neutralizing AP waste

[mls26cwru]

gotta quick question that maybe someone can help with... I have been reading the proceedures for neutralizing AP waste... I have dropped the PMs with copper, dropped the copper with iron... the solution was decanted, and the liquid drawn off and copper set aside for drying later. I read that liquid should be treated with garden lime (a mix of magnesium and calcium carbonate). I have done this, but cant seem to get it above ph of 6. I have added about a pound to a 5 gallon bucket... is this normal, do i need to keep adding more lime? the solution has turned a rusty/coffee color and separates nicely, just my ph just stopped at 6. I tried to add a tiny bit of baking soda to see if there was a reaction, and their was, so i still have a bit of acid in solution. I just wanted to see what others think before i go pouring 5 pounds of lime into solution and have it not work.

thanks!

 

[NoIdea]

Hi Yah - personally i would distill off the acid for re-use.

Deano

 

[butcher]

I normally add sodium hydroxide to adjust pH for the most part, it is a very strong hydroxide with a pH of around 14 pH, baking soda pH about 8, lime calcium magnesium carbonate somewhere around pH 8, calcium hydroxide about 12 pH.

I use both sodium hydroxide and lime, the sodium hydroxide for moving the pH range and precipitate the largest portion of metals, and the calcium magnesium carbonate (lime) because it helps to precipitate some of the very reactive metals, I also use wood ash many times to adjust pH as it is caustic in solution.

I suspect once you get close to the pH of your lime (about 8) and it is not strong enough to tip the balance, it takes much more lime to move the pH range, try a little NaOH sodium hydroxide, with it being a stronger base it is easier for it to move the scale

Don’t forget to raise the pH to about 9 Remove insoluble metal hydroxides the lower it again to pH 7 to precipitate the soluble metal hydroxides, your solution should become a clear salt water

 

[mls26cwru]

thank you butcher, i will see where i can find some sodium hydroxide

 

[Geo]

i would question you about WHY you want to neutralize your AP. this is a valuable chemical and can be used over and over until it is so fouled that it cant digest more metal. ive rarely gotten to that point and only by using it to digest alot of iron. if you dont need it now, seal it in a bucket with a lid to use later.

 

[mls26cwru]

i suppose i should have been a bit more specific.... most of the stuff from the AP is just rinse water... when i take the fingerboards out of the AP, i give them all a good wash to recover foils that stick to the boards. A bit of acid and water from the refining rinses get added to the bucket as well. most of my original AP is still being used

 

[Geo]

slowly evaporate the excess water from the rinse and add the solution back to the AP. keep the heat below 100 degrees C or just below the boiling point of water until green crystals start to form and remove it from the heat.

 

[Alentia]

I normally add sodium hydroxide to adjust pH for the most part, it is a very strong hydroxide with a pH of around 14 pH, baking soda pH about 8, lime calcium magnesium carbonate somewhere around pH 8, calcium hydroxide about 12 pH.

I use both sodium hydroxide and lime, the sodium hydroxide for moving the pH range and precipitate the largest portion of metals, and the calcium magnesium carbonate (lime) because it helps to precipitate some of the very reactive metals, I also use wood ash many times to adjust pH as it is caustic in solution.

I suspect once you get close to the pH of your lime (about 8) and it is not strong enough to tip the balance, it takes much more lime to move the pH range, try a little NaOH sodium hydroxide, with it being a stronger base it is easier for it to move the scale

Don’t forget to raise the pH to about 9 Remove insoluble metal hydroxides the lower it again to pH 7 to precipitate the soluble metal hydroxides, your solution should become a clear salt water

Butcher,

Interestingly enough, I use Lime and NaOH too. What is even more interesting is that I am getting very weak ammonia solution in my 55gl drum, when using both chemicals.

What more, and it is annoying, I am getting thick layer of black Sulfur above iron layer, which I think came from SMB.

Do you know how to get rid of Sulfur or just let it be?

 

[butcher]

I would not worry about an insoluble sulfur.

The ammonia would concern me, are you adding ammonia waste to your barrel (I keep my ammonia waste separate), or do you think you may be somehow forming ammonia from nitric acid waste?

 

[Alentia]

This drum is half full with crap from about 1 year of operations. I am thinking ammonia is being formed. It only started forming with introduction of lime to the drum. With NaON only cleaning, I have never had an ammonia smell.

In any case, by the sense of the smell, I would estimate the concentration of around 0.25% or less, so it not significant.

I am able to drain about 25 gallon of clean water on every cycle, but lately started to get some sulfur in the water once in a while. I either need to get sulfur settled down somehow or cut siphoning pipe by an inch, so it does not reach sulfur layer.

 

[butcher]

I am not very good at chemistry, only learning a little here and there on my own.

From the way I understand it ammonia would need a high pH to form as ammonia is a base, now ammonium salts could more likely form at the pH range you are shooting for,

But even then if you had ammonium chlorides you may be forming ammonia gas leaving the barrel.
2 NH4Cl + 2 CaO → CaCl2 + Ca(OH)2 + 2 NH3

I think it would be hard to form ammonia from nitrates even though metals can act as catalyst, I do not see how at these temperatures how it could occur, but again I am no chemist.

I suspect somewhere you have ammonia or ammonium chlorides or some other ammonium waste involved here, it think it is best to keep these wastes separate as much as possible.

Neutralizing this should form salts (ammonium salts with your metal sludge), just as a precaution I do not think I would store this close to something flammable like my shed, keep covered but do not seal the lid, allow gases to escape, take care if force drying sludge with heat, You probably will not have any problems but then again you never know.

Maybe someone with some more experience or understanding of chemistry can help out with this.