Maximum Phosphate Adsorption Capacity Research Articles

Synthesis of Fe/Mg-Biochar Nanocomposites for Phosphate Removal.

Magnetic biochar derived from agricultural biomass has been recognized as a cost-effective biochar sorbent for phosphate removal. This study evaluated the use of novel Fe/Mg-biochar nanocomposites (WBC1x), prepared by impregnating ground walnut shell in a solution with a different molar ratio of Fe2+ to Mg2+, then pyrolyzing slowly, at a temperature of 600 °C, to remove phosphate. The results showed that MgO and Fe3O4 were loaded onto the biochar successfully through the impregnation-pyrolysis method and the composites were able to be separated easily by magnetic field. Meanwhile, a higher surface area and point of zero charge on WBC1x were observed compared to the non-magnetic biochar (WBC). Moreover, the isothermal adsorption and kinetics data further suggested the that phosphate adsorption onto WBC1x resulted from chemisorption. Additionally, the maximum phosphate adsorption capacity of WBC1x was 6.9 mg.g−1, obtained though the Langmuir–Freundlich model, which was threefold higher than WBC, where MgO addition could enhance the adsorption capacity of WBC1x markedly by improving the surface charge.

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

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

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

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

Phosphogypsum as a novel modifier for distillers grains biochar removal of phosphate from water

A novel biochar composite was fabricated via the pyrolysis of distillers grains treated phosphogypsum for phosphate removal from water. Batch adsorption experiments were performed on the adsorption characteristics of phosphate. Effects of pyrolysis temperature, solution pH, the dosage of adsorbent, ambient temperature on phosphate adsorption were also investigated. The results demonstrated that the optimum initial solution pH for phosphate adsorption was 6.0, and high pyrolysis temperature was favorable for phosphate adsorption. The optimal dosage of biochar was 1.25 g L−1. A pseudo-second-order kinetic model can well explain the adsorption kinetics, indicative of the energetically heterogeneous solid surface of the composite. The maximum phosphate adsorption capacity of the phosphogypsum modified biochar obtained from Langmuir isotherm reached 102.4 mg g−1 which was almost five times that of distillers grains biochar alone (21.5 mg g−1). The mechanism is mainly attributed to electrostatic adsorption, surface precipitation and ligand exchange. The ideal adsorption performance indicated that biochar supported phosphogypsum can be used as high-quality adsorbent for phosphate removal in wastewater treatment.

Removal of phenol and phosphate from aqueous solutions using activated carbons prepared from oily sludge through physical and chemical activation.

Preparation and characterization of activated carbons (ACs) from oily sludge by physical and chemical activation using steam, ZnCl2 and FeCl3 were investigated. The characteristics of produced adsorbents were determined by iodine number, Brunauer-Emmett-Teller (BET) equation, Fourier transform infrared spectrometry and scanning electron microscopy analyses. Batch adsorption experiments for phenol and phosphate were performed to evaluate the efficiency of adsorbents. The optimum porous structure of adsorbents with a BET surface area of 1,259 m2 g-1, total pore volume of 1.22 cm3 g-1 and iodine number of 994 mg g-1 was achieved by ZnCl2 activation at 500 °C and impregnation ratio of 1:1. The adsorption data were well fitted to the pseudo-second-order kinetic model (R2>0.99) and Freundlich isotherm (R2>0.99). The maximum adsorption capacity of phenol (238 mg g-1) and phosphate (102 mg g-1) based on the Langmuir model was achieved at pH of 6.0 and adsorbent dose of 1 g L-1. Thermodynamic parameters were negative and showed that adsorption of phenol and phosphate onto the AC was feasible, spontaneous and exothermic. The results suggested that prepared AC was an effective adsorbent for removal of phenol and phosphate ions from the polluted water.

Biochar from microwave pyrolysis of rice husk for tertiary wastewater treatment and soil nourishment

Abstract The present study investigated the potential tertiary treatment of wastewater by adsorption using rice husk biochar (RHC) obtained from microwave pyrolysis of rice husk. Adsorption experiments with RHC indicated phosphate and nitrate adsorption of 65% and 75% respectively. The adsorption kinetics indicated pseudo-second-order adsorption model for adsorption of nutrients on biochar with an R2 value more than 0.98. In addition, the Langmuir-Freundlich isotherm was observed to represent the adsorption of phosphate on RHC, whereas adsorption data of nitrate depicted Langmuir isotherm followed by Temkin and Dubinin-Radushkevich isotherms. The maximum phosphate and nitrate adsorption capacity were 71 mg/kg and 497 mg/kg respectively using Langmuir isotherm model. The desorption study indicated a release of 96.6% and 44.4% of adsorbed phosphate and nitrate, respectively. Hence, from 1 kg of nutrient loaded RHC about 68 mg of phosphate and 220 mg of nitrate can be extracted for land application.

Tracking Internal Electron Shuttle Using X-ray Spectroscopies in La/Zr Hydroxide for Reconciliation of Charge-Transfer Interaction and Coordination toward Phosphate.

Metallic hydroxides have been applied as the adsorbents of oxyanion contaminants, with the oxygen-bonded metal (M-O) considered as the core site for adsorption. For enhanced adsorption toward oxyanions, multimetallic modification of M-O is a promising approach for high removal performance. Here, bimetallic La/Zr hydroxides were prepared via a solvothermal route with varying La/Zr dosages. Bimetallic La/Zr hydroxides exhibited higher oxyanion adsorption capacity than La or Zr hydroxide. A maximum phosphate adsorption capacity of ∼160 mg g-1 was achieved under the La/Zr atomic ratio of 1:1, representing a new record among comparable adsorbents. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy showed that the incorporation of [LaO6] and [ZrO6] can induce an internal charge shuttle owing to the electronegativity difference of La and Zr. The charge transfers from La to Zr through the surrounding O 2p ligand, where the electrons in the highest occupied molecular orbitals of the [LaO6] octahedron filled unoccupied π orbitals of [ZrO6]. The as-induced internal electron shuttle in the bimetallic hydroxides primarily strengthened the formation of [MO6]···PO4 species (backdonation interaction). Further, the σP-O donation interaction between [LaO6] and [PO4] was clearly increased via intensification of the covalent coordination with O, as confirmed by the P K-edge XANES spectra for the as-used samples.

La2O3-modified MCM-41 for efficient phosphate removal synthesized using natural diatomite as precursor.

In this study, an ordered mesoporous silica modified with lanthanum oxide was synthesized using diatomite as silica source and applied for adsorption of phosphate from aqueous solution. By taking cost-effectiveness for practical application into consideration, the adsorbent with a theoretical La/SiO2 molar ratio of 0.2 (La0.2M41) possessed a promising performance. In the batch adsorption tests, the adsorbents with La2O3 loading possessed markedly enhanced adsorption capacities. Phosphate uptake by La0.2M41 was pH-dependent with the highest sorption capacities observed over a pH range of 3.0-6.0. Coexistent anions displayed an adverse effect on phosphate adsorption following the order of CO3 2- > F- > NO3 - > Cl- > SO4 2-. In the kinetic study, phosphate adsorption onto La0.2M41 followed the pseudo-second-order equation better than the pseudo-first-order, suggesting chemisorption. The Langmuir isothermal model well described the adsorption isotherm data, showing a maximum adsorption capacity for phosphate of up to 263.16 mg/g at 298 K. In a real treated wastewater effluent with phosphate concentration of 2.5 mg P/L, La0.2M41 efficiently reduced the phosphate concentration to 28 µg P/L.

Phosphate Removal from Secondary Effluents Using Coal Gangue Loaded with Zirconium Oxide

Phosphorus from secondary effluents and coal gangue from coal mining have caused serious environmental problems. The feasibility of phosphate removal from secondary effluents using calcinated coal gangue loaded with zirconium oxide (CCG-Zr) was explored. Major influencing factors like the calcinated temperature, CCG-Zr ratio, adsorbent dose, time and solution pH, etc. were investigated. Newly developed CCG-Zr accomplished a significantly higher phosphate removal for phosphate (93%) compared with CCG (35%) at a calcinated temperature of 600 °C and CCG-Zr mass ratio of 1:1. For CCG-Zr the maximum phosphate removal rate (93%) was noted at an initial phosphate concentration of 2 mg/L within 20 min. The CCG-Zr displayed a higher phosphate removal rate (85–98%) over a wide range of solution pH (2.5~8.5). The adsorption isotherms fitted better to the Freundlich (R2 = 0.975) than the Langmuir model (R2 = 0.967). The maximum phosphate adsorption capacity of the CCG-Zr was 8.55 mg/g. These results suggested that the CCG-Zr could potentially be applied for the phosphate removal from secondary effluents.

La-modified ZSM-5 zeolite beads for enhancement in removal and recovery of phosphate

Abstract ZSM-5 zeolite beads (ZB) modified with lanthanum (La) were prepared by impregnating ZB in a lanthanum nitrate solution (denoted as La-ZB). La-ZB was characterized via SEM, BET, ICP-OES and XRD techniques, which confirmed the doping of La on the surface of the ZB. The surface area and pore volume of La-ZB decreased marginally after the La-modification due to a partial pore blockage by the La dopant. La-ZB showed an improved phosphate adsorption compared to ZB, and the maximum phosphate adsorption capacities by ZB and La-ZB (determined by Langmuir isotherm) were 59.8 and 106.2 mg/g, respectively. Moreover, the adsorption kinetics proceeded according to the mechanism of the pseudo-second-order model. The phosphate adsorption by La-ZB exhibited an optimum at pH 6. In regeneration process of phosphate-loaded La-ZB, five times adsorption-desorption cycles were applied and 81.8% phosphate was recovery. In a test using wastewater containing a high phosphate concentration (218.6 mg/L), La-ZB exhibited 96.8% phosphate removal, which is 1.8 times higher than that of ZB (53.5%). The results indicate that La-ZB can be a promising recyclable adsorbent for the removal and recovery of phosphate from wastewater.

Removal of phosphate and nitrate ions from aqueous solution using La3+ incorporated chitosan biopolymeric matrix membrane

The present investigation was carried out for the removal of phosphate and nitrate ions from aqueous solution using lanthanum incorporated chitosan membrane (La@CS) prepared by casting method. Systematic adsorption studies were performed by varying the influencing parameters like contact time, dosage, pH, interfering anions and temperature were optimized for the maximum phosphate and nitrate adsorption capacities. The adsorption equilibrium process was examined by Freundlich, Langmuir and Dubinin-Radushkevich isotherm models. The La@CS membrane showed an adsorption capacity of 76.6 and 62.6 mg/g for phosphate and nitrate ions respectively. Thermodynamic parameters such as ∆G°, ∆H° and ∆S° were calculated to understand the nature of adsorption. The synthesized La@CS membrane was characterized by FTIR, SEM, EDAX with mapping analysis, XRD, AFM, TGA-DSC and zero point charge analysis. The possible adsorption mechanism was found to be electrostatic attraction as well as by ion exchange between La@CS membrane and both anions like phosphate and nitrate. The experimental results clearly indicated that the prepared La@CS membrane could be utilized for the removal of phosphate and nitrate ions from aqueous solution.

Removal of phosphate from aqueous solution by a novel Mg(OH)2/ZrO2 composite: Adsorption behavior and mechanism

In this work, Mg(OH)2 was incorporated into ZrO2 to obtain a novel Mg(OH)2/ZrO2 composite (MZ) by a simple co-precipitation method for phosphate adsorption. For comparison purpose, pure ZrO2 and Mg(OH)2 were also fabricated. The as-prepared MZ, ZrO2 and Mg(OH)2 were characterized by SEM, EDS, N2 adsorption/desorption and pHPZC, and their phosphate adsorption properties were comparatively investigated in batch mode. The MZ samples before and after phosphate adsorption were characterized by XPS, and the phosphate-adsorbed MZ was characterized by 31P NMR. The results showed that MZ was mainly composed of ZrO2 and Mg(OH)2. In addition, MZ had a larger specific surface area than single-component ZrO2 and Mg(OH)2. MZ exhibited a much higher affinity towards phosphate in aqueous solution than pure ZrO2 and Mg(OH)2. The Langmuir maximum phosphate adsorption capacity of MZ was 87.2 mg PO4/g at initial pH 7, which was 84% and 4.3 times higher than those of single-component ZrO2 and Mg(OH)2, respectively. Phosphate was adsorbed onto the MZ surface mainly via a ligand exchange between the ZrO2 phase and phosphate forming inner-sphere phosphate complexes as well as the reaction between the Mg(OH)2 phase and phosphate forming Mg-P compounds such as MgHPO4 and Mg3(PO4)2. The enhanced phosphate adsorption by the incorporation of Mg(OH)2 into ZrO2 could be attributed to: (i) the increase in the specific surface area of the adsorbent material; and (ii) the enhanced adsorption of phosphate on the ZrO2 component by the presence of Mg2+ that was dissolved from the Mg(OH)2 component. Results of this work indicate that MZ is a more promising adsorbent for the removal of phosphate from wastewater than Mg(OH)2 and ZrO2.

Adsorption Behavior of Phosphate from Water on Zirconium-loaded Granular Zeolite-amended Sediment

In this study, a zirconium-loaded granular zeolite (ZrGZ) was prepared, characterized and used as a sediment amendment to control internal phosphorus (P) loading in water samples from a heavily polluted river. The adsorption characteristics of phosphate on ZrGZ-amended sediment were investigated using batch experiments, and the stability of P in phosphate-adsorbed ZrGZ was evaluated using a sequential chemical extraction method. Results showed that the Langmuir isotherm model was more suitable for describing the equilibrium adsorption data of phosphate on ZrGZ-amended sediment than the Freundlich and Dubinin-Radushkevich isotherm models. The adsorption process of phosphate on ZrGZ-amended sediment could be well described by the pseudo-second-order and Elovich kinetic models, and both film and intra-particle diffusion controlled the adsorption rate during the gradual adsorption stage. The coexistence of SO42- and HCO3- inhibited the adsorption of phosphate on ZrGZ-amended sediment, while coexisting Na+, K+, Mg2+ and Ca2+ enhanced the phosphate adsorption, and this promoting effect decreased in the order of Ca2+ > Mg2+ > Na+/K+. The ZrGZ-amended sediment exhibited a higher phosphate adsorption capacity than the unamended sediment, and the maximum phosphate adsorption capacity derived from the Langmuir isotherm model was found to be 336 mg·kg-1, which was higher than that for the unamended sediment (215 mg·kg-1). Sequential tests showed that P in phosphate-adsorbed ZrGZ mainly existed in the form of NaOH-rP and Res-P, which was relatively unreactive. These results indicated that ZrGZ addition enhanced the phosphate adsorption capacity of river sediment, and that ZrGZ was a promising amendment for controlling the release of P from river sediment.

Adsorption for phosphate by crosslinked/non-crosslinked-chitosan-Fe(III) complex sorbents: Characteristic and mechanism

Fe(III)-doped chitosan (CTS-Fe) and crosslinked Fe(III)-chitosan (CTS-Fe-CL) composites were developed for the removal of phosphorus from aqueous solution. The characteristics of adsorbents, performance on adsorption and pathway of phosphate transformation were investigated in batch studies. The SEM images and hardness tests showed that CTS-Fe-CL exhibited a three-layer structure with well-developed pore size, while CTS-Fe had more compact structure and stronger strength than CTS-Fe-CL. The low pH value was favorable for the adsorption of phosphate on the chitosan-Fe complex. Moreover, raw CTS-Fe showed better adsorption capacity than after crosslinking in a wide pH range. XPS and FTIR analyses demonstrated that under acidic conditions, the route of the adsorption process was the reaction between phosphate and functional groups (NH2 and NH3+) by electrostatic attraction and iron hydrolysates by ligand exchange, respectively. In addition, Fe(III) could release large quantities of hydrogen ions during the hydrolysis reaction process, which could enhance the protonation and electrostatic attraction under acidic conditions. Owing to the increase of challenging OH− ions, the electrostatic attraction weakened and ligand exchange was the dominant mechanism for phosphate adsorption under alkaline conditions. Moreover, the maximum phosphate adsorption capacity for CTS-Fe and CTS-Fe-CL was 15.7 and 10.2 mg-P g−1 at 303 K, respectively. The present study revealed the phosphate adsorption mechanism on Fe-modified chitosan under different pH conditions.

ZrO2 nanoparticles confined in metal organic frameworks for highly effective adsorption of phosphate

Highly dispersed ZrO2 particles confined in the MIL-101 (denoted as MIL-101@Zr(DS)) with varied ZrO2 loading amounts were prepared by the double solvents method. For comparison, ZrO2 loaded MIL-101 samples were synthesized by the conventional impregnation method (denoted as MIL-101@Zr(I)) and the deposition method (denoted as MIL-101@Zr(D)). The characterization results indicated that for MIL-101@Zr(DS), ZrO2 particles were dominantly confined in MIL-101 with a much higher dispersion as compared with MIL-101@Zr(I) and MIL-101@Zr(D). The maximum phosphate adsorption capacity and ZrO2 content normalized phosphate adsorption capacity of the MIL-101@Zr(DS) were 21.28 mg P·g−1 and 1120.0 mg P·g−1, respectively. Additionally, the ZrO2 content normalized phosphate adsorption capacity was significantly larger than that for MIL-101@Zr(I) and MIL-101@Zr(D) as well as the reported values for other Zr-based adsorbents. The effects of solution chemistry on phosphate adsorption to MIL-101@Zr(DS), MIL-101@Zr(I) and MIL-101@Zr(D) were also examined. Compared with MIL-101@Zr(I) and MIL-101@Zr(D), the adsorption of phosphate on MIL-101@Zr(DS) was less affected by the coexistence of anions and dissolved humic acid. Increasing pH from 3 to 12 led to decreased phosphate adsorption capacity of MIL-101@Zr(DS) from 10.38 mg P·g−1 to 2.03 mg P·g−1. Accordingly, used MIL-101@Zr(DS) could be effectively regenerated under alkaline conditions and exhibited stable adsorption-desorption performance.

Surface-Engineered Blood Adsorption Device for Hyperphosphatemia Treatment.

Correspondence: Melanie S. Joy, PharmD, PhD, University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences, Department of Pharmaceutical Sciences, Mail Stop C238, Room V20-4108, 12850 East Montview Blvd, Aurora, CO 80045. Email: Melanie.Joy@ucdenver.edu The research employed surface engineering methods to develop, optimize, and characterize a novel textile-based hemoadsorption device for hyperphosphatemia in hemodialysis-dependent end-stage kidney disease. Phosphate adsorbent fabrics (PAFs) were prepared by thermopressing alumina powders to polyester filtration fabrics and treatment with trimesic acid (TMA). For static experiments, phosphate adsorption capacity in buffer solution, plasma, and blood were evaluated by submersing the PAFs in 100 ml. For dynamic experiments, PAFs were equipped in a device prototype and incorporated in a pump-driven circuit. Phosphates were determined by a colorimetric assay and an Ortho Clinical Diagnostics Vitros 5600 Integrated analyzer. The maximum loading amount of TMA-alumina on PAFs was approximately 35 g/m under 260°C processing temperature. Phosphate adsorption capacity increased with initial concentration. Adsorption isotherms from buffer demonstrated a maximum phosphate adsorption capacity of approximately 893 mg/m at 37.5°C, pH 7.4, with similar results from plasma and whole blood. Measured phosphate concentrations during simulations demonstrated a 42% reduction, confirming the high capacity of the PAFs for removing phosphate from whole blood. Results from the current study indicated that an alumina-TMA treated PAF can dramatically reduce phosphate concentrations from biological samples. The technology could potentially be used as a tunable adsorbent for managing hyperphosphatemia in kidney disease.

Effect of precipitation pH and coexisting magnesium ion on phosphate adsorption onto hydrous zirconium oxide.

To understand the effect of precipitation pH and coexisting Mg2+ on phosphate adsorption onto zirconium oxide (ZrO2), ZrO2 particles precipitated at pH 5.3, 7.1 and 10.5, i.e., ZrO2(5.3), ZrO2(7.1) and ZrO2(10.5), respectively were prepared and characterized, then their adsorption performance and mechanism in the absence and presence of Mg2+ were comparatively investigated in this study. The results showed that the Elovich, pseudo-second-order and Langmuir isotherm models correlated with the experimental data well. The adsorption mechanism involved the complexation between phosphate and zirconium. Coexisting Mg2+ slightly inhibited the adsorption of phosphate on ZrO2(5.3), including the adsorption capacity and rate, but coexisting Mg2+ greatly increased the adsorption capacity and rate for ZrO2(7.1) and ZrO2(10.5). The enhanced adsorption of phosphate on ZrO2(7.1) and ZrO2(10.5) in the presence of Mg2+ was mainly due to the formation of Mg2+-HPO42- ion pair (MgHPO40) in the solution and then the adsorption of MgHPO40 on the adsorbent surface, forming the phosphate-bridged ternary complex Zr(OPO3H)Mg. In the absence of Mg2+, the maximum phosphate adsorption capacity at pH 7 calculated from the Langmuir isotherm model decreased in the order of ZrO2(7.1) (67.3 mg/g) > ZrO2(5.3) (53.6 mg/g) ≈ ZrO2(10.5) (53.1 mg/g), but it followed the order of ZrO2(7.1) (97.0 mg/g) > ZrO2(10.5) (79.7 mg/g) > ZrO2(5.3) (51.3 mg/g) in the presence of Mg2+. The results of this work suggest that ZrO2(7.1) is more suitable for use as an adsorbent for the effective removal of phosphate from municipal wastewater than ZrO2(5.3) and ZrO2(10.5), because Mg2+ is generally present in this wastewater.

Effect of pre-treatment of bentonite with sodium and calcium ions on phosphate adsorption onto zirconium-modified bentonite

To understand the influence of the pre-treatment of bentonite with Na+ and Ca2+ on the adsorption of phosphate on zirconium-modified bentonite, three kinds of adsorbent materials including zirconium-modified raw, Na+-pretreated and Ca2+-pretreated bentonites were synthesized and characterized firstly, and afterward their adsorption performance and mechanism for phosphate were studied comparatively. The phosphate adsorption ability for zirconium-modified bentonite decreased after the pre-treatment of bentonite with Na+, but it increased after the pre-treatment of bentonite with Ca2+. The maximum phosphate adsorption capacity calculated from the Langmuir isotherm model for zirconium-modified Ca2+-pretreated bentonites (13.4 mg P/g) was much higher than that for the zirconium-modified raw bentonite (9.06 mg P/g). The pre-treatment of bentonite with Na+ and Ca2+ did not change the interaction type between zirconium-modified bentonite and phosphate, i.e., the coordination of phosphate to zirconium. The decreased phosphate adsorption capacity for zirconium-modified bentonite induced by the Na+ pre-treatment could be mainly attributed to the decrease of the specific surface area and the content of exchangeable Ca. The increased phosphate adsorption capacity for zirconium-modified bentonite induced by the Ca2+ pre-treatment could be mainly due to the increase in the amount of exchangeable Ca. Results of this work suggest that the zirconium-modified Ca2+-pretreated bentonite is more suitably used as an adsorbent for the removal of phosphate from wastewater than the zirconium-modified raw and Na+-pretreated bentonites.

Synergetic effects of anhydrite and brucite-periclase materials on phosphate removal from aqueous solution

The objectives of this study were to prepare brucite-periclase material (BPM), and a cost-effective anhydrite-BPM sorbent (ABPM) for the removal of phosphate. The samples were characterized by X-Ray Diffraction (XRD), X-ray fluorescence (XRF), BET surface area, scanning electron microscope (SEM), and transmission electron microscope (TEM). The characterization results show that the BPM was successfully prepared after calcination and hydration, with flaky structure transforming into ellipsoidal structural aggregation. The effects of mixed mass ratios, reaction time, pH, co-existing anions, humid acid and initial phosphate concentration on phosphate removal were investigated by batch experiments. The kinetic adsorption process was well described by pseudo-second-order model with high correlation coefficient (R2 > 0.99). The Langmuir model provided a better described for the adsorption process than the Freundlich model. The maximum phosphate adsorption capacity was 23.66, 24.96 and 26.14 mg·g−1 at 298 K, 303 K and 308 K, respectively, with a 99% removal rate. The P concentration after adsorption was lower than 0.1 mg∙L−1 when the initial P concentration was 10 mg∙L−1.The significant synergetic effects of BPM on anhydrite were observed: firstly, the significant improvement of phosphate removal rate (99.28%) of ABPM can be observed, compared with anhydrite (1.26%) and BPM (45.10%); secondly, a special sustained-release effect was described by the Stumm kinetic mode and an alkaline environment was proved to be made by BPM; finally, the adsorption and precipitation sites were provided by BPM. Thus, the mechanism of phosphorus removal is suggested by two steps: chemical adsorption and Ca-phosphate precipitation. Firstly, the phosphate adsorbed on the BPM by chemical adsorption as the precursor; secondly, the amorphous calcium phosphate compounds formed as the precursors of hydroxyapatite and the phosphate was immobilized by chemical precipitation.

Selective recovery of phosphorus from acid leach liquor of iron ore by garlic peel adsorbent.

Dephosphorisation of iron ore is an important challenge to the sustainable development of iron-making industry. Hydrometallurgical processing is quite effective in the reduction of phosphorus level from iron ores, where dilute sulfuric acid is commonly chosen as the lixiviant due to its prominent cost-effectiveness. A cheap and effective biosorbent synthesized from garlic peel was proposed in present study to recover phosphorus selectively from acid leach liquor directly under acidic conditions near pH 1–2, allowing high purity phosphorus to be recovered and the residual acid to be recycled for the next round of leaching. This proposal would sharply reduce the dephosphorisation costs of iron ore. Various batch experiments were carried out under different conditions including varying pH, contact time, adsorbent dosages, and metal ion concentration to identify the optimal adsorption parameters for the model solutions. Results showed that the optimal pH for phosphate adsorption was around 1.5 and adsorption equilibrium was attained in 240 min, and the maximum adsorption capacity for phosphate was 1.40 mmol g−1 and 0.81 mmol g−1 at equilibrium pH of 1.5 and 6.5, respectively. A NaOH solution was effective to elute the adsorbed phosphate, and the eluted solution contained mainly Na3PO4 and NaOH. Recovery of phosphorus from the iron ore leach liquor by the garlic peel adsorbent was quite effective, and the adsorption efficiency could retain 85% of the original adsorption capability even after five cycles of adsorption and desorption. In summary, the Zr-loaded garlic peel appears a potential low-cost and effective adsorbent for phosphate recovery from the acid leach liquor of high phosphorus iron ore.