Hydrometallurgical treatment of biotite ore for production of magnesium hydroxide (Mg(OH)₂) for industrial value addition

Abstract

Magnesium hydroxide is a popular inorganic compound used in wide range of applications such as: flame retardant in polymers, special ceramics, fillers in bleaching agent and a raw material for preparation of magnesium oxide, which were currently imported into Nigeria from foreign countries using hard earned currency. Thus, this current study focused on dissolution kinetics of a biotite ore treated via leaching in sulphuric acid leachant. During leaching, parameters such as leachant concentration, particle size and reaction temperature on the extent of ore dissolution were examined. At optimal leaching conditions (2.5 mol/L H₂ SO₄ , 80°C), 98.23 % of the initial 10 g/L ore reacted within 120 minutes. The shrinking core dissolution model was adopted to evaluate the various dissolution parameters for better understanding of the rate determining step. Experimental results indicated that the reaction rate of the leaching process was controlled by diffusion model, with calculated activation energy (Ea) of 38.56 kJ/mol. By considering the solubility differences of corresponding elements, a two-step precipitation process was applied to remove Fe and Al and recovery of Mg. Subsequently, magnesium hydroxide was prepared by precipitation from the leach solution with ammonia as the precipitant. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses showed that the high purity Mg(OH)₂ existed in the form of flower-like spherical aggregation. Furthermore, the final solution of ammonium–potassium chlorate can be used for agricultural compound fertilizer.

Keywords: inorganic, optimal, leaching, ammonium-potasium chlorate, fertilizer