Experimental Study On The Mechanism Of Low-level Radioactive TBP/OK Organic Liquid Solidificated By Metakaolin Phosphoric Acid Based Geopolymer

The radioactive waste extraction agent produced in the process of spent fuel reprocessing is degraded by the effects of tributyl phosphate and kerosene organic liquid?TBP/OK?by chemical and radiation,containing a variety of radionuclides such as U and Cs.The industrial treatment and disposal of the waste liquid is a worldwide problem.This research proposes a method for curing simulated radioactive TBP/OK organic liquid using metakaolin phosphate base polymer,and studies the curing mechanism.The main work is as follows:A metakaolin phosphate base polymer was synthesized,and the fluidity and coagulability of the geopolymer were improved.The results showed that the degree of response of geopolymers was positively correlated with curing temperature and negatively correlated with curing humidity.The suitable curing temperature of metakaolin phosphate base polymer was 50?,and the humidity was greater than 98%.Melamine can effectively improve the flowability of geopolymers.A sol-gel method was used to synthesize silicon-aluminum powder,which reacts rapidly with phosphoric acid and the setting time can be effectively shortened.Based on the characterization of different proportions of geopolymers,a reaction model was proposed and verified by experiments.The study demonstrated that metakaolin was depolymerized into oligomeric silicon and Al³⁺under the action of phosphoric acid,and PO₄^3-was dissociated by phosphoric acid.These silicon-oxygen tetrahedrons,aluminum-oxygen tetrahedrons,and phosphorus-oxygen tetrahedrons were bonded and condensed into geopolymers.During the polycondensation,the phosphorus-oxygen tetrahedrons were bonded to each other and bonded to the aluminum-oxygen tetrahedron to form a P-O-P-O-Al unit.The silicon-oxygen tetrahedron demetrified from metakaolin was also bonded to the phosphorus-oxygen tetrahedron to form Si-O-P-O-Si units.These two units were connected into a three-dimensional network structure to form a geopolymer gel.The geopolymer gels were attached to the dealuminated silica layer of metakaolin to form geopolymers.The pseudo-boehmite was used as the Al donor,the nano-si lica sol was used as the Si donor,and the hardened adhesive was synthesized by phosphoric acid excitation.The aluminum dihydrogen phosphate was used as the P and Al donor,and the nano-silica sol was used as the Si donor.Hardened adhesive.The characterization results of the two types of dry glue were similar to those of the geopolymers,which verified the correctness of the model.The TBP/OK organic liquid was cured using an emulsion curing method.Using Tween 80?T80?as an emulsifier,a TBP/OK phosphate emulsion was prepared by an ultrasonic dispersion method,and the emulsion was used to excite metakaolin to prepare a geopolymer solidified body.The test results showed that the strength of the cured body was 59.9 MPa when the capacity of TBP/OK was 18%.After 42 days of immersion in deionized water at 25°C,the strength decreased by 12%,and after 5 freeze-thaw cycles,the strength decreased by 23%,which met the requirements of Chinese standards.The leaching test revealed that the amount of TBP/OK leaching in the solidified body was limited,and the TPP/OK solidification by the geopolymer was a physical seal.Cs⁺was cured with metakaolin phosphate base polymer,and the curing effect met the requirements of the specification.The specific surface area of phosphoric acid base polymer is small and the adsorption capacity for Cs⁺is weak due to the encapsulation of the silicone layer by the geopolymer gel.H₂PO₄^-dissociated from phosphoric acid combines with Cs⁺to form cesium dihydrogen phosphate?CsH₂PO₄.6H₂O?crystals,which makes Cs⁺exists as a crystalline mineral,but the solidification of Cs⁺by geopolymers is mainly physical sealing.The curing formula of metakaolin phosphate base polymer suitable for industrial production was developed,and a curing test of radioactive TBP/OK simulation machine fluid was conducted.The mechanical properties and anti-soaking performance of the obtained cured body met the requirements of the specification.