Wet-process phosphoric acid is a key raw material in the phosphate chemical industry. However, due to impurities in the phosphate ore, the acid often contains ions such as iron, magnesium, aluminum, and sulfate. These impurities not only affect product purity but also reduce the quality of downstream phosphate or fertilizer products. Traditional solvent extraction purification methods, while mature, are energy-intensive, costly, and environmentally risky.
Diffusion dialysis membrane separation is an emerging purification technology that uses concentration gradients to separate hydrogen ions from metal ions. The use of polyolefin-based anion exchange membranes allows the process to operate efficiently at low energy consumption while effectively removing multivalent cation impurities. The fixed charge structure of the membrane enables selective ion transport, achieving precise separation.
The study shows that under a membrane flux of 0.80–0.85 L/(m²·h) and an acid-to-water volume ratio of 1.0–1.1, the rejection rates of Fe³⁺, Mg²⁺, and Al³⁺ reached 82%–83%, while the P₂O₅ recovery rate remained at 55%–60%. After desulfurization pretreatment, the rejection rate increased further to 83%–89%.
For a purification plant with a capacity of 50,000 tons of P₂O₅ per year, the treatment cost per ton using membrane separation is less than RMB 500, compared with more than RMB 3,000 for traditional extraction methods. This demonstrates the significant economic advantage of membrane separation in industrial applications.
The phosphoric acid purified by membrane separation has high purity and can be directly used for the production of water-soluble fertilizers and industrial-grade phosphates. With the continuous improvement of membrane materials and reduction in manufacturing costs, this technology has broad prospects in clean phosphate production, resource recycling, and green manufacturing.
