Deep Purification of Wet-process Phosphoric Acid Using Acetone as a Green Organic Solvent

Abstract

Wet-process phosphoric acid contains a range of mineral impurities that negatively impact acid quality and restrict its use in producing high-purity phosphate products. This study investigates an integrated purification process that combines defluorination using microcrystalline silica, desulfation with strontium carbonate, and acetone-assisted purification. After preliminary treatment, the phosphoric acid was standardised to 35 wt.% P₂O₅ and subjected to acetone treatment under varying acid-to-acetone weight ratios and contact times. The optimal conditions were identified as an acid-to-acetone mass ratio of 1:3 at 25 °C for 30 minutes, which achieved an effective balance between impurity removal and phosphorus retention. Under these parameters, the precipitation efficiencies for CaO, MgO, Fe₂O₃, Al₂O₃, SO₃, and F were 75.99%, 95.37%, 99.40%, 99.50%, 99.66%, and 98.97%, respectively, while P₂O₅ precipitation was limited to 18.02%. Following separation and vacuum acetone removal, the purified acid contained 35.06 wt.% P₂O₅, with CaO and MgO concentrations reduced to 0.13 and 0.03 wt.%, respectively, and Fe₂O₃, Al₂O₃, SO₃, and F below detection limits. The purified acid exhibited a consistent decrease in density and dynamic viscosity as temperature increased from 20 to 90 °C, indicating improved flowability for handling and transport. Material balance analysis indicated an acetone recovery rate of 98.96% and a solvent loss of 1.04%, with 78.27% of the initial P₂O₅ retained in the final product. These results indicate that the acetone-assisted purification route shows considerable promise for laboratory-scale production of high-quality phosphoric acid suitable for further phosphate fertiliser processing. Keywords: wet-process phosphoric acid, acetone, deep purification, defluorination, desulfation, rheological properties, phosphate products.