What is the Nickel Electrowinning Process?

What is the Nickel Electrowinning Process?

In most electrowinning processes, electrodes are immersed in an electrolyte bath. A direct current is applied and charged particles (e.g. ions) within the solution are drawn to either the positive or negatively charged electrode. This process is known as electrolysis. Specific parameters for the reaction depend on the materials involved and other factors.
For nickel electrowinning, two chemical bases are in use, one using a sulfuric acid solution, and another using hydrochloric acid solution (HCl). The sulfuric electrolyte process can yield more than 99,9% pure nickel.

Nickel electrowinning is done by submerging metal electrodes into H2SO4 with a high nickel ion concentration. A DC current is applied, creating an electrical potential between the two different types of electrodes, anodes (positively charged) and cathodes (negatively charged). This process is contained within a cell.  
When the current is applied, the following occurs. The positively charged nickel ions (Ni2+) accumulate on the cathode by bonding with two electrons. Meanwhile, at the anode oxygen (O2) gas and hydrogen ions (H+, aqueous) materialize. When the solution reaches a low nickel ion concentration, the cathode is harvested for nickel (or a new solution is introduced).

The hydrogen ion excess generated at the anode increases the acidity of the electrolyte. If the hydrogen ions can move to the cathode, the cathode reaction will yield H2 gas instead of nickel plating. Therefore, it is necessary to separate the hydrogen ions generated at the anode from the cathode.