Process and kinetics of the selective extraction of cobalt from high-silicon low-grade cobalt ores using ammonia leaching

An ammonia-based system was used to selectively leach cobalt (Co) from an African high-silicon low-grade Co ore, and the other elemental impurities were inhibited from leaching in this process. This process was simple and environmentally friendly. The results revealed that the leaching ratio of Co can reach up to 95.61% using (NH₄)₂SO₄ as a leaching agent under the following materials and conditions: (NH₄)₂SO₄ concentration 300 g/L, reductant dosage 0.7 g, leaching temperature 353 K, reaction time 4 h, and liquid–solid ratio 6 mL/g. The leaching kinetics of Co showed that the apparent activation energy of Co leaching was 76.07 kJ/mol (i.e., in the range of 40–300 kJ/mol). This indicated that the leaching of Co from the Co ore was controlled by an interfacial chemical reaction, and then the developed leaching kinetics model of the Co can be expressed as 1-(1-\alpha )^1/3= 28.01\times 10^3\times r_0^-1\times C_(\rm NH_4)_2\rmSO_4^1.5\times \rm exp(-76073/8.314T)\timest, where α is the leaching ratio (%) of Co, r₀ is the average radius (m) of the Co ore particles, T is the temperature (K), and C_(\rm NH_4)_2\rm SO_4is the initial reactant concentration (kg/m³).