Simultaneous CO2 mineral sequestration and nickel separation from laterite leachate: Thermodynamic and experimental study

Global warming resulting from escalating CO2 emissions and rising nickel demand present dual challenges to the sustainable development. In this study, a process for simultaneous nickel separation and CO2 mineral sequestration was proposed by using the leachate derived from the process of roasting laterite with copperas followed by water leaching. From the thermodynamic study, it was found that nickel can dissolve in the leachate in the form of nickel-ammonium complexes, while magnesium precipitated as carbonates. Furthermore, Eh-pH (potential vs. pH) results demonstrated that the conditions for the formation of nickel-ammonium complexes closely resemble those for magnesium carbonates. Under optimized conditions with the initial solution pH of 10.8, CO32-/ Mg molar ratio of 2, reaction temperature of 30 degrees C, and reaction time of 1 h; over 95 % of Mg and 100 % of Fe can be converted into carbonates or hydroxides, with no more than 1 % Ni loss. Higher pH and CO32-/Mg molar ratios, along with lower temperatures, facilitated the separation of nickel from the magnesium and iron. The phase and microstructure of the precipitates were significantly influenced by the reaction temperature. At 30 degrees C, the precipitation product was MgCO3.3H2O, exhibiting a microstructure resembling porous spherical flowers; whereas at 80 degrees C, the precipitated phase was Mg5(OH)2(CO3)4.4H2O, also displaying a microstructure akin to porous spherical flowers. Efficient separation of nickel and magnesium in NH3-(NH4)2CO3-H2O was achieved by leveraging their distinct reaction properties, simultaneously sequestering CO2. This process achieved the maximum selective Ni recovery and CO2emission reduction in one step.