CaFe-layered Double Hydroxides Research Articles

Efficient mineralization of cadmium and arsenic by poorly crystalline CaFe-layered double hydroxide in soil: Performance and mechanism

The co-contamination of arsenic (As) and cadmium (Cd) in the environment is of most concern. In this work, poorly crystalline CaFe-layered double hydroxide (CaFe-LDH) was synthesized with a Ca-to-Fe molar ratio of 4 to ensure effective immobilization of Cd and As in soil. The application of Ca4Fe-LDH in soil remediation demonstrated that the targeted heavy metals gradually mineralized into a relatively stable oxidizable and residual state. At a soil remediation dosage of 1.6%, the availability levels of Cd and As decreased significantly, achieving stabilization efficiencies of 99% and 85.2% respectively. Cd is trapped through isomorphic substitution and dissolution-reprecipitation of calcium (Ca) laminate, resulting in the formation of CdCaFe-LDH mineralization products. As is immobilized through ion exchange with interlayer anions, redox with Fe(III), and Fe-Cd-As complexation. Moreover, the results of the characterization and density functional theoretical (DFT) calculations demonstrate that the CdCaFe-LDH formed by isomeric substitution of Ca for Cd enhanced the adsorption of As on the (110) plane of LDH, indicating that the trap mechanism of Cd and As by Ca4Fe-LDH is synergistically promoted. Overall, the above results prove that mineralization using Ca4Fe-LDH is a promising method to remediate soils combined contaminated by both Cd and As.

Developed Recyclable CaFe-Layered Double Hydroxide for Efficient Cadmium Immobilization in Soil: Performance and Bioavailability

Powdered layered double hydroxide (CaFe-LDH) was synthesized via hydrothermal co-precipitation, demonstrating successful preparation upon characterization. Subsequently, experiments were conducted to assess its efficacy in immobilizing divalent cadmium (Cd(II)). The findings substantiated the effectiveness of CaFe-LDH in immobilizing Cd(II) within soil. Various influencing factors, including LDH dosage, pH, and soil heavy metal concentration, were systematically investigated, revealing CaFe-LDH’s superiority in Cd(II) immobilization. Notably, the leaching concentration of Cd(II) was notably reduced from 142.30 mg/L to 32.99 mg/L, with a maximum adsorption capacity of 31.10 mg/L, underscoring the significant role of CaFe-LDH in Cd(II) removal. Furthermore, the stability of CaFe-LDH was confirmed via toxicity characteristic leaching procedure (TCLP) experiments and plant potting tests. In-depth analysis of the immobilization mechanism through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) elucidated isomorphous substitution and surface adsorption as the primary mechanisms responsible for Cd(II) immobilization in contaminated soils. Additionally, isomorphic substitution and adsorption onto oxygen-containing functional groups were observed. This comprehensive study underscores the promising potential of CaFe-LDH in immobilizing Cd(II) in contaminated soil. With its commendable immobilization properties and recyclability, CaFe-LDH emerges as a promising solution for remediating heavy-metal-contaminated soils.

Selective Separation of Sulfate and Chloride Ions from Industrial Wastewater by In Situ Generation of CaFe-Layered Double Hydroxides and the Related Resource Utilization

Selective Separation of Sulfate and Chloride Ions from Industrial Wastewater by In Situ Generation of CaFe-Layered Double Hydroxides and the Related Resource Utilization

CaFe-layered double hydroxide corn straw biochar reduced heavy metal uptake by Brassica campestris L. and Ipomoea aquatic F.: Rhizosphere effects and oxidative stress alleviation

In the present study, CaFe-layered double hydroxide corn straw biochar (CaFe-LDH@CSB) was applied to the rhizosphere soil of both pakchoi (Brassica campestris L. ssp. Chinensis Makino, B. campestris L.) and water spinach (Ipomoea aquatic F., I. aquatic F.) to explore and clarify the potential mechanism by which CaFe-LDH@CSB helps vegetables reduce heavy metal (HM) uptake and alleviate oxidative stress. Pot experiments were conducted with CaFe-LDH@CSB applied at four levels: control (CK), T1 (5 g kg−1), T2 (10 g kg−1) and T3 (20 g kg−1). The results indicated that the application of CaFe-LDH@CSB significantly increased pH and decreased the acid-soluble forms of Cd, Pb, Zn and Cu in the rhizosphere soil of both B. campestris L. and I. aquatic F.; decreases of 39.4%, 18.0%, 10.0% and 33.3% in B. campestris L. and of 26.6%, 49.1%, 13.2% and 36.8% in I. aquatic F., respectively, were observed at the T3 level. Moreover, CaFe-LDH@CSB application reduced HM uptake by B. campestris L. and decreased HM-induced oxidative stress through the regulation of soil physicochemical properties and microbial abundance. For B. campestris L., variations in Sordariomycetes helped alleviate the accumulation of HMs in the aerial part, while GSH and –SH from the nonenzymatic system played an important role in scavenging H2O2 in leaves, thus helping B. campestris L. alleviate HM-induced oxidative stress. For I. aquatica F., variations in Vicinamibacteria and Mortierellomycetes helped alleviate the accumulation of HMs in plants, while GSH and PCs from nonenzymatic systems played an important role in removing ·O2− in leaves, thereby helping I. aquatica F. alleviate HM-induced oxidation stress. Our study indicated that the application of CaFe-LDH@CSB improved the rhizosphere soil environment and rebuilt the soil microbial community, helping B. campestris L. and I. aquatica F. alleviate HM-induced oxidative stress and promoting the growth of both vegetables.

Insights into the heavy metal adsorption and immobilization mechanisms of CaFe-layered double hydroxide corn straw biochar: Synthesis and application in a combined heavy metal-contaminated environment

Biochar is an emerging eco-friendly and high-efficiency heavy metal (HM) adsorbent that exhibits satisfactory HM remediation effects in both water and soil environments. However, few studies have investigated the mechanisms and application of biochar in the remediation of combined HM-contaminated environments. Therefore, in the present study, a novel corn straw biochar-loaded calcium-iron layered double hydroxide composite (CaFe-LDH@CSB) was synthesized via the coprecipitation method and applied as a remediation adsorbent to remove HMs in both water and soil environments. The results indicated that the HM adsorption mechanism of CaFe-LDH@CSB in the aquatic phase involved a chemical endothermic adsorption process of functional group-complexed monolayers, dominated by precipitation, ion exchange, complexation and π bond interactions. The maximum adsorption capacity for Cd(II), Pb(II), Zn(II) and Cu(II) in the aqueous phase reached 24.58, 240.96, 57.57 and 39.35 mg g−1, respectively. In addition, application of CaFe-LDH@CSB in the combined HM-contaminated soil treatment helped to increase the soil pH, which increased by 5.1–17.9% in low-contamination (LC) soil and by 7.0–13.9% in high-contamination (HC) soil. Moreover, application of CaFe-LDH@CSB effectively decreased the acid-soluble fraction of HMs and increased the HM residual fraction. The immobilization mechanism of CaFe-LDH@CSB in the soil was concluded to involve pore filling, functional group action and electrostatic interactions. Overall, this study provided a novel LDH biochar composite that can be effectively applied in the remediation of combined HM-contaminated water and soil environments.

Enhanced improvement of soda saline-alkali soil by in-situ formation of super-stable mineralization structure based on CaFe layered double hydroxide and its large-scale application

In-situ super-stable mineralization technology with mineralizers (CaSO4, Fe2(SO4)3) and attapulgite (ATP) clay were applied to improve soda saline-alkali soil. The addition of mineralizers and the existence of OH and CO32− in soil resulted in the formation of CaFe-layered double hydroxide (CaFe-LDH) with super-stable mineralization structure (Ksp = 1.512 × 10−61), which was confirmed by the characterization of physicochemical properties and density functional theory (DFT) calculation. The fixation of OH− and CO32− during the formation process of CaFe-LDH led to the transformation of the existing forms of OH− and CO32− in soil from free to stable state, resulting in the permanent decrease of soil pH and CO32− concentration. The effect of ATP clay on the decrease of soluble Na ions in soil through electrostatic attraction and cation exchange was also indicated. Furthermore, mineralizers (1.2 t/ha CaSO4 and 0.75 t/ha Fe2(SO4)3) and ATP clay (1.2 t/ha) were applied to 1.33 ha soda saline-alkali land, and Rumex patientia L. was seeded meanwhile for the identification of improved performance. After five months of improvement, the physical and chemical properties of soil were improved that pH, electrical conductivity (EC), the concentration of CO32− and soluble Na ions, and soil bulk density decreased significantly. In addition, the emergence rate of Rumex patientia L. increased from 0% to 98.3%. All above indicated that in-situ super-stable mineralization technology with the properties of high efficiency, long-term and cost-effective (234.88 $/ha) displays excellent potential in the improvement of soda saline-alkali soil.

Synthesis and Structural Analysis of Ternary Ca–Al–Fe Layered Double Hydroxides with Different Iron Contents

Hydrocalumite structured layered double hydroxides (LDHs) with various Fe3+ ratios were prepared through a coprecipitation method. In order to control the Fe3+ content in LDH, binary Ca–Fe LDHs were first synthesized with various Ca/Fe ratios. The X-ray diffraction pattern showed that only a limited Ca/Fe ratio resulted in LDH formation. The Fe3+ content in LDH was controlled by applying Al3+ while the divalent and trivalent metal ratio was set to 2. Through X-ray diffraction patterns, ternary LDHs with Ca–Al–Fe composition were successfully synthesized without significant impurities, with the Al increasing crystallinity. Quantification showed that Al moiety participated in the formation of the LDH framework more than Ca and Fe, implying a structural stabilization in the presence of Al. In order to investigate the global and local structure of Fe moiety in the LDH, both solid state UV-vis and X-ray absorption spectroscopies were carried out. Both spectroscopies revealed that the existence of Al induced slight local distortion in coordination but global crystal stabilization.

Conventional or mechanochemically-aided intercalation of diclofenac and naproxen anions into the interlamellar space of CaFe-layered double hydroxides and their application as dermal drug delivery systems

The intercalation/encapsulation of the anionic forms of diclofenac and naproxen anti-inflammatory drugs into CaFe-layered double hydroxides (LDHs) were investigated by four techniques. A novel mechanochemically-aided pathway was used and compared to the conventional co-precipitation, direct anion exchange and dehydroxylation-rehydration routes. The evolved average crystal thicknesses (23–35 nm) showed good correlation with the high drug-loading content (26–55% w/w) of the LDH solids. The as-prepared hybrid nanocomposites were studied in detail by X-ray diffractometry, Fourier-transform infrared and Raman spectroscopies, scanning electron microscopy, thermogravimetric and dynamic light scattering analyses. The drug−LDH solids were dispersed in hydrogels and the light microscopic size analysis imaged particles mainly of area between 5 and 10 μm2. In Franz diffusion cells, the in vitro drug release tests (collated by the Korsmeyer–Peppas kinetic model) registered slow release of the organic molecules from the external surface and the interlayer region of the LDH particles highly depending on the applied intercalation techniques. Compared to hydrogels without LDH solids, the liberation of drug molecules were found to be 15–70% slower from their LDH-capsulated forms. Raman mapping of the ex vivo human skin penetration tests visualized the transdermal route of the drug molecules and attested their accumulation in the epidermis and upper zone of the dermis from the LDH − hydrogel preparations.

DESALINATION BEHAVIOR OF NATURAL ZEOLITE IN SEAWATER

In recent years, it has been considered to secure water and food using seawater desalination technology, and a new simple desalination material for reducing high concentration sodium chloride in seawater is required. In this study, desalting agents were prepared from natural zeolite with addition of calcined Ca-Fe type layered double hydroxide (LDH) to desalinate seawater for agricultural use. Mordenite type natural zeolite from Fukushima, Japan was used. The salinity and pH of seawater used in this study were 3.61% and 8.0, respectively. When more than 250 g/L of natural zeolite was added, the salinity decreased from about 3.56% to about 2.92% (reduction : about 18.0%) after stirring for 1 h. With higher dosage of calcined Ca-Fe LDH, the reduction time of salinity and the increase of pH became faster, while the reduction rate of salinity was almost same and pH value increased. When the mixture was used at the mixing ratio of natural zeolite and calcined Ca-Fe LDH was 5:4, the salinity decreased to 1.0% (reduction : about 70.0%) after stirring for 1 h, and the pH of the solution increased to 9.0 - 9.7. Radish sprouts could be harvested using seawater treated with a mixture of natural zeolite and calcined Ca-Fe LDH (5 : 4), while it was not possible to harvest using seawater and seawater treated with natural zeolite with lower addition of calcined Ca-Fe LDH.

Structure-modulated CaFe-LDHs with superior simultaneous removal of deleterious anions and corrosion protection of steel rebar.

The three anionic species; chloride (Cl−), sulfate (SO42−), and carbonate (CO32−), are typical chemical factors that environmentally accelerate failure of concrete structures with steel rebar through long-term exposure. Efficient removal of these deleterious anions at the early stage of penetration is crucial to enhance the lifespan and durability of concrete structures. Here, we synthesize CaFe-layered double hydroxide (CaFe-LDHs) by a simple one-step co-precipitation technique and structural modulation by calcination process. It is applied for the removal of Cl−, SO42−, and CO32− anions as well as corrosion inhibition on steel rebar in aqueous solutions. The synthesized CaFe-LDHs with phase transfer show notable improvement of removal capacity (Qmax) toward Cl− and SO42− over 3.4 times and over 5.69 times, respectably, then those of previous literatures. Furthermore, the steel rebar exposed to an aqueous solution containing the three anionic sources shows a fast corrosion rate (1876.56 × 10−3 mm per year), which can be remarkably inhibited showing 98.83% of corrosion inhibition efficiency when it is surrounded by those CaFe-LDHs. The novel adsorption mechanisms of these CaFe-LDHs-induced crystals and corresponding corrosion protection properties are elucidated drawing on synergy of memory effects and chemical reactions.

PREPARATION OF DESALINATION AGENT FROM CA-TYPE CLAY MINERALS

The desalination technology of seawater is considered to secure water and food in recent years, and a new simple desalting material to decrease the high concentration of sodium chloride in seawater is desired. In this study, preparation of the desalting agent from two Ca-type clay minerals, natural zeolite and Ca-Fe type layered double hydroxide (LDH), attempted to desalinate seawater for agricultural water[1][2][5]. Natural zeolites used in this study were mordenite-type zeolite from Fukushima prefecture, Japan and clinoptilolite-type zeolite from Kagoshima prefecture, Japan, and raw and Ca-substituted zeolites were used for seawater desalination[1][2][3][4][5]. Regardless of zeolite type, desalination behaviors of Ca-substituted zeolite were almost same as those of raw zeolite. The salinity and pH of seawater were 3.46% and 8.0, respectively, while clinoptilolite decreased the salinity to 3.20%, mordenite decreased to 2.09%, above 5.0 g/L zeolite addition. As increasing the Calcined Ca-Fe LDH addition to seawater, the salinity decreased to 3.3%, and pH of the solution increased to pH 11.5, and then became almost constant above 2.0 g/L addition of Calcined Ca-Fe LDH. As increasing the mixing ratio of Calcined Ca-Fe LDH to raw mordenite, the salinity decreased to 0.8% (79.2% reduction) while pH of the solution was neutral (about 7.6~8.0). Radish sprouts could be harvested using the seawater treated with a mixture of raw mordenite-type natural zeolite and Calcined Ca-Fe LDH, although those could not be harvested using seawater, the seawater treated with natural zeolite or Calcined Ca-Fe LDH.

Using Ca[sbnd]Fe layered double hydroxide transformation to optimise phosphate removal from waste waters

Single phase CaFe layered double hydroxide (LDH) minerals containing Cl− species in the interlayer was synthesized by coprecipitation with a CaII: FeIII ratio of 2: 1. In both phosphate (PO4) free water and at low aqueous PO4 concentration, the LDH was fully transformed into a mixture of a “ferrihydrite-like” material, calcite and soluble calcium species. Mössbauer spectroscopy and transmission electron microscopy showed that phosphate was removed by the “ferrihydrite like” phase that contained a significant quantity of Ca. At high phosphate concentration the Ca species released from the LDH precipitated to form hydroxyapatite leading to a maximal removal capacity of ~ 130 mg P-PO4 g−1. The CaFe LDH was deposited onto a pozzolana volcanic rock in order to perform a column experiment under hydrodynamic conditions for 70 days. A high removal capacity was observed, a qB of ~ 4 mg P-PO4 g−1 was measured at the breakthrough of the column, however the pH in the outflow was measured to be higher than 11. Such an increase was due to the very high solubility of the CaFe LDH.

Removal Mechanism of Concrete Deterioration Factor Using Expanded-Cafe Layered Double Hydroxides

The main deterioration factor ions cause corrosion and expansion of concrete with chloride, sulfate and carbonate ions. It is a major problem in field of construction resulting in a huge economic loss, also inducing serious safety disasters frequently. Layered double hydroxides (LDHs) has been successfully used for various purposes owing to its anion-exchange property. Among them, the calcium-based LDHs can improve immobilizing the migration of chloride, sulfate and carbonate ions in cement-based materials. In this study, we will focus on the description of the structural transformation of CaFe LDHs and anion exchange mechanism of immobilizing deterioration factors. The formation of expanded-CaFe LDHs occurred under the calcination conditions (400℃, 550℃ and 700℃, respectively). The characterizations of the expanded-CaFe-LDH after the adsorption was investigated using ion chromatography, x-ray fluorescence, fourier transform infrared spectroscopy, x-ray diffraction, field emission scanning electron microscopy and transmission electron microscope. The adsorption mechanism of ions by the CaFe LDHs related with structure property variation that happens during calcination process.

Structural reconstruction of mechanochemically disordered CaFe-layered double hydroxide

CaFe-layered double hydroxide (CaFe-LDH) was prepared by the co-precipitation technique and was treated mechanochemically in a mixer mill. The impacts of grinding frequency (3–21 Hz) and duration of milling (5–240 min) were mapped to learn about the deterioration steps of the layered structure. The possibility of structural reconstruction of the mechanochemically disordered chloride-containing LDH was tested in distilled water as well as in nitrate-containing aqueous solution. The main methods to follow the deformation and the rearrangement process were X-ray diffractometry and infrared spectroscopy, but electron microscopy techniques and thermal analysis were also applied to better understand and visualize the disruption and reconstitution of the LDH framework.

Effects of ultrasonic irradiation on the synthesis, crystallization, thermal and dissolution behaviour of chloride-intercalated, co-precipitated CaFe-layered double hydroxide

The output power (30–150 W) and the periodicity (20–100%) of ultrasound emission were varied in a wide range to regulate and improve the crystallization process in the commonly used co-precipitation technique of chloride-intercalated CaFe-layered double hydroxides. The influence of ultrasound irradiation on the as-prepared materials was studied by X-ray diffractometry, dynamic light scattering, UV–Vis–NIR diffuse reflectance spectroscopy, specific surface area measurement, pore size analysis, ion-selective electrode potentiometric investigations and thermogravimetry. Additionally, structural alterations due to heat treatment at various temperatures were followed in detail by Fourier-transform infrared and X-ray absorption spectroscopies as well as scanning electron microscopy. The ultrasonic treatment was capable of controlling the sizes of primarily formed (from 19 nm to 30 nm) as well as the aggregated (secondary) particles (between 450 nm and 700 nm), and thus modifying their textural parameters and enhancing the incorporation of chloride anions into the interlamellar space. For the first time, the optical energy gap of CaFe-LDH was reported here depending on the nature of applied stirring (4.18–4.34 eV). The heat-treatment investigations revealed that the layered structure was stabile until 200 °C, even at the atomic level.

Surfactant-modified magnetic CaFe-layered double hydroxide for improving enzymatic saccharification and ethanol production of Artemisia ordosica

The utilization of bio-surfactant rhamnolipid (RL) modified magnetic CaFe-layered double hydroxides (RL-LDH) was successfully carried out to enhance the enzymatic saccharification and ethanol production of Artemisia ordosica (AO). The RL-LDH pretreatment could effectively improve enzymatic hydrolysis of AO. The ethanol yield reached 167.4 mg/g (the reducing sugar yield achieved 540.3 mg/g) when pretreatment pH was 9, RL-LDH to AO mass ratio was 1.5:1, pretreatment time was 1 h, enzymatic hydrolysis temperature was 50 °C, cellulase loading was 50 FPU/g, and simultaneous saccharification and fermentation (SSF) time was 120 h. RL-LDH could stabilize the enzymes and yeast, resulting in increased the reducing sugar and ethanol yields and decreased conversion costs of biofuel. Furthermore, the conversion yields were still higher than that of control group (without RL-LDH) after the RL-LDH was used for 5 times repeatedly. Therefore, utilization of recyclable RL-LDH is promising for future applications in enzymatic hydrolysis and fuel conversion of biomass.

Ultrasonically-enhanced preparation, characterization of CaFe-layered double hydroxides with various interlayer halide, azide and oxo anions (CO32−, NO3−, ClO4−)

An ultrasonically-enhanced mechanochemical method was developed to synthesize CaFe-layered double hydroxides (LDHs) with various interlayer anions (CO32−, NO3−, ClO4−, N3−, F−, Cl−, Br− and I−). The duration of pre-milling and ultrasonic irradiation and the variation of synthesis temperature in the wet chemical step were investigated to obtain the optimal parameters of preparation. The main method to characterize the products was X-ray diffractometry, but infrared and synchrotron-based X-ray absorption spectroscopies as well as thermogravimetric measurements were also used to learn about fine structural details. The synthesis method afforded successful intercalation of the anions, among others the azide anion, a rarely used counter ion providing a system, which enables safe handling the otherwise highly reactive anion. The X-ray absorption spectroscopic measurements revealed that the quality of the interlayered anions could modulate the spatial arrangement of the calcium ions around the iron(III) ions, but only in the second coordination sphere.

Mg–Ca–Fe layered double hydroxide–gold nanoparticles as an efficient electrocatalyst for ethanol oxidation

In this work, the influence of Mg–Ca–Fe layered double hydroxide (LDH) on the electrocatalytic activity of gold nanoparticles (AuNPs) electrodeposited on a glassy carbon electrode for ethanol oxidation in alkaline medium was investigated. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and cyclic voltammetry (CV) were used to characterize the synthesized Mg–Ca–Fe LDH powder and to investigate the electrochemical behaviors of the prepared electrodes. The results showed that the AuNPs/GCE exhibits higher current density for ethanol oxidation (about 2.9 times) and higher active surface area (about 2.5 times), after the deposition of the Mg–Ca–Fe LDH on its surface. It was also found that the ethanol oxidation reaction at the LDH/AuNPs/GCE is an adsorption-controlled process, while at the AuNPs/GCE it is a diffusion-controlled process. The investigation of the long-term stability of the electrodes using CV and chronoamperometry methods indicated that the Mg–Ca–Fe LDH by providing OHads species at the surface of the catalyst improves the endurance of the AuNPs against poisoning effects of intermediate species. Accordingly, the Mg–Ca–Fe LDH can be used to improve the electrocatalytic performance of supported AuNPs in the anode of alkaline ethanol fuel cells.

Mechanochemical synthesis and intercalation of Ca(II)Fe(III)-layered double hydroxides

A mechanochemical method (grinding the components without added water – dry grinding, followed by further grinding in the presence of minute amount of water or NaOH solution – wet grinding) was used in this work for the preparation and intercalation of CaFe-layered double hydroxides (LDHs).Both the pristine LDHs and the amino acid anion (cystinate and tyrosinate) intercalated varieties were prepared by the two-step grinding procedure in a mixer mill. By systematically changing the conditions of the preparation method, a set of parameters could be determined, which led to the formation of close to phase-pure LDH. The optimisation procedure was also applied for the intercalation processes of the amino acid anions. The resulting materials were structurally characterised by a range of methods (X-ray diffractometry, scanning electron microscopy, energy dispersive analysis, thermogravimetry, X-ray absorption and infra-red spectroscopies). It was proven that this simple mechanochemical procedure was able to produce complex organic–inorganic nanocomposites: LDHs intercalated with amino acid anions.

Removal behavior research of orthophosphate by CaFe-layered double hydroxides

The different removal behavior of orthophosphate (OP) over the CaFe-layered double hydroxides (CaFe-LDH) was investigated. The results displayed that the existence of Ca2+ in the solution could promote the phosphorus removal, the removal efficiency could reach 100% with 1.473 mmol P/g LDH. The kinetics fitting parameters showed that the removal process of OP was in accordance with the secondary dynamic equation, and it changed from the homogeneous reaction to heterogeneous reaction according to Elovich equation. Moreover, Freundlich isothermal adsorption equation preferably described the removal process of OP, indicated that it was a complicated process including physical and chemical adsorption. The main removal mechanism was the formation of hydroxyapatite by PO43- and Ca2+ dissolved from LDHs, and ferrihydrite could also strengthen the OP removal effect via the formation of surface complexes.