the first responsibility for its proper disposal rests with the laboratory worker. These experimentalists are in the best position to know the characteristics of the materials they have used or synthesized. It is their responsibility to evaluate the hazards and assess the risks associated with the waste and to choose an appropriate strategy to handle, minimize, or dispose of it. As discussed earlier in this volume (see Chapter 3, section 3.B), there are numerous sources of information available to the laboratory worker to guide in the decision making, including those required under various Occupational Safety and Health Administration (OSHA) regulations. 7.B CHEMICALLY HAZARDOUS WASTE 7.B.1 Characterization of Waste Because proper disposal requires information about the properties of the waste, it is recommended that all chemicals used or generated be identified clearly. In general, they must be retained in clearly marked containers, and if they have been generated within the laboratory, their source must be defined clearly on the container and ideally in some type of readily available notebook record. In academic laboratories where student turnover is frequent, it is particularly important that the materials used or generated be identified. This practice can be as important for small quantities as it is for large quantities of material. It is usually quite simple to establish the hazardous characteristics of clearly identified waste. Unidentified materials present a problem, however, because treatment disposal facilities are prohibited from accepting materials whose hazards are not known. In those cases when the identity of the material is not known, it is possible to carry out simple tests to determine the hazard class into which the material should be categorized. Because the generator may be able to apply some gen-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals eral information, it is usually advisable to carry out the hazard categorization process before the materials are removed from the laboratory. Having the analysis done at the laboratory is also usually cheaper than having it performed by the treatment disposal facility or an outside contractor. Generally, it is not necessary to determine the molecular structure of the unknown material precisely. Hazard classification information usually satisfies the regulatory requirements and those of the treatment disposal facility. However, it is important to establish that the disposal facility will accept the analytical data that are ultimately provided. The first concern in identification of an unknown waste is safety. The laboratory worker who carries out the procedures should be familiar with the characteristics of the waste and any necessary precautions. Because the hazards of the materials being tested are unknown, it is imperative that proper personal protection and safety devices such as fume hoods and shields be employed. Older samples can be particularly dangerous because they may have changed in composition, for example, through the formation of peroxides. (See Chapter 3, section 3.D.3.2, and Chapter 5, section 5.G.3, for more information on peroxides.) The following information is commonly required by treatment disposal facilities before they will consider handling unknown materials: physical description, water reactivity, water solubility, pH and possibly also neutralization information, ignitability (flammability), presence of oxidizer, presence of sulfides or cyanides, presence of halogens, presence of radioactive materials, presence of biohazardous materials, and presence of toxic constituents. The following test procedures should be readily accomplished by a trained laboratory worker. The overall sequence for testing is depicted in Figure 7.1 for liquid and solid materials. Physical description. The physical description should include the state of the material (solid, liquid), the color, and the consistency (for solids) or viscosity (for liquids). For liquid materials, describe the clarity of the solution (transparent, translucent, or opaque). If an unknown material is a bi- or tri-layered liquid, describe each layer separately, giving an approximate percentage of the total for each layer. After taking appropriate safety precautions for handling the unknown, including the use of personal protection devices, remove a small sample for use in the following tests. Water reactivity. Carefully add a small quantity of the unknown to a few milliliters of water. Observe any changes, including heat evolution, gas evolution, and flame generation. Water solubility. Observe the solubility of the unknown in water. If it is an insoluble liquid, note whether it is less or more dense than water (i.e., does it float or sink?). Most nonhalogenated organic liquids are less dense than water. pH. Test the material with multirange pH paper. If the sample is water-soluble, test the pH of a 10% aqueous solution. It may also be desirable or even required to carry out a neutralization titration. Ignitability (flammability). Place a small sample of the material (<5 milliliters (mL)) in an aluminum test tray. Apply an ignition source, typically a propane torch, to the test sample for one-half second. If the material supports its own combustion, it is a flammable liquid with a flash point of less than 60 °C. If the sample does not ignite, apply the ignition source again for one second. If the material burns, it is combustible. Combustible materials have a flash point between 60 and 93 °C. Presence of oxidizer. Wet commercially available starch-iodide paper with 1 N hydrochloric acid, and then place a small portion of the unknown on the wetted paper. A change in color of the paper to dark purple is a positive test for an oxidizer. The test can also be carried out by adding 0.1 to 0.2 grams (g) of sodium or potassium iodide to 1 mL of an acidic 10% solution of the unknown. Development of a yellow-brown color indicates an oxidizer. To test for hydroperoxides in water-insoluble organic solvents, dip the test paper into the solvent, and then let it evaporate. Add a drop of water to the same section of the paper. Development of a dark color indicates the presence of hydroperoxides. Presence of sulfide. The test for inorganic sulfides is carried out only when the pH of an aqueous solution of the unknown is greater than 10. Add a few drops of concentrated hydrochloric acid to a sample of the unknown while holding a piece of commercial lead acetate paper, wetted with distilled water, over the sample. Development of a brown-black color on the paper indicates generation of hydrogen sulfide. Because of the toxicity of the hydrogen sulfide formed during this test, only a small sample should be tested, and appropriate ventilation should be used. Presence of cyanide. The test for inorganic cyanides is carried out only when the pH of an aqueous solution of the unknown is greater than 10. Prior to testing for

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals FIGURE 7.1 Flow chart for categorizing unknown chemicals. This decision tree shows the sequence of tests that may need to be performed to determine the appropriate hazard category of an unknown chemical. DWW, dangerous when wet; nos, not otherwise specified. cyanides, the following stock solutions should be prepared: 10% aqueous sodium hydroxide (solution A), 10% aqueous ferrous sulfate (solution B), and 5% ferric chloride (solution C). Mix 2 mL of the sample with 1 mL of distilled water and 1 mL each of solutions A, B, and C. Add enough concentrated sulfuric acid to make the solution acidic. Development of a blue color (Prussian blue, from ferric ferrocyanide) indicates cyanide. Because of the toxicity of the hydrogen cyanide formed during this test, only a small sample should be tested, and appropriate ventilation should be used. Presence of halogen. Heat a piece of copper wire until red in a flame. Cool the wire in distilled or deionized water, and then dip the wire into the unknown. Again heat the wire in the flame. The presence of halogen is indicated by a green color around the wire in the flame. 7.B.2 Regulated Chemically Hazardous Waste An important question for planning within the laboratory is whether or not a waste is regulated as hazardous, because regulated hazardous waste must be handled and disposed of in rather specific ways. This determination has very important regulatory implications, which can lead to significant differences in disposal cost. The Environmental Protection Agency

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals (EPA) defines chemically hazardous waste under the Resource Conservation and Recovery Act (RCRA), and the U.S. Nuclear Regulatory Commission (U.S. NRC) defines radioactivity hazards. Biological hazards are generally not defined within federal regulations. Although we must consider and pay close attention to the regulatory definitions and procedures that govern the handling and disposal of waste, primary importance must be given to the safe and prudent handling of this material. It is important to remember that the danger associated with a specific hazardous waste depends not only on the composition of the waste, but also on its quantity. In fact, regulations recognize quantity in many of their definitions for hazard compliance as well as in the definitions of waste generators. The concept of de minimis quantities, that is, very small amounts of material, though not defined clearly, is also a consideration in determining hazardous waste risk. Enlightened risk management dictates that the amount of material be one factor in the decisions on handling and disposal of waste. Waste that is regulated as hazardous because of its chemical properties is defined by EPA in two ways: (1) waste that has certain hazardous characteristics and (2) waste that is on certain lists of chemicals. The first category is based on properties of materials that should be familiar to every laboratory worker. The second category is based on lists, established by EPA and certain states, of certain chemicals common to industry. These lists generally include materials that are widely used and recognized as hazardous. Chemicals are placed on these RCRA lists primarily on the basis of their toxicity. (To determine if waste is hazardous or not, see Chapter 9, section 9.D.2.) Regardless of the regulatory definitions of hazard, understanding chemical characteristics that pose potential hazards should be a fundamental part of the education and training of any laboratory worker. These characteristics may be derived from knowledge of the properties and/or precursors of the waste. The characteristics may also be established by specific tests cited in the regulations. (Regulatory issues, specifically RCRA, are discussed further in Chapter 9, section 9.D.) 7.B.2.1 Definition of Characteristic Waste The properties that pose potential hazards are as follows: Ignitability. Ignitable materials are defined as having one or more of the following characteristics: Liquids that have a flash point of less than 60 °C or some other characteristic that has the potential to cause fire. Materials other than liquids that are capable, under standard temperature and pressure, of causing fire by friction, adsorption of moisture, or spontaneous chemical changes and, when ignited, burn so vigorously and persistently as to create a hazard. Flammable compressed gases, including those that form flammable mixtures. Oxidizers that stimulate combustion of organic materials. Ignitable materials include most common organic solvents, gases such as hydrogen and hydrocarbons, and certain nitrate salts. Corrosivity. Corrosive liquids have a pH of 2 or less or 12.5 or greater or lead to corrosion of certain grades of steel. Most common laboratory acids and bases are corrosive. Solid corrosives, such as sodium hydroxide pellets and powders, are not legally considered by RCRA to be corrosive. However, laboratory workers must recognize that such materials can be extremely dangerous to skin and eyes and must be handled accordingly. Reactivity. The reactivity classification includes substances that are unstable, react violently with water, are capable of detonation if exposed to some initiating source, or produce toxic gases. Alkali metals, peroxides and compounds that have peroxidized, and cyanide or sulfide compounds are classed as reactive. Toxicity. Toxicity is established through the Toxicity Characteristic Leaching Procedure (TCLP), which measures the tendency of certain toxic materials to be leached (extracted) from the waste material under circumstances assumed to reproduce conditions of a landfill. The TCLP list includes a relatively small number of industrially important toxic chemicals and is based on the concentration above which a waste is considered hazardous. Failure to pass the TCLP results in classification of a material as a toxic waste. 7.B.2.2 Definition of Listed Waste Although EPA has developed several lists of hazardous waste, three regulatory lists are of most interest to laboratory workers: the F list: waste from nonspecific sources (e.g., spent solvents and process or reaction waste), the U list: hazardous waste (e.g., toxic laboratory chemicals), and the P list: acutely hazardous waste (e.g., highly

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals toxic laboratory chemicals, that is, chemicals having an LD50 of less than 50 mg/kg (oral; rat)). These lists may be updated periodically by EPA. 7.B.2.3 Determining the Status of a Waste The EPA regulations place on the waste generator the burden of determining whether the waste is regulated as hazardous and in what hazard classification it falls. Testing is not necessarily required, and in most cases the laboratory worker should be able to provide sufficient information about the waste to allow the hazard classification to be assigned. If the waste is not a common chemical with known characteristics, enough information about it must be supplied to satisfy the regulatory requirements and to ensure that it can be handled and disposed of safely. Often, information on only the components present in amounts greater than 1% is required, but confirmation is needed from the treatment/disposal facility. The information needed to characterize a waste also depends on the method of ultimate disposal. (See the discussion of disposal methods in sections 7.B.6 to 7.B.8 below.) 7.B.3 Collection and Storage of Waste 7.B.3.1 At the Location of Generation The first step in the disposal sequence usually involves the accumulation and temporary storage of waste in or near the laboratory (satellite accumulation). This step directly involves the laboratory workers who are familiar with the waste and its generation and is a most important part of ensuring that the disposal process proceeds safely and efficiently. It is often the time at which a decision can be made to recycle or reuse surplus materials rather than sending them for disposal. All of the costs and benefits of either decision should be evaluated here. Again, safety considerations must be of primary concern. Waste should be stored in clearly labeled containers in a designated location that does not interfere with normal laboratory operations. Ventilated storage may be appropriate. Federal regulations allow the indefinite accumulation of up to 55 gallons of hazardous waste or 1 quart of acutely hazardous waste at or near the point of generation. However, prudence dictates that the quantities accumulated should be consistent with good safety practices. Furthermore, satellite accumulation time must be consistent with the stability of the material. It is generally recommended that waste not be held for more than 1 year. Within 3 days of the time that the amount of waste exceeds the 55-gallon (or 1 quart) limit, it must be managed under the storage and accumulation time limits required at a central accumulation area. (See Chapter 9, section 9.D.4, for more information.) Often, different kinds of waste can be accumulated within a common container. Such commingled waste must be chemically compatible to ensure that heat generation, gas evolution, or another reaction does not occur. (See the discussion of commingling in section 7.B.3.2 below.) Packaging and labeling are a key part of this initial in-laboratory operation. Waste must be collected in dependable containers that are compatible with their contents. Glass containers have traditionally been the most resistant to chemical action, but they can break easily. Metal containers are sturdier than glass, but often are corroded by their contents. Various chemically resistant plastic containers are becoming preferable substitutes for containers of glass or metal. Safety cans, metal or plastic, should be considered for holding flammable solvents. It is advisable to use secondary containers, such as trays, in case of spills or leakage from the primary containers. Containers are required to remain closed except when their contents are being transferred. Containers of incompatible materials should be separated physically or otherwise stored in a protective manner. Every container must be labeled with the material's identity and its hazard (e.g., flammable, corrosive). Although the identity need not be a complete listing of all chemical constituents, it should enable knowledgeable laboratory workers to evaluate the hazard. However, when compatible wastes are collected in a common container, it is advisable to keep a list of the components to aid in later disposal decisions. Labeling must be clear and permanent. Although federal regulations do not require posting the date when satellite accumulation begins, some states do require this. The institution may suggest that this information be recorded as part of its chemicals management plan. 7.B.3.2 At a Central Accumulation Area The central accumulation area is an important component in the organization's chemicals management plan. In addition to being the primary location where waste management occurs, it may also be the location where excess chemicals are held for possible redistribution. Along with the laboratory, the central accumulation area is often where hazard reduction of waste takes place through allowable on-site treatment processes. The central accumulation area is often the appro-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals priate place to accomplish considerable cost savings by commingling (i.e., mixing) waste materials. This is the process where compatible wastes from various sources are combined prior to disposal. Commingling is particularly suitable for waste solvents because disposal of liquid in a 55-gallon drum is generally much less expensive than disposal of the same volume of liquid in small containers. Because mixing waste requires transfer of waste between containers, it is imperative that the identity of all materials be known and their compatibility be understood. Safety in carrying out the procedures, including the use of personal protective devices as well as engineering controls such as fume hoods, must be of high priority. In some cases, the disposal method and ultimate fate of the waste may require that different wastes not be accumulated together. For example, if commingled waste contains significant amounts of halogenated solvents (usually above 1%), disposing of the mixture can be markedly more costly. In such cases, segregation of halogenated and nonhalogenated solvents is economically favorable. Based on federal regulations, storage at a central accumulation area is normally limited to 90 days, although more time is allowed for small-quantity generators or other special situations (180 or 270 days). The count begins when the waste is brought to the central accumulation area from the laboratory or satellite accumulation area. It is important to know that a special permit is required for long-term storage, that is, storage beyond the limit of 90 days (or 180 or 270 days, depending on the particular situation). Obtaining such a permit is usually too expensive and too time-consuming for most laboratory operations. (See RCRA and Chapter 9, section 9.D.4, for more information.) Waste materials stored within a central accumulation area should be held in appropriate and clearly labeled containers, separated according to chemical compatibility as noted in the previous section. The label must include the accumulation start date and the words "Hazardous Waste." Fire suppression systems, ventilation, and dikes to avoid sewer contamination in case of a spill should be considered when such a facility is planned. Training of employees in correct handling of the materials as well as contingency planning for emergencies is expected to be a part of the central accumulation area operations. Transportation of waste between laboratories (satellite accumulation areas) and the central accumulation area also requires specific attention to safety. Materials transported must be held within appropriate and clearly labeled containers. There must be provision for spill control in case of an accident during transportation and handling. For larger institutions, it is advisable to have some kind of internal tracking system to follow the movement of waste. If public roads are used during the transportation process, additional Department of Transportation (DOT) regulations may apply. Final preparations for off-site disposal usually occur at the central accumulation area. Decisions on disposal options are best made here, as the larger quantities of waste are gathered. Identification of unknown materials not carried out within the laboratory must be completed at this point because unidentified waste cannot be shipped to a disposal site. Laboratory waste typically leaves the generator's facility commingled in drums as compatible wastes or within a Lab Pack. Lab Packs are containers, often 55-gallon drums, in which small containers of waste are packed with an absorbent material. Lab Packs had been used as the principal method for disposing of laboratory waste within a landfill. However, recent landfill disposal restrictions severely limit landfill disposal of hazardous materials. Thus, the Lab Pack has become principally a shipping container. Typically, the Lab Pack is taken to a disposal facility, where it is either incinerated or unpacked and the contents redistributed for safe, efficient, and legal treatment and disposal. 7.B.4 Records Records are needed both to meet regulatory requirements and to help monitor the success of the hazardous waste management program. Because the central accumulation area is usually the last place where waste is dealt with before it leaves the facility, it is often the most suitable place for ensuring that all appropriate and required records have been generated. For regulatory purposes, the facility needs to keep records for on-site activities that include the quantities and identification of waste generated and shipped, documentation of analyses of unknown materials if required, manifests for waste shipping as well as verification of disposal, and any other information required to ensure compliance and safety from long-term liability. Records of costs, internal tracking, and so forth, can provide information on the success of the hazardous waste management program. 7.B.5 Hazard Reduction Hazard reduction is part of the broad theme of pollution prevention that is addressed in previous chapters

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals of this book. From a chemical point of view, it is feasible to reduce the volume or the hazardous characteristics of many chemicals by reactions within the laboratory. In fact, it is becoming common practice to include such reactions as the final steps in an experimental sequence. Such procedures, as part of an academic or industrial experiment, usually involve small amounts of materials, which can be handled easily and safely by the laboratory worker. Chemical deactivation as part of the experimental procedure can have considerable economic advantage by eliminating the necessity to treat small amounts of surplus materials as hazardous waste. Furthermore, the handling and deactivation of potential waste by the laboratory worker benefit from the expertise and knowledge about the materials of the person who has generated them. The question of what is considered treatment under RCRA regulations has posed a dilemma for laboratory workers. RCRA regulations define treatment as "any method ... designed to change the physical, chemical, or biological character or composition of any hazardous waste so as to neutralize such waste, or so as to recover energy or material resources from the waste, or so as to render the waste non-hazardous or less hazardous ... " (U.S. Congress, 1978). Under RCRA, treatment, with very limited exceptions, must be permitted by EPA. The regulatory procedures and costs to be a "permitted" treatment facility are beyond the resources and mission of most academic and industrial laboratories. Yet it is prudent to carry out small-scale "treatment" as a part of laboratory procedures. This fact has been recognized by state agencies and some regional EPA offices through "permit-by-rule," that is, by allowing categorical or blanket permitting of certain small-scale treatment methods. For example, elementary acid-base neutralization is usually allowed, as is treatment that is the last step of a chemical procedure. Most EPA regions also allow treatment in the waste collection container. It is important to note that treatment restrictions apply only to wastes that are addressed by EPA regulations. A bill has been promoted in Congress to allow small-scale treatment by laboratory personnel. However, specific legislation has not been enacted at this time. The fact that regional EPA offices have interpreted such small-scale reactions differently further complicates decisions at the laboratory level. Because illegal treatment can lead to fines of up to $25,000 per day, it is most important that, before carrying out any processes that could be considered treatment, the responsible laboratory worker or the institution's environmental health and safety office check with the local, state, or regional EPA to clarify its interpretation of the rules. (Section 7.D below provides methods for small-scale treatment of common chemicals.) 7.B.6 Disposal Options Decisions on the ultimate disposal method are an important part of the on-site planning for handling of waste. The method of collection has an impact on, for example, how waste will be stored so as to most efficiently accomplish its transfer to the treatment, storage, and disposal facility (TSDF). Waste generators often use several disposal options because each has its own advantages for specific wastes. Disposal in the sanitary sewer, though appropriate in some cases, is becoming an unacceptable option in many communities. At the same time the options for landfill disposal are also disappearing rapidly. Incineration is becoming the most common disposal method. However, the long-term outlook for this method may be limited by increasing environmental concerns as well as the difficulty in obtaining permits for commercial incineration facilities. Waste minimization is the management strategy of the future. (See Chapter 4, section 4.B, for step-by-step instructions on source reduction and Chapter 7, section 7.C, for general information on minimizing hazardous waste.) 7.B.6.1 Incineration Incineration is becoming the disposal method of choice for several reasons. It promises to give the generator the best assurance of long-term safety from liability. It also leads to a minimum amount of residues that must be disposed of in landfills. However, at this time, incineration is still one of the more expensive disposal options. It is becoming increasingly difficult to obtain a permit to establish a commercial incinerator because of local opposition (the "not in my backyard" syndrome) and environmental concerns centering on questions regarding the effectiveness of the incineration process. Nevertheless, most disposal companies are moving toward incineration disposal, particularly for the kinds of hazardous waste generated by laboratories. Their typical variety of different wastes, usually in small quantities, makes incineration a favorable option. Laboratory waste can often be incinerated in its shipping Lab Packs without any further handling. Commingled flammable solvents are commonly blended with the incinerator fuel and thus destroyed as they provide energy for the burning process. Earlier editions of this book were optimistic that small laboratory incinerator systems would be developed for efficient destruction of waste at the point of

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals generation. That has not happened. Several factors, including the cost of development and concern about how regulatory agencies would view this kind of "treatment," surely have contributed to the lack of progress. A changing regulatory environment could provide a favorable basis for development of such thermal treatment systems. 7.B.6.2 Disposal in the Normal Trash Laboratory workers may be surprised to learn the number of wastes they generate that can be disposed of in the normal trash. However, because the disposal of trash from households and businesses is normally controlled by the local municipality, the local agency should be approached to establish what is allowed. When disposing of chemicals in the normal trash, certain precautions should be observed. Because custodians, who usually empty the trash containers, are not usually familiar with laboratory operations, no objects that could cause harm to them should be disposed of in those containers. Such objects include containers of chemicals, unless they are overpacked to avoid breakage, and powders, unless they are in closed containers. Free-flowing liquids are usually prohibited. Sharp metal and broken glassware, even though they may be considered nonhazardous trash, should be collected in specially marked containers, never in the normal trash baskets. 7.B.6.3 Disposal in the Sanitary Sewer Disposal in the sewer system (down the drain) had been a common method of waste disposal until recent years. However, environmental concerns, the viability of publicly owned treatment works (POTW), and a changing disposal culture have changed that custom markedly. In fact, many industrial and academic laboratory facilities have completely eliminated sewer disposal. Again, like trash disposal, most sewer disposal is controlled locally, and it is therefore advisable to consult with the POTW to determine what is allowed. Yet, it is often reasonable to consider disposal of some chemical waste materials in the sanitary sewer. These include substances that are water-soluble, that do not violate the federal prohibitions on disposal of waste materials that interfere with POTW operations or pose a hazard, and that are allowed by the local sewer facility. Chemicals that may be permissible for sewer disposal include aqueous solutions that readily biodegrade and low-toxicity solutions of inorganic substances. Water-miscible flammable liquids are frequently prohibited from disposal in the sewer system. Water-immiscible chemicals should never go down the drain. Disposal of regulated hazardous waste into the sanitary sewer is allowed only in limited situations. The total wastewater must be a mixture of domestic sewage along with the waste whose amount and concentration meet the regulations and limits of the POTW. If approved of by the local district, it may be allowable to dispose of dilute solutions of metals and other hazardous chemicals into the sanitary sewer. Under the Clean Water Act, some exemption from regulation as a hazardous waste for wastewater containing laboratory-generated listed waste is allowed. In 1993, this exemption was expanded to include corrosive and ignitable wastes. For the exemption to apply, these laboratory wastes must be 1% or less of the annual total wastewater quantity reaching the facility's headworks or have an annualized average concentration of no more than 1 part per million (ppm) of the wastewater generated by the facility. Waste should be disposed of in drains that flow to a POTW, never into a storm drain and seldom into a septic system. Waste should be flushed with at least a 100-fold excess of water, and the facility's wastewater effluent should be checked periodically to ensure that concentration limits are not being exceeded. 7.B.6.4 Release to the Atmosphere The release of vapors to the atmosphere, via, for example, open evaporation or fume hood effluent, is not an acceptable disposal method. Apparatus for operations expected to release vapors should be equipped with appropriate trapping devices. Although the disposition of laboratories under the Clean Air Act is not established at this time, it is reasonable to expect that releases to the atmosphere will be controlled. Fume hoods, the most common source of laboratory releases to the atmosphere, are designed as safety devices to transport vapors away from the laboratory in case of an emergency, not as a routine means for volatile waste disposal. Units containing absorbent filters have been introduced into some laboratories, but have limited absorbing capacity. Redirection of fume hood vapors to a common trapping device can completely eliminate discharge into the atmosphere. (See Chapter 8, sections 8.C.11 and 8.C.12, for more detail.) 7.B.7 Disposal of Nonhazardous and Nonregulated Waste Many laboratories do not distinguish between waste that is hazardous and waste that neither poses a hazard

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals nor is regulated as hazardous. If these different types of waste are combined, then the total must be treated as hazardous waste, and the price for disposal of the nonhazardous portion increases markedly. When safe and allowed by regulation, disposal of nonhazardous waste via the normal trash or sewer can substantially reduce disposal costs. This is the kind of waste segregation that makes economic as well as environmental sense. It is wise to check the rules and requirements of the local solid waste management authority and develop a list of materials that can be disposed of safely and legally in the normal trash. This includes waste that is not regulated because it does not exhibit any of the hazardous characteristics (ignitability, corrosivity, reactivity, or toxicity) as defined by EPA and is not listed as hazardous. The common wastes usually not regulated as hazardous include certain salts (e.g., potassium chloride and sodium carbonate), many natural products (e.g., sugars and amino acids), and inert materials used in a laboratory (e.g., noncontaminated chromatography resins and gels). 7.B.8 Disposal of Spills Most chemical spills can and should be cleaned up by laboratory workers themselves. In general, these are spills of known composition that do not involve injury, do not represent a fire or personal hazard, and are less than 1 gallon (or less for very toxic materials). Regulations allow laboratory workers to clean up such spills, although it is advisable that they have training to handle spills and adequate equipment to carry out the cleanup safely. Outside help, properly trained, should be requested if there is any doubt about the ability of the laboratory personnel to clean up the spill safely. But once help is requested from outside the immediate spill area, specific personnel training requirements and other regulatory control may apply. General guidelines for cleaning up spills are as follows: Assess the potential hazard presented by the spill to personnel within the work area as well as within other parts of the facility and the outside environment. Remove possible sources of ignition if the spilled material is flammable: Turn off hot plates, stirring motors, and flames. Shut down equipment in the area that could increase danger. Secure the area so that no one will walk through the spill or interfere with the cleanup efforts. Choose appropriate personal protection devices: Always wear protective gloves and goggles or a face shield. If there is a chance of body contact with the spill, wear an apron or coveralls. Wear rubber or plastic (not leather) boots if there is a chance of stepping into the spill. Wear a respirator if there is danger of inhalation of toxic vapors, though only when proper training has preceded its use. Note that protective devices must be chosen carefully to be appropriate for the anticipated hazard. Often training is appropriate or required (e.g., with respirators) prior to their use. Locate a spill control kit or other appropriate absorbent and cleanup supplies. Confine or contain the spill: Do not let any of the spilled material enter the sewer system, for example, through a floor drain. Cover the spill with an absorbent material; paper towels may be appropriate for small, unreactive materials. Sweep up or in other ways collect the absorbed materials and place them in a container that can be securely closed. If the spilled material is an acid or a base, use a neutralizing material; sodium bicarbonate is commonly used for acids, and sodium bisulfate for bases. Spill control kits are commercially available for the cleanup of many kinds of chemical spills. (Chapter 6, section 6.F.2.1 , has further information on spill control kits and spill absorbents.) Dispose of the absorbed spill appropriately as hazardous or nonhazardous waste. (See Chapter 5, sections 5.C.11.5 and 5.C.11.6, for more detail on spill cleanup.) 7.B.9 Monitoring of Off-Site Waste Disposal The ultimate destination of waste is usually a treatment, storage, and disposal facility (TSDF). Here waste is held, treated (typically via chemical action or incineration), or actually disposed of. Although the waste has left the generator's facility, the generator retains the final responsibility for the long-term fate of the waste. It is imperative that the generator have complete trust and confidence in the TSDF, as well as in the transporter who carries the waste to the TSDF. In some cases the destination of waste is a recycler or reclaimer. The procedures for preparing and transporting the waste to such a facility are similar to those described above. (See section 7.B.3.)

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals into the flask. A few milliliters of the acid derivative are added drop wise with stirring. If the derivative is a solid, it can be added in small portions through a neck of the flask. If reaction occurs, as indicated by a rise in temperature and dissolution of the acid derivative, addition is continued at such a rate that the temperature does not rise above 45 °C. If the reaction is sluggish, as may be the case with less soluble compounds such as p-toluenesulfonyl chloride, the mixture is heated before adding any more acid derivative. When the initial added material has dissolved, the remainder is added drop wise. As soon as a clear solution is obtained, the mixture is cooled to room temperature, neutralized to about pH 7 with dilute hydrochloric or sulfuric acid, and washed down the drain with excess water. 7.D.2.3 Aldehydes Many aldehydes are respiratory irritants, and some, such as formaldehyde and acrolein, are quite toxic. There is sometimes merit in oxidation of aldehydes to the corresponding carboxylic acids, which are usually less toxic and less volatile. Procedure for permanganate oxidation of 0.1 mol of aldehyde: A mixture of 100 mL of water and 0.1 mol of aldehyde is stirred in a 1-L round-bottomed flask equipped with a thermometer, dropping funnel, stirrer, steam bath, and, if the aldehyde boils below 100 °C, a condenser. Approximately 30 mL of a solution of 12.6 g (0.08 mol, 20% excess) of potassium permanganate in 250 mL of water is added over a period of 10 minutes. If the temperature rises above 45 °C, the solution should be cooled. If this addition is not accompanied by a rise in temperature and loss of the purple permanganate color, the mixture is heated by the steam bath until a temperature is reached at which the color is discharged. The rest of the permanganate solution is added slowly at within 10 °C of this temperature. The temperature is then raised to 70 to 80 °C, and stirring continued for 1 hour or until the purple color has disappeared, whichever occurs first. The mixture is cooled to room temperature and acidified with 6 N sulfuric acid. (CAUTION: Do not add concentrated sulfuric acid to permanganate solution because explosive manganese oxide (Mn2O7) may precipitate.) Enough solid sodium hydrogen sulfite (at least 8.3 g, 0.08 mol) is added with stirring at 20 to 40 °C to reduce all the manganese, as indicated by loss of purple color and dissolution of the solid manganese dioxide. The mixture is washed down the drain with a large volume of water. If the aldehyde contains a carbon-carbon double bond, as in the case of the highly toxic acrolein, 4 mol (20% excess) of permanganate per mol of aldehyde is required to oxidize the alkene bond and the aldehyde group. Formaldehyde is oxidized conveniently to formic acid and carbon dioxide by sodium hypochlorite. Thus 10 mL of formalin (37% formaldehyde) in 100 mL of water is stirred into 250 mL of hypochlorite laundry bleach (5.25% NaOC1) at room temperature and allowed to stand for 20 minutes before being flushed down the drain. This procedure is not recommended for other aliphatic aldehydes because it leads to chloro acids, which are more toxic and less biodegradable than corresponding unchlorinated acids. 7.D.2.4 Amines Acidified potassium permanganate efficiently degrades aromatic amines. Diazotization followed by hypophosphorus acid protonation is a method for deamination of aromatic amines, but the procedure is more complex than oxidation. Procedure for permanganate oxidation of 0.01 mol of aromatic amine: A solution of 0.01 mol of aromatic amine in 3 L of 1.7 N sulfuric acid is prepared in a 5-L flask; 1 L of 0.2 M potassium permanganate is added, and the solution allowed to stand at room temperature for 8 hours. Excess permanganate is reduced by slow addition of solid sodium hydrogen sulfite until the purple color disappears. The mixture is then flushed down the drain. 7.D.2.5 Organic Peroxides and Hydroperoxides (CAUTION: Peroxides are particularly dangerous. These procedures should be carried out only by knowledgeable laboratory workers.) Peroxides can be removed from a solvent by passing it through a column of basic activated alumina, by treating it with indicating Molecular Sieves®, or by reduction with ferrous sulfate. Although these procedures remove hydroperoxides, which are the principal hazardous contaminants of peroxide-forming solvents, they do not remove dialkyl peroxides, which may also be present in low concentrations. Commonly used peroxide reagents, such as acetyl peroxide, benzoyl peroxide,

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals t-butyl hydroperoxide, and di-t-butyl peroxide, are less dangerous than the adventitious peroxides formed in solvents. Removal of peroxides with alumina: A 2 x 33 cm column filled with 80 g of 80-mesh basic activated alumina is usually sufficient to remove all peroxides from 100 to 400 mL of solvent, whether water-soluble or water-insoluble. After passage through the column, the solvent should be tested for peroxide content. Peroxides formed by air oxidation are usually decomposed by the alumina, not merely absorbed on it. However, for safety it is best to slurry the wet alumina with a dilute acidic solution of ferrous sulfate before it is discarded. Removal of peroxides with Molecular Sieves®: Reflux 100 mL of the solvent with 5 g of 4- to 8-mesh indicating activated 4A Molecular Sieves® for several hours under nitrogen. The sieves are separated from the solvent and require no further treatment because the peroxides are destroyed during their interaction with the sieves. Removal of peroxides with ferrous sulfate: A solution of 6 g of FeSO4 · 7H2O, 6 mL of concentrated sulfuric acid, and 11 mL of water is stirred with 1 L of water-insoluble solvent until the solvent no longer gives a positive test for peroxides. Usually only a few minutes are required. Diacyl peroxides can be destroyed by this reagent as well as by aqueous sodium hydrogen sulfite, sodium hydroxide, or ammonia. However, diacyl peroxides with low solubility in water, such as dibenzoyl peroxide, react very slowly. A better reagent is a solution of sodium iodide or potassium iodide in glacial acetic acid. Procedure for destruction of diacyl peroxides: For 0.01 mol of diacyl peroxide, 0.022 mol (10% excess) of sodium or potassium iodide is dissolved in 70 mL of glacial acetic acid, and the peroxide added gradually with stirring at room temperature. The solution is rapidly darkened by the formation of iodine. After a minimum of 30 minutes, the solution is washed down the drain with a large excess of water. Most dialkyl peroxides (ROOR) do not react readily at room temperature with ferrous sulfate, iodide, ammonia, or the other reagents mentioned above. However, these peroxides can be destroyed by a modification of the iodide procedure. Procedure for destruction of dialkyl peroxides: One milliliter of 36% (w/v) hydrochloric acid is added to the above acetic acid/potassium iodide solution as an accelerator, followed by 0.01 mol of the dialkyl peroxide. The solution is heated to 90 to 100 °C on a steam bath over the course of 30 minutes and held at that temperature for 5 hours. 7.D.3 Inorganic Chemicals 7.D.3.1 Metal Hydrides Most metal hydrides react violently with water with the evolution of hydrogen, which can form an explosive mixture with air. Some, such as lithium aluminum hydride, potassium hydride, and sodium hydride, are pyrophoric. Most can be decomposed by gradual addition of (in order of decreasing reactivity) methyl alcohol, ethyl alcohol, n-butyl alcohol, or t-butyl alcohol to a stirred, ice-cooled solution or suspension of the hydride in an inert liquid, such as diethyl ether, tetrahydrofuran, or toluene, under nitrogen in a three-necked flask. Although these procedures reduce the hazard and should be a part of any experimental procedure that uses reactive metal hydrides, the products from such deactivation may be hazardous waste that must be treated as such on disposal. Hydrides commonly used in laboratories are lithium aluminum hydride, potassium hydride, sodium hydride, sodium borohydride, and calcium hydride. The following methods for their disposal demonstrate that the reactivity of metal hydrides varies considerably. Most hydrides can be decomposed safely by one of the four methods, but the properties of a given hydride must be well understood in order to select the most appropriate method. (CAUTION: Most of the methods described below produce hydrogen gas, which can present an explosion hazard. The reaction should be carried out in a hood, behind a shield, and with proper safeguards to avoid exposure of the effluent gas to spark or flame. Any stirring device must be spark-proof.) Decomposition of lithium aluminum hydride: Lithium aluminum hydride (LiA1H4) can be purchased as a solid or as a solution in toluene, diethyl ether, tetrahydrofuran, or other ethers. Although drop-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals wise addition of water to its solutions under nitrogen in a three-necked flask has frequently been used to decompose it, vigorous frothing often occurs. An alternative is to use 95% ethanol, which reacts less vigorously than water. A safer procedure is to decompose the hydride with ethyl acetate, because no hydrogen is formed. To the hydride solution in a flask equipped with a stirrer, ethyl acetate is added slowly. The mixture sometimes becomes so viscous after the addition that stirring is difficult and additional solvent may be required. When the reaction with ethyl acetate has ceased, a saturated aqueous solution of ammonium chloride is added with stirring. The mixture separates into an organic layer and an aqueous layer containing inert inorganic solids. The upper, organic layer should be separated and disposed of as a flammable liquid. The lower, aqueous layer can often be disposed of in the sanitary sewer. Decomposition of potassium or sodium hydride: Potassium and sodium hydride (KH, NaH) in the dry state are pyrophoric, but they can be purchased as a relatively safe dispersion in mineral oil. Either form can be decomposed by adding enough dry hydrocarbon solvent (e.g., heptane) to reduce the hydride concentration below 5% and then adding excess t-butyl alcohol drop wise under nitrogen with stirring. Cold water is then added drop wise, and the resulting two layers are separated. The organic layer can be disposed of as a flammable liquid. The aqueous layer can often be neutralized and disposed of in the sanitary sewer. Decomposition of sodium borohydride: Sodium borohydride (NaBH4) is so stable in water that a 12% aqueous solution stabilized with sodium hydroxide is sold commercially. In order to effect decomposition, the solid or aqueous solution is added to enough water to make the borohydride concentration less than 3%, and then excess equivalents of dilute aqueous acetic acid are added drop wise with stirring under nitrogen. Decomposition of calcium hydride: Calcium hydride (CaH2), the least reactive of the materials discussed here, is purchased as a powder. It is decomposed by adding 25 mL of methyl alcohol per gram of hydride under nitrogen with stirring. When reaction has ceased, an equal volume of water is gradually added to the stirred slurry of calcium methoxide. The mixture is then neutralized with acid and disposed of in the sanitary sewer. 7.D.3.2 Inorganic Cyanides Inorganic cyanides can be oxidized to cyanate using aqueous hypochlorite following a procedure similar to the oxidation of thiols. Hydrogen cyanide can be converted to sodium cyanide by neutralization with aqueous sodium hydroxide, and then oxidized. Procedure for oxidation of cyanide: An aqueous solution of the cyanide salt in an ice-cooled, three-necked flask equipped with a stirrer, thermometer, and dropping funnel is cooled to 4 to 10 °C. A 50% excess of commercial hypochlorite laundry bleach containing 5.25% (0.75 M) sodium hypochlorite is added slowly with stirring while maintaining the low temperature. When the addition is complete and heat is no longer being evolved, the solution is allowed to warm to room temperature and stand for several hours. The mixture can then be washed down the drain with excess water. The same procedure can be applied to insoluble cyanides such as cuprous cyanide (though copper salts should not be disposed of in the sanitary sewer). In calculating the quantity of hypochlorite required, the experimenter should remember that additional equivalents may be needed if the metal ion can be oxidized to a higher valence state, as in the reaction, A similar procedure can be used to destroy hydrogen cyanide, but precautions must be taken to avoid exposure to this very toxic gas. Hydrogen cyanide is dissolved in several volumes of ice water. Approximately 1 molar equivalent of aqueous sodium hydroxide is added at 4 to 10 °C to convert the hydrogen cyanide into its sodium salt, and then the procedure described above for sodium cyanide is followed. (CAUTION: Sodium hydroxide or other bases, including sodium cyanide, must not be allowed to come into contact with liquid hydrogen cyanide because they may initiate a violent polymerization of the hydrogen cyanide.) This procedure also destroys soluble ferrocyanides and ferricyanides. Alternatively, these can be precipitated as the ferric or ferrous salt, respectively, for possible landfill disposal.

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals (See Chapter 6, section 6.D, for details on working with hazardous gases.) 7.D.3.3 Metal Azides Heavy metal azides are notoriously explosive and should be handled by trained personnel. Silver azide (and also fulminate) can be generated from Tollens reagent, which is often found in undergraduate laboratories. Sodium azide is explosive only when heated to near its decomposition temperature (300 °C), but heating it should be avoided. Sodium azide should never be flushed down the drain. This practice has caused serious accidents because the azide can react with lead or copper in the drain lines to produce an azide that may explode. It can be destroyed by reaction with nitrous acid: Procedure for destruction of sodium azide: The operation must be carried out in a hood because of the formation of toxic nitric oxide. An aqueous solution containing no more than 5% sodium azide is put into a three-necked flask equipped with a stirrer and a dropping funnel. Approximately 7 mL of 20% aqueous solution of sodium nitrite (40% excess) per gram of sodium azide is added with stirring. A 20% aqueous solution of sulfuric acid is then added gradually until the reaction mixture is acidic to litmus paper. (CAUTION: The order of addition is essential. Poisonous, volatile hydrazoic acid (HN3) will evolve if the acid is added before the nitrite.) When the evolution of nitrogen oxides ceases, the acidic solution is tested with starch iodide paper. If it turns blue, excess nitrite is present, and the decomposition is complete. The reaction mixture is washed down the drain. 7.D.3.4 Alkali Metals Alkali metals react violently with water, with common hydroxylic solvents, and with halogenated hydrocarbons. They should always be handled in the absence of these materials. The metals are usually destroyed by controlled reaction with an alcohol. The final aqueous alcoholic material can usually be disposed of in the sanitary sewer. Procedure for destruction of alkali metals: Waste sodium is readily destroyed with 95% ethanol. The procedure is carried out in a three-necked, round-bottomed flask equipped with a stirrer, dropping funnel, condenser, and heating mantle. Solid sodium should be cut into small pieces with a sharp knife while wet with a hydrocarbon, preferably mineral oil, so that the unoxidized surface is exposed. A dispersion of sodium in mineral oil can be treated directly. The flask is flushed with nitrogen and the pieces of sodium placed in it. Then 13 mL of 95% ethanol per gram of sodium are added at a rate that causes rapid refluxing. (CAUTION: Hydrogen gas is evolved and can present an explosion hazard. The reaction should be carried out in a hood, behind a shield, and with proper safeguards (such as in Chapter 5, sections 5.G.4 and 5.G.5) to avoid exposing the effluent gas to spark or flame. Any stirring device must be spark-proof.) Stirring is commenced as soon as enough ethanol has been added to make this possible. The mixture is stirred and heated under reflux until the sodium is dissolved. The heat source is removed, and an equal volume of water added at a rate that causes no more than mild refluxing. The solution is then cooled, neutralized with 6 M sulfuric or hydrochloric acid, and washed down the drain. To destroy metallic potassium, the same procedure and precautions as for sodium are used, except that the less reactive t-butyl alcohol is used in the proportion of 21 mL/g of metal. (CAUTION: Potassium metal can form explosive peroxides. Metal that has formed a yellow oxide coating from exposure to air should not be cut with a knife, even when wet with a hydrocarbon, because an explosion can be promoted.) If the potassium is dissolving too slowly, a few percent of methanol can be added gradually to the refluxing t-butyl alcohol. Oxide-coated potassium sticks should be put directly into the flask and decomposed with t-butyl alcohol. The decomposition will require considerable time because of the low surface/volume ratio of the metal sticks. Lithium metal can be treated by the same procedure, but using 30 mL of 95% ethanol per gram of lithium. The rate of dissolution is slower than that of sodium. 7.D.3.5 Metal Catalysts Metal catalysts such as Raney nickel and other fine metal powders can be slurried into water; dilute hydrochloric acid is then added carefully until the solid dissolves. Depending on the metal and on local regulations, the solution can be discarded in the sanitary sewer or with other hazardous or nonhazardous solid waste. Precious metals should be recovered from this process. 7.D.3.6 Water-Reactive Metal Halides Liquid halides, such as TiCl4 and SnCl4, can be added to well-stirred water in a round-bottomed flask cooled by an ice bath as necessary to keep the exothermic

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals reaction under control. It is usually more convenient to add solid halides, such as AlCl3 and ZrCl4, to stirring water and crushed ice in a flask or beaker. The acidic solution can be neutralized and, depending on the metal and local regulations, discarded in the sanitary sewer or with other hazardous or nonhazardous solid waste. 7.D.3.7 Halides and Acid Halides of Nonmetals Halides and acid halides such as PCl3, PCl5, SiCl4, SOCl2, SO2Cl2, and POCl3 are water-reactive. The liquids can be hydrolyzed conveniently using 2.5 M sodium hydroxide by the procedure described earlier for acyl halides and anhydrides. These compounds are irritating to the skin and respiratory passages and, even more than most chemicals, require a good hood and skin protection when handling them. Moreover, PCl3 may give off small amounts of highly toxic phosphine (PH3) during hydrolysis. Sulfur monochloride (S2Cl2) is a special case. It is hydrolyzed to a mixture of sodium sulfide and sodium sulfite, so that the hydrolyzate must be treated with hypochlorite as described earlier for sulfides before it can be flushed down the drain. The solids of this class (e.g., PCl5) tend to cake and fume in moist air and therefore are not conveniently hydrolyzed in a three-necked flask. It is preferable to add them to a 50% excess of 2.5 M sodium hydroxide solution in a beaker or wide-mouth flask equipped with a stirrer and half-filled with crushed ice. If the solid has not all dissolved by the time the ice has melted and the stirred mixture has reached room temperature, the reaction can be completed by heating on a steam bath, and then the acidic solution neutralized and disposed of in the sanitary sewer. 7.D.3.8 Inorganic Ions Many inorganic wastes consist of a cation (metal or metalloid atom) and an anion (which may or may not contain a metalloid component). It is often helpful to examine the cationic and anionic parts of the substance separately to determine whether either possesses a hazard. If a substance contains a ''heavy metal," it is often assumed that it is highly toxic. While salts of some heavy metals, such as lead, thallium, and mercury, are highly toxic, those of others, such as gold and tantalum, are not. On the other hand, compounds of beryllium, a "light metal," are highly toxic. In Table 7.1, cations of metals and metalloids are listed alphabetically in two groups: those whose toxic properties as described in the toxicological literature present a significant hazard, and those whose properties do not. The basis for separation is relative, and the separation does not imply that those in the second list are "nontoxic." Similarly, Table 7.2 lists anions according to their level of toxicity and other dangerous properties, such as strong oxidizing power (e.g., perchlorate), flammability (e.g., amide), water reactivity (e.g., hydride), and explosivity (e.g., azide). Materials that pose a hazard because of significant radioactivity are outside the scope of this volume, although they may be chemically treated in a manner similar to the nonradioactive materials discussed in this chapter. Their handling and disposal are highly regulated in most countries. Low-level radioactive mixed waste is discussed in section 7.C above. 7.D.3.8.1 Chemicals in Which Neither the Cation nor the Anion Presents a Significant Hazard Chemicals in which neither the cation nor the anion presents a significant hazard consist of those chemicals composed of ions from the right-hand columns of Tables 7.1 and 7.2. Those that are soluble in water to the extent of a few percent can usually be disposed of in the sanitary sewer. Only laboratory quantities should be disposed of in this manner, and at least 100 parts of water per part of chemical should be used. Local regulations should be checked for possible restrictions. Dilute slurries of insoluble materials, such as calcium sulfate or aluminum oxide, also can be handled in this way, provided the material is finely divided and not contaminated with tar, which might clog the piping. Some incinerators can handle these chemicals. If time and space permit, dilute aqueous solutions can be boiled down or allowed to evaporate to leave only a sludge of the inorganic solid for landfill disposal. However, appropriate precautions, including the use of traps, must be considered to ensure that toxic or other prohibited materials are not released to the atmosphere. An alternative procedure is to precipitate the metal ion by the agent recommended in Table 7.1. The precipitate can often be disposed of in a secure landfill. The most generally applicable procedure is to precipitate the cation as the hydroxide by adjusting the pH to the range shown in Table 7.3. 7.D.3.8.2 Precipitation of Cations as Their Hydroxides Because the pH range for precipitation varies greatly among metal ions, it is important to control it carefully. The aqueous solution of the metal ion is adjusted to the recommended pH (Table 7.3) by addition of a solu-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals TABLE 7.1 High-and Low-Toxicity Cations and Preferred Precipitants High Toxic Hazard Low Toxic Hazard Cation Precipitanta Cation Precipitanta Antimony OH-, S2- Aluminium OH- Arsenic S2- Bismuth OH-, S2- Barium SO42-, CO32- Calcium SO42-, CO32- Beryllium OH- Cerium OH- Cadmium OH-, S2- Cesium   Chromium(III)b OH Copperc OH-, S2- Cobalt(II)b OH-, S2- Gold OH-, S2- Gallium OH- Ironc OH-, S2- Germanium OH-, S2- Lanthanides OH- Hafnium OH- Lithium   Indium OH-, S2- Magnesium OH- Iridiumd OH-, S2- Molybdenum(VI)b,e   Lead OH-, S2- Niobium(V) OH- Manganese(II)b OH-, S2- Palladium OH-, S2- Mercury OH-, S2- Potassium   Nickel OH-, S2- Rubidium   Osmium(IV)b,f OH-, S2- Scandium OH- Platinum(II)b OH-, S2- Sodium   Rhenium(VII)b S2- Strontium SO42- CO32- Rhodium(III)b OH-, S2- Tantalum OH- Ruthenium(II)b OH-, S2- Tin OH-, S2- Selenium S2- Titanium OH- Silverd Cl, OH-, S2- Yttrium OH- Tellurium S2 Zincc OH-, S2- Thallium OH-, S2- Zirconium OH- Tungsten(VI)b,e       Vanadium OH-, S2-     a Precipitants are listed in order of preference: OH-, CO32- =base (sodium hydroxide or sodium carbonate), S2- = sulfide, SO42- = sulfate, and Cl- = chloride. b The precipitant is for the indicated valence state. c Very low maximum tolerance levels have been set for these low-toxicity ions in some countries, and large amounts should not be put into public sewer systems. The small amounts typically used in laboratories will not normally affect water supplies, although they may be prohibited by the local publicly owned treatment works (POTW). d Recovery of these rare and expensive metals may be economically favorable. e These ions are best precipitated as calcium molybdate(VI) or calcium tungstate(VI). f CAUTION: Osmium tetroxide, OSO4, a volatile, extremely poisonous substance, is formed from almost any osmium compound under acid conditions in the presence of air. Reaction with corn oil or powdered milk will destroy it. tion of 1 M sulfuric acid, or 1 M sodium hydroxide or carbonate. The pH can be determined over the range 1 through 10 by use of pH test paper. The precipitate is separated by filtration, or as a heavy sludge by decantation, and packed for disposal. Some gelatinous hydroxides are difficult to filter. In such cases, heating the mixture close to 100 °C or stirring with diatomaceous earth, approximately 1 to 2 times the weight of the precipitate, often facilitates filtration. As shown in Table 7.1, precipitants other than a base may be superior for some metal ions, such as sulfuric acid for calcium ion. For some ions, the hydroxide precipitate will redissolve at a high pH (Table 7.3). For a number of metal ions the use of sodium carbonate will result in precipitation of the metal carbonate or a mixture of hydroxide and carbonate. 7.D.3.8.3 Chemicals in Which the Cation Presents a Relatively High Hazard from Toxicity In general, waste chemicals containing any of the cations listed as highly hazardous in Table 7.1 can be precipitated as their hydroxides or oxides. Alternatively, many can be precipitated as insoluble sulfides by treatment with sodium sulfide in neutral solution (Table 7.4). Several sulfides will redissolve in excess sulfide ion, and so it is important that the sulfide ion concentration be controlled by adjustment of the pH. Precipitation as the hydroxide is achieved as described above. Precipitation as the sulfide is accomplished by adding a 1 M solution of sodium sulfide to the metal ion solution, and then adjusting the pH to

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals TABLE 7.2 High- and Low-Hazard Anions and Preferred Precipitants High-Hazard Anions Ion Hazard Typea Precipitant Low-Hazard Anions Aluminium hydride, AlH4- F, W — Bisulfite, HSO3- Amide, NH2- F, Eb — Borate, BO33-, B4O72- Arsenate, AsO3-,AsO43- T Cu2+, Fe2+ Bromide, Br- Arsenite, AsO2-, AsO33- T Pb2+ Carbonate, CO32- Azide, N3- E, T — Chloride, Cl- Borohydride, BH4- F — Cyanate, OCN- Bromate, BrO3- O, F, E — Hydroxide, OH- Chlorate, ClO3- O, E — Iodide, I- Chromate, CrO42-, Cr2O72- T,O c   Oxide, O-       Cyanide, CN- T — Phosphate, PO43- Ferricyanide, {Fe(CN)6}3- T Fe2+ Sulfate, SO42- Ferrocyanide, {FE(CN)6)4- T Fe3+ Sulfite, SO32- Fluoride, F- T Ca2+ Thiocyanate, SCN- Hydride, H- F, W —   Hydroperoxide, O2H- O, E —   Hydrosulfide, SH- T —   Hypochlorite, OCl- O —   Iodate, IO3- O, E —   Nitrate, NO3- O —   Nitrite, NO2- T, O —   Perchlorate, ClO4- O, E —   Permanganate, MnO4- T, O —   Peroxide, O22- O, E d   Persulfate, S2O82- O —   Selenate, SeO42- T Pb2+   Selenide, Se2- T Cu2+   Sulfide, S2- T e   a T = toxic; O = oxidant; F = flammable; E = explosive; and W = water reactive. b Metal amides readily form explosive peroxides on exposure to air. c Reduce and precipitate as Cr(III). d Reduce and precipitate as Mn(II); see Table 7.1. e See Table 7.4. neutral with 1 M sulfuric acid. (CAUTION: Avoid acidifying the mixture because hydrogen sulfide could be formed.) The precipitate is separated by filtration or decantation and packed for disposal. Excess sulfide ion can be destroyed by the addition of hypochlorite to the clear aqueous solution. The following ions are most commonly found as oxyanions and are not precipitated by base: As3+, As5+, Re7+, Se4+, Se6+, Te4+, and Te6+ . These elements can be precipitated from their oxyanions as the sulfides by the above procedure. Oxyanions of Mo6+ and W6+ can be precipitated as their calcium salts by the addition of calcium chloride. Some ions can be absorbed by passing their solutions over ion-exchange resins. The resins can be landfilled, and the effluent solutions poured down the drain. Another class of compounds whose cations may not be precipitated by the addition of hydroxide ions are the most stable complexes of metal cations with Lewis bases, such as ammonia, amines, and tertiary phosphines. Because of the large number of these compounds and their wide range of properties, it is not possible to give a general procedure for separating the cations. In many cases, metal sulfides can be precipitated directly from aqueous solutions of the complexes by the addition of aqueous sodium sulfide. If a test-tube experiment shows that other measures are needed, the addition of hydrochloric acid to produce a slightly acidic solution will often decompose the complex by protonation of the basic ligand. Metal ions that form insoluble sulfides under acid conditions can then be precipitated by drop wise addition of aqueous sodium sulfide. A third option for this waste is incineration, provided that the incinerator ash is to be sent to a secure landfill. Incineration to ash reduces the volume of

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals TABLE 7.3 pH Ranges for Precipitation of Metal Hydroxides and Oxides  

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals TABLE 7.4 Precipitation of Sulfides Precipitated at pH 7 Not Precipitated at Low pH Soluble Complex at High pH Ag+     As3+a   x Au+a   x Bi3+     Cd2+     Co2+ x   Cr3+a     Cu2+     Fe2+a x   Ge2+   x Hg2+   x In3+ x   Ir4+   x Mn2+a x   Mo3+   x Ni2+ x   Os4+     Pb2+     Pd2+a     pt2+a   x Re4+     Rh2+a     Ru4+     Sb3+a   x Se2+   x Sn2+   x Te4+   x Tl+a x   V4+a     Zn2+ x   NOTE: Precipitation of ions listed without an x is usually not pH-dependent. a Higher oxidation states of this ion are reduced by sulfide ion and precipitated as this sulfide. SOURCE: Swift and Schaefer (1961) waste going to a landfill. Waste that contains mercury, thallium, gallium, osmium, selenium, or arsenic should not be incinerated because volatile, toxic combustion products may be emitted. 7.D.3.8.4 Chemicals in Which an Anion Presents a Relatively High Hazard The more common dangerous anions are listed in Table 7.2. Many of the comments made above about the disposal of dangerous cations apply to these anions. The hazard associated with some of these anions is their reactivity or potential to explode, which makes them unsuitable for landfill disposal. Most chemicals containing these anions can be incinerated, but strong oxidizing agents and hydrides should be introduced into the incinerator only in containers of not more than a few hundred grams. Incinerator ash from anions of chromium or manganese should be transferred to a secure landfill. Some of these anions can be precipitated as insoluble salts for landfill disposal, as indicated in Table 7.2. Small amounts of strong oxidizing agents, hydrides, cyanides, azides, metal amides, and soluble sulfides or fluorides can be converted into less hazardous substances in the laboratory before being disposed of. Suggested procedures are presented in the following paragraphs. 7.D.3.8.5 Procedure for Reduction of Oxidizing Salts Hypochlorites, chlorates, bromates, iodates, periodates, inorganic peroxides and hydroperoxides, persulfates, chromates, molybdates, and permanganates can be reduced by sodium hydrogen sulfite. A dilute solution or suspension of a salt containing one of these anions has its pH reduced to less than 3 with sulfuric acid, and a 50% excess of aqueous sodium hydrogen sulfite is added gradually with stirring at room temperature. An increase in temperature indicates that the reaction is taking place. If the reaction does not start on addition of about 10% of the sodium hydrogen sulfite, a further reduction in pH may initiate it. Colored anions (e.g., permanganate and chromate) serve as their own indicators of completion of the reduction. The reduced mixtures can often be washed down the drain. However, if large amounts of permanganate have been reduced, it may be necessary to transfer the manganese dioxide to a secure landfill, possibly after a reduction in volume by concentration or precipitation. Do not dispose of chromium salts in the sanitary sewer. Hydrogen peroxide can be reduced by the sodium hydrogen sulfite procedure or by ferrous sulfate as described earlier for organic hydroperoxides. However, it is usually acceptable to dilute it to a concentration of less than 3% and dispose of it in the sanitary sewer. Solutions with a hydrogen peroxide concentration greater than 30% should be handled with great care to avoid contact with reducing agents, including all organic materials, or with transition metal compounds, which can catalyze a violent reaction. Concentrated perchloric acid (particularly when stronger than 60%) must be kept away from reducing agents, including weak ones such as ammonia, wood, paper, plastics, and all other organic substances, because it can react violently with them. Dilute perchloric acid is not reduced by common laboratory reducing agents such as sodium hydrogen sulfite, hydrogen sulfide, hydriodic acid, iron, or zinc. Perchloric acid is most easily disposed of by stirring it gradu-

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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals ally into enough cold water to make its concentration less than 5%, neutralizing it with aqueous sodium hydroxide, and washing the solution down the drain with a large excess of water. Nitrate is most dangerous in the form of concentrated nitric acid (70% or higher), which is a potent oxidizing agent for organic materials and all other reducing agents. It can also cause serious skin burns. Dilute aqueous nitric acid is not a dangerous oxidizing agent and is not easily reduced by common laboratory reducing agents. Dilute nitric acid should be neutralized with aqueous sodium hydroxide before disposal down the drain; concentrated nitric acid should be diluted carefully by adding it to about 10 volumes of water before neutralization. Metal nitrates are generally quite soluble in water. Those of the metals listed in Table 7.1 as having a low toxic hazard, as well as ammonium nitrate, should be kept separate from oil or other organic materials because on heating such a combination, fire or explosion can occur. Otherwise, these can be treated as chemicals that present no significant hazard. Nitrites in aqueous solution can be destroyed by adding about 50% excess aqueous ammonia and acidifying with hydrochloric acid to pH 1:

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