Abstract: There are disclosed method and apparatus for recovering chromium from chromium-containing wastes, using an electrolytic oxidation cell divided by an anion exchange membrane and a coupled transport module containing a membrane containing a chromium(VI) complexing agent.

Abstract: The residual metal content of tightly chelated heavy metal-containing effluents is reduced by carrying out a sulfide precipitation process in the presence of a seed material comprising an added unchelated soluble heavy metal salt, preferably with an adjustment of pH to at least above about 9.0, with optional variations including passage through a mixed filter media comprising at least two particulate ingredients and regeneration of the used filter media.

Abstract: A system and process has been devised for measuring and constantly maintaining a desired concentration of soluble sulfides in a processing solution for the purpose of fully maintaining its function. Sulfide regenerating solution is automatically introduced into the processing solution in an amount as constantly determined by concentration variations in the processing solution, to thus provide the processing solution with its most effective sulfide content. A constant take-off flow of processing solution is thoroughly mixed with a sulfide stabilizing solution flow to provide a tempered solution flow that is passed through a flow block having a sulfide measuring electrode and a reference electrode. Variable negative voltage generated on the sulfide electrode is sensed and compared with a substantially constant voltage generated on the reference electrode and is amplified in a controller assembly.