The ultrasound leaching kinetics of gold in the thiosulfate leaching process catalysed by cobalt ammonia

The effect of ultrasound on gold leaching rate and kinetics was investigated in the Co-NH3-S2O32- system. First, the effects of ultrasound power, temperature, the concentration of thiosulfate, cobalt and ammonia on gold leaching rate were studied under ultrasound. The optimized leaching parameters are 0.03 M Co2+, 0.2 MS2O32-, 1 M NH3, 323 K, and 750 W ultrasonic power. Moreover, the leaching rate of gold is 8 times faster, and the extraction percentage is approximately 25% higher, under ultrasound than under conventional conditions. The experimental results show that ultrasound can effectively enhance the leaching rate and the extraction percentage. The kinetic analysis indicates that the internal diffusion step controlled the ultrasound leaching process. The increase in the leaching rate under ultrasound is due to the decrease of activation energy from 22.65 kJ/mol to 13.86 kJ/mol. Therefore, ultrasound efficiently improved the leaching rate of gold in the Co-NH3-S2O32- leaching system.