Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Radioactive metal
Patent
1996-10-28
1998-10-20
Miller, Edward A.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Radioactive metal
423 18, 423 82, 423 86, C01G 4300, C01F 1300
Patent
active
058261621
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for facilitating the removal of impurities, especially but not only radionuclides such as uranium and thorium and their radionuclide daughters, from titaniferous materials, and is concerned in particular embodiments with the removal of impurities, including especially uranium and thorium, from products formed from weathered or "altered" ilmenite.
BACKGROUND ART
Ilmenite (FeTiO.sub.3) and rutile (TiO.sub.2) are the major, commercially-important, mineral feedstocks for titanium metal and titanium dioxide production and generally occur together in nature as components of "mineral sands" or "heavy minerals", along with zircon (ZrSiO.sub.4) and monazite ((Ce, La, Th)PO.sub.4). Natural weathering of ilmenite results in partial oxidation of the iron, originally present in ilmenite in the ferrous state (Fe.sup.2+), to ferric iron (Fe.sup.3+). To maintain electrical neutrality, some of the oxidised iron must be removed from the ilmenite lattice. This results in a more porous structure with a higher titanium (lower iron) content. Such weathered materials are known as "altered" ilmenites and may have TiO.sub.2 contents in excess of 60% TiO.sub.2, compared with 52.7% TiO.sub.2 in stoichiometric (unaltered) ilmenite. As weathering, or alteration, of the ilmenite proceeds, impurities such as alumino-silicates (clays) are often incorporated into the porous structure as discrete, small grains that reside in the pores of the altered ilmenite. It appears that uranium and thorium can also be incorporated into the ilmenite during this process.
Most of the world's mined ilmenite is used for the production of titanium dioxide pigments for use in the paint and paper industries. Pigment-grade titania (titanium dioxide, TiO.sub.2) has been traditionally produced by reacting ilmenite with concentrated sulphuric acid and subsequent processing to produce a TiO.sub.2 pigment--the so-called sulphate route. However, this process is becoming increasingly undesirable on environmental grounds due to the large volumes of acidic liquid wastes which it produces. The alternative process--the so-called chloride route--involves reaction with chlorine to produce volatile titanium tetrachloride (TiCl.sub.4) and subsequent conversion to TiO.sub.2 . Unlike the sulphate route, the chloride route is capable of handling feedstocks, such as rutile, which are high in TiO.sub.2 content and low in iron and other impurities. Consequently the chloride-route presents fewer environmental problems and has become the preferred method for TiO.sub.2 pigment production. Natural rutile supplies are insufficient to meet the world demands of the chloride-route. Thus, there is an increasing need to convert the more-plentiful ilmenites and altered ilmenites (typically 45 to 65% TiO.sub.2) to synthetic rutile (containing over 90% TiO.sub.2). A number of different processes have been developed to upgrade ilmenite to synthetic rutile, the most widely used, commercially, being the Becher process.
The Becher process involves the following main stages. ilmenite feed largely to metallic iron, at temperatures in the range 900.degree.-1200.degree. C., using coal as the heat source and the reductant. The principal product is known as reduced ilmenite (RI). reduction kiln. the metallic iron to iron oxide particles discrete from the TiO.sub.2 -rich mineral particles. -rich mineral. Hereinafter the product of this step is referred to as "aerated product". some manganese and magnesium.
Whether ilmenite is marketed as the raw mineral or as upgraded, value-added, synthetic rutile, producers are being increasingly required to meet more stringent limits for radioactivity levels in their products. To meet the limits requires the removal of uranium and thorium and their radionuclide daughters from the material. The Becher synthetic rutile process does not reduce significantly the levels of uranium and thorium in the product and so there has been an increasing need to develop an economic and effective process for removal of uran
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Aral Halil
Bruckard Warren John
Freeman David Edward
Grey Ian Edward
Harris Harold Robert
Miller Edward A.
RGC Mineral Sands Limited
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