The Interaction of Phosphate with Calcite

Abstract

Adsorption isotherms of phosphate on calcite were shown to be described by a two‐region Langmuir isotherm equation, i.e., the plot showed two distinct linear portions. The break in the slope of the Langmuir plot was found, on a solubility diagram of the calcium phosphates, to correspond closely to the division between octocalcium phosphate and hydroxylapatite.The adsorption data were also found to be described by the BET equation. The monolayer capacity computed from the BET equation was found to correspond closely with the adsorption maximum computed from the initial solpes of the Langmuir plots. Comparison of monolayer capacities with the total surface area of the calcite indicated that only approximately 5% of the total surface was covered with phosphate ions.The differential isosteric heat of adsorption, was computed from the adsorption data. A plot of as a function of phosphate sorbed revealed a discontinuity at the region 1 boundary of the adsorption data.Kinetics of phosphate reaction with calcite were found to be consistent with heterogeneous nucleation theory and are discussed in terms of the previous adsorption data.It was concluded that the interaction of phosphate with the calcite surface could be described as a heterogeneous nucleation process.

Genetic Manipulation of a “Vacuolar” H+-PPase: From Salt Tolerance to Yield Enhancement under Phosphorus-Deficient Soils

“…Sorption and precipitation reactions are involved. The sorption of inorganic P from solution is related to the presence of iron and aluminum oxides and hydrous oxide minerals (Fried and Dean, 1955;Fox and Kamprath, 1971;Cogger and Duxbury, 1984) and CaCO 3 (Cole et al, 1953;Griffin and Jurinak, 1973;Holford and Mattingly, 1975). P sorption is limited to relatively low initial P solution concentrations, and precipitation becomes a more important mechanism of P removal from the soil solution at higher P concentrations (Cole et al, 1953).…”

Phosphorus Status of Calcareous and Sodic Soils Treated With Cheese Whey

“…The combination of these two Ca sources provided sufficient Ca for ortho-P precipitation (Lewis and Raca, 1969). The added ortho-P and any organic P that was converted to ortho-P, that was not measured as bicarbonate extractable ortho-P, was likely adsorbed to the soil or precipitated as one of several possible calcium phosphates (Griffen and Jurinak, 1973). Even though this soil retained the bicarbonate extractable ortho-P from a very high single P application rate.…”

Metal-Induced Sulfate Adsorption by Soils

“…Obtaining adsorption data at different temperatures allows the differential isosteric heat of adsorption, AH, to be determined by applying the Clausius-Claperon equation to the system where the surface coverage, 0, is assumed constant (Griffin and Jurinak, 1973): where Cj is the equilibrium concentration at temperature, T,, Cg is the equilibrium concentration at temperature, Tj, and AH and R are as defined above.…”

“…This technique was followed by Taylor and Ellis (1978) to estimate the C, term for PO^^ adsorption by resin. It should be noted, however, that the BET equation alone is not sufficient to conclude that adsorption is definitely a polymolecular (Griffin and Jurinak, 1973;Mehadi and Taylor, 1988;Taylor and Ellis, 1978). Multiple adsorption could be involved, in part, through 80^^' adsorption.…”

“…The third possible reasons for the non-linearity in the C/X vs. C (or X/C vs. X) plots is the nucleation of the various SO/' species and the consequent precipitation reactions (Griffin and Jurinak, 1973;Muljadi et al, 1966, Sposito, 1982. From a previous discussion, precipitation reactions of the various SO/' forms were ruled out based on the solubility principles.…”