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THERMOOXIDATIVE AND OXIDATIVE DESTRUCTION OF THE WEATHERED AND URANIUM-RICH ESTONIAN DICTYONEMA OIL SHALE

1993; Estonian Academy Publishers; Volume: 10; Issue: 2/3 Linguagem: Inglês

10.3176/oil.1993.2/3.04

1736-7492

R Veski, V Palu, H Taal, E Pukkonen, L Pobul, S Sidorova, E Rajavee,

Petroleum Processing and Analysis

The Tremadoc Dictyonema (Oil) Shale (DS) is one of the most problematical sedimentary rocks occurring in Estonia (Fig. 1).Due to its specific chemical composition (e.g.high heavy metals content) it should have found use in the national economy long ago already but investigations carried out so far have not yet yielded results applicable to practice.This is why about 70 million tonnes of crushed shale have been dumped in the Maardu phosphorite quarry.The weathering of DS in the dumps leads to its self-ignition, 11-15 cases taking place per every million tonnes of buried shale each year [l].The thermal processing and burning of DS is difficult to carry out due to its low organic and high pyritic and organic sulphur content.The concentration of sulphur compounds in combustible gases and thermolysis products is high.As a result of the inner burning of DS in dumps, also elemental sulphur and sulphur products are released [2, 3].Simultaneous leaching of uranium and other heavy metals compounds is a serious environmental impact at Maardu as well.Until now the composition and distribution of the weathering products of geochemically active DS and pyrite have been dealt with in many researches [4-7].The weathered as well as uranium-rich DS, however, have been investigated very little.This work aimed at finding suitable methods for characterizing the weathered and irradiated DS samples.The weathered, uranium-rich and X-ray irradiated samples, some of them being also high-sulphur, were studied by thermooxidative and oxidative destruction.The composition of the organic acids formed was determined by gas chromatography.The research procedure has been described elsewhere [B, 9]. Samples'Altogether nine DS samples, five from the Maardu deposit and four from north eastern Estonia, were studied (Fig. 1).The U concentration of the DS from the Maardu deposit is relatively low (20-50 ppm or g/t), decreasing even more during weathering as a result of U leaching.So, the U content of the nonweathered DS sample from Borehole M-30 is 39 ppm (Table 1).The nonweathered DS sample from which extracts were removed before study (hereinafter nonirradiated sample)was taken from the middle section of the southern region of the Maardu deposit.The latter sample was exposed to X-ray irradiation at 25 °C for 133 h (hereinafter irradiated sample).The procedure was carried out in a gamma contour of a nuclear