Sulfuric Acid Regeneration from Magnesium Sulfate Streams: Process Chemistry, Recovery Technologies, and Industrial Challenges

Sulfuric acid regeneration from magnesium sulfate streams is an increasingly relevant challenge in hydrometallurgy, mineral processing, battery recycling, pickling operations, and industrial wastewater treatment. Magnesium sulfate is often formed when sulfuric acid reacts with magnesium-bearing minerals, neutralizing agents, or process residues, resulting in acid loss, sulfate accumulation, increased effluent volumes, and challenging brine management. This critical review examines the process chemistry, recovery technologies, and industrial constraints associated with converting magnesium sulfate streams into reusable sulfuric acid or valuable by-products. The discussion covers thermal decomposition, crystallization, membrane-based acid recovery, electrodialysis, diffusion dialysis, solvent-assisted separation, precipitation routes, and hybrid process configurations. Particular attention is given to reaction equilibria, water balance, impurity behavior, energy demand, scaling risk, acid quality, and integration with upstream and downstream unit operations. Although several technologies are technically feasible, industrial application is limited by high energy consumption, low selectivity in multicomponent liquors, fouling, corrosion, and uncertain economics at large scale. The review highlights that magnesium sulfate regeneration should be evaluated as a process-integration problem rather than as an isolated acid-recovery step.