Understanding Partition Coefficient, Kd, Values, Appendix E

APPENDIX E Partition Coefficients For Chromium(VI)Appendix E Partition Coefficients For Chromium(VI) E.1.0 Background The review of chromium K data obtained for a number of soils (summarized in Table E.1) dindicated that a number of factors influence the adsorption behavior of chromium. These factors and their effects on chromium adsorption on soils and sediments were used as the basis for generating a look-up table. These factors are: C Concentrations of Cr(III) in soil solutions are typically controlled by dissolution/precipitation reactions therefore, adsorption reactions are not significant in soil Cr(III) chemistry. C Increasing pH decreases adsorption (decrease in K ) of Cr(VI) on minerals and soils. The ddata are quantified for only a limited number of soils. C The redox state of the soil affects chromium adsorption. Ferrous iron associated with iron oxide/hydroxide minerals in soils can reduce Cr(VI) which results in precipitation (higher K ). Soils containing Mn oxides oxidize Cr(III) into Cr(VI) form thus resulting din lower K values. The relation between oxide/hydroxide contents of iron and dmanganese and their effects on K have not been adequately quantified except for a few dsoils. C The presence of competing anions reduce Cr(VI) adsorption. The inhibiting effect varies 2- - 2- 2- - - -in the order HPO , H PO >>SO CO /HCO Cl , NO . These effects have been 4 2 4 4 3 3 3quantified as a function of pH for only 2 soils. The factors ...