Hydrometallurgical processing of magnesium minerals – A review

Abstract

Magnesium and magnesium-derived alloys are critical to a diverse set of industries, due to their particular physicochemical properties, including biocompatibility, low density, mechanical dampening, and hydrogen-storage capacity. Moreover, the magnesium compounds are themselves vital in agricultural, pharmaceutical, construction and broad industrial applications. Leaching is a critical step in the recovery of magnesium from magnesium-bearing ore, and the most common leaching agents are organic and inorganic acids, as well and ammonium salts, the efficacy of which depends on the mineral feed. Organic acids are used with minerals having fast leaching kinetics; these acids have less dissolving power but are more selective and are less destructive to the equipment. In contrast, inorganic acids have more dissolving power and are easier to source. However, the inorganic acids are less selective and cause more damage to equipment, as they complicate pH control. The objective of this work has been to review studies on the kinetics of magnesium mineral extraction, and the effects of critical parameters depending on the feed mineral and the reagents. Several works are presented on the leaching kinetics of natural and calcined dolomite and magnesite, and hydrated magnesium salts, as well as ferromagnesian silicates and serpentinite, which are important sources of magnesium. It has been shown that the most influential parameters in dissolving magnesium are the temperature and the reagent concentration, which have a direct effect on magnesium extraction rates. However, there is a point at which increases in these parameters result in more impurities and/or have insignificant effects on magnesium dissolution. Particle size has an inverse relationship to magnesium extraction since the area of contact with the leaching surface is greater with smaller particles. The effect of the agitation speed is insignificant with magnesite feeds, given that the process is controlled largely by surface chemical reactions, while the leaching kinetics of serpentinite is controlled by diffusion through the product layer.