Optimization of composite admixtures used in cementation formula for radioactive evaporator concentrates

• Evaporator concentrate was solidified by sulfoaluminate cement blending.
• The effect of admixtures on waste form was studied by Plackett–Burman design.
• The composite admixture was optimized by desirability function.

The radioactive evaporator concentrates were solidified by sulfoaluminate cement blending with zeolite, blast-furnace slag, silica fume and fly ash. Particular attention was paid to the effect of admixtures and to the optimization of composite admixture. The effects of admixtures on waste form performances were investigated by Plackett–Burman design. The results indicated that blast-furnace slag and silica fume showed positive effect on 7d compressive strength while zeolite and fly ash negative effect when blending amount was less than 10%. Blast-furnace slag and fly ash increased the fluidity of paste while zeolite and silica fume decreased it. Higher Cs+ leachability index was achieved with increasing amounts of all four admixtures. The composite admixtures were optimized by desirability function as follows: 5.0% zeolite, 10.0% blast-furnace slag, 9.0% silica fume and 4.0% fly ash. The composite admixtures improved the performances of waste forms synthetically: the 7d compressive strength, fluidity and Cs+ leachability index reached to 13.6 MPa, 230.0 mm and 9.36, respectively.