Electrochemistry PLEASE HELP a noob with the cell

[dan63]

I'm new to this site and to PMs. this is the third thread I've started and am sensitive to that.

I've been having a great time and have learned a lot!! I have a long way to go... especially when it comes to modifying a process to fit unique settings. today I ran about 3 lbs of RF connectors through the reverse electroplating cell. I had great success. I moved on to some large pins and used the copper screen that I bought from goldrecovery.us . this worked ok... not totally satisfied with it... I often had to add pressure to the pins and still had quite a few in each batch that did not de-plate completely. (if de-plate is a term I can use). I like the idea but just not quite satisfied... I was thinking of taking a medium sized SS serving spoon and drilling small holes through it and using that as my electrode... any thoughts???? I could bend the handle or even modify the handle to hang over the side of the cell. I think this would be a little more stable than the screen and would allow for some stirring and pressure on the pins to help the process along???? has anyone tried anything like this... I have some 1/16" copper sheet that would also make a more rigid basket if SS would be a problem in the cell. I'll experiment a bit and report back.

OK here is where I could really use some help... I ran into a road block with some supper small pins. I have about 2 lbs of pins that are less than 1.5mm long and very thin. I could not get the cell to work on these in the copper mesh. I had the copper screen pretty flat so I don't think I was creating a faraday cage... Hmmmm but maybe because the pins are so small it may have had the same effect??? does anyone have any experience with very small pins? I searched the site for "small pins" and a few variations of that and did not find anything, if I missed it please direct me in that direction.

I'm thinking about trying a different process with these very small pins... I was think about HCl/Cl or AP. these pins don't have a copper core so the standard AP process won't work well, but could I add a bunch of peroxide and rapidly dissolve the gold off the pins then poor off the gold in solution before the pins have a chance to dissolve?? then I'd just drop the gold with SMB???? I could do essentially the same thing with HCl/Cl... any reason this would not work?? I'm trying to avoid AR. just because I don't have any and am really watching my costs. thanks in advance for your thoughts!!!

 

[Harold_V]

You do understand the principle of base metals cementing values, don't you?

Harold

 

[BAMGOLD]

Harold, I'm actually having an issue with that, I'm about half way through Hoke, she is good, but seems to miss some steps(points,reasoning) along the way aswell.

 

[martyn111]

Bamgold, if you check out the reactivity series, link below, any metal higher in the series will cement out metals lower in the series in a solution.
The way I remember it is this, the more reactive a metal is the less it wants to stay as a solid, prefering to go into solution, the less reactive the metal the more it wants to be a solid rather than a solution.

http://www.zephyrus.co.uk/thereactivityseries.html

 

[dan63]

You do understand the principle of base metals cementing values, don't you?

Harold

Harold I think I understand the basic idea, but your question made me realize that I don't know it as well as I should... especially the application. so thanks for pointing me in the that direction. I'll do a bit more reading, see what that yields.

 

[butcher]

A little reading about the reactivity series of metals will also help you understand the principle, also read up on displacement reactions.

The acid will prefer the base metal in solution, cementing out any dissolved metal that is lower in the reactivity series of metals (like gold) which are dissolved into solution, so the gold would just plate back out of solution onto the base metals until all of the base metals were put into solution, this and the fact at the end of all of this you can have base metals dissolved in solution with values dissolved in solution creating troubles.

 

[Harold_V]

Pretty much what butcher said. The only place I may differ is that there are methods by which you can take advantage of the base metals, and process directly with aqua regia. It requires patience, and slow working, testing regularly along the way.

It works like this.

Start with a small amount of AR (far less than would be needed to dissolve everything), which should dissolve values along with base metals. The dissolution of values will expose base metals, so values can then be cemented on the exposed surfaces. That puts the values back with the solids, albeit finely divided. That's not a problem.

When all of the values are removed, they will have effectively dissolved traces more of the base metal. Water is added and the solution then allowed to settle well. It is siphoned off, then the process is repeated. This removes the dissolved base metals from the circuit. Each iteration removes more of the base metal, all the while leaving the values behind. When very little of the base metal remains, you then dissolve everything and handle the pregnant solution as one normally would. With good fortune, you will have removed the vast majority of the base metals.

As the base metal diminishes with each iteration, the cementing will take longer and longer (because of diminished surface area, and a greater amount of value in solution). I advise it be done with heat, and a covered vessel (use a watch glass). By heating, the reaction takes place faster, and the solution is constantly stirred.

Always test the solution after cementation, to ensure that all of the values have been recovered.

Harold