Another way to deal with Copper (i) Chloride

[haveagojoe]

I'm currently running a batch of low grade mixed pins in Copper Chloride etch and I stumbled across a possible variation of the method which seems to work quite well.

Pin-type material generally tends to create massive amounts of white Copper (i) Chloride (alongside other metal chlorides) - even with an air bubbler the white salt crystals seems to precipitate out and mix with the pins and foils.

Usually I decant most of the solution and then add fresh HCl to redissolve the Copper (i) Chloride back into Copper (ii) Chloride solution, but this generates an ever-growing volume of solution and consumes excessive HCl.

This time I settled and decanted the solution and simply left the remaining solids (partly digested pins mixed with Copper (i) Chloride crystals and gold foils) to sit in air for a couple of days. When I returned, the Copper (i) Chloride appeared to have fully oxidized to a sludge of green Copper Oxide* (edit - see below), which immediately redissolved when I re-added the original Copper Chloride solution. This allowed me to filter the foils out of the solution easily without the filter clogging up with Copper (i) Chloride and without extending the volume of my solution.

I'm curious to hear if anyone else has come across this method. It seems like quite a handy tactic for dealing with problematic amounts of Copper (i) Chloride when the bubbler is insufficient to keep it in solution and when it's mixed with gold foils. Simply oxidizing in air was like a magic fix for this annoying problem.

Edit- Correction: the greenish sludge of oxidized Copper (i) Chloride is, I believe, Copper Oxychloride rather than Copper Oxide.

 

[Yggdrasil]

I'm currently running a batch of low grade mixed pins in Copper Chloride etch and I stumbled across a possible variation of the method which seems to work quite well.

Pin-type material generally tends to create massive amounts of white Copper (i) Chloride (alongside other metal chlorides) - even with an air bubbler the white salt crystals seems to precipitate out and mix with the pins and foils.

Usually I decant most of the solution and then add fresh HCl to redissolve the Copper (i) Chloride back into Copper (ii) Chloride solution, but this generates an ever-growing volume of solution and consumes excessive HCl.

This time I settled and decanted the solution and simply left the remaining solids (partly digested pins mixed with Copper (i) Chloride crystals and gold foils) to sit in air for a couple of days. When I returned, the Copper (i) Chloride appeared to have fully oxidized to a sludge of green Copper Oxide, which immediately redissolved when I re-added the original Copper Chloride solution. This allowed me to filter the foils out of the solution easily without the filter clogging up with Copper (i) Chloride and without extending the volume of my solution.

I'm curious to hear if anyone else has come across this method. It seems like quite a handy tactic for dealing with problematic amounts of Copper (i) Chloride when the bubbler is insufficient to keep it in solution and when it's mixed with gold foils. Simply oxidizing in air was like a magic fix for this annoying problem.

It is the same mechanism as the air bubbling.
Maybe you don't have agressive enough bubbling?

 

[haveagojoe]

It is the same mechanism as the air bubbling.
Maybe you don't have agressive enough bubbling?

Yes it's effectively the same reaction, but more efficient perhaps. It's true my aquarium bubbler is not very powerful, but for a kilo or so of pin-type material I think even multiple bubblers would struggle to prevent Copper (i) Chloride from forming. With this approach I just let the air do the job passively, which it seemed to do quite quickly really, perhaps because of the high surface area which the mass of pins create.
I'll still continue to use the bubbler as normal, but it was a handy discovery to be able to do this if I get in a mess with large amounts of CuCl(i), without resorting to using up fresh HCl.

 

[Yggdrasil]

Yes it's effectively the same reaction, but more efficient perhaps. It's true my aquarium bubbler is not very powerful, but for a kilo or so of pin-type material I think even multiple bubblers would struggle to prevent Copper (i) Chloride from forming. With this approach I just let the air do the job passively, which it seemed to do quite quickly really, perhaps because of the high surface area which the mass of pins create.
I'll still continue to use the bubbler as normal, but it was a handy discovery to be able to do this if I get in a mess with large amounts of CuCl(i), without resorting to using up fresh HCl.

Since the Copper is already in a salt it reacts quite fast with the Oxygen and the CO₂ in the air.
And as you correctly point out the surface are is quite important.
Maybe a cycling between the air and the solution will.be most effective.

 

[haveagojoe]

Since the Copper is already in a salt it rects quite fast with the Oxygen and the CO₂ in the ar.
And as you correctly point out the surface are is quite important.
Maybe a cycling between the air and the solution will.be most effective.

Yes I think it will be a useful method- pouring off the settled solution and allowing oxidation of the solids, then re-adding the solution to dissolve the oxide and then filtering.. However I don't think the salt will stay in solution for long, especially if I don't use the bubbler to keep it there. Need to filter the foils out immediately rather than waiting for them to settle and decanting.

If I end up repeating the cycle multiple times, then after decanting the solution from the pins I'm thinking maybe it would be a good idea to let it sit awhile longer, to let more CuCl(i) to precipitate out of before decanting the solution off again and then re-adding to the pin material. The disadvantage though would be that any foils still floating about when I decanted could then end up mixed with the CuCl(i) crystals. It could become a bit of a game of cat and mouse, decanting, oxidizing and filtering with diminishing returns after a few cycles.

This sort of thing wouldn't be necessary for nice clean finger-type material, it's just these low-grade pins which generate so much CuCl(i), probably mixed with lots of other salts. In particular I think Nickel Chloride Hexahydrate may be present although I suspect the Nickel tends to stay in solution more readily.

 

[haveagojoe]

As a side note, another thing I learned recently is to watch out for Zinc in low grade material- in computers and laptops there are sometimes what I would call "tabs", thin springy sheetmetal pieces with a gold flashing; apparently these are made of Zinc as they seem to make the Copper drop out of solution rapidly, turning it clear and rendering it useless for etching. The flash is so thin they are surely not worth bothering with anyway.

 

[Shark]

How many gallons of AP are you running for a kilo of pins. My experience has been that even one pound of pins per gallon will cement the copper out of solution. That is why I started search for other ways to aerate my AP. My search led to the use of an air lift pump to "wash" the pins until dissolved.

 

[haveagojoe]

How many gallons of AP are you running for a kilo of pins.

Only about 3 liters, a bit over half a gallon. I don't aim to dissolve the material completely, just to release most of the gold on the first cycle, which I filter out, then I pour the solution back with the pins to try to get more with further cycles. I do it in 5 litre plastic bottles which have a cap which allows me to shake up the material vigorously to help release the gold. The disadvantage of this much aggitation is that a lot of the gold is broken up into finely divided black powder rather than larger flakey foils, but that's not a big problem I think, as there aren't nice big foils from this kind of material anyway.

Usually with this type of material I get a lot of CuCl(i) mud in the filter, and more in amongst the remaining pins, but in both cases just leaving it to oxidize in air seems to make it soluble again in the original solution. After 3 or 4 cycles there's very little gold left on the pins and lots of salts so it becomes unproductive.

With the filters, after letting the solids oxidize in the filter for a couple of days, I pour a little of the original solution through which clears some of the greenish mud, and then I rinse the filter with a spray bottle into a beaker of about 100ml of fresh HCl, where the remaining greenish copper mud (oxychloride?) is dissolved back into solution. There is usually a lot of black powder below the green mud in the filter, which seems to be a mixture of finely divided gold and oxides/hydroxides of nickel and other metals. Some of these dissolve in the HCl too, and when I've accumulated a thick layer of foils and black powder in the beaker I pour off the solution and replace it with fresh HCl. Later when I dissolve the gold with HCl and pool chlorine tablets, some of the junk is filtered out, and then the rest I think must stay in solution when I drop the gold with SMB.

I think the main culprit for cementing copper out of solution is Iron, so it depends largely on how much Iron is in the source material. I should probably separate it out with a magnet but as yet I still don't do this.

I don't achieve full recovery this way, but when I've recovered as much of the gold from the material as I think practical, I empty the remaining metal pins material into a container of well-used solution where it sits for the long term and is gradually broken down. Once in a while I try to recover more gold from this container but there generally isn't much to be had.

 

[Martijn]

As a side note, another thing I learned recently is to watch out for Zinc in low grade material- in computers and laptops there are sometimes what I would call "tabs", thin springy sheetmetal pieces with a gold flashing; apparently these are made of Zinc as they seem to make the Copper drop out of solution rapidly, turning it clear and rendering it useless for etching. The flash is so thin they are surely not worth bothering with anyway.

Iron does the same thing by reactivity.

Good find, letting it open to the air.

Can the green sludge be copper carbonate due to the reaction with air?
What about letting the sludge sit in a large filter and occasionaly add a bit if AP or HCl and let the salts dissilve in the filter?

 

[Yggdrasil]

Iron does the same thing by reactivity.

Good find, letting it open to the air.

Can the green sludge be copper carbonate due to the reaction with air?
What about letting the sludge sit in a large filter and occasionaly add a bit if AP or HCl and let the salts dissilve in the filter?

Yes I guess it becomes a mix of Carbonates, Chlorides and Oxides.
Doing it in a filter seem like a good idea.
Maybe check how the filter holds up first.

 

[Taleeho]

It is the same mechanism as the air bubbling.
Maybe you don't have agressive enough bubbling?W

Your mention of aggressive bubbling made me think of DAF (dissolved air flotation) used in water purification. Water coming out of a DAF unit has so many microscopic air bubbles that it looks like milk. This may be over-kill and/or impractical to scale down to our level, and air-lift (suggested below) is probably better. Could someone provide details about setting air-lift up in 1-5 gal set-ups?

 

[Martijn]

Yes I guess it becomes a mix of Carbonates, Chlorides and Oxides.
Doing it in a filter seem like a good idea.
Maybe check how the filter holds up first.

I use a plastic kitchen strainer and those big coffee filters. They hold up to AP and HCl.

 

[Yggdrasil]

I use a plastic kitchen strainer and those big coffee filters. They hold up to AP and HCl.

Yes, but I was thinking on days of drying and remoisturizing.

 

[haveagojoe]

What about letting the sludge sit in a large filter and occasionaly add a bit if AP or HCl and let the salts dissilve in the filter?

Yea that's basically how I stumbled across it- I usually shake up the bottle to get the foils floating about in suspension, then decant it off from the metal pins into a filter, but one time my filtration was so slow with all the CuCl(i) mud I just left it for a couple of days. When I came back the solution had filtered through, the CuCl(i) mud had gone green in the filter, and the remaining pins in the bottle were also covered with green sludge. Pouring some of the original solution back through the filter again redissolved most of the sludge in the filter, leaving foils and black powder, and pouring it back in with the pins redissolved most of the sludge in there too, leaving the solution dark but clear not cloudy, with more foils floating about, ready to be filtered again. Filtration is still painfully slow because of the black powder but I can just leave it again, any CuCl(i) will be oxidized in the filter and in the bottle and I can just repeat the cycle.
It's a bit of a longwinded and slow process but with some patience it works to get a reasonable recovery from this low grade material, my main aim is to not use up large volumes of HCl just to get rid of the salts.

Edit to add- the impressive factor which allows this to happen is that Copper Chloride solution can hold up to 600g of copper per litre when fully saturated (under ideal conditions, or so I read somewhere). As we know it tends to precipitate out well before that, but with enough oxygen it's amazing how much it can dissolve.

 

[haveagojoe]

Yes, but I was thinking on days of drying and remoisturizing.

I'm using coffee filters too, they are remarkably tough, as long as they are wet. They do tear sometimes when dry though.
In another thread I talked about my method of forcing air back up through the filter to clear it when it gets clogged, I do this over and over again and I've only once had one burst. Maybe with stronger HCl they might start to degrade but I only use 10% and they hold up very well.

Edit to add- I try to empty out the bottle of filtrate periodically during filtering so that if one does burst, the volume of unfiltered solution which passes through is minimized so refiltering doesn't take too long.

 

[haveagojoe]

Could someone provide details about setting air-lift up in 1-5 gal set-ups?

I made a crude one with a piece of 3/4" plastic pipe- I just drilled a hole in the side about halfway up, about an inch above where the surface of the solution sits. Then I fed my bubbler tube down the pipe from the top until its about an inch from the bottom of the pipe. The bubbles rise up inside the tube and draw the solution along, and when it gets to the hole it spills out the side.
I works pretty well and I can still switch to "normal mode" just by pushing the tube down further until it sticks out from the bottom of the pipe.

 

[Martijn]

Yes, but I was thinking on days of drying and remoisturizing.

Just edited: did something similar and no problems.

 

[Shark]

This is from a two gallon bucket. I also run two of these at a time. I can normally dissolve around two pounds into a gallon of solution using this set up.



When using air lifts the trick is to get a large number of tiny bubbles moving in solution. A a cubic inch of air in a single bubble has less surface area than a cubic inch of air broken into a thousand small bubbles. Effectively adding air into solution quicker, and in more volume through the exposure to greater surface area.

Edit to add.

These tiny bubbles also allow a greater volume to be lifted higher as well.