Separation of Nickel and Magnesium from Laterite Ore for Simultaneous Co2 Mineralization and Nickel Recovery by Using Waste Copperas

CO2 mineral sequestration is one of the most promising strategies for combating global warming, which is composed of direct and indirect pathways. However, the high cost and energy consumption for recycling reagents used in the indirect carbonation process is the biggest obstacle for its widespread applications. In this study, a novel process by using a solid waste, copperas, as reagent to extract magnesium and nickel from laterite ore was proposed for simultaneous CO2 mineralization and recovery of nickel. Thermodynamic results indicated the co-extraction of magnesium and nickel from laterite by roasting with copperas was feasible. The effects of process parameters on the extraction were investigated systematically. It was found that the optimal roasting conditions were as follows: laterite particle size of 100-200 mesh, temperature of 650 °C, copperas to laterite mass ratio of 4:1 and roasting time of 2 h. The addition of trace Na2SO4 could effectively improve the extraction of Mg and Ni. The maximum extraction efficiency of 93.7% for Mg and 87% for Ni was achieved at Na2SO4 dosage larger than 10wt%. The addition of Na2SO4 promoted the formation of low melting point substances, converting the gas-solid reactions into gas-liquid-solid multi-phased reactions, thus the extraction was enhanced. The carbonation of MgSO4-riched leachate results indicated that the optimal CO2 storage capacity was approximately 291 kg·t-1 laterite ore. The mineralized product was mainly MgCO3·3H2O at lower temperature and Mg5(CO3)4(OH)2·4H2O at higher temperature. Compared with the conventional acid-based Mg extracted process for CO2 mineralization, the cheap copperas avoided the recycle of reagent and obtained weak acidic leachate, reducing the amount of alkali used in the subsequent carbonation process