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Removing lead from silver bars

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4metals

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Post February 6th, 2010, 12:59 pm

Removing lead from silver bars

Two guys I work with are producing fine silver electrolytically, one of them is plagued by lead. It seems his sources of scrap are heavily electronic and the bars run high 80% silver (88-89.5) and the test for lead (qualitative not quantitative) shows lead on 30% of his bars. The lead is never very high in concentration, the primary contaminant is copper.

Now classically a digestion in nitric and cementation with copper will remove the lead from the silver but that requires a substantial chemical usage. So I went to my bookshelf and was reading in Silver by Butts & Coxe (that's really the authors names so don't ban me for this) that at the Oroya silver refinery they charge the molten metal from their thum cells with sodium nitrate to remove traces of lead and bismuth. I would prefer to remove it before it goes into a cell.

Has anyone here ever tried this method? I have access to a reverberatory furnace and plan on trying this method to clean up the bars before making them into anodes but I'm curious if anyone has tried this.
Last edited by 4metals on February 6th, 2010, 1:34 pm, edited 1 time in total.
We make a living by what we get, but we make a life by what we give.
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james122964

Post February 6th, 2010, 1:24 pm

Re: Removing lead from silver bars

Do you think it would be better to add lead to get the silver content down to a much lower percentage to hopefully lower the melting point, then use zinc to collect the silver, then distill the zinc from the silver.
This is the parkes process, it is used for removing gold and silver from lead bullion seem that zinc and lead are not very soluble in each other, but silver is supposed to be 300 times more soluble in zinc than lead, point is to use the zinc to gather the silver, then skim off the zinc/silver alloy. I think the silver/lead ratio would have to be much lower than the 80 percent you currently have in order to keep the silver from being the solute.

jim
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4metals

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Post February 6th, 2010, 1:33 pm

Re: Removing lead from silver bars

The lead in the bars is very low in concentration most of the impurity is copper and traces of tin. The material is mostly from coin silver. The Parkes process is a bit over the top for the lead level in these bars. Having re-read my original post I should go clarify that point.

Thanks for the input.
We make a living by what we get, but we make a life by what we give.
Sir Winston Churchill
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james122964

Post February 6th, 2010, 1:38 pm

Re: Removing lead from silver bars

Oh, I guess that would make a difference, I was thinking 80 percent silver and 20 percent lead, if that was the case you could just keep a molten pot of lead add the silver then zinc and with retort recover zinc for subsiquent silver recovery.

Jim
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Juan Manuel Arcos Frank

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Post February 8th, 2010, 4:03 pm

Re: Removing lead from silver bars

4metals:

How about to dissolve those silver bars in nitric acid and precipitate with common salt?.Lead chloride is soluble in hot water,silver chloride is not soluble so you can remove all the lead.This is the Karo syrup method just using hot distilled wter instead of tap water to rinse the white mud of chlorides.(Lead chloride seems like silver chloride).

I hope it helps.

Kindest regards.

Manuel
"Precious metal recovering gives me money,women take it away from me"
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Platdigger

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Post February 8th, 2010, 10:21 pm

Re: Removing lead from silver bars

Manuel,
4metals said: "Now classically a digestion in nitric and cementation with copper will remove the lead from the silver but that requires a substantial chemical usage."

Just thought I would save 4metals the responce... 8)
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Lou

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Post February 10th, 2010, 6:59 pm

Re: Removing lead from silver bars

The copper is a complicating factor for the nitrate treatment, as it also oxidizes. It does remove lead as PbO/PbO2 but that's extremely hard on your lining and flue. It also necessitates a very efficient scrubber. You ought to be able to line your reverb with MgO and use it til lead levels become a problem again, then chip out the lining and tamp in more magnesia.
Like chemistry? Try http://sciencemadness.org/talk

All that glitters is not gold. Occasionally it's rhodium :)
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johnon

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Post April 6th, 2010, 1:20 pm

Re: Removing lead from silver bars

Liquation? Greeks used it.
"Professional typing by the ten-fingered is beyond my means" - J.R.R. Tolkien
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Lou

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Post April 6th, 2010, 3:39 pm

Re: Removing lead from silver bars

Call me partial, but I thought my idea was quite good...perhaps good enough to get some consulting cash :P
Like chemistry? Try http://sciencemadness.org/talk

All that glitters is not gold. Occasionally it's rhodium :)

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