to allow the mercury to run very slowly through a tiny hole in a conical filter paper. The filter should be covered to reduce the evaporation of mercury. This method is slow but does produce a reasonably clean product that is adequate for a number of uses. Commercial recycling of mercury usually involves multiple distillations, resulting in a high-purity product. Distillation within the laboratory should be discouraged because it is very difficult to avoid contaminating the surrounding area with spilled or vaporized mercury.
Inorganic qualitative analysis experiments typically include some toxic metal elements, such as cadmium, chromium, and lead. If the single-element "knowns" and "unknowns" can be collected separately, they can be readily precipitated for reuse in the next term's classes. Mixed samples can be precipitated and used as a starting material in a separations experiment. Although the amount of this type of waste may be quite small, it can require very expensive disposal if a commercial vendor must be used.
Many recycling processes will result in some amount of residue that will not be reusable and will probably have to be handled as a hazardous waste. See Chapter 7 for further information.