The effect of iron precipitation upon nickel losses from synthetic atmospheric nickel laterite leach solutions: Statistical analysis and modelling

Atmospheric acid leaching (AL) of low-grade nickel laterite ores can produce a pregnant leach solution (PLS) containing large amounts of soluble iron. Purification of the leach solution by iron precipitation with an alkaline reagent often causes an associated loss of valuable nickel. In this study, the effects of the factors governing the iron precipitation process upon nickel loss were investigated in synthetic nickel laterite AL liquors containing just nickel and iron by statistical analysis and modelling. The factors examined in this study were pH, temperature, neutralizing agent, initial Fe/Ni ratio in the PLS and stirring speed. The significance of each factor and their interactive effects were evaluated using statistically-designed experiments, where iron removal efficiency (%) and nickel loss (%) were the measured responses. A one quarter fractional factorial design was performed to screen for factors that have more important effects on the responses, and then the principal factors were further optimized in a Box–Behnken Design (BBD) experiment. The BBD which is an effective response surface methodology was applied to fit quadratic models to describe the relationships between the responses and factors. Quadratic response functions were derived for iron removal efficiency (%) and nickel loss (%) by applying a least squares method. The three-dimensional response surface and corresponding contour plots clearly showed the relationships between the responses and interactive factors.