Behaviour of arsenic(III) and antimony(III) during electrowinning of nickel from aqueous sulphate solutions

The effects of As(III) and Sb(III) over a concentration range of 0 to 1000 mg dm− 3 on the electrowinning of nickel from sulphate solutions have been studied. The cathodic current efficiency decreases whilst the energy consumption increases in the presence of arsenic as well as antimony. Both arsenic and antimony depolarise the cathode when added to the nickel sulphate solution resulting in the cathodic reduction of nickel at more positive potentials. X-ray diffraction (XRD) studies revealed that irrespective of the presence of As(III) or Sb(III) in the nickel sulphate bath up to 100 mg dm− 3, the (200) plane is the most preferred plane of crystal growth. However, at higher concentrations the (111) plane becomes the most preferred one. Scanning electron micrographs show that the crystallites of the electrodeposits obtained in the presence of either As(III) or Sb(III) become non-uniform and are of finer sizes in comparison to that produced from pure nickel sulphate bath, however the deposits deteriorated more in the presence of Sb(III). With the increase in As(III) and Sb(III) in the solution to 1000 mg dm− 3 the deposits become very brittle and peel off the cathode. Energy dispersive X-ray (EDX) analyses indicate that the purity of the nickel deposits decreases with the increase in As(III) or Sb(III) content in the electrolytic solutions but the contamination of the deposit was more due to the presence of As(III) when compared with Sb(III) at higher concentrations.