New insights into coagulation-enrichment and hydrometallurgical recovery of Sn, Cu, Ni from electroplating wastewater

Abstract

The tin plating industry is widely utilized in steel rolling and furniture manufacturing industries, employing tin-containing agents for electroplating. This process inevitably discharges electroplating wastewater. Such wastewater was rich in heavy metals and poses serious environmental hazards. The recovery of heavy metals from the wastewater was of research in recent decades. Herein, a novel strategy was developed to recover Tin (Sn), Copper (Cu) and Nickel (Ni) from the wastewater via a combined coagulation and hydrometallurgy route. The wastewater contained 397 mg/L tin, 85 mg/L copper and 31 mg/L nickel, and was coagulated by adding a high dosage of 300 mg/L polyaluminium chloride (PAC). After that, Tin, Copper, Nickel were enriched in the generated sludge, and then completely leachate into mixed nitric and hydrochloric acid. The acid leachate was treated by a two-step hydrothermal route with the addition of glucose/nitrate, to firstly crystallized 99.23 % tin as cassiterite particles (contained 98.5 % Tin), and then to precipitate 97.31 % aluminum as natroalunite sphere (contained 99.2 % aluminum), with the loss of copper/nickel <4 %. The thermodynamic analysis showed that the hydrolysis of tin as cassiterite spontaneous started at 120 °C at pH 0.3, and that of aluminum as natroalunite also occurred in the presence of sulfate, but these of copper/nickel did not occur at pH < 0.7. After that, the resulting leachate was extracted by using Acorga M5640 and HBL110, respectively, to separate 91.9 % copper as copper sulfate hydrate and 93.6 % nickel as nickelblodite. This proposed a practical strategy for the enrichment and recovery of heavy metals from wastewater.