||Alkaline Noncyanide Zinc Plating with Reuse of Recovered Chemicals.
Peden, J. M. ;
||Illinois Dept. of Energy and Natural Resources, Champaign. Hazardous Waste Research and Information Center.;Environmental Protection Agency, Cincinnati, OH. Risk Reduction Engineering Lab.
Zinc coatings ;
Water pollution control ;
Water treatment ;
Waste water reuse ;
Chemical removals(Sewage treatment) ;
Materials recovery ;
Waste recycling ;
Cost engineering ;
Waste minimization ;
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A metal finishing process can create environmental problems because it uses chemicals that are not only toxic but also resistant to degradation or decomposition. A study was undertaken at a zinc electroplating operation to achieve zero discharge of wastewater and total recycle of recovered precipitates. The first step in this project was to change an existing zinc cyanide (CN) plating line to one that used an alkaline noncyanide (ANC) zinc bath. The project then investigated a closed-loop system to treat plating rinsewater from the ANC zinc plating line so the plating chemicals were recovered and the water purified. The goal was to return both the recovered zinc hydroxide and the clean water to the plating line for continued use. The replacement of this single CN line with an ANC line resulted in an annual savings to P&H Plating of $14,000 from the elimination of the need to pretreat the plating line rinsewater to oxidize cyanide. The addition of the recovery/recycle system increased the company's savings to $62,000/year. The reuse of 30% of the recovered zinc hydroxide and 70% of the treated rinsewater reduced annual water usage and wastewater discharge by 841,911 gallons and reduced the amount of sludge disposed annually by 14 cubic yards. The payback period for the recovery/recycle system is slightly less than 18 months.