INFLUENCE OF CATION SATURATION ON PHOSPHORUS ADSORPTION BY SELECTED CLAY MINERALS

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Abstract
Three clay minerals, a kaolinite, an illite and a montmorillonite, were saturated with different cations (Li+, Na+, K+, Mg++, Ca++, Sr++, and Ba++) before equilibration with dilute phosphorus solutions. The phosphorus adsorption data conformed to the Langmuir adsorption isotherm. The relative magnitude of the phosphorus adsorption constants (b and k) could be qualitatively predicted from the type of exchangeable cations for any one clay mineral.The patterns of the adsorption isotherms and adsorption constants, b and k, can be explained on the basis of P adsorption at the edges of the clay minerals; the possibility of precipitation of the phosphorus with divalent cations or aluminum in solution was considered but rejected.