Equilibrium and kinetic modelling of adsorption of phosphorus on calcined alunite

The adsorption of phosphorus onto calcined alunite has been studied. Its equilibrium isotherm has been measured. The isotherm was determined by shaking 1.0 g calcined alunite, particle size range 90 - 150 mum, with 100 mL phosphorus solution of initial concentrations from 0.5 to 2.5 mmol/L. The water bath shaking a constant rate of 200-rpm was used and the temperature maintained at 298 +/- 2 K. A contact time of 120 min was required to achieve equilibrium. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich equations. The monolayer adsorption capacity is 1.355 mmol P per g calcined alunite. Three simplified kinetic models including a pseudo first-order equation, pseudo second-order equation and intraparticle diffusion equation were selected to follow the adsorption process. Kinetic parameters, rate constants, equilibrium sorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the adsorption of phosphorus could be described by the pseudo second-order equation.