TEMPERATURE EFFECT ON ION EXCHANGE SORPTION OF PHOSPHATE

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Abstract
Phosphate sorption on the strong basic anion exchanger Amberlite IRA-400 (Cl− form) is studied as a function of temperature ( 25°C–50°C), at two initial pH values (5 and 9 ) in the concentration range 120–190 ppm. Chloride released/phosphate sorbed ratios increase with the increase both in temperature and pH and decrease with the increase in the concentration of solution. It is suggested that phosphate sorption takes place initially as HPO4 2− followed by H2PO4 −. The data is explained with the help of a modified Langmuir and mass law action equations. Various thermodynamic parameters (ΔG°,ΔH° and ΔS°) are presented. The differential isosteric heat of adsorption, is computed at different temperatures, showing the sorption of phosphate to be endothermic on the anion exchanger Amberlite IRA-400.