Iron or Aluminum Coatings in Relation to Sulfate Adsorption Characteristics of Soils

Abstract

Abstract Studies were conducted to investigate the effects of hydrous Fe‐ and Al‐oxides in relation to pH upon SO 4 retention by Soils. “Less SO 4 ‐retentive” soils exhibited SO 4 adsorption of the Latosols or Ando soils after coating with the hydrous oxides. The pH‐dependent SO 4 retention was much more marked after the coatings were applied. Retentive soils are made much less retentive by treatments for the removal of the hydrous oxides while the less retentive soils show appreciable SO 4 adsorption when the hydrous oxides are added. In the acid range, the amount of SO 4 adsorption is essentially proportional to the amounts of hydrous Fe‐ or Al‐oxides present. Aluminum‐oxides are more effective in retaining SO 4 than Fe‐oxides when both are present as coatings on soil particles. The Fe system exhibited increasing adsorption with increased acidity whereas the Al system showed a maximum at pH 4.0. Subsequent decreases of SO 4 adsorption by Al‐coated soils at lower pH values were shown to be associated with dissolution of the hydrous Al oxide phase.