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High levels of methylmercury accumulation in marine biota are a concern throughout the Arctic, where coastal ocean ecosystems received large riverine inputs of mercury (Hg) (40 Mg·y−1) and sediment (20 Tg·y−1) during the last decade, primarily from major Russian rivers. Hg concentrations in fish harvested from these rivers have declined since the late 20th century, but no temporal data on riverine Hg, which is often strongly associated with suspended sediments, were previously available. Here, we investigate temporal trends in Russian river particulate Hg (PHg) and total suspended solids (TSS) to better understand recent changes in the Arctic Hg cycle and its potential future trajectories. We used 1,300 measurements of Hg in TSS together with discharge observations made by Russian hydrochemistry and hydrology monitoring programs to examine changes in PHg and TSS concentrations and fluxes in eight major Russian rivers between ca. 1975 and 2010. Due to decreases in both PHg concentrations (micrograms per gram) and TSS loads, annual PHg export declined from 47 to 7 Mg·y−1 overall and up to 92% for individual rivers. Modeling of atmospheric Hg deposition together with published inventories on reservoir establishment and industrial Hg release point to decreased pollution and sedimentation within reservoirs as predominant drivers of declining PHg export. We estimate that Russian rivers were the primary source of Hg to the Arctic Ocean in the mid to late 20th century.

Subject of Research. We study the effect of physical and chemical properties of finely-dispersed coal sludges of “MMK-UGOL” on their floatability. Method. Petrographic analysis of coal was carried out using the analyzer of petrographic properties of SIAMS 620 coal. To identify the presence of the main functional groups in the macromolecule of the organic mass of coal, the method of automated analysis of coal by infrared reflection spectra (IR-spectrum) was used. The electrical conductivity of the pulp with a crushed coal sample was determined by ANION 4100 liquid analyzer. Flotation studies were carried out in laboratory flotation machine of FML-1 type (Research and Production Company “Mechanobr-Technika”, Russia). Main Results. The action mechanism of new reagents in the flotation of finely-dispersed coal sludges has been identified. The flocculating action of “Sinterol” new reagent on the mineral particles of finely-dispersed coal sludges has been elucidated, that improves significantly the selectivity of the flotation process. The optimum flotation mode of thin coal sludges has been developed on the basis of laboratory researches, which increases resource efficiency of coal enrichment technological process due to the decrease in organic weight loss with waste by 33%. Thus, the consumption of the consumed reagents is reduced by 3 times. Practical Relevance. The efficiency of “Sinterol” reagent-flocculant has been confirmed by industrial tests on JSC MMK-COAL (Russia). Thus when applying “Sinterol” reagent- flocculant in the flotation process in an amount of 0.001–0.003 kg/t and simultaneously reducing the total consumption of reagents by an average of 13.0% from 3.000 to 2.613 kg/t, the concentrate yield has increased by 2.5–8.5%, the ash content of the concentrate has decreased by 2.7–3.0%, while the ash content of waste has increased by 2.9–12.3%.