47076

Cobalt Electrowinning Precipitate [South Africa] 

November 20, 2007

Hi,
I'm attempting to electrowin Cobalt from a HCl / Cobalt Chloride leach solution. At the moment this is on a laboratory scale with a view to scaling up depending on the results.

Concentration of Cobalt in solution is approximately 60 g/l and pH <1.
I initially tried to use a Titanium anode but experienced some passivation effects within minutes of starting (Cobalt oxyhydroxide perhaps?).
I've since used a Titanium anode (Iridium Oxide coated) and a Stainless Steel cathode. Whilst I have managed to plate Cobalt to the cathode, I'm witnessing a white precipitate forming in the bottom of the tank (small scale approx 10 litres) and the pH is rising to 4.
The plating has formed primarily at the edges and corners of the cathode and is very dendritic in nature. I think my current density may be too high (50 A/dm2) but I'm not sure as I have been told that Cobalt plating can be dendritic regardless. I reduced the current density to 8 A/dm2 but the dendritic plating is still forming at the edges.

I have 2 questions.
1. Can anybody help me on the formation of the white precipitate during plating.
2. How can I avoid the dendritic plating formation.

Thanks
AOG

Adam O'Grady
Chem Engineer - Johannesburg, South Africa

Hello Adam,
Divalent cobalt ions are oxidized forming cobalt (III) oxyhydroxide anode scale - yep, you are right. Sounds like you are using the right anodes. Are they bagged and the anodes cleaned frequently? This will help you with the precipitate formation, and dangerous gas evolution. As far as the dendrites, the CD may have to be lowered even more. Good Luck!

Mark Baker
Process Engineer - Syracuse, NY, USA

Thanks Mark.

I've been finding it difficult to control the current density with such small electrodes. I'm arranging larger ones and this should make things easier.

I do not have the anodes bagged, but will look into this straight away.

Thanks again.
Adam

Adam O'Grady
- Jo'burg, South Africa