Treatment of real deplating wastewater through an environmental friendly precipitation-electrodeposition-oxidation process: Recovery of silver and copper and reuse of wastewater

In order to avoid the discharge of deplating wastewater with high concentration of NO3−, an environmental friendly process, consisting of precipitation, electrodeposition and oxidation, is developed in this research for the treatment of real high acidic deplating wastewater containing Ag+, Cu2+, NO3− and chemical oxygen demand (COD). The wastewater is treated by precipitation to remove Ag+, electrodeposition to remove Cu2+, oxidation to reduce COD successively and then reused for deplating plastic plated parts. In precipitation process, 99.9% Ag+ in wastewater is precipitated by HCl and silver metal is then recovered through the replacement of AgCl by iron powder. Because of the high conductivity, Cu2+ in wastewater is then separated and recovered as copper metal on cathode through electrodeposition. The effect of electrodeposition parameters including cathode material, current density, electrode distance, reaction temperature and Cu2+ initial concentration is investigated. Up to 89.3% Cu2+ can be recovered in 80 min at the optimal condition. Finally, the COD is removed from 1360 mg L−1 to 378 mg L−1 in subsequent H2O2 oxidation process to ensure the reuse of water. Because the valuable Ag and Cu metals are recovered and the COD is removed, the wastewater can be reused as deplating solution. The estimated profit of this precipitation-electrodeposition-oxidation process reveals its practical feasibility. Furthermore, the process realizes the cleaner production of the deplating technology because it avoids the discharge of unmanageable wastewater with high NO3− concentration. More importantly, the process can also be improved to treat similar wastewater.