High-efficiency adsorption of phosphate by Fe-Zr-La tri-metal oxide composite from aqueous media: Performance and mechanism

Advanced removal of phosphate from water by a novel lanthanum manganese oxide: Performance and mechanism

A novel lanthanum manganese oxide (La_0.96Mn_0.96O₃, LMO) was synthesized for advanced phosphate removal to alleviate water eutrophication process. The adsorbent had a specific surface area of 18.51 m²/g with pH at point of zero charge of 6.6; exhibited excellent phosphate adsorption capacity of 168.4 mg/g; performed well in a wide pH range from 3 to 10. The phosphate removal was not interfered by coexisting ions. The adsorbent remained 94.8% of its initial adsorption efficiency after reused for four times. Phosphate adsorption process conformed to pseudo-second-order model (R²=0.992) and Langmuir model (R²=0.935). Ligand exchange and electrostatic interaction played important roles in phosphate removal. In addition, the actual sewage secondary effluent was used to further verify the phosphate removal performance of LMO. For practical water treatment, the LMO showed high phosphate removal efficiency of 83.4% and low residual P of 0.1 mg/L. LMO is a potential candidate for low-concentration phosphate removal in real water environment.

Enhanced phosphate adsorption studies on several metal-modified aluminum sludge: preparation optimization, adsorption behavior, and mechanistic insight

To solve the problems such as water eutrophication caused by excess phosphorus, the potential residual value of aluminum sludge was fully exploited and its phosphate adsorption capacity was further improved. In this study, twelve metal-modified aluminum sludge materials were prepared by co-precipitation method. Among them, Ce-WTR, La-WTR, Y-WTR, Zr-WTR, and Zn-WTR showed excellent adsorption capacity for phosphate. The adsorption performance of Ce-WTR on phosphate was twice that of the native sludge. The enhanced adsorption mechanism of metal modification on phosphate was investigated. The characterization results showed that the increase in specific surface area after metal modification was 9.64, 7.5, 7.29, 3, and 1.5 times, respectively. The adsorption of phosphate by WTR and Zn-WTR was in the accordance with Langmuir model, while the others were more following the Freundlich model (R² > 0.991). The effects of dosage, pH, and anion on phosphate adsorption were investigated. The surface hydroxyl groups and metal (hydrogen) oxides played an important role in the adsorption process. The adsorption mechanism involves physical adsorption, electrostatic attraction, ligand exchange, and hydrogen bonding. This study provides new ideas for the resource utilization of aluminum sludge and theoretical support for preparing novel adsorbents for efficient phosphate removal.

Preparation and Phosphorus Removal Performance of Zr–La–Fe Ternary Composite Adsorbent Embedded with Sodium Alginate

Using single metal salts of zirconium, lanthanum, and iron as raw materials and sodium alginate as a cross-linking agent, a new composite adsorbent was prepared via the co-precipitation method and embedding immobilization technology, and its phosphorus adsorption performance in wastewater was evaluated. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used for characterization, and a 0.5 mol·L−1 sodium hydroxide solution was used to regenerate the adsorbent. The experimental results demonstrated that the adsorption rate reached 99.88% when the wastewater volume was 50 mL, the initial concentration of phosphorus-containing wastewater was 5 mg·L−1, the pH was 5, the dosage of composite adsorbent was 0.2 g, and the adsorption time was 200 min. The prepared adsorbent could reduce the initial phosphorus concentration of 5 mg·L−1 to 0.006 mg·L−1 in simulated wastewater, and from 4.17 mg·L−1 in urban sewage to undetected (<0.01 mg·L−1), thus meeting the discharge requirements of the grade A standard of the Urban Sewage Treatment Plant Pollutant Discharge Standard (GB18918-2002). The adsorption process conformed to the Freundlich adsorption isothermal equation and quasi-second-order kinetic equation, and the adsorption reaction was exothermic and spontaneous. More importantly, after three lye regeneration tests, the removal rate of phosphorus in water remained above 68%, that is, the composite adsorbent could be reproducibly fabricated and recycled. The characterization results showed that the surface of the composite adsorbent was rough, with a complex pore structure. After phosphorus removal, the surface morphology of the composite adsorbent showed a similar honeycomb structure, with a P-H, P-O stretching vibration peak and a characteristic P2p peak. At the same time, the proportion of hydroxyl groups (M-OH) on the metal surface decreased after adsorption. Our findings thus demonstrate that the mechanism of phosphorus removal is mainly based on the coordination exchange reaction between phosphate and metal active sites and surface hydroxyl groups, resulting in the formation of granular phosphate deposits.

Metal-based adsorbents for water eutrophication remediation: A review of performances and mechanisms

Controlling eutrophication requires satisfying stringent phosphorus concentration standards. Metal-based adsorbents can effectively remove excess phosphorus from water bodies and achieve ultra-low phosphorus concentration control for wastewater. This review focuses on the material properties and phosphorus removal mechanism of metal-based adsorbents (Fe, Al, Ca, Mg, La). There are significant differences in physical and chemical properties of different metal materials, due to the different preparation methods and synthetic materials. The main factors affecting phosphorus removal performance include particle size, crystal structure and pH_PZC. Smaller particle size, more disordered crystal structure and higher pH_PZC are more favorable for phosphorus removal. The main mechanism of phosphorus removal by metal-based adsorbents is ligand exchange, which makes it exhibit excellent adsorption capacity, fast kinetics and well selectivity for phosphate. In addition, in order to improve the phosphorus removal performance, the surface properties of the adsorbent (e.g., surface charge, surface area, and functional groups) can be effectively improved by dispersion of biochar carriers or combination of multiple metal materials. In further studies, we should improve the absorption capacity of the adsorbent under high pH conditions and the resistance to coexisting ion interference. Finally, in order to ensure the effective application of metal-based adsorbents in the phosphorus removal field, experimental scale should be expanded in future work to suit the actual water body conditions.