Waste Treatment, copper cementation.

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Gsracer

Well-known member
Joined
Dec 21, 2020
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Hello gents! Ive been keeping my copper waste solutions from my silver refining in 5 gallon buckets filled with iron for about a month at a time to ensure the copper and other metals are being cemented out before further processing. They have agitation (bubbler) going constantly. Recently ive gotten to a point where the waste solutions are stacking up on me and i wanted to see if i can revisit my process to make it more efficient.

Question is how long should it take for the copper and other metals to cement out on the iron, or is there a way for me to test the green iron solution for copper and such before further processing?

Just trying to be thorough as i can be.

Thanks in advance.
 
I imagine you could take a sample and add ammonia to see if you get a blue color. Not sure if that's sensitive enough for proper wastewater disposal or not, but it would be good enough for me on a small scale.
 
I had thought about ammonia. However as dark green as the solution is. I doubt I would be able to tell the color change.

I’m hoping to cut down to a week per cementacion. I know 4 metals mentions in the thread on dealing with waste that it’s a few hours. But I’m unsure if that’s in a commercial setting or under certain conditions. Etc.
 
Stibnut said:
I think the ammonia would drop both iron(II) and iron(III) as Fe(OH)2/3, which should allow you to see the blue color of tetraamminecopper. It would be a good idea to test that first on a ferrous sulfate solution though.
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It will go to some extent, but precipitate of iron hydroxides is very gooey and voluminous. Depends on how accurately you like to test it. If there is significant copper in solution, you will see it no matter how much iron you will have in solution. Then it only depend on your eyesight :)

I once did rough test like this (ammonia "shortage" happened to me):
Cut and sand some small piece of steel sheet. No need to be perfect, but it should be fairly clean, rust-free, exposing fresh metal. Take like 100mL of the suspected "spent" solution and dip the steel sheet in for several hours. Personally, if I did not see any Cu precipitation/coating/mud forming, I conclude the solution is sufficently copper-free :) I trusted my eye to recognize copper precipitate from other possible metals cementing.
If you are not sure, just collect bit of the coating/mud and add few drops of HCl/peroxide or easier - nitric. And than test with ammonia.
It sound complicated and time consuming, but it could be done in a minute.
 
Kinda unrelated but interesting.. I learned today that Ammonia has more hydrogen atoms than even hydrogen.. 100lbs of ammonia contains more hydrogen then 100lbs of hydrogen.....

Kind makes my head hurt...
 
Ohiogoldfever said:
Kinda unrelated but interesting.. I learned today that Ammonia has more hydrogen atoms than even hydrogen.. 100lbs of ammonia contains more hydrogen then 100lbs of hydrogen.....

Kind makes my head hurt...
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I don´t get it. Nitrogen 14g/mol hydrogen 1g/mol. Ammonia is 82% nitrogen by weight...
Maybe measuring it by volume will do that magic difference, as liquid hydrogen is extremely light.
 
I think it has to do with how you see it, by volume or weight.
One mol of Nitrogen as Ammonia stores 3 moles of Hydrogen.
 
Well ammonia can be combusted directly or converted to hydrogen for FC electric use. There are a couple of ships beeing built for Ammonia motors in Norway now.
 
Gsracer said:
I had thought about ammonia. However as dark green as the solution is. I doubt I would be able to tell the color change.

I’m hoping to cut down to a week per cementacion. I know 4 metals mentions in the thread on dealing with waste that it’s a few hours. But I’m unsure if that’s in a commercial setting or under certain conditions. Etc.
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You could dilute the solution down. If there is decent amount of metal you will still see it. Alternatively, Dilute solution by adding 50% water, warm to 40-50c and add a clean piece of iron to see if any copper cements out. you should see some copper plating out fairly quickly if there's any remaining.
 
Well thank you for the replies.

I did the ammonia test after a week and a half in my waste processing rig.

What i did was take a sample from the solution in a test tube, i diluted it 50 percent with water. I then added some ammonia and i did get a browish black precipitate with the consistency of silver chloride that settled pretty quickly upon agitation. I assumed this was the iron as stibnut and orvi suggested.

Most importantly the solution after the precipitate cleared up substantially and was relatively clear and not blue at all.

This helps me out tremendously and i can start processing my was quicker.

Thank you everyone again!
 
Yggdrasil said:
I think it has to do with how you see it, by volume or weight.
One mol of Nitrogen as Ammonia stores 3 moles of Hydrogen.
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Yes, it has more with what is called "volume energy density".
Liter of liquid hydrogen weight 71 grams approx.
Liter of liquid ammonia weight 730 grams approx.

So there is 10 times more mass per unit of volume. Additionally, when you burn hydrogen, you produce water. Burning the ammonia also produce nitrogen (and other stuff) alongside water. So you get the energy also from burning that "nitrogen" part.

deltaH(combustion) for ammonia is 319 kJ/mol
deltaH(combustion) for hydrogen is 286 kJ/mol

But you must consider that mole of hydrogen weight approx. 2grams. Mole of ammonia 17grams.
When you add density for the comparison of "volume performance", you get 35,5mol of H2 in 1L of liquid H2. That means it is capable of producing 10,2 MJ of heat energy.
Liter of liquid NH3 contains approx. 43 moles of NH3, thus combustion of liter of ammonia will produce 13,7 MJ of heat energy.
Aspects of the storage are also preferring ammonia, as it does not require that high pressure to store as liquid.
On the other hand, you must manufacture the ammonia in the first place :D and that is energy intensive process requiring hydrogen to start with. Nevertheless, Haber-Bosch and Ostwald processes are one of the most important chemical discoveries for humanity in past 150 years.
 
I think they have discovered an alternative not too long ago, but it may not be available yet.
They are working hard at all these old processes now, to try to replace or refine them with less energy intensive processes.
 
The thing with testing for metals in solution by formation of hydroxides, is that iron comes out first at around pH 3. This is rusty brown. Copper will still stay in solution until you reach pH 5 / 6 or so.
theroetical-solubility-of-metal-hydroxides-vs-ph-1.png
Putting clean iron in will indicate if there are still heavy metals above iron in the reactivity series present.
Leaving the iron in too long will consume the iron completely. Once the color of the solution has become a pale green and after a few days, you can pretty much assume most copper is out and move on to raising pH.
The solution will become clear as you said, but you need to measure pH and raise it too at least 9 to get all copper out and then to 11 to ensure all metals are out.
Adding a pH + substance like soda ash or lye will indicate if any metals are left. At Ph11 you can discard the filtered solution.


Martijn.
 
Thank you for the explanation martin, after i cement out. I raise the pH in the steps as you stated with lye. I mix it thoroughly and the iron hydroxide usually settles in a day or two. Then i filter and dry the precipitate and dispose of the clear liquid. My main concern was speeding the iron cementation process as up till now i had no quantifiable way of knowing it was complete for sure. So in caution I just added an abundant excess of iron and lots of time.
 
I just tap the copper cement off the rebar every now and then. You'll see when no more cement is forming after a while.
And depending on what you dissolved, there are other metals between iron and copper that will cement out on iron.
https://en.wikipedia.org/wiki/Reactivity_seriesI use a 10 liter see through bucket for the small amounts of what i process. It helps seeing whats going on.
 
Martijn said:
The thing with testing for metals in solution by formation of hydroxides, is that iron comes out first at around pH 3. This is rusty brown. Copper will still stay in solution until you reach pH 5 / 6 or so.
View attachment 48263
Putting clean iron in will indicate if there are still heavy metals above iron in the reactivity series present.
Leaving the iron in too long will consume the iron completely. Once the color of the solution has become a pale green and after a few days, you can pretty much assume most copper is out and move on to raising pH.
The solution will become clear as you said, but you need to measure pH and raise it too at least 9 to get all copper out and then to 11 to ensure all metals are out.
Adding a pH + substance like soda ash or lye will indicate if any metals are left. At Ph11 you can discard the filtered solution.


Martijn.
Click to expand...
Could you trace the source of the graph you added to your post ? I will like to read more about this, if it is a part of some article or so :)
 

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