Mechanism and kinetics study of Mg²⁺ removal from wet-process phosphoric acid by Sinco-430 resin

The reaction mechanism and kinetics of Sinco-430 cation exchange resin removing Mg²⁺ from wet-process phosphoric acid (WPA) were studied. Fourier transform infrared and X-ray photoelectron spectroscopy analyses revealed that the main functional group of the resin that combined with Mg²⁺ ions was -SO₃H. To investigate the most suitable conditions for Mg²⁺ removal, the operating parameters that could affect Mg²⁺ removal were studied. The results demonstrated that under optimal conditions (T = 50°C, solid to liquid mass ratio = 0.3, and P₂O₅ content = 20 wt.%) the reaction reached equilibrium in 8 min and Mg²⁺ removal rate reached 59.09%. The kinetic model and activation energy of the reaction were second-order and 19.11 kJ/mol according to kinetic analysis, respectively. The diffusion model of Mg²⁺ removal was determined as pore diffusion according to the comparison of three different diffusion models. H₃PO₄ was recovered using deionized water and Mg²⁺ was removed from the loading resin with 20 wt.% H₂SO₄. In addition, after eight loading/regeneration cycles, the Mg²⁺ removal ability of the Sinco-430 resin remained the same. The Mg²⁺ removal rate in a fixed-bed reactor was 98.83%, higher than that obtained in a continuous stirred-tank reactor. (author)