Thermodynamic simulation of metal behaviors in Cu2+-Ni2+-NH3-NH4+-C2O42--H2O system

Abstract

To investigate the behaviors of Cu2+ and Ni2+ with the change of conditions in Cu2+-Ni2+-NH3-NH4+- C2O42--H2O reaction system, mathematical models of thermodynamics based on the principle of mass conservation were established. The simulation results indicate that the precipitation of metal ions from the aqueous phase is a complicated dynamic equilibrium process, during which the coordination reactions of Cu2+ and Ni2+ with NH3 forming [Cu(NH3)n]2+ (n=3-5) and [Ni(NH3)m]2+ (m=3-6) are predominant under high pH conditions, respectively. The pH ranges for the simultaneous precipitation of Cu2+ and Ni2+ are 2.0-6.5 and 2.0-5.5 when [NH3]T equals 0.6 and 4.2 mol/L, respectively, with the prefixed [C2O42-]T of 0.6 mol/L. Due to the fractional precipitation of Cu2+ and Ni2+, Cu-Ni composite is obtained after the thermal decomposition of Cu-Ni oxalate complex salts prepared in a pure water system when pH>7.0. By applying the mixed solvent (water/ethanol) as the precipitation medium, the Cu-Ni alloy rods can be finally fabricated with high purity and crystallinity.