Effective extraction of nickel and cobalt from sintered nickel alloy via reduction roasting and leaching

In this work, a carbothermic reduction technique is developed to improve the extraction of valuable metals from sintered nickel alloys by atmospheric acid leaching. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) analyses indicate that NiO in the sintered nickel alloy and the NiO coated by Ni2O3 hinders further dissolution of nickel. Nickel oxides can be transformed into easily leached metallic nickel by carbothermic reduction. The reduction roasting was investigated and optimized by thermodynamic analysis, thermogravimetry-mass spectrometry, XRD, and response surface methodology (RSM). The results show that the leaching efficiencies of nickel and cobalt are respectively increased from 80.34% and 69.92% to 98.65% and 96.71% after the reduction roasting under the optimized conditions: 935 °C of temperature, 50 min of time, and 29.9% of carbon dosage. The leaching of nickel was optimized by single-factor test method and the optimum conditions have been established as: 150 g/L of H2SO4 concentration, 25% of H2O2 dosage, 10 mL/g of liquid–solid ratio, 400 rpm of stirring speed, 80 °C of temperature, and 80 min of time. The kinetic analysis of leaching process shows that the activation energies of nickel and cobalt leaching are 20.71 kJ/mol and 16.33 kJ/mol, respectively, indicating that the leaching process is an internal diffusion control process. This study provides a feasible and effective approach to extract nickel from sintered alloys.