Characterization of groundwater composition in Punjab state with special emphasis on uranium content, speciation and mobility

摘要

Groundwaters (borewell and handpump) were sampled from two districts (Bathinda and Mansa) of Punjab state and analyzed for their major ionic concentrations and uraniumisotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The major ionic concentrations of waters were plotted on a Piper diagram and grouped into four dominant hydrochemical facies as (Na+K)-SO_4+Cl type (69%–73%), (Ca+Mg)-SO_4+Cl type (6%–21%), (Ca+Mg)–HCO_3 type (4%–6%) and (Na+K)-HCO_3 type (2%–19%). It was observed that mobility of uranium in groundwater was very much influenced by TDS (total dissolved solids). To investigate the various mechanisms for deriving the elevated uranium concentrations in groundwater, ~(234)U/~(238)U activity ratios (ARs) were calculated using the determined activity levels of ~(234)U and ~(238)U. ThemeanARswas found to be near unity (i.e. secular equilibrium) in the study regions confirmed that uranium in groundwaters was mainly resulted from its host/parent rocks through weathering processes. The concentration of HCO_3~? in ground water showed one order ofmagnitude higher than the total dissolved SiO_2 indicates that carbonateweathering was the dominant process due to major water–rock interaction. The uranium speciation in groundwaters was investigated by an equilibrium model calculation using MEDUSA (make equilibrium diagrams using sophisticated algorithms) under the influence of redox conditions and complexant concentration. At the observed range of pHvalues, the predominant redox speciationof uraniumwasobservedashydroxo-carbonatocomplexes of (UO_2)_2(CO_3)(OH)_3~? and hydroxyl complexes of UO_2(OH)_3~? whichmight be caused for increasing the solubility of uranium. Due to very low concentration of phosphate in groundwater, its effects on U(VI)-aqueous speciation was negligible.