Date of Award
Doctor of Philosophy
M. A. Tabatabai
A rapid and precise method for determination of surface charge density of soils was developed. The method involves saturating the negative and positive exchange sites with NH[subscript]4[superscript]+ and NO[subscript]3[superscript]-, respectively, removing the excess solution, and determining the ions on the exchange sites by steam distillation.;Studies on the effect of pH and exchangeable cations on P adsorption by six slightly acid, Iowa surface soils showed that the minimum adsorption occurred at a narrow pH range (ca. zpc, 4.5 to 5.5), below and above which phosphate adsorption increased sharply. The increase in P adsorption below this minimum adsorption was attributed to the effect of Al and Fe oxides, and the P adsorption above this pH range was attributed to the effect of exchangeable cations. This was confirmed by saturating the exchange sites with NH[subscript]4[superscript]+.;Adsorption of P by NH[subscript]4-saturated soils was less than that by untreated or water-leached soils when water was used as a matrix solution, and it was the greatest when 0.01 M CaCl[subscript]2 was the matrix solution. The amounts of NH[subscript]4[superscript]+ released to 0.01 M CaCl[subscript]2 confirmed the importance of exchangeable Ca in P adsorption. The amounts of P adsorbed by alkali metal-saturated soils decreased in the order of the following metals: K ≥ Na > Rb > Cs > Li > untreated soils when 0.01 M CaCl[subscript]2 was the matrix solution. The amounts of P adsorbed by alkaline earth metal-saturated soils were greater than those adsorbed by alkali metal-saturated soils. Regardless of the matrix solution used, the amounts of P adsorbed by the alkaline earth metal-saturated soils decreased in the order of the following metals: Ba > Ca > Mg > Sr > untreated soil. Saturation of soils with selected heavy metals increased P adsorption, and these increases were greater than those obtained for alkali metal- and alkaline earth metal-saturated soils. The amounts of P adsorbed were affected by the saturating heavy metal, with the following decreasing order: Pb > Cu > Zn > Ni > Cd > Mn. Precipitation reactions were considered, but they were rejected for alkali metal- and alkaline earth metal-saturated soils, but they were possible for Cu-, Zn-, or Pb-saturated soils. Application of the Langmuir model showed that the adsorption maximum (X[subscript] m) and the affinity coefficient (k) are affected by the type of exchangeable metal and the matrix solution used.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Ibrahim Bakry Abdul Razaq
Razaq, Ibrahim Bakry Abdul, "Effect of pH and exchangeable metals on phosphate adsorption by soils " (1989). Retrospective Theses and Dissertations. 9170.