GB991468A - Electrochemical liquid treatment device - Google Patents

Abstract

<PICT:0991468/C6-C7/1> <PICT:0991468/C6-C7/2> <PICT:0991468/C6-C7/3> <PICT:0991468/C6-C7/4> In an electrochemical liquid treatment device, such as an electrodialysis or ion exchange device, the electrodes are electrically connected such that deposits which would impair their efficiency do not build up on them. A first electrode is of one polarity whereas second and third electrodes in close proximity with one another can alternately be connected so as to be of opposite polarity to the first electrode. Fig. 1 shows an electrodialysis device comprising a central anode 19 and electrodes 12, 13 (shown in detail in Fig. 2) which can be alternately connected as cathode by means of a reversing switch 33 and timer control 35. The electrode of 12 and 13 not connected as cathode serves as an anode but takes a reduced current through a resistance 34. Cation and anion selectively permeable membranes 22, 23 extend in a spiral path between the anode and cathodes from a tube 20 perforated at 25 to a tube 24 perforated at 26. Liquid to be treated is supplied to the tube 20, flows through the space between the membranes, is electrodialytically diluted and discharges through tube 24. Flushing liquid is supplied to and removed through apertures 27, 28. Fig. 4 shows a liquid treatment apparatus containing ion exchange material 56 which is regenerated electrolytically. A central carbon anode 42 and Pt electrodes 12, 13 are electrically connected similarly to the electrodes shown in Fig. 1. A permeable ceramic diaphragm 50 retains the ion exchange material. Liquid to be treated is supplied intermittently at 59 and removed at 541 and flushing liquid is supplied and removed continuously at 55 and 54. Electrolysing current is supplied continuously. Fig. 5 shows electrodialysis apparatus with two switches 33 actuated by a single timer control 35. In one switch position electrodes 66 are anodes, 67 are cathodes, 65 are slightly cathodic and 68 are slightly anodic. In the other switch position, electrodes 65 are anodes, 68 are cathodes, 66 are slightly cathodic and 67 are slightly anodic. 62 and 63 are cation and anion permselective membranes. Anion permselective membranes 63P are porous to some extent and let the liquid pass through them to the electrode compartments to wash the electrodes. Further embodiments wherein the electrodes are washed and electrode products are prevented from migrating through the membranes of the stack are illustrated in Figs. 8 and 9 (not shown). In alternative embodiments, Figs. 3 and 7 (not shown), electrodes used in apparatus similar to that shown in Figs. 1 and 5 are in the form of helices and spirals. In further alternative embodiments, one set of the alternately used electrodes may pass no current while the other set operates or more than two sets of electrodes may be used in sequence controlled by rotary multipole switches.