PhD student: Mercedes Baxter

The fuel ponds at Sellafield contain a brucite-rich sludge, with a pH of 9 – 10. The focus of the PhD is on storing the sludge and making it safe, by converting the waste to a magnesium silicate hydrate (M-S-H) based binder.

Magnesium silicate hydrate cements are a relatively new type of binder that can be made using brucite (or MgO) and soluble silica to form an amorphous M-S-H gel. This has a pH of 9.5 – 10.5, which is compatible with other products also contained in the sludge (e.g. Al, Mg). M-S-H therefore offers a potential for waste volume reduction and immobilisation, as the sludge would effectively be part of the stabilising cement. The long-term durability and behaviour of M-S-H gel is largely unknown.

The overall aim of the research is to determine how the sludge should be pre-treated to produce a suitable M-S-H based wasteform and to characterise its long-term durability. This will be achieved by creating an artificial sludge like material by slow formation and sedimentation of Mg(OH)2. The simulated sludge will then be processed to produce M-S-H based wasteforms. These M-S-H based wasteforms will then be studied, focusing on the composition, microstructure, mechanical and durability properties at different ages and under varying conditioning regimes.