Method of inhibiting formation of and breaking of mercury butter in chlor-alkali cells

A method of inhibiting the formation of and/or breaking of preformed mercury butter during electrolysis of alkali metal brines to produce chlorine and caustic alkali using a flowing mercury cathode which consists essentially of the following steps:

• (a) electrolysis of the brine in an electrolyser,
• (b) removal of an alkali metal rich amalgam from the electrolyser,
• (c) removal of the alkali metal from the rich amalgam in a denuder,
• (d) withdrawal of the amalgam substantially reduced in alkali metal content from the denuder, and
• (e) recirculation of the amalgam from step (d) into the electrolyser for step (a),
• characterized in that an aqueous solution containing between 10 ppm and 0.1% by weight of a surfactant material capable of increasing the interfacial tension of the sodium amalgam-aqueous interface to and/or maintaining the interfacial tension of the sodium amalgam-aqueous interface at a value of at least 180 dynes/cm is introduced at one or more of the above steps (a) to (e) so as to be in contact with the circulating mercury or amalgam.