Thermodynamic Aspects of the Roasting Processes in the Pre-treatment of Nickelferrous Garnierites

Abstract

The chemistry of pre-calcination and reduction roast processes with H₂ + H₂O gaseous mixture was analyzed, in order to find the best nickel and cobalt recoveries after selective roasting of nickelferrous laterites

A thermodynamic analysis of the pre-reduction of garnieritic ores aiming NiO and CoO reduction showed that the low NiO activity in the ore demands highly aggressive reducing conditions to attain reasonable nickel recoveries. Between 650-850°C, the highest nickel recoveries through amoniacal leaching was obtained at 750°C with 60% H₂ + 40% H₂0. Tests at 900°C revealed an unexpected high nickel recovery probably due to the presence of metallic iron which acted as a solvent for metallic nickel, favoring in consequence its metallization.