Phosphorus removal from aqueous solutions by adsorptive concrete aggregates

The purpose of this study is to investigate the adsorption characteristics of granular aggregates under identical experimental conditions for potential applications in highly adsorptive concrete. In this study, industrial by-products (steel slag), lightweight aggregates (expanded silica) and bio-materials (peach shell and miscanthus) are used for phosphorus (P) removal from aqueous solutions. The effects of several parameters such as the initial concentrations of P, reaction time and pH value on adsorption capacity and efficiency of P are investigated using an IC analyzer. Results show that the phosphorus adsorption of all absorbents follows the adsorption isotherms with a varying phosphorus concentration from 5 mg/L to 700 mg/L, and the adsorption isotherms data are fitted well by Langmuir equation. The steel slag exhibits a higher P-adsorption capacity and adsorption efficiency compared to lightweight aggregates and bio-materials, with an estimated maximum adsorption capacity by steel slag of 20.4 mg/g. Moreover, the P-desorption results show that steel slag has a very low P-desorption. Heat treatment is used to increase the adsorption capacity of the miscanthus owing to the change in pore structure characteristics determined by BET. The adsorption kinetic data of the steel slag follows a pseudo-second-order model. The ICP-AES, XRD and SEM-EDS analyses show that the P-adsorption of the miscanthus and peach shell follows physical adsorption, whereas the adsorption mechanism of the steel slag can be attributed to the Ca²⁺ released from the steel slag, which can react with P and form a stable Ca–P precipitate. It is suggested that steel slags can function as effective adsorptive aggregate for the manufacture of highly adsorptive concrete.