Atmospheric leach process for the recovery of nickel and cobalt from limonite and saprolite ores

Abstract

A process is provided for leaching nickeliferous laterite ores by hydrometallurgical methods at temperatures below the boiling point of the pulp and at atmospheric pressure from which high overall nickel and cobalt extractions are obtained. The high iron fraction of the laterite, referred to as limonite, is first contacted with a concentrated mineral acid to partially or completely dissolve the iron and nickel in solution. During this process, a reducing agent is used to keep the redox potential in solution below 1000 mV to enhance cobalt dissolution and more advantageously between 1000 and 900 mV to avoid reduction of ferric iron. Further mixing of the leach slurry in the presence of sodium, potassium, or ammonium will allow the formation of iron jarosite at ambient pressure. The resulting acid from iron hydrolysis is neutralized with the low iron fraction of the laterite ore (saprolite) dissolving nickel into solution. The resulting slurry can then be treated with conventional methods to recover nickel and cobalt solution.