Adsorption performance and mechanism of a starch-stabilized ferromanganese binary oxide for the removal of phosphate

Effective removal of phosphate from water is essential for preventing the eutrophication and worsening of water quality. This study aims to enhance phosphate removal by synthesizing starch-stabilized ferromanganese binary oxide (FMBO-S), discover the factors, and investigate adsorption mechanisms. FMBO and FMBO-S properties were studied using Scanning Electron Microscopy, BET analysis, Polydispersity Index (PDI), Fourier Transform Infrared Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). After starch loading, the average pore diameter increased from 14.89 Å to 25.16 Å, and significantly increased the pore volume in the mesopore region. FMBO-S showed a PDI value below 0.5 indicating homogeneous size dispersity and demonstrated faster and higher adsorption capacity: 61.24 mg g-1 > 28.57 mg g-1. Both FMBO and FMBO-S adsorption data fit well with the pseudo-second-order and Freundlich models, indicating a chemisorption and multilayered adsorption process. The phosphate adsorption by FMBO was pH-dependent, suggesting electrostatic attraction as the dominant mechanism. For the FMBO-S, phosphate adsorption was favored in a wide pH range, despite the weaker electrostatic attraction as evident from the point of zero charge and zeta potential values, indicating ligand exchange as a main mechanism. Moreover, the XPS analysis shows a significant change in the proportion of Fe species for FMBO-S than FMBO after phosphate adsorption, indicating significant involvement of Fe. Meanwhile, phosphate adsorption was almost unaffected by the presence of Cl-, NO3-, and SO42- anions, whereas CO32- significantly reduced the adsorption capacity. This study revealed that FMBO-S could be a promising, low-cost adsorbent for phosphate removal and recovery from water.

Phosphate adsorption on dried alum sludge: Modeling and application to treatment of dairy effluents

This study evaluates Alum sludge from drinking water treatment plants for the efficient and cost-effective removal of phosphates from aqueous solutions. Extensive characterization and batch experiments have established that optimal phosphate removal was achieved with a sludge dosage of 20 g L-1 (at an initial phosphate concentration of 100 mg L-1), a pH of 5, a temperature of 23 °C, and a stirring speed of 200 rpm. These conditions significantly reduced phosphate levels, ensuring compliance with legal discharge limits. The Langmuir isotherm, pseudo-second-order kinetic and intraparticle diffusion models best described the adsorption process, highlighting the spontaneous and endothermic nature of the phenomenon. The sludge effectively reduced phosphate concentrations to acceptable levels when applied to dairy effluents. This study underscores the potential of Alum sludge as a viable solution for phosphate management in environmental cleanup efforts.

An application of hierarchical MgAl hydrotalcite in the highly efficient treatment of oilfield macromolecular contaminants

In this work, salicylic acid (SA) was used to induce the self-assembly of octadecyl trimethyl ammonium chloride (OTAC), a cationic surfactant, into three-dimensional wormlike micelle aggregates. These aggregates act as a soft template for hierarchical MgAl hydrotalcite (LDH) to create a multi-level pore structure adsorption material. Scanning electron microscopy characterization showed that the surface of the hierarchical hydrotalcite exhibited a dense layered structure, unlike the monolayer structure of ordinary hydrotalcite. Furthermore, the hierarchical MgAl-LDH possesses a significantly larger specific surface area (113.94 m2/g) and wide pore size distribution ranging more extensively from 2 to 80 nm, which significantly has an impressive adsorption effect on sulfonated lignite (SL), with a maximum adsorption capacity of 192.7 mg/g at pH = 7. Extensive research has been conducted on the adsorption mechanism of hierarchical MgAl-LDH, attributing it to surface adsorption due to the unique multi-level structure of the adsorbent. After two cycles of regeneration experiments, the adsorption capacity of the adsorbent remained at a high level of 179.1 mg/g, demonstrating the excellent renewability of hierarchical MgAl-LDH. Moreover, the hierarchical hydrotalcite showed high adsorption capacity in the adsorption of sulfonated lignite, which was attributed to its larger specific surface area and superior pore structure to expose more active sites.

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.

Efficient phosphate elimination from aqueous media by La/Fe bimetallic modified bentonite: Adsorption behavior and inner mechanism

Nowadays, eutrophication problem in surface waterbodies has attracted specific attention. Herein, we reported facile synthesis and application of La/Fe engineered bentonite (LFB) for efficient phosphate elimination. Results indicated that bimetallic modified LFB composite could achieve efficient phosphate removal at pH 2-6, and satisfactory selectivity was implied by stable phosphate capturing within the interference of competing species (Cl^-, NO₃^-, HCO₃^-, SO₄^2-, F^- and HA). Pseudo-second-order model could satisfactorily depict the kinetic behavior at different initial concentrations, indicating chemisorption of phosphate on LFB surface. Isotherm study suggested that phosphate adsorption behavior could be fitted well with Sips isotherm equation, indicating that both homogeneous monolayer adsorption and heterogeneous multilayer coverage of phosphate on LFB surface occurred within the investigated conditions. Adsorption thermodynamics implied the spontaneous and endothermic feature of phosphate loading on LFB composite. Characterization analysis confirmed successful La and Fe loading on bentonite, and electrostatic attraction and ligand exchange were the main adsorption mechanism. The high adsorption capacity, cost-effective feature and strong affinity towards phosphate demonstrated certain potential of as-prepared LFB composite for phosphate separation from eutrophic water.

Al2O3 encapsulated by calcium alginate as composite for efficient removal of phosphate from aqueous solutions: batch and column studies

Activated alumina (Al₂O₃) has been widely used to remove aqueous anionic pollutants such as phosphate for preventing the eutrophication phenomenon. While Al₂O₃, as a fine powder material, cannot be stably packed into continuous flow treatment, which limits its practical applications. Herein, we proposed a new strategy in which Al₂O₃ was encapsulated by calcium alginate (CA) to fabricate Al₂O₃/CA composite, which has relatively large particle size and can be suitable for application in columns. The BET surface area of Al₂O₃/CA increased to 51.73 m²/g compared with 37.31 m²/g of Al₂O₃. The maximum adsorption capacity of phosphate on Al₂O₃/CA was estimated at 1.92-fold compared with that of pure Al₂O₃ by Langmuir fitting. The main mechanism of phosphate adsorption was the formation of aluminum phosphate precipitation. Moreover, the column studies showed that the adsorption of phosphate on Al₂O₃/CA was affected by the amount of outer calcium alginate, bed height, influent flow rates and phosphate concentration. This study demonstrated that Al₂O₃/CA composite has better adsorption capacity and can be used in the dynamic adsorption system as a promising approach for phosphate removal from water.