Improved thiourea leaching of gold with additives from calcine by mechanical activation and its mechanism

Abstract

• Thiourea leaching with mechanical activation was proposed to extract gold from calcine. • The addition of CMN can effectively prevent the passivation by sulfur and the agglomeration of particles. • The mechanism of CMN and mechanical activation is revealed. • This process proposed in this work can efficiently and cleanly extract gold. • This process has a potential application in industry. Non-cyanide gold leaching serves as a promising green approach for eliminating cyanide utilization and the resulting environmental pollution from cyanide use. In this work, thiourea leaching combined with mechanical activation was employed to extract gold from a refractory gold concentrate calcine. The optimal reaction conditions were determined as: 2.5 g/L thiourea, 2 g/L Fe 3+ , 0.6 g/L CMN, 45 Hz input frequency, liquid to solid ratio (L/S) of 4, temperature of 40 °C, and leaching time of 55 min. Addition of sodium lignosulfonate increased gold extraction from 93.6% to 96.5%. Mechanical activation proved to be a promising method to reduce the particle size of minerals, which effectively increases the specific surface area and pore diameter of minerals and thus strengthens the leaching reaction. Furthermore, CMN is capable of preventing particle agglomeration and the coating by a sulfur passivation layer, which enhances gold extraction efficiency. Additionally, a pilot-scale test was conducted to validate the reliability of this novel technique. The pilot-scale tests proved this method to be an efficient process for gold extraction with opportunities for scaling up.