Pigments from spent Zn, Ni, Cu, and Cd electrolytes from electroplating industry

One of the problems of electroplating industry is the periodic discharge of concentrated spent electrolytes together with rinsing wastewater. This leads to irreversible loss of valuable components, as well as to the risk of heavy metal ions entering the environment, which have toxic, mutagenic, and carcinogenic effects. The paper presents research on the processing of spent electrolytes from electroplating industry of zinc, nickel, copper, and cadmium plating, collected over 3 years. Pigments of various colors were obtained by precipitation of zinc, nickel, copper, and cadmium ions by phosphate, hydroxide, and sodium carbonate. By their properties, i.e., whiteness 95-97%, residue after sieving on a sieve up to 0.04 wt.%, etc., the resulting pigments are not inferior to those currently presented on the world market. Following previous studies, a basic technological scheme for processing waste electrolytes with pigments production is proposed. Processing of spent electrolytes according to the proposed technology will make it possible to reduce the concentration of heavy metal ions to acceptable values (0.13-0.65 mg/L) for discharge. This will ensure stable and uninterrupted operation of local treatment facilities of electroplating industry.