Simultaneous Adsorption of Ammonium, Phosphate and Arsenate from Wastewater by Walnut Husk Modified with Dolomite and Activated with Nitrogen/Steam

The simultaneous adsorption of ammonium, phosphate and arsenate from wastewaters by walnut husk modified by dolomite and activated by nitrogen/steam was investigated. The performance of the process was studied by carrying out physical and chemical analyses before and after the adsorption of ions, for a range of experimental conditions and by simulating experimental data using two isotherm models. During the simultaneous adsorption of the ions, removal efficiency by the solid was greatly enhanced, suggesting that there was no competition between them for sorption sites. When the raw material was modified by dolomite, the uptake of ammonium was improved, that of phosphate was almost complete, while that of arsenate was practically unaffected. All experimental data were best fitted by the Freundlich isotherm model. The maximum adsorption capacity of dolomite-modified WH material was 52.1 mg/g for ammonium, 74.3 mg/g for phosphate and 63.8 mg/g for arsenate. The potential adsorption mechanisms were chemical complexation for all ions, electrostatic attraction for ammonium and phosphate and ligand exchange for phosphate and arsenate.