THE RELATIONSHIP BETWEEN ADSORPTION OF Cr(VI) AND SOIL PROPERTIES

摘要

The adsorption of hexavalent chromium from dilute aqueous solution onto fifteen Taiwan soils has been investigated using pH as the major variable. The soil samples were thoroughly characterized for their physical chemical properties and composition of organic matter and metal oxides. The adsorption of Cr(VI) followed the Langmuir relation and decreased with increasing pH between pH 2.5 and 9.5. At constant pH and metal concentration, soils with greater organic matter content adsorbed more Cr(VI). The experimental results were tested in a partition coefficient model to relate the adsorption of the Cr (VI) by the different soil with soil components: organic matter, iron oxide, aluminum oxide and manganese oxide. This model was not successful when applied to measurements at the natural soil pH because of the competition of hydroxyl ions with hexavalent chromium for available sites. However, partition coefficients obtained from experimental data at a fixed pH were highly correlated with those calculated for a partition coefficient between hexavalent chromium and organic matter alone. Normalization of the partition coefficients. K_d, for the organic matter content of the soils, K_om, greatly improved the correlation between the partition coefficient and pH (R~2 increased from 0.602 to 0.855). This suggests that the surficial adsorption sites are principally due to organic matter.