Electrochemistry Copper electrorefining question

[EdwinEL]

Hello everybody,

First off; let me introduce myself.
My name is Edwin, 23 years old and from The Netherlands. Education Marketing and communication (blegh) working expertise; supervisor of a plastic recycling company (recycling 200 tons used flower pots per week booming business in The Netherlands :lol.
Together with my father (53 years old and used to own a hotel :lol we are trying to set up a PCB recycling company. Which until now works very good.

Let me tell how we expect to start working;
Buying PCB (3 tons in stock to test with)
Shred the pcb to have less problems with flame retardants etc.
Melting it (we have a smal 350 KW furnace in order should be here in 2 weeks).
Copper electrorefining.
Working the anode slime chemically and electrochemically.

Now we have created allmost everything by ourselfs except the melting furnace and the power supply for the electrorefining process.
We have a nice scrubber system which neutralizes the offgasses from the smelting (we have a small 5 kg furnace which we use to test).

Now we test our electrorefining system on a small scale;
Conditions of the electrorefining system
316 SS as the 2 cathodes
1x +/- 90% pure anode (can not get all the slag out as the crucible is very small).
1x Power supply used at 0.5 Volts and 10 amps (which is around 300 amps per M2).
Electrolyte 37% h2so4
1 gram bone glue added to make it adheve better.
Working under 55 degrees celcius.

Now everything starts off very nice in the beginning, nice even plating.
But after a while the crystals are getting rougher and do not attach enough to the other copper at the cathode.
Result; a bunch of copper in my anode slime..

I think the solution should be pretty simple (although I do not know what it is :x )..

More pictures of our machines etc are on request.
We are not unwilling to show it, but just not to everybody on Google .

You guys have a great forum and have been watching and learning for a couple of years now!
Keep up all the good work.

 

[EdwinEL]

I forgot the other cathode picture..

 

[Harold_V]

In order to part copper effectively, purity of the anode should approach 99%. 90% purity is way too low, as it contaminates the electrolyte prematurely, creating all of the problems you have experienced. Also, when you have things right, you won't have need for the bone glue. The copper will deposit firmly, albeit in nodules.

I worked as a machinist in life (before refining became my livelihood). I lived in the Salt Lake City valley, where one of the largest copper mines in the world is located (Bingham Canyon, in the Oquirrh Mountain Range, west and south of Salt Lake City. The shop where I was employed made a large number of starter sheets for the copper refinery. They were made of titanium. Stainless is not suitable, not even 316. If you can't get titanium, use a thin sheet of copper as a starter.

You will not enjoy success unless you can increase the level of purity of your copper anodes. The alternate would be to continually replace the electrolyte, which is not really a good option.

Harold

 

[EdwinEL]

Hello Harold,

I totally agree with you that the 90% anode is way to low and it ruins the electrolyte. for the sake of testing it I will just try using a plate of pure copper bar.

However I do have a question regarding the starter sheets..
I am aware that a pure copper starter sheet always works best, but because of the price of copper it is a expensive hobby.
Now I very positive that the ISA Kidd process uses 316 SS starter sheets, so I am curious how this could be different from that.

Edwin

 

[kjavanb123]

Edwin,

Welcome to the forum, I have tried what you are doing here, and by looking at your anode picture, there is a copper coating it which I think should not be the case and the color of anode is found the part that stays on top of electrolyt.
So you check your power supply as it might have pole issues and somehow alternate.

Regards
Kevin

 

[nickvc]

As you are working with small amounts to test I would advise taking Harolds advice and increase the purity of your anode and also to use titanium or copper sheet for your cathode. Long term the copper your refining can be used to increase the purity of your anodes but trying to short cut the purity level will give you nothing but problems, the point to remember is that you need to process serious amounts of copper to recover the values in worthwhile amounts, the big copper refiners are huge enterprises processing and refining tonnage daily. Many have tried this but all have failed including myself and Harold, there are no short cuts. It may pay you to melt assay and onward sell to the big copper refiners who will settle in around 90 days but to make that worthwhile you are going to need serious volumes and big furnaces to cast big ingots to keep assay charges to a minimum.

 

[EdwinEL]

Hello Kevin, I have check the poles and everything seems allright. This might be because of the high purity that Harold was talking about is missing..
But thank you very much with thinking with me!

Hello Nick, thank you for your response.
I understand your scepticism towards another person finding the goose with the golden eggs . While we are not finding nor looking for the goose with the golden eggs I agree fully with your comment about skipping steps. There is no other direction then the wrong and the right direction.

I also agree that with refining copper (be it from copper ore or copper scrap) that you need ten's of tonnes per day to turn somewhat of a profit.
The idea behind our operation is not to refine for the copper but all the metals in a PCB, the melting furnace that is on it's way melts around 750 KG per hour. Which creates anodes of around 200 KG.
I am simply testing with some pure copper strip now, and looking forward towards the results.

Thanks everybody!

 

[solar_plasma]

Doesn't sound like a market niche, since you are living quite near to Aurubis.

 

[solar_plasma]

Why not melting in order to reduce the amount to transport, assay and sell to someone like Aurubis?

 

[EdwinEL]

Hello Solar_Plasma

Depends on the volume you process. The company I worked before recycled plastic flower pots. we only did a small tonnage of 200 ton per week.
While the company Remondis plano also stationed in Lünen Germany (as is Aurubis) did business with us.

When your not very big you can always chew a little bit of ff the market, why would the be so many clothing stores .

Saw your second post when typing;
Because we think/believe that it is better to process it ourselfs.
And how could we do that if the market is more focussed on let's say Aurubis or Umicore?

Please note; I am open for discussion, I can be a little harsh sometimes; I do not mean it by this.
Someone with a good argument is always welcome

 

[solar_plasma]

Sounds as if you know,what you are doing. Later this day I will post some good links to copper refining texts.

 

[g_axelsson]

While I was writing this response there were four more appearing on the forum, some of them covering part of what I was writing too, but I'll post it as it is.
Edwin, nice to see that you can take a discussion and not getting defensive, we get too many new members here that only listens to what they want to hear. 8)

To dilute the copper feedstock with already refined copper is just stupid. (sorry nickvc, but it is)

For example if you run 1 kg of 90% copper until you need to replace the electrolyte and it takes you a day.
With 99% copper you could run ten times as much and it will take ten days before you need to replace electrolyte.
To get to 99% copper you need 1 kg 90% and 9 kg 100% copper.
In the end you spent longer time, more electricity, handled more material and just refined 1 kg of your original feedstock, just as in the first example.

The only time you can use dilution is when you have a good feedstock you could blend it into. The only reason to do it is to get a more homogenous feedstock so the process can be trimmed in to maximize productivity. The electrolyte will be fouled just as much if you run it all at once or blended into a larger feedstock.

My question is what is the 10% made up of? Maybe you can use standard copper pyrometallurgical processes to refine it up to acceptable levels.
Iron and aluminum should slag out before copper if you blow oxygen onto it, zinc ought to boil off after prolonged heating. This is only theoretical as I've only read about the processes, not worked with them.

My first impression is that it will never be possible to set up a small refinery profitable but I might be wrong. The larger companies (Boliden, Umicore, ...) builds large complexes that recovers tin, lead, copper, zinc, precious metals, nickel, chromium, .... and so on. The highly specialized systems can extract high percentages from the metals in the scrap. The only problem here is that they demands larger lots, 10 tons and up to accept it.
There might be a niche for a refinery of smaller lots between 1 and 10 tons but then you must learn a lot about refining and extracting the metals. Right now I'm seeing someone that knows enough to think refining is easy and not enough to know the pitfalls.
Maybe the solution is to pour refiners bars and sell them to a refinery that extracts the copper and precious metals. Arubis has been mentioned on the forum as a buyer of refiners bars. ( http://www.aurubis.com/en/ )

Since you seems to be economically committed and have started to order expensive equipment I can only wish you good luck.
If you get your operation up and going I might be one of your customers. I'm struggling to get to the point that I can send stuff to Umicore and finally get paid for the real content. I'm no longer selling the scrap to the local junkyard as they pay too little. They only get the low value brown boards and power supplies now.

Göran

 

[goldsilverpro]

I agree with Harold. What happened to you is exactly what I would expect. At first, the cathode deposit is good, but when the contaminating metals (Ni, Fe, etc.) start building up in the solution, the cathode deposit starts degrading. It becomes non-adherent and starts sloughing off of the cathode. I know of no remedy for this.

 

[nickvc]

Goran I don't take offence but it is the only way to refine the copper successfully, lower % bars just cause problems that can't be overcome. Copper refining is one of the oldest refining technologies and if a better method was available the multinational companies involved I'm sure would be using it, they have the advantage of huge feed stocks and can blend the refiner bars into their systems without too much hassle plus laboratories to constantly test the feed stock and the electrolyte, I just can't see a way past the problems small refiners are going to encounter trying to do this ,it has been discussed many times in the past and no one amongst some of the cleverest refiners and or chemists on the planet has yet found a method that's economical or even possible.

 

[solar_plasma]

Extractive Metallurgy of Copper by Davenport (chapter 16 contains everything you want to know, but I guess the whole book is interesting for you).

I am sure I have read some good pieces more, I just can't find them right now.

EDIT: I just wanted to add, the electrolyte gets continuously replaced and recycled in some large copper refining plants, as far as I have read. Maybe I am a killjoy and of course I am no professional, but I don't believe this recycling of the electrolyte can be done economically at this scale, copper with nickel is quite a headache in my mind.

 

[EdwinEL]

Everybody, thank you for all the conversation, I am amazed how much knowledge there could be in 1 place!
Nice to be part of the conversation!

Solar_plasma;
Well, i think I have allot figured out, I am not saying that I am an expert, nor do I say that I believe it is a golden goose. But I believe that with the company we are trying to build I could give my father something he never had in his work. A nice and joyfull day, he never liked working in the hotel but was forced to do so by hy parents (my grandparents) and I hope he could this way enjoy his working time as long as it still lasts!

Göran;
Being open for someone elses ideas only brings creativity to one! Also very much liked your post.
I truly agree with your statement about contaminating your electrolyte. And as proposed by Harold and Nick it surely helps by ramping up the purity.
I took some pure copper strip to try the statement out and it worked. I won't say like a charm, because it's not a perfect plate yet. But It will get me there.
PS. the reason the anode was contaminated is because we did not have the tools to get the last pieces of slag out. For the bigger furnace there will be normal slag scrapers etc.
So the contaminations where mostly Iron and Aluminum.

Well we will see how it goes to create a small scale refinery. We would like to work it a couple of months, and if our results are positive I am always open for business proposals. So if the time comes I will surely contact you about it.
However I totally agree that refining is not easy, and I am not trying to say it is easy. But it is not easy trying to bring your thoughts in a couple of posts.

Thank you for your best wishes and I will keep you updated!

Gold Silver Pro;
Yes that is exactly what happend, and probably is unavoidable. But I need to start of with a higher purity anode.
But what I do not understand/want to understand is why stainless steel 316 won't work.
I mean the ISA Kidd process is uses by several larger refineries, and they still use that?
So I am very curious why it would not work.

Down below some pictures of a quick batch. I cleaned the electrolyte again and freshend up the cathode.
I will let it go for today and tonight and check on the results again in the morning. Maybe It cleans up while growing.

Thank you all for your advice and I am really happy with all the comments!

 

[EdwinEL]

Thank you solar_Plasma, I wil try and read it in the comming day's!

 

[solar_plasma]

And this one:
Copper electrowinning: theoretical and
practical design
by N.T. Beukes* and J. Badenhorst
http://www.saimm.co.za/Journal/v109n06p343.pdf

Davenport and this one are that extraordinarily good, that I almost feel I could build a plant on my own after having read those :lol: ...and if I had some hundred million euros I probably would, - just for the fun. :twisted:

 

[g_axelsson]

Goran I don't take offence but it is the only way to refine the copper successfully, lower % bars just cause problems that can't be overcome.

Long term the copper your refining can be used to increase the purity of your anodes

Nickvc, what is the problem that returning refined copper back for more rounds through the electrolysis cell would solve?

I thought that the main problem of low grade copper anodes was the short lifetime of the electrolyte. When for example a zinc atom is dissolved from the anode a copper atom is plated out at the cathode and the electrolyte becomes weaker. This goes on until the electrolyte is too much garbage and too little copper and then it needs to be replaced.

Is there some other problem that I'm not aware of?

I agree with you that it would be very hard to run low grade bars effectively, the process would need constant attention. But as I see it diluting the feedstock with pure copper would not serve any purpose and only create more work and expenses.
I also agree that this is the most effective way to refine copper we know of so far. (Leaving open for newer developments 8) )

Please, correct me if I'm wrong.

Göran

 

[solar_plasma]

Göran, I think the problem is, a smooth, continuous process will only work at 98,4-99,8% copper (Davenport) in order to get 99,99% purity. So, if you don't want to prepare the copper by acid refining, you have no other choice, than to blend it with at least about 9/10 millberry scrap,which should be pure enough,but also benefits from being refined. Also, the slow exchange of electrolyte will work much better, if it takes 10 days, than if it takes only one. The contaminant level won't jump up and down every day, but it will be more controllable.

I understand making pure metal more impure sounds stupid and normally it is, in everything we do here, but in fact there is no choice. I think this is one reason, why copper refining is something for the big boys. It only works, if you have a lot all the time.

My conclusion is, he will have to think big (enough) or it will not work. Only thinking about the continuous measuring,the recycling of the electrolyte, the storage tanks, the reactors and the size of the plant at all, this is a millions of dollars project. ...just to make it work, not said, it will amortize at this scale.