The effect of acidity 'at temperature' on the morphology of precipitates and scale during sulphuric acid pressure leaching of laterites

Sulphuric acid pressure leaching is the process of choice to recover nickel and cobalt from laterites with variable iron and magnesium contents. The l atter influences the acidity levels required for effective leaching of nick el and cobalt, and during leaching, iron is rejected in-situ as hematite. C lassical solid/liquid separation is performed via a CCD circuit, the perfor mance of which depends upon the size and shape of precipitated particles. i n this paper, precipitates obtained by acid-leaching of various lateritic f eeds at 270 degrees C are characterized using SEM/EDX and laser particle si ze analysis. It is shown that as acidity increases, the shape of the precip itates gradually changes from platelets to spheres, thus improving the S/L separation properties of the residue. The use of hydrogen ion concentration "at temperature, " calculated from a speciation analysis, allows the expla nation of this change of morphology independently of the type of the ore fe ed the possibility of precipitating magnesium sulphate "at temperature" is also discussed. In order to lake advantage of this precipitation for scale reduction las has been proposed in the past) without compromising the resid ue quality, [H+] "at temperature" must be controlled within an optimum rang e.