Carbothermic reduction of low-grade laterite-graphite composite pellets

Abstract

The appropriate carbothermic reduction parameters of low-grade laterite-graphite pellets and the influence of calcined temperature on these for upgrading the nickel (Ni) content in pellets were evaluated. Afterward, the impact of the additive (Na2SO4) on Ni grade and Ni recovery of calcined pellets at optimal reduction conditions was also investigated. XRD analysis, thermodynamic calculation, isothermal reduction experiment, BET-specific surface area analysis, bromine methyl alcohol solution analysis, and chemical composition analysis were used in order to obtain the associated parameters. In this study, it showed the improvement of Ni grade and Ni recovery rate of 673 K-calcined laterite-graphite pellets can respectively reach > 30 mass % and 90.2 mass % under the conditions of reduction temperature = 1373 K, reduction time = 30 min, and the mole ratio of fixed carbon to reducible oxygen of iron and nickel in laterite nickel ore (C/O) = 0.6. The reasons were proposed that the 673 K-calcined laterite ores have the highest specific surface area of 46.8 m2/g with pores in the size of 29.7 Å to provide faster Ni reduction at the initial stage followed by reduction. The addition of 5 mass % additive resulted in the best Ni grade of > 30 mass % and the best Ni recovery rate of 93.8 mass % in pellets at the same reduction temperature, time and (C/O) molar ratio.