Green Solvent-Based Purification of Phosphoric Acid: Process Development and Efficiency Assessment

Compared to traditional methods of refining phosphoric acid, purification using green solvents offers a safer means of achieving high product purity for large scale, industrial use with significantly reduced use of hazardous chemicals. This work develops and tests a more ecologically friendly method of purification for wet-process phosphoric acid (WPA) using biodegradable green solvents to preferentially extract metallic impurities and fluorine, without a significant loss of phosphorus. Optimization of the method was undertaken in a systematic way and included the use of various solvents, the organic to aqueous (O/A) phase ratio, extraction time, temperature, and multiple extraction–stripping stages. Chemical testing and analysis were done to determine extraction and stripping efficiencies, rejection of impurities and phosphorus, recycling of solvents, and the overall energy costs of the purification method. For the method to be considered optimized, the O/A phase ratio of 3:1, extraction time of 15 minutes, extraction temperature of 40 °C, and a total of three extraction-stripping cycles had to be used. The optimized method resulted in the removal of ≥ 98.9% of iron, ≥ 99.4% of aluminum, ≥ 95.8% of magnesium, ≥ 75.8% of calcium, ≥ 94.9% of fluoride, 91.8% of sulfate impurities, and 89.7% of organic contaminants. The remaining heavy metals cadmium, lead, chromium, and arsenic were reduced by 93.2 – 99.1%.  The wet-process phosphoric acid used in this study was produced via the dihydrate process and supplied by JSC “Ammofos-Maxam” (Uzbekistan). The phosphoric acid purity increased from 18.23 wt.% P₂O₅ in the raw WPA to 35.00 wt.% P₂O₅ after purification, with the extraction and stripping methodology demonstrating a loss of 1.8% of total phosphorus. The purification method demonstrated a solvent regeneration efficiency of greater than 96.5% after five consecutive purification cycles, with a total loss of less than 2.3% of the total solvent used, demonstrating a high level of stability and reusability. Less chemical usage, energy demand, and carbon emissions compared to traditional solvent extraction systems are 31.6%, 24.8%, and 29.4% improvements, respectively. The purification strategy used in this study establishes that green solvent extraction is an effective and environmentally conscious method for manufacturing high-quality phosphoric acid. The process, due to its high removal of impurities, high recovery of phosphorus, low usage of solvents, and low environmental impact, is likely to be used in an industrial setting. The process design also demonstrates that green solvent extraction advances sustainable management of phosphorus in a circular manner. Since the design embodies the principles of clean production, the process design is likely to be incorporated in the industrial manufacture of economically advantageous phosphoric acid for use in the next generation of green fertilizers and specialty chemicals.