Processing Sulphide Based Ores

[Mad Machinist]

Except for arsenopyrite. We'll leave that one out for now as it gets real complicated real quick. And if you mess up, the gold is gone.

In a serious effort to make small scale mining more "environmentally friendly" and stuff it up the eco's rear ends, I've been doing a lot of research on this. So here ya go.

Activated charcoal (AC) is very effective at removing the sulfur dioxide that is created when roasting sulfide based ores. And as we all know, the EPA has been on a rampage against the powerhouses because of it. So they can kiss my arse after this one.

Carbon Air Filters - Carbon Filter Selection

So a 1" thick bed of AC will remove 80% of the existing SO2. So if there is 100 ppm of SO2 is present, 1 layer of AC will reduce it to 20 ppm. Add in multiple layers and the SO2 gets reduced even further. So a 5 layer system will reduce our hypothetical 100 ppm of SO2 to 0.032 ppm. Filled columns work even better, but I am trying to find some hard numbers in the research that everyone will understand.

Now I know some of you will say the AC will cost too much. So here is another answer.

http://acs.omnibooksonline.com/data/papers/1997_ii128.pdf

The SO2 combines with the oxygen in the AC to form sulfur trioxide. The AC can be washed with water which will remove the sulfur trioxide forming a dilute sulfuric acid. The sulfuric acid has market value so what was once a pollutant now becomes a profit stream.

The AC at this point can be dried, heated to reactivate, and reused until it falls apart.

More to follow. But for now.......

 

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[Mad Machinist]

Further research shows that a wet scrubber would work just as well, be cheaper and easier to build and maintain, would have less to go wrong, and would have no need for the AC as the water mist inside would cause a direct conversion of the sulfur dioxide to dilute sulfuric acid. Working on a drawing now.

 

[kcm]

Great post MM!! I had wondered long ago about using water mist as a pre-scrubber for the gases. Never did try to work through the process, however.

I would think using a set amount of water recirculated through until a sensor notifies that the water is of a certain acidic level. Then the water could be drained and fresh water added. The more simple the process, the better.

 

[Mad Machinist]

Here's some more info. And hopefully you all will start to understand why I am so big on knowing EXACTLY what is in your ore.

Calcium carbonate

The part we are concerned with as far as processing sulphide based ores is about half way down the page. It is a one to one reaction and with a little compressed air blown through the precipitate, it now converts from sulfur dioxide to calcium sulfate, better known as gypsum. Yes it is the same stuff that the sheetrock in your house is made of. So it can be either disposed of as construction waste at your local landfill or used for other purposes in you are so inclined.

I checked my local Tractor Supply and a 50 pound bag of lime is $2.99, less if bought in bulk through other Agriculture supply stores.

Considering how the eco freaks are trying to beat us into the ground over pollution, we would be rather stupid not to take advantage of a little chemistry to stick it to them.

For our purposes, a packed bed wet scrubber would work perfect, be cheap and easy to construct, and have great benefits in painting us as environmentally friendly.

A little picture of said scrubber. It would need to be made of plastic so the sulfur dioxide doesn't eat it away.

The lime could be mixed with the water and sprayed in directly (probably best) or it could be held in another container and the water circulated through.

 

[ClaimStake]

great stuff, I've thought about using a high pressure 3 or 4 inch blower with a 55 gal drum and a bubble screen at the bottom.

graphene would work even better than AC.

 

[Golden_Crab]

Ecofreaks will always freak because they are too stupid to comprehend any semblance of a logical concept based on facts and not their insecure ego based reality.

Good info here... lots of super rich sulfide ore belts exist on the east coast that remain untouched.

 

[gold tramp]

seems with all the modern leachant on the market, one could most likley do away with the roasting of the ores.

 

[Mad Machinist]

seems with all the modern leachant on the market, one could most likley do away with the roasting of the ores.

Yea they are close. But for right now it is out of reach for the little guy. And all the currently available leachants on the market get chewed up by the Sulphur in the ores.

Roasting is the cheapest way for the small guy as long as it is done in an environmentally friendly matter. Especially if the burner was setup to use some type of waste oil.

 

[Mad Machinist]

Still trying to figure out a way to use the waste oil side of this. The roaster in the video from Action Mining is priced at $13.5K. I understand that there are development costs and all that but that puts it out of reach for all but a few of the small guys, especially considering that it will only do 350 pounds per hour. And that is not based on a good roast, just how much material it would push through.

I have to admit though, that things like this really irritate me. Charging exuberant prices for things that are very simple. The heating elements in this are more than likely nothing more than Nichrome or Kanthal wire, from your standard pottery kilns, wrapped around a black iron pipe and set inside multiple layers of Kaowool insulation. For the price he wants for this he could have at least use a piece of stainless pipe which would be resistant to the sulfur dioxide created and last a lot longer.

Don't get me wrong everybody. I am not bashing this guy. I actually commend him for getting things like this out there. It's just when prices get too high very little action takes place.

 

[kenpodetector]

Good post nice gear but still very expensive for the micro miner. And honestly its all been done before. One thing lots of environmentally friendly companies are doing are using a "bug" or I should say bacteria to do the processing for them you might look into that. I been around this stuff for along time and I have a relative whom is essentially my best friend who is a Geologist I have gone up and down with this stuff lots of times and it always turns out its just not worth it for small / micro scale. When you get 35% out of your say your roasting and add up all the costs and time involved you still end up in the hole let alone anyone catches you doing it (not that they would) the issues with idiots like that. I know it sucks and I know you can get some gold back but when it all comes out in the wash as they say its not a very good financial proposition for a small miner.. Just my 2 cents.

 

[SaltwaterServr]

I wonder if you could just do a fluidized bed reactor using the AC? I need to read more on it too.

CIP is commonly in use for the big guys, I wonder if scaling down would work for us.

 

[Mad Machinist]

Good post nice gear but still very expensive for the micro miner. And honestly its all been done before. One thing lots of environmentally friendly companies are doing are using a "bug" or I should say bacteria to do the processing for them you might look into that. I been around this stuff for along time and I have a relative whom is essentially my best friend who is a Geologist I have gone up and down with this stuff lots of times and it always turns out its just not worth it for small / micro scale. When you get 35% out of your say your roasting and add up all the costs and time involved you still end up in the hole let alone anyone catches you doing it (not that they would) the issues with idiots like that. I know it sucks and I know you can get some gold back but when it all comes out in the wash as they say its not a very good financial proposition for a small miner.. Just my 2 cents.

Last I checked a couple of plastic 55 gal drums could be had for around $100.00. Probably less if you can find them used.

Some PVC pipe to resist the sulfuric acid, a pump to circulate the water, a few sprayers, and some media for the water and sulfur dioxide to condense on.

Nothing expensive, nothing super technical about this.

I'll be this could be easily built for under $500. Set it up as a "batch roast" of a few hundred pounds of concentrated material and your off to the races.

I know all about the "bug" style of leaching. Not even close to being viable for the little guy. We used it here for a little while and went back to leaching the oxide ore with sulfuric acid. It is cheaper, faster, and more effective.

The biggest cost with this is heating the ore. If that can be done through using a waste product, like used motor oil, then the costs get reduced significantly. I do know that an Air Force Gun Burner from an oil furnace can be modified to run used oil very cheaply. And we have successfully run a diesel engine on used motor oil after thinning 50/50 with offroad diesel and filtering down to 3 microns.

No "standard" solution exists for us, so it's time we think outside of the box.

 

[SaltwaterServr]

I bet you could do it for less than $500. I'd go bigger scale, multi-pass. I would look at using those big square cage polyethylene tanks that are dang cheap if you get me used. Quite a few large car washes get their detergents in those. I was looking at picking some up here around Phoenix and they were less than $75 each.

An alternative would be to use small with air tight lids. Plumb the air lines in parallel. Use either that matting they use for evaporative swamp coolers, perlite, or coco coir as your filter media.

The heat is still the road block though. I'm in an area of the desert i can collect dead wood for 100 square miles but that's going to be cost and time prohibitive eventually. Best practice would be a two or three shelf kiln so that 2/3rd of the roasted ore is helping to heat the new 1/3 batch.

 

[kcm]

Last I checked a couple of plastic 55 gal drums could be had for around $100.00. Probably less if you can find them used.

It's funny...I remember reading in one of my wife's magazines (Mother Earth News...for the gardening articles, ONLY!) about this guy in California who was getting empty 55-gal. plastic barrels by the hundreds for free, and how there were thousands more just sitting there waiting to be claimed. Shoot, haven't seen a free barrel (plastic OR steel) in so many years I can't even remember! Around here, used plastic is going for about $25-$35 each. Steel is slightly less.

 

[kcm]

I bet you could do it for less than $500. I'd go bigger scale, multi-pass. I would look at using those big square cage polyethylene tanks that are dang cheap if you get me used. Quite a few large car washes get their detergents in those. I was looking at picking some up here around Phoenix and they were less than $75 each.

An alternative would be to use small with air tight lids. Plumb the air lines in parallel. Use either that matting they use for evaporative swamp coolers, perlite, or coco coir as your filter media.

The heat is still the road block though. I'm in an area of the desert i can collect dead wood for 100 square miles but that's going to be cost and time prohibitive eventually. Best practice would be a two or three shelf kiln so that 2/3rd of the roasted ore is helping to heat the new 1/3 batch.

I was outside earlier and passed about 3' away from a mirror. The sun hit my face, fortunately not blinding me. However, if I had stayed there for any length of time, it would have caused serious burns. Why not put the sun to work for ya'? Instead of buying fuel, could invest in some large, concentrating mirrors that will build up far too much heat, and then have an automatic vent that will prevent the heat from being excessive.

I know it would only "work" in the daytime and on sunny days, but isn't that what you guys have most in the desert?

Instead of a barrel (steel), I'd use 1/4"-wall steel pipe or steel plate. Make it so that it can be well-sealed. Then set up an air-scrubber system that will circulate the air and scrub the gases.

Load up your batch of ore, let it 'cook' for a pre-determined amount of time, then crush and pan, or however you want to proceed.

...Guess a lot depends on just how "small scale" an operation is. Could probably make a trailer-mount unit that could be towed home every day.


EDIT: Sorry. Good idea, but not practical. My mind has been all over the place lately - everywhere but on mining. But, it's there, so might as well leave it.

 

[Nitric]

I'm still fairly uneducated(?) in this area......But would it be beneficial or helpful to run a 4 or 6 inch plastic pipe horizontal about 6ft or longer with a spray bar/mister running along the top of the inside with a little drop on the pipe to get the water or mix to flow to one end...The run off or out would then be y'd off at the end the liquid drops out into the recirculating system and the air runs out the top to the next phase. Almost like a Pre scrubber(?). To maximize the contact with the fumes as fast as possible.

I was thinking about this when thinking about how I was going to make some kind of air cleaner or filter for a fume hood. If I ever get that far. I still have a lot to learn! Before I start experimenting with mixing chems or cooking anything.

 

[Mad Machinist]

I bet you could do it for less than $500. I'd go bigger scale, multi-pass. I would look at using those big square cage polyethylene tanks that are dang cheap if you get me used. Quite a few large car washes get their detergents in those. I was looking at picking some up here around Phoenix and they were less than $75 each.

An alternative would be to use small with air tight lids. Plumb the air lines in parallel. Use either that matting they use for evaporative swamp coolers, perlite, or coco coir as your filter media.

The heat is still the road block though. I'm in an area of the desert i can collect dead wood for 100 square miles but that's going to be cost and time prohibitive eventually. Best practice would be a two or three shelf kiln so that 2/3rd of the roasted ore is helping to heat the new 1/3 batch.

Phoenix, huh? I about 4 hours east of you, over by the New Mexico line.

As a heat source, take a look on Craigslist there. Pottery kilns are going dirt cheap over there. Converting one to gas or oil fired is a simple deal. Throw in a pyrometer and manually control the fuel/air for temp and we're off to the races. I'm betting that the whole set up could be done under a grand for a "batch roast" setup.

Used motor oil is definitely NOT in short supply at my house. The boys truck and mine both take 8 quarts. The wife's car takes 6 and the Jeep takes 6. That's 5 gallons of oil for one round and that doesn't count the transmission, transfer case, and differential fluids. 16 quarts for my transmission alone. Yea, oil coolers get a little thirsty. A friend of mine breaks down Gold Wings for parts to sell, so there is some more.

And if I remember right, it is cheaper to get 100 lb propane cylinders filled than it is the little 20 pounders. Just have to go to a welding supply place.

 

[SaltwaterServr]

I was outside earlier and passed about 3' away from a mirror. The sun hit my face, fortunately not blinding me. However, if I had stayed there for any length of time, it would have caused serious burns. Why not put the sun to work for ya'? Instead of buying fuel, could invest in some large, concentrating mirrors that will build up far too much heat, and then have an automatic vent that will prevent the heat from being excessive.

I know it would only "work" in the daytime and on sunny days, but isn't that what you guys have most in the desert?

Instead of a barrel (steel), I'd use 1/4"-wall steel pipe or steel plate. Make it so that it can be well-sealed. Then set up an air-scrubber system that will circulate the air and scrub the gases.

Load up your batch of ore, let it 'cook' for a pre-determined amount of time, then crush and pan, or however you want to proceed.

...Guess a lot depends on just how "small scale" an operation is. Could probably make a trailer-mount unit that could be towed home every day.


EDIT: Sorry. Good idea, but not practical. My mind has been all over the place lately - everywhere but on mining. But, it's there, so might as well leave it.

The reaction chamber needs to be inert like HDPE (high density polyethlene or something similar) so that the reactions Mad Machinist is outlining for the lime/sulfur will be within the lime and sulfur solely. If you introduce metallic elements into the system you'll end up creating a whole different set of reactions not to mention degradation to the container itself.

The mirror system term you're looking for is "heliostat", that is a mirror system that tracks the movement of the sun and then redirects the reflection to a specific point. They work in places where there is very little cloud cover, (deserts) but not in areas where there's a lot of wind with sand (deserts) that ends up scouring the reflectors. Making a heliostat really isn't hard at all, I've got a plan for the tracking mechanism and construction of the reflectors at home.

With a heliostat you wouldn't heat the kiln directly, you usually heat a secondary sink such as oil or salt so that the residual heat can be held overnight. The oil or molten salts then are circulated around the target media. The use I had planned it for was a desalination plant.

 

[SaltwaterServr]

Phoenix, huh? I about 4 hours east of you, over by the New Mexico line.

As a heat source, take a look on Craigslist there. Pottery kilns are going dirt cheap over there. Converting one to gas or oil fired is a simple deal. Throw in a pyrometer and manually control the fuel/air for temp and we're off to the races. I'm betting that the whole set up could be done under a grand for a "batch roast" setup.

Used motor oil is definitely NOT in short supply at my house. The boys truck and mine both take 8 quarts. The wife's car takes 6 and the Jeep takes 6. That's 5 gallons of oil for one round and that doesn't count the transmission, transfer case, and differential fluids. 16 quarts for my transmission alone. Yea, oil coolers get a little thirsty. A friend of mine breaks down Gold Wings for parts to sell, so there is some more.

And if I remember right, it is cheaper to get 100 lb propane cylinders filled than it is the little 20 pounders. Just have to go to a welding supply place.

Heck yeah, you're right down the road. Wouldn't be a hop skip and a jump to run on over your way to knock some of this out sometime.

I wonder if you could hit some of the local oil change places and buy it off of them. Not sure if they have to pay to get it recycled or they get paid for it. Cut a deal with the manager/owner and see what you could do. Same with rental truck places. They'd more than likely have some they're ready to get rid of. You know them big diesels hold a good amount in 'em.

Back to the reaction vessels. I was thinking that stacking two barrels on top of each other is going to be problematic with respect to leaks. I know they make the barrels with threaded tops, not just the little ported ones, and if there is a coupler that would work great. However, if you've got to plastic weld two together it's going to be easier to mitigate leaks by putting several linked together through plumbing.

The threaded plastic barrels or snap top barrels are the way to go for us I believe. It gives us full and easy access to the misting system as well as the reaction media. You can see them on the right side of this picture.



I built three pretty large backyard hydroponic fruit and vegetable gardens together between 2013 and 2015. All of them either used drip or spray emitters. Even in a three or four tank system you'd only need a 900 gph 110v aquarium pump to run your misting system. Those things are designed to run in nasty salt solutions so a high/low pH wouldn't affect it too much. You can use 5/8" black irrigation line you pick up at Lowe's or Home Depot to bring in the water to the barrel interior.

I think you could get the smoke from the kiln pulling through the tanks by using an attic fan to pull the gases through the tanks. Hook a light dimmer switch or two on the electrical feed to slow down or max out the air flow.

I'm leaning toward using this sort of thing for the interior of the barrel. You can cut it down if necessary with a razor knife, roll it up, and stuff it into the barrels no problem. The plastic stuff won't break down like the wood or coco coir can.

4 ft. x 101 ft. Polypropylene Single Net Excelsior Erosion Control Blanket-17687-4-101 - The Home Depot

Ton of surface area, cheap to use and inert as well. I'd bet we can find it a lot cheaper if we did more hunting around the internets. Grainger probably has it.

If the gypsum builds up on the matrix pretty thick, run it between two rollers to crush it out as a powder or just drop it off at the dump.

The bottom of the barrels each need a drain of course, gravity fed only. Have to be careful about having too much air flow pulling the water up against the resistance of gravity. In reality, you don't need much airflow through the tanks to get the kiln exhaust coming through them. If its an issue, I would say the first tank (I envision three) would use a heavier water flow than number 2 and 3 so that the pull of the attic fan doesn't cause excessive evaporation, which is certain to occur.

The exhaust gasses coming out of the kiln are going to be too dang hot for PVC to handle straight-away so they'll need to be cooled. Finding something that can handle 600+ degrees and cool it with water is the first step here.

Honestly, you've already nailed down the hard part, the chemistry of the reduction process. The rest is just technical stuff that can be figured out by trial and error.

Oh, we'll be able to tell if the system isn't working by installing an inline pH meter. Large hydroponic farms have them and they adjust their nutrient solutions in real time. For us, we just need a monitor to see if the water is getting too acidic.

 

[Mad Machinist]

The barrels are HDPE, nothing exotic. Grab a butane torch and some HDPE plastic rod from Harbor Freight and weld that stuff. It's really easy and good training for the real thing.

The exhaust fan is a specific one. I'll find it and post it up tomorrow. I have to 8 week old Rottweilers thinking my toes are chew toys right now.