Reduction of Plutonium in Acidic Solutions by Porous Carbon Solids

摘要

Manipulation and control of the oxidation state of plutonium is applicable to almost all processes involving remediation, separation and chemical purification of plutonium, both in industrial and academic laboratory settings. Electrochemical methods using a potentiostat are generally preferred for preparation of the different Pu oxidation states in chemistry laboratories. Reduction of Pu in any oxidation state at a platinum cathode will yield Pu(Ⅲ), but if the starting oxidation state is Pu(Ⅴ) or Pu(Ⅵ), the reduction is quite slow due to the large overvoltage required for the Pu(Ⅴ)-Pu(Ⅳ) reduction. Reduction by this method is time-consuming and not feasible if there is a large volume of solution to be reduced. Alternative methods generally involve the addition of chemical reducing agents, such as Fe(Ⅱ), or NO_2~-. However, the addition of chemicals can further complicate the solution chemistry, leading to more purification steps. Thus, the idea of Pu(Ⅵ) reduction to a lower oxidation state by simple contact with a solid surface is appealing. Furthermore, the ability to concentrate Pu(Ⅵ) from large solutions onto a solid, and then strip the Pu in a lower oxidation state with a small volume of acid for reprocessing would help the laboratory avoid expensive transuranic waste requisitions, with very little time commitment. Porous carbon materials with high surface areas are electrically conductive and may behave as reducing agents toward Pu and other metals. In our previous work, both as-synthesized and chemically oxidized nanocast mesoporous carbon showed superior Pu sorption capacity compared to activated carbon, and X-ray absorption spectroscopy (XAS) showed that oxidized Pu(Ⅴ/Ⅵ) were reduced to Pu(Ⅳ) at the mesoporous carbon surface in solutions with pH 2-7.