GB1215392A - Improvements in or relating to the operation of alkali metal chlorine cells - Google Patents

Abstract

1,215,392. Electrolytically purifying mercury. PPG INDUSTRIES Inc. April 2, 1968 [April 11, 1967], No.15910/68. Heading C7B. A method of purifying mercury, the mercury (a) having been removed from a commercial electrolytic alkali metal chlorine cell having a mercury cathode and (b) containing metallic impurities which are not removed in a denuder, comprises introducing at least a portion of the mercury to an auxiliary electrolytic cell, utilizing the mercury as the cell anode, conducting electrolysis in the cell in the presence of the mercury at an anode potential controlled with respect to a reference electrode so as to be sufficient to cause metallic impurities contained in the mercury to be removed there from but insufficient to cause dissolution of mercury in the cell electrolyte, and removing from the auxiliary cell mercury depleted in metallic impurities. The electrolyte in the auxilliary cell may be brine or alkali metal hydroxide. Fig. 1 illustrates an assembly 1 of alkali metal chlorine cells having mercury cathodes with flow of Na/Hg therefrom through a line 2 to a denuder 3 from which part of the mercury is returned to the cell assembly via a line 11, pump 12 and line 9 and part is returned via an electrolytic cleaning cell 6 wherein the mercury serves as anode. A plurality of alkali metal chlorine cells may be used with series flow of mercury and with series or parallel flow of brine therethrough Fig. 3 (not shown). As illustrated in Fig. 4 (not shown), mercury circulates from a chlorine cell (141) to a denuder (146) and back to the cell (141) via lines (145 and 144), part of the mercury from the denuder (146) being bled to an auxiliary denuder (149) and then through an electrolytic mercury clean-up cell (148) before being returned to the cell (141). Fig. 5 (not shown) illustrates an anodic mercury cleaning cell comprising an epoxy resin lined steel box with a baffle (111) and an expanded steel cathode (103) mounted on polyvinyl dichloride float members (109) which float on mercury (105) being cleaned as it flows through the cell. The anode potential in the cleaning cell is maintained constant within Œ 0À025 volt at 0À3 to 0À6v by means of a control circuit including a sensing probe (104) connected through a salt bridge (121), Fig.6 (not shown) to a reference cell (122). Thereby, a signal is sent through a voltage divider 123 to an electronic controller 124 which regulates the A. C. input to a rectifier 120 supplying electrolyzing current to the cleaning cell. Specified anode materials for the alkali metal chlorine cell are graphite, carbon platinized Ti, and Cu electrodes brazed with Ti and containing a Pt surface.