Natural zeolites enhance groundwater quality: evidences from Deccan basalts in India

The zeolite minerals characterized with hydrated aluminosilicates, negative ionic charge and 3D framework structure are well known for purifying the groundwater occurring in basaltic aquifer systems. However, the filtering mechanism at in situ field conditions is a complex process, which is rarely studied, and hence, it needs to be demonstrated. This paper explores the mechanism of hydrochemical processes and evolution of natural zeolites associated with basaltic rock to enhance groundwater quality. We present the hydrochemical findings and evolution processes derived from 46 groundwater samples (N-t = 46) belong to zeolitic (N-z = 25) and non-zeolitic (N-nz = 21) zones of a micro-watershed (4.4 km(2)) beset over basaltic terrain, Deccan Volcanic Province (DVP), India. The groundwater samples collected for one hydrological cycle (pre- and post-monsoons) are examined for major ion chemistry to determine the aqueous solution mechanism and ion-exchange process occurred in zeolitic and non-zeolitic zones. Further, the hydrochemical parameters are appraised by means of dominancy of ions, rock-water interactions, silicate weathering, chloro-alkaline indices, cation-exchange bivariate plots and the mechanism controlling groundwater chemistry. The results show that: 1) the purifying efficiency of zeolites for total ionic strength is observed as 63.85 and 68.58% during preand post-monsoons, respectively, 2) the significant reduction (36.51%) in total hardness attributed to the positive trend of chloro-alkaline indices depicting the ionexchange phenomenon between Na+ and K+ (alkalies) and Ca2+ and Mg2+ (alkali-earth) elements in the zeolitic zone, 3) Gibbs plot shows the rock-water interaction as the predominant mechanism controlling groundwater chemistry in the zeolitic zone, and 4) the groundwater quality parameters from zeolitic zone are found within the permissible limit of WHO drinking water standards.