Abstract: The present invention is concerned with a method for the substantially selective extraction of tellurium from copper electrorefining slimes. The method comprises maintaining a molar ratio Ag/Se, Ag/S or Ag/Se+S at a value of about 2 or less in the slimes during leaching thereof in an autoclave. The excess of selenium and/or sulphur allows the formation of Ag.sub.2 Se or Ag.sub.2 S, which remains insoluble during autoclave leaching.

Abstract: An oscillator supplies a signal of adjustable frequency to drive power ultrasonic actuators. The oscillator frequency is varied and the phase between the voltage and current of the signal is continuously measured. A computer determines the sign of the variation in the absolute value of the phase in the course of successive sampling cycles of predetermined duration and produces therefrom frequency correction signals for the oscillator. A frequency correction is applied to the oscillator in the same direction as the frequency correction applied previously if the variation in absolute value of the phase is negative, and in the opposite direction if the variation in absolute value of the phase is positive. If the variation in absolute value of the phase is zero, a frequency correction of random sign is applied to the oscillator.

Abstract: The present invention is concerned with a method for electrorefining silver in a Moebius cell whereby the anode is completely dissolved and the gold mud is removed without handling of any partially dissolved anodes. The cell is conventional except that the anodes are placed in a basket made of a thermoplastic material and surrounded by a cloth, the electrical contact between the anode and the power source takes place outside the electrolyte. The bottom of the basket is provided with apertures allowing the gold mud produced to tall into the cloth until the anode is completely dissolved.