Phosphate adsorption on aluminum-impregnated mesoporous silicates: surface structure and behavior of adsorbents

Exploring the influence of aquatic phosphate on Fe floc dynamics in water treatment

The formation of flocs is crucial in the coagulation process of water treatment. However, the nature of ligand exchange on the surface of primary nanoparticles (PNPs) during floc formation requires further investigation to enhance our understanding of the coagulation mechanism. Phosphate (P) is a ubiquitous nutrient ion in aquatic surface water, in this study, the impact of P on floc growth under different pH conditions were investigated. The results revealed that floc growth patterns depended on both P dosage and pH. The mode of ligand exchange between P and in-situ formed ferric hydroxide within a pH range of 5 to 10 was further explored, and remarkable disparities in pH changes induced by P addition were observed. At lower pH levels, OH- release occurred relatively slowly, stabilizing with continued P addition. At neutral pH, OH- release was comparatively higher with P addition, while under alkaline conditions, both the quantity of OH- and its release rate decreased. It was deduced that Fe-OH21/2+ sites function as "active sites," while Fe-OH1/2- sites act as "inert sites" on the surface of PNPs formed during flocculation. These sites are crucial in the interconnections between flocs formed during coagulation and in floc growth. Analyses of Fe PNPs by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), with and without P addition, revealed that the introduction of P inhibits or interferes with the self-crystallization of Fe PNPs through chemical coordination reactions. The results offer deeper insights into the coagulation mechanism and the transformation of Fe flocs in raw waters containing P during water treatment practices.

Selective Adsorption of Sr(II) from Aqueous Solution by Na3FePO4CO3: Experimental and DFT Studies

The efficient segregation of radioactive nuclides from low-level radioactive liquid waste (LLRW) is paramount for nuclear emergency protocols and waste minimization. Here, we synthesized Na3FePO4CO3 (NFPC) via a one-pot hydrothermal method and applied it for the first time to the selective separation of Sr2+ from simulated LLRW. Static adsorption experimental results indicated that the distribution coefficient Kd remained above 5000 mL·g-1, even when the concentration of interfering ions was more than 40 times that of Sr2+. Furthermore, the removal efficiency of Sr2+ showed no significant change within the pH range of 4 to 9. The adsorption of Sr2+ fitted the pseudo-second-order kinetic model and the Langmuir isotherm model, with an equilibrium time of 36 min and a maximum adsorption capacity of 99.6 mg·g-1. Notably, the adsorption capacity was observed to increment marginally with an elevation in temperature. Characterization analyses and density functional theory (DFT) calculations elucidated the adsorption mechanism, demonstrating that Sr2+ initially engaged in an ion exchange reaction with Na+. Subsequently, Sr2+ coordinated with four oxygen atoms on the NFPC (100) facet, establishing a robust Sr-O bond via orbital hybridization.

Efficient phosphate removal by Mg-La binary layered double hydroxides: synthesis optimization, adsorption performance, and inner mechanism

Layered double hydroxides (LDH) hold great promise as phosphate adsorbents; however, the conventional binary LDH exhibits low adsorption rate and adsorption capacity. In this study, Mg and La were chosen as binary metals in the synthesis of Mg-La LDH to enhance phosphate efficient adsorption. Different molar ratios of Mg to La (2:1, 3:1, and 4:1) were investigated to further enhance P adsorption. The best performing Mg-La LDH, with Mg to La ratio is 4:1 (LDH-4), presented a larger adsorption capacity and faster adsorption rate than other Mg-La LDH. The maximum adsorption capacity (87.23 mg/g) and the rapid adsorption rate in the initial 25 min of LDH-4 (70 mg/(g·h)) were at least 1.6 times and 1.8 times higher than the others. The kinetics, isotherms, the effect of initial pH and co-existing anions, and the adsorption-desorption cycle experiment were studied. The batch experiment results proved that the chemisorption progress occurred on the single-layered LDH surface and the optimized LDH exhibited strong anti-interference capability. Furthermore, the structural characteristics and adsorption mechanism were further investigated by SEM, BET, FTIR, XRD, and XPS. The characterization results showed that the different metal ratios could lead to changes in the metal hydroxide layer and the main ions inside. At lower Mg/La ratios, distortion occurred in the hydroxide layer, resulting in lower crystallinity and lower performance. The characterization results also proved that the main mechanisms of phosphate adsorption are electrostatic adsorption, ion exchange, and inner-sphere complexation. The results emphasized that the Mg-La LDH was efficient in phosphate removal and could be successfully used for this purpose.

Iron-coated nutshell waste bioadsorbents: Synthesis, phosphate remediation, and subsequent fertilizer application

The increasing incidence of freshwater nutrient pollution worldwide has highlighted the need for improved phosphate capture technologies. Successful phosphate recovery from agricultural sources and commercial wastewater can help prevent freshwater algal bloom contamination, while also reducing the dependency on finite phosphate reserves. Biodegradable biosorbents have the potential to remove phosphate from water; however, their potential as slow-release fertilizers has not been tested. Novel biosorbents were developed by coating pistachio and walnut shells with iron oxides; batch and column experiments were conducted to investigate their adsorption capacities and performances. Surface characterization studies were also conducted to investigate changes in the surface area and morphology. The potential of using iron-coated shells loaded with phosphorus as slow-release fertilizers was also evaluated. Advanced characterization techniques (scanning electron microscopy, Brunauer-Emmett-Teller (BET) physisorption analysis, and x-ray diffraction) showed that hematite was successfully coated onto the surface, resulting in increased surface area and roughness. The iron-coated pistachio and walnut shell phosphate removal capacity was 12.63 mg g-1 and 9.25 mg g-1, respectively. The phosphate sorption data fitted well with the Freundlich isotherm model and pseudo-second-order kinetics. Inner sphere complex formation, coprecipitation, diffusion, and electrostatic attraction were the main uptake mechanisms. Results from sequential release experiments with simulated pore water suggested both fast and slow desorption components. The Mehlich-3 extraction revealed that more than 90% of the released phosphate was available for plant uptake. In addition, nutrient priming showed that corn seed shoot growth increased by more than 43% when pretreated with phosphate-loaded biosorbents, demonstrating that the released phosphate could be used for plant growth. This research provides a pathway for two important zero-waste, cyclical economic goals: (1) the beneficial use of agricultural waste, and (2) a low-cost technology that can recover phosphorus from waste streams while potentially adding an additional unconventional phosphate source to apatite mineral ores.

Comparative assessment of formation pathways and adsorption behavior reveals the role of NaOH of MgO-modified diatomite on phosphate recovery

The phosphate adsorption behavior on MgO-modified diatomite has been routinely investigated. Batch experiments tend to show that the addition of NaOH during preparation largely promoted adsorption performance, but comparative studies of MgO-modified diatomite with and without NaOH (MODH and MOD) based on morphology, composition, functional groups, isoelectric points and adsorption behavior have not been reported. We demonstrated that NaOH can etch the structure of MODH and promote the migration of phosphate to active sites, which allowed MODH to have a faster adsorption rate, superior environmental adaptability, adsorption selectivity and regeneration performance. The phosphate adsorption ability was enhanced from 96.73 (MOD) to 197.4 mg P/g (MODH) under optimum conditions. Furthermore, the partially hydrolyzed Si-OH group reacted with Mg-OH via a hydrolytic condensation reaction to form a new Si-O-Mg bond. Intraparticle diffusion, electrostatic attraction and surface complexation may be the main modes of phosphate adsorption by MOD, while the MODH surface mainly relied on the synergy of chemical precipitation and electrostatic attraction due to the abundant MgO adsorptive sites. Indeed, the present study provides a new understanding of the microscopic analysis of sample differences.

Effect of corn pre-puffing on the efficiency of MgO-engineered biochar for phosphorus recovery from livestock wastewater: mechanistic investigations and cost benefit analyses

To improve the phosphorus (P) recovery efficiency from livestock wastewater, a novel MgO doped mildewed corn biochar with thermal pre-puffing treatment (Mg-PBC) and without pre-puffing (Mg-BC) was synthesized and tested. The thermal-puffing pretreatment improved the effectiveness of metal soaking and MgO dispersion. P recovery time with Mg-PBC (7 h) was significantly shorter than that with Mg-BC (12 h). Moreover, Mg-PBC showed significantly higher P recovery capacity (241 mg g−1) than Mg-BC (96.6 mg g−1). P recovery capacity of the Mg-PBC fitted to the Thomas model was 90.7 mg g−1, which was 4 times higher than that of Mg-BC (22.9 mg g−1) under column test conditions. The mechanisms involved in P recovery included precipitation, surface complexation, and electrostatic interaction. After adsorption, both Mg-BC and Mg-PBC showed relatively low regeneration abilities. The P loaded Mg-BC (Mg-BC-P) and Mg-PBC (Mg-PBC-P), the later particularly, obviously increased the available P content and promoted plant growth. The release of P increased with time in the Mg-PBC-P treated soil, while it decreased with time in the P fertilizer treated soil. A cost–benefit analysis revealed that thermal-puffing pretreatment greatly increased the profit of MgO doped biochar from −0.66 to 5.90 US$ kg−1. These findings highlight that biomass pre-puffing is a feasible treatment to produce MgO modified biochar and to recover P from livestock wastewater, and that the Mg-PBC-P can be used as a slow-release P fertilizer.

Graphical Abstract

Adsorption Characteristics of Phosphate Based on Al-Doped Waste Ceramsite: Batch and Column Experiments

Phosphorus widely existing in rainfall and wastewater impacts the water environment. In this study, sludge, cement block, and coal fly ash were employed as ceramsite material to synthesize Al-doped waste ceramsite (Al-ceramsite) for removing phosphate (PO₄^3--P) from aqueous solutions. Batch static adsorption-desorption experiments were designed to investigate the effect of various parameters such as Al-ceramsite dosage, PO₄^3--P concentration, temperature, initial pH, coexisting ions, and desorbents on the removal of PO₄^3--P. Also, the fate of PO₄^3--P removal efficiency in actual rainwater was studied through dynamic adsorption column experiments using Al-ceramsite. Results showed that Al-ceramsite could remove PO₄^3--P efficiently under the optimum parameters as follows: Al-ceramsite dosage of 40 g/L, initial PO₄^3--P concentration of 10 mg/L, temperature of 25 °C, and pH of 5. Besides that, the Al-ceramsite could completely remove PO₄^3--P in actual rainwater, and the effluent PO₄^3--P concentration was lower than the environmental quality standards for surface water Class Ⅰ (0.02 mg/L). The adsorption characteristics of Al-ceramsite on PO₄^3--P by X-ray photoelectron spectroscopy (XPS) were further explained. As a result, ligand exchange and complexation were confirmed as the main PO₄^3--P removal mechanism of Al-ceramsite. Thus, Al-ceramsite was prepared from industrial waste and has shown excellent potential for phosphorus removal in practical applications.

Converting Chrysotile Nanotubes into Magnesium Oxide and Hydroxide Using Lanthanum Oxycarbonate Hybridization and Alkaline Treatment for Efficient Phosphate Adsorption

Magnesium oxide and hydroxide nanomaterials comprise a class of promising advanced functional metal nanomaterials whose use in environmental and material applications is increasing. Several strategies to synthesize these nanomaterials have been described but are unsustainable and uneconomic. This work reports on a processing strategy that turns natural magnesium-rich chrysotile into magnesium oxide and hydroxide nanoparticles via nanoparticle hybridization and an alkaline process while enabling La-based nanoparticles to coat the chrysotile nanotube surfaces. The adsorbent's resulting hybrid nanostructure had an outstanding capacity for phosphate uptake (135.2 mg P g^-1) and enhanced regeneration performance. Furthermore, the adsorbent featured wide applicability with respect to the coexistence of competitive anions and a broad range of pH conditions, and its high-performance phosphate removal from sewage effluent was also demonstrated. Spectroscopic and microscopic analyses revealed the scavenging ability of phosphate by the La-based and Mg-based nanoparticles and the multiple capture mechanisms involved, including surface complexation and ion exchange. This proposed approach expands chrysotile's potential use as a magnesium-rich nanomaterial and harbors great promise for the removal of pollutants in a variety of real-world settings.

Enhanced Nutrient Removal in A2N Effluent by Reclaimed Biochar Adsorption

The excessive nitrogen and phosphorus discharged into the water environment will cause water eutrophication and thus disrupt the water ecosystem and even exert biological toxicities. In this study, the absorption removal of nitrogen and phosphorus from the anaerobic tank in an anaerobic−anoxic/nitrifying system using four different kinds of biowaste-reclaimed biochars were investigated and compared. The effects of temperature and pH on nutrient adsorption removal were further investigated. The four kinds of biochar were successfully prepared and well characterized using a scanning electron microscope, fourier transform infrared spectroscopy, X-ray diffraction and Brunner−Emmet−Teller methods. Generally, there was no significant change in chemical oxygen demand (COD) and NH4+-N removal efficiencies when treated by the different biochars, while the activated sludge biochar (ASB) displayed the highest total phosphorus (TP) removal efficiency. The initial TP concentrations (<40 mg/L) displayed no remarkable effects on the TP adsorption removal, while the increase of temperature generally enhanced TP and NH4+-N adsorptions on the ASB. Besides, the increase of pH significantly promoted NH4+-N removal but depressed TP removal. Moreover, the adsorption process of TP by the ASB complies with the secondary kinetic model, suggesting the chemical precipitation and physical electrostatic interaction mechanisms of TP adsorption removal. However, the adsorption of NH4+-N conformed to the inner-particle diffusion model, indicating that the NH4+-N adsorption was mainly involved with pore diffusions in the particles.

Wastewater in India: An untapped and under-tapped resource for nutrient recovery towards attaining a sustainable circular economy

Wastewater (WW) contains nitrogen (N) and phosphorus (P), where N oxidizes to nitrate followed by denitrification to release N₂ and P is accumulated in sludge. Higher concentrations of N and P leads to eutrophication and algal blooming, thereby threatening the aquatic life systems. Such nutrients could be potentially recovered avoiding the fertilizer requirements. Distinct nutrient recovery systems have been demonstrated including chemical precipitation, ion-exchange, adsorption, bio-electrochemical systems, and biological assimilation at various scales of volumes. This study focusses on the nutrient recovery possibility from wastewater in India. The resource estimation analysis indicates that at 80% recovery, 1 million liters per day (MLD) of sewage can generate 17.3-kg of struvite using chemical precipitation. When compared with traditional fertilizers, nutrient recovery from sewage has the potential to avoid 0.38-Mt/a in imports. Replacing conventional fertilizer with struvite recovered from WW avoids 663.2 kg CO_2eq/ha in emissions (53%). Prevailing WW treatment looks at maintaining the discharging standards while recovering nutrients is an advanced option for a self-reliant and sustainable circular economy. However, more detailed assessments are necessary from techno-economic and environmental perspective in realizing these technologies at an industrial scale.

Enhanced phosphate removal with fine activated alumina synthesized from a sodium aluminate solution: performance and mechanism

Fine activated alumina (FAA) acting as an adsorbent for phosphate was synthesized from an industrial sodium aluminate solution based on phase evolution from Al(OH)₃ and NH₄Al(OH)₂CO₃. This material was obtained in the form of γ-Al₂O₃ with an open mesoporous structure and a specific surface area of 648.02 m² g⁻¹. The phosphate adsorption capacity of the FAA gradually increased with increases in phosphate concentration or contact time. The maximum adsorption capacity was 261.66 mg g⁻¹ when phosphate was present as H₂PO₄⁻ at a pH of 5.0. A removal efficiency of over 96% was achieved in a 50 mg L⁻¹ phosphate solution. The adsorption of phosphate anions could be explained using non-linear Langmuir or Freundlich isotherm models and a pseudo-second-order kinetic model. Tetra-coordinate AlO₄ sites acting as Lewis acids resulted in some chemisorption, while (O)_nAl(OH)₂⁺ (n = 4, 5, 6) Brønsted acid groups generated by the protonation of AlO₄ or AlO₆ sites in the FAA led to physisorption. Analyses of aluminum-oxygen coordination units using Fourier transform infrared and X-ray photoelectron spectroscopy demonstrated that physisorption was predominant. Minimal chemisorption was also verified by the significant desorption rate observed in dilute NaOH solutions and the high performance of the regenerated FAA. The high specific surface area, many open mesopores and numerous highly active tetra-coordinate AlO₄ sites on the FAA all synergistically contributed to its exceptional adsorption capacity.

A fine activated alumina with high specific surface area was prepared by phase evolution from sodium aluminate solution, Al(OH)₃ and NH₄Al(OH)₂CO₃. The maximum adsorption capacity was 261.66 mg g⁻¹ and the regenerated material exhibited high performance phosphate removal.

Coagulation removal of phosphorus from a southern China reservoir in different stages of algal blooms: Performance evaluation and AlP matching principle analysis

Due to excessive nutrient discharge, many reservoirs in southern China suffer from eutrophication and harmful algal blooms. Several methods for phosphorus (P) removal have been proposed, including coagulation, adsorption, and biological methods. Among these methods, coagulation is preferable because of its quick effect, simple operation, and low cost. To investigate the effect and mechanism of coagulation on dephosphorization in reservoir water, the performances of Al-based (AlCl₃ and polyaluminum chloride (PACl)) and Fe-based coagulants (FeCl₃ and FeSO₄) were evaluated in this work. For reservoir water with a total phosphorus (TP) concentration of approximately 0.080 mg/L, aluminum salts showed stable advantages in dephosphorization. AlCl3 reduced the TP level by over 90% when treating the water sample collected at the initial stage of algal blooms, and PACl reduced by over 80% during the blooming stage. To reveal the dephosphorization mechanism and AlP matching principle, synthesized water samples were prepared and treated with AlCl₃ and [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ (Al₁₃). While simulating the water quality characteristics of reservoir water, important influencing factors were considered. The factors include P content (dissolved phosphorus (DP) and particulate phosphorus (PP)), pH, and extracellular organic matter (EOM). The pH was set to 7.66 and 8.29, with PP proportion set to 20%, 50%, and 80%. Simulated water treatment results indicated that, except for the coagulants species, pH significantly affected the dephosphorization efficiency. Moreover, the effects of P speciation and EOM were confirmed. Based on the coagulation performance and coagulation product characterization, chemical precipitation and inner-sphere complexation were estimated to be the most predominant way that DP and PP match with Al and were efficiently removed by Al-based coagulants.

Confined La2O3 particles in mesoporous carbon material for enhanced phosphate adsorption

Novel phosphate adsorbents with confined La2O3 inside mesoporous carbon were fabricated by the solid-state grinding method using pristine mesoporous carbon material CMK-3 (PCMK-3) and oxidized CMK-3 (OCMK-3) as the matrixes (denoted as La2O3@PCMK-3 and La2O3@OCMK-3). Compared with pure La2O3, La2O3@PCMK-3 and La2O3@OCMK-3 exhibited higher normalized phosphate adsorption capacity, indicative of efficient loading of La2O3 inside the mesopores of the carbon materials. Furthermore, La2O3 loading led to substantially enhanced phosphate adsorption. The adsorption capacities of La2O3@OCMK-3 samples were higher than those of La2O3@PCMK-3 samples, possibly owing to the oxygen-containing groups forming in OCMK-3 during HNO3 oxidation, which enhanced the dispersion of La2O3 in the mesopores of OCMK-3. The adsorption capacities of La2O3@PCMK-3 and La2O3@OCMK-3 increased with the La2O3 loading amount. Phosphate adsorption onto La2O3(14.7)@PCMK-3 followed the pseudo-second-order kinetics with respect to correlation coefficient values (larger than 0.99). As pH increased from 3.4 to 12.0, the phosphate adsorption amounts of La2O3(14.7)@PCMK-3 and La2O3(15.7)@OCMK-3 decreased from 37.64 mg g-1 and 37.08 mg g-1 to 21.92 mg g-1 and 14.18 mg g-1, respectively. Additionally, La2O3@PCMK-3 showed higher adsorption selectivity towards phosphate than coexisting Cl-,NO 3 - andSO 4 2 - . The adsorbent La2O3(14.7)@PCMK-3 remained stable after five regeneration cycles.

MOFs-derived conductive structure for high-performance removal/release of phosphate as electrode material

Porous metal-organic frameworks (MOFs) have drawn increasing attention as promising phosphate adsorbents. Yet the potential agglomeration of MOFs particles and the difficult collection process largely thwarted their application. Meanwhile, adsorbents regeneration might destroy MOFs structures due to the use of strong alkaline solution. In this work, we reported a strategy for designing and fabricating an electrode to remove phosphate based on MIL-101 derived metal/carbon via a two-step carbonization step, which not only introduced C doping but also created a stable structure. With the assistance of electric field, the migration and capture of phosphate anions were greatly enhanced. Under 1 V condition, the material exhibited a high maximum removal capacity of 97.73 mg P/g. Adsorption kinetics and parameters for phosphate at different conditions were analyzed. Langmuir and Freundlich isotherms were employed to validate the adsorption data. More importantly, the regeneration of electrode was achieved in a more facile and efficient way than micro/ nanoparticles adsorbents by simple voltage control. Such an intriguing approach may provide a new platform to further expand the use of MOFs for adsorption process.

Low-cost chitosan-calcite adsorbent development for potential phosphate removal and recovery from wastewater effluent

Phosphorous (P) recovery from wastewater will become increasingly vital in the future as terrestrial rock phosphate deposits are expended. Effective management of P as a critical resource will require new techniques to recover P from wastewater, ideally in a form that can be used in agriculture as fertiliser. In this study, batch and fixed-bed column conditions were tested using a novel KOH deacetylated calcite-chitosan based adsorbent (CCM) for P removal from aqueous solutions and wastewater effluents. The unique characteristics of this adsorbent as a phosphate adsorbent were the result of rich surface functionality (amine and sulphur functional groups of the chitosan and proteins) and the CaCO₃ content (providing donor ligands; and additionally beneficial if the material were used as fertiliser, buffering soil acidification caused by nitrogen application). The maximum P adsorption capacity was determined to be 21.36 mgP/g (at 22 °C) and the endodermic process reached equilibrium after 120 min. The experimental data was best described using a Langmuir isotherm and a pseudo-second order kinetic model. The diffusion kinetic analysis highlighted the importance of both film and intraparticle mass-transport. Material characterisation suggested that the adsorption process involved interactions between P and functional groups (mostly -NH₃⁺) due to electrostatic interaction on the chitosan chain or involved ligand exchange with CO₃^2-. Analysis of materials using X-Ray Powder Diffraction (XRPD) and Thermogravimetric Analysis (TGA) indicated a microprecipitation-type mechanism may occur through the formation of hydroxylapatite (Ca₅(PO₄)₃(OH)). Desorption studies demonstrated that the P-laden CCM (derived from crab carapace) had the potential to be reused in soil amendment as a slow-release P fertiliser. The effects of different operating parameters were explored in a fixed-bed column, and the experimental data fitted well to the Clark model (R² = 0.99). The CCM also showed excellent P adsorption potential from secondary and final wastewater effluent in dynamic conditions, even at low P concentrations. Finally, a scale-up approach with cost analysis was used to evaluate the price and parameters needed for a potential large-scale P recovery system using this adsorbent.

Removal of phosphate from wastewater by modified bentonite entrapped in Ca-alginate beads

Methods of removing phosphate from wastewater with a low phosphate concentration are of great environmental significance. In this study, immobilized beads were prepared by entrapping modified bentonite powder in calcium-alginate (Al-NaBT-CA), and the potential of the beads for phosphate removal from wastewater was investigated. The effects of pH (1-10) and initial phosphate concentration (0.5-50 mg/L) were also examined in batch experiments with Al-NaBT-CA beads. The optimum pH value for phosphate removal by Al-NaBT-CA beads was pH 3. In addition, a high initial phosphate concentration promoted phosphate adsorption. Adsorption kinetics showed that the adsorption of phosphate using beads followed a pseudo-second-order kinetic model (R² = 0.98-0.99). The adsorption isotherm data was well fitted by the Sips adsorption model. The maximum phosphate adsorption capacity of the Al-NaBT-CA beads was 15.77 mg/g, which was slightly less than that of the modified powder. The specific surface area of the Al-NaBT-CA beads was 17.01 m²/g, and their average pore size was 13.41 nm. Scanning electron microscopy suggested that the high inner porosity and rough outer surface of the beads facilitated phosphate transfer.

Phosphorus removal from wastewater by waste concrete: influence of P concentration and temperature on the product

This study investigated the feature of phosphorus uptake by low-cost waste concrete. Adsorption isotherms, metal dissolution, influence of P concentration and temperature, as well as adsorbent regeneration were investigated. Chemical extraction, SEM, XRD, FTIR, and XPS were employed to determine the products of P sequestration. Results demonstrated that phosphate adsorption fitted the Langmuir isotherm model well, with estimated maximum phosphate adsorption capacity of 80.5 mg/g (10 °C). Of adsorbed phosphate, 72.1% could be desorbed when 0.1 M citrate buffer was used as eluant, and waste concrete could be recovered and reused for 4 times by the combination of eluting and roasting. Mechanisms including Ca/alkali dissolution, surface adsorption, and chemical precipitation are involved in the sequestration of phosphorus from wastewater by waste concrete. Weakly adsorptive phosphorus and Ca-P precipitate were the main products. P concentration was the major factor that affected P removal capacity and the product types, while temperature had certain effect at low P concentration. The dominant product was weakly adsorptive phosphorus for low P concentration at low temperature, which was substituted by Ca-P precipitate as temperature or P concentration increased. The increase of P concentration assisted both the increase of P removal potential and the formation of Ca-P precipitate to crystal DCPD.

Ruthenium on phosphorous-modified alumina as an effective and stable catalyst for catalytic transfer hydrogenation of furfural

Supported ruthenium was used in the liquid phase catalytic transfer hydrogenation of furfural. To improve the stability of Ru against leaching, phosphorous was introduced on a Ru/Al₂O₃ based catalyst upon impregnation with ammonium hypophosphite followed by either reduction or calcination to study the effect of phosphorous on the physico-chemical properties of the active phase. Characterization using X-ray diffraction, solid state ³¹P nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, temperature programmed reduction with H₂, infrared spectroscopy of pyridine adsorption from the liquid phase and transmission electron microscopy indicated that phosphorous induces a high dispersion of Ru, promotes Ru reducibility and is responsible for the formation of acid species of Brønsted character. As a result, the phosphorous-based catalyst obtained after reduction was more active for catalytic transfer hydrogenation of furfural and more stable against Ru leaching under these conditions than a benchmark Ru catalyst supported on activated carbon.

Phosphorous induces structural changes in Ru/Al₂O₃ that make it more active and more stable for liquid phase hydrogenation of furfural.

Sterile phosphate as a novel calcic adsorbent for phosphorus removal from wastewater

Sterile phosphate (SP) was investigated for phosphorus removal from wastewater using batch adsorption experiments. The novel adsorbent is a mining by-product obtained from the phosphate mining plants having a strong affinity with phosphorus ions present in wastewater. The results of the batch adsorption experiments indicated that 30 min of contact time between the adsorbent and wastewater was sufficient for attaining equilibrium. The phosphorus removal from wastewater increased with increasing initial phosphorus concentration, adsorbent dose and temperature, while it decreased with increasing initial pH values. The maximum phosphorus removal efficiency was noted to be 94.4%. It was achieved in slightly acidic conditions (pH = 4), with an adsorbent dose and initial phosphorus concentration of 3 g L^-1 and 20 mg L^-1, respectively, and at room temperature. Kinetic analysis showed that phosphorus adsorption onto sterile phosphate was best fitted with the pseudo-second order kinetic model. The adsorption equilibrium data fitted well to the Langmuir model equation, indicating monolayer coverage of the adsorbent. The adsorption capacity calculated from the Langmuir model equation was found to be 7.962 mg g^-1. Comparing with some industrial products and natural mineral adsorbents, sterile phosphate was found to be the most efficient adsorbent for phosphorus removal from wastewater.

Adsorption and recovery of phosphate from water by amine fiber, effects of co-existing ions and column filtration

A weak-base adsorption fiber, acrylic amine fiber (AAF), was prepared for removal and recovery of phosphate from water. The adsorption properties of the AAF for phosphate and effects of co-existing ions were investigated using batch and column filtration experiments, scanning electron microscope, and Fourier transform infrared techniques. Experimental results showed that AAF had a high phosphate adsorption capacity of 119 mg/g at pH 7.0. The effects of calcium, sulfate, carbonate, nitrate, and fluoride showed that sulfate and calcium inhibited phosphate adsorption. However, AAF showed higher binding affinity toward phosphate than sulfate. Column filtration results showed that AAF could filter 1420 bed volumes of tap water containing 1.0 mg-P/L of phosphate. The saturated AAF could be regenerated using 0.5 mol/L hydrochloric acid solution and reused. After desorption, phosphate was recovered through precipitation of hydroxyapatite (Ca₅(PO₄)₃OH). The easy of regeneration, good adsorption performance, and the fiber morphology of AAF make it an attractive alternative for phosphate recovery from multiple water sources.

Technological Challenges of Phosphorus Removal in High-Phosphorus Ores: Sustainability Implications and Possibilities for Greener Ore Processing

With the present rates of iron ore consumption, currently unusable, high-phosphorus iron ore deposits are likely to be the iron ores of the future as higher-grade iron ore reserves are depleted. Consequently, the design and timely development of environmentally-benign processes for the simultaneous beneficiation of high-phosphorus iron ores and phosphorus recovery, currently a technological challenge, might soon become a sustainability challenge. To stimulate interest in this area, phosphorus adsorption and association in iron oxides/hydroxyoxides, and current efforts at its removal, have been reviewed. The important properties of the most relevant crystalline phosphate phases in iron ores are highlighted, and insights provided on plausible routes for the development of sustainable phosphorus recovery solutions from high-phosphorus iron ores. Leveraging literature information from geochemical investigations into phosphorus distribution, speciation, and mobility in various natural systems, key knowledge gaps that are vital for the development of sustainable phosphorus removal/recovery strategies and important factors (white spaces) not yet adequately taken into consideration in current phosphorus removal/recovery solutions are highlighted, and the need for their integration in the development of future phosphorus removal/recovery solutions, as well as their plausible impacts on phosphorus removal/recovery, are put into perspective.

Highly sensitive and selective fluorescent detection of phosphate in water environment by a functionalized coordination polymer

Phosphate, due to its somatotrophic effect on organisms, can cause severe eutrophication with excessive content in water. Conventional methods for phosphate detection, which are based on complicated instruments, are time-consuming. Here we report a luminescent lanthanide functionalized coordination polymer (Eu@BUC-14) by doping Eu³⁺ cations to BUC-14 nanocrystals. This Eu³⁺ functionalized hybrid (Eu@BUC-14) presents excellent luminescence features of Eu³⁺ ion that originated from efficient energy transfer from the ligand. The detection results show that Eu@BUC-14 is a highly efficient luminescent probe for phosphate detection in aqueous solutions, exhibiting high sensitivity with a low detection limit of 0.88 μM and a short response time of within 5 min. More significantly, Eu@BUC-14 has a high specificity for PO₄^3- over fifteen other pollutant anions and eleven metal cations. The sensing mechanism is proposed via an in-depth analysis of the interaction between PO₄^3- and Eu³⁺. Simultaneously, it displays high adsorption ability toward PO₄^3- (57.9 mg P/g), making it an outstanding multifunctional material. And the adsorption process plays an important role in preconcentration of PO₄^3- which can lead to a quick fluorescent response with high quenching efficiency. The practicality of Eu@BUC-14 was also validated by sensing PO₄^3- in real environment water samples.

Chromium and fluoride sorption/desorption on un-amended and waste-amended forest and vineyard soils and pyritic material

Using batch-type experiments, chromium (Cr(VI)) and fluoride (F^-) sorption/desorption were studied in forest and vineyard soil samples, pyritic material, pine bark, oak ash, hemp waste and mussel shell, as well as on samples of forest and vineyard soil, and of pyritic material, individually treated with 48 t ha^-1 of pine bark, oak ash, and mussel shell. Pine bark showed the highest Cr(VI) sorption (always > 97% of the concentration added) and low desorption (<1.5%). Pyritic material sorbed between 55 and 98%, and desorbed between 0.6 and 9%. Forest and vineyard soils, oak ash, mussel shell and hemp waste showed Cr(VI) sorption always < 32%, and desorption between 22 and 100%. Pine bark also showed the highest F^- retention (sorption between 62 and 73%, desorption between 10 and 15%), followed by oak ash (sorption 60-69%, desorption 11-14%), forest soil (sorption 60-73%, desorption 19-36%), and pyritic material (sorption 60-67%, desorption 13-15%), whereas in vineyard sorption was 49-64%, and desorption 24-27%, and in hemp waste sorption was 26-36%, and desorption 41-59%. Sorption data showed better fitting to the Freundlich than to the Langmuir model, especially in the case of Cr(VI), indicating that multilayer sorption dominated. The addition of by-products to the forest and vineyard soils, and to the pyritic material, caused an overall increase in F^- sorption, and decreased desorption. Furthermore, the pine bark amendment resulted in increases in Cr(VI) retention by both soils and the pyritic material. These results could be useful to favor the recycling of the by-products studied, aiding in the management of soils and degraded areas affected by Cr(VI) and F^- pollution, and in the removal of both anions from polluted waters.

Amphiphilic Block Copolymers Directed Interface Coassembly to Construct Multifunctional Microspheres with Magnetic Core and Monolayer Mesoporous Aluminosilicate Shell

Core-shell magnetic porous microspheres have wide applications in drug delivery, catalysis and bioseparation, and so on. However, it is great challenge to controllably synthesize magnetic porous microspheres with uniform well-aligned accessible large mesopores (>10 nm) which are highly desired for applications involving immobilization or adsorption of large guest molecules or nanoobjects. In this study, a facile and general amphiphilic block copolymer directed interfacial coassembly strategy is developed to synthesize core-shell magnetic mesoporous microspheres with a monolayer of mesoporous shell of different composition (FDUcs-17D), such as core-shell magnetic mesoporous aluminosilicate (CS-MMAS), silica (CS-MMS), and zirconia-silica (CS-MMZS), open and large pores by employing polystyrene-block-poly (4-vinylpyridine) (PS-b-P4VP) as an interface structure directing agent and aluminum acetylacetonate (Al(acac)₃ ), zirconium acetylacetonate, and tetraethyl orthosilicate as shell precursors. The obtained CS-MMAS microspheres possess magnetic core, perpendicular mesopores (20-32 nm) in the shell, high surface area (244.7 m² g^-1 ), and abundant acid sites (0.44 mmol g^-1 ), and as a result, they exhibit superior performance in removal of organophosphorus pesticides (fenthion) with a fast adsorption dynamics and high adsorption capacity. CS-MMAS microspheres loaded with Au nanoparticles (≈3.5 nm) behavior as a highly active heterogeneous nanocatalyst for N-alkylation reaction for producing N-phenylbenzylamine with a selectivity and yields of over 90% and good magnetic recyclability.

Phosphate removal from aqueous solution using iron oxides: Adsorption, desorption and regeneration characteristics

Dynamics of phosphate (PO₄^3-) adsorption, desorption and regeneration characteristics of three lab-synthesized iron oxides, ferrihydrite (F), goethite (G), and magnetite (M) were evaluated in this study. Batch experiments were conducted to evaluate the impact of several adsorption parameters including adsorbent dosage, reaction time, temperature, pH, and ionic strength. The results showed that PO₄^3- adsorption increased with reaction time and temperature while it decreased with an increase in solution pH. Adsorption isotherm data exhibited good agreement with the Freundlich and Langmuir model with maximum monolayer adsorption capacities of 66.6 mg·g^-1 (F), 57.8 mg·g^-1 (M), and 50.5 mg·g^-1 (G). A thermodynamics evaluation produced ΔG < 0, ΔH > 0, and ΔS > 0, demonstrating that PO₄^3- adsorption onto tested minerals is endothermic, spontaneous, and disordered. The PO₄^3- removal mostly occurred via electrostatic attraction between the sorbate and sorbent surfaces. Moreover, the PO₄^3- sorption was reversible and could be desorbed at varying rates in both neutral and alkaline environments. The good desorption capacity has practical benefits for potential regeneration and re-use of the saturated particles in wastewater treatment systems.

Effects of Changing pH, Incubation Time, and As(V) Competition, on F- Retention on Soils, Natural Adsorbents, By-Products, and Waste Materials

The purpose of this work was to elucidate the repercussion of changing pH, incubation time and As(V) competition on fluoride (F⁻) sorption on forest and vineyard soil samples, pyritic, and granitic materials, as well as on the by-products pine sawdust, oak wood ash, mussel shell ash, fine and coarse mussel shell, and slate processing waste fines. To reach this end, the methodological approach was based on batch-type experiments. The results indicate that, for most materials, F⁻ sorption was very high at the start, but was clearly diminished when the pH value increased. However, oak wood ash and shell ash showed high F⁻ sorption even at alkaline pH, and pine sawdust showed low F⁻ sorption for any pH value. Specifically, F⁻ sorption was close to 100% for both ashes at pH < 6, and around 70% at pH 10, while for forest soil it was close to 90% at pH < 2, and around 60% at pH values near 8. Regarding the effect of incubation time on F⁻ sorption, it was very low for both soils, pyritic material, granitic material, and both kinds of ashes, as all of them showed very rapid F⁻ sorption from the start, with differences being lesser than 10% between sorption at 30 min and 1 month of incubation. However, sawdust and slate fines sorbed 20% of added F⁻ in 30 min, remaining constant up to 12 h, and doubling after 30 days. And finally, mussel shell sorbed 20% at 30 min, increasing to close to 60% when incubation time was 30 days. This means that some of the materials showed a first sorption phase characterized by rapid F⁻ sorption, and a slower sorption in a second phase. As regards the effect of the presence of As(V) on F⁻ sorption, it was almost negligible, indicating the absence of competition for sorption sites. In view of that all, these results could aid to appropriately manage soils and by-products when focusing on F⁻ removal, in circumstances where pH value changes, contact time vary from hours to days, and potential competition between F⁻ and As(V) could take place.

Engineered/designer biochar for the removal of phosphate in water and wastewater

During the past decade, biochar has attracted immense scientific interest for agricultural and environmental applications. A broad range of biochars with advantageous properties (e.g., high surface area, flexible architecture, and high porosity) has been developed for pollution abatement. Nevertheless, biochar suffers from certain drawbacks (e.g., limited sorption capacity for anions and poor mechanical properties) that limit their practical applicability. This review focuses on recent advancements in biochar technology, especially with respect to its technical aspects, the variables associated with removing phosphates from water, and the challenges for such abatement. The attention paid to the specific remediation of phosphate from water using biochar is limited (n=1114 - Scopus) compared to the application of biochar to other common water pollutants (n=3998 - Scopus). The subject warrants immediate rigorous research because of the undesirable effects of excess phosphate in water bodies. This review will thus facilitate the construction of a roadmap for further developments and the expansion of this challenging area of research.

Adsorptive removal of phosphate from water using mesoporous materials: A review

Mesoporous materials have significant potential for use as adsorbents for removal of phosphate from water. The chemical and structural properties of materials greatly affect their capacity and rate in the phosphate adsorption process. This paper reviews recent activities in the development of mesoporous materials as phosphate adsorbents. In particular, it mainly focuses on the synthesis, properties and phosphate removal efficiency of various materials with mesoporosity, including metal-coordinated amino-functionalized silicas, ammonium-functionalized silicas, metal-doped mesoporous silicas, metal oxides, metal sulfate and carbon.

Al-intercalated acid activated bentonite beads for the removal of aqueous phosphate

The separation of fine spent sorbents from treated water after remediation is a major difficulty associated with phosphate wastewater treatment technology. In this study, a novel aluminium-pillared acid activated bentonite powder (Al-ABn) and alginate immobilized aluminium-pillared acid activated bentonite beads (Al-ABn-AB) were synthesized and used for the removal of aqueous phosphate. The phosphate removal behaviour of adsorbents were evaluated by batch experiments as a function of various parameters such as pH, initial concentration, contact time, temperature, adsorbent dose and presence of coexisting ions. The sorption isotherm studies by Langmuir model showed 12.87 and 11.11 mgP/g maximum phosphate uptake capacity for Al-ABn and Al-ABn-AB, respectively. The kinetic studies confirm that the adsorption of phosphate by Al-ABn and Al-ABn-AB follows a pseudo-second-order model. The feasibility of Al-ABn-AB was also assessed in continuous mode in fixed bed column and the loading capacity obtained was 4.55mg/g. The adsorption capacity of Al-ABn-AB beads remained at relatively high even after four regeneration cycles. Furthermore, the applicability of the synthesized adsorbents towards real municipal wastewater confirmed that novel synthesized Al-ABn and Al-ABn-AB are the promising adsorbents for the removal of phosphate from contaminated water.