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nimgoldman
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[*] posted on 9-12-2019 at 15:37
Copper disposal issues


I have a huge amounts of liquid copper waste but the disposal methods don't work for me.

Some of the waste come from pyridine synthesis where I used basic copper carbonate as catalyst.

I kept adding 10% hydrogen peroxide to the waste water beaker (containing combined rinses) and it turned brown with some black precipitate. Unfortunately, there is only a minute amount of precipitate (not corresponding to the amount of catalyst used) and adding sodium carbonate soln. does not precipitate anything.

The solution is strongly acidic. Should I first neutralize or make it basic before adding sodium carbonate soln. ?

Another waste container contains dissolved copper sulfate and copper(II) chloride - assuming the copper is already in +2 state, I don't have to add any peroxide, just the sodium carbonate soln.?

Based on the wiki, one should oxidize Cu to +2 state with hydrogen peroxide, then precipitate it as carbonate, but this does not seem working for me as I have already spent lots of peroxide with no results:

http://www.sciencemadness.org/smwiki/index.php/Copper#Dispos...

How do you dispose your liquid copper waste?

Now I have to reduce the huge amount of liquid by e.g. distillation, but I am afraid the concentration of peroxide is very high and I don't want to blow myself up...
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[*] posted on 9-12-2019 at 15:51


Quote: Originally posted by nimgoldman  
adding sodium carbonate soln. does not precipitate anything.

The solution is strongly acidic. Should I first neutralize or make it basic before adding sodium carbonate soln. ?


yea, you can't precipitate copper carbonate from acidic solution....

as for the other copper salts, just add sodium carbonate, copper is already in the +2 state, there's no need to wate hydrogen peroxide...

all your copper is already in the +2 state, why did you use all that hydrogen peroxide? you just wasted it





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nimgoldman
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[*] posted on 9-12-2019 at 15:57


Sorry i meant basic. The waste solution was about pH 10 and no precipition took place by adding Na2CO3.

I tried to make the solution acidic, then add Na2CO3 but same result, no precipitation, it just neutralized.

In past I added lots of H2O2 because each addition caused small amount of precipitation but it needed HUGE amount to get just small amount of precipitate.

After all experiments, I measured Cu(II) concentration by a heavy metal test strip and it showed there is about 200 ppb of Cu(II) ions.

So maybe it is just too dilute to see any sort of precipitate, it might just as well float in the solution and could not be removed without very fine filters...

My second waste solution is over 1000 ppb and I know there is over 5 g/L of CuSO4 and CuCl2 combined, but it does not react to addition of Na2CO3 ... this makes me perplexed.

I am too impatient at this point so I will probably sit down and learn how to neutralize the excess peroxide, then concentrate the solution and proceed slowly...
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[*] posted on 9-12-2019 at 17:11


if you can boil the solution to remove any excess hydrogen peroxide you could try adding sodium sulfide (or bubble in the solution H2S) to precipitate copper sulfide (it has a much lower solubility)




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nimgoldman
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[*] posted on 9-12-2019 at 17:40


Yes I can do that. I've used sodium sulfide with success for mercury waste cleanup.

I've read so far than one can also remove excess hydrogen peroxide with a reducing agent such as sodium thiosulfate, but I don't want to introduce any more ions to the already complex solution.
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[*] posted on 9-12-2019 at 18:04


Why not reduce it to Cu.



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[*] posted on 9-12-2019 at 18:34


You could boil to dryness then heat to above 290oC to decompose it to CO2 and CuO ?
You could use the CuO for an energetic thermite with aluminium powder,
or reduce it to copper using carbon and heat,
make copper nitrate, sulphate, chloride using the appropriate acid,
or keep it for future use as a reactant.




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nimgoldman
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[*] posted on 9-12-2019 at 19:50


There is usually only minute amount of copper(II) to remove (I use it as a catalyst in gram amounts), so it is not feasible to recover it after each reaction - maybe just collect the precipitates for later refining.

I just realised the reaction I used the copper for was a reduction reaction, so perhaps the copper was reduced to +1 state and this is why I cannot precipitate it without first oxidising to +2.

The big problem I have is about 5 liters of liquid copper waste which I believe is now very dilute, but might contain substantial amount of H2O2. I plan to first remove the peroxide by reacting it perhaps with sodium hypochlorite (produces just oxygen, salt and water), then concentrate it and finally precipitate the residual copper....
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[*] posted on 9-12-2019 at 20:07


Quote: Originally posted by nimgoldman  
I just realised the reaction I used the copper for was a reduction reaction, so perhaps the copper was reduced to +1 state and this is why I cannot precipitate it without first oxidising to +2.


Copper(I) is unstable in aqueous solution without large concentrations of stabilizing ligands- it reacts with itself to give copper metal and copper(II).




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[*] posted on 10-12-2019 at 04:28


Quote: Originally posted by nimgoldman  

The big problem I have is about 5 liters of liquid copper waste which I believe is now very dilute, but might contain substantial amount of H2O2. I plan to first remove the peroxide by reacting it perhaps with sodium hypochlorite (produces just oxygen, salt and water), then concentrate it and finally precipitate the residual copper....


If you boil this down you are going to decompose the H2O2 for sure.

I am facing a similar problem with copper nitrate waste. I have over 10 liters of the stuff from silver refining with still a bit of silver in.
The plan is to treat the waste with HCL (so as not to add to my onIon soup) then drop out the copper to reuse it after making bars.




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[*] posted on 10-12-2019 at 05:01


If it is just copper you wish to get out, why not electrolysis? (Edit: lead is a suitable anode.)
Sure, it will take a while but it is a set and forget kind of operation and a whole lot less effort (and energy) than boiling down.

One of the good things about copper is that it is visibly blue at relatively low concentrations and so you can see when you are close to being done. And of course you can test for the presence of remaining copper at even lower concentrations by taking a sample, boiling it down and testing with concentrated ammonia.

What is the goal here? Is it to recover the Cu for later use or simply to avoid killing fish in the environment? You do need to remember that copper salts are sold as root killers and fungicides and are sprinkled directly on the soil. The soil and organisms can cope with a bit of copper without suffering. It is waterways that you want to avoid contaminating. And even here, dilution is your friend. You may be losing a sense of perspective in your efforts to act responsibly.

[Edited on 10-12-2019 by j_sum1]
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[*] posted on 10-12-2019 at 05:53


If the solution is only 200 ppm by weight in copper, then I would simply discard it and flush it down the drain. H2O2 will quickly be gone in the environment and 200 ppm means 0.2 grams of copper per liter of waste. So, with 5 liters of waste you only have 1 gram of copper. As j_sum1 mentioned, copper sulfate is sold for agricultural purposes and sprinkled on the soil, often mixed with soil or other nutrients. With such uses, much much more than 1 gram of copper is introduced in the soil.



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