Adsorption removal of ammonium and phosphate from water by fertilizer controlled release agent prepared from wheat straw

This paper presents a study of the adsorption of ammonium and phosphate ions from aqueous solution using a new fertilizer controlled release agent (FCRA) which is produced through graft copolymerization with wheat straw, acrylic acid (AA), acrylic amide (AM) and dimethyl diallyl ammonium chloride (DMDAAC). A series of batch experiments were conducted to examine the effects of solution pH, adsorbent dosage, the initial concentration of adsorbate and contact time. The findings indicated that the new fertilizer controlled release agent had a significant effect on the adsorption of ammonium and phosphate ions. The adsorption could reach equilibrium through 4 h reaction, and had the best adsorption amount at the pH values from 4 to 8. The adsorption amount increased with the increasing initial concentration of adsorbate. The adsorption amount of NH4+ decreased with the increasing of adsorbent dosage while the adsorption of PO43- showed the opposite trend. Kinetic analysis showed that the adsorption of ammonium and phosphate ions on the new fertilizer controlled release agent followed the pseudo-second-order model well. Equilibrium isotherm data of adsorption of NH4+ were well fitted to the linear Langmuir and Freundlich models, while the data of adsorption of PO43- were well fitted to the Freundlich model. The desorption experiments also showed that the desorption of NH4+ and PO43- on FCRA could reach saturation at the time of 5 h and 4 h, respectively. And the pH had a large effect on desorption. (C) 2011 Elsevier B.V. All rights reserved.