Designing copolymers for the encapsulation of 85SR(II) and 134CS(I)

Abstract

Geopolymers have been used as building materials, encapsulation for hazardous materials and radioactive waste. This study involves the investigation of a series of geopolymers of molar ratio Si/Al 1-2 and Na/Al 1-1.3 for the encapsulation of radioactive cesium and strontium. Each geopolymer was prepared with a known quantity of Sr(ll) and Cs(l) doped with radioactive 85Sr and 134Cs, respectively. The 134Cs (t1/2= 2.065 years) was produced by neutron irradiation of natural Cs2C03 and the 85Sr purchased from a commercial supplier.

Once mixed the geopolymers were cured at 22 oc for 24 hours followed by 60 oc for a further 24 hours. They were then ground to a powder and known quantities incubated in acetate solution (0.001M; 4 - 10 mL) at 22 oc for 7 days. The acetate solutions were sampled [3 x (20-100) uL] without treatment for the release of 85Sr and 134Cs over various time intervals using a gamma counter. The detection limits for 85Sr and 134Cs was correlated to Sr and Cs released at subpicomolar concentrations. Results showed there was no evidence of 85Sr leaching from any of the geoploymers however the 134Cs release rates varied across the series of geopolymers. A number of techniques were used to determine the porosity of the geopolymers including positron annhiliation lifetime spectroscopy. In conclusion, geopolymers can be designed for controlled encapsulation of Sr and Cs, and tailored to release metal ions at various rates.