Phosphate Retention by Iron and Aluminum in Cation Exchange Systems

Abstract

Phosphate retention by a kaolinitic soil clay and cation exchange resins was studied to evaluate both the nature of retention and the effect of cations on the system. Calcium in the system always effected greater retention of phosphate by the exchange material than did sodium. Surface coatings of iron or aluminum on the exchange material were found to retain a large proportion of the added phosphate. The amount of this retention increased as the concentration of phosphorus in solution increased. The percentage of the retained phosphate that exchanged with radiophosphorus in solution was a function of both the concentration of phosphorus in solution and the length of time allowed for equilibration. In these reports both the coated resins and a soil clay acted similarly. Under the conditions of these experiments, the iron-coated resin was capable of retaining only slightly more phosphate than the aluminum-coated resin. However, in a mixed system most of the phosphate was retained by the iron-resin system. The results indicate that retention in these systems probably involves exchange of phosphate from solution with ions on the surface of the particles. The hydrous oxides of iron and aluminum are undoubtedly involved in this retention. The presence of other cations, Ca, Na, and H, affect the extent of this retention.