Maximum Phosphate Adsorption Capacity Research Articles

Diatomite Composited with a Zeolitic Imidazolate Framework for Removing Phosphate from Water.

Adsorption technology based on various adsorbents has been widely applied in wastewater treatment containing phosphate. A novel diatomite adsorbent composited with ZIF-8 (CZD) was developed for removing phosphate from water in this work. The chitosan was used to pre-modify the diatomite so that ZIF-8 could be anchored on the surface of the diatomite solidly and uniformly. The diatomite composited with ZIF-8 was then used to remove phosphate in water by an adsorption process, the process variables such as adsorption time, temperature, pH, and competitive ions were investigated. The electrostatic attraction was the primary mechanism of phosphate removal. The adsorption reached equilibrium within 90 min, and its sorption capacity increased when adsorption time and temperature increased. Especially, CZD had a rapid adsorption rate and 85% of the phosphate in the solution can be adsorbed within the first 10 min. The maximum phosphate adsorption capacities of the modified diatomite reached 13.46, 13.55, and 13.95 mg/g at 25, 35, and 45 °C, respectively. The removal efficiencies of CZD for phosphate were more than 98% and even came up to 100% at 45 °C. The adsorption isotherms fit well with the Langmuir isotherm model. The Freundlich isotherm and Temkin isotherm showed that the adsorption process is physical in nature. The kinetic data of the adsorption process were fitted by the pseudo-second-order kinetics. Thermodynamic parameters indicated that the adsorption process was endothermic. This adsorbent provided an alternative for phosphate removal on account of the high adsorption efficiency in a short time. Therefore, CZD could be a promising and eco-friendly phosphate adsorbent for wastewater treatment.

Iron-loaded magnetic alginate-chitosan double-gel interpenetrated porous beads for phosphate removal from water: Preparation, adsorption behavior and pH stability

Phosphate removal from water relies mainly on the effective adsorbent. Iron-loaded magnetic alginate-chitosan double-gel interpenetrated porous beads (M-IACBs) were prepared from waterworks iron sludge, magnetic nanoparticles, sodium alginate, and chitosan where magnetic nanoparticles were also synthesized from iron sludge. The interpenetrating network constructed by sodium alginate and chitosan improves the stability of the beads, while iron sludge acts as the main functional body for phosphate adsorption. M-IACBs with uniform size (~ 2 mm) and strong saturation magnetization intensity (~ 15.0 emu/g) maintain good stability in the pH range of 4–8. They have good selectivity for phosphate in the presence of competing ions. The phosphate adsorption by the beads followed the Langmuir model, indicating that the adsorption was dominated by monolayer adsorption, and the fitting yielded a maximum phosphate adsorption capacity of 18.5 mg/g. The pseudo-second-order model better agrees with the experimental data. The adsorption properties of iron sludge and beads were compared. Granulation was found to enhance the availability of the adsorbent but slow down the adsorption kinetics. The adsorption mechanisms of phosphate are ligand exchange and electrostatic attraction. This study provides a reference pathway for phosphate removal and resource utilization of iron sludge in waterworks.

Bottom-up synthesis of MOF-derived magnetic Fe-Ce bimetal oxide with ultrahigh phosphate adsorption performance

The intrinsic properties of metal-based adsorbents originate from multiples factors such as surface functional groups, electronic and dimensional structures. However, the synthetic strategies are limited to top-down methods, which inhibited the improvement of adsorbent performance. Herein, Fe-Ce bimetal oxide composites are prepared by a bottom-up modified MOF template method. MOF template-directed nano rod-like morphology can expose more active sites and facilitate phosphate access to active sites. The introduction of citric acid effectively increased the amount of surface –OH groups and greatly improved the phosphate adsorption capacity. Furthermore, the Fe dopant enables the high Ce(III) fraction and generate magnetic property for Fe-Ce bimetal oxide composites, which are capable of enhancing the intrinsic phosphate adsorption performance. The results show that the optimized Fe-Ce bimetal adsorbent showed remarkably high phosphate adsorption capacity, achieving a maximum phosphate adsorption capacity of 357 mg g−1 by Langmuir model. High adsorption capacity and high magnetic separation efficiency characteristics make this adsorbent a promising material for phosphate treatment. The above results further prove the effectiveness of the bottom-up strategy in the design process of environmental functional materials.

Preparation of FeOOH supported by melamine sponge and its application for efficient phosphate removal

Water eutrophication caused by the excessive discharge of phosphate has been a topic theme in decades and phosphate removal from aqueous solution is of great significance. Adsorbents of iron (hydroxyl)oxides particles exhibited its great potential in environmental pollution remediation. However, iron (hydroxyl)oxides are easy to aggregate, resulting in the decreased reactivity. In this study, we immobilized FeOOH on the surface of melamine sponge (MS). The characterization results of scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) revealed that FeOOH was well-dispersed on melamine sponge. Further phosphate removal experiments results elucidated that the maximum phosphate adsorption capacity of the synthesized material (FeOOH@MS) was 115.5 mg P/g when the theoretical mass ratio of Fe to MS was 5:1. Meanwhile, the physical adsorption with electrostatic attraction and chemical adsorption with the formation inner-sphere complex were involved for phosphate treated by FeOOH@MS without pH adjustment. Subsequently, we investigated the phosphate removal performance of FeOOH@MS in a packed column, and found that capacity of phosphate removed by FeOOH@MS reached 11.3 mg/g, and the packed column with FeOOH@MS would be penetrated at 1201 BVs around 41 h, suggesting that application of FeOOH@MS to treat phosphate-contained wastewater was feasible. Moreover, when the phosphate-containing lake water was treated with FeOOH@MS, the algae growth in the treated water was significantly inhibited, indicating that FeOOH@MS could be utilized to control the water eutrophication. Overall, this study provided a promising adsorbent for phosphate-contained water treatment.

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.

Fabrication of alumina decorated graphene oxide nanocomposite for efficient removal of aqueous phosphate

Graphene-oxide/alumina (GO/Al2O3) nanocomposite was synthesized and applied for the removal of phosphate from water through adsorption. Various parameters like the influence of adsorbent dose, adsorption time, solution pH, and initial phosphate concentration on the phosphate removal capacity were examined. It was observed that the second-order kinetics model fitted better compare to the first-order kinetics. The adsorption isotherm was best fitted with Langmuir isotherm compare to Freundlich isotherm. The GO@Al2O3 nanocomposite showed maximum phosphate adsorption capacity 33.2 mg/g at pH 6 and room temperature 30 °C.The new phosphate adsorbents can be produced in a variety of structures using a simple technique and are likely to be applied to industrial applications in phosphate contaminated wastewater management.

Electrospinning preparation and adsorption properties of La2O3 nanofibers and photoluminescence properties of La2O3: Eu nanofibers

One-dimensional La2O3 and La2O3:Eu nanofibers were prepared by a simple electrospinning method and heat treatment using polyvinylpyrrolidone as electrospinning template. The structures and morphologies of the products were characterized by the X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It was found that the La2O3 nanofibers were stacked with 30–55 nm La2O3 nanoparticles in ordered arrangement, which highly exposed the active sites. In consequence, La2O3 nanofibers showed rapid and high phosphate removal capacity due to the strong chemical affinity of phosphate/lanthanum bonds. The maximum adsorption capacity of phosphate on La2O3 nanofibers reached up to 172 mg P/g at the initial phosphate concentration higher than 4.0 mg P/L, which is 1.17 times higher than the best reported value. In particular, the nanofibers could remain fibrous in the aqueous solution, which reduces the secondary pollution caused by separating the adsorbent from the aqueous solution. Lanthanum oxide nanofibers have the advantages of convenient recovery and resistance to anion interference. Furthermore, the La2O3:Eu nanofibers exhibited strong photoluminescence properties.

A new carbon nanotube modified by nano CaO2 for removal of chromate and phosphate from aqueous solutions

Chromate and phosphate simultaneously exist in several types of waste streams (e.g., leather tannery). Herein, we developed a new carbon nanotube (CNT) modified by the nano calcium peroxide particles in-situ formed for the treatment. The CNTs with different ratios were prepared and tested for the performance. The CNT (CNT-3) prepared by 0.5-M CaCl2 and 0.5-M H2O2 demonstrated the best performance. It had a total -O-O- group content of 5.24 ± 0.68 mmol/g, and was uniformly covered by synthesized particles with an average diameter of 20–50 nm. At a dosage of 200 mg/L, the removal efficiency of Cr(VI) and phosphate was achieved with the percentage of 81 and 99%, respectively, at a contact time of 120 min. The maximum phosphate adsorption capacity was 126.74 mg-P/g, much higher than that of many adsorbents such as the reported Ca-based, Zr-based and La-based adsorbents. Commonly existing anions (namely SO42-, CO32–, SiO32-, NO3–, and Cl-) showed negligible effects on the simultaneous removal of oxyanions. However, the presence of arsenite greatly decreased the treatment efficiencies for both oxyanions; that of fluoride had no effect on the reduction of Cr(VI), but decreased the adsorption of phosphate. Acidic condition (e.g., pH 3.0) was beneficial for the Cr(VI) removal, but caused the negative effect on the phosphate removal. The chemical and physical properties of CNT-3 were studied via several analytical approaches (e.g., BET, Zeta potential, FESEM-EDX, XRD and XPS). Cr(VI) was removed via chemical reduction to Cr(III) by H2O2 released from CaO2 on CNT-3; phosphate was adsorbed via chemical precipitation (forming hydroxyapatite (Ca10(PO4)6(OH)2)) due to the presence of calcium ion and electrostatic interaction. This research indicates CNT-3 has a great potential for treatment of wastewater containing chromate and/or phosphate oxyanions.

Synthesis and optimization of spherical nZVI (20-60nm) immobilized in bio-apatite-based material for efficient removal of phosphate: Box-Behnken design in a fixed-bed column.

In the present study, bio-apatite/nZVI composite was synthesized through Fe(III) reduction with sodium borohydride and was fully characterized by FTIR, XRD, SEM-EDX, TEM, BET, BJH, and pHPZC. Column experiments were carried out for the removal of phosphate as a function of four operational parameters including initial phosphate concentration (100-200mg L-1), initial solution pH (2-9), bed height (2-6cm), and influent flow rate (2.5-7.5mLmin-1) using a response surface methodology (RSM) coupled with Box-Behnken design (BBD). 2D contour and 3D surface plots were employed to analyze the interactive effects of the four operating parameters on the column performance (e.g., uptake capacity and saturation time). According to ANOVA analysis, the influent flow rate and bed height are the most important factor on phosphate uptake capacity and saturation time, respectively. A quadratic polynomial model was excellently fitted to experimental data with a high coefficient of determination (> 0.96). The RSM-BBD model predicted maximum phosphate adsorption capacity of 85.71mgg-1 with the desirability of 0.995 under the optimal conditions of 135.35mg L-1, 2, 2cm, and 7.5mLmin-1 for initial phosphate concentration, initial solution pH, bed height, and influent flow rate, respectively. The XRD analysis demonstrated that the reaction product between bio-apatite/nZVI composite and phosphate anions was Fe3 (PO4)2. 8H2O (vivianite). The suggested adsorbent can be effectively employed up to five fixed-bed adsorption-desorption cycles and was also implemented to adsorb phosphate from real samples.

Removal of phosphate from aqueous solution by using thermally modified clamshell

The removal of phosphate (PO[Formula: see text] from an aqueous solution by clamshell treated by heat process was investigated through batch experiments. The effects of initial phosphate concentrations, pH value, and contact time on the phosphate removal were carried out. The phosphate adsorption isotherm was described by the Langmuir and Freundlich models. As the result, the adsorption process correlated well to both models, and the theoretical maximum phosphate adsorption capacity was 319.0 mg/g by the Langmuir isotherm model. The influence of pH was investigated from 5 to 10, and the value of pH had no significant effect on phosphate adsorption capacity. This finding indicated the application of calcined clamshell in the large range of pH for phosphate removal. The phosphate adsorption capacity and phosphate removal efficiency were obtained at 209.0 mg/g and 38.7% at the initial phosphate concentration of 540 ppm at 25∘C for 24 h, respectively. The clamshell modified by heat treatment exhibited its substantial potential for fast and efficient phosphate removal in water and wastewater.

Synergistic role of inherent calcium and iron minerals in paper mill sludge biochar for phosphate adsorption

Phosphate adsorption using metal-based biochar has awakened much attention and triggered extensive research. In this study, novel Ca/Fe-rich biochars were prepared via a one-step process of pyrolyzing paper mill sludge (PMS) at various temperatures (300, 500, 700, and 800 °C) under a CO2 atmosphere for phosphate removal. Batch adsorption experiments showed that the biochar obtained at 800 °C (PB-800), which could be easily separated magnetically, exhibited the best phosphate adsorption capacity in a wide range of solution pH (5–11). Based on the Langmuir model, the maximum phosphate adsorption capacity for PB-800 was 17.33 mg/g. Besides, the effects of ambient temperature as well as coexisting ions on phosphate removal were also investigated. Kinetic and thermodynamic analysis revealed that chemisorption dominated the adsorption process. The calcium carbonate and ferric salts in the sludge were converted into CaO and Fe3O4 through pyrolysis at 800 °C. The CaO inherent in PB-800 was proved to serve as active sites for the chemical precipitation, showing its synergistic effect with iron oxide compounds (i.e., Fe3O4, α-Fe2O3) on phosphate removal through chemical precipitation, ligand exchange, and complexation. This study not only provides a feasible waste-to-wealth strategy for converting PMS into a Ca/Fe-rich magnetic biochar that can be used as an effective phosphate adsorbent, but also offers new insights into the synergistic effect of calcium and iron species for the adsorption of phosphate using biochar.

Enhanced adsorption performance of subordinate magnesium sites in pinhole magnesium oxide nanosheets with rich oxygen vacancies

Phosphorus recovery from wastewater is important for protecting the aquatic environment and achieving sustainable development. However, as a typical phosphorus adsorbent, nanoscale magnesium oxide (MgO) exhibits aggregation and limited adsorption ability. Herein, melamine foam (MF) was selected as a self-sacrifice template to prepare an oxygen-vacancy-rich MgO/MF phosphate adsorbent with high dispersion and a multistage pore structure. Density-functional theory calculations reveal that the phosphate preferentially adsorbed on the hollow sites rather than top sites of MgO when there were oxygen vacancies, which improved the intrinsic adsorption ability of MgO/MF. The MgO/MF adsorbent exhibited excellent phosphorus removal from water within a wide pH range of 2–12; the maximum adsorption capacity of phosphate was as high as 1226 ​mg/g. The adsorption capacity of the MgO/MF adsorbent after phosphate adsorption was reactivated to ca. 100%. After six adsorption cycles, MgO/MF with a high phosphate content of 117.5 ​mg ​P/g is a potential high-quality fertilizer. This work provides a promising strategy for constructing an efficient adsorbent for wastewater treatment and resource recovery.

Phosphate Adsorption onto an Al-Ti Bimetal Oxide Composite in Neutral Aqueous Solution: Performance and Thermodynamics

Phosphorus (P) pollution and phosphorus recovery are important issues in the field of environmental science. In this work, a novel Al-Ti bimetal composite sorbent was developed via a cost-effective co-precipitation approach for P removal from water. The adsorptive performance and characteristics of P onto Al-Ti sorbent were evaluated by batch adsorption experiments. The effects of Al:Ti molar ratio, initial P concentration and reaction temperature were investigated. The microstructural characteristics of the Al-Ti sorbent were confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, and nitrogen adsorption-desorption measurements. Kinetic studies showed that the adsorption of P on Al-Ti oxide proceeds according to pseudo-second-order kinetics. The maximum adsorption capacity of phosphate on the Al-Ti oxide calculated from linear Langmuir models was 68.2 mg-P/g at pH 6.8. The Al-Ti oxide composite sorbent showed good potential for P recovery, owing to its large adsorption capacity and ease of regeneration.

Concurrent removal of phosphate and ammonium from wastewater for utilization using Mg-doped biochar/bentonite composite beads

This study reports a strategy for concurrent removal of phosphate and ammonium by a new adsorbent of Mg-doped biochar/bentonite composite bead (SA-Mg@BC/BT), with a high specific surface area and abundant functional groups to facilitate the adsorption process. The maximum phosphate and ammonium adsorption capacities of SA-Mg@BC/BT reached 132.2 mg/g and 39.5 mg/g respectively, apparently surpassing those of SA-BC/BT in this study and other relevant adsorbents in literatures. The removal ability for phosphate kept stable with coexisting monovalent anions (NaCl, MgCl2, KNO3 and KF), while decreased slightly in the presence of divalent anions (MgSO4, CaSO4 and K2SO4). Interestingly, the adsorption capacity for the ammonium removal was even found enhanced by divalent salts (12.0%, 23.9% and 15.0 for MgCl2, MgSO4 and CaSO4 respectively) and K2SO4 (17.9%). For the actual wastewater, the excellent concurrent removal ability of 98.3% for phosphate and 35.6% for ammonium was validated, and adsorption capacity in actual wastewater was almost the same as that in simulated wastewater. Such an excellent concurrent removal ability for phosphate and ammonium by SA-Mg@BC/BT can be ascribed to the struvite crystallization, ion exchange and Mg-P complexation formation. Finally, the leaching and pot experiments indicated the slow-release ability of the adsorption saturated SA-Mg@BC/BT as a fertilizer, providing a new possibility of nutrient recovery.

Phosphate abatement using calcium silicate hydrate synthesized from alum factory solid waste residue

ABSTRACT Calcium silicate hydrate (CSH), synthesized from the solid waste residue (SWR) of Awash Melkassa Alum Factory was examined for phosphate removal from an aqueous solution. The synthesized CSH was characterized using BET surface area analyzer, Scanning Electron Microscopy, Powder X-ray diffraction, and Fourier-transform infrared spectroscopy. Response surface methodology (RSM) adapted to assess a model equation that correlates the phosphate removal efficiency (R %) with the factors affecting adsorption such as initial phosphate concentration (Co), adsorbent dosage, pH, and time (t). Optimum removal efficiency of 95.69% attained at Co =5.5 mg/L, dose = 5 g/L, pH = 5, and t = 90 min at which consecutive experiments conducted. The adsorption kinetics experimental data fitted well to both pseudo-second-order model (R2 = 0.999) and Elovich model (R2 = 0.996) imply that chemisorption is dominant adsorption mechanism for phosphate adsorption on CSH. The isotherm experimental data fitted well to the Langmuir model (R2 = 0.965). The maximum phosphate adsorption capacity (qm) of 82.58 mg/g obtained at 45°C. The attained negative standard free energy (ΔGo = −5.18 kJ/mol) and positive enthalpy (ΔHo = 7.10 kJ/mol) confirms the spontaneity and endothermic nature of phosphate adsorption by CSH. The synthesized CSH tested for its phosphate removal (R = 63.78%) using real wastewater collected from a local wastewater treatment plant. Bicarbonate and sulfate observed to compete for active sites on the adsorbent during phosphate removal. Generally, the synthesized CSH can be considered as a low-cost silicate material for phosphate abatement.

Efficient and stable removal of phosphate from aqueous solutions by hollow microspheres of MgO/ZrO2 composite oxide

Excessive phosphorus is regarded as one of the main causes of eutrophication, destroying the balance of the original ecosystem of water bodies and endangering human health. In this study, a novel MgO/ZrO2 composite oxide with a hollow structure (MgZr-CS) was prepared by a simple carbon template method, and served as an adsorbent for the efficient uptake of phosphate from aqueous solutions. For comparison, MgO/ZrO2 bimetal oxide (MgZr) was also prepared by the conventional co-precipitation method. The effects of pH and coexisting anions on the adsorption of phosphate were studied. The adsorption performance of materials was described by the adsorption kinetic model and isothermal model. The adsorption capability of both MgZr-CS and MgZr was negligibly affected by coexisting ions (e.g., Cl−, NO3−, HCO3− and SO42−) in water. The adsorption kinetic of both MgZr-CS and MgZr was better correlated with the pseudo-second-order kinetic model, while the adsorption isotherm followed the Langmuir model. However, the Langmuir maximum phosphate adsorption capacity of MgZr-CS was 149.3 mg/g at initial pH of 7, which was about twice that of MgZr. Remarkably, different from MgZr that only presented well phosphate adsorption performance under the acidic environment, MgZr-CS could maintain the excellent adsorption performance within a particularly wide pH range of 3–11. Compared to adsorbents reported in previous papers, MgZr-CS also exhibited larger adsorption capacity and higher pH stability. Moreover, MgZr-CS performed prominent in the treatment of actual domestic sewage, and its phosphate removal rate could reach 99.3%. The adsorption mechanism analysis revealed that the excellent phosphate performance of MgZr-CS was mainly due to the existence of oxygen vacancies providing more active adsorption sites. Results shown here indicated that MgZr-CS can be used as a potential adsorbent for phosphate.

Immobilization of β-FeOOH nanomaterials on the basalt fiber as a novel porous composite to effectively remove phosphate from aqueous solution

A novel porous basalt fiber (BF) loaded with β-FeOOH adsorbent (FeOOH/BF) was successfully fabricated and used to effective removal of phosphate in the aqueous solution. The FeOOH/BF composite was thoroughly characterized by X-ray diffraction, Fourier transform infrared spectrometer, Scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results demonstrated that dense β-FeOOH nanomaterials with 17.2 nm were immobilized on the surface of BF. The BET surface area of composite was 105.79 m2/g with a pore volume of 0.163 cm3/g and average pore diameter of 6.177 nm. The best phosphate removal efficiency was achieved in the pH range of 5–10. Adsorption kinetics and isothermal adsorption studies showed that the pseudo-second-order model and the Freundlich isotherm fitted the experimental data better, indicating that the phosphate adsorption onto FeOOH/BF tend to multi-molecular layer and chemical adsorption, and the maximum phosphate adsorption capacity of 39.08 mg/g was calculated. The coexisting anions (e.g., Cl-, SO42- and NO3-) had slight effects on phosphate adsorption compared with the obvious disturbance of CO32-. Ligand exchange, inner-sphere complexation and electrostatic attraction were the main mechanisms of FeOOH/BF for removal of phosphate. The used FeOOH/BF could be effectively regenerated by 0.3 mol/L NaOH and the adsorption efficiencies still maintaining 80% of initial adsorption capacity after three cycles. The proposed FeOOH/BF might be acted as a promising adsorbent for efficient and preferable phosphate removal from contaminated water.

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

In this study, Fe-Zr-La tri-metal oxide (FZLO) composite was synthesized by co-precipitation method as new complex adsorbent for effective phosphate removal from aqueous media. The scanning electron microscopic study revealed that the adsorbent was of amorphous structure and consisted of the inhomogeneous aggregated nanoparticles with different sizes. Various influencing parameters such as pH values, initial concentration of phosphate ions, contact time, temperature and co-existing anions were studied to perform batch adsorption experiments. The experimental results demonstrated that the adsorption process was highly pH-dependent and obtained the maximum phosphate adsorption capacity of 101.0 mg g−1 at pH = 6. The adsorption process occurred on surface of FZLO composite has been found to be mono-layered and chemisorption dominated in nature as the data fitted well to Langmuir isotherm as well as the pseudo-second-order kinetic model. The structure and properties of the adsorbent before and after adsorption using FT-IR, XRD and XPS techniques suggested that the adsorption mechanisms involved electrostatic attraction, complexation and ligand exchange. After the adsorption, the remained P concentration met the permissible limit by the Environmental Protection Agency. The Fe-Zr-La tri-metal oxide composite could be a promising adsorbent for phosphate removal from aqueous media.

La(OH)3 loaded magnetic nanocomposites derived from sugarcane bagasse cellulose for phosphate adsorption: Characterization, performance and mechanism

The magnetic nanomaterials Mg-Al-La LDH/Fe3O4/C were prepared using Fe3O4/C as a precursor by hydrothermal and co-precipitation method, and served as adsorbents for the efficient uptake of phosphorus from aqueous solutions. The effects of adsorbent dosage, pH and co-existing ions on the adsorption of phosphate were studied. The adsorption performance of the material was described by the adsorption kinetic model, isothermal model and thermodynamic model. When the pH value of the solution is in 4–7, it shows a high phosphate removal rate (>98.7%). The maximum phosphate removal rate (99.43%) was obtained at pH=6. The phosphate adsorption process by Mg-Al-La LDH/Fe3O4/C was best described by the Langmuir isotherm model and pseudo-second-order reaction kinetics. The maximum adsorption capacity for phosphate was evaluated as 106.21 mg/g. The optimization of phosphate adsorption was carried out by response surface design. The adsorption mechanism of Mg-Al-La LDH/Fe3O4/C for phosphate could be explained by ion exchange, electrostatic attraction and ligand exchange. Experiments have proved that Mg-Al-La LDH/Fe3O4/C nanocomposite can be used as a potential material for adsorbing phosphate in polluted water.

Improved holding and releasing capacities of coal gangue toward phosphate through alkali-activation

Activation is an effective method to improve adsorption capacity of coal gangue, however, most activated gangues reported have limited adsorption capacity for phosphate because of the electronegativity, affecting their use in agricultural production and environmental protection. In order to enhance the phosphate absorption capacity of coal gangue through alkali-activation, three alkali-activated silicate coal gangue according to fine-size (AS-FCG1), medium-size (AS-MCG2), and large-size (AS-LCG3) were prepared through grinding, calcining (800 °C) and stimulating with Ca(OH)2 solution (0.1 M), and raw coal gangue (RCG4) was used as control. The results revealed that AS-FCG has the best modified effects, its maximum phosphate adsorption capacity, according to Langmuir model, was 11.796 mg g−1, which was 4.41, 8.16 and 73.73 times higher than that of AS-MCG, AS-LCG and RCG, respectively. The adsorption penetration time of AS-FCG packed column was over 30 h, which was longer than that of other samples. Besides, when the AS-FCG packed column loaded with phosphate was desorbed with distilled water, the phosphate concentration of filtrate was low and rapidly tended to 0 mg L−1, while when it was desorbed with NaHCO3 solution, the concentration remained high sustainably. The best adsorption performance of AS-FCG were associated with generation of calcium silicate hydrate gel and ettringite, which provided more Ca2+, Al3+, hydroxyl and larger specific surface area. It is suggested that alkali-activation is able to truly realize the recycling of solid waste, AS-FCG is an inexpensive, durable and eco-friendly material, which could not only be used to hold phosphate, but also release it slowly as fertilizer.