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 ۵۴% concentration, and its performance was compared with various common adsorbents. The carbon black adsorbent achieved a ۲۷.۸۱% removal of iron cations, a ۳۸.۷۲% 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 (۱۱ to ۸۰), contact time (۳۰ to ۵۴۰ minutes), initial concentrations of iron cations (۷۳۱۰ to ۴۶۰ ppm), and magnesium cations (۱۱۹۵۰ to ۷۵۰ ppm), temperature (۲۵ to ۶۵ °C), and stirring rate (۱۰۰ to ۱۰۰۰ rpm). Optimal results were achieved at a stirring rate of ۵۰۰ rpm, a contact time of ۳۰۰ minutes, a temperature of ۲۵ °C, initial concentrations of iron cations ۴۶۰ ppm and initial concentrations of magnesium cations ۷۵۰ ppm, and an acid-to-adsorbent ratio of ۱۶, resulting in the removal of ۳۹.۱۳% of iron and ۴۸% 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.

کلیدواژه ها:

Purification ، Phosphoric acid ، Surface adsorption ، adsorbent ، carbon black