Adsorption isotherms, kinetics and thermodynamics of NH4+–N from aqueous solutions using modified ceramsite and its regeneration performance

Abstract

Ceramsite was prepared from solid wastes by high-temperature sintering process and modified using NaCl solution. The adsorption of ammonium nitrogen (NH4+–N) from aqueous solution by modified ceramsite (MC) and its chlorination regeneration were investigated. The results showed that the qe of MC was 2.49 mg/g after being stirred for 180 min when initial concentration of NH4+–N was 100 mg/L at 328 K, which was 1.79 times higher than that of ceramsite. The adsorption process of NH4+–N on MC can be well described by the Langmuir isotherm model in the whole experiments, with R2 > 0.95 and root mean squared error (RMSE) < 0.02. On the contrary, the adsorption process of NH4+–N on ceramsite followed the Freundlich isotherm model, with R2 > 0.95. Compared with the pseudo-second-order reaction kinetics, the adsorption of NH4+–N onto MC fitted better in the pseudo-first-order reaction kinetics when initial concentration of NH4+–N was 35 mg/L at 298 K, with R2 > 0.95, standard deviation error <0.13 and RMSE <0.13. The thermodynamics results indicated that the adsorption process of NH4+–N onto MC was a spontaneous, endothermic and physisorption process. Moreover, the regeneration results demonstrated that NaClO solution was an effective regenerant for the recovery of exhausted MC, the qe of MC was about 1.50 mg/g even after 15 cycles and no significant change compared with initial.