Sciencemadness Discussion Board - Pure In from 50/50 In/Pb

Pure In from 50/50 In/Pb

densest - 21-9-2009 at 18:01

I've got about 10lbs of 50/50 lead/indium solder. Given that I can't find a metal recycler who will give more than $1/lb for it, I thought I might be able to do something with it.

Naively, solder + dil HNO3l -> Pb(NO3)2 + In(NO3)3 + gases
Pb(NO3)2 + Na2SO4 -> 2 NaNO3 + PbSO4 (ppt)
leaving mixed In+3 and Na+ in an oxidizing soup.
Adding urea to kill the NO3+
Solvent extraction?
giving In2(SO4)3 or something like it

Plausible? Or is there a better/cheaper way - it would take a lot of HNO3.
Maybe grind it up and extract with HCl or H2SO4 leaving depleted lead grains?

JohnWW - 21-9-2009 at 18:23

What is 50:50 Pb-In solder used for, that ordinary Pb-Sn solders (often with a small amount of Sb and/or Bi to harden it) are unsuitable to use for? The In in it, if it could be separated as the metal, could be used as In foil for radiochemical experiments, or in InAs (low voltage gap) semiconductors, or in small quantities as a dopant in Ge semiconductors (also lower voltage gap than Si ones).

To separate the In and Pb in aqueous solution by precipitation, which would initially require HNO3 to dissolve the solder, would depend on differential solubilities of In and Pb salts in water. The Handbook Of Chemistry & Physics, and possibly the International Critical Tables, should have tables of solubilities of In and Pb salts. I have an idea that In2(SO4)3 and especially In2SO4 are much more soluble than PbSO4, but the In(III) salt may be more liable to hydrolysis. Alternatively, the nitrates (in strongly acid solution) could be passed through some sort of ion exchange resin column known to separate them.

If you had a sufficiently large amount, another possibility may be some sort of zone-refining operation, in which the solder, packed in a steel cylinder, is progressively melted along its length, solidifying behind the heating coil as it is moved along. The metal of lower melting-point would accumulate behind the melt zone. This may not be possible if the In and Pb form some sort of intermetallic compound; the American Society Of Metals Handbook may have something about this, as well as the phase diagram.

P.S. Here is a link for an article on In-Pb solders, which has the In-Pb phase diagram:
http://asmcommunity.asminternational.org/static/Static%20Fil...

[Edited on 22-9-09 by JohnWW]

12AX7 - 21-9-2009 at 18:59

Phase diagram shows everything's in solid solution, alpha lead. It has a fair slushy range (must be shitty solder

), so you'll get some seperation in one pass, same as distillation yielding something closer to the azeotrope. But in the same way, you'll only get as far as the eutectic, which is lower in lead, but not anywhere near pure In. You can get fairly pure Pb though.

I wonder how solvent extraction would go. Any clue where to find the partition coefficient of In, Pb and Zn?

Tim

watson.fawkes - 21-9-2009 at 20:53

It's possible that lead sulfide forms more readily that indium sulfide.

merrlin - 21-9-2009 at 21:52

Attached are two patent applications that describe processes for electrowinning of indium.

Attachment: United States Patent Application 0080081009_Method for recovering indium from indium-containing material.mht (70kB)
This file has been downloaded 743 times

Attachment: United States Patent Application 0080190779_Method for Recovering Indium.mht (68kB)
This file has been downloaded 1019 times

merrlin - 21-9-2009 at 21:58

Quote: Originally posted by watson.fawkes

It's possible that lead sulfide forms more readily that indium sulfide.

I believe you are correct. The previously referenced patent applications disclose bubbling hydrogen sulfide through an indium containing solution to remove various cationic species such as copper and lead.

garage chemist - 22-9-2009 at 05:11

Dissolve in HNO3, dilute with water, titrate with dilute H2SO4 until no more PbSO4 precipitates. Filter, wash PbSO4 cake with water, boil down filtrate (using a still to recover the HNO3) and strongly heat residue of In(NO3)3*xH2O to obtain pure In2O3.

not_important - 10-5-2010 at 22:47

Seeing as this has come up again

Make up an electrolyte using sulfamic acid, ammonium sufamate, and a touch of NaCl or HCl, plus some H2SO4. Electroplate from the PbIn to a iron or steel cathode, or a carbon or graphite one. Use as low of a voltage that gives a decent plating rate, but no more than an amp per square decimeter. Monitor the pH and add H2SO4 to keep it around 2-3. Use a small breaker to mostly surround the solder, you want to keep the PbSO4 formed from drifting about.

Strip or melt the In off the cathode, form into anodes. Repeat the plating over, this should eliminate most if not all the Pb, H2SO4 being the main reagent consumed. Likely you'd want to analyse the indium to check for lead, at that point you might have to resort to sulfide precipitation if there's still lead in the indium.

densest - 11-5-2010 at 13:40

@not_important - Thanks! This sounds like a very feasible method. Sulfamic acid seems to be easily available & I have the rest. This avoids a large and messy wet workup which I was avoiding very hard.

I will post results when it's done - there are a couple of urgent projects for the next 5 weeks including brewing some dubbel & tripel & starting to grow koji for sake'.

not_important - 12-5-2010 at 06:36

After checking a bit, it looks like ~100 g/l sodium sulfamate, ~50 g/l ammonium sulfamate, ~60 g/l sulfamic acid, ~50 g sodium sulfate, ~25 g NaCl. Use H2SO4 to keep pH in the range of 1.5 to 2.5, as PbSO4 is formed the pH will rise. You could make up the solution with jusy Na2SO4, NaCl, and the total amount of sulfamic acid needed, the add NH3 and NaOH/Na2CO3 to create the needed amounts of their sulfamates.

You should be able to be pretty sloppy for the 1st plating, it's just to get rid of most of the lead. A loose weave bag around the solder also might help, again to keep the PbSO4 from drifting about. With the solubility of PbsO4 being less the 50 mg/l at 20 C, most should be trapped rather than plating over.

A final electrorefining would pay more attention to concentrations, and might do the earlier suggested trick of controlling th pH while slowly bubbling H2S through the bath to trap the last of the Pb as the sulfide.