| Batch and column experiments were conducted to elucidate the mechanisms of arsenic mobilization from the mine tailings in the presence of a natural organic matter (NOM, represented by a Fluka humic acid, HA) and a biosurfactant (represented by JBR425, mixed rhamnolipids), and to evaluate the feasibility of using NOM and biosurfactant in remediating arsenic contaminated mine tailings or soils. It was indicated that HA addition might help retain arsenic and heavy metals in the mine tailings under acidic conditions. Both HA and rhamnolipid were capable of increasing arsenic mobility from the mine tailings under alkaline conditions. It was shown that the introduction of HA at a low mass ratio of HA to mine tailings (below 2 mg/g) under acidic conditions inhibited arsenic mobilization. Generally, arsenic mobilization by HA increased with an increase in mass ratio. When the mass ratio reached 10 mg/g at pH 11, arsenic was mobilized the most after a 24-hour reaction. The mobilization of arsenic in the presence of rhamnolipid increased with the mass ratio and pH. When the mass ratio was 10 mg/g at pH 11, rhamnolipid mobilized the most arsenic after a 24-hour reaction. A desorption isotherm was developed to predict arsenic mobilization from the mine tailings in the presence of the organic additives. The addition of three low-molecular-weight-organic-acids (i.e., aspartic acid, cysteine, and succinic acid) under acidic to neutral conditions inhibited arsenic mobilization and arsenic was mobilized the most at pH above 9. Higher arsenic mobilization was obtained in column experiments. Rhamnolipid was found to be more efficient in mobilizing arsenic, probably due to its efficiency in lowering the interfacial tension and mobilizing other metals. Capillary electrophoresis analyses indicated that arsenic redox reaction might not have a significant effect on arsenic mobilization. The mobilization of co-existing metals might, to some extent, enhance arsenic mobilization by helping incorporate it into soluble complexes in the presence of organic additives. The findings will be important in advancing our understanding of the fate and transport cycle of arsenic in the environment and the cause of arsenic contamination in groundwater. NOM and biosurfactants might be used potentially for the remediation of arsenic contaminated sites. |
