Optimizing water purification with Shungite: a metric approach for characterizing its efficiency in removing contaminants

Shungite is a Precambrian carbon-rich metamorphic rock from the Lake Onega region (Karelia, Russia), consisting of fullerene- like polyhedral carbon within a silicate matrix. Its high carbon content and extended conjugation confer notable sorptive and catalytic behavior. We evaluated its multifunctional potential for water purification targeting organic, inorganic, and microbial contaminants. Two grades (Type I, Type III) were characterized by X-ray diffraction, Scanning Electron Microscopy combined with Energy Dispersive X-ray Spectroscopy, and Raman spectroscopy, and tested under batch conditions within a metric framework combining removal efficiency and distribution coefficient. After 7 days (Type I), removals were: 32.5% for Mercury, 14.9% for Lead, 20.8% for Cadmium, 32.7% for Arsenic, 13.6% for Zinc, and 21.0% for Aluminium. Microbial counts decreased by up to 0.24 log10 for total coliforms and 0.18 log10 for Escherichia coli and Enterococcus. Corresponding distribution coefficient values for Type I ranged from 15 to 1300 L/kg, consistently exceeding Type III for cationic metals (notably Mercury), while Arsenic(V) responses depended on pH/speciation. Organic-load indicators (Chemical Oxygen Demand, Biochemical Oxygen Demand (5 days), Total Organic Carbon) increased by 10–16%, consistent with Chemical Oxygen Demand leaching; mitigation (e.g., pre-washing or hybridization with activated carbon) is discussed. Overall, results support Shungite as a versatile sorbent/reactive medium, particularly for cationic metals and microbial indicators. The proposed metrics enable direct comparison with conventional carbons and mineral adsorbents under similar conditions.