Investigation of the Removal of Interfering Iron and Magnesium Ions from Industrial Phosphoric Acid Using Different Surface Adsorbents

Among the various methods employed to purify Industrial Phosphoric Acid (IPA), the adsorption method has received considerable attention in both research and industrial settings. In this study, for the first time, carbon black was used as an adsorbent for the discoloration and removal of interfering iron and magnesium ions from Industrial Phosphoric Acid (IPA) at a 54% concentration, and its performance was compared with various common adsorbents. The carbon black adsorbent achieved a 27.81% removal of iron cations, a 38.72% removal of magnesium cations, and a complete removal of color from the IPA. A univariate algorithm was employed to examine the impact of operating conditions, such as the acid-to-adsorbent ratio (11 to 80), contact time (30 to 540 minutes), initial concentrations of iron cations (7310 to 460 ppm), and magnesium cations (11950 to 750 ppm), temperature (25 to 65 °C), and stirring rate (100 to 1000 rpm). Optimal results were achieved at a stirring rate of 500 rpm, a contact time of 300 minutes, a temperature of 25 °C, initial concentrations of iron cations 460 ppm and initial concentrations of magnesium cations 750 ppm, and an acid-to-adsorbent ratio of 16, resulting in the removal of 39.13% of iron and 48% of magnesium. Adsorption kinetics, isotherms, and thermodynamics were investigated. The findings indicate a stronger alignment with the pseudo-second-order kinetic model for the system. For iron cations, the strongest correlation is observed with the Temkin isotherm model, while for magnesium cations, it corresponds more closely with the Dubinin-Radushkevich isotherm model. The thermodynamic analysis reveals that the adsorption process for iron cations is endothermic and spontaneous, demonstrating an increase in disorder following surface adsorption. In contrast, the adsorption process for magnesium cations is exothermic and non-spontaneous, leading to a decrease in system disorder.