A Comprehensive Review of Spent Acid Treatment and Resource Recovery Techniques

This review comprehensively investigates technologies for treating spent acids and recovering metals, highlighting applications in industries including steel manufacturing, electroplating, semiconductors, nuclear fuel processing, mining, and battery recycling. Spent acids, characterized by high acidity and heavy metal content, pose significant environmental and economic challenges. To address these, this paper classifies and evaluates eight major treatment techniques (Neutralization and Precipitation, Crystallization, Thermal Hydrolysis, Ion Exchange, Membrane Distillation, Solvent Extraction Biological Treatment, and Electrochemical Processes) based on separation mechanisms, advantages, limitations, and industrial feasibility. Emphasis is placed on tailoring each technology to specific spent acid compositions and recovery targets, with recent advances in hybrid techniques reviewed for their synergistic potential. In addition, the results of the life cycle assessment (LCA) and techno-economic assessment (TEA) for each method are summarized, and a recommendation matrix is proposed to evaluate suitability across industrial sectors. This structured comparison serves as a practical guide for selecting the optimal technology according to industry type, acid characteristics, and resource recovery objectives, ultimately supporting the development of efficient and sustainable spent acid recycling strategies.