Equilibrium, kinetic and thermodynamic studies of phosphoric acid adsorption onto activated carbon

摘要

To deduce information that could be used in the treatment of industrial effluents containing phosphoric acid, a thermodynamic, equilibrium, and kinetic study on the adsorption behaviour of phosphoric acid onto grained and powdered activated carbon was carried out. In the experiments, which were run batch-wise, the initial concentration of phosphoric acid and the temperature were varied, and the amount of acid adsorbed at predefined time intervals was measured. The amount of solute adsorbed increased with an increase in acid concentration, and temperature of the milieu. In the thermodynamic study, the variation in entropy, enthalpy and Gibbs free energy were calculated from their dependence on the distribution coefficient, KD (ratio between the concentration of phosphoric acid adsorbed on the activated carbon (mg/g) and the concentration of phosphoric acid in the aqueous solution (mg/cm3)) and temperature. The result showed that the adsorption of phosphoric acid onto activated carbon was a spontaneous and endothermic process. The high correlation coefficient values (R2) showed that the adsorption process on the activated carbon was well represented by the Langmuir and Freundlich isotherms, and the pseudo second order kinetic model.