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To comply with zinc effluent regulations, we investigated the influence of plating chemicals on zinc removal from zinc chloride solutions by coagulation with sodium hydroxide. Plating chemicals including ethylenediaminetetraacetic acid disodium salt (EDTA･2Na) , ammonium chloride, sodium citrate, triethanolamine (TEA) , sodium diphosphate, and potassium dihydrogen phosphate decrease zinc removal capabilities. The zinc removal capability in the solutions depends on the concentrations of additive compounds. Especially, the addition of EDTA･2Na and sodium diphosphate exert an important influence that is attributable to the complex forming reaction of zinc and EDTA･2Na. For the addition of 8.8 mg/L EDTA･2Na, removal of zinc from the solutions and exceeding the effluent regulation value of zinc was difficult. Furthermore, to reduce compounds interfering in wastewater, we examine emissions management. Results demonstrated that the drain of barrel processing increases the interfering compounds in wastewater. Plating chemicals disturb the zinc wastewater treatment.

Purpose To comply with the effluent regulation of boron, replacement of boric acid with citric acid in a nickel electroplating bath is proposed. Although the bath avoids the discharge of boron, it increases the discharge of nickel owing to the chelating effect of citric acid, which disturbs the wastewater treatment. To balance this trade-off, the environmental impacts of a traditional nickel plating process (the Watts bath) and the citrate bath must be compared by life cycle assessment. Methods The life cycle impact assessment method was LIME2. To estimate the trade-off between boron and nickel discharge into wastewater, the characterization and damage factors on human toxicity and ecotoxicity were calculated. The processes were then compared using data from actual processes. The functional unit was Bplating per 1-kg part.Ĥ owever, the plating efficiency depends on the type, shape, and surface area of the part. The data of the citrate bath were modeled. In the modeling, the amounts of nickel chloride and nickel sulfate in the citrate bath were based on the Watts bath. Results and discussion In comparison with other chemicals, the calculated characterization and damage factors of boron and nickel were found to be reasonable. The integration results revealed that the citrate bath exerted greater environmental impact than the Watts bath. Although the Watts bath involved more environmentally damaging processes than the citrate bath, the sum of these impacts was much smaller than the impact of effluent from the citrate bath. Moreover, the environmental impact of effluent can be significantly reduced by flocculants, with almost no additional environmental impact incurred by the increased sludge. Conclusions The newly developed citrate plating bath exerts higher environmental impact than the traditional Watts bath because the environmental impacts of the release of nickel chelated with citric acid exceed the reduced boron emissions. Therefore, there is a trade-off between the two methods. When installing the citrate bath, the wastewater treatment must be altered to reduce the nickel emissions.

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