Patent Number: 056132433
Section: description

The following examples further illustrate the invention. EXAMPLES Chloride solutions having the compositions indicated in the attached Table 1 were first evaporated to dryness at 80.degree. C. to produce solid residues. These residues were then held under a flow of steam at 200.degree. C. for one hour and then under a flow of steam and air at 800.degree. C. for two hours, ensuring both the completion of all possible hydrolysis and the development of crystalline properties. The granular solid residues were then allowed to cool in air. The solid wastes were then leached at room temperature (62.5 gpL) in synthetic groundwater (5 gpL sodium chloride, 500 mgpL sulphuric acid) maintained at pH below 5 by periodic additions of acetic acid. The leach was continued for 24 hours, after which the residue was filtered, washed with fresh synthetic groundwater and dried. Roasted and leached wastes were subjected to chemical analysis and gamma spectroscopy analysis for major elements and radionuclides. Radionuclide extraction from the solid wastes in leaching is also indicated for each case in the attached Table 1. Clearly those samples having lanthanide (eg. Ce) and P additions under circumstances which produced a waste needing little or no acid addition to maintain pH below 5 provided wastes which did not subsequently allow leaching of radionuclides. The absence of these elements or conditions resulted in a far less stable waste. However, it is expected that other elements may substitute for these main constituents, allowing for a range of effective compositions, provided that the effective circumstances as disclosed are maintained. Further, the addition of barium salts (made to liquor A1-9 of the attached table in a separate test) was found to have a strongly negative impact on the stability of uranium and radium in the wastes produced by otherwise identical treatment. Hence wastes containing barium, lanthanide and phosphorus (as have previously been produced in waste forms, due to the composition of wastes from nuclear fuel processing which contain zirconium and phosphorus) are herein disclosed as ineffective for the purposes for which the present invention is practised. In general where the effectiveness of the process depends on the presence of phosphorus and lanthanides the presence of elements which form more stable phosphates than lanthanides may require the addition of incremental compensating phosphorus for all other identical conditions. Solutions derived from the production of synthetic rutile by acid leaching of thermally treated ilmenite to which additives were made to result in solutions having the composition indicated in the attached Table 2 were also treated according to the method described above. Roasted and leached wastes were subjected to chemical analysis and gamma spectroscopy analysis for major elements and radionuclides. Radionuclide extraction from the solid wastes in leaching is also indicated for each case in the attached Table 2. TABLE 1 __________________________________________________________________________ Liquor Compositions and Waste Stability, Illustrating the Process Disclosed. A1-6 A1-9 A2-1 A2-2 A2-3 A2-4 A3-1 A3-2 A3-4 A3-5 A1-2 __________________________________________________________________________ Liquor, g/L Fe 0.25 23.2 0.27 0.27 0.27 0.27 0.27 0.27 58.1 0.27 36.8 Zr 2.01 2.01 1.98 1.98 1.98 1.98 1.98 1.98 -- 1.98 0.73 Si 0.058 0.058 0.29 0.29 0.29 0.29 0.29 0.29 -- 0.29 -- Ti 0.064 0.064 0.064 0.064 0.064 0.064 0.064 0.064 -- 0.064 -- Y 0.172 0.172 -- 0.172 -- 0.172 0.172 0.172 0.172 0.172 -- Mg 0.169 0.169 -- -- 0.169 0.169 0.169 0.169 -- 0.169 -- Al 0.43 0.43 0.43 -- -- 0.43 0.43 0.43 -- 0.43 -- P &lt;0.020 &lt;0.020 -- -- -- -- 0.09 0.09 0.09 0.135 -- Ca 6.50 6.50 6.50 6.50 6.50 6.50 6.50 6.50 -- 6.50 4.69 Ce 0.01 0.01 -- -- -- -- -- 0.011 -- 0.011 -- Hf 0.062 0.062 0.062 0.062 0.062 0.062 0.062 0.062 -- 0.062 -- Cl 71.0 114.7 71.0 71.0 71.0 71.0 71.0 71.0 110.7 71.0 78.5 Na -- -- 0.42 0.42 0.42 0.42 0.42 0.42 -- 0.42 -- U -238 0.028 0.028 0.029 0.029 0.029 0.029 0.029 0.029 0.029 0.029 0.5 Th -232 0.070 0.070 0.070 0.070 0.070 0.070 0.070 0.070 0.070 0.070 0.5 Ra -226 400 400 400 400 400 400 400 400 400 400 6000 H.sub.2 SO.sub.4 14.2 14.2 15.7 15.7 15.7 15.7 15.7 15.7 15.7 15.7 10.9 Addition (g/l) Waste Leach Results Acetic 0 0 47.6 33.2 41.4 46 3.9 48.4 0 0 0 Acid Addition 0.5.M mL/L U Extraction 0 6.2 8.0 3.6 8.6 6.5 13.0 0 13.3 0 69 Th Extraction 0 3.6 6.1 0 3.8 0 16.0 0 14.6 0 0 % Ra Extraction 0-10 21 18 34 71 44 0 28 11 15 44 % __________________________________________________________________________ TABLE 2 ______________________________________ Liquor Compositions and Waste Stability ______________________________________ Liquor, g/L A4-1 A4-2 A4-3 ______________________________________ Fe 84.4 86.9 83.8 Zr 0.009 5.15 5.12 Si 0.023 0.028 0.028 Ti 0.177 0.171 0.150 Y 0.011 0.012 0.012 Mg 2.29 2.41 2.10 Al 0.146 0.175 2.70 P 0.097 1.38 2.65 Ca 0.110 0.115 0.116 Ce 0.048 0.158 0.168 Hf -- -- -- Cl n.d. n.d. n.d. Na 0.515 0.555 0.546 U -238 0.180 0.182 0.158 Th -232 0.102 0.106 0.090 Ra -226* H.sub.2 SO.sub.4 Addition (g/l) 0 0 0 Waste Leach Results Acetic Acid Addition 0.5 .M mL/L 0 5.2 5.0 U Extraction % 19.8 0.13 0.08 Th Extraction % 0.11 0 0 Ra Extraction % 3 7 4 ______________________________________ n.d. = not determined *in radiochemical equilibrium with uranium