Abstract
As demand for low-carbon materials increases, the magnesium industry faces growing pressure to reduce the environmental impact of primary magnesium production. Current production is largely based on the energy-intensive Pidgeon process, which relies on dolomite as the main magnesium-bearing feedstock. While dolomite is abundant and widely available, alternative hydrometallurgical routes remain underdeveloped. Existing studies on dolomite leaching are limited, use inconsistent methodology, and report widely varying kinetics and extraction efficiencies. In addition, impurity removal strategies required to produce electrolysis-grade magnesium chloride have not been systematically investigated, limiting assessment of hydrometallurgical magnesium production as an industrial option.
This study presents an integrated experimental approach for hydrometallurgical magnesium production from dolomite, combining leaching optimization with multi-stage purification suitable for downstream molten-salt electrolysis. The leaching behaviour of uncalcined, semi-calcined, and fully calcined dolomite was first examined. Thermogravimetric analysis (TGA), including non-isothermal and isothermal measurements, together with X-ray diffraction (XRD), was used to characterize thermal decomposition, phase evolution, and apparent calcination kinetics. These results were used to link thermal pretreatment history and phase composition to subsequent leaching performance.
The results demonstrate that direct leaching of uncalcined dolomite provides higher magnesium extraction than leaching of calcined materials. Thermal pretreatment promoted the formation of hydroxide-rich phases, which increased slurry viscosity, and led to mass-transfer limitations during acid leaching. Based on these findings, a Central Composite Design (CCD) was implemented to optimize the leaching of uncalcined dolomite. The effects of hydrochloric acid concentration, temperature, reaction time, solid to liquid ratio, and particle size were evaluated to identify key parameters controlling magnesium dissolution kinetics and acid consumption.
After leaching, a multi-stage purification process was developed to remove impurities such as iron, boron, and sulfate, which negatively affect electrolyte stability and current efficiency during magnesium electrolysis. The purification strategy progressively conditioned the leach solution toward electrolysis-grade MgCl₂ by controlling impurity speciation, precipitation, and solution chemistry.
Overall, this work demonstrates a technically robust hydrometallurgical route for magnesium production from dolomite by combining optimized leaching with targeted impurity removal. The results provide practical insights into process sensitivities, operational limits, and feedstock requirements relevant to the development of scalable and low-carbon magnesium production pathways.