Fate and transport of strontium in groundwater from a layered sedimentary aquifer system

In this article, strontium distribution in sedimentary coastal aquifers of Eastern India was studied and its association with groundwater particles has been ascertained using hydrochemical and morphological tools. Groundwater contains Sr²⁺ in the range of 0.08-4.0 mg/L with higher concentrations in Cretaceous formation. The particle number in groundwater varies from 4.5 × 10⁵ to 3.3 × 10⁶ per liter and follows the power law distribution with respect to the particle diameter. The calculated β values (2.54 and 4.03) signify the abundance of smaller particles over larger ones. The particle concentration of size range 0.45-8 μm is found to be 0.64-2.6 mg/L. Elemental data of groundwater particles clearly suggest their origin from the host rock minerals. Zeta potential data indicates diverse nature of colloids suggesting prevalence of both positive and negative charged species in the groundwater. The hydrochemical interpretation along with speciation studies infers that high Sr²⁺ in groundwater is a result of incongruent dissolution of carbonate minerals and the dissolved Sr²⁺ partitions into both dissociated and un-dissociated forms. Based on the Sr²⁺/Ca²⁺ ratio and mineral saturation indices, it can be inferred that the Sr²⁺ is preferentially associated with colloids over large particles and the migration takes place through sorption of Sr²⁺ onto clay-bound (extrinsic) colloids in groundwater. This study describes the mechanism of strontium release into groundwater and provides insights into the role of groundwater particles in controlling the strontium migration to deep aquifers.