Patent Number: 047708174
Section: summary

BACKGROUND OF THE INVENTION A formidable impediment to the widespread use of nuclear power is concern over the safe disposal of nuclear waste products. While a great many proposals have been advanced for sealing these products in various glasses and other types of materials, many of these processes are expensive and do not utilize materials of great long-term stability and resistance to leaching by subsurface water. A particularly desirable material for the storage of radioactive waste is .alpha.-alumina. This material is extremely stable and resistant to chemical attack and physical erosion. The difficulty in using it, however, is that it melts at a very high temperature and other materials have a low solubility in it. Radioactive materials cannot be easily processed at high temperatures because some of them can volatilize and may escape into the atmosphere unless great care is exercised. SUMMARY OF THE INVENTION We have discovered that radioactive waste and other solids which are dissolved in a liquid or formed into a colloid, can be sealed in an .alpha.-alumina matrix. The method makes use of a special Al.sub.2 O.sub.3 which has a large open porosity and which non-destructively converts to .alpha.-Al.sub.2 O.sub.3 at 1200.degree. C. by elimination of its entire porosity. The waste products are impregnated in the pores of this Al.sub.2 O.sub.3 initially, then the material is converted to .alpha.-Al.sub.2 O.sub.3, trapping and encapsulating the waste. Unlike prior processes for encapsulating radioactive waste material, this invention is a low temperature process requiring no thermal reaction of Al.sub.2 O.sub.3 with the waste material to form a stable crystalline or glassy phase with Al.sub.2 O.sub.3, nor does it require solubility of the waste material in alumina. It is also a simple and inexpensive process. The invention utilizes aluminum oxide, one of the best materials for containing radioactive waste, yet is able to seal the waste at a much lower temperature than the melting point of the aluminum oxide. PRIOR ART U.S. Pat. No. 3,941,719 discloses the preparation of non-particulate transition alumina having a porosity of about 63%. An article by Bulent E. Yoldas entitled, "A Transparent Porous Alumina," in The American Ceramic Society Bulletin, Vol. 54, No. 3, March, 1975, describes a non-particulate transition alumina having a porosity of about 63%. U.S. Pat. No. 4,012,337 discloses a process of forming .alpha.-alumina compositions from hydrated .beta.-alumina. The .alpha.-alumina is used as a support for catalyst compositions. U.S. Pat. No. 4,156,658 discloses a method for fixing radioactive ions in a porous media by injecting into the porous media a water-soluble organic monomer which is polymerizable to a gel structure with an ion exchange site. The monomer is polymerized to form ion exchange gels.