Manufacturing reactive magnesia from nickel laterite waste solution via nesquehonite precipitation

Abstract

Nesquehonite is an attractive magnesium precipitation product as it sequesters CO2 and exhibits good filterability. Upon calcination, high-quality reactive magnesia is produced. As part of the hydrometallurgical processing of nickel, magnesia is used as a precipitating agent to recover nickel and cobalt in the form of a Mixed Hydroxide Precipitate (MHP). However, a waste solution with elevated concentration of magnesium is formed which can be an environmental liability. Chemical thermodynamic equilibrium modeling of magnesium carbonate precipitation from magnesium sulfate liquor predicted a high reaction extent of 99% could be achieved. Magnesium carbonate precipitation experiments were carried out by gradually mixing sodium carbonate solution and synthetic industrial liquor in a batch reactor at 25 °C, while monitoring solution concentrations and pH, used to estimate the supersaturation index. Calcination of the resulting solid at temperatures ranging from 450 to 650 °C produced magnesia with acetic acid activities ranging from 14 s to 41 s. The most reactive magnesia was obtained at the lower temperature of 450 °C with an activity of 14.7 ± 0.6 s, which meets industrial product specifications. Periclase was identified as the dominant magnesia mineral phase along with thenardite as a minor component.