Phosphate Adsorption Process Research Articles

Corn stover waste preparation cerium-modified biochar for phosphate removal from pig farm wastewater: Adsorption performance and mechanism

The high phosphorus content in livestock and poultry wastewater is a significant factor contributing to water eutrophication. It is imperative to seek an economically efficient method for phosphate recovery. This study employed cerium-modified biochar to recover phosphate from pig farm wastewater. An investigation was conducted to examine the adsorption performance and removal mechanism of phosphate. Among the different samples, 0.1CeB-500℃ was selected for subsequent experiments. It exhibited a phosphate adsorption capacity of 9.58 mg/g and a removal efficiency of 95.75 %. The results showed that the phosphate adsorption process followed not only the pseudo-second-order kinetic model, but also the Langmuir isotherm model. It suggested that the adsorption of phosphate onto the biochar occurred in a monolayer chemical manner, with a maximum adsorption capacity of 10.86 mg/g. Phosphate adsorption was minimally affected within the pH range of 2–9, with Cl- having negligible impact, NO3- slightly inhibiting, and HCO3- and CO32- significantly hindering phosphate adsorption. A series of characterization results indicated that phosphate removal occurred through surface precipitation forming CePO4, ligand exchange between carbonate and phosphate, inner-sphere complexation, and electrostatic attraction. The phosphate removal efficiency from pig farm wastewater was 43.25 %, demonstrating promising potential for practical application.

Development of the Diffusive Gradient in Thin Film (DGT) Method with CaO/Biochar Binding Agent from Eggshells and Rice Straw Waste for Determining the Concentration of Phosphate

Phosphorus, often found in the form of phosphate in the environment, especially aquatic environments, has been identified as the primary contaminant that causes algae blooms and eutrophication. Phosphate adsorption in the aquatic environment was carried out by comparing the adsorption capabilities of eggshell (CaO), rice straw (BC) and CaO/biochar materials at mass variations of 1:1, 1:2 and 2:1 from the use of eggshell and rice straw waste. Each material was synthesized using ball milling and pyrolysis methods. The adsorption isotherm and kinetics of the material are by the Langmuir adsorption isotherm and are pseudo-second-order (PSO) adsorption kinetics. The CaO/biochar 1:2 material shows the highest phosphate adsorption capacity at pH 12 with a contact time of 24 hours. CaO/biochar 1:2 was applied in the phosphate adsorption process using the Diffusive Gradient in Thin Film method as a binding agent, which acts as an adsorbent. The DGT technique is an in situ sample preparation technique for identifying the presence of phosphate, a labile species. The binding agent material was characterized using FTIR, XRD, and BJH-BET instruments. The success of synthesizing CaO/biochar 1:2 binding gel and ferrihydrite was demonstrated by the appearance of the same adsorption as the diffusive gel using FTIR. The CaO/biochar binding gel demonstrated that it is a better material compared to the ferrihydrite binding gel for phosphate adsorption, achieving CDGT values of 10.1727 mg/L and 2.5959 mg/L at pH 5 and 3, respectively, with a phosphate concentration of 10 mg/L. These findings underscore the potential of CaO/biochar as a more effective material for phosphate removal applications.

Calcium silicate hydrate complex konjac glucomannan-based hydrogel selectively adsorbed phosphate in low alkalinity solution

The selective recovery of phosphate from wastewater can manage nutrients and realize the recycling of phosphorus resources. In this study, a novel konjac glucomannan/pectin/calcium silicate composite hydrogel (KP-CSH) was developed for efficient recovery of phosphate in aqueous solution. The amount of alkali released after the reaction of KP-CSH in a neutral solution was small (the pH of the solution after the reaction was < 9). In a wide initial pH range (3–10), the adsorption capacity of KP-CSH in 50 mg-P/L phosphate solution reached 39∼45 mg-P/g. Besides, even if the pH of the solution after the reaction was less than 8, it could still well adsorb phosphate. The kinetic and isothermal adsorption experiments indicated that the adsorption process of phosphate by KP-CSH was chemical adsorption, and the maximum adsorption capacity was 61.2 mg-P/g. KP-CSH preferentially adsorbed phosphate even in the presence of high concentrations of competitive ions. In the actual biogas slurry, KP-CSH also exhibited the strongest selectivity/affinity for phosphate, and its distribution coefficient (Kd) was significantly higher than that of other co-existing anions and cations. The adsorption mechanism analysis indicated that Ca was the main adsorption site of KP-CSH, and that the adsorption process of target pollutants mainly involved ligand exchange and the intra-sphere complexation. Further plant seed germination and seedling growth experiments suggested that KP-CSH after phosphate recovery did not exert a negative effect on the growth of plant seedlings, and increased the chlorophyll content of seedling leaves. These results demonstrate that KP-CSH is a potential adsorbent for efficient phosphate recovery, which can be used as a slow-release phosphate fertilizer after recovering phosphate.

Innovative iron‑manganese modified microalgae biochar for efficient phosphate iron removal from water: Preparation and adsorption mechanisms

This study developed a novel FeMn composite biochar (FMBC) with the pyrolysis raw resource of Chlorella, applying for phosphates removal from the aqueous. Under optimal conditions, the FMBC prepared from microalgae achieved a phosphate removal rate of approximately 91.6 % (adsorption capacity: 23.23 mg/g) within 120 min, demonstrating superior adsorption performance compared to the pristine biochar. Response Surface Methodology (RSM) was applied for FMBC preparation optimization. To improve the metal loading capacity of biochar, Ethylene Diamine Tetraacetic Acid (EDTA) was used as a chelating agent during the preparation process. The optimum preparation conditions for FMBC were Fe/biomass(w/w) ratio of 1.25, Mn/biomass(w/w) ratio of 1.10, pyrolysis time of 120 min, and pyrolysis temperature of 650 °C, which presented a large specific surface area (14.681 m2/g), pore volume (0.036 cm3/g) with the rich oxygen-containing functional groups. Phosphorus removal kinetic and isotherm process were better described by pseudo-second-order model and the Dubinin-Radushkevinch (D-R) isotherm. In addition, the optimal adsorption conditions for FMBC were as follows: biochar dosage of 0.1 g, initial pH of 7.0, adsorption temperature of 25 °C, and initial phosphate concentration of 50 mg/L. Physical adsorption, surface complexation, precipitation, electrostatic attractions, and ion exchange were responsible for phosphate adsorption process by FMBC. The main innovation of this study is the use of explosive growth algae to prepare metal-modified biochar for phosphorus removal from water bodies, to realize the goals of resource utilization of waste biomass and eutrophication control in water, which are significant for sustainable development.

Sludge-derived alginate-like extracellular polymers (ALE) for preparation of Fe-ALE and FeCaMg-ALE: Application to the adsorption of phosphate

Excess phosphorus (P) in wastewater has potential risk of causing harmful algal bloom and eutrophication in receiving wastewater. In this study, alginate-like extracellular polymers (ALE) derived from conventional activated sludge were modified with ionic cross-linking agents (Fe3+, Ca2+, and Mg2+) to develop Fe-ALE and FeCaMg-ALE for the adsorption of phosphate from wastewater. The adsorption process of phosphate by Fe-ALE and FeCaMg-ALE can be well described by pseudo-second-order kinetics and Freundlich isotherm model with a high level of accuracy, indicating that the adsorption processes were chemical, multi-layer adsorption process. The maximum adsorption capacity of dry Fe-ALE and FeCaMg-ALE concerning phosphate were 15.06 and 20.10 mg/g, respectively at 298 K. The adsorption capacity remained relatively consistent across a pH range of 2.0–11.0. FT-IR, XRD, SEM coupled with XPS analysis demonstrated the ALE had been successfully compounded with Fe3+ or Fe3+/Ca2+/Mg2+. Based on the experimental results and characteristic analysis, the main mechanism of phosphate by Fe-ALE and FeCaMg-ALE are physical filling, electrostatic attraction, ligand exchange and precipitation reaction. This work provides a new perspective for preparing ALE-based adsorbent using conventional activated sludge as raw material, realizing the treatment of waste with waste and effectively recovering phosphate from wastewater.

Hierarchical ZnO/ZnFe2O4 yolk-shell adsorbent as a promising material for phosphate recovery and adsorption of organic pollutants from the simulated wastewater

Mitigation of phosphate contamination is essential to preserve the health and integrity of the water ecosystem. Therefore, to prevent eutrophication and preserve water resources, it is essential to establish an effective and long-lasting phosphate removal process. Herein, a highly efficient and eco-friendly ZnO/ZnFe2O4 (ZZFO) yolk-shell microsphere was designed by the glycothermal method followed by calcination for phosphate removal and adsorption of Congo red (CR) organic dye aqueous solution. ZZFO demonstrated an outstanding Langmuir hypothetical optimum phosphate adsorption ability of 103.2 mg-P/g in batch phosphate adsorption studies. This value is 5.54 and 8 times higher than that of pristine ZnO and Fe2O3, respectively, and the adsorbent was readily removed with the use of an external magnetic field. The anions experiments showed that, except chlorine and fluoride ions, other regular anions have a slight influence on the phosphate adsorption process. The Langmuir and pseudo-second-order model showed excellent correlation constants. Moreover, ZZFO exhibited the capability to adsorb CR aqueous solution, which is a significant finding for aquatic remediation. Our experimental findings have significant implications for the fabrication of sustainable adsorbents for the treatment of wastewater.

Advanced thermodynamic approach to adsorption of charged adsorbates from aqueous electrolyte solutions

This study present estimation of the thermodynamic parameters and the influence of ionic activity coefficient on the thermodynamic equilibrium constant of adsorption of phosphates on fly ash. The adsorption was conducted over a wide range of initial phosphate concentrations at different pH values pH = (3; 7; 10). The adsorption results were treated using the Langmuir, Freundlich and Sips adsorption isotherms, which provide information about the maximum adsorption capacity. The Langmuir and Sips isotherms were a satisfactory fit to the adsorption data, especially at pH = 3, with an acceptable regression coefficient over the entire concentration range, Langmuir (r2 = 0.9737) and Sips (r2 = 0.9969). The estimated maximum phosphate sorption capacity of fly ash was 6.21 ± 0.68 (mmol·g−1) according to Langmuir and 4.19 ± 0.16 (mmol·g−1) according to the Sips model, at pH = 3.0. However, there is no data in the published literature for estimating the thermodynamic parameters of the phosphate adsorption process using thermodynamic models for activity coefficients. Novel approach of this paper was determination of the thermodynamic equilibrium constant and Gibbs free energy, using the Pitzer ion-interaction model to predict the nature of adsorption. The Pitzer-ion interaction model was used for the mixed ionic systems, taking into consideration the effect of other present ions besides phosphates in the equilibrium solution resulting from fly ash desorption. The procedure for comprehensive estimation of the ion activity coefficient at maximum adsorption capacity and the dimensionless thermodynamic equilibrium constant using Langmuir's and Sips’s constants was presented. The calculated value of the phosphate activity coefficient in the equilibrium solution was γH2PO4,e = 0.7003 ± 0.0027 and the converted molar activity coefficient was γH2PO4,e = 0.6903 ± 0.0027. The estimated values of Gibbs free energy were: ΔGL = −6.788 ± 0.521 kJ·mol−1 based on Langmuir equilibrium constant and ΔGa = −7.707 ± 0.527 kJ·mol−1 based on activity and thermodynamic equilibrium constant. According to Sips model, the adsorption process is even more spontaneous, with the Gibbs free energy calculated using the phosphate activity coefficient and the thermodynamic equilibrium constant, ΔGa = −9.707 ± 0.617 kJ·mol−1. Consideration of the ionic activity coefficient is particularly important for large, charged adsorbates at higher concentrations, as the absolute difference in free energy for adsorption is app. 12 %. The scientific contribution is reflected in obtaining the necessary and more accurate information for the improvement of adsorption processes and possibly for the upgrading of fly ash in overall wastewater treatment technology.

Performance study of phosphate removal from water using synergistic interaction between lanthanum-magnesium bimetallic organic frameworks and polyethyleneimine

Aiming at the water solubility of Mg-MOFs and the problems of unstable adsorption performance and low life of pure MOFs caused by metal leakage, lanthanum and polyethyleneimine co-doped Mg-MOFs (2.0LMBP-2.5) were synthesized by solvothermal and impregnation methods. 2.0LMBP-2.5 not only has strong resistance for co-existing anions and acid-base, but also has excellent reusability and stability. Its maximum phosphate adsorption capacity was 514.15 mg·g−1. The phosphate removal rate reached 90.53 %-96.04 % in the pH range of 3.0–11.0. The results of kinetic, isothermal adsorption and thermodynamics showed that the phosphate adsorption process of 2.0LMBP-2.5 was a spontaneous heat absorption process and dominated by monolayer adsorption and chemisorption. FT-IR spectroscopy and XPS revealed a synergistic mechanism between MOFs and polyethyleneimine. The introduction of lanthanum improved the coordination metal bond strength of Mg-MOFs, effectively overcame the water solubility problem of Mg-MOFs. The introduction of lanthanum and polyethyleneimine significantly increased the adsorption capacity of Mg-MOFs, from 21.79 to 273.61 mg·g−1 and 273.61 to 514.15 mg·g−1, respectively.

Synthesis of Al-modified hydrochar from corn stover for efficient phosphate removal

The development of a simple and feasible process for preparing adsorbent materials to recover phosphorus resources would have significant environmental and social benefits. In this study, the Al-modified hydrochar was synthesized for phosphate adsorption by hydrothermal carbonization in one pot using corn stover as raw material. The results showed that phosphate adsorption mainly depended on the precipitation reaction between Al element and phosphate, in which the hydrochar carrier played a synergistic role. Al element through the hydrothermal treatment loaded on hydrochar expressed a much higher phosphate adsorption performance than that on pyrochar. When the concentration of AlCl3 solution added in the hydrothermal process was 2 mol·L−1 and the hydrothermal temperature exceeded 180 ℃, Al element could transform from the amorphous state, which was less effective for phosphate adsorption, to Al24O11(OH)44Cl6 crystal with high adsorption performance and could be more stably loaded onto the hydrochar. Although the preparation process was simple, the adsorption performance of hydrochar is good. The phosphate adsorption capacity and removal efficiency by the hydrochar prepared at 260 °C reached to 114.40 mg·g−1 and 76.27%, which could be further increased by adjusting the dosage of adsorbent and pH of water. The pseudo-second-order kinetic model and Langmuir isotherm model could better describe the phosphate adsorption process on Al-loaded hydrochar. Phosphate was rapidly adsorbed on the surface of the hydrochar rich in mesoporous structure and bound to the surface-active sites. This study could transform agricultural waste into a functional hydrochar-based adsorbent and provide a low-cost, simple operation and efficient phosphate removal technology.

Efficiency and mechanism of phosphate adsorption and desorption of a novel Mg-loaded biochar material.

Phosphate removal is complicated by the need for resource recovery. Biochar shows promise for efficient phosphate adsorption, but it must be modified to enhance its adsorption capacity. In this work, magnesium (Mg)-loaded biochar was synthesized through a two-step dipping and calcination process, and the MgBC600 product was used to adsorb phosphate from simulated water and biogas slurry wastewater. The phosphate adsorption capacity of Mg-loaded biochar was 109.35mg/g, which was 12 times higher than that of unmodified biochar. The R2 of the Langmuir and pseudo-second-order kinetic models were 0.988 and 0.990, respectively, which fitted the phosphate adsorption process of MgBC600. Phosphate adsorption by MgBC600 was a spontaneous and endothermic process. The adsorption mechanism study showed that phosphate adsorption was controlled by the formation and electrostatic attraction of MgHPO4. In addition, 98% of chemically adsorbed phosphate was released after regeneration. Using phosphate-adsorbed MgBC600 as a soil amendment, Arabidopsis thaliana was 1.47 times higher than that in the biochar-only group, demonstrating that this is a promising strategy for enhancing phosphate adsorption efficiency and adsorbent recycling.

Dual nature brilliant adsorbent engineering by converting an Al-based MOF to defect rich quasi-MOF

Introducing defects into porous metal-organic frameworks is very important for improving adsorption performance. Due to their simplicity of synthesis and improved efficiency in MOFs applications, Quasi-MOFs have recently been considered as underutilized variant of large-scale, fundamentally deficient MOFs with substantial amounts of unsaturated metal sites to offset the drawbacks of MOFs. Herein, a quasi-MOF was produced using a water-stable MOF (MOF-303) which is based on one of the best phosphate-interacting metals (Al3+), that underwent controlled thermolysis in an air atmosphere at various temperatures between 430 and 470 °C. The acquired Quasi-MOF-303 underwent thorough characterization. The highest adsorption value of 488 mg·g−1 for phosphate was achieved at 298 K at an intact pH value of medium(which is roughly 25 times more than the intact structure). The experimental results demonstrated an exothermic spontaneous mechanism for the phosphate adsorption process that fit the pseudo-second-order and Langmuir isotherm models. The findings show that defect sites are crucial for improving phosphate uptake capability. This is further supported by several advanced characterizations, which resulted in the highest reported phosphate adsorption rate among all known adsorbent MOFs.

Synthesis of porous Mg(OH)2 nanowires for phosphate removal from water

Mg(OH)2 is an inorganic material with a wide range of applications in water purification, especially the adsorption of phosphates. In this study, porous Mg(OH)2 nanowires were synthesized by a facile hydrothermal conversion method to remove phosphate from aqueous solutions. The porous Mg(OH)2 nanowires can be readily obtained using magnesium hydroxide chloride hydrate (MHCH) whiskers as precursors in NaOH ethanol-water solution and exhibit good adsorption performance for phosphate. OH- ions diffused into the lattice to bind with Mg2+, while H2O and Cl- escaped from the lattice, resulting in the formation of porous Mg(OH)2 nanowires. The ethanol prevented the collapse of these pores. The adsorption process of phosphate on the porous Mg(OH)2 nanowires conforms to pseudo-second-order kinetics and is spontaneous, endothermic, and entropy-increasing. It was substantiated to be a complexation process of Mg2+ and HPO42- and H2PO4-. The maximum adsorption amount at 313 K was 162.15 mg g−1, minimally affected by coexisting ions and demonstrated good recycling performance. This work highlights the potential of porous Mg(OH)2 nanowires as an eco-friendly and low-cost adsorbent for phosphate removal and recovery.

Adsorption of phosphate in water by La/Al bimetallic-organic frameworks-chitosan composite with wide adaptable pH range

The limited metal sites of monometallic MOFs and the high influence of pH limit their adsorption capacity. To solve these problems, La/Al bimetallic MOFs/chitosan composite was prepared by hydrothermal synthesis and impregnation methods and then characterized by XRD, FTIR, SEM, BET and XPS techniques. The doping of La has no obvious effect on the structure of Al-MOFs, but chitosan has greatly changed the structure of La/Al bimetallic MOFs. The phosphate adsorption of the composite was affected by La/Al molar ratio, chitosan/bimetallic MOFs mass ratio, temperature, phosphate initial concentration, adsorbent dosage, pH, and coexisting ions. The optimum molar ratio of La/Al and mass ratio of chitosan/bimetallic MOFs are 0.5:1 and 5.0%, respectively. The addition of La and chitosan can provide additional adsorption active sites, inhibit metal leaching, and enhance the phosphate adsorption performance, stability, and acid-alkali resistance of the composite. Its maximum adsorption capacity was 264.48 mg·g−1. Its phosphate removal efficiency is above 90% at pH= 3.0–9.0. The actual phosphorus-containing wastewater with 7.064 mg·L−1 PO43- and initial pH 7.4 can be treated to meet Chinese first-class effluent quality standard. La, Al, amino groups, and hydroxyl groups play an important role in the adsorption process of phosphate. When pH < pHpzc (4.99), phosphate is adsorbed by electrostatic gravitation between it and protonated positively charged amino and hydroxyl groups on La and Al, while when pH > pHpzc, phosphate is removed by ligand exchange between it and hydroxyl groups on La and Al. A stable, low-cost, and efficient bimetallic MOFs-based phosphate adsorbent was designed and prepared in this paper, and the results can provide reference for researchers in environmental chemical engineering.

Performance and mechanism of phosphorus adsorption removal from wastewater by a Ce-Zr-Al composite adsorbent.

With the increasingly serious eutrophication of global water bodies and the strict discharge standards of tail water in wastewater treatment plants (WWTPs), there is an urgent technology need for efficient deep phosphorus removal from wastewater. A composite cerium-based adsorbent (Ce-Zr-Al) was synthesized by coprecipitation method for the adsorption of low concentration phosphorus in water. The performance of the Ce-Zr-Al composite adsorbent was explored, and the mechanism was also revealed through the analyses including SEM, BET, XPS, and FT-IR. The results showed that the composite adsorbent had excellent phosphorus removal performance. The phosphorus removal rate reached up to 92.6%, and the phosphorus concentration in effluent was less than 0.074 mg/L. The phosphate adsorption capacity of saturation was 73.51 mg/g. The adsorption process of phosphate was in accordance with pseudo-second-order kinetic model and Langmuir model. In addition, the composite adsorbent had a high zero potential point (pH PZC= 8) and a wide range of pH application. After the repeated desorption for 10 times in NaOH solution, the composite adsorbent still maintained good adsorbability (adsorption rate > 94%). The ligand exchange and electrostatic adsorption played the main role for the phosphorus removal from water using the composite adsorbent.

In-situ growth of MOF-based composites on nylon membrane for effective phosphate removal

A membrane adsorbent has been rationally designed to simplify the solid-liquid separation process and avoid adsorbent loss and leakage. The iron-based MOF was grown in situ on the surface of nylon membrane substrates by layer-by-layer method, and the as-synthesized MIL@nylon was post-treated with sodium borohydride to generate iron oxide nanoparticles within the MOF, named HFO@MIL@nylon. SEM, XRD, FT-IR and XPS characterization confirmed successful loading of MOF and the generation of nanoparticles in the MOF. The adsorption properties of HFO@MIL@nylon were tested. The results show that the adsorption process of phosphate accords with Langmuir and quasi-second-order kinetic model, with an adsorption capacity of 63.3 mg/g based on the mass of HFO@MIL. HFO@MIL@nylon could maintain high performance in a wide pH range. And the common interference ions SO42-, NO3-, Cl- only extended minus effect on the removal which means HFO@MIL@nylon has a good selectivity towards phosphorus. In addition, HFO@MIL@nylon membrane could work as a filter membrane, purifying 550 mL water of 200 μg-P/L with a water permeance of 1054 L/m2 h MPa.

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

A novel lanthanum manganese oxide (La0.96Mn0.96O3, 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 168.4mg/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 0.1mg/L. LMO is a potential candidate for low-concentration phosphate removal in real water environment.

The Study of Optimal Adsorption Conditions of Phosphate on Fe-Modified Biochar by Response Surface Methodology.

A batch of Fe-modified biochars MS (for soybean straw), MR (for rape straw), and MP (for peanut shell) were prepared by impregnating biochars pyrolyzed from three different raw biomass materials, i.e., peanut shell, soybean straw, and rape straw, with FeCl3 solution in different Fe/C impregnation ratios (0, 0.112, 0.224, 0.448, 0.560, 0.672, and 0.896) in this research. Their characteristics (pH, porosities, surface morphologies, crystal structures, and interfacial chemical behaviors) and phosphate adsorption capacities and mechanisms were evaluated. The optimization of their phosphate removal efficiency (Y%) was analyzed using the response surface method. Our results indicated that MR, MP, and MS showed their best phosphate adsorption capacity at Fe/C ratios of 0.672, 0.672, and 0.560, respectively. Rapid phosphate removal was observed within the first few minutes and the equilibrium was attained by 12 h in all treatment. The optimal conditions for phosphorus removal were pH = 7.0, initial phosphate concentration = 132.64 mg L-1, and ambient temperature = 25 °C, where the Y% values were 97.76, 90.23, and 86.23% of MS, MP, and MR, respectively. Among the three biochars, the maximum phosphate removal efficiency determined was 97.80%. The phosphate adsorption process of three modified biochars followed a pseudo-second-order adsorption kinetic model, indicating monolayer adsorption based on electrostatic adsorption or ion exchange. Thus, this study clarified the mechanism of phosphate adsorption by three Fe-modified biochar composites, which present as low-cost soil conditioners for rapid and sustainable phosphate removal.

Interception of phosphorus release from sediment by magnetite/lanthanum carbonate co modified activated attapulgite composite: Performance and mechanism

The release of phosphorus from sediment and the high concentration of phosphorus in the water environment make the water body continuously eutrophic, so it is very important to develop new phosphorus removal materials to reverse the eutrophication of river and lake. In this study, the effect and mechanism of magnetic lanthanum carbonate modified attapulgite (MT-LCMT) prepared by co-precipitation in fixed water and prime phosphorus were studied. The results showed that MT-LCMT had excellent magnetic hysteresis performance and its maximum model adsorption of phosphate could reach 51.69 mg/g. The phosphate adsorption process mainly followed the co-kinetics of intraparticle diffusion and membrane diffusion and conformed to the Redlich-Peterson model and Sips model. After five adsorption-desorption cycle experiments, MT-LCMT exhibited stable adsorption and regeneration properties, which may also be used for the removal of phosphate from actual water bodies. The experiment of exploring the factors affecting the adsorption of phosphate by MT-LCMT shows that the adsorption capacity of phosphate is the highest when the pH is between 3 and 8, and the existence of HCO3-, CO32- and humic acid reduce the adsorption capacity of phosphate. The binding mechanism of MT-LCMT to orthophosphate involves coordination exchange, precipitation and electrostatic attraction. MT-LCMT capping can significantly reduce the risk of sediment releasing mobile phosphorus (Mobile-P), bioavailable phosphorus (BAP), overlying water dissolve reactive phosphorus (DRP) and available phosphorus with medium diffusion gradient in thin film (DGT-P) to the overlying water, and the unstable phosphorus (NH4Cl-P and BD-P) of surface sediment are converted into stable phosphorus (HCl-P and NaOH85-P). The above results indicated that MT-LCMT had a high potential to be used as an active capping material for managing phosphorus loads inside surface water bodies and substrates.

Preparation of CaMgAl-calcined layered double hydroxides and application on the removal of phosphates.

A calcined CaMgAl-layered double hydroxide nanocomposite, CaMgAl-LDH (CCMA-0.83-600), was prepared by introducing Mg on the basis of CaAl-LDHs for the removal of phosphate from wastewater. The structure of the as-synthesized CCMA-0.83-600 was confirmed by XRD and SEM analyses. Parameters affecting the adsorption process of phosphate adsorbed by CCMA-0.83-600 were thoroughly explored, such as initial pH, adsorbent dosage and co-existing anions. The adsorption kinetic study suggested that the adsorption process accorded with the pseudo-second-order kinetic model and the adsorption rate was controlled by both the liquid film diffusion and intra-particle diffusion. The adsorption isotherm study indicated the adsorption process followed by the Langmuir isotherm model. Thermodynamic analysis suggested that the adsorption of phosphate was spontaneous and exothermic. The obtained results indicated that CCMA-0.83-600 is a suitable candidate for the removal of phosphate from wastewater.

Controllable Preparation of Superparamagnetic Fe3O4@La(OH)3 Inorganic Polymer for Rapid Adsorption and Separation of Phosphate.

Superparamagnetic Fe3O4 particles have been synthesized by solvothermal method, and a layer of dense silica sol polymer is coated on the surface prepared by sol-gel technique; then La(OH)3 covered the surface of silica sol polymer in an irregular shape by controlled in situ growth technology. These magnetic materials are characterized by TEM, FT-IR, XRD, SEM, EDS and VSM; the results show that La(OH)3 nanoparticles have successfully modified on Fe3O4 surface. The prepared Fe3O4@La(OH)3 inorganic polymer has been used as adsorbent to remove phosphate efficiently. The effects of solution pH, adsorbent dosage and co-existing ions on phosphate removal are investigated. Moreover, the adsorption kinetic equation and isothermal model are used to describe the adsorption performance of Fe3O4@La(OH)3. It was observed that Fe3O4@La(OH)3 exhibits a fast equilibrium time of 20 min, high phosphate removal rate (>95.7%), high sorption capacity of 63.72 mgP/g, excellent selectivity for phosphate in the presence of competing ions, under the conditions of phosphate concentration 30 mgP/L, pH = 7, adsorbent dose 0.6 g/L and room temperature. The phosphate adsorption process by Fe3O4@La(OH)3 is best described by the pseudo-second-order equation and Langmuir isotherm model. Furthermore, the real samples and reusability experiment indicate that Fe3O4@La(OH)3 could be regenerated after desorption, and 92.78% phosphate removing remained after five cycles. Therefore, La(OH)3 nanoparticles deposited on the surface of monodisperse Fe3O4 microspheres have been synthesized for the first time by a controlled in-situ growth method. Experiments have proved that Fe3O4@La(OH)3 particles with fast separability, large adsorption capacity and easy reusability can be used as a promising material in the treatment of phosphate wastewater or organic pollutants containing phosphoric acid functional group.