SULFATE SORPTION BY ACID FOREST SOILS

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Abstract
Sulfate adsorption was studied in 4 acid forest soils to determine the adsorption capacities of these soils and to compare different adsorption equations in describing sulfate adsorption. The adsorption capacity of the Fe-podzols (P1 and P5) was nearly double that of the semipodzol (P4) and the brown earth (P6), but none of the soils showed a tendency to reach maximum within the SO4-2 concentration range (10-800 .mu.g S/ml) tested. The Fe-podzols also showed a higher affinity for SO4-2 adsorption than the semipodzol and brown earth. Not only the adsorption capacity but also the affinity for sulfate adsorption was reduced when the SO4-2 adsorption data were corrected for isotopically exchangeable SO4-2. Of the 5 adsorption equations, the Freundlich, extended Freundlich, Langmuir, Sibbesen and Temkin-compared, the Freundlich equation was the best in describing SO4-2 adsorption. The Langmuir equation provided the alternative, if the already adsorbed SO4-2 was not taken into account. The adsorption coefficients of these 2 equations were well correlated. For example, A [adsorption coefficient] of the 2 equations was highly correlated (r = 0.876). The isotopically exchangeable SO4-2 in these soils was highly correlated (r = 0.955) with the already present SO4-2 (phosphate-extractable).