Reductive leaching behaviour of manganese and cobalt phases in laterite and manganese ores

The reductive leaching behaviour of manganese (Mn) and cobalt (Co) in a laterite and a pure manganese ore was investigated by varying and optimising various leaching parameters for the recovery of Mn and Co. The effect of different reducing agents (FeSO4, Na2SO3), sulfuric acid concentration, reductant/ore mass ratio, leaching time, and reaction temperature on the dissolution of Mn and Co from the laterite and manganese ores were studied. Furthermore, the kinetics of Mn and Co leaching from laterite ore was studied. The Mn and Co recovery from both ores increased with increasing H2SO4 concentration, reductant/ore mass ratio, leaching time, and reaction temperature. Based on the manganese and cobalt extraction efficiency, FeSO4 was the best reductant among the two evaluated reductants. The optimum leaching of Mn and Co from the laterite ore occurred at a H2SO4 concentration of 0.51 M, a reductant/ore mass ratio of 2.7, a leaching time of 5 h, and a reaction temperature of 363.15 K. For the manganese ore the optimum leaching of these elements at the same temperature occurred at a higher H2SO4 concentration of 1.02 M, a reductant/ore mass ratio of 2.4, and a shorter leaching time of 2 h. The results from the optimization studies showed that the leaching trends of Mn and Co phases in the manganese ore are similar to those of the Mn and Co phases in the laterite ore. Moreover, Co was co-leached together with Mn suggesting a degree of correlation of cobalt to manganese mineral phases in both, the laterite, and the manganese ores. The kinetics of the reductive leaching of Mn and Co for the laterite ore could well be described by the Avrami model reflected by high correlation coefficient values of R2 > 0.95. The leaching of Mn and Co occurred rapidly at the initial leaching stage but gradually slowed down with prolonged leaching time. This was indicated by the modal parameter (n) values that were <1, at varying reaction temperatures. The experiments showed further that Mn and Co leaching in laterite ore is a diffusion-controlled reaction, which was indicated by the apparent activation energy of 11.7 kJ mol- 1 and 11.1 kJ mol-1, respectively.