Bioleaching arsenopyrite and other sulphide based ores.

[Mad Machinist]

Another one that deserves it's own thread.

As a continuation of what started in another thread:

Mad Machinist:

This MIGHT be the Grail for arsenopyrite. It seems during the bioleaching process both ferric arsenate and ferric hydroxide are created. These two substances will react together starting rather quickly to form scorodite, which effectively locks up the arsenic rendering it stable. As time goes by more of the arsenic is locked up rendering it stable.

I need to do more research on exactly how this happens. I'll post up more as I find it.
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SaltwaterServr:

https://www.researchgate.net/publica...ction_A_Review

I've been reading on it all day. It looks like our best bet for locking up the arsenic and avoiding having to deal with any sulfide gas products due to roasting.

Google this article: Gold recovery from a refractory pyrrhotite ore by biooxidation

From what I can tell, in the solid/liquid separation stage they dump lime into the bio-oxidized solution and it locks up the arsenic and turns the sulfur to gypsum.

From the one article, it looks like a residence time of 7 days was getting you almost 85% of the gold as long as you do a downstream cyanide leach process.

I wonder if chlorination and zinc digestion would work at the leaching and precipitation phases since I'm not keen on working with cyanide.
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Mad Machinist:

I spent some time talking to our environmental people today and the information I was given was eye opening to say the least.

The whole purpose of this is to find a better way to do this and paint us in an "environmentally friendly" light. And to shove all the eco lies straight up there arses sideways. And further research has shown me that the ferric arsenate/ferric (oxy)hydroxide method is the EXACT process that the EPA uses to remediate arsenic Superfund sites. Research has also shown me that this is one of the processes that is used to remove arsenic from municipal water supplies and the resultant product is then interned at the local landfill. As the ferric hydroxide crumbles down, it exposes fresh surfaces to react with the ferric arsenate thus further reducing the amount of available arsenic until it is all locked up. So the longer they are together, the less toxic the arsenic becomes.

I am starting to think that this could be used by us to "remediate" all the low grade arsenopyrite tailings out there, thus removing on more part of the "toxic legacy" of mining.

Don't let the eco freaks fool you. Take a look at the whole Lake Combi fiasco. They ARE NOT against mining when they are the ones who will benefit from it monetarily. They simply re-term the mining with words like remediation and clean up.
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SaltwaterServr:
https://www.researchgate.net/publica...ction_A_Review

I've been reading on it all day. It looks like our best bet for locking up the arsenic and avoiding having to deal with any sulfide gas products due to roasting.

Google this article: Gold recovery from a refractory pyrrhotite ore by biooxidation

From what I can tell, in the solid/liquid separation stage they dump lime into the bio-oxidized solution and it locks up the arsenic and turns the sulfur to gypsum.

From the one article, it looks like a residence time of 7 days was getting you almost 85% of the gold as long as you do a downstream cyanide leach process.

I wonder if chlorination and zinc digestion would work at the leaching and precipitation phases since I'm not keen on working with cyanide.

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Mad Machinist:

Still have more reading to do to understand the process fully. I've been on Research Gate a lot along with JSTOR. I'm starting to think this may not be to bad to set up on a small batch type system using concentrated ore.

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SaltwaterServr:

You have much experience with floatation for making cons?

It seems like the same basic process we use in marine biology to remove dissolve proteins from the water column. Bubble it up using a venturi water pump or assisted with an air pump and away it goes.

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This should bring us current.


If we can do that, heck, I think we've got a dang good ecologically friendly-enough small batch system.

 

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[Mad Machinist]

SaltwaterServr,

Yea I have quite a bit of experience with flotation cells. But I don't know if a full on flotation cell, along with the added costs and chemicals, would be necessary.

Recovery of the PM's can be accomplished through simple carbon in pulp (CIP) afterwards.

 

[SaltwaterServr]

I've read about floatation, CIP/CIL, etc, but for me it's only academic experience at this time. I've never seen any of it run other than a floatation cell videos on youtube.

 

[Mad Machinist]

The specific gravity of arsenopyrite is 6.1. Most host rock is going to be in the 2.0-3.0 range. So this leads me to believe that a standard shaker table could be adjusted to provide some concentration of the sulphides.

 

[SaltwaterServr]

The specific gravity of arsenopyrite is 6.1. Most host rock is going to be in the 2.0-3.0 range. So this leads me to believe that a standard shaker table could be adjusted to provide some concentration of the sulphides.

I was figuring on building a long Tom sluice with corduroy carpet to catch the heavies and let the quartz wash out. My millsite has water and I'll have a generator, but I don't trust the snow diggers out there in the winter that might come across the shack. Idiots will try to tear down anything that they think has relics or artifacts in it to take home with them.

From my reading, looks like H2SO4 to get the pH down under 2 for the optimized environment for the bacteria. Carbon also seems a limiting factor in their growth. The stirring should be plenty for aeration.

What are you coming across in how they pull out the ferric arsenic compounds before leaching process starts?

 

[Mad Machinist]

Wifey is still shopping so I am being lazy for once.

From what I get on the arsenic and the rest of the sulphides is that they are dissolved in the water and are put through a thickener tank to separate the solids out. Then it is processed through limestone to reduce he acidity to allow the ferric arsenate and ferric (oxy)hydroxide to form.

 

[SaltwaterServr]

Wifey is still shopping so I am being lazy for once.

From what I get on the arsenic and the rest of the sulphides is that they are dissolved in the water and are put through a thickener tank to separate the solids out. Then it is processed through limestone to reduce he acidity to allow the ferric arsenate and ferric (oxy)hydroxide to form.

Came across that about 10 minutes ago. The residence times seem to be all over the place, but 7 days should do it for us. 7 tanks running, one per day switching out provided you're taking enough ore out of the ground. Or fill one container with concentrates and let it run a week.

Probably need to inoculate a new batch of ore from an old batch's solution. You could also hang a new piece of ore into the old tank about day 5 to let it get a colony growth on it, then transfer it to the new batch.

You could also just grow a batch and inoculate each time. ATCC.org has the pure strains of the bacteria species we need. T. thiooxidans is only $60 for a pure strain.

Once a tank is done running, drain the solution and wash the solids once. Run that water and solution into a tank holding powdered limestone. Let the reactions take place over a few days. The ferrous oxides should be heavier than the calcium compounds and settle out at the bottom.

Now what in the world are we going to do with the neutralized solution

 

[Mad Machinist]

One thing at time. No need to worry about the neutralized solution just yet. Still a lot to be done before we get to that stage.

 

[Mad Machinist]

Change of plans today. I will be doing a lot of research today since I am stuck at home dealing with a snake bit pup.

 

[Mad Machinist]

Saltwaterservr,

From reading a whole lot of papers, I don't think we will be able to get around the flotation thing. With the recovery efficiencies of a finer grind for flotation and the increase in the speed of the leaching with a finer grind, I think we are kinda stuck with using the sodium isopropyl xanthate in a floatation cell in order to recover as much suphide material as possible.

On a plus side, I do think that the bioleaching bacteria would break down the xanthate since it contains sulfur but the question remains what would the xanthate turn into and is it toxic.

Some info from 911 metallurgist for everyone who is following this.

https://www.911metallurgist.com/blog/category/flotation

 

[SaltwaterServr]

One thing at time. No need to worry about the neutralized solution just yet. Still a lot to be done before we get to that stage.

Hopefully your pup recovers quickly.

Look at fluidized bed reactors. We use them in biology for culturing non-flocculating substrate-dependent bacteria and other larger microscopic organisms. No moving parts other than an air pump.

I think the stirring isn't giving enough gas exchange at the gas/fluid interface on the tanks therefore they're not able to go higher than 10% of solids by volume. Pumping air in would give an ample supply of CO2 and O2 as necessary. If the tank is well insulated with a couple of wraps of rock wool, temperature variations would be negligible.

 

[SaltwaterServr]

Saltwaterservr,

From reading a whole lot of papers, I don't think we will be able to get around the flotation thing. With the recovery efficiencies of a finer grind for flotation and the increase in the speed of the leaching with a finer grind, I think we are kinda stuck with using the sodium isopropyl xanthate in a floatation cell in order to recover as much suphide material as possible.

On a plus side, I do think that the bioleaching bacteria would break down the xanthate since it contains sulfur but the question remains what would the xanthate turn into and is it toxic.

Some info from 911 metallurgist for everyone who is following this.

https://www.911metallurgist.com/blog/category/flotation

Quick look, if the bacteria can attack the sulfur, you'll liberate the Na which would combine with additional OH in the tank, I think. Might mess with pH a little. The CH3 groups would get utilized as a carbon source. A wash or two of the concentrates should be fine to remove enough to not have to worry about it. I haven't seen much in my research that shows an intermediary step of washing before biological tank introduction.

Looked up the MSDS. It formes CS2 which can spontaneously combust. However, that's exactly what our little bacteria would snack on all day. Not considered a hazardous substance, requires no special disposal.

 

[Mad Machinist]

My pup will be ok. Been on and off the phone with the vet since I am an hour away. Vet said if he is still breathing after this long he should be fine. I hit him with 50 mg of Benadryl as soon as I realized he was bitten. Vet said that was pretty much the same thing they would have done.

I did one of these a little bit ago because the gravity separation thing didn't dawn on me.

Yea, it needs to be that big. It is a fluid bed so to speak. Put a mineral jig on the output of the ball mill and the sulphides will sink to the bottom for further processing.
https://www.911metallurgist.com/blog/ball-mill-discharge-spiral-trommel-screen

Mineral jig would go under the screen with the oversize being returned to the rod/ball mill for further grinding.

 

[solarsmith]

very recently I had a ton of gold ore with an assay of 17 grams per ton gold (all in pyrite) run on a sluice . then I had the cons from the sluice assayed and it was 2 grams per ton gold. sluicing hard rock sulfide gold ore that has no free milling gold is counter productive. Bryan in Denver Colorado.

 

[Mad Machinist]

very recently I had a ton of gold ore with an assay of 17 grams per ton gold (all in pyrite) run on a sluice . then I had the cons from the sluice assayed and it was 2 grams per ton gold. sluicing hard rock sulfide gold ore that has no free milling gold is counter productive. Bryan in Denver Colorado.

Brian,

Yea, sluicing sulphide based ores won't work. But with the mineral jig, it would work. It would all depend on the ragging used in the mineral jig. Sulphides were separated out back in the day in this very way to prepare the ore for cyanidation.

The whole point of this is to try and get away from using any chemicals, thus added cost in materials and disposal fees, to make smaller deposits profitable for the little guy. Yea there is the added cost for additional equipment, however, equipment can be moved and used again and again. where as the chemicals are a one time use thing. And I do believe the crushing circuit could be set up on a trailer to minimize the footprint at the mine thus reducing reclamation costs.

I still can't believe the mineral jig didn't dawn on me with the gravity separation thing. I work on and fabricate mining equipment everyday for a living so I kinda deserve the Picard face palm.

The only problems I see at this point is the ball mill. Used ones are pretty clapped out and new ones are WAY out of the price range of most. I'm working on that though. It will take some welding and machine work, but I have a plan for a ball mill.

 

[Mad Machinist]

Quick look, if the bacteria can attack the sulfur, you'll liberate the Na which would combine with additional OH in the tank, I think. Might mess with pH a little. The CH3 groups would get utilized as a carbon source. A wash or two of the concentrates should be fine to remove enough to not have to worry about it. I haven't seen much in my research that shows an intermediary step of washing before biological tank introduction.

Looked up the MSDS. It formes CS2 which can spontaneously combust. However, that's exactly what our little bacteria would snack on all day. Not considered a hazardous substance, requires no special disposal.

If you can handle the chemistry side of this, I'll take care of the machinery side. My chemistry skills are ok, but not great. I am geared more towards the mechanical side if things like machining, welding, and millwrighting.

 

[SaltwaterServr]

I'll do my best on the Chem side. Minored in polymer chemistry in college but this is a lot of inorganic hydrometallurgy. I spent my college summers welding and as a fitter in my dad's company building material conveying systems and aggregate plants.

 

[SaltwaterServr]

From what I can tell, we'll need a grind size of 80% <75 microns for effective leaching. I'll have to get deeper into it to see if we can do chloride leaching or if it's going to have to be cyanide.

 

[911Met]

hi guys, run your situation by all those mineral processing https://www.911metallurgist.com/forum/ engineers.

 

[Mad Machinist]

From what I can tell, we'll need a grind size of 80% <75 microns for effective leaching. I'll have to get deeper into it to see if we can do chloride leaching or if it's going to have to be cyanide.

I'm thinking that if we can maintain at least an 80% concentration of sulphides in the bioleach tanks then we wouldn't need any other type of leach. I am also thinking that after the bioleach, what is left could then be smelted into a dory bar and then further refined.