Rare Earth Elements (REEs) are chemically similar elements that have unique properties and are sought after in many industrial manufacturing processes including energy, defense, and electronics. This report details the usage of an electrically conductive carbon-nanotube coated PVDF ultrafiltration membrane to exploit the low solubility of aqueous REE hydroxides and precipitate these species on its surface. When a sufficient potential difference is applied to two electrodes placed in an aqueous environment, hydroxide ions are produced at the surface of the cathode as a result of water splitting. In turn, the local pH of the solution directly adjacent to the cathode becomes more basic than the pH of its greater surroundings. Initial experiments evidence the ability of the electrically charged ultrafiltration membrane to precipitate Fe(OH)2 and several REE(OH)x species with clear favorableness of scandium and thorium precipitation. Several experimental parameters were investigated including metal ion concentration and constituents, solution pH, and time. Membrane samples were analyzed using EDXRF and/or WDXRF, and the metal ion concentration in the feed was analyzed via ICP-MS. A mixed metal solution containing an array of REE ions in HNO3 along with Fe, Mn, Mg, and K was adjusted to pH 6.4 using NaOH. A cross-flow membrane filtration cell was used to house a UB70 UF membrane that was pressure deposition coated with CHASM AC200 carbon nanotubes. The membrane was set as the cathode while a titanium rectangle roughly ~2 mm above the membrane was used as an anode; the potential difference was set at 1.5 V using a RIGOL waveform generator. The solution was pumped through the cell with a controlled pressure of ~20 psi. The test ran for a span of four days and the metal ion concentration of both the initial and final feed solutions were analyzed via ICP-MS.

Direct capture of rare earth elements via electrochemical precipitation on an electrically conductive ultrafiltration membrane

2019 Fall National Meeting

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