Effect of organics on selenite uptake by cementitious materials

The behaviour of three organic ligands in suspensions of fresh and degraded hydrated ordinary Portland cement pastes (HCP) has been investigated. EDTA arises as a decontamination product whilst ISA (isosaccharinic acid) is a main degradation product of cellulose. GLU (gluconic acid) is used as a retarding organic admixture in concrete. The affinity of EDTA, ISA and GLU with HCP increases with the degradation state. At long contact times, ISA and GLU desorbed from HCP, perhaps as a result of carbonation. Their influence on the uptake of selenium (as SeO3(2-)) on HCP has been studied as a function of time, addition order and HCP degradation state. The sorption study of Se(IV) also shows a positive effect of the HCP degradation with R(d)=120 mLg(-1) for fresh HCP and 1000 mLg(-1) for degraded HCP. The addition order of Se(IV) and EDTA or ISA is important as pre-equilibration of HCP with either EDTA or ISA drastically decreases the uptake of Se(IV) to 10-30 mLg(-1). Mixing of cement with GLU seems to reduce the strong competitive effect of other organic compounds on Se(IV) sorption.