cementation questions

[chemistrycoach]

hello to everybody ! got 3 questions regarding cementation process that needs some help, any guidance and suggestions are deeply appreciated !

does nitric needs to be taken out in an AR solution before cementing out values ?
does temperature important in cementing values?
can silver cement gold and pgm's in a pregnant gold and pgm solution ?

thank you very much and more power to all !

 

[FrugalRefiner]

coach,

I'll take a shot at your questions. If I make any mistakes I'm sure someone will be along shortly to correct me.

1) If you don't use up all the nitric in your AR prior to cementing, the excess nitric will first dissolve some of the metal you're using to cement, but will then progress into the replacement reaction. A small amount of nitric is desirable to get the cementation reaction going, but your goal should always be to use only enough nitric to dissolve your values.

2) heat increases the speed of most chemical reactions, so a warmer solution will generally react more quickly. More important is circulation of the solution. The precious metal ions in the solution you're trying to cement most come into contact with the metal you're using to cement the precious metal. Circulation is more important than heat.

3) In theory, any metal higher in the reactivity series will replace all metals lower in the series, so since silver is more reactive, it should cement gold and the PGMs. However, gold and the PGMs are usually found as chlorides in a solution of HCl. SIlver does not dissolve in HCL. It would likely form an impervious coating of silver chloride on the metallic silver and stop any possible replacement reaction.

Dave

 

[MysticColby]

I like and agree with all 3 of your answers, very skillfully said too.

I'll elaborate on #3 a bit: gold dissolved by AR means gold chloride is in the solution. silver will indeed 'cement' gold out of solution, but will form silver chloride, which is also a solid, thus not separate the gold and silver and will likely form, as FrugalRefiner said, a layer of silver chloride which will prevent further cementing. The same would happen to PGM in this solution.

Though I hear it is possible to dissolve PGM in nitric alone, and it should be possible to cement this using silver. (as it was explained: if there is a small amount of PGM in an alloy of a large amount of silver, say <5% PGM, then the PGM will get carried along into solution when the silver gets dissolved)

 

[FrugalRefiner]

MysticColby, thanks for the kind words.

I hadn't considered using silver to cement PGMs from a nitric solution since chemistrycoach originally asked about AR and a "pregnant gold and pgm solution". Gold would not be in a nitric solution, so I only considered a chloride solution.

It seems that I've read a bit about progressive cementation on the forum and that it wasn't quite as clean as it might seem based only on the reactivity series. If I understand correctly, the PGMs get tricky, possibly existing in more than one state and those states can be more or less reactive.

Perhaps Lou or one of the other chemists will explain this further.

Dave

 

[samuel-a]

It seems that I've read a bit about progressive cementation on the forum and that it wasn't quite as clean as it might seem based only on the reactivity series. If I understand correctly, the PGMs get tricky, possibly existing in more than one state and those states can be more or less reactive.

Been there, done that
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=9664&p=93154&hilit=+palladium+cementing#p93135


Apparently, when it comes to PM's, the electronegativity differences are just too small to support simple replacement reactions.

 

[chemistrycoach]

thank you very much Samuel-a, Frugalrefiner your advices are a lot of help !

 

[chemistrycoach]

thank you mystic colby !

 

[4metals]

I have had the ability to cement values from dental refining using 325 mesh copper as my source of copper. The reaction is very fast and complete leading to more complete recovery at speeds never imagined.

 

[chemistrycoach]

yes 4 metals i think the greater the surface area of the metal the faster it works too. thank you.

 

[frontiermetals]

I have had the ability to cement values from dental refining using 325 mesh copper as my source of copper. The reaction is very fast and complete leading to more complete recovery at speeds never imagined.

Did you de-nox first or just allow the copper to dispose of the excess nitric?

Will copper work just as well with HCl peroxide leach to drop values?

Thanks!

 

[4metals]

I only cement after the gold is dropped so free nitric is never an issue. The atomized copper will work faster and from what I have seen more completely than slabs of metal primarily due to large surface area and the metal can dissolve quickly rather than be oxidized as it hangs in the solution and becomes passive. It will work in any solution that conventional copper works in.

 

[aaron_cameron408]

Ok what about aluminum wire from a big transistor? I had green sloution that tested positive for gold, When I used the wire it started to fizz then form copper around it then turn the sloution clear. Does that mean that there is no values left in the sloution?

 

[Palladium]

Ok what about aluminum wire from a big transistor? I had green sloution that tested positive for gold, When I used the wire it started to fizz then form copper around it then turn the sloution clear. Does that mean that there is no values left in the sloution?

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=15270&p=154613#p154613