Adsorptive removal of phosphorus from aqueous solution using sponge iron and zeolite

Phosphorus adsorptive removal is an important and efficient treatment process in constructed subsurface flow wetlands. Many materials have been proposed for removal of excess phosphorus from wastewater. Selecting a substrate with a high phosphorus adsorption capacity is therefore important in obtaining significant phosphorus removal. In this study, the phosphorus removal capacities of sponge iron and zeolite were evaluated and related to their physico-chemical characteristics. The potential mechanisms affecting the adsorptive removal of phosphorus from aqueous solutions onto sponge iron and zeolite were investigated in batch experiments. The pseudo-second-order kinetics were useful since the adsorption rate data fitted well. The Freundlich and Langmuir models well described the adsorption isotherm data. The results of static experiments and dynamic experiments (column experiments) indicated that the adsorption of phosphorus onto sponge iron was more apt to chemical combination, but zeolite was more apt to electrostatic attraction or ion-exchange. For sponge iron, some iron (iii) (Fe(3+)) or iron (ii) (Fe(2+)) and phosphate ions (P) form Fe-P, the solid phases compound was fixed. For zeolite, aluminum oxide and silicon oxide formed complexes in aqueous solution. It was observed that positive or negative charge surface sites favored the adsorption of phosphate due to the electrostatic attraction or ion-exchange.