Abstract
Phosphorus (P) is one of the essential nutrients for all life but also is involved in the major factor of water eutrophication. This study aimed to investigate a low-cost approach for highly efficient P removal and recovery from wastewater with blast furnace slag (BFS) as the adsorbent. The adsorption characteristics were consistent with the Langmuir adsorption isotherm (q0 0.1370~0.3848 mg/g) and quasi-secondary kinetic model (R2 = 0.9986~0.9997), suggesting monomolecular-layer chemical adsorption might be the dominant pathway. According to the determination of scanning electron microscope and energy dispersive spectroscopy, P was distributed uniformly with other elements in the surface of BFS and even formed needle-like crystals. This indicated that P might be also further deposited in the surface of BFS after the initially chemical adsorption via coordination with the active sites, which led to the slow accumulation of P along with the adsorption experiments. The binding energy and atomic composition analysis of X-ray photoelectron spectroscopy revealed that phosphate mainly existed as HPO42− in the surface of BFS, especially for those non-magnetic particles with relative low Fe content (<30%), indicating the preference of P to the hydroxyl basic sites. Compared with those magnetic particles, the adsorption capacity of the non-magnetic particles was larger and could be restored more easily with the elution of sulfate acid, resulting in about two times the P recovery capability. Based on the P adsorption mechanism in the surface of BFS, the operation conditions of the BFS adsorption column for P recovery were optimized in an alkaline condition with a low phosphate concentration and long residual time. Therefore, non-magnetic BFS with small size could be used to recover P resources from rural wastewater with low P concentration and facilitated the on-site reuse of P resources in rural districts.
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