In this paper, we report new data on the lithological and chemical compositions of the surface layer (0–2 cm) of bottom sediments from various zone of the Kara Sea: the estuaries of the Ob and Yenisei rivers, open part of the shelf, Eastern Novaya Zemlya Trough, Voronin Trough, and Novaya Zemlya bays. The sediments were collected during five cruises of the R/V Akademik Boris Petrov (2000, 2001, and 2003) and the R/V Akademik Mstislav Keldysh (2015 and 2016). Based on the statistical analysis of the obtained data array, all the bottom sediments were divided into cluster groups comprising their lithological and geochemical types. The obtained clusters and REE + Y systematics were used to distinguish facies genetic types of the bottom sediments and determine the accumulation zones of Holocene sequences. They are bounded by river estuaries, a shallow marine zone adjoining the southeastern coast of the sea, and deep troughs. The main sources of Holocene sediments in the Kara Sea are the suspended particulate materials of the Ob and Yenisei and materials transported by glacial meltwater from the Novaya Zemlya and Severnaya Zemlya archipelagoes. The dispersion of fine suspensions is controlled by the circulation of surface sea currents. The accumulation of suspended materials on the bottom is complicated by wave effects and circulation of bottom sea currents, which remove fine sediment fractions from the shallow regions of the sea and transport them into the deepest hydrodynamically calm parts of troughs.

The Kara Sea is part of the Western Arctic shelf of Eurasia. The deposition of sediments in this shallow sea is largely determined by solid runoff from two great Siberian rivers (the Yenisei and Ob) and the glacial periods when the sea area repeatedly (during the Quaternary) dried up and was covered by continental glaciers. The rise of the World Ocean due to Holocene warming resulted in a significant expansion of the sea area to the south and complete degradation of the ice sheet. In this article, new data on the geochemical composition of the surface (0- to 2-cm) layer of sea-bottom sediments are considered, which reflects the spatial distribution of marine sediments during the maximum sea level. Cluster analysis of the variance for 24 chemical elements reveals sediment chemotypes, and critical analysis of their relationship with lithotypes is performed. The presented data have been collected on cruises of the R/V Akademik Boris Petrov in 2000, 2001, and 2003 and the R/V Akademik Mstislav Keldysh in 2015.

In view of ecological problems stemming from the leakage of reservoirs with liquid radioactive wastes (LRW) and groundwater contamination with radioactive Cs+ and Sr2+, we have estimated the physicochemical (including sorption) characteristics of clinoptilolite-bearing tuff (CBT) from the Chankanai deposit in Kazakhstan. Data were obtained on the chemical and phase composition of CBT, its total cationexchange capacity, and equilibrium (exchange isotherms) and kinetic (diffusion coefficients) characteristics in sorbing radioactive Cs+ and Sr2+ from 0.07 n CaCl2 solution (model solutions of groundwaters). We proved that CBT efficiently sorbs Cs from this solution and practically does not sorb Sr and elucidated the reasons for the low selectivity with respect to Sr2+. Based on the equilibrium and kinetic characteristics of the process, a mathematical model is suggested for Cs sorption under dynamic conditions. The protection lifetime of the clinoptilolite-based geochemical barrier is evaluated.

This paper addresses the distribution of heavy metals (Co, Ni, Cu, Zn, Cd, Sn, Sb, Pb, and Bi) as well as Si, Al, Fe, and Mn in the surface (0–2 cm) layer of bottom sediments of the Kara Sea. The contents of these elements are determined in each of the previously distinguished facies-genetic types of terrigenous sediments: fluvial, glacial, estuarine, shallow water–marine, “background” marine, and relict sediments. It is shown that these types reflect the modern conditions of accumulation of river discharge material, which forms fans of two greatest Siberian rivers, Ob and Yenisei. The main stages are distinguished in heavy metal accumulation. The first stage is related to the avalanche sedimentation of terrigenous sediments in the estuary and characterized by the elevated contents of Co, Ni, Cu, Zn, Cd, Sb, and Bi. The second stage reflects the mechanical differentiation of sedimentary material by waves and bottom currents in a shallow-water sea part adjacent to the estuarine zone, with accumulation of Pb- and Sn-bearing “heavy” ore minerals. The deepwater background terrigenous–marine sediments accumulate mainly Ni, Zn, and Cd, as well as Mn. The relict sediments differ in the high contents of Si, Mn, and Sn.

Holocene sequences of the Russian Arctic shelf seas are controlled by a combination of three main factors: deglaciation of the Late Pleistocene Barents–Kara ice sheet, global sea-level rise, and river runoff from Eurasia. Sedimentation in the Kara Sea is mainly defined by two latter factors. The lithological, grainsize, mineralogical, and micropaleontological compositions of the Holocene sequences of this basin have been widely studied, but only a few works report geochemical data. This paper considers comprehensive geochemical data on two cores from the Yenisei transect obtained during cruise of the R/V Akademik Petrov in 2000. Both the cores were dated by radiocarbon accelerator mass spectrometric method (AMS 14C) and analyzed using XRF and ICP MS methods. The study revealed and described differences in their chemical composition, which are caused by different facies settings of accumulation, their grain size composition, and influence of river run-off.

Methods have been developed for the preparation of samples containing organic matrices (natural high-color waters, soils, bottom sediments, aquatic organism tissue) to the determination of mercury and other toxic elements (As, Cd, Pb, Se) by different procedures of microwave digestion under elevated pressure (closed systems, vessels with partial removal of the gas phase). It is found that, under optimal oxidative and temperature-time conditions, the partial removal of the gas phase does not lead to losses of volatile elements if sample portions under 2 g are used. The duration of preparation of a series of samples does not exceed 40 min. The detection limits for mercury in the cold vapor atomic absorption spectrometry and for Cd, Pb, As, and Se by electrothermal atomic absorption spectrometry are 5 and 0.13, 6, 13, and 13 μg/kg, respectively. The accuracy of determination is confirmed by the results of analysis of certified reference materials of water and plant materials and also by the standard addition method. The selected conditions of preparation of sludge samples have ensured the determination of mercury by the cold vapor atomic absorption spectrometry in drinking, natural, and sewage waters with a detection limit of 0.07 μg/L.

Рассмотрены общие принципы и современное состояние методов микроволновой подготовки проб, а также возможности их применения для решения геохимических и экологических задач.

The review considers the general principles and current status of microwave sample preparation and the areas of its application to solving geochemical and ecological problems.

A technique of microwave-assisted preparation of natural and commercial silicate materials for subsequent spectrophotometric determination of the major rock-forming components (silicon, aluminum, iron, titanium, and phosphorus) is described. The total duration of analysis is several times less than for a standard technique. In particular, the time taken for the digestion is shortened to 1 h for ten samples undergoing digestion simultaneously; the time of complexation of aluminum with aluminon and of phosphorus with molybdenum heteropoly acid is reduced from a few hours to 12 min.

The current state and specific features of analytical methods using microwave heating are analyzed. Output laboratory microwave systems are described, such as dryers; muffle furnaces for ashing, burning, and alloying at atmospheric and increased pressure; and systems for decomposition and extraction. The possibilities and trends of the application of microwave radiation for intensification of the analytical operations of sample preparation, in particular, sorption and extraction concentration, are considered. Examples of using microwave radiation for obtaining substances and materials with analytical and technological purposes are given.

A procedure is proposed for determining 0.40 to 7.00 mg of iridium (RSD = 1–4%) in Ir(NO2)3-6. The procedure involved the fast conversion of Ir(NO2)3-6 into IrCl2-6 by heating it with an HCl solution in a microwave oven and the controlled-potential coulometric determination of iridium using the Ir(IV)/Ir(III) redox system.

A procedure for the controlled-potential coulometric (CPC) determination of ruthenium is proposed. The procedure is based on the redox reaction [Ru(CO)Cl5]2–/[Ru(CO)Cl4(H2O)]2– followed by the synthesis of the [Ru(CO)Cl5]2– depolarizing complex under microwave irradiation. The procedure was used in the analysis of a domestic commercial Ru(OH)Cl3 preparation.

Methods of cyclic voltammetry and potential-controlled coulometry in combination with spectrophotometry were used to establish that, at E-c = -0. 14 and -0.37 V (saturated calomel electrode), in the 10(-4) M acetonitrile solution [Ir-3(mu(3)-N)(mu-CH3COO)(6)Py-3] which is a mixture of trinuclear nitridohexaacetates with the axial Py ligands and acetonitrile, a single-electron reduction Ir-3(IV, III, III) --> Ir-3(III, III, III), occurs. The considerable shift of the E-c of nitridocentered iridium hexaacetates toward negative potentials as compared to the E-c of the corresponding oxocentered iridium hexaacetates is supposed to be due to the intensification of the sigma-donating properties of nitrogen as compared to those of oxygen.

A rapid method is proposed for the preparation of binuclear rhodium(II) tetraacetate [Rh2(OAc)4(HOAc)2] under the action of microwave radiation. This complex is potentially suitable for the coulometric determination of rhodium. The mechanism of the redox process Rh2(III, II) ⇄ Rh2(II, II) in acetic acid solutions of this complex has been characterized by cyclic voltammetry, controlled-potential coulometry, and spectrophotometry.