The Performance of Various Pozzolanic Materials in Improving Quality of Strontium Liquid Waste Cementation

Cementation is one method to immobilize liquid radioactive waste in order to protect the environment from radionuclide release. Rice husk ash (RHA) and fly ash (FA) of a coal fired power plant have been success used as pozzolanic materials for several years. The aim of this research is to understand the ability of RHA and FA pozzolan on strontium liquid waste cementation process. This research was conducted by mixing strontium liquid waste with sand, Portland cement, various water-cement ratios (w/c) and 10v/o of RHA and FA. The cement blocks were tested by a pressing machine to determine their compressive strength after cured for 28 days. Strontium leaching rate encapsulated on the blocks was analyzed by Hitachi Zeeman 8000 Atomic Absorption Spectrophotometer for 21 days. The strontium adsorption process of RHA and FA were also analyzed by X-ray Diffraction (XRD). The effect of the initial strontium concentration and the flow rate of waste on the adsorption ability of both materials was also studied. This research showed that the addition of pozzolanic material increase the compressive strength of mortar. The compressive strength of mortar with FA is 158%∼253% stronger than RHA one due to the difference of of SiO2 content and grain size of both materials. The leaching rates of strontium in pozzolan-mortars are lower than IAEA standard which FA-mortar is 140% higher than the RHA one due to the adsorption capacity and the content of Na2O on both materials. So, the addition of pozzolanic material could improve the quality of strontium liquid waste cementation.