A process for the extraction of nickel, cobalt and manganese from slurries of their ores such as laterite, saprolite or manganese nodules in an aqueous acid solution while irradiating the solution with electromagnetic energy such as microwave energy. The acid may be hydrochloric acid, sulphurous acid and/or sulphuric acid and the acid solution may be blended with high concentrations of halite and magnesium ions to further control the dissolution of magnesia from the ore. A reactor including electromagnetic wave generators is also included.