Possibility of fly ash as backfill material sorbability and permeability of fly ash

Sorption and permeability experiments on bentonite/sand/fly-ash mixtures were carried out to examine the feasibility of using fly ash as backfill material. Each type of fly ash had distinct sorption characteristics of Sr, Cs, and Co according to its chemical properties. The most favorable sorbent for Sr was a weakly-alkaline ash, whereas that for Cs and Co was a highly-alkaline ash. In addition, highly-alkaline ash caused a sedimentation/dissolution reaction, which enhanced Co sorbability. On the other hand, the permeability of the mixtures greatly depended on bentonite content and dry density, regardless of the type and the content of fly ash. These results suggest that fly ash can be used as an efficient additive of backfill material if the pertinent mixing ratio of materials is chosen in accordance with waste inventories