Retention of vanadium (V) by three Finnish mineral soils

Retention of V(V) by three Finnish mineral soils from 10^?4m and 10^?5m sodium vanadate solutions was investigated at room temperature in the pH range 2.3–7.5. In adsorption experiments, 0.02 m KCl was used as ionic medium, and the samples were left to equilibrate for 72 h. The solid: solution ration was 1:100 (m: v). Maximum adsorption occurred at pH ～4, where 70–80% of the added V (350–400 μg g^?1 from 10^?4m solution and 35–40 μg g^?1 from 10^?5m solution) was retained by each soil. Retention was significant even at pH 6, where adsorption of a similar anion, molybdate, is negligible. Desorption of the retained V was measured by adding 50.0 cm³ of 0.02 M KCl into weighed soil samples and shaking for 17 h in a mechanical stirrer. Only a minor part of retained V could be removed from each soil by the KCl treatment. Retention of different ionic species of V from 10^?5m solution is approximated using values of log K obtained from the literature. In these calculations, kaolin is used as a reference material.