Quick and efficient co-treatment of Zn(2+)/Ni(2+) and CN(-) via the formation of Ni(CN)4(2-) intercalated larger ZnAl-LDH crystals

Abstract

The wide use of metal electroplating involving CN(-) necessitates the cost-effective treatment of both CN and metals (Zn, Cu, Ni etc.). In this research, we developed a novel strategy - Ni(2+)-assisted layered double hydroxide (LDH) precipitation - to simultaneously remove aqueous CN and Zn/Ni metals. The strategy is to convert CN(-)/Zn(CN)4(2-) to Ni(CN)4(2-) first, and then to quickly precipitate Ni(CN)4(2-)/CN(-) into LDH crystals. The conversion has been clearly evidenced by the change of CN characteristic FTIR bands of Zn-CN solution before and after adding Ni(NO3)2. The intercalation and efficient removal of CN have also been confirmed through the formation of LDH crystals XRD and SEM. In particular, a set of optimized experimental factors has been obtained by investigating their effects on CN removal efficiency in the simulated tests. Remarkably, over 95% CN were removed with high removal efficiencies of metals. Our results thus suggest that the current strategy is a quick, efficient and promising way to simultaneously treat both Ni and metals/CN rich electroplating wastewaters.

Keywords: Cyanide complex; Cyanide removal; Electroplating wastewater treatment; Larger crystals; Layered double hydroxide.