Abstract: A process and equipment is disclosed for minimizing sludge formation in removal of chromium and heavy metals from chromium contaminated groundwater by using sodium sulfite for oxygen removal thereby minimizing the amount of ferrous salt necessary for reduction of chromium VI to chromium III in an alkaline solution and also minimizing the amount of excess iron salt to coprecipitate as an hydroxide to effect essentially complete removal of other heavy metals.

Abstract: A method and compositions using a first ferrous iron containing solution with the iron concentration in excess of theoretical requirements to treat a contaminated site to reduce hexavalent chromium to trivalent chromium and coprecipitate trivalent chromium with other heavy metals and using a second solution of silicate containing a destabilizing salt to form a relatively impermeable gel in the contaminated site thereby fixing metals and organics to the extent that there should be no detectable ground water contamination.

Abstract: An integrated process for heavy metal and cyanide removal in aqueous waste stream from plating processes wherein cyanide is oxidized by hypochlorite at approximately pH of 11.5 and hexavalent chromium is reduced to trivalent chromium at ambient temperature with ferrous sulfate at pH of 9.5; excess hypochlorite from cyanide destruction reacts with ferrous sulfate and additional ferrous sulfate is added to reduce hexavalent chromium to trivalent chromium to allow hydroxide co-precipitation with hydroxides of the ferric iron and hydroxides of copper, chromium, zinc, cadmium, manganese, etc., which are then separated by settling and filtration.