Study of Nickeliferrous Laterite Reduction

Abstract

<p>Laterite is an important resource for the production of nickel. Pre-reduction of laterite is a critical step for all laterite based nickel production processes. The main kinds oflaterite, limonitic and serpentinic ore, behave differently upon reduction. In this study, general knowledge of laterites and nickel production were introduced. Research on laterite pre-reduction was reviewed. Using the compositions of two of laterite samples received from INCO Ltd, a thermodynamic study was carried out using F*A*C*T (Facility for the Analysis of Chemical Thermodynamics, a thermodynamic software). Several graphs were plotted based on the theoretical calculation to predict nickel recovery and final nickel grade in the metallic phases for reduction at different temperatures with varied ratios of CO/C02• A series of reduction experiments was done using CO/C02 to examine reduction behaviour of Sample D, a serpentinic laterite supplied by INCO. The effect of calcination time, temperature, reducing potential and other parameters were studied and discussed. The reduction mechanism and mineral phase change during reduction process were investigated using X-ray diffraction. This showed that with the serpentinic laterite studied here there was a temperature range, 700-800 °c, where serpentine had decomposed but not crystallized to form the high temperature phase. This resulted in a highly reducible ore. Optimum reducing conditions to maximize nickel recovery have been proposed for operation in this temperature range. Partially reduced laterite pellets were chemically analysed. The data was subjected to kinetic study by using the Grain Model. This yielded detailed knowledge about gas diffusion through the solid matrix. Various reducing gas properties and other necessary parameters of the Grain Model were estimated. Some kinetic data were finally obtained.</p>