Abstract
Due to the sharp increase in demand and prices for nickel and cobalt, the search for new sources of raw materials has become a pressing issue. This study presents a comprehensive thermodynamic and kinetic analysis of the combined method of oxygen-deficient oxidative roasting and subsequent acid leaching to extract nickel and cobalt from pyrite waste sourced from Kazakhstani enterprises. The thermodynamic analysis showed that, under oxygen deficiency, thermal decomposition of higher sulfides forms non-stoichiometric, soluble lower sulfides of iron, nickel, and cobalt. The kinetic study revealed that the process is complex and multi-stage, and that it proceeds at a high rate in the 610–680 °C range, where kinetic factors control it. Activation energies were calculated for three stages: 105–115 kJ/mol for Stage I (450–479.3 °C), 310–320 kJ/mol for Stage II (661.8 °C), and 390–420 kJ/mol for Stage III (749.7–789 °C). Experimental studies confirmed the effectiveness of roasting at 700 °C for 60 minutes. Subsequent sulfuric acid leaching of the obtained sinders under optimal conditions (sulfuric acid excess coefficient R of 1.5 times the stoichiometric amount, temperature of 100 °C, and a duration of 2 hours) yielded high metal recoveries: 94.5% Fe, 93.4% Ni, and 91% Co. The developed technology, combining thermal activation and leaching, proved effective and is recommended for processing similar raw materials.