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, Fe6(OH)12(CO3), Ca6Fe2(SO4)3(OH)12 • 26H2O and Ca3B2O6, 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, Ca3AlFe(SiO4)(OH)8, known as C3(A,F)SH4 in cement chemistry nomenclature.