Studies on treatment and recycling system for non-electrolytic metal-plating wastes

非电解金属涂覆技术已广泛用于在基材上表面沉积镍、铜、金或银等。金属电镀溶液除了含有感兴趣的金属离子外，还含有诸如亚磷酸盐（1.2M）和次磷酸盐（0.8M）的还原剂。然而，金属电镀溶液的还原能力在重复使用后降低，最终电镀溶液变得不可用。另一方面，根据日本环境保护法，废水中总磷酸盐的极限浓度被限制为16 mg/L。为了保护环境，需要从废水中回收和循环利用磷。采用简单快速的氧化沉淀法，建立了化学处理电镀废液中亚磷酸盐和次磷酸盐的方法。推荐的处理程序如下：向50.0mL的废样品溶液中加入25 mL的4 M氢氧化钠以沉淀Ni（OH）_2。过滤除去沉淀后，加入13 mL 3 M过氧化氢和0.4 mL 0.2M铜溶液，在70 ℃下加热20.0 mL滤液40 min。然后用Chelex-100树脂吸附分离滤液中残留的铜离子。由于所得溶液（5.0 mL）仅含有磷酸根离子，因此向5.0 mL 1.3M氯化铵和10.0 mL 1.3M氯化镁中加入氨以调节pH 8.3至8.8。作为上述化学处理的结果，超过95%的磷酸盐以铵盐的形式回收，如果获得细粒度的沉淀物，则其可用于肥料。化学氧化工艺可为镀镍液的回收利用提供有益的参考。因此，为了环境保护，避免了废料的排放。

A non-electrolytic metal-coating technique has been widely used for the surface deposition of nickel, copper, gold or silver etc. onto base materials. The metal electroplating solution contains such reducing agents as phosphite (1.2M) and hypophosphite (0.8M) in addition to the metal ion of interest. The reducing ability of metal electroplating solutions, however, decreases after repeated uses, and finally the electroplating solution becomes unusable. On the other hand, the limit concentration of total phosphate in wastewater is restricted to 16 mg/L according to the Japanese Environmental Protection Law. A recovery and recycling technique of phosphorus from the wastewateris needed to protect the environmental. We have tried to establish a method of chemical treatment of phosphite and hypophosphite in metal plating wastes by using a simple and rapid oxidation followed by precipitation. The recommended treatment procedure is as follows : To 50.OmL of a waste sample solution, 25 mL of 4M sodium hydroxide was added to precipitate Ni (OH)_2. After the precipitate was removed by filtration, 20.0 ml of the filtrate was heated after addition of 13 mL of 3M hydrogen peroxide and 0.4 mL of 0.2M cupric solution at 70 ℃ for 40 min. The cupric ion, which remained in the filtrate, was then separated by adsorption with Chelex-100 resin. Because the resultant solution(5.O mL) contained only phosphate ion, 5.0 ml of 1.3M ammonium chloride and 10.0 mL of 1.3M magnesium chloride was added with ammonia to adjust pH 8.3〜8.8. The precipitate NH_4MgP0_4 was formed finally.As a result of the chemical treatment described above, more than 95 % of the phosphate was recovered as the ammonium salt, which could be used for a fertilizer if the fine particle size of the precipitate was obtained. The chemical oxidation process may be helpful for the recycling technique of a nickel-plating solution used. Thus, the emission of the waste materials to be avoided for environmental protection.