Pu(Ⅴ) Adsorption And Reduction On Montmorillonite

In the environment conditions, the predominent oxidation state of aqueous phase Pu is Pu(Ⅴ). It is important to study the Pu(Ⅴ) sorption and reduction reaction on the solid-phase in assessing the transport fate of Pu in environment. Techniques to analyzing the aqueous-and solid-phase oxidation state distribution of Pu and preparing of single oxidation state of trace plutonium solution were built. Based on these techniques, changes in aqueous-and solid-phase oxidation state was monitored and the dynamic of sorption and reduction was studied in the process of Pu(V) sorption on the montmorillite, which was purified from the bentonite from Toksun County of Xinjiang China.As a result,(1) The Pu(Ⅳ) solution was prepared by heating the solution until dryness in1mol/L HNO3repeatedly, and Pu(Ⅵ) solution was obtained by keeping Pu (Ⅳ) in0.5-1mol/L HNO3-O.1mmol/L KMnO4system for24hours. Pu(Ⅵ) was autoreduced to Pu(Ⅴ) in the dark for5days.(2) The oxidation state distribution of the solution was analyzed using solvent extraction methods, which Pu(Ⅳ) was extracted with TTA and Pu(Ⅳ+Ⅵ) was separated by HDEHP. Oxidation state of Pu in solid-phase was determined by leaching with0.05mol/L HCIO4for15min, which Pu(Ⅴ+Ⅵ) was leached into aqueous followed by an TTA/HDEHP extraction technique. The capability of the technique to measure Pu oxidation state was verified using232Th(Ⅳ)、237Np(Ⅴ)、238U(Ⅵ) as the Pu oxidation state analogues.(3) The oxidation distribution of Pu in aqueous and solid was monitored over the process of Pu(Ⅴ) sorbing on montmorillite. Pu(Ⅴ) was keeping steady in solution for a long period and if it was sorbed onto the solid-surface it would reduce to Pu(Ⅳ) immediately.(4) In the pH range2.3to6.3, the adsorption and overall reaction(describing both adsorption and reduction of Pu(Ⅴ)) rate were found to be of order0.34and0.58with respect to the [H+], respectively. In the pH6.3-9.4, both of the rate were approximately first order with respect to the montmorillite concentration and inherently with the concentration of NaCl and [H+]. In the process of Pu(Ⅴ) sorbed onto the montmorillite, adsorption was a rate-limiting step, and reduction was mediated by the solid phase.