Sciencemadness Discussion Board

Separating metals out of a coin

CobaltChloride - 13-3-2018 at 10:48

How would you suggest separating the metals from an alloy of 80% Cu, 15% Zn and 5% Ni (a certain coin in my country)? I was thinking of dissolving them in nitric acid and then adding sodium carbonate, which would precipitate the carbonates in increasing order of solubility product, but I can't seem to find the solubility product of ZnCO3. Would this method work and what is the solubility product of ZnCO3?

[Edited on 13-3-2018 by CobaltChloride]

DraconicAcid - 13-3-2018 at 11:02

I'd start (after dissolving in acid, of course) by adding enough sodium hydroxide to precipitate the copper and nickel as hydroxides, while dissolving the zinc as a complex ion.

walruslover69 - 13-3-2018 at 11:06

I found a literature source for zinc carbonate to be 1.46×10^-10. What are you wanting as an end result? do you need to separate all three metals into individual compounds or is there just one specific one that you need? Dissolving in nitric acid is a good first step but trying to separate carbonates based on solubility is probably not the best path to go down.

CobaltChloride - 13-3-2018 at 11:58

Quote: Originally posted by walruslover69  
I found a literature source for zinc carbonate to be 1.46×10^-10. What are you wanting as an end result? do you need to separate all three metals into individual compounds or is there just one specific one that you need? Dissolving in nitric acid is a good first step but trying to separate carbonates based on solubility is probably not the best path to go down.

I only really want the nickel.

Not really based on solubility, but I was thinking that the carbonate ions would preferentially combine with the metal cations which would make the most insoluble compound. Given the solubility products, CoCO3 would first precipitate, then ZnCO3 and then Cu2CO3(OH)2. Won't this work? Is there a better option for separating the metals?

[Edited on 13-3-2018 by CobaltChloride]

[Edited on 13-3-2018 by CobaltChloride]

walruslover69 - 13-3-2018 at 12:25

how are you going to know when you are done precipitating copper and only have Nickel left in solution?

CobaltChloride - 13-3-2018 at 13:02

Quote: Originally posted by walruslover69  
how are you going to know when you are done precipitating copper and only have Nickel left in solution?

I know the exact composition of the coins. I also know their mass. Thus I can easily calculate how much copper II nitrate is in solution, so I can calculate how much sodium carbonate I need for the reaction.

unionised - 13-3-2018 at 13:57

Did you use an excess of acid when dissolving the coin?
Did any evaporate?

CobaltChloride - 13-3-2018 at 14:28

Quote: Originally posted by unionised  
Did you use an excess of acid when dissolving the coin?
Did any evaporate?

All of this is still theoretical as I don't want to waste nitric acid without being sure that this is a good method. In any case, I plan to use as much as is needed to dissolve the coin, which would probably be more than stoichiometrically necessary as some is bound to decompose/evaporate. I know that the excess will also react with sodium carbonate, so I plan to leave the solution to dry and then redissolve the salt mixture.

unionised - 13-3-2018 at 14:29

You might want to search the site for copper aspirinate.

CobaltChloride - 13-3-2018 at 14:50

Quote: Originally posted by unionised  
You might want to search the site for copper aspirinate.

Ok, but do you know if nickel aspirinate isn't insoluble as well? I would try it on a small scale, but I don't have any nickel beside the one from the coins, but those are huge and melting one to make small beads isn't an option.

DraconicAcid - 13-3-2018 at 15:31

I think it's been made clear in the thread that we've tried making nickel aspirinate, and haven't gotten any precipitate. And trying these things on a small scale is easy- take your solution, and add aspirin to only a small aliquot of it.

That being said, I've had mixed results with making copper(II) aspirinate at the best of times....

The classic way of separating nickel and copper is with sulphide in acidic solution, but you've have to have a good fume hood for that- copper(II) sulphide will precipitate out, while nickel sulphide will only precipitate from a neutral solution.

Alternatively, you could reduce the copper and precipitate it as copper(I) iodide.

CobaltChloride - 13-3-2018 at 15:40

Quote: Originally posted by DraconicAcid  
I think it's been made clear in the thread that we've tried making nickel aspirinate, and haven't gotten any precipitate. And trying these things on a small scale is easy- take your solution, and add aspirin to only a small aliquot of it.

That being said, I've had mixed results with making copper(II) aspirinate at the best of times....

The classic way of separating nickel and copper is with sulphide in acidic solution, but you've have to have a good fume hood for that- copper(II) sulphide will precipitate out, while nickel sulphide will only precipitate from a neutral solution.

Alternatively, you could reduce the copper and precipitate it as copper(I) iodide.

I didn't have time to search through all those pages to see that you didn't get a precipitate with Ni II. The idea of using a soluble iodide is great! Thanks for the help!

DraconicAcid - 13-3-2018 at 15:43

And if the cost of iodide is a problem, you can probably reduce it with sulphite in the presence of bromide or even chloride, as these will also give insoluble copper(I) compounds (while nickel won't be reduced or precipitate).

PirateDocBrown - 14-3-2018 at 00:25

If you want to get Ni out of coins that only have 5% of it, you are better off switching coins. Try foreign ones that have higher nickel content. Some issues are pretty much pure nickel.

Sulaiman - 14-3-2018 at 00:57

For pure nickel I bought these https://www.ebay.co.uk/itm/Pure-Nickel-99-96-Low-Resistance-...
easy shape to dissolve or use as a small electrode.
Getting the 5% anything from an OTC source is worth doing at least once to develop skills.

Foeskes - 14-3-2018 at 17:15

I have come up with 1 method for separating Cu and Ni, but it's impractical basically copper sulfate decomposes at around 500 C and nickel sulfate is way over that so if you heat it around 500-600 C for a while you should get soluble (anhydrous) nickel sulfate and insoluble copper oxide. This is dangerous and you need good gas scrubbing(the decomposition releases SO3), maybe you can make oleum?
Note: I have not tried this method yet.

[Edited on 15-3-2018 by Foeskes]

PirateDocBrown - 14-3-2018 at 18:18

I posted, long ago, a method for separating Ni and Cu derived from cupronickel coins. If there is also Zn, precipitating it out selectively as ZnO2 under oxidizing conditions should be straightforward.

Or you can go the electrowinning route, if you've got the gear.

Some old, yet still abundant, Canadian coins are 99%+ Ni. I'd just go there.

CobaltChloride - 15-3-2018 at 08:38

Quote: Originally posted by Foeskes  
I have come up with 1 method for separating Cu and Ni, but it's impractical basically copper sulfate decomposes at around 500 C and nickel sulfate is way over that so if you heat it around 500-600 C for a while you should get soluble (anhydrous) nickel sulfate and insoluble copper oxide. This is dangerous and you need good gas scrubbing(the decomposition releases SO3), maybe you can make oleum?
Note: I have not tried this method yet.

[Edited on 15-3-2018 by Foeskes]

Just wanted to let you know that I did the decomposition of copper sulfate in a school setting and it produced SO2 and O2, but no SO3. I think this is because there is some sort of temperature-dependent equilibrium between SO3 and SO2+O2 and it is very hard to control the temperature sufficiently so that SO3 is the main gaseous product.

CobaltChloride - 15-3-2018 at 08:45

Quote: Originally posted by PirateDocBrown  
I posted, long ago, a method for separating Ni and Cu derived from cupronickel coins. If there is also Zn, precipitating it out selectively as ZnO2 under oxidizing conditions should be straightforward.

Or you can go the electrowinning route, if you've got the gear.

Some old, yet still abundant, Canadian coins are 99%+ Ni. I'd just go there.

I think it is easier to use the aforementioned method to separate zinc by means of its soluble complex with sodium hydroxide as the reagent is cheaper.

As for going to Canada, that's not an option. Nor is electrowinning because I don't have a variable DC power supply.

[Edited on 15-3-2018 by CobaltChloride]

fusso - 6-4-2018 at 06:50

@CoCl2 No wonder you want to separate metals from that specific compo. I googled about coins in ur country and found out ur coins only have that compo, other than sth plated on steel.

[Edited on 6/4/18 by fukko]