Characterization, isotherm and kinetic studies for ammonium ion adsorption by light expanded clay aggregate (LECA)

The possibility of ammonium ion removal from aqueous solution using light expanded clay aggregate (LECA) was investigated in this work. FESEM and XRF analyses are used to determine the sorbent characterization. The influences of some effective parameters on ammonium ion adsorption process such as initial pH (3-9), initial ammonium ion concentration (10-100 mg/L), temperature (15-45 °C), and the contact time (0-180 min) were studied. Also, the equilibrium behavior of LECA in ammonium ion removal was investigated in the temperature range of 15-45 °C. The results showed that the equilibrium data were fitted well with two Langmuir and Freundlich isotherm models in all the studied temperature range. The maximum monolayer adsorption capacity estimated by Langmuir isotherm was obtained from 0.229 to 0.254 (mg/g). The required contact time to achieve the equilibrium condition was 150 min. Also, the regression coefficients of the kinetic models and more conformity of the experimental adsorption capacity (qexp) to the calculated adsorption capacity (qcal) were confirmed that the experimental data follow the pseudo-second-order kinetic model. The controlling rate of NH4+ adsorption process by the Webber-Morris model was proved both by film diffusion and intra-particle diffusion models.