Author: M.Y. Solar
48th Conference of metallurgists - COM2009, August 23 - 26, 2009, Sudbury, Canada
Abstract
Nickel recoveries in laterite smelters are normally 90 to 97% if unaccounted losses and unusual dust losses are ignored. About two thirds of the total loss occurs in the electric furnace slag both as dissolved nickel oxide and entrained metal prills. These “chemical” and “mechanical” losses are reportedly roughly equal and some operations have actually started to subject their furnace slag to magnetic separation. The equilibrium between nickel in the metal and slag phases is often described in terms of its partition coefficient, [%Ni]/(%Ni), which can vary from 80 to 260. This is a much wider range than can be accounted for by the reductions achieved by various operators. Different plants must thus experience different levels of mechanical losses. However the speciation of slag losses is not a routine determination and there is no guarantee that the occasional measurement is a fair measure of the average operation. The present paper attempts to estimate more precisely the proportion of the two loss mechanisms for eleven selected smelters, using readily available production and thermodynamic data. The conclusion is that the mechanical losses do vary significantly from plant to plant, from about 0.6 to 2 times the chemical losses. The correlation with slag viscosity, if any, is contrary to expectations: mechanical entrainment decreases
with increasing viscosity. The other significant factors are charge bank management, and slag depth and head over the slag tap hole.
