Phosphate Adsorption Kinetics Research Articles

Phosphate uptake from water on a Surfactant-Modified Zeolite and Ca-zeolites

The phosphate adsorption kinetics are determined in batch-wise (noted B) and fixed-bed column (noted C) experiments on a Surfactant-Modified Zeolite (SMZ) and various Ca-zeolites. The influence of phosphate concentration (0.08 or 0.8 mmol/L), presence of NO3−, HCO3−, SO42− and Cl− competing anions (individual concentration = 0.8 meq/L) and flow rate Q (1–30 mL/min) is studied. Preliminary experiments lead to the selection of the most efficient Ca-LTA and SMZ samples for the subsequent studies. In B experiments, the nature of the used system does not influence the equilibrium removal rate R (≈80%) but affects the adsorption kinetics. The equilibrium times are shorter on SMZ than on Ca-LTA, increasing with the phosphate concentration and the presence of competing anions, respectively in the ~0.5–6 or ~3–24 h ranges. In C experiments, the phosphate uptake performances on SMZ are higher than in the corresponding B experiments, with in particular higher final q/qm values. The deterioration of the performances on SMZ in presence of competing anions or with increase of Q is due to the effect of the slow phosphate ion-exchange kinetics and the short used contact time. For similar reasons, sorption on Ca-LTA is lower than on SMZ. For instance, with a 0.8 mmol/L phosphate concentration and a 10 mL/min flow rate, the time-decreasing R values become close to 50 and 10% after filtration of 10 bed-volumes respectively in presence of SMZ and Ca-LTA. Globally, SMZ is clearly more efficient than Ca-LTA, being furthermore a versatile and easily regenerable material.

Thermodynamic and kinetic investigations of phosphate adsorption onto hydrous niobium oxide prepared by homogeneous solution method

The adsorption kinetics of phosphate onto Nb 2O 5·nH 2O was investigated at initial phosphate concentrations 10 and 50 mg L − 1. The kinetic process was described by a pseudo second-order rate model very well. The adsorption thermodynamics was carried out at 298, 308, 318, 328 and 338 K. The positive values of both ΔH and ΔS suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG values obtained were negative indicating a spontaneous adsorption process. The Langmuir model described the data better than the Freundlich isotherm model. The peak appearing at 1050 cm − 1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The effective desorption could be achieved using water at pH 12.

Phosphate Removal from Aqueous Solution by Adsorption on Modified Giant Reed

The use of modified giant reed (MGR) as an adsorbent to remove phosphate from an aqueous solution was investigated. The dosage of MGR, pH of the phosphate solution, thermodynamics, and the effects of several factors on kinetics (concentration of phosphate solution, solution temperature, and shaking speed) were studied in batch experiments. The results showed that MGR was particularly effective to remove phosphate and that the effective pH range for the phosphate removal was between 4 and 9. The adsorption process could reach equilibrium in 25 minutes. Three kinetic models have been evaluated to fit the experimental data. It was shown that the pseudo-second-order model best described the adsorption kinetics of phosphate on MGR. The low activation energy of the adsorption suggested a physisorption process for phosphate adsorption. The equilibrium isotherm showed that the adsorption system was consistent with the Langmuir equation. The negative values of standard free energy (AG) and enthalpy (AH) indicated that the adsorption of phosphate onto MGR was a spontaneous and exothermic process.

Adsorption behavior of phosphate on Lanthanum(III) doped mesoporous silicates material

A series of lanthanum doped meosoporous MCM-41 (La x M41, x is Si/La molar ratio) was prepared by sol-gel method. The surface structure of the materials was investigated with X-ray diffraction and N 2 adsorption/desorption technique. The content of La in the materials was determined by ICP. It was found that the La content of La 25M41, La 50M41 and La 100M41 was 7.53%, 3.89% and 2.32%, respectively. The phosphate adsorption capacities increased with increasing amount of La incorporation. With 0.40 g La 25M41 99.7% phosphate could be removed. The effects of Si/La molar ratio, La x M41 dose, pH, initial concentration of phosphate solution, co-ions on phosphate adsorption were also evaluated. The phosphate adsorption kinetics of La x M41 could be well-described by the pseudo second-order model, and Langmuir isotherm fit equilibrium data much better than the Freundlich isotherm.

Adsorção de íons fosfato em óxido de nióbio hidratado

The adsorption kinetics of phosphate on Nb2O5.nH2O was investigated at initial phosphate concentrations 0.25, 0.50 and 1.00 mg.L-1. The kinetic process was described by a pseudo-second-order rate model very well. The adsorption thermodynamics was carried out at 298, 308, 318, 328 and 338 K. The positive values of both ΔH and ΔS suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG values obtained were negative indicating a spontaneous adsorption process. The Langmuir model described the data better than the Freundlich isotherm model. The effective desorption could be achieved using water at pH 12.

Adsorption kinetics of phosphate and arsenate on goethite. A comparative study

The adsorption kinetics of phosphate and arsenate on goethite is studied and compared. Batch adsorption experiments were performed at different adsorbate concentrations, pH, temperatures and stirring rates. For both oxoanions the adsorption rate increases by increasing adsorbate concentration, decreasing pH and increasing temperature. It does not change by changing stirring rate. The adsorption takes place in two processes: a fast one that takes place in less than 5 min and a slow one that takes place in several hours or more. The rate of the slow process does not depend directly on the concentration of phosphate or arsenate in solution, but depends linearly on the amount of phosphate or arsenate that was adsorbed during the fast process. Apparent activation energies and absence of stirring rate effects suggest that the slow process is controlled by diffusion into pores, although the evidence is not conclusive. The similarities in the adsorption kinetics of phosphate and arsenate are quantitatively shown by using a three-parameters equation that takes into account both the fast and the slow processes. These similarities are in line with the similar reactivity that phosphate and arsenate have in general and may be important for theoretical and experimental studies of the fate of these oxoanions in the environment.

Kinetics of phosphate adsorption on goethite: Comparing batch adsorption and ATR-IR measurements

The adsorption kinetics of phosphate on goethite has been studied by batch adsorption experiments and by in situ ATR-IR spectroscopy at different pH, initial phosphate concentrations and stirring rates. Batch adsorption results are very similar to those reported by several authors, and show a rather fast initial adsorption taking place in a few minutes followed by a slower process taking place in days or weeks. The adsorption kinetics could be also monitored by integrating the phosphate signals obtained in ATR-IR experiments, and a very good agreement between both techniques was found. At pH 4.5 two surface complexes, the bidentate nonprotonated (FeO) 2PO 2 and the bidentate protonated (FeO) 2(OH)PO complexes, are formed at the surface. There are small changes in the relative concentrations of these species as the reaction proceeds, and they seem to evolve in time rather independently. At pH 7.5 and 9 the dominating surface species is (FeO) 2PO 2, which is accompanied by an extra unidentified species at low concentration. They also seem to evolve independently as the reaction proceeds. The results are consistent with a mechanism that involve a fast adsorption followed by a slow diffusion into pores, and are not consistent with surface precipitation of iron phosphate.

The adsorption characteristics and adsorption thermodynamics parameter of phosphate on lake sediments

The adsorption isotherms,kinetics and thermodynamics parameters of phosphate on three sediments that are in different trophic levels respectively were studied in simulated condition,and the differences of phosphate adsorption on different sediments were also compared.The conclusions are as follows. (1) The Qmax,K,m,NAP and EPC_(0) of phosphate adsorption on the sediments from the East Taihu and the Gonghu lakes were almost the same,and the Qmax,K,NAP and EPC_(0) of the two sediments were lower than that from the Wuli Lake,but m was higher.That means the Qmax and K of the sediment from the heavily polluted Wuli Lake were higher than that from the slightly polluted East Taihu and Gonghu lakes.At the same time NAP and EPC_(0) of the Wuli Lake were also higher,the risk of phosphorus release of the sediment from the lake was higher,and m was lower.So the polluted state of sediment has significant effect on its phosphate adsorption.For the sediments from the East Taihu and the Gonghu lakes,they maintained a phosphate adsorption-desorption equilibrium state between the sediments and the overlying water,and for the sediment from the Wuli Lake,it tended to release phosphate into the lake′s overlying water. (2) The phosphate adsorption rate of the lake sediment within 0.5 h was the highest,and was 10 times or 100 times higher than that sampled in other time intervals,so the majority of phosphate adsorption on sediment was completed within 0.5 h.The phosphate adsorption rate within 0.5 h of the sediments from the Gonghu Lake was almost the same as the sediment from the East Taihu Lake,and the rate of the two sediments was higher than that from the Wuli Lake.Phosphate adsorption on sediment mainly depends on its physical and chemical properties such as distribution of sediment grain size.In this study,the adsorption rate within 0.5 h had no strong positive correlation with its volume percentage of fine particles less than 63μm.This suggests that the phosphate adsorption on the sediments studied was not only affected by its volume percentage of the fine particles,but also by its other physical and chemical properties. (3) The adsorption isotherms of phosphate on the sediments from the Wuli,the Gonghu and the East Taihu lakes at 283 K,298 K and 308 K were studied.The results show that the adsorption process of phosphate on the sediments was the endothermic reaction as the phosphate adsorption rate increased along with the increase of temperature.ΔH~(0) of the sediments from the East Taihu,the Wuli and the Gonghu lakes were 7.84,15.49 and 8.59 kJ·mol~(-1),and ΔG~(0) were 8.50,5.95 and 8.07 kJ·mol~(-1),respectively.The effect of phosphate adsorption by temperature was lower for the sediment from the Wuli Lake,and higher for the sediments from the East Taihu and the Gonghu lakes in this study.

Evidence for surface precipitation of phosphate on goethite.

Recent studies have suggested that the interaction between phosphate and goethite includes ternary adsorption/ surface precipitation as well as surface complexformation. The ternary adsorption/surface precipitation process envisioned involves the dissolution of the goethite crystal and subsequent adsorption of iron on the surface-bound phosphate. Further evidence to support the suggested process is needed. The process was investigated using two approaches. First, the sorption of iron spiked into a slurry of phosphated goethite and the effect of the iron sorption on phosphate uptake kinetics were investigated to determine whether iron would be adsorbed on the phosphated surface and whether it would enhance phosphate adsorption. Lead was also spiked into solution for comparison. Second, changes in the xi-potential of phosphated goethite were monitored with time. Adsorption of iron on the surface of phosphated goethite should increase the xi-potential of the goethite. Iron spiked into a phosphated goethite slurry was adsorbed on the solid with a concurrent adsorption of phosphate. The iron adsorption did not change the slow phosphate adsorption kinetics. Lead spiked into the solution was also sorbed but to a lesser extent than iron and with a lower apparent P:Pb mole ratio. Lead addition also changed the phosphate adsorption kinetics. With time, the xi-potential of phosphated goethite became more positive, returning almost to the potential of unphosphated goethite at low surface coverages. The slow increase in xi-potential over time indicates that long-term reactions are occurring on the goethite surface, most likely involving the dissolution of goethite to release iron and the subsequent reaction between the iron and surface-bound phosphate. These results provide strong support for the surface precipitation model, and are inconsistent with models envisioning the reaction between phosphate and the goethite surface as involving only monolayer surface complex formation.

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

Inhibitory Effects of Crop Residue-Derived Organic Ligands on Phosphate Adsorption Kinetics

This study was conducted to investigate the effects of dissolved organic matter isolated from field corn (Zea mays L.) and wheat (Triticum aestivium L.) residue on the kinetics of phosphorus (P) adsorption of an acidic soil. Phosphorus adsorption studies were conducted with the following experimental variables: P concentrations from 10 to 70 µM, pH from 4.51 to 5.38 and surface area of soil from 13.3 to 39.8 m2 L−1. Initial rate of reaction was determined through polynomial fitting of solution [P] at 0, 2, 4, 6, 8, and 10 rain after soil addition. Double-logarithmic plots were used to obtain reaction orders of 0.64 ± 0.05 for [P], −0.07 ± 0.04 for −log [H], and 1.04 ± 0.17 for surface area. Thus, the experimental rate equation was written as: d [P]/dt = kf s [P]0.64, where [P] is the P concentration in solution, kf is the forward rate constant in L m−2 s−1 units, and s is surface area in m2 L−1. The rate constant, kf, was (1.61 ± 0.16) × 10−6 L m−2 s−1. The rate constant declined linearly and Al release into solution increased linearly with increasing concentration of dissolved organic matter in solution. This suggests that P adsorption is occurring through reaction with soil Al. Reaction rates determined at 8.8, 15.5, 20.0, 26.0, and 33.5°C demonstrated that Al release from the soil was surface controlled, while P adsorption was under diffusion control. The results of this study suggests that management systems that return crop residues back into the soil may increase the availability of P by decreasing the adsorption of P onto soil surfaces.

The adsorption and release of phosphate from sediments of a river receiving sewage effluent

Data are reported which are relevant to the possible effects of river sediments on the concentration of phosphate in its water. This is significant for the Kentish River Stour in view of discrepancies in the mass balance of phosphorus, P, downstream from Ashford Sewage Treatment Works, STW. Sediment samples were collected from the sites at Longport Bridge, LB, Godmersham Park, GP, and Shalmsford Street, SS, which are located 1, 10 and 16 km, respectively, from STW. Characterisation of the samples by chemical analysis showed that the percentage Fe and Fe-bound P decreased with increasing distance from STW whereas the percentage Ca and saloid-P increased. X-ray diffraction showed that phlogopite, a mica mineral, was the main constituent whilst calcite was apparent in the SS sediment. Phosphate adsorption or desorption kinetics exhibited an initial rapid stage followed by a slower process, whose data fitted a reversible second-order equation. The forward rate constants, k 1 were between 1 and 2 dm 3 mol -1 min -1 and were dependent on pH, calcium and nitrate ion concentrations. Adsorption rates under nitrogen at pH 8.0 and 25°C increased in the order: LB < GP < SS whereas the order was GP < LB < SS for adsorption in air. For the LB deposit, the marked depression of k 1 on excluding air by nitrogen was related to its high Fe content. Rates of native phosphate release increased with increased distance from STW and on replacing air by nitrogen especially for the SS deposit. The results suggest that the bonding of P is weaker in calcareous compared to iron-containing sediments. On the basis of the results obtained some phosphate strategies are discussed as well as the relevance of the data to other watercourses.

Kinetics of phosphate adsorption by sandy and clayey soils

The kinetics of phosphate (P) adsorption for Gray Lowland soil (Fujimi sandy soil) and Yellow soil (Takashigahara clayey soil) was determined by equilibrating the soils with various concentrations of P solutions. The soil/solution ratio was approximately 7 : 2, which was equivalent to the field capacity. The kinetic equation of P adsorption was derived by regression analysis of the experimental data. The empirical equation, ∂S/∂t = kCmSn , was inadequate to describe the kinetics of P adsorption, where S is the amount of P adsorbed per unit mass of soil, C is the concentration of P in the soil solution, t is time, and k, m, and n are constants. Kuo's equation, S = a'Cotb' , was unsuitable for the prediction of the P adsorption kinetics under field moist conditions especially at a low initial P concentration, where Co is the initial P concentration, a' and b' are constants. The rate equation which best fitted the experimental data was S = atbCd , where a, b, and d are constants. The correlation coefficients for this equation were larger than 0.99.

Kinetics of phosphate adsorption by iron oxyhydroxides in aqueous systems

The rate of uptake of phosphate onto synthetic Fe(III)- and Fe(II)-derived oxyhydroxides has been studied using reaction conditions similar to those encountered in natural waters. Kinetic analyses were carried out on the adsorption profiles and both first-order and second-order conditional rate constants were obtained. The temperature dependence of some of the rate constants was investigated and corresponding apparent activation energies calculated. Similar experiments and analyses were undertaken using Fe from natural sources and in general the conditional rate constants obtained in seawater were in agreement with the synthetic ones. The results of this study are of value when comparing the time scales of adsorption processes in natural waters with the time scales of mixing and advection.

Phosphate adsorption kinetics of resuspended sediments in a shallow lake, Neusiedlersee, Austria

Phosphate adsorption kinetics of resuspended sediments in a shallow lake, Neusiedlersee, Austria

Phosphate adsorption kinetics of resuspended sediments in a shallow lake, Neusiedlersee, Austria

Phosphate adsorption kinetics of resuspended sediments in a shallow lake, Neusiedlersee, Austria

Kinetics of Phosphate Adsorption and Desorption by Lake Sediments

AbstractThe objectives of the present investigation were to gain information on the rate and extent of phosphate adsorption and desorption and the energy of phosphate adsorption by lake sediments, and to evaluate the influence of the sediments on the phosphorus status of lake waters. While phosphate adsorption by sediments from Sebasticook Lake, Maine, could be described by the Freundlich equation over a large phosphorus concentration range, the Langmuir equation provided a good fit to the experimental data only at low phosphorus concentrations. The deviation from the Langmuir isotherm at high phosphorus concentrations was explained by an increase in total negative potential of the surface due to phosphorus adsorption and increased interaction between adsorbate molecules. The rate of phosphorus adsorption by the sediments could be described by the equation X = KC0t1/m. The calculated activation energy was 2.7 kcal/mole.The desorption of phosphorus from minerals and sediments was dependent on the anionic species present in the solution. The replacing power of the anions appeared to be related to their ionic potential and complexing ability. The rate of phosphorus desorption could be described by the proposed kinetic equation.

Kinetics of Phosphate Adsorption by Calcium Carbonate and Ca‐Kaolinite

AbstractThe objective of the present investigation was to elucidate the time‐dependence of phosphate adsorption by calcium carbonate and Ca‐kaolinite and to suggest a mechanism of adsorption. The phosphate adsorption by calcium carbonate and Ca‐kaolinite at low phosphate concentrations in solution could be described by Langmuir adsorption isotherms, indicating that a monolayer of phosphate is formed on the surface. The calculated maximum surface saturation was 25µg/g for calcium carbonate and 187µg/g for Ca‐kaolinite. A second‐order kinetic equation was developed which considers both the change in phosphate concentration in solution and the surface saturation of the adsorbent during the adsorption process. The rate constant of phosphate adsorption was about 30,000 times greater for calcium carbonate than for Ca‐kaolinite. About 80% of the phosphate adsorption by calcium carbonate was completed within 10 sec. The variation of the second‐order rate constant with phosphate concentration was different in the two systems. The rate constant decreased in the calcium carbonate‐phosphate system and increased in the Ca‐kaolinite‐phosphate system with increasing phosphate concentration. It was suggested that phosphate ions are adsorbed by displacing coordinated water molecules and/or coordinated anions.

Studies of Anion Adsorption on Platinum by the Multipulse Potentiodynamic (M.p.p.) Method. I. Kinetics of Chloride and Phosphate Adsorption and Associated Charge at Constant Potential1

Studies of Anion Adsorption on Platinum by the Multipulse Potentiodynamic (M.p.p.) Method. I. Kinetics of Chloride and Phosphate Adsorption and Associated Charge at Constant Potential¹