Phosphate adsorption characteristics of La(OH)3-modified, canna-derived biochar

Three-dimensional, multi-functionalized nanocellulose/alginate hydrogel for efficient and selective phosphate scavenging: Optimization, performance, and in-depth mechanisms

Challenges in developing adsorbents with sufficient phosphate (P) adsorption capacity, selectivity, and regeneration properties remain to be addressed. Herein, a multi-functionalized high-capacity nanocellulose/alginate hydrogel (La-NCF/SA-PEI [La: lanthanum, NCF: nanocellulose fiber, SA: sodium alginate, PEI: polyethyleneimine]) was prepared through environmentally friendly methods. The La-NCF/SA-PEI hydrogel, featuring a 3D porous structure with interwoven functional groups (amino, quaternary ammonium, and lanthanum), demonstrated a maximum P adsorption capacity of 78.0 mg/g, exceeding most La-based hydrogel adsorbents. The kinetic and isotherm fitting results confirmed the multilayer chemisorption process. Comprehensive experimental results, instrumental analysis, and computational results revealed that the ammonium phosphate complex (NH3+-O-P) and the inner-sphere complex (La-O-P) formed by La(OH)3 dominated the selective P adsorption process. Density-functional theory (DFT) was employed to calculate the bond length between phosphate and each component of the La-NCF/SA-PEI. The calculation results revealed the double-bridge adsorption between the N (apex) atom on La-NCF/SA-PEI and the O (apex) atomic site in phosphate, including electrostatic adsorption and two hydrogen bonds (bond lengths 1.001 and 1.008 Å) between the O of PO43- and the H+ of the protonated amino group. Except the remarkable P adsorption performance (both municipal sewage and aquaculture tail water), the La-NCF/SA-PEI hydrogel's high selectivity toward P, environmental compatibility, and easy separability from water underscore its significant potential for phosphate-contaminated water remediation. The multi-functionalized La-NCF/SA-PEI demonstrate promising potential for P removal applications and advanced the development of sustainable, biomass-based adsorbents design.

In-situ synthesis of lanthanum-coated sludge biochar for advanced phosphorus adsorption

Eutrophication and phosphorus scarcity pose significant environmental and resource management challenges, necessitating the development of efficient phosphorus removal and recovery technologies. In this study, lanthanum hydroxide-coated sludge biochar adsorbent was prepared via in-situ liquid precipitation and its phosphorus adsorption performance was evaluated. The adsorbent obtained under the optimized conditions, i.e., 5:1 ratio of La to sludge and 550 °C of annealing temperature (designated as La-C-550), exhibited a maximum phosphorus adsorption capacity of 76.4 mg-P/g at 25 °C. Mechanistic analysis revealed a multilayer adsorption process involving both physical and chemical interactions, with chemical adsorption primarily driven by the complex substitution of hydroxyl by phosphate. La-C-550 demonstrated stable performance across a pH range of 3-7, and maintained resilience against interference from common anions and humic acid. In continuous flow tests using actual secondary effluent, the adsorbent stably reduced phosphorus concentrations to below 0.1 mg-P/L, complying with the Chinese Surface Water Environmental Quality Class II standards. These results underscore the potential of La-C-550 as a cost-effective and highly efficient material for phosphorus removal in wastewater treatment applications.

Lanthanum-modified sepiolite for real application of phosphate removal from rural sewage

Being able to cause eutrophication, a severe ecological problem that leads to the demise of aquatic animals, excessive phosphate in water bodies, has been a threat to the environment. Aiming to remove phosphate from wastewater in rural areas, adsorption is a promising method. In this study, a novel phosphate adsorbent, SEP-La, was synthesized by doping lanthanum into sepiolite. Characterization and batch adsorption experiments were performed. Lanthanum was loaded on sepiolite through hydrogen bond as forms of peroxides, and it greatly enhanced the adsorption capacity of sepiolite, reaching 135.78 mg/g. Pseudo-second-order kinetic model described the adsorption kinetics the best, indicating a chemisorption process. An endothermic yet spontaneous adsorption process was revealed by the fitting of the Langmuir isotherm model. The adsorbent exhibited great tolerance to pH change and interference ions. The remaining 67.82% of the original performance after 6 cycles of adsorption-desorption demonstrated its robust recyclability. Its real application potential was also manifested through column experiments using locally collected real wastewater and was able to treat 2072 mL of water per gram of adsorbent, which represents a significant milestone in translating theory into practice. FT-IR, XRD, and XPS were performed to prove that its mechanism involved electrostatic interaction and ligand exchange. This work provides an affordable while auspicious phosphate adsorptive material with the potential to effectively address the issue of excessive phosphate in water at a low cost.

Enhanced phosphate removal from aqueous environments using three-dimensional La-doped carboxylic carbon nanotubes/alginate: Performance and mechanisms

The excessive amounts of phosphorus (P) discharged and usage have caused eutrophication and algal blooms, which seriously jeopardize the environment even the human health. In this study, carbon nanotubes (CNTs) served as carriers to develop a lanthanum-based sodium alginate hydrogel (La-CNT-COOH/SA) aimed at efficiently removing phosphate from wastewater. Characterization results confirmed successful deposition of La(OH)3 nanoparticles onto CNT-COOH. The optimal adsorption efficiency of La-CNT-COOH/SA hydrogels occurred at pH 4, with a maximum adsorption capacity of 54.4 mg/g under an initial phosphate concentration of 60 mg/L. Batch experiments demonstrated that La-CNT-COOH/SA performed well across a favorable pH range and exhibited high tolerance to common coexisting ions during phosphate adsorption. Adsorption isotherms indicated a dominance of both physical and chemical mechanisms in phosphate removal by La-CNT-COOH/SA. At elevated phosphate concentrations, the adsorption process followed quasi-second-order kinetics, primarily driven by chemical adsorption. Multi-instrument characterization emphasized that the substantial loading of La(OH)3 on CNT-COOH significantly contributed to adsorption, alongside crosslinked lanthanum ions on sodium alginate and abundant hydroxyl groups. Mechanisms of adsorption by La-CNT-COOH/SA encompassed electrostatic interactions, surface precipitation, and in-sphere complexation (La-O-P). These findings on fabrication, properties, and adsorption mechanisms of the phosphate-removal hydrogel lay a theoretical foundation for applying biomass-based materials in large-scale remediation practices.

Phosphate adsorption characteristics of CeO2-loaded, Eucommia ulmoides leaf residue biochar

In this study, a Ce-loading biochar (Ce-BC) was synthesized by the optimal modification method of pre-pyrolysis impregnation, a pyrolysis temperature at 600 °C, and a CeCl3 concentration of 1.00 mol L-1 for efficient adsorption phosphorus (P) from wastewater. The results revealed that Ce-BC could achieve a maximum P removal rate of 100% under specific conditions: an adsorbent concentration of 2.00 g L-1, an initial solution pH of 3.00, an adsorption temperature of 25 °C, and an initial P concentration of 20.00 mg L-1. The adsorption process followed the quasi-secondary kinetic model, suggesting the Ce-BC was particularly effective in acidic environments. Meanwhile, Ce-BC has a strong resistance to anion interference and good cycling performance (the P adsorption capacity of Ce-BC was 59.77% of its initial value after four cycles). Field emission scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) indicated that Ce-BC contained a porous structure and rich functional groups (hydroxyl and carboxyl), and compounds of CeO2 and MgCeO3 were formed. The Ce loading favored the exchange with P through ligands, inner-sphere complexation, ion exchange, and electrostatic interaction to form inner-sphere complex-cerium P (CePO4), and the surface complex of Ce-O-P replaced O-H. In addition, the Ce-BC adsorption columns substantially affected P removal in actual wastewater. Overall, Ce-BC is a promising material for the treating P-containing acidic wastewater.

Metal-doped biochar for selective recovery and reuse of phosphate from water: Modification design, removal mechanism, and reutilization strategy

Phosphorus (P) plays a crucial role in plant growth, which can provide nutrients for plants. Nonetheless, excessive phosphate can cause eutrophication of water, deterioration of aquatic environment, and even harm for human health. Therefore, adopting feasible adsorption technology to remove phosphate from water is necessary. Biochar (BC) has received wide attention for its low cost and environment-friendly properties. However, undeveloped pore structure and limited surface groups of primary BC result in poor uptake performance. Consequently, this work introduced the synthesis of pristine BC, parameters influencing phosphate removal, and corresponding mechanisms. Moreover, multifarious metal-doped BCs were summarized with related design principles. Meanwhile, mechanisms of selective phosphate adsorption by metal-doped BC were investigated deeply, and the recovery of phosphate from water, and the utilization of phosphate-loaded adsorbents in soil were critically presented. Finally, challenges and prospects for widespread applications of selective phosphate adsorption were proposed in the future.

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

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

Monodispersed and Organic Amine Modified La(OH)3 Nanocrystals for Superior Advanced Phosphate Removal

Advanced phosphate removal is critical for alleviating the serious and widespread aquatic eutrophication, strongly depending on the development of superior adsorption materials to overcome low chemical affinity and sluggish mass transfer at low phosphate concentrations. Herein, the first synthesis of monodispersed and organic amine modified lanthanum hydroxide nanocrystals (OA-La(OH)3) for advanced phosphate removal by modulating inner Helmholtz plane (IHP), is reported. These OA-La(OH)3 nanocrystals with positively charged surfaces and abundant exposed La sites exhibit specific affinity toward phosphate, delivering a maximum adsorption capacity of 168 mg P g⁻1 and a wide pH adaptability from 3.0 to 11.0, as well as a robust anti-interference performance, far surpassing those of documented phosphate removal materials. The superior phosphate removal performance of OA-La(OH)3 is attributed to its protonated organic amine in IHP, which enhances the electrostatic attraction around the adsorbent-solution interface. Impressively, OA-La(OH)3 can treat ≈5 000 and ≈3 200 bed volumes of simulated and real phosphate-containing wastewater to below extremely strict standard (0.1 mg L⁻1) in a fixed-bed adsorption mode, exhibiting great potential for advanced phosphate removal. This study offers a facile modification strategy to improve phosphate removal performance of nanoscale adsorbents, and sheds light on the structure-reactivity relationship of La-based materials.

Lanthanum-modified tobermorite synthesized from fly ash for efficient phosphate removal

Phosphate removal from water by lanthanum-modified tobermorite synthesized from fly ash (LTFA) with different lanthanum concentrations was studied. LTFA samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and Brunauer‒Emmett‒Teller specific surface area analysis. The results showed that the LTFA samples were mainly composed of mesoporous tobermorite-11 Å, and LTFA1 with a lanthanum concentration of 0.15 M had a high specific surface area (83.82 m2/g) and pore volume (0.6778 cm3/g). The phosphate adsorption capacities of LTFA samples were highest at pH 3 and gradually decreased with increasing pH. The phosphate adsorption kinetics data on LTFA samples were most accurately described by the Elovich model. The adsorption isotherms were in the strongest agreement with the Temkin model, and LTFA1 showed the highest phosphate adsorption capacity (282.51 mg P/g), which was higher than that of most other lanthanum-modified adsorbents. LTFA1 presented highly selective adsorption of phosphate with other coexisting ions (HCO3-, Cl-, SO42-, and NO3-). In addition, phosphate was adsorbed onto LTFA samples by forming inner-sphere phosphate complexes and amorphous lanthanum phosphate. This study provides technical support for development of efficient fly ash-based phosphate adsorbents.

Nano La(OH)3 modified lotus seedpod biochar: A novel solution for effective phosphorus removal from wastewater

Effective removal of phosphorus from water is crucial for controlling eutrophication. Meanwhile, the post-disposal of wetland plants is also an urgent problem that needs to be solved. In this study, seedpods of the common wetland plant lotus were used as a new raw material to prepare biochar, which were further modified by loading nano La(OH)3 particles (LBC-La). The adsorption performance of the modified biochar for phosphate was evaluated through batch adsorption and column adsorption experiments. Adsorption performance of lotus seedpod biochar was significantly improved by La(OH)3 modification, with adsorption equilibrium time shortened from 24 to 4 h and a theoretical maximum adsorption capacity increased from 19.43 to 52.23 mg/g. Moreover, LBC-La maintained a removal rate above 99% for phosphate solutions with concentrations below 20 mg/L. The LBC-La exhibited strong anti-interference ability in pH (3-9) and coexisting ion experiments, with the removal ratio remaining above 99%. The characterization analysis indicated that the main mechanism is the formation of monodentate or bidentate lanthanum phosphate complexes through inner sphere complexation. Electrostatic adsorption and ligand exchange are also the mechanisms of LBC-La adsorption of phosphate. In the dynamic adsorption experiment of simulated wastewater treatment plant effluent, the breakthrough point of the adsorption column was 1620 min, reaching exhaustion point at 6480 min, with a theoretical phosphorus saturation adsorption capacity of 6050 mg/kg. The process was well described by the Thomas and Yoon-Nelson models, which indicated that this is a surface adsorption process, without the internal participation of the adsorbent.

Efficient Adsorption of Nitrogen and Phosphorus in Wastewater by Biochar

Nitrogen and phosphorus play essential roles in ecosystems and organisms. However, with the development of industry and agriculture in recent years, excessive N and P have flowed into water bodies, leading to eutrophication, algal proliferation, and red tides, which are harmful to aquatic organisms. Biochar has a high specific surface area, abundant functional groups, and porous structure, which can effectively adsorb nitrogen and phosphorus in water, thus reducing environmental pollution, achieving the reusability of elements. This article provides an overview of the preparation of biochar, modification methods of biochar, advancements in the adsorption of nitrogen and phosphorus by biochar, factors influencing the adsorption of nitrogen and phosphorus in water by biochar, as well as reusability and adsorption mechanisms. Furthermore, the difficulties encountered and future research directions regarding the adsorption of nitrogen and phosphorus by biochar were proposed, providing references for the future application of biochar in nitrogen and phosphorus adsorption.

Aluminium dross waste utilization for phosphate removal and recovery from aqueous environment: Operational feasibility development

The need to minimize eutrophication in water bodies and the shortage of phosphate rock reserves has stimulated the search for sequestration and recovery of phosphate from alternative sources, including wastewater. In this study, aluminium dross (AD), a smelting industry waste/by-product, was converted to high-value material by encapsulation in calcium alginate (Ca-Alg) beads, viz. Ca-Alg-AD and utilized for adsorptive/uptake removal and phosphate recovery from an aqueous environment. Encapsulation of AD in alginate beads solves serious operational difficulties of using raw AD material directly due to density difference constraining efficient contact of AD with pollutants present in water and post-treatment recovery of AD material. The phosphate removal was evaluated in both batch and continuous flow operation modes. The batch adsorption study revealed 96.86% phosphate removal from 10 mg L-1 of initial phosphate concentration in 70 min of optimal contact time. Further, the phosphate removal potential of Ca-Alg-AD beads turned out to be independent of solution pH, with an average of 95.93 ± 1.40 % phosphate removal in the 2-9 pH range. The result reflects phosphate adsorption on Ca-Alg-AD beads following a second-order pseudo-kinetic model. Ca-Alg-AD beads-based adsorption followed Freundlich and Langmuir isotherm models. Further, a continuous packed bed column study revealed a total phosphate adsorption capacity of 1.089 mg g-1. The chemical composition, physical stability, and surface properties of Ca-Alg-AD beads were analyzed by means of state-of-the-art analytical techniques, such as Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDX), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetry/Differential Thermal Analysis (TG/DTA). These characterization techniques comprehend the mechanism and influence of surface properties and morphology on the phosphate adsorption behaviour, which induce the involvement of multiple mechanisms such as ligand complexation, ion exchange, and electrostatic attraction for phosphate adsorption on Ca-Alg-AD beads.

Adsorption recovery of phosphorus in contaminated water by calcium modified biochar derived from spent coffee grounds

Phosphate recovery from water is essential for reducing water eutrophication and alleviating the phosphorus resource crisis. In this study, spent coffee grounds and CaCl2 were used as raw materials and a modifier, respectively, to create a novel calcium modified biochar (MBC) for removing phosphorus from water. The modified biochar (MBC) was the best at removing phosphorous when the modifier concentration was 1.5 M with theoretically maximum adsorption capacity of 70.26 mg/g. MBC also performed well in the wide pH range of 3-11 under different phosphorus concentration gradients, with phosphorus removal efficiency of more than 50 %. According to kinetic analysis, the adsorption process at low phosphorus concentrations (50-100 mg/L) can be more properly described by the pseudo-first-order model, while the pseudo-second-order model best describes the adsorption process at high concentrations (200-600 mg/L). The thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. Characterization results revealed that surface precipitation, complexation, and ligand exchange were the dominant mechanisms of phosphorus adsorption. MBC has great potential to recover phosphorus from wastewater.

Functional biochar fabricated from red mud and walnut shell for phosphorus wastewater treatment: Role of minerals

A novel functional biochar (BC) was prepared from industrial waste red mud (RM) and low-cost walnut shell by one facile-step pyrolysis method to adsorb phosphorus (P) in wastewater. The preparation conditions for RM-BC were optimized using Response Surface Methodology. The adsorption characteristics of P were investigated in batch mode experiments, while a variety of techniques were used to characterize RM-BC composites. The impact of key minerals (hematite, quartz, and calcite) in RM on the P removal efficiency of the RM-BC composite was studied. The results showed that RM-BC composite produced at 320 °C for 58 min, with a 1:1 mass ratio of walnut shell and RM, had a maximum P sorption capacity of 15.48 mg g^-1, which was more than double that of the raw BC. The removal of P from water was found to be facilitated significantly by hematite, which forms Fe-O-P bonds, undergoes surface precipitation, and exchanges ligands. This research provides evidence for the effectiveness of RM-BC in treating P in water, laying the foundation for future scaling-up trials.

Ca-La layered double hydroxide (LDH) for selective and efficient removal of phosphate from wastewater

Adsorption showed advantages in removing phosphorus (P) at low concentrations. Desirable adsorbents should have sufficiently high adsorption capacity and selectivity. In this study, a Ca-La layered double hydroxide (LDH) was synthesized for the first time by using a simple hydrothermal coprecipitation method for phosphate removal from wastewater. A maximum adsorption capacity of 194.04 mgP/g was achieved, ranking on the top of known LDHs. Adsorption kinetic experiments showed that 0.02 g/L Ca-La LDH could effectively reduce PO₄^3-P from 1.0 to <0.02 mg/L within 30 min. With the copresence of bicarbonate and sulfate at concentrations 17.1 and 35.7 times of that of PO₄^3-P, the Ca-La LDH showed promising selectivity towards phosphate (with a reduction in the adsorption capacity of <13.6%). In addition, four other (Mg-La, Co-La, Ni-La, and Cu-La) LDHs containing different divalent metal ions were synthesized by using the same coprecipitation method. Results showed much higher P adsorption performance of the Ca-La LDH than those LDHs. Field Emission Electron Microscopy (FE-SEM)-Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), and mesoporous analysis were performed to characterize and compare the adsorption mechanisms of different LDHs. The high adsorption capacity and selectivity of the Ca-La LDH were mainly explained by selective chemical adsorption, ion exchange, and inner sphere complexation.

Fe-modified fly ash/cotton stalk biochar composites for efficient removal of phosphate in water: mechanisms and green-reuse potential

Excessive phosphate content input into natural water can lead to the waste of resource and eutrophication. Biochar is a kind of low-cost adsorbent. However, its adsorption capacity for phosphate is low. In order to solve this problem, Fe compound-modified fly ash/cotton stalk biochar composites (Fe-FBC) were prepared through co-pyrolyzed fly ash and cotton stalk at 800℃, followed by infiltration of FeSO₄ solution. The samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, and zeta potential. After modification, the hydrophilicity and polarity of Fe-FBC increased. In addition, the pore volume, specific surface area, and surface functional groups were significantly improved. The adsorption behavior of Fe-FBC for the removal of phosphate from water can be well fitted by the pseudo-second-order kinetic and Sips isotherm adsorption model, with a maximum adsorption capacity of 47.91 mg/g. Fe-FBC maintained a high adsorption capacity in the pH range of 3-10. The coexisting anions (NO₃^-, SO₄^2-, and Cl^-) had negligible effects on phosphate adsorption. The adsorption mechanisms of Fe-FBC include electrostatic attraction, ligand exchange, surface complexation, ion exchange, chemical precipitation, and hydrogen bonding. Moreover, the desorption process of phosphate was investigated, indicating that the phosphate-saturated Fe-FBC could use as slow-release phosphate fertilizer. This study proposed a potentially environmental protection and recycling economy approach, which consists of recycling resources and treating wastes with wastes.

B-site metal modulation of phosphate adsorption properties and mechanism of LaBO3 (B = Fe, Al and Mn) perovskites

La-based adsorbents are widely used for controlling phosphate concentration in water bodies. In order to explore the effect of different B-site metals regulating La-based perovskites on phosphate adsorption, three La-based perovskites (LaBO₃, B = Fe, Al, and Mn) were prepared using the citric acid sol-gel method. Adsorption experiments showed that LaFeO₃ exhibited the highest adsorption capacity for phosphate, which was 2.7 and 5 times higher than those of LaAlO₃ and LaMnO₃, respectively. The characterization results demonstrated that LaFeO₃ has dispersed particles exhibiting larger pore size and more pores than LaAlO₃ and LaMnO₃. Spectroscopy analysis and density functional theory calculation results showed that different B-positions cause a change in the type of perovskite crystals. Among them, the differences between lattice oxygen consumption ratio, zeta potential and adsorption energy are the main reasons for the differences in adsorption capacity. In addition, the adsorption of phosphate by La-based perovskites were well fitted with Langmuir isotherm and pursues the pseudo-second-order kinetic models. The maximum adsorption capacities were 33.51, 12.31 and 6.61 mg/g for LaFeO₃, LaAlO₃ and LaMnO₃, respectively. The adsorption mechanism was mainly based on inner-sphere complexation and electrostatic attraction. This study provides an explanation for the influence of different B sites on phosphate adsorption by perovskite.

Preparation and Characterization of an Invasive Plant-Derived Biochar-Supported Nano-Sized Lanthanum Composite and Its Application in Phosphate Capture from Aqueous Media

Invasive plants pose a great threat to natural ecosystems owing to their rapid propagation and spreading ability in nature. Herein, a typical invasive plant, Solidago canadensis, was chosen as a novel feedstock for the preparation of nano-sized lanthanum-loaded S. canadensis-derived biochar (SCBC-La), and its adsorption performance for phosphate removal was evaluated by batch adsorption experiment. The composite was characterized by multiple techniques. Effects of parameters, such as the initial concentration of phosphate, time, pH, coexisting ions, and ionic strength, were studied on the phosphate removal. Adsorption kinetics and isotherms showed that SCBC-La shows a faster adsorption rate at a low concentration and SCBC-La exhibits good La utilization efficiency than some of the reported La-modified adsorbents. Phosphate can be effectively removed over a relatively wide pH of 3-9 because of the high pH _pzc of SCBC-La. Furthermore, the SCBC-La shows a strong anti-interference capability in terms of pH value, coexisting ions, and ionic strength, exhibiting a highly selective capacity for phosphate removal. Additionally, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements reveal that hydroxyl groups on the surface of SCBC-La were replaced by phosphate and manifest the reversible transformation between La(OH)₃ and LaPO₄. Considering its high adsorption capacity and excellent selectivity, SCBC-La is a promising material for preventing eutrophication. This work gives a new method of pollution control with waste treatment since the invasive plant (S. canadensis) is converted into biochar-based nanocomposite for effective removal of phosphate to mitigate eutrophication.

A critical review on the development of lanthanum-engineered biochar for environmental applications

Biochar and lanthanum (La) have been widely used in environment. However, there is a lack of knowledge and perspective on the development of La-engineered biochar (LEB) for environmental applications. This review shows that LEBs with a variety of La species via pre-/post-doping routes are developed for environmental applications. Specifically, precipitation, gelation, and calcination are the common sub-processes involved in the pre-/post-doping of La on the resultant LEB. The dominant La species for LEBs is La(OH)₃, which is formed through precipitation of La ions with various bases. Various La carbonates, e.g., LaOHCO₃, La₂(CO₃)₃, La₂CO₅, and NaLa(CO₃)₂, are also involved in the preparation of LEBs. The LEBs are high-efficient in the adsorption of phosphate, arsenic, antimonate and fluoride ions, attributed to the strong affinity of La to oxyanions and Lewis hard base. Lanthanum is also favorable for co-doping with transition metal species to further enhance the performances in adsorption or catalysis. This review also analyzes the prospects and future challenges for the preparation and application of LEBs in environment. Finally, this review is beneficial to inspire new breakthroughs on the preparation and environmental application of LEBs.

Green and Efficient Al-Doped LaFexAl1-xO3 Perovskite Oxide for Enhanced Phosphate Adsorption with Creation of Oxygen Vacancies

La-based metal oxide materials are environmentally friendly and show promise for phosphate adsorption. A series of Al-doped perovskite oxides, such as LaFe_xAl_1-xO₃, were prepared using a facile citric acid-assisted sol-gel method. The characterization results demonstrated that with optimized Al doping, there was a significant increase in the specific surface area and increased defect content of perovskite oxide LaFe_xAl_1-xO₃. Adsorption experiments showed that the performance of phosphate removal by LaFe_xAl_1-xO₃ was largely enhanced due to the improved adsorption capacity, which is maximum eight times higher compared with control perovskites prepared under neutral conditions. The mass transfer rate for adsorption was considerably boosted with phosphate removal within the initial 15 min. Spectroscopy analysis and density functional theory calculation results showed that the process of phosphate removal by the Al-doped perovskite oxides LaFe_xAl_1-xO₃ involved electrostatic interactions, an inner-sphere complex, and surface oxygen vacancies, among which the creation of oxygen vacancies caused by the Al doping was the predominant mechanism for reducing the bonding barrier during adsorption and generating adsorption sites. The results enable the development of a green and efficient perovskite adsorbent with a La-based perovskite material for phosphorus removal.

One-pot synthesis of novel flower-like LaCO3OH adsorbents for efficient scavenging of phosphate from wastewater

Phosphorus removal from wastewater has been considered as an effective method to control eutrophication and mitigate phosphorus deficiency. Phosphate adsorption using lanthanum-based materials has awakened much attention and triggered extensive research. In this study, novel flower-like LaCO₃OH materials were synthesized via a one-step hydrothermal method and evaluated for phosphate removal from wastewater. The adsorbent with flower-like structures prepared at the hydrothermal reaction time of 4.5 h (BLC-4.5) exhibited the optimum adsorption performance. BLC-4.5 had a rapid removal rate with more than 80% of the saturated adsorbed phosphate removed within 20 min. Furthermore, the maximum phosphate adsorption capacity of BLC-4.5 was as high as 228.5 mg/g. Notably, the La leaching amount of BLC-4.5 was negligible in the pH range of 3.0-11.0. BLC-4.5 outperformed most of the reported La-based adsorbents in terms of removal rate, adsorption capacity, and La leaching amount. Moreover, BLC-4.5 had broad pH adaptability (3.0-11.0) and high selectivity for phosphate. BLC-4.5 also displayed excellent phosphate removal efficiency in actual wastewater and great recyclability. The potential adsorption mechanisms of phosphate on BLC-4.5 were precipitation, electrostatic attraction, and inner-sphere complexation via ligand exchange. This study demonstrates that the newly developed flower-like BLC-4.5 reported here is a promising adsorbent for the effective treatment of phosphate in wastewater.

Pyrolysis temperature affects the physiochemical characteristics of lanthanum-modified biochar derived from orange peels: Insights into the mechanisms of tetracycline adsorption by spectroscopic analysis and theoretical calculations

Biochar (BC) derived from orange peels was modified using LaCl₃ to enhance its tetracycline (TC) adsorption capacity. SEM-EDS, FT-IR, XRD, and BET were used to characterize the physiochemical characteristics of La-modified biochar (La-BC). Batch experiments were conducted to investigate the effects of several variables like pyrolysis temperature, adsorbent dosage, initial pH, and coexisting ions on the adsorption of TC by La-BC. XPS and density functional theory (DFT) were used to elucidate the TC adsorption mechanism of La-BC. The results demonstrated that La was uniformly coated on the surface of the La-BC. The physiochemical characteristics of La-BC highly depended on pyrolysis temperature. Higher temperature increased the specific surface area and functional groups of La-BC, thus enhancing its TC adsorption capacity. La-BC prepared at 700 °C (BC@La-700) achieved the maximum adsorption capacity of 143.20 mg/g, which was 6.8 and 4.6 times higher than that of BC@La-500 and BC@La-600, respectively. The mechanisms of TC adsorption by La-BC were most accurately described by the pseudo-second-order kinetic model. Furthermore, the adsorption isotherm of La-BC was consistent with the Freundlich model. BC@La-700 achieved good TC adsorption efficiencies even at a wide pH range (pH 4-10). Humic acid significantly inhibited TC adsorption by La-BC. The presence of coexisting ions (NH₄⁺, Ca²⁺, NO₃^-) did not significantly affect the adsorption capacity of La-BC, particularly BC@La-700. Moreover, BC@La-700 also exhibited the best recycling performance, which achieved relative high adsorption capacity even after 5 cycles. The XPS results showed that π-π bonds, oxygen-containing functional groups, and La played a major role in the adsorption of TC on La-BC. The result of DFT showed that the adsorption energy of La-BC was the greatest than that of other functional groups on biochar. Collectively, our findings provide a theoretical basis for the development of La-BC based materials to remove TC from wastewater.

Fe12LaO19 fabricated biochar for removal of phosphorus in water and exploration of its adsorption mechanism

Phosphorus (P) runoff from untreated wastewater and agricultural runoff has become an issue of concern because excessive P is detrimental to the health of water bodies and aquatic organisms such as fishes. Hence, different methods are being developed to salvage this challenge. However, most of the methods are expensive, while some are unsustainable. In this study, a simple method was employed in fabricating an absorbent through the co-precipitation of iron and lanthanum on the matrix of biochar prepared from the spent coffee ground for P uptake. The adsorbent named Fe₁₂LaO₁₉@BC was able to attain equilibrium fast within 60 min when used to adsorb P with 98% P removal within the first 30 min Fe₁₂LaO₁₉@BC also maintained high P adsorption across a pH range of 3-7. In the presence of other anions (SO₄^2-, CO₃^2-, NO₃^-, Cl^-, HCO₃^-) in the solution, Fe₁₂LaO₁₉@BC enabled 71.5-97.8% uptake of P. 81.58 mg P/g maximum adsorption capacity at was reached at 40 °C. The reusability test reveals that about 60% of P uptake was maintained after five adsorption cycles with almost an undisturbed desorption efficiency. The negative value of ΔG°, as shown by the thermodynamic analysis, indicates a favorable and spontaneous reaction during P removal by Fe₁₂LaO₁₉@BC. The XRD analysis showed a major peak corresponding to Fe₁₂LaO_19, which is believed to have facilitated the adsorption of P. The adsorption was controlled by multiple mechanisms. An overview of the study indicates Fe₁₂LaO₁₉@BC as a promising adsorbent for the removal of P in the water.

Study on the management efficiency of lanthanum/iron co-modified attapulgite on sediment phosphorus load

Attapulgite co-modified by lanthanum-iron (MT-LHMT) was used to study its effectiveness and mechanism in controlling phosphorus release from sediments. MT-LHMT has high adsorption capacity for phosphate and the maximum adsorption capacity of MT-LHMT to phosphate can reach 75.79 mg/g. The mechanism mainly involved electrostatic action, surface precipitation and ligand exchange between MT-LHMT bonded hydroxyl and phosphate to form La-O-P and Fe-O-P inner-sphere complexes. MT-LHMT has excellent adsorption performance in the pH range of 3-8. In addition to HCO₃^-, CO₃^2- and HA^- had a negative effect on the phosphorus removal of MT-LHMT, while NO₃^-, Cl^-, SO₄^2-, K⁺, Ca²⁺ and Mg²⁺ had a positive or no effect on phosphorus removal. MT-LHMT significantly reduced the risk of phosphorus release from overlying water in different dose effects and covering methods, as well as the unstable inactivation of flowing phosphorus, sediment dissolved reactive phosphorus (DRP) and available phosphorus with medium diffusion gradient in thin film in the sediment-water interface (Labile-P_DGT). The MT-LHMT capping wrapped with fabric can reduce the risk of nitrogen release from sediment to overlying water more than only MT-LHMT capping. The results of this study showed that the MT-LHMT capping wrapped with fabric has high potential and can be used as an active capping material to manage the nitrogen and phosphorus load in surface water.

Egg White-Mediated Fabrication of Mg/Al-LDH-Hard Biochar Composite for Phosphate Adsorption

Phosphorus is one of the main causes of water eutrophication. Hard biochar is considered a promising phosphate adsorbent, but its application is limited by its textural properties and low adsorption capacity. Here, an adhesion approach in a mixed suspension containing egg white is proposed for preparing the hybrid material of Mg/Al-layered double hydroxide (LDH) and almond shell biochar (ASB), named L-AE or L-A (with or without egg white). Several techniques, including XRD, SEM/EDS, FTIR and N2 adsorption/desorption, were used to characterize the structure and adsorption behavior of the modified adsorbents. The filament-like material contained nitrogen elements at a noticed level, indicating that egg white was the crosslinker that mediated the formation of the L-AE hybrid material. The L-AE had a higher phosphate adsorption rate with a higher equilibrium adsorption capacity than the L-A. The saturation phosphate adsorption capacity of L-AE was nearly three times higher than that of L-A. Furthermore, the number of surface groups and the density of the positively charged surface sites follow the ASB < L-A < L-AE order, which is consistent with their phosphate adsorption performance. The study may offer an efficient approach to improving hard biochar’s adsorption performance in wastewater treatment.

Phosphate adsorption improvement using a novel adsorbent by CaFe/LDH supported onto CO2 activated biochar

It is imperative to remove phosphate from the aquatic system. This nutrient in excess can cause environmental problems such as eutrophication. Therefore, aiming to enhance phosphate removal, this work presents a novel adsorbent developed from the construction of Ca²⁺/Fe³⁺ layer double hydroxides (CaFe/LDH) supported onto biochar physically activated with CO₂ [CaFe/biochar (CO₂)]. Pristine biochar was produced from the pyrolysis of Eucalyptus saligna sawdust, activated with CO₂, and then impregnated with CaFe/LDH. The CaFe/biochar (CO₂) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET). The characterization confirmed a proper synthesis of the new adsorbent. Experiments were conducted in the form of batch adsorption. Results indicated that the optimum pH and adsorbent dosage were 2.15 and 0.92 g L^-1, respectively. Adsorption kinetics, isotherms, and thermodynamics were also evaluated. Adsorption kinetics and isotherms were better fitted by the pseudo n order and Freundlich models, respectively. Results also indicated a better adsorption capacity (99.55 mg·g^-1) at 55 °C. The thermodynamic indicators depicted that the adsorption process was favorable, spontaneous, and endothermic. Overall, CaFe/biochar (CO₂) could be potentially applied for the adsorptive removal of phosphate from an aqueous solution.

Zirconium-modified biochar as the efficient adsorbent for low-concentration phosphate: performance and mechanism

Achieving advanced treatment of phosphorus (P) to prevent water eutrophication and meet increasingly stringent wastewater discharge standard is an important goal of water management. In this study, a low-cost, high-efficiency phosphate adsorbent zirconium-modified biochar (ZrBC) was successfully synthesized through co-precipitation method, in which the biochar was prepared from the pyrolysis of peanut shell powder. ZrBC exhibited strong adsorption ability to low-concentration phosphate (< 1 mg·L^-1) in water, and the phosphate removal reached 100% at the investigated dosage range (0.1-1.0 mg·L^-1). The adsorption process could be described well by pseudo-second-order model and Langmuir isotherm model, indicating that the phosphate adsorption by ZrBC was mainly a chemical adsorption and single-layer adsorption process. The calculated static maximum phosphate adsorption capacity was 58.93 mg·g^-1 at 25 °C. The ligand exchange between surface hydroxyl groups and phosphate was the main mechanism for the phosphate adsorption on ZrBC. The presence of coexisting anions except for SO₄^2- had little effect on the phosphate removal. At the column experiment, ZrBC showed superior treatment capacities for simulated secondary effluents and the breakthrough time for 0.5 mg·L^-1 effluent phosphate concentration reached 190 h. ZrBC highlights the potential as an effective and environment-friendly adsorbent for the removal of low-concentration phosphate from secondary effluents of municipal wastewater treatment plants (WWTPs).

Metal-based adsorbents for water eutrophication remediation: A review of performances and mechanisms

Controlling eutrophication requires satisfying stringent phosphorus concentration standards. Metal-based adsorbents can effectively remove excess phosphorus from water bodies and achieve ultra-low phosphorus concentration control for wastewater. This review focuses on the material properties and phosphorus removal mechanism of metal-based adsorbents (Fe, Al, Ca, Mg, La). There are significant differences in physical and chemical properties of different metal materials, due to the different preparation methods and synthetic materials. The main factors affecting phosphorus removal performance include particle size, crystal structure and pH_PZC. Smaller particle size, more disordered crystal structure and higher pH_PZC are more favorable for phosphorus removal. The main mechanism of phosphorus removal by metal-based adsorbents is ligand exchange, which makes it exhibit excellent adsorption capacity, fast kinetics and well selectivity for phosphate. In addition, in order to improve the phosphorus removal performance, the surface properties of the adsorbent (e.g., surface charge, surface area, and functional groups) can be effectively improved by dispersion of biochar carriers or combination of multiple metal materials. In further studies, we should improve the absorption capacity of the adsorbent under high pH conditions and the resistance to coexisting ion interference. Finally, in order to ensure the effective application of metal-based adsorbents in the phosphorus removal field, experimental scale should be expanded in future work to suit the actual water body conditions.

Multifunctional Fe3O4/TiO2/NH2-UiO-66 with integrated interfacial features for favorable phosphate adsorption

Excessive use and discharge of phosphate are the decisive factors leading to water eutrophication, and adsorption is deemed among the most effective methods in phosphorus capture. This study prepared the...

Removal of phosphate from aqueous solution by chitosan coated and lanthanum loaded biochar derived from urban dewatered sewage sludge: adsorption mechanism and application to lab-scale columns

A lanthanum modified sludge biochar chitosan (La-SBC-CS) microsphere was successfully synthesized by dropping sludge biochar (BC) and chitosan into a lanthanum chloride solution. Batch adsorption experiments were conducted to investigate the adsorption kinetics and isotherm. Application of continuous phosphate removal was achieved via lab-scale column reactors. The phosphate adsorption equilibrium data of the La-SBC-CS fitted well with the Freundlich isotherm, with a maximum adsorption amount of 81.54 mg p/g at 25 °C. Characterization of the adsorbent using scanning electron microscopy analysis (SEM), X-ray energy spectrum analysis (EDS), X-ray diffraction analysis (XRD) and Fourier infrared analysis (FTIR) techniques suggested that the possible adsorption mechanisms were electrostatic interaction, ligand exchange and complexation. The La-SBC-CS kept 76.37% phosphate removal efficiency after eight recycles. The results of continuous column reactor experiment demonstrated that the breakthrough time increased with an increase in adsorbent filling height, while it decreased with an increase in initial phosphate concentration or flow velocity. The Yoon model was applied to the continuous experimental data to predict breakthrough curves and determined the characteristic adsorption parameters for process design. This study indicated the potential for the practical application of La-SBC-CS in phosphate removal from wastewater.