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topic 14472

Electro-refining of copper




An ongoing discussion from 2002 through 2012 -- your posting can bring it into 2014

(2002)

Q. I am looking for alternative methods to treating our Chemical deburr solution rinses (Nitric Acid) and Brite dip solution rinses (50/50 Nitric/Phosphoric Acid). The Cu is well over 200 ppm and our current chemical treatment creates plenty of sludge. Its pH is around 1. I have heard of platers using winning for stripping solutions. Does anyone know if you could use electrowinning on an acid solution like these?

John Zacharias
- Waseca, Minnesota


(2002)

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.

Lyle Kirman
consultant - Cleveland, Ohio


(2002)

Q. Mr. Kirman:

Thank you for your response. What would be the effect if I neutrialized these acids with caustic soda and brought the pH to around 7. Would that allow the Cu to be plated out without the problems you mentioned.

John Zacharias [returning]
- Waseca, Minnesota



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,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Electrowinning from copper sulfate plating baths

(2004)

Q. We have set up an electrowinning tank about 800 gal which contains a sulfuric copper sulfate solution. We use stainless plates as the cathodes and stainless as the anodes everything works great except the anode keeps dissolving. What do we need to use instead of stainless sheets?

RICHARD LOVELAND
PRINTED CIRCUIT BOARDS - WYLIE, Texas


(2004)

A. Platinized titanium.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2004)

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

paul morkovsky
Paul Morkovsky
- Shiner, Texas, USA


(2004)

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).

Lyle Kirman
- Cleveland, Ohio USA


(2004)

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.

tom baker
Tom Baker
   wastewater treatment specialist
Warminster, Pennsylvania




Copper Electro-refining: I get powder, no adhesion to cathode

June 22, 2008

Q. I Have 250 lbs of silver/copper rocks. Some of the silver is as plain as day visible.
I built a mini electrorefining/electrowinning set up in a fan-vented plastic 5 gallon bucket.
I am using 5.17 volts DC; it was 18 amps at 70 degrees as the temp climbed, so did the amps -- up to 90 Amps. Electrolyte was now up to about 120 degrees. I was hoping to sell the cathode as scrap copper but all I collect is a micro-fine powder -- I mean really fine -- like less than .001 inch particles. So I can't sell this as scrap copper and recover some of my cost! I started with 1 gallon distilled water, 5 lbs copper sulfate penta-hydrate, i.e., only about 2 lbs dissolved -- the rest laid in the bottom-oops! And I added 2.5 gallon of battery acid at 1.265 specific gravity 33%. I wanted to collect the sludge and use nitric acid to extract the silver (estimate 7 lbs and about 1/4 OZ gold should be in sludge). I just want to perfect the copper adhesion problem before I go any further.
... so I can have about $700.00 scrap copper, so I can buy more of the silver bearing rocks.
Cathode was .021 copper sheet wrapped inside the bucket, cleaned with just alcohol to remove any oil. Copper was orange, new sheet metal; no green, but not sanded to brite fresh surface

49089

I am technically inclined... but, I am confident with proper guidance I can make the copper adhere to the cathode -- it just has to look good enough to sell as grade #1 copper.

Unless there is a place to sell this Micro-Fine copper powder for more than $3.00 per lb? If there is then, that would be even better like $5.00 per lb.
Thanks for any and all info! Science frees us to do "Fun Things"! Maybe even profitable!

Ethandrew Prater
newbie - Columbus, Indiana


July 29, 2008

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.

Marc Banks
Blacksmith - Melbourne, Florida



Copper Electrowinning and Electroforming for Science Project

July 5, 2008

Q. Hello, I am the proud father of an aspiring scientist, writing to you during the wee hours of a Saturday morning.

That said, my son Alan is fifteen years old. He is interested in the concepts of electrowinning and electroforming for a summertime garage chemistry project. I have been recruited as the supervisor and procurator for his scientific quest. I haven't fooled around with chemistry in decades, though I have a Gesswein model 12-25 rectified power supply that I once used for copper, silver and gold plating, using cyanides. Alan wants to use this unit for his project; its range is from 0 - 15 volts, 0 - 30 amperes, so it should be adequate for the task.

I know that sulfuric acid is used in copper electroforming and electrowinning processes. According to Alan, both anode and cathode are supposed to be made of copper, placed in a sulfuric acid solution at a temperature of around 50 °C. The question is, if we start out with 1 liter of distilled water, how many milliliters of concentrated sulfuric acid (97% fuming) should be added to the water (slowly, wearing goggles [linked by editor to product info at Amazon], protective gloves [linked by editor to product info at Amazon] and face shield [linked by editor to product info at Amazon], while using a dropper of course) for a proper electrolyte solution? We have been unable to find the proper formula on the Internet - without paying for it, that is, and his science textbooks contain nothing useful with regard to this subject.

Thanks in advance for any help you can give us,

George T.
Hobbyist - Midway, Georgia, USA


Electroplating Engineering Handbook




The Canning Handbook of Surface Finishing Technology




Electrodeposition -- The Materials Science of Coatings and Substrates

July 11, 2008

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 sulfate [linked by editor to product info at Amazon] (root killer), CuS04.5H2O will be a more practical way to make a solution than starting from raw copper and sulphuric acid, because copper won't dissolve in simple mineral acids. You can get Muriatic Acid [linked by editor to product info at Amazon], 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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


July 12, 2008

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?

dave wichern
Dave Wichern
Consultant - The Bronx, New York


July 14, 2008

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.

James Watts
- Navarre, Florida

----
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.


June 10, 2009

Q. Can anybody inform me on the following in electrowinning of copper:

01. Current density per sq.cm
02. Concentration of Copper sulphate gms per litre
03. Voltage across the cell.
04. Duration for electrolysis.

Thanks and regards,

Raman M.S.
consultant - Baroda, Gujarat, India


June 10, 2009

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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


July 17, 2009

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.

asif_nurie
Asif Nurie
- New Delhi, India

With deep regret we
sadly advise that
Asif passed away

on Jan 24, 2016



July 22, 2009

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.

James Watts
- Navarre, Florida


January 19, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. What is the Specific Gravity of a typical Copper Electrowinning Electrolyte? Thank you.

Abbas Mirza
Research - Dallas, Texas (USA)


14472

www.saimm.co.za/Journal/v109n06p343.pdf

January 20, 2012

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 sulphuric 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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

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




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