The disposal of radioactive ferric floc

摘要

An iron hydroxide floc is used as treatment for adsorbing low amounts of actinides during nuclear fuel re-processing. This waste is cemented only after pre-treatment with Ca(OH)_2. Characterisation of all simulant material has been undertaken using XRD, TGA and SEM/EDS. The floc is a moderately alkaline colloidal slurry containing approximately 15 wt percent solids, with the main particulate being an amorphous hydrated iron oxide. The main phase formed during pre-treatment appears to be an X-ray amorphous hydrated calcium-ferrate phase. Embedded within this are small amounts of crystalline Ca(OH)_2, calcite, Fe_6(GH)_12(CO_3), Ca_6Fe_2(SO_4)_3(OH)_12 centre dot 26H_2O and Ca_3B_2O_6, and can form depending on concentrations of Ca(OH)_2 and time. Apart from Ca(OH)_2 and calcite, none of the crystalline phases detected during pre-treatment are detected when the floc is encapsulated in an OPC/PFA composite cement hydrated for 90 days. The main crystalline phase detected in the hardened wasteform is a solid solution hydrogarnet, Ca_3AlFe(SiO_4)(OH)_8, known as C_3(A,F)SH_4 in cement chemistry nomenclature.