Saprolite Leaching and Iron Control in Concentrated Magnesium Chloride Brines

MgCl2 brines present a number of potential advantages for the processing of saprolite ores for nickel production. Concentrated MgCl2 solutions enhance the activity of acid used, allow atmospheric leaching at elevated temperature and inhibit magnesium dissolution, which reduces acid consumption and increases metal selectivity. However, with a chloride system it is economically requisite to recover hydrochloric acid, conventionally accomplished by pyrohydrolysis. This work was performed in conjunction with a novel flowsheet for the processing on saprolite ores, which recovers HCl by the precipitation and subsequent decomposition of magnesium hydroxychlorides, alleviating some of the issues with pyrohydrolysis. Leaching and iron control experiments have been conducted in concentrated MgCl2 brines, up to 4.5 m, to determine the most amenable process conditions. It was determined that > 95% extraction of metals was possible using both aqueous and gaseous HCl. In addition, the feasibility of iron control by precipitation with MgO addition was proven.MAS