Assessment of Fate and Transport of Heavy Metals (Cr, Cd) in Hardrock Aquifers

This study delves into chromium (Cr) and cadmium (Cd) behavior in varied hard-rock aquifer lithologies, exploring their sorption capacities and transport characteristics. The research aims to understand how these heavy metals affect groundwater quality in lithologically diverse settings. Hard rocks, known for their low porosity and heterogeneity, significantly influence the movement of contaminants through fractures and surfaces. Cadmium, a toxic metal primarily from human activities like mining and industrial discharge, poses significant risks to ecosystems. Chromium, particularly its hexavalent form, Cr (VI), originating from industrial and agricultural sources, is also a concern due to its carcinogenicity. WHO guidelines recommend limits of 0.003 mg/L for Cd²⁺ and 0.05 mg/L for Cr (VI) in groundwater, often exceeded in many regions, indicating environmental hazards and health risks. The study involved characterizing hard rock materials and conducting batch-sorption and column transport experiments to gauge contaminant-rock interactions. Results indicated varying sorption capacities across lithologies showing minimum value by granite (499.15 ± 99.41 mg/kg) and maximum value by limestone (872.37 ± 2.37 mg/kg) for 7ppm concentration. In case of studied aquifer systems, basaltic aquifers are demonstrating superior chromium retention compared to granitic ones. Ionic competition minimally affected sorption, prompting the use of NaCl solutions in subsequent experiments. These findings offer insights into the complex interplay between lithological compositions and contaminant sorption, crucial for groundwater management and environmental protection strategies.

Key words: Rocks and minerals, contaminant interaction, batch sorption, column transport.