Patent Number: 053405064
Section: description

The following Examples are given to illustrate the invention, but are not to be taken as limiting the scope of the invention which is defined in the appended claims. EXAMPLE I Typical Preparation of the Sodalite Intermediate The sodalite intermediate was prepared by intimately mixing 2.8 g of NaOH, 32.8 g of Al.sub.2 O.sub.3, and 41.4 g of SiO.sub.2 (mole ratio of 2:1:2; weight ratio of about 1:1.27:6.60). About 100 g of this mixture is placed in a high-fired alumina crucible and heated to 500.degree. C. for 30 hours. The result is the reaction of the NaOH to form water, which is driven off, and compounds such as NaAlO.sub.2, Na.sub.2 SiO.sub.3, and Na.sub.2 Si.sub.2 O.sub.5, which are components of the sodalite intermediate along with Al.sub.2 O.sub.3 and SiO.sub.2. The products are kept dry and ground to a fine powder with particle sizes less than 500 .mu.m. The intermediate prepared in this manner is more reactive than a mixture of the pure materials. The reaction can be carried out in air, but the products are stored under a dry inert atmosphere, for example purified argon or helium. EXAMPLE II Immobilization of Zeolite-Salt Mixture A synthetic zeolite-salt waste material was prepared in a dry, inert atmosphere by mixing about 30 g of molten LiCl-KCl eutectic salt containing about 0.8 wt % SrCl.sub.2 2 wt % BaCl.sub.2, and 4.9 wt % CsCl with about 5 g of the sodium form of zeolite A. After gently mixing the salt and zeolite at 400.degree. C. for 8 hours, 21.8 g of the salt was separated by forcing it through a sintered steel filter having 50 .mu.m pores, and passing a stream of argon gas through the residue for about 1 hour. The filtered molten salt contained reduced amounts of strontium, cesium and barium, and negligible amounts of zeolite decomposition products. The salt-zeolite residue, which weighed 13.2 g, contained about 94% of the strontium, 85% of the barium, and 45% of the cesium that were in the original salt. The salt-zeolite residue was removed from the filter and ground to a powder with a particle size of less than 5005 m. EXAMPLE III Typical Immobilization of Zeolite-Salt Waste Material In a dry, inert atmosphere, 30 g of sodalite intermediate prepared as described in EXAMPLE I, and ground to a particle size of less than 500 .mu.m, was intimately mixed with 6.6 g of the zeolite-salt waste prepared as described in EXAMPLE II above. The resulting mixture contained sufficient intermediate to encapsule the 4.1 g of salt into sodalite if none of the zeolite converted to sodalite. This mixture was placed in a steel die, and heated to 325.degree. C. at 70 MPa for 6.5 hours. The resulting green pellet was sealed in a stainless steel container and heated for 750.degree. C. for 168 hours. The final pellet was hard and strong. EXAMPLE IV Typical Preparation of Sodalite from Waste Salts Crushed salt (LiCl-56 wt % KCl) was intimately mixed with sodalite intermediate prepared as described in EXAMPLE I in proportions that the salt content of the mixture is 10 wt %. The mixture is heated to 360.degree. C. in a steel die and pressed at 60 MPa. The preparation of a suitable green pellet is aided by the temperature being above the salt melting point. This pellet is then placed in a sealed stainless steel container and heated to 700.degree. C. for 100 hours to prepare a final pellet that is white, and very hard. EXAMPLE V The pellet prepared according to EXAMPLE IV was subjected to a leaching test similar to the standard procedure set forth in ANS 16.1. The pellet had a Leachability Index of about 13 for strontium and 12 for cesium indicating that the leach rates of these elements were about one-tenth their leach rates from mortars with the best formulations.