Patent Number: 
Section: description

In the following, the inventor will use some laboratory examples to illustrate in detail the co-solidification method as well as the preparation of solidification agents. These embodiments of the invention, including their procedures, conditions and results, only partly indicate the application range of the invention: they do not represent the full scope of the same and can not be regarded as limits to the same. Take 920 parts (by weight, same for all the parts to be mentioned) of 98 wt. % sodium hydroxide solution and 2760 parts of barium sulfate, and mix them in an agitator, at the same time slowly add in 2300 parts of deionized water. Agitation continues until sodium hydroxide is wholly dissolved, then wait till the solution cools down to 30xc2x0 C., and keep it at that temperature. Before adding in solidification agent, weigh the solution and add in suitable amount of 30xc2x0 C. deionized water to compensate for water loss due to vaporization during the agitation process. Prepare homogeneous powdery solidification agent by mixing and grinding together type-2A cement (a product of Taiwan Cement Cooperation), pozzolanic materials (including blast furnace slag powder and fly ash), and silicon, phosphate, calcium phosphate and magnesium phosphate powders. The major components of this solidification agent are 27.14% SiO2, 6.86% Al2O3, 46.29% CaO, 1.71% Fe2O3, 2.14% MgO, 7.71% P2O5, and 5.57% SO3, by chemical analysis. Then, gradually add this homogeneous powdery solidification agent into the sodium hydroxide and barium sulfate mixture solution, to which vigorous agitation is applied at the same time, till the resultant slurry becomes visibly homogeneous. Weight ratio of solidification agent to the slurry is 0.54. In this experiment, as soon as the last particle of solidification agent is added into the agitator, agitation continues for 10 more minutes, and then immediately pour the slurry into a number of cylindrical polyethylene moulds, each of these moulds being of inner diameter 5 cm and height 11 cm, which are then sealed and laid still in room temperature over a period of 30 days for setting and hardening. And then take out the solidified wastes from the moulds, from which select five and saw off their rough ends to make five standardized cylindrical specimens, 10 cm in length. Compressive strength tests are performed with these five specimens following the test procedures of ASTM C39, according to the requirement of U.S. Nuclear Regulatory Commission (USNRC). The average compressive strength of these five specimens is found to be 50 kg/cm2. Additionally, following the standard test procedures specified by Taiwan Atomic Energy Council for low-level radioactive wastes quality control, it is found that the average compressive strength after water immersion (i.e. the compressive strength of a specimen after its being soaked in water for 90 days) of these specimens is 81 kg/cm2; and their average compressive strength after thawing-and-freezing (i.e. the compressive strength of a specimen after its being placed within weather test chamber run with 30 cycles of temperature from xe2x88x9210xc2x0 C. to +60xc2x0 C., and of relative humidity from 60% to 95%) is 48 kg/cm2. Dissolve 373 parts of 98 wt. % sodium hydroxide solution in 2038 parts of water, then add in 1167 parts of powdery ion-exchange resin (POWDEX, the trade name); vigorously mix them for 30 minutes to form a homogeneous slurry. Prepare powdery solidification agent according to the method given in Embodiment I. The major compositions of this solidification agent are 23.2% SiO2, 4.59% Al2O3, 61.19% CaO, 3.79% Fe2O3, 2.88% MgO, 2.2% P2O5, and 1.58% SO3, by chemical analysis. Apply the same solidification method as before; only this time the weight ratio of solidification agent to the slurry is 0.887. Solidified waste specimens are prepared also in the same way as already discussed in the previous example, from which five are selected for testing. The average compressive strength of these specimens is 59 kg/cm2, their average compressive strength after water-immersion test is 113 kg/cm2, and after thawing-and-freezing test is 72 kg/cm2. Dissolve 482 parts of sodium hydroxide in 1800 parts of water, then add in 1418 parts of barium sulfate and 1354 parts of powdery ion exchange resin (POWDEX); vigorously mix them into a homogeneous slurry. Prepare powdery solidification agent according to the method given in Example I. The major compositions of this solidification agent are 36.05% SiO2, 5.72% Al2O3, 38.61% CaO, 1.43% Fe2O3, 1.79% MgO, 9.61% P2O5, and 4.65% SO3. Apply the same solidification method as before; only this time the weight ratio of solidification agent to the slurry is 0.425. Solidified waste specimens are prepared also in the same way as before, from which five are selected for testing. The average compressive strength of these specimens is 58 kg/cm2, their average compressive strength after water-immersion test is 111 kg/cm2, and after thawing-and-freezing test is 64 kg/cm2. Dissolve 580 parts of sodium hydroxide in 2346 parts of water, then add in 1285 parts of barium sulfate and 1449 parts of powdex; vigorously mix them into a homogeneous slurry. Prepare powdery solidification agent by the same method as shown in Example I. The major compositions of this solidification agent are 30.72% SiO2, 3.08% Al2O3, 41.02% CaO, 2.54% Fe2O3, 1.93% MgO, 19.28% P2O5 and 1.06% SO3. Apply the same solidification method as before; only this time the weight ratio of solidification agent to the slurry is 0.389. Solidified waste specimens are prepared also in the same way as before, from which five are selected for testing. The average compressive strength of these specimens is 39 kg/cm2, their average compressive strength after water-immersion test is 53 kg/cm2, and after thawing-and-freezing test is 56 kg/cm2. Collect 2765 parts of 20 wt. % sodium sulfate liquid waste from Taiwan Nuclear Power Plant II, which is then gradually mixed in with 1226 parts of barium hydroxide powder, Ba(OH)2.8H2O, to produce a barium sulfate and sodium hydroxide mixture solution. The solution is slowly heated up to get rid of 1745 parts of water through vaporization, and then, 864 parts of spent powdery ion-exchange resin (POWDEX) also obtained from the nuclear power plant is mixed in to form a homogeneous slurry. Wait till the temperature of the slurry cools down to 30xc2x0 C., then add in powdery solidification agent which is the same as that of Example III. In this experiment weight ration of solidification agent to the slurry is 0.389. Specimen preparation and compressive-strength test procedures are again same as before. The average compressive strength of these specimens is 43 kg/cm2, their average water-durable compressive strength after water-immersion test is 46 kg/cm2, and after thawing-and-freezing test is 46 kg/cm2. Moreover, by the test method of ANSI 16.1 the average filtration indexes of Co-60, Cs-134 and Cs-137 are found to be 8.34, 6.27 and 6.32 respectively. While the invention has been particularly shown and described with reference to the foregoing embodiments, it will be understood by those who are skilled in the art that other changes can be made therein without departing from the spirit and scope of the invention in its broader aspects.