Antwain
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Seperation of nickel and copper in solution - a practical method.
I decided to post this in case it is of any help to anyone. I have never seen this in literature and developed the idea myself, however it probably
only works well when these are the only two metals present.
A few years back I decided that I wanted some nickel(II) and fortunately in Australia our 'silver' coins are ~25% nickel 75% copper. At the time I
didn't have nitric acid, so I dissolved them in a mixture of sulfuric acid and sodium nitrate, however my research indicated that using the respective
nitrates wasn't a huge advantage, so I would suggest using a mixture of sulfuric and nitric acids anyway.
Unfortunately, the ratio of solubilities of the sulfates is very close to the ratio 1:3 of the metals in the coins anyway, so I needed another method
for separating them. In my specific case, at low temperatures, some of the copper sulfate could be precipitated first, essentially keep reducing the
solution by evaporation until green crystals start to come out as well. This separation is severely tedious anyway so I would recommend getting as
much copper out as possible before continuing.
Next, increase the volume of the solution by dilution to say 4 - 6 times the *cold* saturated solution, heat this to at least luke warm or hotter, and
dissolve several equivalents of ammonium sulfate in the solution (or add an ammonium sulfate solution as part of the dilution, but do this with both
solutions warm).
The theoretical ratio is to form NiSO4.(NH4)2SO4.6H2O, however my experience is that more ammonium sulfate reduces the solubility of the nickel double
salt without noticeably decreasing the solubility of the copper salt. There is also a double salt of ammonium and copper sulfates, but again in my
experience this is not a factor.
Next step is to cool this solution unmercifully in a freezer. The excess ammonium sulfate will stop it freezing. By about -10*C very much most of the
nickel will have precipitated out and hopefully none of the copper will have. If the copper has, then dissolve it again and increase the volume of the
solution before freezing it again.
VERY IMPORTANT - since this separation in the absence of expensive lab equipment will be colourimetric, please note that nickel ammonium sulfate is
BLUE, light blue specifically. The really cold solution should have diluted blue copper(II).4H2O and blue nickel ammonium sulfate crystals.
Take the crystals, dissolve them in a small amount of water at high temperature (the cold solutions are bluer than the hot green solutions, and I
don't know exactly what complex ions are formed so I cant explain this) and add sodium hydroxide or similar (in my experience, if sodium carbonate is
used a large amount of the nickel will stay in solution as the v-dark blue ammine). The apple green powder can be cleaned by repeated fill, wait,
decant procedures or otherwise. By dissolving this in an acid to form the sulfate, nitrate etc and crystalising this, pure nickel salts can be
obtained.
In practice, if you don't want a really crappy yield, it will take many 'fractional recrystallisations' (to abuse the term) between the ammonium
double salt and the sulfate. But if you don't care how many reagents you use, nickel especially, you should get some yield from doing this once. Also
don't trust the literature values for the solubility of nickel ammonium sulfate, most of them are rubbish. Further, it takes a long time to reach
equilibrium, probably because the crystal structure is more complicated, so after 1 hour your solution will still be supersaturated.
Finally, The nickel always drags some copper into the double salt crystals, so a recrys without ammonium sulfate is always necessary. I may have
forgotten to include something, so if you have any questions please post them.
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Ozone
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This is routinely performed in sophomore-level analytical Chemistry lab. They use ion-exchange resin and elute it with HCl of varied concentration.
The bands are colored and thus, are easy to follow.
The separation can be repeated many times with the same resin by first readjustng the strength of the acid in the bed.
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Rosco Bodine
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| Electromotive Series of the Metals |
| from Lange's Handbook of Chemistry, Eighth edition,|
| Handbook Publishers Inc., Sandusky, Ohio, 1952. |
| |
| Metal Voltage |
| |
| Magnesium -2.34 volts |
| Beryllium -1.70 |
| Aluminum -1.67 |
| Manganese -1.05 |
| Zinc -0.76 |
| Chromium -0.71 |
| Iron -0.44 |
| Cadmium -0.40 |
| Nickel -0.25 |
| Tin -0.14 |
| Lead -0.13 |
| Copper +0.34 |
| Silver +0.80 |
| Palladium +0.83 |
| Platinum +1.20 |
| Gold +1.42 |
Never tried any of this ...but anyway ,
Looks like there is about a 0.58 - 0.59 volt difference in the reduction potential for nickel compared to copper . You should be able to use
electrolysis to preferentially plate out the copper first . Possibly you could use iron scrap or filings to first precipitate the copper , and
secondly the nickel as the iron goes into solution .
Gradually adding ferrous sulfate solution might work also selectively reducing the copper first , and then the nickel .
Alternately by a neutralization with washing soda .....
Wonder if the copper would come out first as the basic carbonate ? There might be enough of a color shift there to indicate the midpoint where you
maybe could decant the
nickel containing solution and continue the neutralization
to obtain it as a carbonate precipitate .
[Edited on 11-8-2007 by Rosco Bodine]
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Ozone
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Yep. An iron nail in CuSO4 becomes quite coppery, quite quickly. your copper can be removed with conc. NH4OH, IIRC.
O3
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--Albert Einstein
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not_important
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Using an acidic bath and the coinage metal as anode, you can selectively plate the copper out on the cathode using a low, controlled voltage. The
nickel stays in solution, you may need to add acid during the process to keep the pH where it should be.
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YT2095
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there`s a ~1:15 solubility difference between the Iodates of these 2 metals though, you may be able to exploit that.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Rosco Bodine
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Adding a sodium polysulfide might also selectively reduce the copper and precipitate the copper as copper sulfide .
Separation of nickel and cobalt from copper is not the
easiest of separations ...as all of these can form complexes and multiple salts which may complicate things
well beyond what one would hope should happen .
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The_Davster
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Or just dissolve the coins in acid of choice, leaving a large excess of the coins(preferably cut up) The nickel metal should reduce the copper in the
coins giving more Ni2+, which after the blue colour is gone, the solution can be filtered of the unreaced coinage and precipitated copper, and the
filtrate would contain mostly Ni2+
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12AX7
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Doesn't work very well. Monel is corrosion resistant for one, and for two, the reaction is rather slow anyway. The alloy is a solid solution, not
really two phases that will react in that manner.
A reducing agent in a chloride solution can precipitate CuCl.
Tim
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guy
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I have tried a lot of methods but the best method is selective electroplating of copper. I have a really pure NiCl2 from only coins. I test for
copper by submerging Fe in the solution, and usually no copper is seen.
I set up a solution of HCl with two electrodes, one made from several Nickel coins stacked together and the other graphite or you could also use
nickel coins too.
Then after its done filter off some of the CuCl formed. Add some NaHSO3 and slowly increase the pH until no more precipitate can be seen. Filter
that and you have relatively pure NiCl2.
[Edited on 8/11/2007 by guy]
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Rosco Bodine
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Perhaps HCl + NH4NO3 would also make a good mix for dissolving the copper plus nickel alloy .
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guy
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I tried nitric acid and it is good at dissolving but not nearly as economical as electrolysis.
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S.C. Wack
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| Quote: | | Adding a sodium polysulfide might also selectively reduce the copper and precipitate the copper as copper sulfide. |
Shouldn't NiS precipitate as well? I've read that there is a sulfide separation, with H2S. This depends on NiS not formng in the presence strong
mineral acid, a condition which supposedly does not impede precipitation of CuS from cupric salts.
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Rosco Bodine
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Could be ....I'm not sure .
If you had a solution of the mixed chlorides containing residual acidity as HCl ...then you would get H2S and also
some free sulfur when Na2S3 is added .
[Edited on 11-8-2007 by Rosco Bodine]
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Antwain
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No doubt there are better ways if you have the right equipment and reagents, which I didn't 5 years ago. Electrolysis is probably the best, and I
would go with iodide if iodine grew on trees, the Cu(I)I being completely insoluble and spontaneously formed when I- is in Cu2+ solution. The
Nickel(II)Iodide is very soluble.
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