High-Purity Chromium Metal Supply Issues for Gas-Turbine Superalloys (1995) / Chapter Skim
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3 ELECTROLYTIC CHROMIUM-METAL PRODUCTION
3 ELECTROLYTIC CHROMIUM-METAL PRODUCTION
Pages 29-38
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From page 29... ...
The filtrate is cooled using mother liquor from the ferrous ammonium sulfate circuit and the mixture is conditioned at 80 °C, causing the transformation to the green, non-alum form of chromium. Upon further cooling, the crude iron sulfate crystals form, are separated for 29
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From page 30... ...
FIGURE 3-1 Simplified flow chart for tile production of metallic chromium and chromium compounds. Reprinted courtesy of Grayson (1985)
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From page 31... ...
r Siliceous ~, 1 ~ Aging Electrowinning Chromium Metal FIGURE 3-2 Flow sheet for chromium electrodeposition from chrome-alum solutions. Source: DeBecker et al.
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From page 32... ...
Aging and crystallization are conducted at relatively low temperatures. The kinetics are rather sluggish, but the desired purple ammonium chromium alum eventually forms.
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From page 33... ...
or hexavalent process, the chromicacid electrolyte method is used primarily for surface fimshing and electroplating applications. Chromium trioxide, CrO3, is obtained from sodium dichromate.
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From page 34... ...
The low overall efficiency obtainable with hexavalent chromium makes it nonviable as an alternative method for the production of bulk, high-punty chromium metal for alloys. Thus, this method has not been used when large tonnages are required.
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From page 35... ...
. Catholyte Overflow ~ o Sulfur Dioxide l Reduced Anolyte ~ 35 Recrystallizing Filtering - I L L~rrous Ammonium Sulfate 3 I Chromium O_ ~ O Washing Depassing TMarker FIGURE 34 Flow sheet for production of electrolytic metal by the chrome-alum process.
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From page 36... ...
In the aluminothermic process, electric power is consumed externally to the process proper (in the smelting of aluminum reductant used in the process) but is nevertheless comparable to the electrolytic process in terms of energy consumption.
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From page 37... ...
In general, chromium-containing solutions that exit the process stream are mixed with the main process stream at the ferrochrome leaching stage, a practice driven largely by the cost of chromium units. These solutions include mother liquors from ferrous ammonium sulfate recrystallization and anolyte containing chromium (VI)
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