GB1312682A - Apparatus and method for purifying alkali metal hydroxide solutions - Google Patents

Abstract

1312682 Electrolytically purifying alkali metal hydroxide solutions PPG INDUSTRIES Inc 11 March 1970 [11 March 1969] 11561/70 Heading C7B Metal ion contaminants are electrolytically removed from an aqueous alkali metal hydroxide solution by passing the solution through a porous cathode of a cell so as to deposit the metal ion contamination in the cathode. There is an anode downstream of the cathode and, after passing the cathode and anode pair, the solution is withdrawn from the cell, without being subjected to further electrolysis in the presence of another electrode. For example the quantity of contaminating ions such as Fe, Ni, Cu, Mn, Ca, Mg, Al, Cr, Pb, V, Mo, Ti, Be, Zr, W, Sn, Hg, Sr or Ba can be reduced in solutions of NaOH, KOH or LiOH. The porous cathode may be of graphite, Ni, Ni alloys, Zr, Mo, Ag, steel cast Fe, Cr plated steel or W. The porous cathode, when it has the contaminant metals deposited therein, can be regenerated electrolytically by reversing the polarity of the electrodes and using as electrolyte alkali metal hydroxide, NaCl, KCI, LiCl, NH 4 OH, HCl, H 2 SO 4 , HNO 3 H 3 PO 4 or H 2 CrO 4 so as to remove the contaminating metal. Fig.1, (not shown) illustrates apparatus wherein NaOH feed liquor is passed through a cylindrical cell (1) firstly through a porous disc graphite cathode (4) and then through a Ni screen anode (3). Fig. 2 shows a cell where alkali metal hydroxide solution is passed through an inlet 42, through blind-end cylindrical porous graphite cathodes 31 mounted in an impervious graphite sheet 32, past nickel tube anodes 33 welded shut at their lower ends and welded or screwed at their upper ends into an iron cover 34, and out of the cell through an exit pipe 43. The cell comprises a steel cylindrical body, a steel bottom and is rubber lined on it interior. In modification of the cell shown in Fig. 2, there may be only one or more than seven cathodes. Reference has been directed by the Comptroller to Specification 1169206.