Kinetics and equilibrium adsorption of phosphates removal on activated alumina

The present work is a part of an overall objective to establish the feasibility for removal of phosphates from the simulated wastewater stream using activated alumina adsorbent AA400G (14 x 28 Mesh) and (28 x 48 Mesh) in order that it can be recycled and re-used for industrial purposes.; Activated alumina is an ion exchanger sorbent rather than an adsorbent for phosphoric acid. Equilibrium isotherms for liquid phase ion exchange are generated for phosphate on activated alumina. Data are obtained at variable as well as controlled pH of 4.5 and 6.0. Three temperature levels of 25, 40 and 80°C are conducted for equilibrium isotherms. Data are fitted based on Freundlich Isotherm. Maximum equilibrium ion exchange loading (mg PO 43-/g sorbent) is found for the case of no pH control at high phosphorous equilibrium concentration but initial and final control of pH at 6.0 is found to be the best choice of lowering the equilibrium concentration of phosphorous to less than 1 ppm at 80°C with high adsorbent loading level. It is observed that pH control condition affects the equilibrium adsorbent loading significantly due to competing ions resulting from the addition of buffer solutions 0.1M NaOH and 0.1M H2SO4 that decrease the active adsorption sites of phosphate ions to the surface of the activated alumina adsorbent.; Kinetic data are generated and modeled by HSDM model and the diffusion coefficients Ds were found from the fit. The diffusivity increases with increasing initial phosphate solution as well as increasing the temperature as is expected from Arrhenius' equation. It was found in the case of pH control that the diffusivity is higher than that with no pH control due to promotion by the buffer ions.