Chemistry - Precipitation from wastewater

[Engels]

Hi folks!

Today I failed in etching a big board (coz it was big...)
I used about 800ml of water with 100g of ammonium persulfate (I know I should have used half of the water), and now I stored the blueish liquid on a coke bottle 

So, here's a bit of chemistry, as far as I know.. the reaction equation should be this:

(NH4)2S2O8 + Cu -> CuSO4 + (NH4)2SO4

What I want now is just the CuSO4, the copper sulfate for making some experiments  : (ehm... )
... but... I don't know how to separate the copper from the ammonium sulfate;
I readed that precipitation is the common way, but it's not so clear to me;

A very usefull guide says:

"Copper can be removed by precipitation as
sulfide at pH 8.5. The resulting effluent
concentration is 0.01 - 0.02 ppm"

So have I to increase the pH? (or decrease it?)
I'm not sure if I have the proper equipment for this, I wonder if I could just add something to the mixture and finally obtain the sulfate crystals on the bottom of the bottle 

Another question: with this process, am I going to obtain copper sulfide or copper sulfate? Since the precipitation method says how to obtain the sulfide, while the equation says that I've copper sulfate mixed with ammonium sulfate, my head is exploding! no.. no, it is precipitating!  ;D

Last thing: if this experiment is somewhat utterly stupid, what is the best way for the ammonium persulfate wastewater disposal?

Thanks guys 

I do believe, that our electronic waste can be, somehow, used one more time is another way... for example, old pcb can be used for making paintings or sculpture; we still have lots of copper in our saturated etchant, maybe it can be used in a similar way, imho..

Byebye, to the next silly question, if you don't ban me before  :-X

 

[zebra50]

By changing the pH you will start to do some more chemistry, and it looks like you are going to convert the sulfate to sulfide.

But you may be in luck.

... http://en.wikipedia.org/wiki/Solubility_table

Copper sulfate is substantially less soluble than ammonium sulfate, so the one student lab method would be to boil the liquid until it is saturated, and then leave to stand. The copper sulfate should precipitate first, and if you are lucky you might get some nice crystals too. Filter them off and wash with ice-cold deionised water!

Chemistry can be fussy though - impurities can play havoc with crystallisation, and you might get a mixed salt forming.

If you need good purity then you would be better off just buying some.

Cheers!
Stewart

 

[Engels]

chemistry can be fussy but it is very enchanting by my point of view  :
just a minute after I started this topic, I tryed to increase the pH by adding baking soda and initially I thought that it was working!
The mixture became more cloudy with a nice ocean blue color; on the bottom of the bottle, deep blue crystals were depositing softly...
I wanted to filter them and I took about 1 minute to find the proper tools, but then, when I came back, crystals disappeared and a more torbid substance was floating in the bottle, slowly depositing on the bottom; I thought that It could be the baking soda, but it was just too much (I added just a spoon, and then the whole bottle were fullfilled by the milky substance)... was that the ammonium sulfate?
I'm starting to understand chemistry a little bit more  ;D

 

[DaveP]

"What I want now is just the CuSO4, the copper sulfate for making some experiments  (ehm... )
... but... I don't know how to separate the copper from the ammonium sulfate;
I readed that precipitation is the common way, but it's not so clear to me"

Right, a couple of things, first you can easily tell the pH using a simple universal pH paper.
secondly, it does not have to be pH 8.5, heavy metals are often precipitated from slightly acidic solutions with a bit of a stink of H2S (bad egg gas)  H2S is quite toxic so best done out of doors, it is most dangerous when you stop smelling it as it has knocked out your sensors and is about to kill you.

Copper sulphide would be useless to you in any case and you would have to dissolve it in sulphuric acid to get it back to sulphate again (dangerous).

There are two risky ways and one safe way.

1. Boil the solution down and this happens, at 110C you lose 4H2O from the CuSO4 molecule, at 150C you lose all 5H2O, then at 280C the (NH4)2 SO4 starts to volatilise leaving you with very hot melted copper sulphate (be careful!!!)

2. From the data books (Chemical Rubber) it looks like CuSO4 is soluble in Methanol (dangerous) whereas Ammonium sulphate is not.  So in theory you could dissolve the CuSO4 out of the dry mixture, then evaporate the methanol (toxic)

3. Use electrolysis with suitable electrodes and low voltage <10V and maybe an amp or two
http://www.nuffieldfoundation.org/practical-chemistry/electrolysis-copperii-sulfate-solution

Have to make sure there is ventilation as Hydrogen is produced at the other end.

All these things could be done fairly simply in a well equipped lab (furnaces and fume extraction) but become downright hazardous in a domestic kitchen or garden shed.

Use some common sense here, Environmentally you will use up more resources trying to recycle than just buying fresh.

best
DaveP

(Chemist)

 

[Engels]

"What I want now is just the CuSO4, the copper sulfate for making some experiments  (ehm... )
... but... I don't know how to separate the copper from the ammonium sulfate;
I readed that precipitation is the common way, but it's not so clear to me"

Right, a couple of things, first you can easily tell the pH using a simple universal pH paper.
secondly, it does not have to be pH 8.5, heavy metals are often precipitated from slightly acidic solutions with a bit of a stink of H2S (bad egg gas)  H2S is quite toxic so best done out of doors, it is most dangerous when you stop smelling it as it has knocked out your sensors and is about to kill you.

Copper sulphide would be useless to you in any case and you would have to dissolve it in sulphuric acid to get it back to sulphate again (dangerous).

There are two risky ways and one safe way.

1. Boil the solution down and this happens, at 110C you lose 4H2O from the CuSO4 molecule, at 150C you lose all 5H2O, then at 280C the (NH4)2 SO4 starts to volatilise leaving you with very hot melted copper sulphate (be careful!!!)

2. From the data books (Chemical Rubber) it looks like CuSO4 is soluble in Methanol (dangerous) whereas Ammonium sulphate is not.  So in theory you could dissolve the CuSO4 out of the dry mixture, then evaporate the methanol (toxic)

3. Use electrolysis with suitable electrodes and low voltage <10V and maybe an amp or two
http://www.nuffieldfoundation.org/practical-chemistry/electrolysis-copperii-sulfate-solution

Have to make sure there is ventilation as Hydrogen is produced at the other end.

All these things could be done fairly simply in a well equipped lab (furnaces and fume extraction) but become downright hazardous in a domestic kitchen or garden shed.

Use some common sense here, Environmentally you will use up more resources trying to recycle than just buying fresh.

best
DaveP

(Chemist)

I'm giving up!
Anyway, useless you say?
http://www.artangel.org.uk/images/seizure26_0.jpg
copper sulfate is cool  ;D

Btw, There are too many risks right now; no tools, no proper lab, I must pass from chemistry theory before these kind of stuff 
I'll take my coke bottle tho who knows how to handle it and dispose it 

Thanks for this lesson!
byebye