Phosphorus Adsorption on Blast Furnace Slag with Different Magnetism and Its Potential for Phosphorus Recovery

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.

The Phosphorus Adsorption and Recovery of Mg/Fe-LDHs Mulberry Rod Biochar Composite

“…It is 1.02 times and 2.4 times the maximum phosphorus adsorption capacity (97.9%) of When Ca/P = 2.2, the recovery rate of phosphorus is 99.64%. The recovery rate of phosphorus by MFBCs is about 1.06 times that of the maximum recovery rate of phosphorus (94%) when using the Mg-Al-Fe layered double hydroxides prepared by Jia et al [24].…”

“…The initial phosphorus concentrations were set at 50 and 100 mg•L −1 , and 0.1 g of MFBCs was added to 50 mL of phosphorus-containing synthetic wastewater, the pH of the solution was adjusted to 4.0, and the residual phosphorus concentrations were determined at different periods of 0.25, 0.5, 1, 1.5, 3,5,7,10,12,15,18,24,36, and 48 h. The residual phosphorus concentrations were determined at different periods of 0.25, 0.5, 1, 1.5, 3, 5, 7, 10, 12, 15, 18, 24, 36, and 48 h. The residual phosphorus concentrations were determined at different times. The adsorption process was fitted using quasi-primary and quasi-secondary kinetic models with the linear expressions of [Equations ( 5) and ( 6)].…”

“…With the increase in the initial phosphorus concentration, phosphate adsorption significantly increased and then gradually reached equilibrium. The decrease in phosphate adsorption can be explained by the lack of active sites capable of accommodating the increased phosphate species at immobilized adsorbent doses [24]. The significant increase in phosphorus adsorption after modification compared to unmodified mulberry stem biochar suggested that the combination of porous biochar matrix and positively charged Mg/Fe-LDHs has a strong enhancement effect on anion adsorption.…”

“…When Ca/P = 2.2, the recovery rate of phosphorus is 99.64%. The recovery rate of phosphorus by MFBCs is about 1.06 times that of the maximum recovery rate of phosphorus (94%) when using the Mg-Al-Fe layered double hydroxides prepared by Jia et al [24]. Xiong et al [21] synthesized a novel aqueous phosphorus removal adsorbent by simultaneously loading zirconia and iron oxide onto activated carbon nanofibers (ACF-ZrFe), achieving a maximum phosphorus recovery rate of 1.08 times (91.4%).…”