Precipitating with copper powder

[haveagojoe]

I have been running an electrowinning cell to remove contaminants from used Copper Chloride solution, which has produced some copper powder. I have been considering using it to precipitate gold from solution instead of SMB for my next drop.

I'm not entirely sure about the purity of the copper powder, I cleaned it up with washes in water, Sulfuric, water again, HCl, then water again, it looks quite good but still I doubt it's really pure.

Today I learned that only 0.161g of copper is required per gram of gold for precipitation, and I know that it's important to stop adding it before all the gold is precipitated otherwise it's too easy to overdo the copper and contaminate the gold.

Since I'm expecting less than 10g of gold at the end, is my idea of dropping it with copper powder a bad idea? I think it will be difficult not to overdo it since the quantity required is so small. Would it be more sensible to just cement it out with some bare copper wire, or otherwise just stick to the usual SMB?

I'm curious to try the copper powder but maybe it's better to wait until I have a larger batch, and also maybe make some pure copper powder specially for the purpose which will be properly clean.

 

[4metals]

Thank you for starting a new thread with this!

There are discussions on the forum about cementation with fine powdered copper and when I think about them @kurtak seems to be the most experienced with using the technique to drop high purity metals.

An experiment you could do would be to purchase on line some atomized fine copper powder, it is reasonably priced and it will give you an indication of how much pure copper will do the job. If you had evenly split the solution, you could then use your copper from the copper chloride solution to see if it produces comparable results.

With finely divided copper powder the key is good agitation and slow feed. Feed a little, stir constantly, add a little more and continue until you are done. Remember stannous will still work to tell you where you are and, as with all cementation the copper needs to contact the gold to react so agitation is critical.

 

[4metals]

This thread may help you get started. It is an example of 2 things actually, one is using copper for cementation and two, what not to name a thread if you want anyone to find it. Find the thread HERE

 

[haveagojoe]

purchase on line some atomized fine copper powder

Good idea, although I was thinking I can probably produce some which would be pretty clean by dissolving fresh copper wire in HCl with a little peroxide and then running a clean electrowinning cell to get it back out as deposits while are easily powdered. It would be a lot cleaner than what comes from the used "AP" solutions, but you're right the cleanest would be to buy it fresh. Kurtak's method using busbar sawdust is also a good idea though, should be pretty pure I would imagine.

For my first button I actually used Copper (I) Chloride to precipitate- don't laugh, it was a mistake, I wrongly presumed that's what was meant by Copperas! (This was a long time ago now, lesson learned)

However it worked, and dropped the gold quite well, but after melting the button came out kinda ugly and shows signs of copper contamination. It was the second refine of the powder which I had dropped the first time with SMB. If I had done it the other way around it would probably have come out a lot better, despite my error.


4 grams, although some of that will be copper. I also think it picked up some lead from the old torch I used which had been previously used for soldering pipework and had visible traces of solder stuck to it.

 

[4metals]

this price isn't too bad for high purity. It has come down considerably. For my money I would rather buy it than drill, and screen it for the fines. Not enough hours in my retired day as it is!

 

[Yggdrasil]

Good idea, although I was thinking I can probably produce some which would be pretty clean by dissolving fresh copper wire in HCl with a little peroxide and then running a clean electrowinning cell to get it back out as deposits while are easily powdered. It would be a lot cleaner than what comes from the used "AP" solutions, but you're right the cleanest would be to buy it fresh. Kurtak's method using busbar sawdust is also a good idea though, should be pretty pure I would imagine.

For my first button I actually used Copper (I) Chloride to precipitate- don't laugh, it was a mistake, I wrongly presumed that's what was meant by Copperas! (This was a long time ago now, lesson learned)

However it worked, and dropped the gold quite well, but after melting the button came out kinda ugly and shows signs of copper contamination. It was the second refine of the powder which I had dropped the first time with SMB. If I had done it the other way around it would probably have come out a lot better, despite my error.

View attachment 66079
4 grams, although some of that will be copper. I also think it picked up some lead from the old torch I used which had been previously used for soldering pipework and had visible traces of solder stuck to it.

Well I'd say its the other way around, it shows signs of Gold

 

[haveagojoe]

Well I'd say its the other way around, it shows signs of Gold

Too kind, there's definitely gold in it but not nice and shiny! It hasn't been pickled in Sulfuric so there's probably remnants of Borax on it too.

I'm planning to inquart it with copper along with other buttons when I've got enough to make a sensible sized lot. I heard from Sreetips that copper can make a nice job of inquarting even though it uses more acid. I do have a little silver I could use, it was silver clay for making jewellery, but I don't think it's very pure and I'm not sure I'll have enough.

 

[galenrog]

If I remember correctly, Kurtak made several attempts with copper powder before achieving the results he wanted.

 

[nickvc]

If your button is only gold and copper you can easily dissolve it in AR no need to inquart.

 

[haveagojoe]

If your button is only gold and copper you can easily dissolve it in AR no need to inquart.

Hm yea I guess I could... do you mean dissolve it and then drop it again without filtering? I would imagine the dissolved copper would make the gold drop out again straight away, at least some of it?

I've put it to pickle in some dilute Sulfuric so I'll see how it looks after pickling, I'm hoping the frostyness is just borax and lead on the surface and will clear up.

I've had the thing for about 10 years now and haven't tried to do anything with it because I thought it would need inquarting.

 

[Yggdrasil]

Hm yea I guess I could... do you mean dissolve it and then drop it again without filtering? I would imagine the dissolved copper would make the gold drop out again straight away, at least some of it?

I've put it to pickle in some dilute Sulfuric so I'll see how it looks after pickling, I'm hoping the frostyness is just borax and lead on the surface and will clear up.

I've had the thing for about 10 years now and haven't tried to do anything with it because I thought it would need inquarting.

Inquarting is to overcome the Silver Chloride issue

 

[haveagojoe]

Inquarting is to overcome the Silver Chloride issue

So I can just dissolve it and drop the powder and then clear out the copper with HCl washes? That would be great if I can.

I'm guessing I should probably beat it flat with a hammer to make it easier to dissolve?

 

[kurtak]

There are discussions on the forum about cementation with fine powdered copper and when I think about them @kurtak seems to be the most experienced with using the technique to drop high purity metals.

Yes - copper cementation to recover (precipitate) the PMs from solutions has been my main method of getting my PMs back (from solution) ever since you taught me the value of copper cementation in this thread ----------

https://goldrefiningforum.com/threa...onnects-need-some-advice-_cementation_.22203/

The rest of this post is being post as general info (as you already know all of this 4metals)

That was like ten years ago now & ever since copper has been my "go to" method to get my PMs back out of solution - VERY RARELY do I ever use chemical precipitant any more --- about the only time I use time I use chemical precipitants any more is if I have more then one PM in solution

Now I know that most people think I am nuts - but IMO - at least for the small batch guy (4 - 5 or less ozt) or hobby guys (1ozt or less) copper (IMO) is really the way to go - as long as you only have one PM in solution

And yes - you can most certainly turn out HIGH purity metals (999) with copper cementation (when done right)

To put that in perspective - in my "hobby" refines this year I turned out nine 1 ozt bars of 999 gold - all done by copper cementation

All 9 bars have been confirmed to be 999 by the XRF of the gold buyer I take my gold to for testing (the XRF actually reads out 100% Au) --- of those 9 bars I sold him 4 bars (2 different sales of 2 bars each sale) which he sent to the refiner he deals with - which in turn paid him out on 999 gold --- so my 999 copper cement gold has been confirmed not only by the buyers XRF - but by the refiner he sends it to

I have had this same confirmation on my copper cement gold with the buyer I used to deal with (& the refiner he sent my gold to) before I moved from Wisconsin to here in Oregon - so I have had my copper cemented gold confirmed I don't even know how many times to come back in fact at 999

Now then - does it always come back as 999 - no - BUT - that (as we all know) can & often holds true with chemical precipitation --- this forum is full of threads that talk about needing to do a second &/or even a third refine after chemical precipitation - it just depends on the circumstances/situation/conditions in any given refine on how clean your gold drop comes back - & that is true whether it is done by chem precipitation - or copper cementation

And of course, the washing of your sponge (powder) plays a role in the purity of final melted button or bar --- whether done by chem precipitation - or copper cementation

My point here is that you can in fact turn out HIGH purity gold with copper cementation - even from VERY dirty solutions (provided there is only one PM in that VERY dirty solution)

Here is "one" of the things I really like about copper cementation - you NEVER need to worry about fee nitric in your solution - so you don't need to concern yourself with the step of chemically de-Noxing - the copper takes care of all of that - while at the same time dropping your gold from solution

With all that said - there is most certainly nothing wrong with going the chemical rout to recover PMs from solution (did it for several years before figuring out the benefits of copper) - but for me - once I figured out the real benefits of copper cementation - I have found it to be the quickest & easiest least hassle way to get your gold back (from solution) on small batches (5 ozt or less) & do so with high purity results (when done right)

For what it is worth

Kurt

 

[haveagojoe]

Yes - copper cementation to recover (precipitate) the PMs from solutions has been my main method of getting my PMs back (from solution) ever since you taught me the value of copper cementation in this thread ----------

https://goldrefiningforum.com/threa...onnects-need-some-advice-_cementation_.22203/

The rest of this post is being post as general info (as you already know all of this 4metals)

That was like ten years ago now & ever since copper has been my "go to" method to get my PMs back out of solution - VERY RARELY do I ever use chemical precipitant any more --- about the only time I use time I use chemical precipitants any more is if I have more then one PM in solution

Now I know that most people think I am nuts - but IMO - at least for the small batch guy (4 - 5 or less ozt) or hobby guys (1ozt or less) copper (IMO) is really the way to go - as long as you only have one PM in solution

And yes - you can most certainly turn out HIGH purity metals (999) with copper cementation (when done right)

To put that in perspective - in my "hobby" refines this year I turned out nine 1 ozt bars of 999 gold - all done by copper cementation

All 9 bars have been confirmed to be 999 by the XRF of the gold buyer I take my gold to for testing (the XRF actually reads out 100% Au) --- of those 9 bars I sold him 4 bars (2 different sales of 2 bars each sale) which he sent to the refiner he deals with - which in turn paid him out on 999 gold --- so my 999 copper cement gold has been confirmed not only by the buyers XRF - but by the refiner he sends it to

I have had this same confirmation on my copper cement gold with the buyer I used to deal with (& the refiner he sent my gold to) before I moved from Wisconsin to here in Oregon - so I have had my copper cemented gold confirmed I don't even know how many times to come back in fact at 999

Now then - does it always come back as 999 - no - BUT - that (as we all know) can & often holds true with chemical precipitation --- this forum is full of threads that talk about needing to do a second &/or even a third refine after chemical precipitation - it just depends on the circumstances/situation/conditions in any given refine on how clean your gold drop comes back - & that is true whether it is done by chem precipitation - or copper cementation

And of course, the washing of your sponge (powder) plays a role in the purity of final melted button or bar --- whether done by chem precipitation - or copper cementation

My point here is that you can in fact turn out HIGH purity gold with copper cementation - even from VERY dirty solutions (provided there is only one PM in that VERY dirty solution)

Here is "one" of the things I really like about copper cementation - you NEVER need to worry about fee nitric in your solution - so you don't need to concern yourself with the step of chemically de-Noxing - the copper takes care of all of that - while at the same time dropping your gold from solution

With all that said - there is most certainly nothing wrong with going the chemical rout to recover PMs from solution (did it for several years before figuring out the benefits of copper) - but for me - once I figured out the real benefits of copper cementation - I have found it to be the quickest & easiest least hassle way to get your gold back (from solution) on small batches (5 ozt or less) & do so with high purity results (when done right)

For what it is worth

Kurt

Thanks Kurt, I think it's a great approach, definitely not nuts! It makes a lot of sense. I just need to try it for myself.
My only concern is over how to avoid overshooting the copper when doing very small lots (<10g). Do you weigh the copper powder beforehand? I read that it only takes 0.161g of copper to precipitate each gram of gold, so at that lot size its a very small amount of copper to handle accurately.
If a little too much copper is added, would I be right in thinking that it can be cleared up by the HCl washes of the powder afterwards?

I would imagine the dissolved copper would make the gold drop out again straight away, at least some of it?

I think I see the error in my thinking here: it's only copper going into solution which precipitates gold, taking its place; copper which is already in solution will stay there.

 

[4metals]

As I noticed back when I built my first atomizer the mark ups on fine copper powder is substantial. The link I listed is selling a pound of the powder for $72 while Kitco lists copper at $4.08 a pound. If you are in it for the money all that is needed is a small atomizer, a furnace, and a sifter screen.

Maybe some of our younger profit driven members should realize there is a gold rush working at a mere percent or two margins while the copper dust margins are large. Kurt can do a video schooling of his methods and link to his own dust sales and live out his days in the lap of luxury.

I always knew the value of copper in cementing PM's which is why I advocated the waste treatment by first cementation on copper that many use today. Kurt took it the next step to using the same techniques for higher purity metals using similar techniques. Kudo's to Kurt!!!!! (and all thanks to a thread on the forum about fuzz buttons! To this day I still do not know what a fuzz button is!)

 

[haveagojoe]

would I be right in thinking that it can be cleared up by the HCl washes of the powder afterwards?

I see I am wrong about this also, HCl would not dissolve copper alone, only with an oxidizer. However, perhaps it could be done by using a clean Copper Chloride solution for the first wash?

 

[anarxi]

So I can just dissolve it and drop the powder and then clear out the copper with HCl washes? That would be great if I can.

I'm guessing I should probably beat it flat with a hammer to make it easier to dissolve?

copper from sediment can be removed, also with citric acid and peroxide...
I also use foil-clad PCB, a blank for PCBs.
I don't know if you can buy it in your country.
Here the copper is applied in a very thin layer, several tens of microns.
Theoretically, you can cut out something like a blade and rotate it in the solution using an electric motor.

 

[haveagojoe]

copper from sediment can be removed, also with citric acid and peroxide...

Aha! Yes this could be very useful, thank you. I was trying to think of a way to do it without redissolving gold, this would be ideal. I would imagine the sediment an sit in citric acid with peroxide for as long as we want with no danger of dissolving the gold.

I also use foil-clad PCB, a blank for PCBs.
I don't know if you can buy it in your country.
Here the copper is applied in a very thin layer, several tens of microns.
Theoretically, you can cut out something like a blade and rotate it in the solution using an electric motor.

Interesting idea, yes I can see this is a practical way to do it accurately

But when I say beating it flat I meant about my gold button which I need to redissolve. I think it would take a very long time if I try to dissolve it as it is.

 

[kurtak]

I have been running an electrowinning cell to remove contaminants from used Copper Chloride solution, which has produced some copper powder. I have been considering using it to precipitate gold from solution instead of SMB for my next drop.

haveagojoe - I would not use that copper powder simply because you don't know what "other" metals may (or not) have been electrowon from CuCl3 solutions - metals that "could" result in contamination of your gold when you use this to cement your gold

Concerning cementing gold with copper - a few pointers ----------

You can use any copper as long as you know it is pure copper & clean copper (no dirt, grease or copper oxide on the surface of the copper) so it can be a heavy solid piece of copper like a copper bus bar - or heavy/thick copper wire - or copper powder (the finer the better)

Some people use copper pipe they hammer flat - I am not a fan of this because copper pipe is relatively thin & it gets even thinner as the acid dissolves the copper which can result in "small" pieces of copper falling off the thin copper & ending up in your gold

With copper wire the thicker/heavier the better - I like to use 4 or 6 gauge & at the smallest 8 gauge solid copper wire (can be found at the hardware store as solid copper ground wire - not stranded) - smaller then 8 gauge & you are taking a chance on the same problem as with the copper pipe

When using solid copper (bus bar or wire) it is important that all the copper is completely submerged below the surface of the solution - if it is not completely submerged copper oxide will form on the copper sticking out above the top of the solution & some of that copper oxide will fall off & settle along with the gold contaminating the gold

Examples of how I use the different types of copper

1) If I have say 3 - 3.5 liters of solution in a 5 liter beaker I will hang one or two solid copper bus bars in the solution - I use solid bus bars in this situation because with that much acid it is likely going to dissolve a lot of copper so I don't need to worry about small pieces of copper falling off from the copper getting to thin

2) if it is say 1.5 liters of solution in a 2 liter beaker or 2 liters solution in a 3 liter beaker I will coil up a piece of heavy/thick copper wire - like 3 - 4 feet even 5 feet of wire coiled up

In the Fuzz button link provided in this thread by both myself & 4metals there is a pic showing examples of this (copper in the beakers but no solution)

3) it is when I only have 1 -1.5 liters or less of solution that I use the copper powder

In all 3 of these examples it is important that you stir the solution so that all the dissolved gold ions come in contact with the copper - if the gold ions don't make contact with the copper they will not cement out

To some degree - the motion from the acid reacting with the copper will provide "some" of its own stirring but it also needs some manual stirring

So - with the solid copper - once the acid starts reacting with the copper you can "kind of" just let it go as the motion of the reaction kind of does its own stirring - however - you also want to on occasion give it a good stir with your glass stir rod - this becomes most important once the reaction with the copper starts to die down - not so important when the reaction is going full blown --- the manual stirring (once the reaction starts to slow down) does 3 things ----------

1) as gold starts to settle in the bottom of the beaker that settling gold traps dissolved gold ions in the settled gold sponge/powder --- so you need to stir that settled gold up to bring those dissolved gold ions trapped in the settling gold up & out so they can make contact with the copper

2) When the reaction with the copper is full blown (which is also when you don't really need to stir it) the vigorous reaction will keep the gold knocked of the copper - but when the reaction starts to slow down gold may start to stick to the copper - so stirring helps keep the gold knocked off the copper

3) as gold cements out of solution there gets to be less & less dissolved gold ions in the solution - so the few gold ions that are further away from the copper can't really make contact with the copper in order to allow them to cement out as gold --- so you need to stir it in order to get those gold ions to come around & make contact with the copper

It is aways a good idea to warm you solution before putting the copper in - this helps to get the cementing process better/quicker under way - which in turn allows for more & larger gold particles to cement out at the beginning of the process - which in turn helps with better/faster settling at the end of the process --- once the reaction really gets going you can turn the heat off as the reaction will create its own heat

Like with any reaction you are going to getting foaming so you need to leave head room in the beaker for the foam up (just like when dissolving metals in the first place) & keep your spay bottle handy to knock the foam down in case of a reaction run away (as should be done with all reactions) --- as well this process is going to produce the same brown Nox fumes as seen when first dissolving metals to put them in solution

And that is somewhat how you know when to stop the cementing process (especially if you are after HIGH purity cement gold) - you want to start testing with your stannous &/or consider pulling the copper when the reaction dies WAY down & you see little or no more brown Nox fumes being produced

This is how I do it with larger batches using solid copper

The key to getting HIGH purity cement gold is just to make sure you stop the cementing process "a bit" short of "complete cementation" --- stannous is your friend here as you near the end of the cementing process

When done right you should be able to recover 96 - 98% of your gold (as high purity gold) --- the decanted solution (after settling) along with the washes of the gold powder/sponge goes to the stock pot - just like all decants & washes from chemical precipitation should go to the stock pot for final "dirty" gold recovery

The worst thing that can happen is if you leave the copper in to long resulting in 993 - 997 instead of 999 - or you stop the cementing process to soon & send more gold then need be to the stock pot

Side note here - it is actually hard to over do it with solid copper

This is NOT anywhere as complicated as it may sounds & it goes relatively quick - BUT - just like anything & everything in refining there is a bit of a learning curve

One more thing (for today) unlike SMB precipitation where the solution goes relatively clear after precipitation with cementation the solution goes dark - very dark - due to all the copper going into solution

Copper powder is "a bit" trickier (but not much) but I will have to leave that for another post on another day

Kurt

 

[haveagojoe]

haveagojoe - I would not use that copper powder simply because you don't know what "other" metals may (or not) have been electrowon from CuCl3 solutions - metals that "could" result in contamination of your gold when you use this to cement your gold

Concerning cementing gold with copper - a few pointers ----------

You can use any copper as long as you know it is pure copper & clean copper (no dirt, grease or copper oxide on the surface of the copper) so it can be a heavy solid piece of copper like a copper bus bar - or heavy/thick copper wire - or copper powder (the finer the better)

Some people use copper pipe they hammer flat - I am not a fan of this because copper pipe is relatively thin & it gets even thinner as the acid dissolves the copper which can result in "small" pieces of copper falling off the thin copper & ending up in your gold

With copper wire the thicker/heavier the better - I like to use 4 or 6 gauge & at the smallest 8 gauge solid copper wire (can be found at the hardware store as solid copper ground wire - not stranded) - smaller then 8 gauge & you are taking a chance on the same problem as with the copper pipe

When using solid copper (bus bar or wire) it is important that all the copper is completely submerged below the surface of the solution - if it is not completely submerged copper oxide will form on the copper sticking out above the top of the solution & some of that copper oxide will fall off & settle along with the gold contaminating the gold

Examples of how I use the different types of copper

1) If I have say 3 - 3.5 liters of solution in a 5 liter beaker I will hang one or two solid copper bus bars in the solution - I use solid bus bars in this situation because with that much acid it is likely going to dissolve a lot of copper so I don't need to worry about small pieces of copper falling off from the copper getting to thin

2) if it is say 1.5 liters of solution in a 2 liter beaker or 2 liters solution in a 3 liter beaker I will coil up a piece of heavy/thick copper wire - like 3 - 4 feet even 5 feet of wire coiled up

In the Fuzz button link provided in this thread by both myself & 4metals there is a pic showing examples of this (copper in the beakers but no solution)

3) it is when I only have 1 -1.5 liters or less of solution that I use the copper powder

In all 3 of these examples it is important that you stir the solution so that all the dissolved gold ions come in contact with the copper - if the gold ions don't make contact with the copper they will not cement out

To some degree - the motion from the acid reacting with the copper will provide "some" of its own stirring but it also needs some manual stirring

So - with the solid copper - once the acid starts reacting with the copper you can "kind of" just let it go as the motion of the reaction kind of does its own stirring - however - you also want to on occasion give it a good stir with your glass stir rod - this becomes most important once the reaction with the copper starts to die down - not so important when the reaction is going full blown --- the manual stirring (once the reaction starts to slow down) does 3 things ----------

1) as gold starts to settle in the bottom of the beaker that settling gold traps dissolved gold ions in the settled gold sponge/powder --- so you need to stir that settled gold up to bring those dissolved gold ions trapped in the settling gold up & out so they can make contact with the copper

2) When the reaction with the copper is full blown (which is also when you don't really need to stir it) the vigorous reaction will keep the gold knocked of the copper - but when the reaction starts to slow down gold may start to stick to the copper - so stirring helps keep the gold knocked off the copper

3) as gold cements out of solution there gets to be less & less dissolved gold ions in the solution - so the few gold ions that are further away from the copper can't really make contact with the copper in order to allow them to cement out as gold --- so you need to stir it in order to get those gold ions to come around & make contact with the copper

It is aways a good idea to warm you solution before putting the copper in - this helps to get the cementing process better/quicker under way - which in turn allows for more & larger gold particles to cement out at the beginning of the process - which in turn helps with better/faster settling at the end of the process --- once the reaction really gets going you can turn the heat off as the reaction will create its own heat

Like with any reaction you are going to getting foaming so you need to leave head room in the beaker for the foam up (just like when dissolving metals in the first place) & keep your spay bottle handy to knock the foam down in case of a reaction run away (as should be done with all reactions) --- as well this process is going to produce the same brown Nox fumes as seen when first dissolving metals to put them in solution

And that is somewhat how you know when to stop the cementing process (especially if you are after HIGH purity cement gold) - you want to start testing with your stannous &/or consider pulling the copper when the reaction dies WAY down & you see little or no more brown Nox fumes being produced

This is how I do it with larger batches using solid copper

The key to getting HIGH purity cement gold is just to make sure you stop the cementing process "a bit" short of "complete cementation" --- stannous is your friend here as you near the end of the cementing process

When done right you should be able to recover 96 - 98% of your gold (as high purity gold) --- the decanted solution (after settling) along with the washes of the gold powder/sponge goes to the stock pot - just like all decants & washes from chemical precipitation should go to the stock pot for final "dirty" gold recovery

The worst thing that can happen is if you leave the copper in to long resulting in 993 - 997 instead of 999 - or you stop the cementing process to soon & send more gold then need be to the stock pot

Side note here - it is actually hard to over do it with solid copper

This is NOT anywhere as complicated as it may sounds & it goes relatively quick - BUT - just like anything & everything in refining there is a bit of a learning curve

One more thing (for today) unlike SMB precipitation where the solution goes relatively clear after precipitation with cementation the solution goes dark - very dark - due to all the copper going into solution

Copper powder is "a bit" trickier (but not much) but I will have to leave that for another post on another day

Kurt

Very valuable detail Kurt, thank you so much