quest
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purifying lead pipe
Hi guys,
I bought some residues of old lead pipe.
I melted it to cast some weights some year ago and now I want to make some lead nitrate from it.
I used 70% nitric acid and some 30% H2O2 with the lead, and heated it to 50 degree celsius for about an hour.
In the start I got lead nitrate but after an hour the solution started to become yellow.
My guess is that it is some iron residues in the lead that reacted with the weak nitric acid left.
So first before I try to clean my lead nitrate from iron ions (because I need it for PbO2 anode...) I thought to ask here maybe you know what is used
in lead pipe as additions (Sb for instant...).
As for the cleaning, I guess I will use some XSO4 salt to make PbSO4(s) and FeSO4(aq) and after I will wash the lead sulfate very good I will try to
react it with xNO3(aq) to get my PbNO3(aq) back and some XSO4(s).
thoughts? ideas?
thanks.
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12AX7
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Not gonna happen. Sulfate is a strong acid. Go with carbonate. (You need carbonate anyway: PbSO4 is just barely more soluble than PbCO3, so you can
boil it with Na2CO3 to convert most of it.)
Better still, oxidize the iron to Fe(III) and bring the pH up a little. Fe(OH)3 should precipitate before Pb(OH)2.
Tim
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Jor
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How are you going to react lead(II)sulphate with xNO3? The xSO4 should be even more insoluble than lead(II)sulphate (barium sulphate?) and even then
the reaction will be extremely slow. Besides, it doesnt sound like a really effective process. Your wasting a lot of concentrated nitric on something
like lead. Rather buy lead(II)nitrate if you can, or at least pure lead. Both are cheap.
Tim, both iron carbonates are insoluble as well.
A method that might work:
Precitipate lead(II)chloride bij adding a concentrated chloride solution. Filter off. Wash once with distilled water. Dissolve in hot water (2,9g per
100mL % 90C __ 3,2g per 100mL @ 100C). I do not recommend dissolving in boiling water. The water vapor will contain some Pb2+, and at boiling rate,
this sounds risky.
While still very hot, add hot excess sodium carbonate (or hydroxide) solution. Filter off the lead(II)carbonate. Dissolve this in nitric acid, and
evaporize the solution.
[Edited on 3-4-2008 by Jor]
[Edited on 3-4-2008 by Jor]
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quest
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I used almost all my HNO3 on the lead so I try to find a way with nitrate salt maybe...
any way I think I got about 300-350 gr Pb(NO3)2 so if I will make it into lead chloride and dissolve it in water it will be about 2 gallons of water -
sound like a big project :S
[Edited on by quest]
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Jor
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Well, I cant think of another way. And its a big project already anyways, you used up all your nitric for lead (not to talk about H2O2). Then this
project may obviously not fail. The bromide dissolves 1 more gram per 100mL , so 4,8 (90C) (although this doesnt really make a diff. on molar scale.),
so if you have cheap bromides.... Besides, in cold water , the bromide is less soluble, so your yield will improve with bromides.
BTW, how did you dissolve so much lead safely??!!  Fume hood?
Someone else should give a better way then to get the lead nitrate out.
[Edited on 3-4-2008 by Jor]
[Edited on 3-4-2008 by Jor]
[Edited on 3-4-2008 by Jor]
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quest
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My lab is a shed in the garden, I just put some nylon cover over the baker and gave it to stand there for some hours.
I had another Idea - making lead sulfate (which is soluble about 0.056 gr/100 gr water in 40 degree celsius) and barium nitrate (5gr/100 gr water+-)
or strontium nitrate (88gr/100gr water) and boil this two together in water to get soluble lead nitrate and solid barium/strontium sulfate.
Does this can work?
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Jor
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Well, in theory yes, because lead sulphate is more soluble than both strontium- and barium sulphate. But the reaction will be incomplete and very slow
I think.
The last thing I can think of is strongly complexing iron(III) and precitipating lead hydroxide or lead carbonate.
[Edited on 3-4-2008 by Jor]
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not_important
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Usually precipitating the majority desired ion to purify it is not the best route, especially if you want it in the starting form. A somewhat
traditional method of cleaning up lead nitrate is as follows.
Take a small amount of the crude lead nitrate solution, say 3%. Make it alkaline with NaOH, then convert it to PbO2 using hypochlorite. There are
detailed descriptions in older inorganic chemistry texts. However, do not wash the dioxide with nitric acid, rather use
dilution NaOH followed by distilled/deionised water. You want to remove chloride and sodium, but lead hydroxide or lower oxides in the PbO2 are not
harmful for the intended use. Keep the PBO2 moiste.
Take the remaining lead nitrate solution, add nitric acid until the pH is no higher than 4. Bring the solution to a gentle boil, keep it there for 10
to 15 minutes. Now add roughly half your crude lead dioxide, then stir well and keep at a gentle boil another 5 to 10 minutes.
Add the rest of the pbO2, keep stirring, and use a concentrated solution of NaOH, Na2CO3, or ammonium carbonate, or concentrated aqueous ammonia, to
bring the pH up to around 5 to 6. Boil for another couple minutes, cover, and put aside to settle. Obviously ammonia or ammonium carbonate are better
if you don't want sodium in there, carbonates will create bubbles/foaming when added so they require more careful work than hydroxides; but your
choice may be driven by what you can easily get.
This oxidises iron to Fe(III), the removes it as the low solubility hydroxide. Antimony salt hydrolyse to low solubility oxy-salts or hydrate oxide.
Some of the lead will drop out of solution too.
Let the solution settle for several days, then filter it by carefully pouring it off through a fine high retention filter, you want to avoid
disturbing the precipitate as long as possible, so it goes over in the last bit of liquid. A siphon can be useful for this.
This should remove iron, antimony, and small amounts of copper.
The precipitate usually contains a good deal of lead, and can be used to make PbO2 for another purification. Converting it to PbO2 with alkaline
hypochlorite, then treating that with medium strong HNO3 will dissolve out much of the iron and some of the antimony. Citric or tartaric acid will
dissolve most antinomy out from the PbO2. Alternatively, most useful if you've a lot of the precipitate and know there's a fair amount of antimony in
it, is to treat it with concentrated (35%) hydrochloric acid, evaporate it intil pasty, treat with more conc. HCl, then distill the mess to get at
first HCl gas, the HCl-H2O azeotrope, and finally SbCl3 at 223 C. The PbCl2 left behind can be boiled several times with concentrated Na2CO3 solution
to convert it to lead carbonate.
When starting with a metal, often it can be useful to purify the metal by electrorefining - plating the metal from one electrode to another with a low
voltage difference. Under these conditions most metals higher in the electromotive series go into solution while those lower in the series form a
sludge of the metal or hydroxide/oxide. After that you can dissolve the purified metal in acid, and have a lot less impurities to deal with. Details
can be found in electroplating and older electrochemistry books.
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Aqua_Fortis_100%
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Hello not_important,
great news you are giving!
This week I dissolved a large amount of residue , made a long time ago from nitrate/Pb metal , to dissolve the nitrate/nitrite and decanted/washed the
insoluble part several times to remove sodium , then dried.. Its a entirelly different kind of stuff I achieved this time.. Is a light brown
heterogeneous powder, containing small portions of red lead , litharge , unreacted Pb metal and Fe stuff (from the paint can I did the fusion)..
Probably Sb compounds also are present.
In previous procedures (using Pb fishing weights.. Pure lead, I guess) the insoluble powder was always white or pale yellow in worst case. This time
the Pb was from junk yard.. Its probably some sort of Pb-Sb alloy.
It seems that the same procedure you said may apply to my compound.
BTW, there isnt other ways to purify the lead compounds from other metals (Fe, Sb)? Via sodium plumbate , maybe ?
Thanks.
[Edited on 3-4-2008 by Aqua_Fortis_100%]
"The secret of freedom lies in educating people, whereas the secret of tyranny is in keeping them ignorant."
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quest
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thanks you not_important! sound like a great way to get my lead nitrate as pure as I can.
I will be glad if you can explain me what is happening in the solution when you add the PbO2 and lowering the pH to below 4?
why do you use only half your PbO2 at first?
and why doesn't you get lead carbonate(s) before Fe(III)(s)?
I want to learn from it too, and not just "follow the instructions".
thanks again.
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not_important
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Lead nitrate's pH in solution is in the range of 4 to 6, depending on how dilute it is. You want a little excess acid to keep it from hydrolysing.
Also the excess nitric acid oxidises some of any Fe(II) to Fe(III), boiling helps speed that.
The PbO2 completes oxidation to Fe(III), as well as starting to oxidise any Mn ions (this is sort of a general purification scheme). Again boiling
speeds things up.
Then raising the pH completes the oxidation, and causes Fe(OH)3 to precipitate. The late addition of the rest of the PbO2 is just to make sure all
the iron gets oxidised. Note that some Pb will precipitate as a basic salt or hydroxide, this is acceptanle because it gives some bulk to the
precipitate and is a surface for traces of other metals to absorb onto.
At the same time the increasing pH allows any antimony salts to hydrolise and precipitate.
It actually would be better to raise the pH using Pb(OH)2 or PbCO3 (or a basic carbonate - "white lead") as that would not introduce any other
cations. You could use some of the impure lead nitrate to make Pb(OH)2 (use aq NH3) or a lead carbonate, wash that well with water, but don't dry it.
The neutralisation goes slower with the lead compound, and you'll need to keep stirring, but it gives you a higher purity. For applications like
making PbO2 coating on electrodes, some sodium or ammonium ions likely don't matter, you have to decide if it's worth the extra work.
As for using sodium plumbate as a purification route, I don't know, never looked into it. The strongly basic conditions are a bother to work with,
etching glass and being difficult to filter - glass filters get chewed up and cellulose ones often swell.
[Edited on 4-4-2008 by not_important]
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JohnWW
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| Quote: | Originally posted by not_important
The PbO2 completes oxidation to Fe(III), as well as starting to oxidise any Mn ions (this is sort of a general purification scheme). Again boiling
speeds things up. |
Plumbates are capable of oxidizing Fe(III), Mn(II), and Mn(IV) up to Fe(VI) and Mn(VII), at least in alkaline conditions.
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not_important
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| Quote: | Originally posted by JohnWW
Plumbates are capable of oxidizing Fe(III), Mn(II), and Mn(IV) up to Fe(VI) and Mn(VII), at least in alkaline conditions. |
True, but plumbates are made from PbO2, so that's the typical oxidiser. On top of that adding plumbates to Pb(NO3) solution will result in the
plumbate immediately becoming PbO2 and a nitrate, while precipitating Pb(OH)2
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Nicodem
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This is probably a stupid question, but I simply don't understand something. If the topic of this thread is the purification of lead in the form of
its nitrate, then what is wrong with simply recrystallizing the crude lead nitrate?
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not_important
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In many cases it can be difficult to remove certain impurities through recrystallisation. A classic example is Fe(II) in CuSO4,. The sulfates are
isomorphous, recrystallise Fe(II) contaminated CuSO4 several times and you may not have reduced the level of iron at all. The solution in that case
is to oxidise the iron to Fe(III), then raise the pH enough to get Fe(OH)3 or FeO(OH) to precipitate out; if an excess of Cu(OH)2 is used to raise the
pH then even small amounts of iron that might otherwise end up in colloidal form instead co-precipitate onto the surface of the remaining Cu(OH)2
And even if the contaminates are not isomorphous, form double salts, or other similar problems, it is possible that simple inclusion formation can
drag a significant amount of impurities along. Thus it is better to remove as much of the impurities as praactical, then crystallise.
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JohnWW
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| Quote: | Originally posted by quest
My guess is that it is some iron residues in the lead that reacted with the weak nitric acid left.
So first before I try to clean my lead nitrate from iron ions (because I need it for PbO2 anode...) I thought to ask here maybe you know what is used
in lead pipe as additions (Sb for instant...).
. |
Pb alloys commonly contain Sb to harden them, particularly pewter. Other likely minor constituents are As, Bi, Sn (especially solder), Zn, Cu
(especially lead bronzes), Ag, and traces of Cd, In, Tl, noting that Cu, Zn, and Pb frequently occur together in mineral deposits. It is unlikely that
there would be much Fe.
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12AX7
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Iron doesn't dissolve in lead to any appreciable amount. If there is an iron impurity, it was probably on the metal, not in it.
Tim
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