# Best way to digest large amounts of silver shot without overwhelming scrubber



## snoman701 (Sep 8, 2017)

Using 50:50 Nitric (68%) / Distilled water, what is the best way to digest say ten pounds of shot in one sitting.

Should I meter the acid into a container of silver, or meter the silver shot in to a container of acid? The logistics of either are entirely within my capability. Metering/peristaltic pump for the acid, vibratory feeder for the shot.

Now, yes...I could very well just dump a whole bunch of acid on a pile of silver, but I want to generate a manageable amount of NOx. I'm not scrubbing my fume hood exhaust, just trying to do get a majority of the fumes via vacuum / PVC bubbler scrubber setup with three columns: distilled water, NaOH (aq), then water.

I haven't decided if I'll do this in a stainless container or glass reactor. But I'm leaning towards stainless vessel of some sorts, as it's more durable.

Previously, it was suggested to do it in a poly lined cement mixer. Does the tumbling action help speed it up considerably?


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## nickvc (Sep 9, 2017)

Snowman why not use a silver cell, that way you dissolve less silver so less noxx and then the cell will refine the balance, you may need to stop the cell and add a little more nitric to dissolve more of the silver crystal to keep the cell running well if its sterling your running.


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## snoman701 (Sep 9, 2017)

Lots of contaminants. It's not pure silver. 

75% ag at times, 30% ag at others. Balance being cu, zn, cd, w and pieces of scrap steel. Trying to sort the steel out obviously, as it messes everything up. But it's dirty braze.

No sn as of yet though thankfully!!

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## Iggy-poo (Sep 9, 2017)

Set up a reflux system and use O2 to convert the NO to NO2, which can be hydrated back to Nitric and reused. You save your scrubber and lots of money, especially when digesting base metals.


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## snoman701 (Sep 9, 2017)

Right now most of it re fluxes with just a watchglass. Last night I put a 1/2 lb chunk of the stuff in a beaker. I addded 150 mL of distilled water and then 68% nitric in 30 mL increments until I had an equal amount acid/water. By adding in 30ml increments it kept no2 production to a minimum, but took forever. Once all gas production ceased, I poured off the pregnant leach and repeated this process. 

It's slow to do it this way. I also think I'm using considerably more acid than I would if I just added it and let it digest. 

I don't know how much of a difference it makes though, nor do I know how much of a difference agitation or tumbling the shot would make.

Once I work out a method of digesting, I'll work on reflux. 


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## Iggy-poo (Sep 9, 2017)

Once you have a reflux set up and able to feed oxygen to it, your speed will increase considerably because the NO2 will be able to be converted back to Nitric a lot faster. You can use Air as well, but it will take longer as the Air has only about 15% Oxygen and the rest reports to the scrubber. An inexpensive Oxygen generator can be made using H2O2 catalysed with Manganese Dioxide to split the H2O2 into Oxygen and Water. A Carbon Zinc cell is a convenient source of Manganese Dioxide, and Chlorine-free Bleach is a cheap source of H2O2 to generate the Oxygen. There's not much pressure involved, except for the back pressure from the scrubber. Just drip the H2O2 into a suspension of Water with a small amount of Manganese Dioxide . You will only have to decant off the excess Water now and then. Your reaction rate will be determined primarily by the Manganese Dioxide concentration. Once you get it where you want it, no need to add any additional, as it acts as a catalyst and doesn't dissolve.


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## FrugalRefiner (Sep 9, 2017)

Snoman, you can add a small amount of H2O2 to your digests to help cut down on NOx evolutions and wasted acid. I don't know if I've ever seen any specific amounts, so you'll have to experiment a bit with the "small amount".

Dave


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## Palladium (Sep 9, 2017)

Are you trying to do this on a continual basis and if so how much at a time?


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## snoman701 (Sep 9, 2017)

Continual as in monthly, probably 10 lbs / month but maybe more. 

I have oxygen tanks....don't need another piece of equipment. Bubble the oxygen in or just let a little gas in to condenser at same entry point as no2. I can't remember how large my reactor is. 


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## Topher_osAUrus (Sep 9, 2017)

FrugalRefiner said:


> Snoman, you can add a small amount of H2O2 to your digests to help cut down on NOx evolutions and wasted acid. I don't know if I've ever seen any specific amounts, so you'll have to experiment a bit with the "small amount".
> 
> Dave




Add the peroxide to the water before heating it up and adding acid. If there is acid in there already and its hot, the peroxide will break down very quickly and work the exact opposite way you want it to.

As far as amounts, i dont add a lot, maybe 50mL to a 1L digest.

One thing I would do though snoman. Is forget the water in your #1 a-b train, and put peroxide in it alone. Filling it with 3% peroxide will help convert that gas to nitric.


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## snoman701 (Sep 9, 2017)

Palladium said:


> Are you trying to do this on a continual basis and if so how much at a time?



Let me answer this better.

Within the next few months, I want to be able to run batches of ten pounds at a time, one batch per week, over a couple days if necessary. Conversion of NOx to NO2, chilled and bubbled through water to conserve Nitric isn't a priority as much as being able to clean the silver. 

I'd love to be able to have a room dedicated to digestion, with a poly lined cement mixer, a sprayed wet media scrubber with giant eductor, etc...but it's not going to happen in the next six months.


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## Iggy-poo (Sep 10, 2017)

snoman701 said:


> Continual as in monthly, probably 10 lbs / month but maybe more.
> 
> I have oxygen tanks....don't need another piece of equipment. Bubble the oxygen in or just let a little gas in to condenser at same entry point as no2. I can't remember how large my reactor is.
> 
> ...



The simplest approach is to use an aquarium pump to feed air into your reactor and not worry about the Oxygen content. You will know it's working when it converts the colorless NO to NO2 (red). It will react with the moisture in the reflux column to make Nitric Acid and drip back down into your reactor.
If you see that the NO2 is making it to your scrubber, you can increase the air to compensate or, if on the other hand, The NO2 is being converted before it reaches the column, you can raise the temperature or add more Nitric Acid to speed up the reaction. It's a matter of finding a balance that works for you.


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## Iggy-poo (Sep 10, 2017)

Iggy-poo said:


> snoman701 said:
> 
> 
> > Continual as in monthly, probably 10 lbs / month but maybe more.
> ...


As far as equipment goes, I've used a plastic jug, drilled a hole in the cap, stuck in some tubing and added water, some Manganese Dioxide that I scooped out of a carbon cell into the water and added a bit of H2O2 and screwed the cap back on. We're not talking rocket science. When the flow drops, just add some more Peroxide....


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## Iggy-poo (Sep 10, 2017)

Topher_osAUrus said:


> FrugalRefiner said:
> 
> 
> > Snoman, you can add a small amount of H2O2 to your digests to help cut down on NOx evolutions and wasted acid. I don't know if I've ever seen any specific amounts, so you'll have to experiment a bit with the "small amount".
> ...



The reason I emphasize adding Oxygen gas is to get away from adding water, thus diluting the Nitric and slowing down the reaction, otherwise, the net result is the same. 3% Hydrogen Peroxide is 97% Water.


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## FrugalRefiner (Sep 10, 2017)

Iggy-poo said:


> The reason I emphasize adding Oxygen gas is to get away from adding water, thus diluting the Nitric and slowing down the reaction, otherwise, the net result is the same. 3% Hydrogen Peroxide is 97% Water.


Since we usually dilute our nitric about 50/50, it's not a problem. If you plan to use 500 ml of water and 500 ml of nitric, you just use 450 ml water, 50 ml H2O2, and 500 ml nitric. You're not diluting it any more than you would with water alone, and it's simpler than generating oxygen and piping it in to a reactor when you're not geared up for it yet.

Dave


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## g_axelsson (Sep 10, 2017)

When mixing peroxide and silver, remember that silver will catalytically break down hydrogen peroxide into water, oxygen and a lot of energy. I don't know if braze would still do it or if it has to be pure silver to work.
3% strength would probably at most make a lot of oxygen and getting a bit warmer but high strength hydrogen peroxide and silver is the core in many rockets.

Göran


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## Palladium (Sep 10, 2017)

How will you be filtering and will you use the chloride method or is this for a cell?


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## Iggy-poo (Sep 10, 2017)

Palladium said:


> How will you be filtering and will you use the chloride method or is this for a cell?



Your videos on using Sodium Formate reduction would fit in here, with all the crud he has mixed-in with the Silver.

https://www.youtube.com/watch?v=qSzjH9cSDpw


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## snoman701 (Sep 10, 2017)

Palladium said:


> How will you be filtering and will you use the chloride method or is this for a cell?


For my purposes right now, probably just a large coffee filter, then cement with copper after further diluting. 

Initially I'll sell the cemented copper to topher, but in time a cell of my own. 




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## Topher_osAUrus (Sep 10, 2017)

Not to undercut, uh, myself.. But, a cell is one of the easiest things to do.

Really really simple to make, cheap to set up, effortless to maintain (if high purity silver is the feedstock)

If you have the nitric already, an el'cheapo $50 variable psu, a $7 stainless bowl, couple bucks in alligator clips and wire, $2 in muslin cloth, a jerryrigged way to hold the anode filter and shot (i use a plastic collander with a handle), and thats pretty much it, really. Simple. Simple. Simple.

Edit to fix a vowel


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## snoman701 (Sep 10, 2017)

I know....but I also know how I want to set it up. 

I have minimal space and too many projects. Sometimes it's best to just limit oneself a bit. 


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