Removal of Phosphate from Aqueous Solution Using Layered Double Hydroxide Prepared from Waste Iron-Making Slag

Abstract

Abstract A layered double hydroxide (LDH) type adsorbent for phosphate removal from aqueous solution was prepared from blast furnace slag (BFS) which is vastly discharged by the iron manufacturing industry. The phosphate adsorption performances of the prepared adsorbent and its calcined derivatives were examined using simulated wastewater solutions containing 124 P-mg L−1 which is close to the effluent produced by the sewage sludge dewatering process, and factors such as pH, nature, and amount of adsorbent were studied to establish the optimum adsorption conditions. The adsorbent exhibited a great ability to efficiently remove phosphate in a variety of environments, especially even from 15 ppm phosphorus aqueous solutions, owing to a strong affinity of Ca(OH)x species and an ion-exchange ability of Cl− anions accommodated in the layers. The maximum phosphorus adsorption uptake reached 91.9 P-mg g−1 after 24 h of adsorption at an initial pH of 7.0 and at 25 °C, which was 126-fold higher than that of raw BFS (0.73 P-mg g−1). The adsorption process followed a pseudo-second-order kinetic model and Freundlich adsorption isotherms. The results suggest that the slag-made LDH is a promising low-cost adsorbent for efficient phosphate removal from wastewater streams and phosphorus recovery processes.