This thread is so full of side tracks that it is almost impossible to read.
Charles Connor said:
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.
MysticColby said:
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.
Charles Connor said:
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.
maynman1751 said:
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...
bswartzwelder said:
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
