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AuthorSibanyoni, John
SubjectInstitute for Groundwater Studies
AbstractA key challenge for chromium related activities, such as in ferrochromium industries, is the disposal of waste containing chromium slag or dust with hexavalent chromium (Cr(VI)). Various investigations have shown that hexavalent chromium is a serious concern to both environment and human health because of its mobility and carcinogenicity (Fendorf et al.; 2003). This study evaluates the impact of chromium on groundwater in the unsaturated and saturated zone by human related activities. A South African ferrochromium industry sector based in the Mpumalanga Province, (Middelburg) was selected as a case study to assess a waste dump of ferrochromium slag. The challenges regarding the dumping of slag are the oxidation of trivalent chromium (Cr(III)) to hexavalent chromium, as well as fine dust from the open arc furnaces which contain hexavalent chromium. At the case study site, the historic dump site (HDS), which is not lined, was previously used to dump various waste materials (since 1964), including but not limited to: ï· Ferrochromium slag ï· Phenols ï· Fine dust from open arc furnaces (with hexavalent chromium) ï· Filter cake (with hexavalent chromium) Literature studies indicate that trivalent chromium can be oxidised to hexavalent chromium Cr(VI) through presence of moisture, dissolved oxygen and manganese dioxide (MnO4) (EPA, 1994). The literature also indicates that concentration of hexavalent chromium Cr(VI) greater than 1 mg/l imparts a yellow colour (US EPA (1994) which was used as a visual indicator during field assessments at the HDS. The presence of hexavalent chromium was observed at the toe of the dumps and in low lying areas surrounding the dumps with elevated moisture contents. The presence of hexavalent chromium was also confirmed by monitoring results for both surface and groundwater. The mitigation that has taken place on site, involved the removal of hazardous waste such as fine dust and filter cake with hexavalent chromium from the HDS, and dumping it at a hazardous waste site (Holfontein). Other on-going mitigation at the dump is the usage of ferrous sulphate at the capturing point (infiltration gallery) to reduce hexavalent chromium to trivalent chromium through oxidation-reduction (redox) reaction process. This study has indicated that although some remedial approaches have been performed, the contamination still exists at the site. The findings of the study assessment have indicated the following: ï· Boreholes near the process plant indicated contamination by both trivalent chromium and hexavalent chromium. ï· Dam 4A and 4B have the highest concentration of hexavalent chromium as well as other constituents, such as sulphate (SO4). ï· Boreholes down-gradient of the HDS indicated pollution by hexavalent chromium, sulphate (SO4) and other parameters. ï· The western boreholes showed a trend of increasing pollution by sulphate (SO4), though not by trivalent or hexavalent chromium. Background boreholes did not show any pollution. ï· Contamination to the unsaturated zone is high but also differed when compared to contamination in saturated zones. ï· Contamination by hexavalent chromium is caused mainly by the fluctuating water table during water spraying (cooling) of hot slag, and due to precipitation in the rainy season.
PublisherUniversity of the Free State