Simultaneous adsorption removal of organic and inorganic phosphorus from discharged circulating cooling water on biochar derived from agricultural waste

Abstract

A high level of organic and inorganic phosphorus exists in discharged circulating cooling water (DCCW), therefore, the efficient removal of phosphorus from DCCW is necessary. Herein, the adsorption performance and mechanism of hydroxyethylidene diphosphonic acid (HEDP) and phosphate from DCCW on pyrolysis biochar derived from agricultural waste (wheat and corn straw wastes, and peanut shell powder) were systematically investigated. Among them, biochar prepared from wheat straw and modified with MgCl2 and CeCl3 (molar ratio 3:1), i.e., WS-3Mg/Ce, showed optimal phosphorus removal from DCCW. The pseudo-second-order and Freundlich model well described the adsorption of HEDP, PO43−, and total phosphorus (TP) on WS-3Mg/Ce. Further, negative Gibbs free energy (ΔG) indicated that WS-3Mg/Ce adsorbed HEDP and phosphate through physical adsorption and chemical reactions, with the chemical reaction being dominant. Scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray diffraction results revealed that CePO4 and Mg3(PO4)2 appeared on WS-3Mg/Ce after adsorption, and the diffraction bands of metal oxides or hydroxides decreased. Fourier transform infrared and X-ray photoelectron spectroscopy results showed that O–H, M-O, M-O-P, and O–P on the surface of WS-3Mg/Ce participate in the reaction. This suggests that the adsorption of HEDP and phosphate on WS-3Mg/Ce mainly involves metal binding via Ce and Mg, and chemical complex via OH−. This study provides a promising approach for removing different forms of phosphorus simultaneously from DCCW via biochar and contributes to the resource recovery of agricultural and forestry waste. Future work is needed for the optimization of the biochar to promote the adsorption capacity and renewability in treating real DCCW.