The effect of acidity

CIM Bulletin, Vol. 93, No. 1041, 2000

D.H. Rubisov and V.G. Papangelakis, Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario

Sulphuric acid pressure leaching is the process of choice to recover nickel and cobalt from laterites with variable iron and magnesium contents. The latter influences the acidity levels required for effective leaching of nickel and cobalt, and during leaching, iron is rejected in-situ as hematite. Classical solid/liquid separation is performed via a CCD circuit, the performance of which depends upon the size and shape of precipitated particles. In this paper, precipitates obtained by acid-leaching of various lateritic feeds at 270¡C are characterized using SEM/EDX and laser particle size analysis. It is shown that as acidity increases, the shape of the precipitates 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 explanation of this change of morphology independently of the type of the ore feed. The possibility of precipitating magnesium sulphate Òat temperatureÓ is also discussed. In order to take advantage of this precipitation for s
Keywords: Cobalt, Hydrometallurgy, Leaching of laterites, Laterites, Nickel, Sulphuric acid pressure leaching.