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ELECTROPLATING/ ELECTROWINNING
I just wanted to know whether only copper can be taken out from rota cat which is dissolved in sulphuric acid or rota cat can be used to recover metals like nickel in hydrofluoric acid chromium in hydroufluoric acid iron in hydroufluoric acid zinc in sulphuric acid.
Would be delighted to have an asnwer.
VIDU GOYALMETAL WORKS - Rewari, Haryana
I assume by the term "rota cat" that you are referring generically to a rotating cathode system, and not a particular system commercially sold as a RotaCat. They are two entirely different concepts.
The rotating cathode design (normally a rotating metal cylinder onto which metal is electrodeposited) are useful for a variety of electrowinning applications. The caveat here is that you need to have a proper design on the other side of the reaction - the anode - to allow electrowinning from these types of solutions that you mention. Sulfuric acid based electrolytes are amenable to most electrode designs, however caution must be used on ionic strengths. More is not necessarily better.
The use of any type of anode in a HF environment is severely limited due to the materials of costruction and the cost. You would at a minimum require a niobium substrate and platinum catalyst coating. Normally, this has to be either a hot dipped platinum coating (i.e the patented DeGussa Process", or the platinum could be clad onto niobium in small sheets and slit and expanded to get larger geometries. Depending on how much surface area that you need, you are likely to pay several tens of thousand dollars for anodes in a system such as these - and they might not last 3-6 months time.
There has been some limited success in the use of ion specific membranes to envelope the anodes. This requires a separate electrolyte solution to promote conductivity between the membranes and the electrodes. Fluoride, being a very small ion, will permeate the membrane over time, and you will have to deal with the issues it causes.
I would stay away from any precious metal oxide based electrodes, as these are microcracked coatings and will allow free fluoride attack on the substrate, which will dissolve, and the coating will literally fall off in a process called exfoliation.
As far as the actual process goes (electrode issues aside) the strength of the acids and such wil determine the efficiency of the process. You have to be your own gauge on whether the costs to operate the unit, including power, man-hours to maintain and remove deposits, and replacement parts have a positive value as compared to the recovered value of the metals. Zinc and tin are the least likely to be economical, copper fluctuates, and nickel is usually a positive to break-even consideration. I am not aware of anyone that has successfully electrowon iron from solutions on a commercial scale.
You need to be prepared to run an electrowinning unit much the same as a plating bath, which means additives, buffers, and other things will be required in the case of some metals, such as nickel. Also, remember that deposit integrity is a must - your trying to get a thick deposit, and EVERY inconsistency in the deposit will be magnified, which usually means dendrites, and low quality plating.
Lastly, I would tend to stay away from any electrowinning cell that requires the use of raw media (other than reusable substrates like stainless steel or titanium) to plate on to operate. In some cases, they might tell you that you need copper shot as a starting media. It might have a value of US$3.00/kg, but as soon as you put in the cell and use it, its value drops to type 1 scrap or less - which means you lose money right from the start. Titanium makes for an excellent cathode, and if polished and used correctly, will give you almost immediate release of the reclaimed metals. I have seen too many cells where cathode prep was non-existent, and they use air chisels to try to remove the meta deposits.
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Tom Baker |
Ed. note: We have lost contact |
October 3, 2011
Hello,
I am electrowinning copper chloride with membrane. In a old post in this forum, I read that chlorides stress the deposit and consequently, it grows doing trees and dendrites and takes a lot of space on the cathode for a few grams, that is my problem.
I am would like to know if there is some bath additive that can reduce considerably the formation of dendrite?
Thanks,
metal technician - Bogota, Colombia
October 6, 2011
Try adding some gelatine, coumarin or naphthalene trispulphonic acid. I have never done it with electrowinning, but try about 1g/litre
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Trevor Crichton R&D practical scientist The Pheasantries - Chesham, U.K. |
October 8, 2011
Thanks, I will give a try to gelatin. Do you recommend a special one? from pig? or other?
The solution contains about 10 g/liter of copper. I reduced it first to get only Cu+ chloride complex else the solution etch my cathode. pH is adjusted to 2. Chloride concentration is about 20 g/L.
Regards,
- Bogota, Colombia