Phosphate/Hydroxide Exchange Studies on Amberlite IRA-400

ABSTRACT

Phosphate sorption on the strong basic anion exchanger, Amberlite IRA-400 (OH⁻form) bas been studied as a function of pH (3–11), temperature (25°C – 50°C) and in the concentration range 3.874–6.134 mmol./L. The sorption of phospbate increases with increases in temperature and concentration of the solution. However, increases in the pH above 7 leads to a decrease in the sorption of phosphate which is due to the increased competition from hydroxide ions. The data is explained with the help of a modified Langmuir equation. Various thermodynamic parameters (ΔG°, ΔH° and ΔS°)are calculated. The differential isosteric heat of adsorption,ΔH, is computed at different temperatures, showing the sorption of phosphate to be endothermic on the anion exchanger Amberlite IRA-400. IR spectra of phosphate sorption on OH⁻ and Cl⁻ forms of the resin has also been studied. The phosphate bands (860,890,970,1080,1100 and 1120 cm⁻¹) are more pronounced at higher phosphate concentrations and higher temperatures.