Mechanism Of Phosphate Adsorption Research Articles

Phosphate Adsorption Site on Zirconium Ion Modified MgAl-layered Double Hydroxides

The structure of Zr modified MgAl layered double hydroxide (Zr–MgAl-LDH) was investigated by means of X-ray diffraction and Zr–K edge X-ray absorption experiments, and the mechanism of phosphate adsorption from phosphate-enriched seawater was considered. The Zr–MgAl-LDH consists of binary MgAl-LDH and amorphous ZrO2, which has a relation to its superior phosphate adsorption property.

A study of phosphate absorption by magnesium iron hydroxycarbonate

A study of the mechanism of phosphate adsorption by magnesium iron hydroxycarbonate, [Mg(2.25)Fe(0.75)(OH)(6)](CO(3))(0.37).0.65H(2)O over a range of pH has been carried out. The efficiency of the phosphate removal from aqueous solution has been investigated between pH 3-9 and the resulting solid phases have been studied by elemental analysis, XRD, FT-IR, Raman, HRTEM, EDX and solid-state MAS (31)P NMR. The analytical and spectroscopic data suggest that phosphate removal from solution occurs not by anion intercalation of the relevant phosphorous oxyanion (H(2)PO(4)(-) or HPO(4)(2-)) into the LDH but by the precipitation of either an insoluble iron hydrogen phosphate hydrate and/or a magnesium phosphate hydrate.

Characteristics and mechanisms of phosphate adsorption onto basic oxygen furnace slag

The adsorption characteristics of phosphate adsorption on the basic oxygen furnace (BOF) slag were identified as a function of pH and ion strengths in solution. In addition, adsorption mechanisms were investigated by conducting batch tests on both the hydrolysis and phosphate adsorption process of the BOF slag, and making a comparative analysis to gain newer insights into understanding the adsorption process. Results show that the adsorption capacity from 4.97 to 3.71 mg P/g slag when the solution pH was increased from 2.0 to 13.0 and phosphate initial concentration was 50 mg/L, indicating that adsorption capacity is largely dependent upon the pH of the system. The results of the competitive adsorption between phosphate and typical anions found in wastewater, such as NO 3 −, SO 4 2− and Cl −, onto BOF slag reveal that BOF slag can selectively adsorb phosphate ions. The insignificant effect of NO 3 −, SO 4 2− and Cl − on phosphate adsorption capacity indicates that phosphate adsorption is through a kind of inner-sphere complex reaction. During the adsorption process, the decrease of phosphate concentration in solution accompanied with an increase in pH values and concentrations of NO 3 −, SO 4 2− and Cl − suggests that phosphate replaced the functional groups from the surface of BOF slag which infers that ligand exchange is the dominating mechanism for phosphate removal. At the same time, the simultaneous decreases in PO 4 3− and total calcium, magnesium and aluminum concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.

Relationship between Anion Adsorption and Physicochemical Properties of Aluminum Oxide

This study investigated the adsorption capacity and adsorption mechanism of phosphate by calcined aluminum oxide (GB) at temperatures of 200 to 1150°C. The results showed that GB and GB calcined at a temperature of 200°C exhibited almost no adsorption capacity, and GB calcined at temperatures of 300 or 400°C exhibited the highest adsorption capacity. After that, adsorption capacity tended to decrease with increasing calcination temperature. The specific surface area and the concentration of surface hydroxyl groups exhibited the highest values in GB calcined at temperatures of 300 and 400°C. From the above facts, it is conjectured that the specific surface area and concentration of surface hydroxyl groups contribute to the adsorption of phosphate in calcined GB. The results of X-ray diffraction showed that the structure of GB changed drastically at temperatures of 200 to 300°C and 900 to 1000°C. Also, it was evident that phosphate was adsorbed selectively even in complex solution systems containing chloride, nitrate, sulfate, hydrogen carbonate and phosphate ions, and that calcined GB is suitable for adsorption of phosphate. For the adsorption of phosphate, it was found that the optimum pH is around 4. When calcined GB is suspended in purified water, it is thought that hydroxyl groups form through dissociative adsorption with water molecules, and that these hydroxyl groups conduct ion exchange with phosphate.

Characteristics and mechanisms of phosphate adsorption on dewatered alum sludge

The adsorption characteristics of phosphate adsorption on the dewatered alum sludge were identified as a function of pH and ion strengths in solution. In addition, adsorption mechanisms were investigated by conducting batch tests on both the hydrolysis and P-adsorption process of the alum sludge, and making a comparative analysis to gain newer insights into understanding the adsorption process. Results show that the adsorption capacity decreased from 3.5 to 0.7 mg P/g sludge when the solution pH was increased from 4.3 to 9.0, indicating that adsorption capacity is largely dependent upon the pH of the system. The results of the competitive adsorption between phosphate and typical anions found in wastewater, such as SO 4 2− and Cl −, onto alum sludge reveal that alum sludge can selectively adsorb phosphate ions. The insignificant effect of SO 4 2− and Cl − on P-adsorption capacity indicates that phosphate adsorption is through a kind of inner-sphere complex reaction. During the adsorption process, the decrease of phosphate concentration in solution accompanied with an increase in pH values and concentrations of SO 4 2−, Cl − and TOC (total organic carbon) suggests that phosphate replaced the functional groups from the surface of alum sludge which infers that ligand exchange is the dominating mechanism for phosphate removal. At the same time, the simultaneous decreases in PO 4 3− and total aluminium concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.

ATR–FTIR Spectroscopic Investigation on Phosphate Adsorption Mechanisms at the Ferrihydrite–Water Interface

We investigated the phosphate(P) adsorption mechanisms at the ferrihydrite–water interface as a function of pH, ionic strength (I), and loading level, using a combination of adsorption envelopes, electrophoretic mobility (EM) measurements, and attenuated total reflectance Fourier transform infrared (ATR–FTIR) spectroscopy. The P adsorption envelopes show that: (1) adsorption decreases with increasing pH 3.5–9.5 and (2) adsorption is insensitive to changes in I at pH 4–7.5, but it slightly increases with increasing I from 0.01 to 0.8 at pH>7.5. The EM in 0.1 M NaCl decreases with increasing P concentration from 0 to 50 μmol L−1 at pH 3–9. The results of these macroscopic studies suggest the formation of inner-sphere complexes. The ATR–FTIR investigation shows that inner-sphere surface complexes are nonprotonated, bidentate binuclear species (≡Fe2PO4) at pH≥7.5 and could be associated with Na+ ions at P loading levels of 0.38 μmol m−2. At pH 4–6, protonated inner- sphere complexes are proposed at the loading levels between 0.38 and 2.69 μmol m−2.

Kinetics of phosphate adsorption on iron oxides formed under the influence of citrate

The influence of organic acids on the formation of Fe oxyhydroxides and oxides has been intensively studied. However, scant attention has been paid to the subsequent effect on surface chemistry of the Fe oxides formed. The kinetics and mechanisms of phosphate adsorption by the Fe oxides formed in the presence of citrate ligands at initial citrate/Fe(II) molar ratios (MR) of 0, 0.001, 0.01, and 0.1 were investigated using the conventional batch method. The adsorption studies were conducted at the initial phosphate concentration of 0.5 mM and pH 4.0 during the reaction period from 2 min to 56 h at 278, 288, 298, and 313 K. The results show that the phosphate adsorption followed multiple second-order kinetics and had two distinct rates in each reaction system. The amount, rate coefficient, activation energy and pre-exponential factor of phosphate adsorption by the Fe oxides formed greatly varied with their structural and surface properties. These properties, which included crystal structure, specific surface area, surface porosity, surface geometry, and point of zero salt effect (PZSE), differed significantly with the initial citrate/Fe(II) MR at which Fe oxides were formed. The results of this study have cast the light on the role of organic acids such as citric acid in influencing the surface chemistry of naturally occurring Fe oxides through fundamental structural perturbation and the impact on the dynamics of phosphate in terrestrial and aquatic environments. Key words: Kinetics, activation energy, pre-exponential factor, phosphate, iron oxides, citric acid, structural perturbation

Mechanism of Phosphate Adsorption to a Three-Dimensional Structure of Boehmite in the Presence of Bovine Serum Albumin

A new microcrystalline boehmite (tentatively named PT-A) was synthesized as an efficient phosphate adsorbent to replace aluminum hydroxide gel. The characteristic structure of PT-A was examined by nitrogen adsorption/desorption, X-ray diffraction, deviation microscopy, and scanning electron microscopy to establish a pore structural model of PT-A. With this model structure, the details of the mechanism of interaction between PT-A and phosphate in the presence of bovine serum albumin (BSA) are discussed. PT-A is a spherical particle with a diameter of —100 /μm and a porous surface structure, and its inside is packed with boehmite microcrystals (crystallite size, 2 nm). PT-A has three types of pores in its structure: a micropore with a narrow size-distribution, a mesopore with a broad size-distribution, and a macropore (radii of pores are 0.7, 1-20, and ~300 nm, respectively). When phosphate was incubated with PT-A in human gastric and intestinal juices or in an aqueous solution containing BSA, the amounts of phosphate adsorbed by PT-A were not affected by the presence of proteins. The nitrogen adsorption/desorption isotherms and energy dispersive X-ray analyses demonstrated that phosphate could diffuse to the smaller tunnels freely even if the external surface of PT-A was covered with BSA. It was also demonstrated that the main site of adsorption for phosphate was in micropores of PT-A, whereas BSA was adsorbed only to the external surface and none entered inside smaller tunnels consisting of micro- and mesopores.

Use of TNSAC in phosphate adsorption studies and relationships. Isotherm relationships and utility in the field

The studies related to the phosphate removal potential of a laboratory scale produced adsorbent, the tamarind nut shell activated carbon (TNSAC), have been partly reported in two papers by us which described the production of the various TNSAC forms, and the effects of the process variables (unrinsed and rinsed TNSAC forms and the impregnation ratio) and of the operational variables (adsorbent particle size, initial adsorbate concentration, adsorbent dose and contact time duration) on the performance evaluation of the TNSAC in adsorbing phosphates. The performance predictive models were also presented. This paper discusses the adsorption isotherm relationships and models. The applicability of the system to real field situations, and the reuse possibility and removal of the phosphate loaded adsorbent particles, have also been brought out in this paper. The isotherm plots show higher phosphate adsorptive capacity for greater equilibrium concentration values. The highest adsorptive capacity results at an impregnation ratio of 1.0 for both forms of the TNSAC and at all adsorbent doses. The adsorptive capacity is higher for the unrinsed TNSAC in comparison to the rinsed TNSAC, corresponding to the same equilibrium concentration. The rinsed TNSAC yields an isotherm model similar to the Freudlich isotherm. The unrinsed TNSAC does not yield any conventional isotherm forms, yet they have been modelled. Generalized models for predicting the adsorptive capacity have been evolved, and such models also incorporate the impregnation ratio, and the term for the adsorbent particle size. The models have indicated high correlation coefficients. When present in wastewaters, the adsorption of phosphates on the TNSAC is seen to reduce due to the preferential adsorption of other pollutants present in the wastewaters. The spent and phosphate loaded TNSAC particles are seen to be removable. Physical adsorption is seen to be the predominantly likely mechanism of phosphate adsorption on the TNSAC, which suggests the reuse possibility of the TNSAC.

Adsorption mechanism of ester phosphate on baryum titanate in organic medium. Preliminary results on the structure of the adsorbed layer

Adsorption mechanism of ester phosphate on baryum titanate in organic medium. Preliminary results on the structure of the adsorbed layer

A mechanism of phosphate adsorption on Narrabri medium clay loam soil

SummaryPhosphate adsorption on Narrabri medium clay loam soil followed a four-region Langmuir isotherm equation, i.e. the plot showed four distinct linear portions. These four regions corresponded closely to saturation with respect to hydroxyapatite, β-tricalcium phosphate, octacalcium phosphate and dicalcium phosphate dihydrate, shown by a calcium phosphate solubility diagram. The differential isosteric heat of adsorption, AH, of P adsorption on soil between 4 and 22 °C, plotted against phosphate sorbed, revealed discontinuities corresponding to the breaks in slope found on the Langmuir plot.

Inorganic Phosphate Enrichment with Iron (III) on Cation Exchanger

Inorganic phosphate in solution was concentrated on the Fe adsorbed cation exchange resin and its presence was determined by X-ray fluorescence spectrometry. The limit of detection was 6 ppb in the case of an enrichment factor of 4000. Chloride or sulfite ions did not affect this adsorption system, but the functional groups which did not contribute to Fe adsorption decreased the recovery of phosphate. The adsorption mechanism of phosphate was studied by analyzing the correlation between some chemical species, such as H+, OH-, K+ and PO43- in solution and the resin phase. The adsorption mechanism of phosphate was found to be ion exchange with anions on the Fe sites.

On the mechanism of specific phosphate adsorption by hydroxylated mineral surfaces: A review

Abstract The mechanism of specific phosphate adsorption by hydroxy‐lated mineral surfaces comprises two aspects: the phosphate‐hydroxyl surface reaction and the configuration of the adsorbed phosphate ion. Evidence pointing to ligand exchange as the mechanism of the phosphate‐surface hydroxyl reaction include kinetics of adsorption and desorption; hydroxyl ion release; infrared spectroscopy, and stereochemical calculations. Data pertaining to the coordination of adsorbed phosphate on hydroxy‐lated mineral surfaces have not been conclusive overall. Isotopic exchange experiments and studies of desorption kinetics do not provide definitive information on surface coordination. Measurements of hydroxyl ion release and crystallographic calculations provide support for the existence of both monodentate and bidentate surface complexes of phosphate ions. Infrared spectroscopic investigations suggest a binuclear complex on dried, phosphated goethite. However, these studies cannot be extrapolated automatically to so...

Phosphate adsorption mechanisms in oxidic soils: Implications for P-availability to plants

Factors affecting P solubility were studied for four Hawaiian soils: the Waialua, Wahiawa, Halii and Honokaa series, classified, respectively, as: Haplustoll, Eutrustox, Gibbsihumox and Hydrandept. Phosphate solubility in the oxidic soils depended mainly on salt concentration and cation valency. It was decreased by the accompanying cation according to: K < Mg </ Ca. This cation effect on P solubility decreasedwith increasing contents of layer silicate clay minerals and/or increasing base saturation of the soil. Consequently, it was almost absent in the Haplustoll which contains montmorillonite and kaolinite. The P solubility in all four soils increased greatly when the pH was raised with NaOH. When Ca (OH) 2 was used, however, this effect was almost completely eliminated due to the action of Ca ions. This result explains why in many fertility studies of oxidic soils even moderate liming rates were not found to increase the P availability. In a subsequent pot experiment evidence was obtained on the negative effect of the Ca ion on P uptake by Sudangrass from the Gibbsihumox and Eutrustox.

A Mechanism of Phosphate Adsorption on Soil and Anion Exchange Resin Surfaces

AbstractLangmuir plots of P adsorption isotherms of four soils were shown to fit two intersecting lines. The adsorption data were also found to fit the BET equation. The monolayer capacities computed from the BET equation corresponded closely with the adsorption maxima computed from the initial slopes of the Langmuir plots.Studies of P adsorption on the energetically homogeneous sites of the anion exchange resins Dowex 1 − X8 and Dowex 2 − X4 (Cl − forms) at 25°C, gave results similar to those obtained with soils. Measurements of Cl‐ released during adsorption indicated that initially 2 mmole of Cl‐ were released per mmole of P adsorbed, and this value decreased at higher equilibrium P concentrations approaching 1 mmole of Cl‐. Measurements of pH of the equilibrium P solutions suggested that there was deprotonation of the H2PO4‐ ion during the initial stages of adsorption. Similar results were obtained when the Dowex 1 − X8 was saturated with the IO3‐ ion and P adsorption on the resin studied.The differential isosteric heat of adsorption, ­ΔH, of P adsorption on Dowex 1 − X8 was computed between 11°C and 25°C. ­ΔH decreased sharply over the first region of the isotherm and became almost constant over the second.It was concluded that at low concentrations P was bonded by two points of attachment after deprotonation of the H2PO4‐ ion, followed by one point of attachment at higher P concentrations during adsorption on the resin surface. This resulted in the deviation from linearity predicted by the Langmuir equation. This hypothesis for the mechanism of adsorption is presented to explain the deviation observed on soil and pure soil mineral surfaces.