Phosphate Desorption Research Articles

Kinetics of the Phosphate Interaction with Calcite

AbstractThe kinetics of the phosphate interaction with calcite were studied. The results showed that the reaction did not proceed in the absence of the calcite surface. The kinetics of interaction could be described by two simultaneous reactions. The first reaction was second‐order and was ascribed to the adsorption of phosphate on the calcite surface. The second reaction was first‐order and was considered to be associated with the surface arrangement of phosphate clusters into calcium phosphate heteronuclei.Solubility criteria were used to show that at low phosphate concentrations the ultimate calcium phosphate surface mineral formed was hydroxylapatite.Desorption kinetics were studied by using an anion exchange resin technique. The desorption process could be described as two simultaneous first‐order reactions. The desorption mechanism was postulated to correspond to the dissolution of a surface nucleated calcium phosphate mineral, with the second reaction step being the desorption of phosphate from the calcite surface sites.The rate constants for adsorption and desorption were determined at four temperatures between 0C and 40C. The rate constants were used to compute the activation energies of adsorption and desorption. In addition, the thermodynamic parameters for the enthalpy of activation (ΔH†), the entropy of activation (ΔS†), and the free energy of activation (ΔG†), for both the adsorption and desorption processes were computed and discussed.

Desorption of soil phosphate by anion‐exchange resin

Abstract Kinetics of phosphate desorption from twenty soils by anion‐exchange resin were not satisfactorily explained by either film diffusion (or ion exchange mechanism) mechanism or particle diffusion mechanism. Eut the phosphate desorption process was adequately explained by a two‐constant rate equation. The two constants, the coefficient term (i.e., rate factor) and the constant term (i.e., solution P initially) were significantly correlated with amorphous Al; rate factor increased and solution P decreased with the increase in amorphous Al among the soils. Thus, influence of amorphous Al in P availability from soils must be considered.

Phosphate eesoeption isotherms in four selected tropical soils and one temperate soil

Abstract Phosphate desorption isotherms were constructed for four tropical and one British soil with different chemical properties. Phosphate was released with a oitric acid solution (0.0025 M) adjusted to pH 5.7 and by using different soil/ solution ratios during 18 hours. This citrate level does not operate efficiently for high phosphate sorbing soils (i.e. Bowden Series), so that there is a competition between oitrate and phosphate for sorbing places and some disturbances in the shape of the desorption isotherms appeared. In moderated phosphate sorbing soils (Rengam Series) fairly reasonable desorption isotherms were obtained even at this low oitrate concentration (0.0025 M). An almost linear isotherm curve was obtained when a higher concentration of citrate (0.1 M) was used.

Effects of temperature on phosphate sorption isotherms and phosphate desorption

Abstract Phosphorus sorption isotherms were constructed for two Idaho soils with widely different chemical properties. The soils were equilibrated with various amounts of Ca(H2PO4)2 in 0.01 M CaCl2 for 1, 3, 7, and 11 days at temperatures of 5°C and 20°C. The two soils which had been equilibrated previously for 11 days at 20°C with various amounts of Ca(H2PO4)2 in 0.01 M CaCl2 were desorbed at 5°C and 20°C. The rates of sorption and desorption were decreased as the equilibration temperatures were lowered. The effect of temperature on these processes was detected during the first day of equilibration. Less P was found in the equilibrating solution at the lower temperature. The two soils varied widely in sorption and desorption properties.

Adsorption and desorption of phosphate by soils

Abstract Added P adsorbed, expressed as a percentage of total added P, was closely and inversely related to added P subsequently desorbed, expressed as a percentage of added P adsorbed. This relationship was not linear but followed a hyperbola‐like curve. For the limiting cases where adsorption was 0% and 100%, desorption was 100% and 0%, respectively. If desorption is the mechanism limiting the release of P into the soil solution for plant utilization, then the well‐established relationship between P adsorbed in the laboratory and the recovery of fertilizer P under field conditions is accounted for.

Desorption of Phosphate from Kaolinite by Citrate and Bicarbonate

AbstractPhosphate which cannot be desorbed from kaolinite by chloride at the same pH and ionic strength at which adsorption took place is significantly desorbed by citrate and bicarbonate.In the presence of citrate or bicarbonate, phosphate adsorption by kaolinite is reduced. The extent of reduction depends on the way in which phosphate and citrate or bicarbonate are added to the clay. Maximum reduction in phosphate adsorption occurs when phosphate and citrate or bicarbonate are added together or when phosphate is introduced after citrate or bicarbonate adsorption.These effects are attributed to the fact that mole for mole exchange between phosphate and the other anion does not occur. The reduction in phosphate adsorption results not only from competition but also from a concomitant change in charge.

Desorption of Phosphate from Kaolinite

AbstractInitially all the phosphate adsorbed onto kaolinite is isotopically exchangeable. On washing some of the phosphate ceases to be exchangeable, but if the amount that remains labile is plotted against the solution concentration the original isotherm is preserved. Thus, some of the total phosphate goes into a nonexchangeable “fixed” sink.If phosphate is adsorbed in very small increments some of it is converted directly into the fixed form. In the presence of large concentrations of phosphate, all the adsorbed phosphate becomes exchangeable.

Studies of Anion Adsorption on Platinum by the Multipulse Potentiodynamic (M.p.p.) Method. II. Chloride and Phosphate Desorption and Equilibrium Surface Concentrations at Constant Potential1

Studies of Anion Adsorption on Platinum by the Multipulse Potentiodynamic (M.p.p.) Method. II. Chloride and Phosphate Desorption and Equilibrium Surface Concentrations at Constant Potential¹