Electrically switched cesium ion exchange. FY 1997 annual report

Abstract

An electrochemical method for metal ion separations, called Electrically Switched Ion Exchange (ESIX), is described in this report. In this method, direct oxidation and reduction of an electroactive film attached to an electrode surface is used to load and unload the film with alkali metal cations. The electroactive films under investigation are nickel hexacyanoferrates, which are deposited on the surface by applying an anodic potential to a nickel electrode in a solution containing the ferricyanide anion. Reported film preparation procedures have been modified to produce films with improved capacity and stability. Electrochemical behavior of the derivatized electrodes has been investigated with use of cyclic voltammetry and chronocoulometry. The films show selectivity for cesium in concentrated sodium solutions. Raman spectroscopy has been used to directly monitor changes in oxidation state of the film and imaging experiments have demonstrated that the redox reactions are spatially homogeneous across the film. Requirements

Nanomaterials-Enhanced Electrically Switched Ion Exchange Process for Water Treatment

“…CsNaNiFe II ðCNÞ 6 1 Cs 1 -Cs 2 NiFe II ðCNÞ 6 1 Na 1 (17.5) Cs 2 NiFe II ðCNÞ 6 -CsNiFe III ðCNÞ 6 1 Cs 1 e 2 (17.6) Figure 17.2 shows bench-scale flow cell testing of ESIX systems developed at PNNL using NiHCF films deposited on high surface area nickel foam electrodes with a nominal surface area per volume of 40 cm 2 /cm 3 (60 ppi) [4]. The flow tests using NiHCF material were performed to evaluate the feasibility of the approach as an alternative to conventional ion exchange processes.…”

“…), chromate (CrO 4 22 ), or hydrogen chromate (HCrO 4 2 ). The current maximum contamination level (MCL) for total chromium in drinking water in the United States is regulated by the United States Environmental Protection Agency (EPA) at 100 μg/L.…”

“…from wastewaters using PPy. Elution occurs when the potential is switched to cathode, forcing the ClO 4 2 out of the film into the elution solution. After electrode has been coated with PPy, anions can be reversibly ion exchanged by applying anodic and cathodic potentials.…”

“…4 shows the schematic illustration of PPy preparation and the electrically controlled anion exchange for the separation of the perchlorate ion Schematic illustration for the polymerization of electrically conductive polypyrrole (PPy) and anion intake and elution with the oxidation and reduction of PPy film. Three or four pyrrole units involving one positive charge are considered in oxidized PPy.…”