Problem with silver point batch

[kurt]

Ok – I have run into a bit of a problem on a batch of silver from contact points. & as points tend to go – you always get a certain amount of insoluble precip you need to let settle out before decanting your solution to drop out your silver.

Over the last 4 months I have done enough points to recover about 80 oz of Ag & so far I have only had to let solutions set over night to let the insoluble settle to get a clear solution.

On this batch I am getting the normal insoluble that settles in a few hours – but I am also getting something that is taking days to settle. The other problem is that, at this point, most of the copper (&/or brass) has been dissolved, but it’s still taking an excess of nitric to dissolve the remainder & in fact having reaction stop &/or at least slow way down while still having free nitric (heating has helped with that)

I am relatively sure that part of the problem is an excess of lead in this batch as the solution is a dark blue green & on a test sample of the solution a drop of sulfuric drops out the characteristic lead sulfate & the solution turns a true blue but the cloud that takes days to settle remains.

Adding a little nitric to give it some free nitric doesn’t do anything, nor does diluting with water & yes I incinerated.

I can see the lead being the problem of slowing reaction time down & needing more then normal nitric but the cloud that takes 7 – 9 days to clear has me stumped.

So any ideas on what it might be (so I can maybe avoid it in the future) & or any ideas on what might make it settle faster - or clear it out would be awesome. It goes right through a filter.

Stuff in the bucket is what still needs to be dissolved, - jar on the left is decanted solution, jar on the right is same solution only diluted.

Kurt

 

[Juan Manuel Arcos Frank]

Are you using distilled water?...If you are not probably the mud is an insoluble chloride(like lead chloride)formed with chlorine ions in tap water.Lead chloride is soluble in very hot water.

Keep us posted.

Regards.

Manuel

 

[Harold_V]

The other consideration may be that you are processing tungsten contacts. If so, they degrade with enough boiling in dilute nitric, and leave behind a considerable amount of residue.

Do any of the contacts have a waffle pattern on the back side?

Harold

 

[kurt]

Harold, Manual – thanks for the replies but no – it’s not ether of those problems. I live in the country so am on well water & we have a “lot” of iron bacteria in our water & even though we use chlorine tablets to get rid of the iron bacteria, it doesn’t get rid of it all so I don’t use tap water in the lab at all. I buy my distilled water in bulk from the local Co-op cheap enough that its worth it to me to avoid the contamination of ether chlorine or iron in the lab.

Also, I have done enough points now over the last 6 months that I can identify the tungsten points without any problem so they are processed on there own because of the need to boil them to leach out the silver. I also pull out & process any magnetic points & process separate so there is nothing magnetic in this batch

This is turning into a real nasty batch – besides the lead & the fine particulate that stays suspended, I have something else (cadmium I suspect – or?) what ever it is cements out with ether copper or iron. When cementing with copper most of the silver will come down & as well I can see the characteristic ultra fine black that indicates PGMs, but then near the end the copper will get a “tight” bonding gray cement on it that stops the cementing.

When I process these type of points (points nipped from the bus bar close to the point) I always start with using just enough nitric that it will only remove about ½ the copper without putting silver or PGMs into solution. So I have about a gallon of this copper rich solution that when I put iron in to pull down the copper – it will start to cement the copper but then stop due to the same “tight” bonding gray cement on the iron with little or no copper coming down.

I will post some pics tomorrow as well as results from some other experiments I have run. Today I need to finish cutting up & packaging the deer I got hunting this year.

In the mean time --- *#%**##@@!!!###*** ---if you know what I mean :evil:

Kurt

 

[kurt]

Hmmm - gave it a little more thought - & though I don't think tungsten is in the mix here at this point I guess I shouldn't rule it entirly out.

Also should mention that I am holding off on dissolving whats left in the bucket till I have had some feed back on this one.

Kurt

 

[Geo]

kurt

before you digest the points in nitric acid, do you remove the copper first? you may be able to eliminate some if not all of the copper by running your points through AP to remove the copper first and then incinerate before dissolution in nitric acid. ive done this with small contacts off of circuit boards and it worked fine. remember to sprinkle a little salt into your AP when finished to reclaim any silver in solution.

 

[martyn111]

remember to sprinkle a little salt into your AP when finished to reclaim any silver in solution.

Geo, would there be any silver in solution? I would have thought that the Hcl in the AP would have created Agcl without the addition of the salt. I am no chemist, therefore I am asking if this is correct.

 

[Geo]

some times for whatever reason slight bits of nitrates can make it into your solution, it wont be much but for some reason trace amounts do slip by. i only mentioned it as a safety measure to insure no loss of values.

 

[Harold_V]

some times for whatever reason slight bits of nitrates can make it into your solution, it wont be much but for some reason trace amounts do slip by. i only mentioned it as a safety measure to insure no loss of values.

You missed the point. What he said was you're already working with a chloride solution. It wouldn't make sense to add salt when you already have an abundance of HCl present, which would have, long ago, precipitated silver as silver chloride. Even if traces of nitric got involved, anything that may have been dissolved would have cemented on the base metals that are present. He's right--salt isn't needed.

Harold

 

[Geo]

You missed the point. What he said was you're already working with a chloride solution. It wouldn't make sense to add salt when you already have an abundance of HCl present, which would have, long ago, precipitated silver as silver chloride. Even if traces of nitric got involved, anything that may have been dissolved would have cemented on the base metals that are present. He's right--salt isn't needed.
Harold

ok,nix the salt. ive made a note for my records." no salt needed for hcl solutions for silver precipitation". i cant seem to remember when and where i started doing that but apparently it wasnt something i learned here on the forum.

thanks Harold

thanks martyn111

 

[kurt]

Sorry it took so long to get back to this but I had a few things come up that I had to take care of. Anyway – as I mentioned earlier I have something here in my solution that forms a tight bond when cementing that stops the cementing process.

When cementing the silver out with copper, it’s not till the end that what ever it is forms the tight bond to the copper & stops the cementing process. So most of the silver comes down but not all of it, because if I put a new piece of copper in it will cement more silver.

When trying to cement out the copper on iron it will just start to cement the copper but then what ever this is will bond to the iron & stop the cement process with “very” little copper coming down. (next to none)

It has the appearance of lead (silver gray) But I didn’t think copper or iron would cement lead out.- These are points so I am thinking cadmium maybe – what I don’t know is if copper &/or iron will cement cadmium out.

If that is the case – then maybe what I need to do is let the copper cement as much silver as it will – then use HCL which would drop the remaining silver as silver chloride – along with lead chloride & cadmium chloride – both of which I should be able to remove from the silver chloride with hot water? (according to Wiki cadmium chloride is water soluble)

Sorry about the quality of the picture

Kurt

 

[kurt]

kurt

before you digest the points in nitric acid, do you remove the copper first? you may be able to eliminate some if not all of the copper by running your points through AP to remove the copper first and then incinerate before dissolution in nitric acid. ive done this with small contacts off of circuit boards and it worked fine. remember to sprinkle a little salt into your AP when finished to reclaim any silver in solution.

Geo - thanks for the suggestion , but I get my nitric for $8 a gallon ($120 for a 15 gallon drum) & because I recover both the copper & silver I just use nitric when processing points.

The recovered copper pays for the better part of the nitric used to recover the silver & I don't need to worry about creating & dealing with silver chloride in the mix.

 

[butcher]

Copper is way down the reactivity series of metals (study this do web search), copper is just above the metals we are all looking for. (Iron and cadmium is higher in series).

I am thinking a valuable metal here, contact points have several values even the PGM's, it is possible, maybe you can scrape some off, put into solution (after eliminating copper with nitric, then dissolve in aqua regia (I would do in test tube)(use heat) and test in spot plate). Of course I have been wrong one or two times before, maybe your test will not make me wrong again.

 

[kurt]

Copper is way down the reactivity series of metals (study this do web search), copper is just above the metals we are all looking for. (Iron and cadmium is higher in series).

I am thinking a valuable metal here, contact points have several values even the PGM's, it is possible, maybe you can scrape some off, put into solution (after eliminating copper with nitric, then dissolve in aqua regia (I would do in test tube)(use heat) and test in spot plate). Of course I have been wrong one or two times before, maybe your test will not make me wrong again.

Thanks butcher - I have been wondering about this for quite sometime now but didn't know what to search it under. Tried "reactivity" of elements & got it.