# Capturing SO2



## grizzlygremlin (Dec 24, 2015)

Hey friends, so I've got some ore that I've concentrated via panning. I've got about 100lbs crushed, classified to 20 mesh, and ready for a roast. The ore is mainly sulfides, its a composite from random ores I've collected. I'm in Colorado, and the crushing with panning is showing one or two +50mesh colors and lots of super fly poops per 100 gram sample.
I'm fixing to roast the con's off in a little wood burning foundry that I use to melt my scrap aluminum. Now I'm no Eco but. I'm Env. Scientist, and firm believer that us humans are screwed already. We have gone too far. So I don't care about blasting out So2. What I do care about is personally learning, and utilizing everything I can.
Long story short, I'm looking for a down n dirty to keep my So2. Obviously sulfuric acid is what I'm after. 
My idea is to use my foundry sort of like a still for distillation. Since So2 is soluable in water could I set up a duct fan over my foundry to pull the fumes into some vent ducting, then into basically a "thump can". If I use a few gallon water tank with the ducting coupled and submerged in water, the exhaust will by dispelled into the water, and theoretically the so2 would dissolve and quickly hydrate to h2s04 in the presence of water right, and the colder the better. What other fumes might be water soluable making this a stupid idea? I've heard of people collecting the stuff, but I haven't come across any info if it can be a simple process.


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## butcher (Dec 25, 2015)

sulfur dioxide gas and water form sulfurous acid (not sulfuric acid).
SO2 + H2O --> H2SO3

SO2(g) + O2---with a catalyst for the reaction--> 2SO3

SO3 bubbled into 98% H2SO4 makes oleum, the oleum H2S2O7 diluted in water make H2SO4
H2S2O7 + H2O --> 2H2SO4 

Roasting sulfides will generate SO2, that is not a problem, 
roasting pyrite ore (iron sulfide) or other metal sulfides,
4 FeS(s) + 7 O2(g) --> 2 Fe2O3(s) + 4 SO2(g)

Capturing the gases during the oxidizing roast may be tricky.

Then running them through a catalyst like vanadium oxide, V2O5, mixed with an alkali metal sulfate to get the needed SO3 sulfur trioxide gas, then running this gas through a spay mist of concentrated acid to make oleum, which can be diluted to make sulfuric acid.

See how they do it industrially, maybe you can come up with something that will not stink up the neighborhood and contaminate everything around it or poison the air with acid rain or which will not fill your lungs with H2SO4.

My suggestion is forget about trying it, and study it, trying it can be dangerously deadly without having a very good understanding of the dangers and reactions....

Arsenic, H2S and many other very deadly gases are involved...
Different ores produce different gases, and each with different dangers, even the same ore form the same mine can differ widely in what gases the roasting process could produce...


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## Deano (Dec 25, 2015)

Further to butcher's comments, he is trying to let you down gently.

All of the large commercial smelters and roasters have a strong smell of sulfur products even though they use the best technology for capturing these emissions.

Trying to do it yourself is a recipe for ill health.

An alternative method for treating the sulfides is to take an open topped steel box made of 6mm thick steel plate, fill it completely with the dry ore and cover the open top with a piece of steel plate.

Put the whole thing in a furnace and heat for a few hours until the sulfides have turned into blue sulfates.

These sulfates are water soluble and allow a leach to attack the gold from the sulfides.

Note that the sulfide associated gold is generally so fine that it is not gravity recoverable.

The furnacing time depends on furnace temperature and the shape of the steel box, usually you try to keep it fairly shallow for small scale processing, say about 10 cm. 

This allows the heat to reach the centre of the ore layer reasonably quickly.

If you make the box reasonably accurately there will be no fumes evolved.

Deano


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## Geraldo (Dec 25, 2015)

And just another quick add-on to Butcher's comments:

- the V2O5 catalysts used in acid plants to convert SO2 to SO3 typically run 400-600°C. For a home-spun unit, how do you plan to control the temperature of your catalyst beds? Too low a temperature, and your conversion efficiency drops off towards zero. Too high, and the catalyst will be damaged/inactivated.

- how will you clean your gas before entry into the catalyst beds? You have the risk during roasting of all kinds of volatile materials (like arsenic gases) all of which can poison the catalyst. You also cannot have particulate in your gas stream as these can both poison and clog the catalyst beds. Traditional acid plants attached to metallurgical operations require extensive gas cleaning before the SO2 can be converted.

There are other methods of capturing SO2. There are absorption methods that use amine solutions. There are reactive systems that use hydrogen peroxide. There are adsorption methods using fluidized bed dry lime and lime slurry systems. Of course, none of these will provide you with sulfuric acid, but consider that sulfuric acid is one of the cheapest industrial acids in existence - is it really worth it to you to try to make sulfuric acid from your small roasting operation?

If you are interested in making sulfuric acid despite these hurdles, I recommend reading Davenport's very good book on Sulfuric Acid Manufacture. It will give you some idea of what you are up against.

Just some thoughts.

Best Regards, Geraldo


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## grizzlygremlin (Dec 29, 2015)

You guys are some really smart and involved people. I feel like I'm in a PhD chemistry program! Thanks again for the wealth of information. 
My main goal with this idea is to just hold on to as many byproducts as I can. I love the anaerobic roasting technique! You don't come across that suggestion to often browsing around. If I did this roast, and washed my con's after what would be the proper disposal of that water? Could it be reduced\ condensed? I may have mentioned that I'm mainly a gold dredger, but the availability of ore from so many mines near me makes this hard rock learning experience my only lifeline to that AU while the streams are frozen up.
Ive got some free time so I think some more reading is in order. You guys are way way a dead of me!!
Thanks again!


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## Eamonn (Dec 29, 2015)

Having a bit of difficulty with prospector jargon.
Can anyone give simple meanings of:

1. super fly poops
2. con's
3. thump can
Thanks
Eamonn


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## Deano (Dec 29, 2015)

Assuming that you did the roast properly in a properly made container the dissolved material is pretty well all iron sulfate as ferric sulfate.

There will always be a small amount of sulfur dioxide adsorbed onto the ore solids, this will give you an acid solution when dissolved.

If you filter the solids out from the liquor for further processing you can recover the iron from the liquor as a hydroxide by adding an alkali to pH around 7, flocs will form and precipitate.

These flocs are regarded as non-hazardous and can be filtered out and disposed of in landfill.

Deano


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## Grelko (Dec 30, 2015)

Eamonn said:


> Having a bit of difficulty with prospector jargon.
> Can anyone give simple meanings of:
> 
> 1. super fly poops
> ...



(super fly poop) = super fine gold flakes/dust, the size of fly poop :lol: 

(cons) = concentrates = after seperating the bigger rocks etc, that don't contain many precious metals, you are left with the bulk of the precious metals. Basically sorting out the junk, so that you have the PMs "concentrated or grouped" together, without a lot of the worthless material mixed in.

(thump can) - I haven't heard this before. Maybe the container, that you sifted material into? "Thump" it on the side, to get the heavier pieces to the bottom?


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## grizzlygremlin (Dec 30, 2015)

Haha sorry for the non mining terminology. "Thump can" is an old moonshiners term for basically a booze scrubber. After the ethanol gas was produced from the still it was piped into a barrel filled with water and exhausted out another pipe directed to the condenser or "worm". The distillate would be "scrubbed". Realistically the thump can allowed the distillate to cool slightly allowing for much better condensation and partial removal of methanol.
I'm not sure in refining lingo what it would be called. My idea was to " bubble" my discharged gasses I to a tub or bucket of water hopefully keeping the air clean and my neighbors ignorant of my interests. I'm glad there is easier ways to take care of this. I can also do open roasts out camping. 
I could some pretty neat ore yesterday that I need to post a pic of. It might be calcocite! My specimen is heavy chalcopyrite with some masses and grains that are deep purple and black. 
Oh its off topic, but I figured someone might appreciate it.
This pic is gold from a benched placer. 1.28 grams sluiced out of three 5 gallon buckets! Richest ground I've seen, too bad I got it all!


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## Grelko (Dec 30, 2015)

Ah ok, a thump can should be the same as a scrubber or "water trap".

That's nice for three 5 gallon buckets, I'm sure you'll find more soon. I only get "flour gold" from the creek near my area, and it's about 10 particles per bucket. I get more gold from 1 N/S bridge, but it's still fun panning.

Edit - reworded


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## Eamonn (Dec 30, 2015)

Cheers for the explanation of terms. I know a bit more now.

"Super fly poops" good name for a band.


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## Harold_V (Dec 31, 2015)

grizzlygremlin said:


> I'm fixing to roast the con's off in a little wood burning foundry that I use to melt my scrap aluminum.


Blink! Blink!

Say what?

Do you understand what the word foundry means? 

Didn't think so. 

Please accept my comments in the spirit in which they are offered. 

A foundry is a factory that produces metal castings.

I expect that what you're trying to say is that you'll use a little wood burning ****furnace****, which is not to be confused with a foundry. In a foundry one will find a furnace, or more, but where one finds a furnace there may not be a foundry. 

I make mention because I abhor the misuse of words, especially on this board, where one mistake can lead to disaster for others. Here, we try to be precise, so others don't pick up bad habits. 

Harold


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## beav3r316 (Dec 31, 2015)

grizzlygremlin said:


> ..... utilizing everything I can.
> Long story short, I'm looking for a down n dirty to keep my So2. Obviously sulfuric acid is what I'm after.
> My idea is to use my foundry sort of like a still for distillation. Since So2 is soluable in water could I set up a duct fan over my foundry to pull the fumes into some vent ducting, then ....... ......I've heard of people collecting the stuff, but I haven't come across any info if it can be a simple process.



If you do have your heart set on making sulfuric acid, this may be of use to you.

I read this book about ten years ago, and just picked it back up because of some of the chemicals he made in it that are/can be used in refining.

Personally, a trip to the hardware store seems so much more practical. But, since it seems you are wanting to use what you have, maybe this could help shed some light.







Good luck to you sir


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## grizzlygremlin (Jan 11, 2016)

I'm on a few gold forums, and you guys are by far the most knowlegable people out there. Thanks for all the great advice!


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