Cementing on copper

[bswartzwelder]

I am still in the process of cleaning up my poormans AR solution and am waiting for a new stirring hot plate to be delivered. Hopefully, it should be here sometime later today. I really believe that evaporating my mess down to a syrup, reconstituting with HCl and repeating 3 times will get me to the point where I can precipitate everything with SMB. However, cementing the values on copper has been mentioned and I will keep that in the back of my mind for now.

My question is: If I place a piece of clean copper in the solution, the gold should cement out onto it. When this happens, is the gold firmly attached to the copper where it will need another process to separate it, or will the gold fall off into the bottom of the container? To me, cementing seems like it may possibly be adding more steps and may have other problems associated with it, so I want to recover my gold with the least chance of screwing it up, again. Also, I have some circuit boards which need gold stripped off and I don't want to restart my AP bucket until the present problems have been corrected.

 

[maynman1751]

In my limited experience in doing this, the cemented gold will fall, as a black powder, to the bottom of the vessel. Some may present as a black coating on the copper which is easily removed with a spray of water from a squirt bottle. Hope this helps.

 

[Charles Connor]

It is much better to precipitate the gold with SMB to get it without impurities, from what i know, the copper is used to cement the silver out of solution, but it is much better with NaCl...

 

[bswartzwelder]

I wasn't sure when the gold cements if it would come off the copper easily or if it would be more like is was plated onto the copper in which case you would have to start over again with AP. Thank you.

 

[maynman1751]

I agree with Charles that it would be better if you could drop the gold with SMB. Seeing as it's 'natural' gold it could contain some silver. If you were to use copper,I believe, that the silver would drop first and then the gold leaving you with a mix that would require additional steps to separate the two. I am not absolutely sure on this as I have not experienced this situation.

I don't agree with using NaCl (salt) to drop the silver. Why change the silver to a chloride, which requires more steps to recover and convert, when you will have clean silver nitrate if you used copper.

 

[Geo]

rendering the solution basic will precipitate all the metal in solution. you would have to refine it again. if it is a stock pot (and especially if its anything like mine), it will contain tin and other none friendly stuff. since only metal higher than copper on the reactivity scale (lower reactivity than copper) will cement out, thats why copper is recommended. it will need to be refined, but your not refining from a stock pot but rather reclaiming. even if you precipitate with SMB successfully, you will still have to refine it further. i would recommend cementing values from a stock pot using copper and then refining the powder precipitate.

incinerate the powder and wash with cool, dilute nitric acid first to remove silver. just a reminder, silver nitrate and gold chloride will not remain in solution together due to the conversion of silver nitrate to silver chloride in the presence of hcl. this is a rule but like all rules, there are exceptions. "how can silver stay in solution when processing CPU's in AR" you may ask. well, it doesnt, not easily anyway. the solution will retain a small amount of silver nitrate if the acid is very strong. when diluted, the silver will leave solution as silver chloride.

 

[maynman1751]

Geo, if you cement this solution with copper wouldn't it cement the silver because of the nitric(nitrate)? Or at least a portion of it? Or would it depend on how much HCl there was in solution?

 

[Charles Connor]

The NaCl is the cheaper way to get the silver, also the purity will be the same if it is nitrate or chloride, as a chloride just by melting it you get your silver, it is not a difficult process, also to waste gas and oxigen to melt this silver, it is better to have a big ammount to be worth

 

[glondor]

You do not want to melt silver chloride. You need to convert it to elemental via your favorite process. I like the hcl/aluminum method. Some prefer the corn syrup and lye method. either way, you should convert first before melting.

 

[jonn]

DO NOT attempt to melt silver chloride, convert with Karo or glucose and NAOH first. Follow Geos instruction on this one. Yes, some gold and pgms will stick to your copper, but it may be scraped off. Keep in mind, copper will also cement Mercury... :shock:

 

[Charles Connor]

I have already done this process before, the silver does not comes pure after all this process is done, if refered to the harmful part is the chlorine gas...

 

[jonn]

Charles, please don't give dangerous instructions. Refrain from posting advice until you learn why and how.

 

[MysticColby]

if you dissolved gold and have gold chloride in solution, you do not have silver nitrate in solution, as that would react with the HCl in the AR to make silver chloride (solid)
if you had gold chloride without any HCl and decided to add silver nitrate to it, then added copper, I would expect any silver that gets cemented to go on to cement the gold, but then the silver would be silver chloride. This would probably passivate the piece copper. Some gold will of been cemented before this gets passivated, though. Silver probably does not cement gold as fast as copper does.
Both gold and silver will cement on copper at the same time, and each will be at a different rate of cementation. what that rate is, you would have to experiment, but based on the reactivity series, I would think gold is the more pushy to be a pure metal.

 

[Geo]

Geo, if you cement this solution with copper wouldn't it cement the silver because of the nitric(nitrate)? Or at least a portion of it? Or would it depend on how much HCl there was in solution?

copper will cement all metals that are lower in reactivity. for our purposes, we start at silver though there are a couple other metals that are more reactive than silver but less reactive than copper, mercury being one. silver, gold and the platinum group metals will cement on copper and cementing nothing more reactive. if you had all of these metals in solution at once (theoretically), you can cement all of them out of solution with copper.

 

[Charles Connor]

Im not giving any instructions, what im saying is how i get the silver out of solution based on the question above, im not telling anybody here how to refine, im giving my point of view about these cases... The forum is to share knowlege and experiences when refining gold and other metals, again it is a MUST for the reader to look for the pros and cons and not jumping into the solution and do it... my mistake if i did not wrote the dangerous part of it, but the melting must be done under a good fume...

 

[g_axelsson]

This thread is so full of side tracks that it is almost impossible to read.

It is much better to precipitate the gold with SMB to get it without impurities, from what i know, the copper is used to cement the silver out of solution, but it is much better with NaCl...

There will be no silver to talk about in a chloride solution.
From a dirty solution SMB will precipitate dirty gold as it will drag down impurities. SMB also precipitate lead as lead sulphate if there is any lead chloride in the solution. Lead should be removed before precipitation by adding a bit sulfuric acid before filtering.

if you dissolved gold and have gold chloride in solution, you do not have silver nitrate in solution, as that would react with the HCl in the AR to make silver chloride (solid)
if you had gold chloride without any HCl and decided to add silver nitrate to it, then added copper, I would expect any silver that gets cemented to go on to cement the gold, but then the silver would be silver chloride. This would probably passivate the piece copper. Some gold will of been cemented before this gets passivated, though. Silver probably does not cement gold as fast as copper does.
Both gold and silver will cement on copper at the same time, and each will be at a different rate of cementation. what that rate is, you would have to experiment, but based on the reactivity series, I would think gold is the more pushy to be a pure metal.

You don't need HCl to turn silver nitrate into silver chloride, any chloride ion in solution works. When you mix silver nitrate with gold chloride, silver chloride is precipitated instantly. There will be only gold nitrate and gold chloride to cement on copper as long as there is some gold chloride in solution.

The NaCl is the cheaper way to get the silver, also the purity will be the same if it is nitrate or chloride, as a chloride just by melting it you get your silver, it is not a difficult process, also to waste gas and oxigen to melt this silver, it is better to have a big ammount to be worth

As I've been told you need to flux it properly, melting silver chloride makes it go off as toxic white smoke.

I agree with Charles that it would be better if you could drop the gold with SMB. Seeing as it's 'natural' gold it could contain some silver. If you were to use copper,I believe, that the silver would drop first and then the gold leaving you with a mix that would require additional steps to separate the two. I am not absolutely sure on this as I have not experienced this situation.

I don't agree with using NaCl (salt) to drop the silver. Why change the silver to a chloride, which requires more steps to recover and convert, when you will have clean silver nitrate if you used copper.

Don't believe, investigate! The lower reactivity series metals cements more easily from a solution so gold would cement faster than silver... but it isn't that easy. Both gold and silver cements when it comes in contact with the copper.
Even if the gold originally had some silver, when gold is dissolved and diluted any silver that tagged along drops as silver chloride. Filter until the gold chloride is crystal clear and you don't have any silver to bother with.

As for the original question...

My question is: If I place a piece of clean copper in the solution, the gold should cement out onto it. When this happens, is the gold firmly attached to the copper where it will need another process to separate it, or will the gold fall off into the bottom of the container? To me, cementing seems like it may possibly be adding more steps and may have other problems associated with it, so I want to recover my gold with the least chance of screwing it up, again.

When cementing, the values can come out of solution in many ways, as fine microscopic crystals that drops off or as a solid crust, it all depends on what's in the solution, the temperature and how dilute the solution is. It probably depends on some more things too that you can't control.
If you use a piece of copper to cement gold then you probably get most of it as a black powder but some could stick to the copper. After brushing off the last loose gold just save that piece for other times when you need to cement gold or put it in your stock pot. Any gold left on it will drop to the bottom with the other cemented values.

Göran

 

[maynman1751]

Don't believe, investigate! The lower reactivity series metals cements more easily from a solution so gold would cement faster than silver... but it isn't that easy. Both gold and silver cements when it comes in contact with the copper.
Even if the gold originally had some silver, when gold is dissolved and diluted any silver that tagged along drops as silver chloride. Filter until the gold chloride is crystal clear and you don't have any silver to bother with.

Thank You for the clarification Goran.