濃厚アルカリ溶液中に微量に溶存するガリウムの電解析出に関する研究

抄録

This paper describes the results of preliminary experiment of recovering gallium from sodium aluminate solution, which is used for alumina production in Bayer Process and contains gallate as a minor soluble impurity.
The constant current electrolysis of concentrated caustic or caustic aluminate solution containing no impurities other than a small amount of gallate (0.2g/l as gallium oxide) was carried out in a small glass cell at various temperatures using a cathode of copper plate and an anode of nickel wire or stainless steel plate. The effects of cathodic current density, temperature and alkalinity of the solution on current efficiency of gallium deposition were investigated.
A maximum current efficiency was obtained at a current density of nearly 0.004 A/cm². Such result can be explained, considering the difference between partial polarization curves of hydrogen evolution and gallium deposition. The current efficiency reached about 18% in the electrolysis of 4N caustic solution at 30°C. The fact that gallium was deposited at this temperature, just equivalent to the melting point of gallium, suggests the close relation between the current efficiency and wetting ability of gallium to the cathode.
The increase of dissolution rate of gallium into the caustic solution with the increase of temperature and alkalinity has also a bad effect on the recovery of gallium, so that, decreases current efficiency.
It was estimated, from the analysis of the potential-current curve of the solution obtained by the potential sweep method, that the hydrogen over voltage for gallium cathode is larger than that for copper or platinum cathode and that the current efficiency can be raised by keeping the cathodic potential at a suitable constant value.