Simultaneous removal of NH4(+) and PO4(3-) at low concentrations from aqueous solution by modified converter slag.

In this study, modified converter slag (CS) was characterized in relation to its physicochemical structure, and used for the simultaneous removal of NH4(+) and PO4(3-) at low concentrations from aqueous solutions. The effects of contact time, pH, adsorbent dosage, and temperature on the adsorption process were studied in batch experiments. The results showed that the adsorption capacity of modified converter slag was found to sharply increase as a result of modification. The optimum pH is 5-8. The adsorption process was able to reach equilibrium in 90 minutes. Kinetic data were best described by the pseudo-second-order model. The sorption isotherms were a good fit with the Langmuir model. The maximum adsorption capacities of modified converter slag for NH4(+) and PO4(3-) were 2.59 mg/g and 1.185 mg/g, respectively. Thermodynamic studies indicated that the adsorption was a spontaneous and endothermic process. The calculated values of enthalpy change indicated that ligand exchange, chemical reactions, and precipitation are dominating mechanisms of PO4(3-) removal, while physisorption and ion-exchange are major mechanisms of NH4(+) removal.