The association of cobalt with easily reducible manganese in some acidic permanent grassland soils

SUMMARY The association of cobalt with manganese oxides was examined in some surface and sub‐soils from areas of permanent grassland in England. Hydroquinone (0.2% in ammonium acetate at pH 7.0) was used to extract easily reducible Mn oxides from the soils. Two sequential extractions with this reagent removed significant proportions of the total Co along with the Mn; no significant amounts of iron were extracted. Mn‐rich iron concretions were isolated from two of the soils and these contained from 230 to 880 μg g −1 Co. Approximately 30% of the Co in the concretions was dissolved by two sequential extractions with hydroquinone with concurrent release of considerable amounts of Mn, but, as with the soils, not of Fe. The concretions contained 20–41 mg g −1 Mn and 62–171 mg g −1 Fe that were soluble in acidified H 2 O 2 . It was concluded that significant proportions of the Co in soils is associated with Mn oxides, and will show the same sensitivity to changes in acidity and redox potential as Mn.