Purification of alkaline solutions and wastes from actinides and technetium by coprecipitation with some carriers using the method of appearing reagents: Final Report

Abstract

The coprecipitation of transuranium elements and technetium from alkaline solutions and from simulants of Hanford Site tank wastes has been studied in reducing and oxidizing conditions on uranium(IV,vT) hydroxocompounds, tetraakylammonium perrhenate and perchlorate, and on hydroxides of Fe(m), Co(III), Mn(II), and C r o using the Method of Appearing Reagents (MAR). Coprecipitations in alkaline solution have been shown to give high decontamination factors (DF) at low content of carrier and in the presence of high salt concentrations.Uranium(IV) hydroxide in concentrations higher than 3~1 0 -~ M coprecipitates Pu and Cm in any oxidation state from 0.2 to 4 M NaOH with DFs of 110 to lo00 and Np and Tc with DFs of 51 to 176. UraniumCvI), introduced as a sodium uranate precipitate or the soluble peroxocomplex salt NaUO2(02)3, can be partially reduced in 0.2 to 2 M NaOH by hydrazine to U30~.nH20 in the presence of (1 to 5 )~1 0 -~ M Tc(VII). The Tc(VlI) is first reduced to Tc(IV). The product U308.nH20, at 0.012 to 0.05 M uranium, coprecipitates Np, Pu, Cm, and Tc in any oxidation state with DFs greater than 100 from 0.2 to 1.5 M NaOH. Increasing alkali concentration to 4 M NaOH decreases the DFs slightly for TRU and drastically for Tc. Coprecipitation under the same conditions from simulated tank waste containing 3.2 M NaOH, 0.04 M C1-05-and 11 complex-forming salts yields the following DFs: Np-12, Pu-27, Cm-35, Tc-3. The decrease of DFs in the waste simulant is associated with complex formation and with inhibition of Np and Tc coprecipitation by the Cr(m) hydroxide that is formed before Np(IV) and Tc(IV). Coprecipitated Tc may be effectively leached from U30p-nH20 by oxidation of Tc(IV) to Tc(VII) by use of dilute H202 or by NaOH solution and air bubbling. Under these same conditions, more than 99% of the Pu is retained in the solid phase. iii

Strontium and Actinides Removal from Savannah River Site Actual Waste Samples by Freshly Precipitated Manganese Oxide

“…Examination of the Sr data indicates that the bulk of decontamination occurred within 2 h. This observation mimics that observed in prior studies using manganese oxide to treat Hanford high-level waste. 3 The data indicate that the Manganese without Strontium tests proved the most rapid and the Nominal Manganese tests proved the slowest of all test sets. However, no conclusions on the rates of decontamination should be made given the small number of samples and the minor differences in data.…”

“…This approach follows similar studies performed for Hanford waste. 3 If successful, this process offers increased throughput resulting in decreased equipment size. The DOE also requested that SRTC conduct tests to evaluate the capability of MST in actual high-level waste that contained elevated concentrations of Pu and Np as a means of comparison to the manganese oxide treatment.…”

Process Development for Permanganate Addition during Oxidative Leaching of Hanford Tank Sludge Simulants

“…Two reductants were investigated: hydrogen peroxide and hydroxylamine. It is known that in alkaline solution, hydrogen peroxide can be oxidized by permanganate (Peretrukhin et al 1998), and hydroxylamine was chosen as a potentially more easily handled reductant. The first breakpoint in Figure 3.14 corresponds to a 1:1 hydroxylamine:permanganate stoichiometry and the second to a 1.5:1 hydroxylamine:permanganate stoichiometry.…”

Criticality safety evaluation of disposing of K Basin sludge in double-shell tank AW-105

“…The Potential for Criticality in Hanford Tanks Resultingfrom Retrieval of Tank Waste (Peretrukin et al 1998). …”