| Nuclear power, which is a noticeable and flourishing new energy at the moment, is undergoing a rapid growth whilst some security and environmental-related risks had emerged. The prevention and treatment of nuclear waste has drawn considerable attention, especially after the Fukushima accident.Technetium, with its 6.13% fission yield and 2.13×105 years long radioactive half-life,has been defined as an utmost baneful nuclear waste. Moreover, its common presence of TcO4-,which had shown tremendous mobility in both soil and water,making it impossible for technetium to be geologically disposed, which is an universally accepted disposal method of radioactive waste in the world. Rhenium(75Re), one of Tc’s chemical analogue, was used to avoid the use of Tc at high concentrations.The objectives of this experimental study were to investigate the effectiveness of using micro-nano natural pyrite for reduction-immobilization of Re in both soil and water by batch experiments and column experiments, also to understand whether natural pyrite was a desirable material of nuclear waste repository project.Firstly, micro-nano pyrite was prepared by high energy ball milling, the characterization results showed that the main component of the product(pyrite) was FeS2;Secondly, the effect of various aspects, which were solid-liquid ratio, initial pH, humic acid concentration and ionic strength of the solution, was studied by using batch experiment under hypoxic condition. The results showed that:(1)The removal rate of Re went up with the increasing dosage of pyrite, however, excess of pyrite had no significant positive effect on the removal rate. Therefore a 1:10 solid-liquid was defined as an experimental solid-liquid ratio after the evaluation of various factors;(2)The effect of initial pH revealed that ReO4- can be completely removed rapidly under a strong acidic condition; in terms of alkaline conditions and neutral the experimental data showed that, despite the low reaction speed, the removal rate experienced an upward trend, indicating that pyrite is an applicable barrier material of an underground repository;(3)Probably the presence of humic acid in groundwater is beneficial to the migration of Re(Ⅶ);(4)The presence of NaCl and Na2SO4 had no significant positive or negative effect on the reduction of Re;(5)The pyrite was characterized by XPS after reaction, moreover, insoluble ReO2 was found in the pyrite surface.Finally, quartz sand and pyrite powder were used to launch the column experiments,the results showed that quartz sand had no blocking effect on Re O4-, in contrast, ReO4- went through the pyrite column with a layer thickness of 1cm and 4cm was reduced by 3.727% and 27.930%, respectively. The results illustrated that pyrite can be used as a barrier to prevent perrhenate from transferring into surface or ground water, and the thicker the layer of pyrite, the better the blocking effect.This study proposed the use of micro-nano natural pyrite as a method to deal with nuclear waste that contains technetium. Re was used to replace Tc, and the oxidation-reduction reaction was studied by batch and column experiments, the results show that: due to its stable crystal structure, micro-nano natural pyrite can remain steady in natural environment, thus the contaminants could be purified finally. |
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