Electrochemical reduction of Cr(VI) in the decontamination process ELDECON

One of ABB Atom's methods, ELDECON, is an electrochemical process for decontamination of components used in nuclear power plants. ELDECON removes radioactive species while producing small amounts of waste. However, the waste sludge that is produced in the ELDECON process contains chrornate (Cr(VI)). According to the US Cod of Feguration, 40 CFR 261, if a process in any step creates chromate, the final waste has to be tested in a toxicity characteristic leachate procedure. In order to pass the test, the chromate has to be reduced to chromium (Cr(III)). Electrochemistry has proven to be a valuable tool. When incorporating indirect electrolysis into the ELDECON concept, the chromate ions are reduced. This is done by the use of an electrochemical cell (reactor bed). The method involves ferric nitrate as a reagent which, besides converting the chromate completely, also decreases the reaction time. The reaction time and the amount of solution treated in the cell have a close to linear relationship (i.e. the reaction time is proportional to the amount of solution). This makes the test cell feasible to scale up and use in the industry.