Preferential removal of phosphorus using modified steel slag and cement combination for its implications in engineering applications

Eutrophication is receiving increasing attention globally, and excessive phosphorus (P) discharge is the principal cause. To alleviate this, steel slag, an industrial by-product, was selected to remove P from synthetic solution in this study. High-powered ball grinding technology was used to modify the slag before the experiments, resulting in finer particle size, higher specific surface area and activation, which were characterized by BET, SEM and XRD. Batch experiments were conducted to investigate its adsorption properties. With initial P concentration of 5 mg/L, about 96% of P was removed within 60 min, accompanied by an increase in pH and Ca2+ concentration. The adsorption data was best fitted by the Lagergren pseudo-second-order kinetic model. The Langmuir equation fitted the isotherm data well, with a maximum adsorption capacity of 21.70 mg P/g. When the initial pH was higher than 4.0, P adsorption capacity varied inversely with pH. In a 700 h continuous flow experiment, the cement-slag padding prepared in this study removed around 98.2 % of the influent P, decreasing from 21.0 mg/L to 0.4 mg/L. CaCO3 and amorphous calcium-phosphate compounds generating in the column indicated that the dominant P removal mechanism was through precipitation. The padding proved capable of controlling pH increases, providing a method to prepare slow-release materials containing slag to treat P-contaminated wastewater. (C) 2018 Elsevier B.V. All rights reserved.