Method and apparatus for control of electrowinning of zinc

A method is disclosed for controlling a process for the recovery of zinc from zinc sulfate electrowinning solutions containing concentrations of impurities. The disclosed method includes the steps of establishing a test circuit comprising a test cell, a sample of electrowinning solution, a cathode, an anode and a reference electrode immersed in said sample, a variable voltage source and measuring means electrically connected to the electrodes. A potential is applied to the electrodes in the test cell to obtain a predetermined potential between the cathode and the reference electrode. The potential is decreased from the predetermined value at substantially zero current, the decreasing potential is measured, and the decreasing of the potential is terminated at a value corresponding to the point at which zinc starts to deposit on the cathode and the measured electrode current density increases rapidly from a value of substantially zero for further small decreases in potential. The activation over-potential is determined and is related to the concentration of impurities in the sample, whereupon the process for the recovery of zinc is adjusted to obtain optimum zinc recovery.