Immobilisation of Fe floc: Part 1, pre-treatment of floc with slaked lime

A series of radioactive iron (Fe(3+)) hydroxide flocs are produced during reprocessing of nuclear fuel at Sellafield, UK. Before the flocs can be successfully encapsulated in a pulverised fuel ash/ordinary Portland cement composite cement to form a durable cemented wasteform, they need to be pre-treated with slaked lime. This paper reports results after investigating the reaction between a simulant floc and the slaked lime and shows that the floc reacts readily to form an X-ray amorphous hydrated calcium ferrite. Calcite (CaCO(3)), formed from carbonation of Ca(OH)(2), appears to contribute to the formation of a crystalline iron hydroxy carbonate phase (Fe(6)(OH)(12)(CO(3))). This work concludes that pre-treatment allows a pozzolanic reaction to occur between the pulverised fuel ash and the Ca(OH)(2) produced during cement hydration. This increases the quantity of C-S-H formed and increases the compressive strength of the hardened wasteform enough to withstand forces generated during curing and prevent cracking. (C) 2009 Elsevier B.V. All rights reserved.