The leaching behaviour of Cs and Sr is dependent on how they are retained within the cement. The project found that Cs remains as CsNO3. Sr(NO3)2, however, was not present in the hardened cement and retained within the hydrogarnet and a nitrated AFm phase. Secondly the impact of superplasticisers on the leaching behaviour of the cement matrix containing cerium was also explored using ADVA cast 551. Cerium was chosen as opposed to caesium or strontium as the main concerns in industry due to superplasticisers is regarding the complexion of uranium and plutonium, and Ce is a good simulant for plutonium. It was found that the introduction of ADVA cast 551 increased the fluidity and workability of the cement, did not alter the cement crystal structure however did increase the leached amounts of Ce by approximately 30%. In storage conditions this complexed Ce would come into contact with the cement backfill. A flow through leaching test was used on an NRVB cement sample and synthesised solutions of the leached Ce including the ADVA cast 551 to monitor how much Ce would pass through. It was found that similar amounts of Ce had passed through the NRVB whether the solution contained superplasticiser or not. This project found that the leaching behaviour of ions was dependent on how the ion is present and in which phase. Due to Cs and Sr being incorporated differently the Cs leaches much faster than the Sr, as it is not incorporated into any phase. The Sr is associated with several phases, however is mainly found to be associated with AFm type phases. The most efficient leaching accelerant method is the electrical method; therefore with further investigation this could potentially be used to explore the optimal cement compositions for cementitious waste immobilisation. This could also be used in cement samples containing superplasticiser, given that this increases mobility over short durations, the next step would be to investigate the long-term impacts, via simulation using electrical leaching. List of Abbreviations Cement Nomenclature AFm Alumino-ferrite-mono phase AFt Ettringite C-S-H Calcium silicate hydrate C3S Tricalcium silicate, Ca3SiO5 C2S Dicalcium silicate, Ca2SiO4
The leaching behaviour of Cs and Sr is dependent on how they are retained within the cement. The project found that Cs remains as CsNO3. Sr(NO3)2, however, was not present in the hardened cement and retained within the hydrogarnet and a nitrated AFm phase. Secondly the impact of superplasticisers on the leaching behaviour of the cement matrix containing cerium was also explored using ADVA cast 551. Cerium was chosen as opposed to caesium or strontium as the main concerns in industry due to superplasticisers is regarding the complexion of uranium and plutonium, and Ce is a good simulant for plutonium. It was found that the introduction of ADVA cast 551 increased the fluidity and workability of the cement, did not alter the cement crystal structure however did increase the leached amounts of Ce by approximately 30%. In storage conditions this complexed Ce would come into contact with the cement backfill. A flow through leaching test was used on an NRVB cement sample and synthesised solutions of the leached Ce including the ADVA cast 551 to monitor how much Ce would pass through. It was found that similar amounts of Ce had passed through the NRVB whether the solution contained superplasticiser or not. This project found that the leaching behaviour of ions was dependent on how the ion is present and in which phase. Due to Cs and Sr being incorporated differently the Cs leaches much faster than the Sr, as it is not incorporated into any phase. The Sr is associated with several phases, however is mainly found to be associated with AFm type phases. The most efficient leaching accelerant method is the electrical method; therefore with further investigation this could potentially be used to explore the optimal cement compositions for cementitious waste immobilisation. This could also be used in cement samples containing superplasticiser, given that this increases mobility over short durations, the next step would be to investigate the long-term impacts, via simulation using electrical leaching. List of Abbreviations Cement Nomenclature AFm Alumino-ferrite-mono phase AFt Ettringite C-S-H Calcium silicate hydrate C3S Tricalcium silicate, Ca3SiO5 C2S Dicalcium silicate, Ca2SiO4
Wail%20Gashier%20Thesis.docx