Removal of magnesium from nickel laterite leach liquors by chemical precipitation using calcium hydroxide and the potential use of the precipitate as a filler material

The chemical precipitation of magnesium from sulphate solution, resulting from heap leaching of nickeliferous laterites with sulphuric acid, was studied. Magnesium was removed as hydroxide using calcium hydroxide (Ca(OH)2) and the precipitate produced was a mixture of magnesium hydroxide (Mg(OH)2) and gypsum (CaSO4·2H2O). The variables studied were the temperature and the stoichiometric quantity of Ca(OH)2. The responses measured were magnesium removal and the specific surface of the precipitate. Design of the experiments and statistical analysis of the data were used in order to determine the main effects and interactions of the factors. Scanning electron microscopy (SEM) was also used to investigate the effect of precipitation conditions on the morphological characteristics of the Mg(OH)2–CaSO4·2H2O mixture. Kinetic analysis with the aid of Nielsen theory allowed the determination of the Mg(OH)2 formation mechanism. The use of a magnesium hydroxide–gypsum mixture as a filler material was also examined. The suitability of the precipitate was evaluated by measuring a set of properties that can characterize a material as a filler and by measuring mechanical properties of polymers filled with the precipitate at various addition levels. The magnesium hydroxide–gypsum precipitate proved to be promising for this application, as it was found to have similar properties with other commercial products.