CO₂ mineral sequestration and nickel recovery from laterite ore 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 heat 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. In this process, the copperas was decomposed into SO₂, which sulfated the laterite ore by in situ gas–solid reaction. The addition of Na₂SO₄ facilitated the formation of low melting point substances, converting the gas–solid reactions into a multiphase gas–liquid-solid reaction, thus the extraction was enhanced. Meanwhile, the heat of sulfation of laterite ore can compensate the heat of copperas decomposition, reducing the overall energy consumption. The maximum extraction efficiency of 94 % for Mg and 87 % for Ni was achieved at Na₂SO₄ dosage larger than 10 wt%. The carbonation of MgSO₄-riched leachate experiments revealed the optimal CO₂ storage capacity was approximately 291 kg·t⁻¹ laterite ore. 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.