How does Current Density Effects in Electrowinning Process?

How does Current Density Effects in Electrowinning Process?

In addition to the electrolyte composition, the bath temperature, pH and current density are the main operating parameters in electrowinning and electrorefining of nickel that affect the stress in a nickel deposit in different ways.

In the electrowinning process, the current density is an important factor that determines the metal production rate and has a strong influence on the quality of the deposit. The current density typically used for nickel electrowinning from sulfate electrolytes is relatively low compared with that from chloride electrolytes due to the relatively lower nickel concentration attainable in sulfate electrolytes.

The choice of the current density to be used depends on numerous parameters which may broadly be characterized as those that influence the mass transfer rate of the species to be reduced to the electrode and those that inhibit the plating process itself. Nickel plating from sulfate electrolytes is naturally inhibited and the maximum current density at which good quality deposits can be obtained is typically defined at around one-third of the mass transfer limiting current density, e.g., 200 to 240 A/m2 at a temperature of 60 to 65℃.

The rates at which impurities in the electrolyte are reduced will depend on the reversible potential of the half‐cell reactions involved but are, in many cases, under mass transfer control due to the rather low concentrations at which impurity ions are present in the electrolyte. If it is presumed that the impurities plate uniformly over the whole surface, which is typically not the case, and that the process is at a steady state.