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ALKALINE NONCYANIDE ZINC PLATING WITH REFUSE OF RECOVERED CHEMICALS
Citation:
Peden, J. M. ALKALINE NONCYANIDE ZINC PLATING WITH REFUSE OF RECOVERED CHEMICALS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-94/148 (NTIS PB94-205549), 1994.
Impact/Purpose:
information
Description:
A metal finishing process can create environmental problems because it uses chemicals that are not only toxic but also resistant to degradation or decomposition. 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 system that was designed and installed, at P&H Plating Co., a Chicago area operation, used precipitation by pH adjustment to remove the zinc from the rinsewater. The precipitated zinc hydroxide was coLLected on fitters, dewatered using a fitter press, and stored for reuse in the stating line as needed. Once filtered, the water was recirculated to the rinsing portion of the plating Line. The recovery/recycle system successfully purified the rinsewater and facilitated the recycling of the cleaned water and the precipitated zinc hydroxide. Eliminating cyanide from the plating process meant the Line workers were dealing with a less toxic pLating bath, made compliance with regulations easier, and reduced treatment and disposal costs for the company. he recycling of the recovered water and the zinc hydroxide further reduced the costs for treatment and disposal. 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. Installation and use of this system for other ANC plating operations would result in reductions in wastes and increased economic benefits similar to those experienced by P&H PLating Co.