HCI Leaching and Acid Regeneration using MgCii Brines and Molten Salt Hydrates

HCl leaching using molten salt hydrates has the potential to improve the extraction of nickel from laterite ores. However, recovery of HCl is key to process economics. The authors have developed a proposed laterite leach circuit using an alternative HCl recovery route. This circuit envisions a leach by concentrated (33%) HCl in an MgCii molten salt hydrate or brine medium, followed by nickel and cobalt recovery and iron precipitation. Magnesium and chloride are precipitated from solution as magnesium hydroxychloride; this hydroxychloride is thermally decomposed to produce HCl gas. The proposed flowsheet employs a chloride leach circuit with simpler equipment and lower energy costs than the conventional pyrohydrolysis method. Laboratory work investigated key aspects of the flowsheet, including the precipitation of magnesium hydroxychlorides and their composition, magnesium hydroxychloride thermal decomposition, and iron control. The results indicate a significant improvement in recovery efficiency and reduction in operational costs, making this method a viable alternative for nickel extraction from laterite ores.