Major oxide geochemistry

Disposal of spent nuclear fuel and other radioactive wastes in the subsurface and assessment of the hazards associated with the potential release of these contaminants into the environment require knowledge of radionuclide geochemistry. Plutonium (Pu), for example, exhibits complex environmental chemistry understanding the mechanism of Pu oxidation and subsequent reduction, particularly by Mn-bearing minerals, is of major importance for predicting the fate of Pu in the subsurface. 

Besides NOx oxides, there is nitrous oxide (N2O), which is of special interest in isotope geochemistry. N2O is present in air at around 300 ppb and increases by about 0.2% per year. Nitrous oxide is an important greenhouse gas that is, on a molecular basis, a much more effective contributor to global warming than CO2 and that is also a major chemical control on stratospheric ozone budgets. 

This chapter will examine the ways in which major element data axe used in geochemistry. The discussion will be restricted to the ten elements traditionally listed as oxides in a major element chemical analysis — Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and P. Geochemists make use of major element data in three principal ways — in rock classification, in the construction of variation diagrams and as a means of comparison with experimentally determined rock compositions, whose conditions of formation are known. Each of these uses will be discussed in a separate section of this chapter. In addition, major elements are used, often together with trace elements, in the identification of the original tectonic setting of igneous and some sedimentary rocks. This topic will be discussed in Chapter 5. 

Uranyl sulfate usually appears as a lemon-yellow trihydrate (UO2SO4 3H2O) with a density of 3.28 g cm" and is very soluble in 5 parts of water and 25 parts of alcohol. In geochemistry, oxidation of snlfldes would lead to formation of the sulfate, mainly in an acidic environment where carbonates are not present and cause precipitation of uranium. Uranyl sulfate plays a major role in ore processing as it is readily absorbed on anion-exchange resins and may be extracted with amines. As the uranyl sulfate is very stable, the solutions can be heated to elevated temperatures that help dissolve difficult to digest ores. 

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