Electro-refining of copper

A. Electrowinning is a fine way to remove copper from phosphoric acid, however, the mixture with nitric acid may make this impractical. If the nitric acid is strong enough, it will redissolve the copper as fast as you are plating it out. If it is weak enough, then electrowinning may work, however, I would not expect to get a dense, good quality plate. If you have a lab and a Hull cell, you can try this yourself.

A. Hi John. The problem is not the acidity level of the nitric acid but its oxidizing power -- which leads not only to re-dissolving the copper, but probably the evolution of NOx-ious gasses. Raising the pH will precipitate out the copper, making electrowinning impossible.

While 200 ppm is high as a waste product, it's very low as a feed stream for electrolytic removal. I don't know if you can find an ion-exchange resin which can resist the aggressiveness of your wastes, but if so, ion-exhange would seem to be the way to remove the copper for subsequent electrowinning from the regenerant. Good luck.

Regards,

A. Platinized titanium.

A. Carbon, especially graphite. They make it in Decatur, Texas. It should work for either pole.

A. Iridium oxide coated titanium is the most commonly used anode for this application. It is expensive, but not as expensive as platinized titanium (which also works very well).

A. Depending on your tank design and current requirements, it would be best to use iridium oxide coated titanium mesh instead of plates. They are cheaper than plate, have a higher apparent surface area than plate (meaning you can use smaller anodes than the size of your plates), and should, if properly cared for, last for several years. These can also be recoated.

While platinized titanium will also work, it is not a good coating for this type of application in the long run, as it it much better in an environment that does not primarily produce oygen at the anode surface.

Graphite does work, and is cheap, but it eventually falls apart, and makes sludge in your cell. Expect it to last 4-6 months at best. It also requires a higher voltage to get the current you need for the cell, due to its resistance.

Another tip that you might find interesting is that polished titanium is an excellent cathode, and really makes it easy to get a copper deposit off. Its what they use for copper foil production. You want a particular surface roughness to it, however, or the copper will self remove itself in the cell.

A. Ethandrew,
It sounds like you've already managed to separate the copper from the rest of the sludge, any reason you can't just smelt it into ingots?

I'm going to give you some basic information on casting and some links I've found to be helpful.
Firstly, this doesn't have to be expensive, you can make an expensive setup if you want, but it's not necessary. The highest priced item in what I'm going to lay out for you is going to be a crucible.
Go check out www.backyardmetalcasting.com

The heat.
Propane is cheap, regulators are inexpensive, and it burns at a comfortable temperature. There are plenty of references on the internet about how to setup a good propane burner for high temperature applications. A forced air burner is the easiest to make.

The forms.
Also cheap as you're not casting extremely high temperature material. Go to the thrift store, get some steel muffin pans, poke around, see what you can find. Anything that is made from steel should work fine as a form. Do your pouring over sand anyway, just to be safe.

The metal.
Each of the metals you're working with here have varying melting points; you should be able to do some further refining (if needed) by keeping the setup at a constant temperature.

Good luck sir.

A. Hi, George. A "general formulation" according to the Metal Finishing Guidebook is --

• 26-33 oz/gal Copper Sulphate
• 4-10 oz/gal Sulfuric Acid
• 50-120 ppm Chloride (1 ml/gal of conc. HCl)
• 20-100 Amps/sq.ft.

But starting with copper sulphate (root killer), CuS0₄.5H₂O will be a more practical way to make a solution than starting from raw copper and sulfuric acid, because copper won't dissolve in simple mineral acids. You can get muriatic acid [affil links], which is dilute HCl, read its concentration and adjust accordingly.

You really should not use concentrated acids except when they are indispensable. No matter how careful you are, accidents can happen.

The internet is great for many things, including simple Q&A sessions like this, but it not a good place for tutorial learning because nobody can afford to spend months or years of their life organizing knowledge into a coherent tutorial and then put it on the internet for people to get "without paying for it". So try to get to a large city library and get him some books on electroplating. Make sure they include a chapter on safety and on waste disposal. Good luck!

Regards,

A. The only thing I could add to Ted's excellent advice is to add about 10 drops of blackstrap molasses (yes, molasses from the grocery store) to the plating solution. This helps you obtain a bright deposit.

Left as an exercise for the student: why does this make the deposit shiny?

A. Electrowinning, electroforming and electroplating are all somewhat similar, but are in reality very different.
The learning channel of the history channel has a 1-hour show on refining copper from a mine into copper products with a good bit of the show on the electrowinning.
It would be helpful to have a look at it. The school district or the chemistry teacher may have a copy. I doubt if the library would. It is a bit expensive for my retired budget to buy a copy, but they are for sale.

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Ed. note: Videos seem to come and go on the Learning Channel. We were unable to find that video for sale in 2014, but if anyone does find it, we'd appreciate hearing the URL.

A. Hi, Raman. I think you should probably provide some info on your situation rather than casting your question in the abstract -- because it is possible to successfully recover copper by plating out of a solution of nearly any concentration from saturation down to extremely dilute; at high current density of hundreds of amperes per square foot or at extremely low current densities of 1/1000 of that, at high voltage or extremely low voltage.

Is your interest in the recovery of copper values from electroplating wastewater, or recycling of e-waste, or electrowinning as part of the copper mining/refining process? Dilution to a given concentration might even be illegal in some instances like treatment of wastewater. Some idea of scale may be helpful in deciding what values to operate at, too. Thanks.

Regards,

A. Mr. Raman,

The solution to your issue is a composition of various factors of electrochemistry, solution kinetics and Current distribution as you may have discovered.

If you have a viable project I will suggest you purchase a proven Electrowinning machine and get the project going.

A good consultant in the field with complete answers may be your solution.

A. As Ted said, "it depends".
There is a huge amount of technical and non-technical information available on the internet. Use more than one search engine. This will teach you enough to be dangerous. I like the idea of hiring a sub consultant who is highly qualified.

A. Hi, Abbas. Assuming that the "typical" electrowinning electrolyte that you are speaking of refers to that used in a commercial tankhouse for electropurification of copper ingots associated with copper mining, please take a look at .

This paper has typical data for such facilities and seems to suggest that the copper concentration is a bit over 35 g/l, which would equate to about 140-150 g/l CuSO4.5H2O. Depending on the temperature and the amount of sulfuric acid, etc., it looks to me like the specific gravity would be about 1.1 to 1.2. Copper plating solutions used in commercial electroplating seem to be about 50% more concentrated; and as is the custom with the EPA, they leave us wondering whether it would be a crime to dilute the waste to the proper value :-)

Regards,

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Ed. note: Readers, please see also letter 12375, "How to electrowin copper".