Mechanism of ultrasound-assisted copper cementation in zinc sulfate solution

Abstract

The ultrasound-assisted copper cementation in zinc sulfate solution was investigated from microscopic and macroscopic views. The effect of ultrasound on the morphology of cemented product and Cu2+ removal efficiency under different conditions was analyzed by SEM with EDS, optical microscopy (OM), XRD and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The results show that the ultrasound has a thermal effect on the solution, and higher temperature can promote copper cementation obviously. It revealed a definite correlation between the morphology of cemented product and the removal of impurity Cu2+ in the solution. The increased power of ultrasound can promote Cu cementation, and Cu removal can be up to >99 % when the ultrasound power reaches 1500 W, suggesting that the powerful ultrasound strengthens diffusion in the bulk solution and through the porous product layer with a dendrite structure. The kinetics fitted results and the calculated activation energy (Ea = 10.86 kJ/mol) from the double exponential model indicated that the diffusion step governs ultrasound-assisted cementation, and the diffusion rate k2 increases with the power of the ultrasound field. However, the ultrasound also enhances the hydrogen evolution reaction between zinc and proton in the solution with a low pH level at the same time, leading to excessive zinc consumption and precipitation of basic zinc sulfates. It was actually unfavorable to economical purification for zinc electrowinning.