Sorption Of Phosphate Ions Research Articles

Speciation studies at the Illite - solution interface: Part 1 – Sorption of phosphate ions

Although phosphate ion (hereafter “P”) sorption is known to influence clay surface reactivity and trace metal behavior in the environment, there is still a lack of in situ spectroscopic evidence on the identity of phosphate sorption species formed at the interface between solution and clays with a 2:1 layered structure (2 silica tetrahedral: 1 octahedral layers), which are ubiquitous in soils and clay formations. We studied the surface speciation of phosphate ions by in situ spectroscopic monitoring along P sorption at the interface between a solution and a homoionic Na-illite, as a function of time or aqueous phosphate concentration (20–250 µM) leading to low/moderate P surface coverage. We also combined them with batch sorption experiments and electrophoretic mobility (EM) measurements. Macroscopic data indicated that the percentage of P sorption depends on pH, aqueous phosphate concentration, and the clay/solution ratio of the experiment, i.e., the coverage of the clay surface by P, with a maximal sorption capacity of the clay equal to ca. 6 µmol.g−1 at pH 4. Macroscopic and EM data further suggest that P sorption mechanisms onto illite confer negative charges on the surface and involve several sorption species and/or surface sites present on the clay edges. In situ FTIR spectra showed that, at acidic pH, three types of phosphate surface species exist at the illite-solution interface: an outer-sphere surface complex (OSSC) of phosphate (ΞSOH2+…H2PO4-, with S referring to a sorption site on the clay), an inner-sphere surface complex (ISSC) of phosphate, probably a monodentate binuclear surface complex ((ΞSO)2PO2) formed by surface ligand exchange with high-affinity aluminol sites and, to a lesser extent, low-affinity sites on the clay edges, and, in limited amounts, an Al-phosphate surface precipitate. Phosphate ion sorption occurs through the initial formation of the OSSC of phosphate, which dominates phosphate surface speciation at short reaction times and low P concentrations and transforms over time into the ISSC of phosphate. This study presents the first published in situ surface speciation of phosphate ions sorbed at the interface between a solution and an illite. The evidence of a strong sorption of phosphate ions at this clay surface provides new and sound knowledge to better understand the environmental fate of phosphate ions and trace metals, particularly in agricultural soil - groundwater continua or in clay host rocks considered for high-level radioactive waste disposal.

Sorption of phosphates on macroporous synthetic calcium silicates

The sorption of phosphate ions on macroporous synthetic calcium silicates has been studied and it has been evaluated whether the latter are suitable to serve as sorbents of geochemical barriers preventing phosphorus losses from agricultural soils.

A study of sorption of phosphate ions from aqueous solutions by wood ash

Possibility was studied of performing sorption purification of aqueous solutions to remove phosphate ions, with wood ash formed in burning of wastes formed in processing of crushed wood serving as a sorbent. Kinetic dependences of the sorption process were examined and sorption characteristics of wood ash with respect to phosphate ions were determined.

Chemically Modified Biosorbent for Phosphorus Removal from Aqueous Solution

In the present study, chemically modified Aleppo pine (Pinus halepensis Miller) sawdust was used for removal of phosphate from water. Biosorbent preparation process included size fractionation, extraction for surface activation, acid prehydrolysis, and treatment with urea. Sorption of phosphate ions onto biosorbent was studied using the batch technique. The effect of different parameters such as contact time, adsorbate concentration, and temperature was investigated. The adsorption kinetics data were best described by the pseudo-second-order rate equation, and equilibrium was achieved after 40 min. The Langmuir and Freundlich equations for describing adsorption equilibrium were applied to data. The constants and correlation coefficients of these isotherm models were calculated and compared. The adsorption isotherms obey the Freundlich equation. The thermodynamic parameters like free energy, enthalpy and entropy changes for the adsorption of phosphate ions have been evaluated and it has been found that the reaction was spontaneous and endothermic in nature. The low value of activated energy of adsorption, 3.088 kJ/mol, indicates that the phosphate ions are easily adsorbed on the sawdust. Results suggest that the prepared chemically modified Aleppo pine sawdust has potential in remediation of contaminated waters by phosphate

Adsorptive removal of phosphate from aqueous solution by chemically modified biosorbent

Abstract In the present study, chemically modified biosorbent (Pinus halepensis Miller) was used for removal of phosphate from water. Biosorbent preparation process included size fractionation, extraction for surface activation, acid prehydrolysis, and treatment with urea. Sorption of phosphate ions onto biosorbent was studied using the batch technique. The effect of different parameters such as contact time, adsorbate concentration, and temperature was investigated. The adsorption kinetics data were best described by the pseudo–second-order rate equation, and equilibrium was achieved after 40 min. The Langmuir and Freundlich equations for describing adsorption equilibrium were applied to data. The constants and correlation coefficients of these isotherm models were calculated and compared. The adsorption isotherms obey the Freundlich equation. The thermodynamic parameters like free energy, enthalpy and entropy changes for the adsorption of phosphate ions have been evaluated and it has been found that the...

Removal of phosphorus from aqueous solutions using chemically modified sawdust of Aleppo pine (Pinus halepensis Miller): kinetics and isotherm studies

In the present study, chemically modified Aleppo pine (Pinus halepensis Miller) sawdust was used for the removal of phosphate from water. Biosorbent preparation process included size fractionation, extraction for surface activation, acid prehydrolysis, and treatment with urea. Sorption of phosphate ions onto biosorbent was studied using the batch technique. The effect of different parameters such as contact time, adsorbate concentration, and temperature was investigated. The adsorption kinetics data were best described by the pseudo-second-order rate equation, and equilibrium was achieved after 40 and 80 min for modified and unmodified sawdust, respectively. The Langmuir and Freundlich equations for describing adsorption equilibrium were applied to data. The constants and correlation coefficients of these isotherm models were calculated and compared. The adsorption isotherms obey the Freundlich equation. The thermodynamic parameters like free energy, enthalpy, and entropy changes for the adsorption of phosphate ions have been evaluated, and it has been found that the reaction was spontaneous and endothermic in nature. The low value of activated energy of adsorption, 3.088–3.540 kJ mol−1, indicates that the phosphate ions are easily adsorbed on the sawdust. Results suggest that the prepared chemically modified Aleppo pine sawdust has potential in remediation of contaminated waters by phosphate.

Sorption of phosphate ions with materials based on titanium and lanthanum hydroxides

The possibility of preparing lanthanum(III) hydroxide and a 1:1 mixture of lanthanum(III) hydroxide with hydrated titania by precipitation from aqueous solutions was explored. The maximal sorption capacities of the mixture with respect to phosphate ions in acid and alkaline media were determined. The mechanism by which phosphates are removed was elucidated by IR spectroscopy.

Sorption of phosphate ions on iron(III), zirconium(IV), and chromium(III) oxyhydroxides from aqueous electrolyte solutions

The adsorption of phosphate ions from aqueous solutions with an ionic strength of 0.5 on iron(III), zirconium(IV), and chromium(III) oxyhydroxide hydrogels has been studied as influenced by chloride and sulfate ions. Despite the high concentrations of chloride and sulfate ions, they do not inhibit phosphate adsorption on the hydrogels; they only slightly change the isotherm shape. In the range of equilibrium phosphate concentrations equal to 30–50 mmol/l, all isotherms for iron and zirconium oxyhydroxide gels signify the appearance of a second adsorption layer (two-step isotherms). Both steps are satisfactorily fitted by the Langmuir equation. The maximum adsorptions and adsorption constants have been calculated. For chromium oxyhydroxide gels, the intraduction of an electrolyte dramatically decreases the equilibration rate.

PH dependence of phosphate sorption on aluminum

The sorption of phosphate ions on aluminum was studied by an in situ radiotracer technique. The kinetics and reversibility of sorption and the influence of the solution pH on phosphate coverage were followed in 0.1 mol dm −3 NaCl solution. It was found that phosphate adsorption on aluminum is determined by the surface charge and the protonation state of phosphate in the bulk solution. Despite the high chloride concentration, significant phosphate sorption was identified, indicating strong phosphate binding to the surface. Phosphate sorption increased with pH up to pH=4.7. As the pH of the solution increased further, phosphate desorbed from aluminum. The exchange experiments indicated that the phosphate sorption on the passive aluminum surface is a largely irreversible process. It is assumed that, in near neutral solution, there is an ongoing surface transformation, i.e., oxide film growth, that entraps phosphate ions from the solution.

Phosphate sorption by goethite and kaolinite‐goethite (k‐g) system as described by isotherms

Goethite and kaolinite are active sorbents in soils and sediments. Unfortunately measuring their phosphate sorption capacity is difficult, because of the relatively low proportion of these clay minerals in many natural mixtures and the difficulties involved in concentrating and separating them from accompanying minerals. Under these circumstances, synthetic samples are commonly used to study phosphate sorption. In this study, the objectives were to elucidate the Langmuir, Freundlich, Temkin, Gouy‐Chapman, and Sposito isotherms. The sorption of phosphate ions by goethite (a‐FeOH) and kaolinite‐goethite (k‐g) system depends on several factors including pH, specific surface, cation exchange capacity, time of sorption, surface charge, temperature and concentration. We investigated the effects of pH, time of sorption and concentration on the adsorption of phosphate on goethite and the k‐g system. Batch equilibrium phosphate adsorption experiments were conducted with pH, and initial concentration as changeable parameter in order to produce adsorption envelops. The Langmuir, Freundlich, Temkin, Gouy Chapman and Sposito isotherms were fitted to P sorption data. Each was found to describe phosphorus (P) sorption by goethite and k‐g system with comparable success, with the Sposito, Freundlich and Langmuir being slightly superior for kaolinite‐goethite (k‐g) system and Langmuir for goethite. The total amount of P sorbed by k‐g system and goethite after 103 days in equilibrium concentrations 0.0403–0.4435 mmol P L‐1 and pH 4.0–9.0 was found to range between 2.74–37.00 mmol kg‐1 and 22.97–106.93 mmol kg‐1, respectively.

The Measurement of the Surface Area of Uranium Dioxide Powder

A comparative method was developed for determination of surface areas of UO/sub 2/ powder. The method depends on the sorption of phosphate ions from a solution containing P-32 labeled NaH/sub 2/PO/sub 4/ on the powder surface. By comparison with samples of known surface area, measurements were obtained in the range 1.0-l4 meter/sub 2//gm. The internal consistency of the method is better than plus or minus 5% and agreement with measurements by the BET (Brunauer- EmmettTeller) method averages around plus or minus 5%. The method is simple and fairly rapid, and can be adapted to irradiated material. (auth)

Adsorption of Tagged Phosphute Ions on Glass Surfaces as Related to Alkaline Attack

A preliminary investigation has been made of various factors involved in the sorption of phosphate ions on glass surfaces, particularly with reference to a possible utilization of phosphate sorption as an indicator of alkaline attack of the surface. Sorption has been measured by means of a tracer technique using radioactive phosphorus as trisodium phosphate, and tests have been made with two types of soft glass and with Pyrex‐brand glass, with and without alkaline pretreatments. Radioautographs have been prepared to determine the distribution of sorbed phosphate on soft‐glass specimens treated in various ways. The sorption of phosphate ions from dilute alkaline solutions at room temperature on fused soft glass and Pyrex‐brand glass has been found to be very slight, on the order of one‐thousandth of a μ gm. per sq. in. (roughly equivalent to a thousandth of a monomolecular layer on the macrosurface). Treatment of soft glass for a few minutes in sodium hydroxide solution at 80°C. results in a multifold increase in subsequent sorption of phosphate ions at room temperature. A much longer alkaline pretreatment is required in the case of Pyrex‐brand glass, but a similar increase in sorption is found. The different results obtained with soda‐lime and borosilicate glasses may be explained on the basis of different types of nonadsorbing surface films. Zinc ions in the alkaline pretreatment solution appear to cause an increase in subsequent sorption, and it is proposed that adsorption of polyvalent cations facilitates the adsorption of phosphate ions.