REMOVAL OF PHOSPHORUS BY ION-EXCHANGE RESINS: EQUILIBRIUM, KINETIC AND THERMODYNAMIC STUDIES

The removal of phosphorus by strongly basic anion exchanger was investigated. Removal efficiency increased with contact time, resin mass and initial solute concentration, while temperature showed a reverse effect. Equilibrium data were best fitted onto Langmuir isotherm model (R-2 > 0.99). Maximum sorption capacity of the resin was 66.22 mg/g, namely significantly higher the values reported in the literature. The Freundlich parameter (n = 4.3) and the Langmuir separation factor (R-L = 0.067-0.028) showed that the considered system obeyed to favorable sorption process. The high K-f Freundlich parameter value indicated a high affinity of phosphorus onto the adsorbent. The Temkin isotherm parameters showed high adsorption heat (b(1) = 327.83 kJ/mol) and high maximum bonding energy (k(t) = 1215.8 L/g). Experimental kinetic data was best described by pseudo- second order kinetic model. External mass transfer resistance increased at low initial phosphorus concentrations. Film diffusion was the ratecontrolling step, instead of intraparticle diffusion. Thermodynamic experiments indicated that the considered system was exothermic and thermodynamically spontaneous.