Studies on reduction roasting of chromite overburden in a multiple hearth furnace for extraction of nickel and cobalt

A possibility of extracting nickel and cobalt from chromite over-burden (COB) of Sukinda, Orissa, containing 0.3 to 1.1% Ni and traces of cobalt (0.02 - 0.06%) using reduction roasting followed by ammoniacal leaching process has been examined. The COB used in this investigation contained mainly 0.65% Ni, 39.48% Fe 2 O 3 , 10.64% Cr 2 O 3 and 28.5% SiO 2 with 6% LOI. Significant process variables in the studies of roast reduction include the reducing gas composition, temperature of reduction and residence time etc. Studies were carried out in a oil fired multiple hearth furnace (MHF) of 7 hearths having maximum 0.75 ton / day ore handling capacity. Maximum nickel and cobalt extraction of 78.2 and 57.6% respectively were achieved by reducing the ore in MHF with CO/(CO+CO 2 ) ration of 0.6 at 760°C temperature for 90 minutes under 1-2mm WG pressure. Details of design parameters were evaluated for successful design and operation of a pilot plant.