CARBON BEARING ROCKS (SHUNGITES). ARE THEY SO SAFE FOR DRINKING WATER PURIFICATION?

Abstract

The relevance of the study is caused by the need to obtain consistent information about the possibility of using carbonaceous sedimentary rocks of shungite for drinking water purification. Currently, shungite is used in many industries, their effectiveness has been proven in the treatment of wastewater from organic and oil products. Using the high adsorption capacity of shungite, a number of authors, without good reason, recommend using shungite for purification of water for domestic and drinking use. Purpose: to study the microelement composition of shungite, to assess the possibility of introducing microelements harmful to humans into an aqueous solution of shungite. Objects: samples of shungite from the Paleoproterozoic successions of the Onegian paleobasin, Karelia. Methods: scanning electron microscopy, chemical analysis, Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Results. The macro- and microelement composition of shungites of the Paleoproterozoic of the Onegian paleobasin (Karelia) has been studied. The sulfides and accessory minerals of shungite contain trace elements of various dimensions that are harmful to humans. Their mineral composition mainly consists of quartz (25–65 %), sericite, chlorite, pyrite, carbonate. The organic carbon content varies from 21 to 45 %. Pyrite is present both in the form of nodules and in micro-veins. In addition to pyrite sulphides of zinc, cobaltite, lead oxides are observed. Macroelements (Si, Ti, Al, Fe, Mn, Ca, Mg, Na, K) found in the chemical composition of shungites are mainly part of rock-forming minerals. In addition to macroelements, shungites contain a significant number of trace elements associated with accessory minerals and sulfides of various dimensions. These are S, As, V, Co, Ni, Cr, Cu, Zn, Mo, Ge, B, Sr, Li, Pb, rare earth elements. In the shungites of the Zazhogino Deposit, the chromium content varies from 96 to 151 ppm, the nickel content varies from 102 to 259 ppm. In carbon rich rocks of the Maksovo Deposit chromium is present in the amount of 103–144 ppm, nickel concentrations are determined in the range of 47–196 ppm. For the Shunga Deposit, these values are as follows: Cr is present in an amount of 74–137 ppm, Ni content varies from 86 to 275 ppm. The sulfides and accessory minerals of shungite contain trace elements of various dimensions that are harmful to humans. Having a high sorption capacity, shungite can absorb harmful components from water. At the same time, the reverse process also occurs – the extraction of impurity elements harmful to humans from shungite. The currently existing methods for purifying shungites do not allow them to be purified from micro impurities, therefore, the question of using shungites for treatment of drinking water supply remains open.

Keywords

• shungite
• trace element composition
• karelia
• onegian paleobasin
• ludikovian
• paleoproterozoic