Study on reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H2S in single-metal and multi-metal systems

Determination of reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H2S in single-metal and multi-metal systems were studied to develop a process of metal recovery from plating wastewater. As samples, single-metal model wastewaters containing Cu, Sn, Zn or Ni, and multi-metal model wastewater containing Cu–Zn–Ni or Sn–Zn mixtures were used. In both single-metal and multi-metal systems, the pH value was precisely controlled at a value of 1.5 for CuS and SnS precipitation, 4.5 for ZnS precipitation and 6.5–7.0 for NiS precipitation. Subsequently, the sulfidation of Cu, Sn, Zn and Ni was evaluated. It was found that an amount of H2S equimolar to a given metal was sufficient to achieve almost complete precipitation of the particular metal. Further, the selectivity of metal precipitation was found to be higher than 95% in the Cu–Zn–Ni multi-metal system and higher than 91% in the Sn–Zn system. It was also found that the sulfidation reaction proceeded in accordance with Higbie’s penetration theory and reaction rate constants and mass-transfer coefficients under various experimental conditions were determined. Finally, the reaction rate constants obtained in single-metal and multi-metal systems were found to be almost the same indicating that the precipitation of a particular metal was not significantly affected by the presence of other components.