Emerging lanthanum (III)-containing materials for phosphate removal from water: A review towards future developments

Environmental impacts of selected metal cations for phosphorus capture in natural waters: A synthesis

Cultural eutrophication from excessive human-related nutrient (phosphorus, P, and nitrogen, N) inputs is a major concern for water quality. Because P historically was regarded as the critical nutrient in controlling noxious algal/plant growth, P became the focus of "capturing" techniques, with emphasis on removal performance rather than environmental impacts. Here, we synthesize a literature review of known environmental effects linked to use of metal-cation-based P-capturing materials under eutrophic conditions in freshwaters. P-capturing materials with functional cations based on aluminum (Al), calcium (Ca), iron (Fe), lanthanum (La), and magnesium (Mg) were reviewed in terms of their ecotoxicity, persistence, and bioaccumulation-standard criteria used to evaluate environmental risks of chemical substances. We found very few published studies on environmental impacts of metal-cation-based P-capturing materials under eutrophic conditions. Available reports indicated that environmental effects vary depending on the selected material, dose, target organism(s), and experimental conditions. The Al-based materials had the potential to negatively impact various biota; several Fe-based materials caused various levels of toxicity in a limited group of aquatic organisms; La-based materials can bioaccumulate and some were linked to various harmful effects on biota; and Mg-based materials also adversely affected various organisms. The limited number of published studies underscores the need for further research to characterize the environmental impacts of these materials. Results can be used to guide future work and can assist resource managers in sustainable management strategies. Among various research needs, future assessments should assess the impacts of chronic exposures on sensitive species under realistic field conditions in eutrophic waters.

Mechanistic study of highly effective phosphate removal from aqueous solutions over a new lanthanum carbonate fabricated carbon nanotube film

The effective purification of phosphate-containing wastewater is considered as increasingly important. In this study, a highly effective LC-CNT film was developed for efficient phosphate removal. Kinetic results showed that the adsorbent exhibited an improved mass transfer efficiency and a fast adsorption rate during adsorption (reaching 80% and 100% equilibrium adsorption capacity within 175 and 270 min, respectively). Kinetic model analysis suggested that the adsorption was a combined chemical physical process. Isotherm study revealed that the LC-CNT film showed a superior adsorption capacity (178.6 mg/g, estimated from the Langmuir model) with multiple adsorption mechanisms. pH study suggested that surface complexation and ligand exchange played important roles during adsorption, and the adsorbent worked well within the pH range of 3-7 with little La leakage. The ionic strength and competing anions showed little influence on the adsorbent effectiveness except for the carbonate and sulfate ions. The characterization and mechanism study revealed that the phosphate adsorption of the LC-CNT film was controlled by inner-sphere complexation, outer-sphere complexation and surface precipitation. The LC-CNT film also showed excellent regenerability and stability in cycling runs, further demonstrating its potential in industrial applications.

Sustainable adsorbent frameworks based on bio-resourced materials and biodegradable polymers in selective phosphate removal for waste-water remediation

Phosphorus to an optimum extent is an essential nutrient for all living organisms and its scarcity may cause food security, and environmental preservation issues vis-à-vis agroeconomic hurdles. Undesirably excess phosphorus intensifies the eutrophication problem in non-marine water bodies and disrupts the natural nutrient balance of the ecosystem. To overcome such dichotomy, biodegradable polymer-based adsorbents have emerged as a cost-effective and implementable approach in striking a "desired optimum-undesired excess" balance pertaining to phosphate in a sustainable manner. So far, the reports on adopting such adsorbent-approach for wastewater remediation remained largely scattered, unstructured, and poorly correlated. In this background, the contextual review comprehensively discusses the current state-of-the-art in utilizing biodegradable polymeric frameworks as an adsorbent system for phosphate removal and its efficient recovery from the aquatic ecosystem, while highlighting their characteristics-specific functional efficiency vis-à-vis easiness of synthetic and commercial viability. The overview further delves into the sources and environmental ramifications of excessive phosphorus in water bodies and associated mechanistic pathways of phosphorus removal via adsorption, precipitation, and membrane filtration enabled by biodegradable (natural and synthetic) polymeric substrates. Finally, functionality optimization, degradability tuning, and adsorption selectivity of biodegradable polymers are highlighted, while aiming to strike a balance in "removal-recovery-reuse" dynamics of phosphate. Thus, the current review not only paves the way for future exploration of biodegradable polymers in sustainable cost-effective adsorbents for phosphorus removal but also can serve as a guide for researchers dealing with this critical issue.

Roles of pH and phosphate in rare earth element biosorption with living acidophilic microalgae

The increasing demand for rare earth elements (REEs) has spurred interest in the development of recovery methods from aqueous waste streams. Acidophilic microalgae have gained attention for REE biosorption as they can withstand high concentrations of transition metals and do not require added organic carbon to grow, potentially allowing simultaneous sorption and self-replication of the sorbent. Here, we assessed the potential of Galdieria sulphuraria for REE biosorption under acidic, nutrient-replete conditions from solutions containing ≤ 15 ppm REEs. Sorption at pH 1.5-2.5 (the growth optimum of G. sulphuraria) was poor but improved up to 24-fold at pH 5.0 in phosphate-free conditions. Metabolic activity had a negative impact on REE sorption, additionally challenging the feasibility of REE biosorption under ideal growth conditions for acidophiles. We further examined the possibility of REE biosorption in the presence of phosphate for biomass growth at elevated pH (pH ≥ 2.5) by assessing aqueous La concentrations in various culture media. Three days after adding La into the media, dissolved La concentrations were up to three orders of magnitude higher than solubility predictions due to supersaturation, though LaPO4 precipitation occurred under all conditions when seed was added. We concluded that biosorption should occur separately from biomass growth to avoid REE phosphate precipitation. Furthermore, we demonstrated the importance of proper control experiments in biosorption studies to assess potential interactions between REEs and matrix ions such as phosphates. KEY POINTS: • REE biosorption with G. sulphuraria increases significantly when raising pH to 5 • Phosphate for biosorbent growth has to be supplied separately from biosorption • Biosorption studies have to assess potential matrix effects on REE behavior.

Vertical porous aerogel based on polypyrrole and bimetallic modified β-cyclodextrin polymer-chitosan for efficient solar evaporation

Solar-driven interfacial evaporation (SDIE) stands out as a prospective technology for freshwater production, playing a significant role in mitigating global water scarcity. Herein, a cyclodextrin polymer/chitosan composite aerogel (PPy-La/Al@CDP-CS) with vertically aligned channels was prepared as a solar evaporator for efficient solar steam generation. The vertically aligned pore structure, achieved through directional freezing assisted by liquid nitrogen, not only improves water transport during evaporation but also enhances light absorption through multiple reflections of sunlight within the pores. The polypyrrole particles sprayed on the surface of the aerogel acted as a light-absorbing layer, resulting in an impressive absorbance of 98.15 % under wetting conditions. The aerogel has an evaporation rate of 1.85 kg m-2 h-1 under 1 kW m-2 irradiation. Notably, the vertical pore structure of the aerogel allows it to exhibit excellent evaporation performance and salt resistance even in highly concentrated salt solutions. Furthermore, this aerogel is an excellent solar-driven interfacial evaporator for purifying seawater and fluoride-containing wastewater. This photothermal aerogel has the advantages of excellent performance, low cost, and environmental friendliness, and thus this work provides a new approach to the design and fabrication of solar photothermal materials for water treatment.

Characteristics and mechanism of phosphate removal by lanthanum modified bentonite in the presence of dissolved organic matter

Lanthanum modified bentonite (LMB) is a widely used adsorbent for removing inorganic phosphorus from polluted water to prevent eutrophication. However, its efficiency can be affected by various environmental factors, including dissolved organic matter (DOM), which is still unclear. In this study, we systematically explored the influence of model DOMs, including HA, bovine serum albumin (BSA), and sodium alginate (SA), on phosphate adsorption by LMB, as well as to elucidate the underlying adsorption mechanisms. Our results showed that only HA had a significant effect on phosphate adsorption by LMB, causing inhibition. When three DOMs were mixed with phosphate in different proportions and DOM was mainly HA, the performance of phosphate adsorption on LMB became worse, while BSA can slightly offset this impact. The kinetics of HA and phosphate adsorption on LMB followed the pseudo-second-order kinetic model, and isotherms fitted the Langmuir model, with a maximum adsorption capacity of 5.7 mg g-1 for P and 12 mg g-1 for HA. However, when HA and phosphate were mixed based on their Qm, a C/P molar ratio of 5.35, LMB preferentially adsorbed phosphate. HA invasion was also disadvantageous for phosphate removal by LMB, in which P adsorption was less efficient at low-concentrations. However, during co-adsorption the adsorption capacity for HA was higher. With a secondary addition of higher levels of P, both pollutants were adsorbed more effectively. In the natural water experiment, phosphate concentration decreased with increasing shaking time, while the UV254 value showed a downward trend, indicating that LMB also adsorbed HA. Characterization results showed that La and phosphate formed LaPO4 precipitation, forming La-O-P inner-sphere complexes as the main mechanism of phosphate removal by LMB. La and HA formed La-HA complexes, with O-CO bonds from HA competing for lanthanum with phosphate. Despite HA obstructing pores from adsorbent, LMB still maintained a good binding ability with phosphate. It may form La-P-HA ternary complexes during adsorption to keep HA adsorption amount.

Solar distillation of human urine to recover non-potable water and metal phosphate mineral

Human urine is a readily available nutrient source that can complement commercial fertilizer production, which relies on finite mineral resources and global supply chains. This study evaluated the effectiveness of a simplified solar distillation process for urine to recover phosphorus (P) and nitrogen for agricultural use and water for non-potable purposes. Synthetic fresh, synthetic hydrolyzed, real fresh, and real hydrolyzed urine were exposed to direct sunlight for 6 h in a simple distillation apparatus, which produced distillation bottoms and distillate. Metal phosphate precipitation in the distillation bottoms was evaluated to recover P. The non-potable water was recovered as distillate. Hydrolyzed urine recovered more metal phosphate solid in the distillation bottoms and had a higher conductivity in the distillate than fresh urine. Hydrolyzed urine also achieved greater distillate volume recovery than fresh urine. Hydrolyzed urine had a greater presence of UV-absorbing organics in the distillate than fresh urine and therefore produced a lower-quality product water. There was no significant correlation between the daily high air temperature and the volume of distillate recovered. This study provides a comprehensive data set on simplified solar distillation of human urine considering the fate of nutrients and water for different types of urine.

Organophosphate Esters (OPEs) Flame Retardants in Water: A Review of Photocatalysis, Adsorption, and Biological Degradation

As a substitute for banned brominated flame retardants (BFRs), the use of organophosphate esters (OPEs) increased year by year with the increase in industrial production and living demand. It was inevitable that OPEs would be discharged into wastewater in excess, which posed a great threat to the health of human beings and aquatic organisms. In the past few decades, people used various methods to remove refractory OPEs. This paper reviewed the photocatalysis method, the adsorption method with wide applicability, and the biological method mainly relying on enzymolysis and hydrolysis to degrade OPEs in water. All three of these methods had the advantages of high removal efficiency and environmental protection for various organic pollutants. The degradation efficiency of OPEs, degradation mechanisms, and conversion products of OPEs by three methods were discussed and summarized. Finally, the development prospects and challenges of OPEs’ degradation technology were discussed.

Mineral-hydrogel composites for mitigating harmful algal bloom and supplying phosphorous for photo-biorefineries

Harmful algal blooms (HAB) are a major environmental concern in eutrophic aquatic systems. To mitigate HABs and recover the phosphorus that drives algal growth, this study developed hydrogel composites seeded with calcium phosphate and wollastonite particles, which first adsorb phosphate (P) and then precipitate it as calcium phosphate. Using a fast-growing cyanobacterium, Synechococcus elongatus 2973, as a model microalga, we found that the mineral-hydrogel composites reduced dissolved P in BG11 media from 5.1 mg/L to 0.31 mg/L, initially reducing the biomass growth rate by up to 73 % and ultimately reducing the total biomass concentration by 75 %. When applied to municipal wastewater and agricultural run-off, the composites removed 96 % and 91 % of the dissolved P, respectively. Moreover, when the recovered P-enriched composites were reused as a slow-release bio-compatible fertilizer in a photobioreactor, they effectively supported algal growth without blocking light and interfering with photosynthesis. The P-enriched composites could tune the P concentration in the culture medium and significantly promote algal lipid accumulation. This study demonstrates the mineral-hydrogel composites' potential to treat point sources of P pollution and subsequently facilitate photoautotrophic biofuel production as a nutrient, effectively recycling the captured P.

Design and optimization of an innovative lanthanum/chitosan bead for efficient phosphate removal and study of process performance and mechanisms

Presence of excessive phosphorus in surface waters is the main cause for eutrophication. In this study, a lanthanum/chitosan (La/CS) bead was prepared so as to provide a cost-effective solution to the problem. The optimization of bead for the treatment was conducted, leading to the optimal condition: 30 wt% La/CS bead at a dosage of 30 g L^-1 (wet weight). A higher phosphate removal around 90% was obtained in pH 4.0-10.0. Most of uptake occurred in the first 2 h and the equilibrium was reached in about 6 h. Coexisting ions of Cl^-, [Formula: see text] , [Formula: see text] , and [Formula: see text] had negligible effects on the treatment, while the presence of F^- reduced the uptake by 10.39%. The maximum adsorption capacity of 261.1 mg-PO₄·g^-1 (dried weight) at pH 5.0 was achieved, which is much better than many reported La-based adsorbents. The adsorbed phosphate can be effectively recovered with an alkaline solution. A multi-cycle regeneration-reuse study illustrated that the treated water still met the phosphorus discharge standard. The characterization results demonstrated the disappearance of La(OH)₃ and La₂(CO₃)₃ on the bead and the formation of NH₃⁺ … P and La-P groups after the adsorption, indicating the significant roles of ion exchange and electrostatic attraction on the uptake. The excellent performance found in this study clearly indicates that the optimized La/CS bead is promising in the treatment of phosphate and perhaps its recovery for industrial use.

Lanthanum doped magnetic polyaniline for removal of phosphate ions from water

Herein, magnetic polyaniline was modified with lanthanum nanoparticles (MPANI@La) as adsorbent, aiming to the treatment of high phosphate-containing aquatic solutions. High valent lanthanum doped with polyaniline was a promising adsorbent to uptake phosphate ions with possible electrostatic interaction and cation exchange process. The functional groups, composition, surface morphology, and magnetic property of the adsorbent were investigated using Fourier Transform-Infrared Spectroscopy (FTIR), Energy Dispersive X-ray (EDX), Scanning Electron Microscopic (SEM), and Vibrating Sample Magnetometer (VSM), respectively. During the experimental process, MPANI@La has removed phosphate ions from water >90%, with 80 mg adsorbent, and shaking for 150 min at room temperature. In this regard, the process was fitted with the Pseudo-second-order kinetic model (R2 > 0.999) and the Langmuir isotherm (R2 > 0.99). The proposed nanoparticles provided an appropriate adsorption capacity (qm) of 45.24 mg.g-1 at pH 4 for phosphate ions. Besides, the adsorbent can be used with an efficiency of 92.49% up to three times that reduced to 52.89% after ten times. In addition, the adsorption process was justified by thermodynamics which confirmed the proposed adsorption mechanism. Hence, the models were provided surface adsorption, monolayer pattern, and the physical mechanism of the phosphate removal process using MPANI@La. Hence the proposed adsorbent can be used as an alternative adsorbent in environmental water remediation.

Phosphate removal and recovery by lanthanum-based adsorbents: A review for current advances

Controlling eutrophication and recovering phosphate from water bodies are hot issues in the 21st century. Adsorption is considered to be the best method for phosphate removal because of its high adsorption efficiency and fast removal rate. Among the many adsorbents, lanthanum (La)-based adsorbents have been paid more and more attention due to their strong affinity to phosphorus. This paper reviews research of phosphate adsorption on La-based adsorbents in different La forms, including lanthanum oxide/hydroxide, lanthanum mixed metal oxide/hydroxide, lanthanum carbonate, La³⁺, La-based metal-organic framework (La-MOF) and La-MOF derivatives. The La-based adsorbents can be loaded on many carriers, such as carbon material, clay minerals, porous silica, polymers, industrial wastes, and others. We find that lanthanum oxide/hydroxide and La³⁺ adsorbents are mostly studied, while those in the forms of lanthanum carbonate, La-MOF, and La-MOF derivatives are relatively few. The kinetic process of most phosphate adsorption is pseudo-second-order and the isotherm process is in accordance with the Langmuir model. The cost of La-based and other traditional adsorbents was compared. The adsorption mechanisms are categorized as electrostatic attraction, ligand exchange, Lewis acid-base interaction, ion exchange and surface precipitation. Besides, regeneration methods of La-based adsorbents are mainly acid, alkali, and salt-alkali. In addition, the La-based adsorbents after absorbing phosphate can be directly used as a slow-release fertilizer. This review provides a basis for the research on phosphate adsorption by La-based adsorbents. It should be carried out to further develop La-based materials with high adsorption capacity and good regeneration ability. Meanwhile, studies have been conducted on the reuse of phosphate after desorption, which needs more attention in future research.

Mechanisms of orthophosphate removal from water by lanthanum carbonate and other lanthanum-containing materials

Removing phosphorus (P) from water and wastewater is essential for preventing eutrophication and protecting environmental quality. Lanthanum [La(III)]-containing materials can effectively and selectively remove orthophosphate (PO₄) from aqueous systems, but there remains a need to better understand the underlying mechanism of PO₄ removal. Our objectives were to 1) identify the mechanism of PO₄ removal by La-containing materials and 2) evaluate the ability of a new material, La₂(CO₃)_3(s), to remove PO₄ from different aqueous matrices, including municipal wastewater. We determined the dominant mechanism of PO₄ removal by comparing geochemical simulations with equilibrium data from batch experiments and analyzing reaction products by X-ray diffraction and scanning transmission electron microscopy with energy dispersive spectroscopy. Geochemical simulations of aqueous systems containing PO₄ and La-containing materials predicted that PO₄ removal occurs via precipitation of poorly soluble LaPO_4(s). Results from batch experiments agreed with those obtained from geochemical simulations, and mineralogical characterization of the reaction products were consistent with PO₄ removal occurring primarily by precipitation of LaPO_4(s). Between pH 1.5 and 12.9, La₂(CO₃)_3(s) selectively removed PO₄ over other anions from different aqueous matrices, including treated wastewater. However, the rate of PO₄ removal decreased with increasing solution pH. In comparison to other solids, such as La(OH)_3(s), La₂(CO₃)_3(s) exhibits a relatively low solubility, particularly under slightly acidic conditions. Consequently, release of La³⁺ into the environment can be minimized when La₂(CO₃)_3(s) is deployed for PO₄ sequestration.

Phosphate removal from actual wastewater via La(OH)3-C3N4 adsorption: Performance, mechanisms and applicability

In this study, La(OH)₃ nanoparticles were immobilized on C₃N₄ to effectively restrict their aggregation and subsequently enhance the La utilization efficiency to promote phosphate adsorption. The prepared La(OH)₃-C₃N₄ nanocomposite was characterized by SEM, XRD, FTIR, XPS, BET and Zeta potential analysis. Batch and continuously-fed (fixed-bed column) experiments to assess the adsorption performance of La(OH)₃-C₃N₄ showed that the composite exhibits superior utilization efficiency, resulting to relatively quick adsorption with a short equilibrium time of 30 min. The theoretical maximum P adsorption capacity reached the 148.35 mg·g^-1, efficiency that remained unaffected by the anions and HA present. The adsorption mechanism showed stability in a wide pH range (4.0-11.0) and is considered effective even after extensive use (five-cycles). The dynamics of the adsorption capacity and the half-penetration time values were estimated by 'Thomas' and 'Yoon-Nelson' models showed that are better represented from the experimental values obtained from the fixed-bed column trial. The adsorption mechanisms were attributed to surface precipitation, electrostatic attraction, and inner-sphere complexation via ligand exchange. Furthermore, La(OH)₃-C₃N₄ demonstrated high efficiency in scavenging phosphate from both diluted and concentrated wastewater (natural pond and swine wastewater respectively). The above confirm that La(OH)₃-C₃N₄ is a promising composite material for phosphate management in aqueous environments.

Structural insight into the alginate derived nano-La(OH)3/porous carbon composites for highly selective adsorption of phosphate

In this study, a novel nano-La(OH)3/porous carbon composites derived from La alginate xerogel with egg-box structure had been successfully synthesized by a gradient heat treatment in nitrogen atmosphere. This facile fabrication strategy can be easily employed to considerably encapsulate La(OH)3 nanoparticles uniformly into the porous carbon matrix derived from the alginate macromolecule framework. The optimized sample, labeled as LS-550(N), exhibited extremely high phosphate uptake and great selectivity. The adsorption kinetic process dramatically followed pseudo-second-order model. The Langmuir model fitted maximum equilibrium adsorption capacity is 133.58 mg·g-1. The phosphate adsorption mechanisms could be consist of electrostatic interaction, complexation and ligand exchange interaction on the surface of LS-550(N). The prominent practical applicability of LS-550(N) in the regeneration test suggests that the LS-550(N) could be a potential adsorption candidate for the decontamination of phosphate-containing natural water bodies.

Phosphate removal by a La(OH)3 loaded magnetic MAPTAC-based cationic hydrogel: Enhanced surface charge density and Donnan membrane effect

Cationic hydrogels have received great attention to control eutrophication and recycle phosphate. In this study, a type of La(OH)₃ loaded magnetic MAPTAC-based cationic hydrogel (La(OH)₃@MMCH) was developed as a potential adsorbent for enhanced phosphate removal from aqueous environment. La(OH)₃@MMCH exhibited high adsorption capacity of 105.72±5.99 mg P/g, and reached equilibrium within 2 hr. La(OH)₃@MMCH could perform effectively in a wide pH range from 3.0 to 9.0 and in the presence of coexisting ions (including SO₄^2-, Cl^-, NO₃^-, HCO₃^-, SiO₄^4- and HA). The adsorption-desorption experiment indicated that La(OH)₃@MMCH could be easily regenerated by using NaOH-NaCl as the desorption agent, and 73.3% adsorption capacity remained after five cycles. Moreover, La(OH)₃@MMCH was employed to treat surface water with phosphate concentration of 1.90  mg/L and showed great removal efficiency of 95.21%. Actually, MMCH showed high surface charge density of 34.38-59.38 meq/kg in the pH range from 3.0 to 11.0 and great swelling ratio of 3014.57% within 24 h, indicating that MMCH could produce the enhanced Donnan membrane effect to pre-permeate phosphate. Furthermore, the bifunctional structure of La(OH)₃@MMCH enabled it to capture phosphate through electrostatic attraction and ligand exchange. All the results prove that La(OH)₃@MMCH is a promising adsorbent for eutrophication control and phosphate recovery.

A novel biotechnology based on periphytic biofilms with N-acyl-homoserine-lactones stimulation and lanthanum loading for phosphorus recovery

This study presents an approach for developing periphytic biofilm with N-acyl-homoserine-lactones (AHLs) stimulation and lanthanum (La, a rare earth element) loading, to achieve highly efficient and stable phosphorus (P) recovery from wastewater. AHLs stimulated biofilm growth and formation, also improved stable P entrapment by enhancing extracellular polymeric substance (EPS) production and optimizing P-entrapment bacterial communities. Periphytic biofilms loading La is based on ligand exchanges, and La loading achieved initial rapid P entrapment by surface adsorption. The combination of AHLs stimulation and La loading achieved 99.0% P entrapment. Interestingly, the enhanced EPS production stimulated by AHLs protected biofilms against La. Moreover, a method for P and La separately recovery from biofilms was developed, achieving 89-96% of P and 88-93% of La recovery. This study offers a promising biotechnology to reuse La from La-rich wastewater and recover P by biofilm doped with La, which results in a win-win situation for resource sustainability.

Coupled catalytic dephosphorylation and complex phosphate ion-exchange in networked hierarchical lanthanum carbonate grafted asymmetric bio-composite membrane

The remediation of non-reactive phosphate pollutants in the aquatic system is essential for protecting the ecological niche. In this work, a highly robust protein nanoparticles networked rare-earth metal carbonate-grafted bio-composite membrane (abbreviated as REMC) was fabricated via chemical crosslinking of three-dimensional (3D) hierarchical lanthanum carbonate (mREM) and casein nanoparticles (CsNPs) for selective rejection of non-reactive phosphates. The main components of the REMC membrane are mREM and CsNPs, which were prepared via SDS/CTAB templated homogeneous precipitation and the coacervation/desolvation hybrid method, respectively. The active lanthanum ion (La³⁺) on the 3D spherulitic surface of mREM exhibited excellent phosphate adsorption capacity (maximum adsorption capacity was 358 mg.g^-1) across a wide pH range and in a multi-ionic environment. A series of batch testing and characterizations revealed that the active La³⁺ and dominating phosphate centers in the REMC membrane framework enable non-enzymatic phosphatase-like activity, cleaving the phosphate ester bond of organic phosphates and releasing free phosphate anions. These released phosphate ions are retained in the REMC membrane via an ion exchange mechanism, where they contribute to improved phosphate removal capacities. Furthermore, CsNPs have a dual function in the membrane, acting as a matrix in the REMC membrane framework and contributing to phosphate ion sequestrations in a synergistic manner. The catalysis of para-nitrophenyl phosphates (pNPP) to paranitrophenol (pNP) in a sequential dephosphorylation by REMC offers an estimate of reaction kinetics and elucidates the underlying mechanism of improved phosphate selectivity in a multi-ionic environment. Furthermore, phosphate specificity, homogeneous binding capacity, reusability, and visual observation of REMC membrane saturation binding direct it's useful economic, industrial applications in aqueous phosphate contaminant removal, which could be beneficial for the active recovery of the aquatic ecosystem.

Rare earth elements (REE) for the removal and recovery of phosphorus: A review

There is little doubt that 'rock phosphate' reserves are decreasing, with phosphorus (P) peak to be reached in the coming decades. Hence, removal and recovery of phosphorus (P) from alternative nutrient-rich waste streams is critical and of great importance owing to its essential role in agricultural productivity. Adsorption technique is efficient, cost-effective, and sustainable for P recovery from waste streams which otherwise can cause eutrophication in receiving waters. As selective P sorption using rare earth elements (REE) are gaining considerable attention, this review extensively focuses on P recovery by utilising a range of REE-incorporated adsorbents. The review briefly provides existing knowledge of P in various waste streams, and examines the chemistry and behaviour of REE in soil and water in detail. The impact of interfering ions on P removal using REE, adsorbent regeneration for reuse, and life cycle assessment of REE are further explored. While it is clear that REE-sorbents have excellent potential to recover P from wastewaters and to be used as fertilisers, there are gaps to be addressed. Future studies should target recovery and reuse of REE as P fertilisers using real wastewaters. More field trials of synthesized REE-sorbents are highly recommended before practical application.

Enhanced phosphate removal by zero valent iron activated through oxidants from water: batch and breakthrough experiments

In this study, oxidants including hydrogen peroxide (H₂O₂), hypochlorite (ClO^-) and persulfate (S₂O₈ ^2-) were employed to promote zero-valent iron (ZVI) corrosion and enhance phosphate (P) removal from water through batch and breakthrough experiments. Characterization results indicated that the addition of oxidant can cause large-scale corrosion of the iron surface. This subsequently generates more iron ions and active minerals, resulting in a large number of reaction-adsorption sites for P removal. Therefore, compared with the ZVI alone system (29.4%), the removal efficiency of P by oxidant/ZVI system (H₂O₂ : ClO^- : S₂O₈ ^2- = 33.2% : 54% : 67.1%) was improved. For the oxidant/ZVI system, H₂O₂ can promote the corrosion of ZVI to a certain extent. However, the solution pH could be increased during the corrosion process. This leads to inhibition of P removal performance by the H₂O₂/ZVI system, which only increased by 12.9% to 33.2%. The reaction between NaClO and ZVI consumes less H⁺, and the reaction product Cl^- can pierce the passivation layer on the surface of the ZVI through the pitting effect. As such, the NaClO/ZVI system attained a 54% P removal rate. Compared with H₂O₂ and NaClO, a better P removal effect of about 67.1% can be achieved by using Na₂S₂O₈, since the oxidation corrosion process of Na₂S₂O₈ does not consume H⁺, and it also has the strongest oxidizing properties. Furthermore, an appropriate increase in oxidant dosing (0.1-2 mM) could improve the efficiency at which of P is removed. Five batch cycle experiments showed that the oxidant/ZVI system has a higher removal capacity and longer life-span. In the long-term column running, the P removal capacity and operation life of the NaClO/ZVI column are 9.6 times and 3.2 times higher than that of the ZVI column, respectively. This work demonstrates that an oxidant/ZVI system can be an efficient method for P removal in water, which also provides a new idea for solving the problem of ZVI corrosion passivation.

Scaled-up development of magnetically recyclable Fe3O4/La(OH)3 composite for river water phosphate removal: From bench-scale to pilot-scale study

The use of magnetic lanthanum-based materials for phosphate removal from river water has gained increasing attention. However, challenges to produce and use lanthanum-based materials in large-scale or pilot-scale studies remain. In this work, a kilogram-scale Fe₃O₄/La(OH)₃ magnetically recyclable composite for removing phosphate from river water was developed through a low-temperature precipitation route. The composite was used to remove phosphate from river water at both bench- and pilot-scales. Based on the bench-scale tests, the developed Fe₃O₄/La(OH)₃ composite was found to have excellent magnetic particle separation efficiency (>98%) and a sorption capacity of 11.77 mg/g for phosphate. A 1.0 g/L dosage of the composite in the river water sample was able to selectively reduce the phosphate level from 0.089 to 0.005 mg/L in 60 min over five consecutive adsorption cycles. At the pilot-scale, the Fe₃O₄/La(OH)₃ composite only achieved 36.0% phosphate removal efficiency, which is considerably different from the bench-scale results over an operational time of five months and a total treatment volume of 300 m³. This significantly reduced removal efficiency is mainly attributable to turbidity, suspended solids, and organic matter in the river water and the deteriorated magnetic separation efficiency. This study revealed potential challenges and shed new insights on moving magnetic nanocomposite-based technology from the bench-scale to the pilot-scale, which can inspire new designs for the application of similar technology.

Influence of natural organic matter and pH on phosphate removal by and filterable lanthanum release from lanthanum-modified bentonite

Lanthanum modified bentonite (LMB) has been applied to eutrophic lakes to reduce phosphorus (P) concentrations in the water column and mitigate P release from sediments. Previous experiments suggest that natural organic matter (NOM) can interfere with phosphate (PO₄)-binding to LMB and exacerbate lanthanum (La)-release from bentonite. This evidence served as motivation for this study to systematically determine the effects of NOM, solution pH, and bentonite as a La carrier on P removal. We conducted both geochemical modeling and controlled-laboratory batch kinetic experiments to understand the pH-dependent impacts of humic and fulvic acids on PO₄-binding to LMB and La release from LMB. The role of bentonite was studied by comparing PO₄ removal obtained by LMB and La³⁺ (added as LaCl₃ salt to represent the La-containing component of LMB). Our results from both geochemical modeling and batch experiments indicate that the PO₄-binding ability of LMB is decreased in the presence of NOM, and the decrease is more pronounced at pH 8.5 than at 6. At the highest evaluated NOM concentration (28 mg C L^-1), PO₄-removal by La³⁺ was substantially lower than that by LMB, implying that bentonite clay in LMB shielded La from interactions with NOM, while still allowing PO₄ capture by La. Finally, the presence of NOM promoted La-release from LMB, and the amount of La released depended on solution pH and both the type (i.e., fulvic/humic acid ratio) and concentration of NOM. Overall, these results provide an important basis for management of P in lakes and eutrophication control that relies on LMB applications.

Review of phosphate removal from water by carbonaceous sorbents

In the last decades, phosphate is considered the main cause of eutrophication and has received substantial attention from the scientific community. Phosphate is a major pollutant that deteriorates water quality, which has been increasing in water resources, primarily due to the increasing global population and corresponding activities. Adsorption technology is amongst the different technologies used to decrease the phosphate levels in water, and has been found to be highly effective even at low phosphate concentrations. Carbonaceous materials and their composites have been widely used for phosphate removal due to their exceptional surface properties and high phosphate sorption capacity. Considering the importance of the topic, this study reviews the reported literature in the field of adsorptive removal of phosphate over various carbon-based adsorbents such as activated carbon, charcoal, graphene, graphene oxide, graphite and carbon nanotubes. Moreover, insights into the adsorption behaviour, experimental parameters, mechanisms, thermodynamics, effect of coexisting ions and the possible desorption processes of phosphate onto modified and unmodified carbonaceous adsorbents are also considered. Finally, research challenges and gaps have been highlighted.

Structural Evolution of Lanthanum Hydroxides during Long-Term Phosphate Mitigation: Effect of Nanoconfinement

Lanthanum (La)-based materials are effective in removing phosphate (P) from water to prevent eutrophication. Compared to their bulky analogues, La(OH)₃ nanoparticles exhibit a higher P removal efficiency and a more stable P removal ability when spatially confined inside the host. Consequently, the understanding of the nanoconfinement effects on the long-term evolution of La-P structures is crucial for their practical use in P sequestration and recycle, which, however, is still missing. Here, we describe an attempt to explore the evolution of La-P structures, the P environment, and the status of La(OH)₃ nanoparticles confined in the nanopores of the D201 resin, compared to a nonconfined analogue, over a P adsorption period of 25 days in both simulated wastewater and the real bioeffluent. A combinative use of X-ray diffraction (XRD), cross-polarization nuclear magnetic resonance (CP-NMR), and X-ray photoelectron spectroscopy (XPS) techniques confirms the transition from La-P inner-sphere complexation to the formation of LaPO₄·xH₂O and finally to LaPO₄ in both samples. Interestingly, the rate of structural transformation in the real bioeffluent is substantially reduced. Nevertheless, in both conditions, nanoconfinement results in a much faster rate and larger extent of the structural transition. Moreover, nanoconfinement also facilitates the reverse transformation of stable LaPO₄ back to La(OH)₃. Our work provides the scientific basis of nanoconfinement for the preferable use of La-based nanocomposites in P mitigation, immobilization, and recycle application.