Relation of Relative Colloid Stability Ratio and Colloid Release in Two Lead-contaminated Soils

Potential release of soil colloids into groundwater has attracted considerable attention because of their association with heavy metals. Much effort has been focused on using colloid-depositionbased parameters (batch experiment) to predict colloid release in soils (column experiment), though they are two separate processes. In this paper, relative colloid stability ratio was estimated and used to relate to colloid release in soils. Changes in colloid release with incubation times were measured in two lead-contaminated soils. Colloid stability ratio (W) is defined as the ratio of the colloid flocculation rate of a suspension under normal observation conditions (slow flocculation) to the rate under rapid flocculation conditions. Assuming that colloid flocculation rate is related to changes in light absorbency of a solution, relative colloid stability ratio (RW) was estimated by dividing the rate of absorbency change of soil suspension observed in 0.06 M NaCl (slow flocculation) by that in 0.01 M CaCl2 (rapid flocculation) electrolyte solutions. Both colloid release and R W changed randomly with incubation times in both soils. However, colloid release generally increased as RW increased with correlation coefficients of 0.67–0.89. This result suggests that the overall colloid release from these soils was related to RW, even though they are different conceptually. However, research is needed to further develop the concept of using relative colloid stability ratio to predict colloid release in soils.