Chromitiferous overburden containing nickel in oxide form is reduced with C
O-CO2-N-2 gas mixtures. This converts the nickel oxide to metallic nickel a
nd restricts the iron oxide to the magnetite state to extract the nickel. R
eduction experiments were carried out on 500-g samples in a bench-scale ver
tical reactor. The tests were run. to establish the process parameters, inc
luding the optimum partial pressure of CO, the reducing gas flow rate, gran
ule size and roasting time. The reduced calcine is then subjected to an amm
onia-ammoniacal carbonate leach to extract nickel selectively as its amine
complex. More than 90% of the nickel could be extracted with a volumetric C
O/(CO+CO2) ratio of 0.57 at 750 degreesC and a roasting time of 90 min. The
addition of 2.5% (by weight) charcoal to the granules improved nickel extr
action by 11% to 19%. Nickel leaching efficiency with ammoniacal solution i
s compared to the bromine-methanol method.