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

一种非电解金属涂层技术已被广泛用于在基材上表面沉积镍、铜、金或银等。该金属电镀液除含有感兴趣的金属离子外，还含有亚磷酸盐(1.2M)和次亚磷酸盐(0.8M)等还原剂。然而，金属电镀液的还原能力在重复使用后会下降，最终导致电镀液无法使用。另一方面，根据日本环保法，废水中总磷的极限浓度限制在16毫克/L。为了保护环境，需要一种从废水中回收和循环利用磷的技术。我们试图建立一种简单、快速的氧化-沉淀法化学处理电镀废液中的亚磷酸盐和次磷酸盐的方法。推荐的处理程序为：废样液50 mg，加入25 m L 4M氢氧化钠沉淀Ni(OH)_2，过滤除去沉淀物后，加入3M过氧化氢13 m L，0.2M铜溶液0.4 m L，在70℃下加热40 m in，滤液20.0m l。滤液中残留的铜离子用CHILEX-100树脂吸附分离。由于生成的溶液(5.0mL)中只含有磷酸根离子，因此加入5.0mL1.3M氯化铵和10.0mL1.3M氯化镁，以调节pH值为8.3~8.8。经上述化学处理后，95%以上的磷酸盐被回收为铵盐，如果得到沉淀的细小颗粒，则可将其用作肥料。该化学氧化工艺有助于回收所用镀镍液的技术。因此，要避免废物的排放，以保护环境。

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.