The disposal of radioactive ferric floc

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% 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(OH) 12(CO 3), Ca 6Fe 2(SO 4) 3(OH) 12 · 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.