Testing the hypothesis of fluoride and uranium co-mobilization into groundwater by competitive ion exchange in alluvial aquifers of Southern Punjab, India
Naved Alam, Ajit Kumar, D. K. Singh, Satish Kumar, Mohd Amir Husain, Harald Neidhardt, Elisabeth Eiche, Michael A.W. Marks, Ashis Biswas
Abstract
Co-mobilizing fluoride (F - ) and uranium (U) into groundwater poses a drinking water quality problem globally. Competitive ion exchange with aquifer sediments has been hypothesized to cause their co-mobilization. However, this hypothesis has been postulated merely based on correlations of F - and U with other groundwater parameters without characterizing that F - and U were present as exchangeable in the aquifer sediments. The present study, therefore, tested this hypothesis by determining the abundance and association of F - and U in the aquifer sediments and correlating these data with the groundwater composition in the alluvial aquifers of southern Punjab, India, where the groundwater contamination by F - and U is severe. Our results support the hypothesis that competitive ion exchange can co-mobilize F - and U into groundwater. However, the specific ion exchange reaction involved in the F - and U mobilization can differ. In the study area, the U mobilization into groundwater was linked to increased ionic strength due to the increase in concentration of any ionic species. However, the mobilization of F - was explicitly linked to the changes in OH - and HCO 3 - concentrations rather than the overall ionic strength. Bicarbonate was the most critical ionic species that could cause F - and U co-mobilization.