Experimental and Mechanistic Study on Copper Leaching from Copper Water-Quenched Slag Enhanced by Sodium Gluconate

Copper water-quenched slag (CWQS), a critical secondary copper resource, faces restricted copper leaching during ammonia leaching due to the generation of passivation films on the surface of copper matte. To address this, a novel ammonia-sodium gluconate (SG) oxidation leaching was proposed. Process mineralogy, leaching thermodynamics, single-factor experiments, kinetics, and analyses (metallographic microscope, SEM-EDS and XPS) elucidated the properties of CWQS, scheme feasibility, copper leaching behavior, rate-controlling step and activation energy of the leaching process, and mechanism of SG enhancing copper leaching efficiency. Results show 95.23% copper leaching from CWQS, a 2.99% increase with SG. The leaching process is governed by mixed control and the activation energy was decreased by 4.16 kJ/mol by adding SG. Mechanistically, SG reacts with transient Fe3+ to form soluble Fe (C6H11O7)3, inhibiting Fe (OH)3 passivation film deposition on copper matte. It also reacts with preformed passivation films via complexation-dissolution, reducing thickness from 2.43 to 0.49 μm and transforming structure from dense to porous, thereby facilitating diffusion and accelerating copper leaching kinetics. Economic analysis shows adding SG can generate an incremental revenue of ∼3.40 CNY per ton of CWQS. The approach achieves economical and efficient copper recovery, presenting an alternative for the sustainable utilization of CWQS.