Mineral phases of metals in industrial sediments of St. Petersburg rivers with extreme pollution
The aim of the research was to determine the patterns of distribution of metals and their main mineral phases in technogenic bottom sediments of St. Petersburg watercourses in conditions of extreme pollution. The objects of research were the Yekaterinofka, Okhta, Krasnen'kaya, Smolenka, Karpovka and Chernaya Rechka Rivers. Bottom sediments of urbanized rivers are characterized by abnormally high concentrations of metals and metalloids (TMM). The maximum metal content established in river sediments corresponds to ore concentrations: Cu - 0.487 %, Pb - 5.54 %, Co - 0.129 %, Cd - 0.0439 %, Ba - 6.32 % and Zn - 0.818 %.According to the Geoaccumulation Index (Igeo), TMMs are characterized from moderate and severe pollution (Cr, Co, Ni, Zn, As) to extremely severe (Cu, Cd, Sb, Hg). The rivers have their own geochemical specialization of bottom sediments: the Okhta River is characterized by the highest concentrations of Ba, As, Sb, Zn and Hg; the Ekaterinofka River - Cr, Co, Mn, Pb, Cd; Smolenka River - Cu; Red - Fe, V, Sc; Chernaya Rechka River - Ni. Based on the method of the main components of factor analysis, paragenetic associations are identified that indicate the main sources of pollution: the production of batteries using Sb-Cd-Pb-Co-Mn (Yekaterinofka River) and Ni (Karpovka River), paints and varnishes using Ba-Hg-As-Zn (Okhta River) and metal processing Cu-Cr (Yekaterinofka, Smolenka and Chernaya Rechka Rivers). Scanning electron micrographs studies showed a variety of authigenic minerals, among which barite, hematite, magnetite, goethite are of primary importance. The amount of barite formed is proportional to the concentration of Ba in the sediments. There are metal sulfides, framboidal pyrite, sphalerite, chalcopyrite, galena. An important feature of early diagenetic changes in the composition of sediments under extreme pollution conditions of the studied rivers is shown - the formation of native metals (Fe, Pb) and aggregates of complex composition (Fe, Pb, Zn, Cu). This is probably one of the significant mechanisms of the flow of metals under conditions of sustainable technogenesis.