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Waste solid residuals from zinc and chromium plating

Hello all, my name is Andres Bernal, a project engineer in an electroplating shop in Colombia. We are treating the wastewater from acid zinc and chromium plating and we do not know what we should do or how we should treat the solids that come out of it. We have now about 3 tones of dried mud which we can not throw away. Not even our government knows how to dispose them. Does anybody knows what should be done with those? how to treat them?

Thanks a lot for your help.

Andres Bernal
heat treaters and electroplaters - Bogotá, Colombia
2007

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I assume you are using standard chemical treatment processes, including reduction of hexavalent chromium to trivalent before precipitation of all metals by pH rise. The US government considers this sludge to be hazardous waste even if it is not hazardous as long as it comes from nearly any type of electroplating. Testing by the USEPA Toxicity Characteristic Leachate Procedure should determine if it is hazardous. If it is, it can be stabilized by mixing with a generous quantity of Portland cement and then landfilled. If you do not stabilize it with the cement it will eventually leach the metals into the water table and you will regret it.

Paul Morkovsky
- Shiner, Texas, USA
2007