Removal of Phosphate from Aqueous Solutions by Chemical- and Thermal-Modified Bentonite Clay

The study investigated phosphate adsorption from aqueous solutions using chemical- and thermal-modified bentonite in batch system. The adsorbent was characterized by SEM, BET, and FTIR spectroscopy. Contact time, beginning phosphate concentration, pH of the solution, and the effects of the temperature on phosphate adsorption capacity were determined by a series of experimental studies. In a wide pH range (3-10), high phosphate removal yields were obtained (between 94.23 and 92.26 %), and with the increase in temperature (from 25 to 45 degrees C), phosphate removal increased. Langmuir and Freundlich isotherms were used to determine the sorption equilibrium, and the results demonstrated that equilibriumdata displayed better adjustment to Langmuir isotherm than the Freundlich isotherm. Phosphate sorption capacity, calculated using Langmuir equation, is 20.37 mg g(-1) at 45 degrees C temperature and pH 3. Mass transfer and kinetic models were applied to empirical findings to determine the mechanism of adsorption and the potential steps that control the reaction rate. Both external mass transfer and intra-particle diffusion played a significant role on the adsorption mechanism of phosphate, and adsorption kinetics followed the pseudo-second-order-type kinetic. Furthermore, thermodynamic parameters (Delta H degrees, Delta G degrees, Delta S degrees) which reveal that phosphate adsorption occur spontaneously and in endothermic nature were determined. The results of this study support that bentonite, which is found abundant in nature and modified as an inexpensive and effective adsorbent, could be used for phosphate removal from aqueous solutions.