Determination of Ultra Trace Level of Uranium in Ground Water of Different Geo-Chemical Environment by Adsorptive Stripping Voltammetry

Abstract

The mineral mobilisation in ground water due to rock water interaction largely depends on the localized subsurface geo-chemical environment. During this work, traces of uranium were measured by adsorptive stripping voltametry (AdSV) in groundwater having various level of dissolved minerals. Experimental solutions were prepared in the laboratory by spiking natural groundwater with standard solutions of major cations (Ca2+, Mg2+, K+), anions (Cl−1, F−1, and \( {\text{PO}}^{{3 - }}_{4} \)), trace metal ions (Cu and Pb) and DOC (Dissolved Organic Carbon). The concentrations of these anions, cations and DOC in subsurface water changes due to changes in the geo-chemical environment at different locations. Experimental results show that major anions do not have any pronounced impact on the analysis of uranium. In the case of cations, only Cu2+ shows strong interferences. However addition of 2% Ethylene Diammine Tetra-acetic Acid (EDTA) solution in the ratio of 1:25 removes interference due to copper upto a concentration of <0.2 ppm. Interference with copper was also studied by varying the accumulation potential, pH and concentration of chloroanilic acid. Though no interferences were observed in ground water having dissolved organic carbon (DOC) in the range of 0.01–15 ppm, between 15–16 ppm of DOC, the ability to detect uranium by AdSV decreases sharply. Further, if DOC exceeded 16 ppm it was not possible to do the analysis of uranium by AdSV without destruction of DOC, as DOC is a surface active organic compound and accumulates on Hg electrode preferentially over uranium-chloroanilic complex.