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Dissolution Rates of Phosphate Rocks¹

ABSTRACT

The activity concept of phosphate-rock solubility was tested kinetically with three phosphate rocks covering a wide range of solubility. Two approaches were used: a single extraction solution of low solid/solution ratio (0.2 g/500 ml) and successive extractions at a high ratio (5 g/500 ml). The solution used was 1N NH₄OAc (pH 4.8). The results showed that the phosphate rocks differed in their solubility and each rock apparently contained two fractions which differed in solubility. The rate constant was found to depend on the degree of carbonate substitution for phosphate in apatite structure and the solid/solution ratio used.

¹ Contribution from the Fert. Tech. Div., Int. Fert. Develop. Center, Florence, AL 35630.

² Research Chemist (Soils).

Received for publication September 7, 1976. Accepted for publication February 18, 1977.