Solubility of Apatite in Clay and Zeolite Bearing Systems

The various forms of apatite release Ca+2 and P-bearing anions into solution. The generally low solubility of these phases, however, has been a drawback to the use of apatite as a direct source of nutrient P in agriculture. Apatite has for the most part been used as a raw material for the production of the more soluble phases used in conventional fertilizers. This necessitates industrial processing by such techniques as acidulation or heat treatment, processes that inevitably increase the cost of the finished product. An alternative is to introduce a cation exchanger which will take up Ca ÷ ~, inducing further breakdown of apatite to produce a high enough concentration of Pbearing anions in solution to sustain a crop. Here, we demonstrate that framework, 2:1 sheet, and fibrous sheet silicates ( zeolite, vermiculite and palygorskite) when added to apatite - H20 systems, work in this way.