Cementing

[Jbroadway]

Hi everyone,

I have spent a lot of time reading through all the posts in this forum and I had a thought and I'm not sure if I am being dim or not? I have been looking for quantity/surface area needed to cement contaminated metals out and cannot find a value.

My thought was when we have a solution with everything in it including Au and Pd why don't we cement everything to Ag to that all is left in solution is Ag & Pd? I know there's flaws or it would have been done already I am just not sure why, is it quantity of silver needed or something else?


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[FrugalRefiner]

Gold is generally dissolved in chloride solutions. Silver won't dissolve in these solutions, so it can't displace the gold.

Dave

 

[Jbroadway]

And there's the flaw... thank you Dave I knew I was missing something


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[kernels]

Yep, as above, silver does not dissolve into AR because the chloride in HCl turns it into Silver Chloride.

You can obviously use copper to cement Au and other PMs out of solution and also use copper to cement Silver from a Silver Nitrate solution.

Quantity / Surface area is not all that important, find a big piece of copper (I usually use a sheet made by cutting open a copper pipe) and throw it in there. If your AR has free Nitric, then that will consume some extra copper, but eventually the copper will be covered by a brown / black powder which is your PMs. The more chemically literate people can probably confirm this, but I assume for a single replacement reaction, 1 Mol of copper replaces 1 Mol of PM in the solution, so as long as there is a large chunk of copper in there, all the PMs should cement out.

It also helps to stir the solution every now and then, I usually find that it takes a day or two to cement out any left over PMs before beaker-sized solutions are barren.

 

[kernels]

A little catch for your players with the cementing - You may be tempted to hang a copper sheet in the solution, suspended by some braided copper wire which is hooked over the edge of the beaker . . . terrible idea, the solution will 'wick' quite a long way up the copper wire and eventually you will find a largish puddle of solution next to your beaker!

 

[Jbroadway]

Oh wow thanks guys, my mind was all over the place I thought the copper cemented the lower values not higher...


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[4metals]

Here's a thread from the library that you may not find otherwise as the title is not indicative of what is discussed, which is ultimately cementation.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=85&t=22203