Nickel Electrowinning and Impurities Influence

Nickel Electrowinning and Impurities Influence

Electrowinning from aqueous solutions using insoluble anodes is a well-established process for metals like zinc, copper, nickel, cobalt, cadmium, manganese and others. The metal is electrodeposited at the cathode from a solution of one of its salts, most commonly a sulfate. Water is decomposed at the anode, which is usually made of lead or a lead alloy; oxygen is evolved and acid (hydrogen ions) is formed.

Successful electrowinning and electrorefining processes for the production of high purity and compact electroplated metal require the optimization of the electrolyte composition and operating parameters. In nickel electrowinning and electrorefining plants, the optimization of the electrolyte composition for good deposit morphology, optimal adhesion to the substrate, and minimum energy requirements remains a challenge.

Nickel is usually plated by electrowinning or electrorefining on permanent cathodes made of stainless steel, with suitable dimensions and mechanical properties, to avoid additional processes required to produce and form substrates of thin starter metals.

In modern nickel electrowinning and electrorefining plants where the cell configuration is such that the anode and the cathode are parallel and separated by a relatively short distance (typically around 20 mm), the above mentioned consequences of high stresses can cause among others, short circuits in the electrodeposition cells in case of direct contact of anode and cathode, causing serious losses in terms of current efficiency, energy consumption and production.  

Impurities present in the electrolytes, among many other causes of stress development in nickel deposits, may significantly affect stress generation, and thus adhesion to the substrate and deposit morphology, on top of their effects on the efficiency of the plating process and the purity of the plated nickel. Electrolytes always contain trace or relatively higher concentrations of impurities due to the limitations of the purification processes and the accumulation of impurities in the electrolyte over time.