GB938206A - Process for the production of purest indium - Google Patents

Abstract

938,206. Preparing pure indium. DUISBURGER - KUPFERHUTTE. June 5, 1961 [July 12, 1960], No. 20220/61. Class 41. Pure indium is prepared by electrolysis of an aqueous indium salt solution using a flowing mercury cathode, with which the deposited indium forms an amalgam, in several stages wherein the indium amalgam formed in stage 1 is used as anode in stage 2 to form a purified indium electrolyte from which indium is again deposited on mercury to form an amalgam. Impurity metals are removed from both electrolyte and amalgam by counter flowing mercury from the last cell to the first, and also introducing a second electrolyte, e.g. HCl, in counter-flow with the depleted indium salt electrolytes. In a final stage the purified indium amalgam is used as anode, with a water-free molten pure indium salt, e.g. halide, as electrolyte, preferably in admixture with LiCl and other alkali metal or alkaline earth metal halides, the temperature being maintained above the melting-point of indium metal and the electrolyte, e.g. 200‹ to 250‹ C. The pure liquid indium is drawn off from the cathode area. In the Figure, indium chloride solution is fed at a line 5 into three cells la, 1b, 1c, in series, through which mercury flows in reverse and is drawn off by a pump 13. A level overflow regulator 34 is provided. Chlorine is evolved at carbon anodes 9, 10, 11 and the depleted electrolyte flows out to discharge at 12. The indium amalgam is pumped into cell 2 provided with a partition 19, and the indium dissolves in the electrolyte 16 from the amalgam anode 15, and reforms an amalgam 17. A second similar process is effected in stage 3. HC] is injected at line 28 and flows through stages 3 and 2 to stage 1a by-passing the stages 1b 1c. The acid removes noble metals, zinc and iron, and the rate of flow is adjusted to equal that of the electrolyte flow out at 12. Mercury is added through at line 31, and enters the cathode zone of stage 3. In the final zone 4 the purified indium amalgam 24 is decomposed via the electrolyte 25 and pure liquid indium metal is drawn off at 27. Preferably a large anode surface is used relative to the cathode. Any traces of mercury are removed by heating to 800‹ C. in vacuo, in hydrogen or an inert gas.