Chemistry of iron in soils. ferric hydrolysis products

Abstract

A method has been developed for dividing hydrolysed ferric species into unpolymerized, polymerized and precipitated species. The colour developed with 8-hydroxy-7-iodoquinoline-5-sulphonic acid measures the concentration of unploymerized species and centrifugation gives the precipitated species. Polymeric species are found by difference. The pH and polymeric species decreases, precipitate formation increases and unpolymerized species remain constant on aging a partially neutralized ferric solution. With increasing OH/Fe ratio at a given age, the pH, polymeric and precipitated species increase and the unpolymerized species decrease. The concentration of unpolymerized species was independent of the anion (NO3, ClO4 or Cl). Goethite, lepidocrocite and �-FeOOH were formed in the solutions under various conditions. The rate and amount of precipitate formation was dependent on the degree of anion penetration for the polycations and precipitates and the total anion concentration. The ferric hydroxy polycations had V= 0.286 and empirical compositions of [Fe(OH)x 3-x]n where 2.2 < x < 2.9.