Bioleaching arsenopyrite and other sulphide based ores.

[SaltwaterServr]

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.

What I've read you'll still have 50-55% by weight and an unknown amount by volume of the reacted solids. With that much left over to still smelt, we might end up losing a lot of gold as the iron and magnetite will sinter pores closed, trapping it in the slag. It's on the nano particle level, but there's a lot there to be lost or gained.

Let me do some hunting around to see if I can find some production circuits using bioleach. I can't think of any modern circuit I've seen diagramed that didn't have a leach/recovery in it somewhere.

Got the waste effluent worked out, to a degree, thanks to reading some of the books I haven't yet waded through here. We'll probably be able to use the same fluid 3 or 4 times, depending on mercury content of the rock. Once it comes off of the solids in the bioleach tank, hit it with powdered limestone to neutralize it. It can be then used again in the bioleach tank. Other than that, it'll be limestone, lime, off to disposal.

 

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[Eu_citzen]

Not really a miner here, but...

I know Boliden in Sweden uses Bioleaching. But darn, I forgot how they did it, to many years ago.
Believe they bioleached it 2-3 times, in separate tanks. If they used different cultures? No idea. They may have a patent for it.

Otherwise, in small-scale leaching I've been experimenting with hydrogenperoxide as a leaching agent.
Using the idea of adding calcium, perhaps it'll end up quite environmentally friendly. But if it's economical or even practical? No idea, yet.

 

[Mad Machinist]

What I've read you'll still have 50-55% by weight and an unknown amount by volume of the reacted solids. With that much left over to still smelt, we might end up losing a lot of gold as the iron and magnetite will sinter pores closed, trapping it in the slag. It's on the nano particle level, but there's a lot there to be lost or gained.

Let me do some hunting around to see if I can find some production circuits using bioleach. I can't think of any modern circuit I've seen diagramed that didn't have a leach/recovery in it somewhere.

Got the waste effluent worked out, to a degree, thanks to reading some of the books I haven't yet waded through here. We'll probably be able to use the same fluid 3 or 4 times, depending on mercury content of the rock. Once it comes off of the solids in the bioleach tank, hit it with powdered limestone to neutralize it. It can be then used again in the bioleach tank. Other than that, it'll be limestone, lime, off to disposal.

Yea, your right on that one. Got too much on my mind right now with the other equipment design.

 

[Mad Machinist]

Not really a miner here, but...

I know Boliden in Sweden uses Bioleaching. But darn, I forgot how they did it, to many years ago.
Believe they bioleached it 2-3 times, in separate tanks. If they used different cultures? No idea. They may have a patent for it.

Otherwise, in small-scale leaching I've been experimenting with hydrogenperoxide as a leaching agent.
Using the idea of adding calcium, perhaps it'll end up quite environmentally friendly. But if it's economical or even practical? No idea, yet.

Economical and practical is the problem everywhere when it comes to small scale mining. Not much research has been done in that area. It is basically up to all of us to try it and trade notes to find a way to get 'er done in an environmentally friendly way.

The big problem is that most of the easy, near surface oxide ores have been depleted, with the exception of the small pockets. SO now we are going to have to deal with the sulphide based ores that more often that not chew up any kind of leaching agent through hreaction with the sulfur contained therein.

I hope all this work is worth it because some of this is a real pain to figure out.

 

[Eu_citzen]

Economical and practical is the problem everywhere when it comes to small scale mining. Not much research has been done in that area. It is basically up to all of us to try it and trade notes to find a way to get 'er done in an environmentally friendly way.

The big problem is that most of the easy, near surface oxide ores have been depleted, with the exception of the small pockets. SO now we are going to have to deal with the sulphide based ores that more often that not chew up any kind of leaching agent through hreaction with the sulfur contained therein.

I hope all this work is worth it because some of this is a real pain to figure out.

I hear ya, will try to remember to post updates on that leaching-agent experiment.
Usually I work more with the prospecting bit of things, but a recent find with 14% copper and 10 ppm silver got my interest to experiment a bit.
You guessed it, sulphides.

I think it'll be worth it. If nothing else, its knowledge gained.

 

[Mad Machinist]

I hear ya, will try to remember to post updates on that leaching-agent experiment.
Usually I work more with the prospecting bit of things, but a recent find with 14% copper and 10 ppm silver got my interest to experiment a bit.
You guessed it, sulphides.

I think it'll be worth it. If nothing else, its knowledge gained.

Post it up and we'll figure it out one way or another.

 

[Mad Machinist]

Ok, back at this now things are lightening up a little. Today was a "lazy day" as I am recovering from a mild bought of pneumonia.

www.sciencedirect.com/science/article/pii/S0892687512002695

It would appear that rotating drum reactor would be more efficient for our purposes as it allows a higher pulp content and still effectively oxides the arsenic and other sulfides.

Perhaps this combined with the eco-goldex is where we need to go. Wonder if anyone would think something is up if I bought a whole pallet of aluminum foil at Costco?

 

[SaltwaterServr]

Ok, back at this now things are lightening up a little. Today was a "lazy day" as I am recovering from a mild bought of pneumonia.

www.sciencedirect.com/science/article/pii/S0892687512002695

It would appear that rotating drum reactor would be more efficient for our purposes as it allows a higher pulp content and still effectively oxides the arsenic and other sulfides.

Perhaps this combined with the eco-goldex is where we need to go. Wonder if anyone would think something is up if I bought a whole pallet of aluminum foil at Costco?

Tell 'em its for your hats, and if they hear the voices too. I don't see a problem.

You got your pneumonia, and I got my shingles.

For the bioreactor, I can see a rotating drum made out of 55 gallon barrels considering how acidic the bugs like it. IIRC, its about a pH of 2, give or take? That'll limit us to plastics. I'll have to put some thought into it. Maybe put them at a 45 degree angle so you can get greater than 50% fill without worrying about leakage. The rotation rate doesn't have to be really all that high either. Hmmm.

I have more experience with fluidized bed systems so I might go to that for a start. Use air to mix it all to keep anoxic zones from forming. No moving parts other than the air pumps and you can use air lifts through pipes to keep the drums mixing with each other, or not if it turns out not to work.

 

[Mad Machinist]

Tell 'em its for your hats, and if they hear the voices too. I don't see a problem.

You got your pneumonia, and I got my shingles.

For the bioreactor, I can see a rotating drum made out of 55 gallon barrels considering how acidic the bugs like it. IIRC, its about a pH of 2, give or take? That'll limit us to plastics. I'll have to put some thought into it. Maybe put them at a 45 degree angle so you can get greater than 50% fill without worrying about leakage. The rotation rate doesn't have to be really all that high either. Hmmm.

I have more experience with fluidized bed systems so I might go to that for a start. Use air to mix it all to keep anoxic zones from forming. No moving parts other than the air pumps and you can use air lifts through pipes to keep the drums mixing with each other, or not if it turns out not to work.

Feeling better but not 100% yet.

Yea with the acidic nature of the mix we are stuck with either plastics or stainless. I wonder if a steel reinforcing cage out of angle would be enough to hold one of those tractor supply water tanks together?

I spent most of the weekend reading up on gravity separation of the sulfides. After a lot of reading, I really don't see any advantages of using anything other than a run of the mill mineral jig with ragging around a 3-3.5 specific gravity. Gets around the chemicals used in flotation so its more environmentally friendly as those chemicals won't have to be dealt with later. Lots of places using the old school stuff again to make things cheaper.

Need to check on using a water spray in an impact mill. Definitely don't want dust flying around if one is processing arsenopyrite.

 

[SaltwaterServr]

Feeling better but not 100% yet.

Yea with the acidic nature of the mix we are stuck with either plastics or stainless. I wonder if a steel reinforcing cage out of angle would be enough to hold one of those tractor supply water tanks together?

I spent most of the weekend reading up on gravity separation of the sulfides. After a lot of reading, I really don't see any advantages of using anything other than a run of the mill mineral jig with ragging around a 3-3.5 specific gravity. Gets around the chemicals used in flotation so its more environmentally friendly as those chemicals won't have to be dealt with later. Lots of places using the old school stuff again to make things cheaper.

Need to check on using a water spray in an impact mill. Definitely don't want dust flying around if one is processing arsenopyrite.

On my chain mill I use a series of buckets with a leaf blower acting as a vacuum. I run it on idle and it takes care of the dust, capturing it in the buckets. I do have a little more coming out at the end, but it's 10' downwind from where I'm putting rock into the crusher. We might look at something like that. A small blower with a bag or three attached could act as dust collector, or pick one up from Harbor Freight.

I'm all for a mineral jig rather than a float cell bank, even if we lose some of the metals. From both the standpoint of not having to deal with the chemicals in the float water, and from the simplicity of design. At least from a cursory glance, there seems to be fewer moving parts in the mineral jig and possibly less power consumption.

 

[Mad Machinist]

Yea, it's kind of a toss up between a mineral jig and a shaker table. I think both could be tuned to work rather well. Gekko makes ceramic ragging with specific gravities of 1.6 up to 5. Both would cost about the same but the jig would be easier to build. And the jig would have a higher throughput.

But on the flip side, if an impact mill was used, a shaker table would work just fine. Six of one, half a dozen of the other. Guess it would depend on how much ore there was to process and the grade.

So far I'm thinking jaw crusher for primary break down to either 1/2" minus or 1/4" minus with secondary crushing with an impact mill. Toss in the dust collection, maybe a standard Shop Vac with a HEPA filter. Then feed to either a mineral jig or a shaker table.

I still need to think and research the mineral jig vs. shaker table thing. Trying to maintain maximum flexibility with minimal outlay of cash.

 

[kurtak]

Perhaps this combined with the eco-goldex is where we need to go.

Hi Mad Machinist & SaltwaterServr

SaltwaterServr - I read your post this morning on GRF & posted a reply - your post (on GRF) prompted me to check back in here on TN - Glad I did

Concerning the Eco-Goldex product - BEWARE of snake oil salesmen !!! --- some of us on GRF have tried the goldex product (including me) & we have discussed it "extensively" over on GRF --- it IS NOT all it is cracked up to be !!!!!!!

First of all - their claim that it is more "eco friendly" (&/or safer) then cyanide is flat out NOT TRUE --- the fact is IT IS CYANIDE & NEEDS to be treated with EXACTLY the same respect as cyanide - once it is put to work in the leaching process

What is true - is that BEFORE it is put to work for leaching - then & ONLY then is it safer then cyanide !!!!

The "active" ingredient in the goldex product is potassium ferrocyanide --- because of the iron complex (bonding) with the cyanide it is a safe complex of cyanide & is in fact used in the food industry such as an anticaking agent in table salt & in wine production etc. etc.

In other words it is actual a food grade additive that is actually consumable --- as long as the iron bond is not broken !!!

What that means - is that in its dry form - it is safe for shipping, handling, & storage & therefore does not require any hazmat regulations &/or permitting for shipping, handling or storage --- as the dry product that are associated with actual potassium cyanide

The problem is - that in order for potassium ferrocyanide to work for leaching gold --- the iron bonging NEEDS to be broken --- & once it is - you then have potassium cyanide - which is why it will then leach gold

What eco-goldex has done - is mix the potassium ferrocyanide with some other chemicals (its a list of something like 5 or 6 added chemicals) one of (or some of) which act to break the iron bond "when you dissolve" the goldex product --- thereby freeing the "potassium cyanide" for leaching the gold

So - in other words - once you dissolve it to leach your gold - what you have is a solution of "potassium cyanide" along with some other added chemicals

These "added chemicals" can (& most likely will) also cause problems with the recovery of your gold from the solution (which has been discussed on GRF) what has not yet been discussed is whether or not these additive in the goldex also pose a problem with treating the waste for proper disposal

So - here is the thing - you DO NOT need these added chemicals to break the iron bonding of the potassium ferrocyanide in order to "free" the potassium cyanide so it is able to leach your gold

All that is needed to break the iron bonding is provide UV exposure to the potassium ferrocyanide during the leaching process - this can be done by natural sun light exposure - or by providing artificial UV light exposure

In other words - you do not need the eco-goldex product with its chemical additives to leach your gold --- you can use straight potassium ferrocyanide - which again has NO hazmat regulation &/or permits needed when it come to the shipping, handling & storage - as opposed to actual cyanide

So - the reality is two fold (1) why use the goldex - with its added chems - which by the way reduces the active ingredient (potassium ferrocyanide) to about (plus or minus) 20% --- when you can use the straight (pure form) of potassium ferrocyanide instead - and (2) when the iron bond is broke (in order for it to work for leaching) it is in fact "potassium cyanide" & NEEDS to be treated with the SAME respect as "potassium cyanide"

Make no mistake about that - in fact - from the eco-goldex instructions --- "have your lab technician treats eco-goldex reagent the same way as cyanide as eco-goldex reagent has the same operation conditions and procedures as cyanide"

And then they add --- "except eco-goldex is low-toxic and eco-friendly." --- don't be fooled by that last statement - it is ONLY less toxic & eco-friendly BEFORE it gets used as a leach !!!

Kurt

 

[Mad Machinist]

Kurt,

Thank you for the heads up. I haven't really spent a lot of time looking into the eco-goldex. I kinda figured with it containing potassium ferrocyanide that at some point it broke down into one form of cyanide or another.

I still working out the equipment side of things right now so actual use is a little ways off.

 

[SaltwaterServr]

Hi Mad Machinist & SaltwaterServr

SaltwaterServr - I read your post this morning on GRF & posted a reply - your post (on GRF) prompted me to check back in here on TN - Glad I did


Kurt

Haven't been over there today, but I did read that entire thread on Goldex a few times, including the post showing the constituents and came away with that it's just fancy marketing. Buy the potassium ferrocyanide and move on with life. Put in a bubbler, keep that pH at 11, and go to town.

Like MM said though, we're a little bit off from that step yet.

 

[Mad Machinist]

Haven't been over there today, but I did read that entire thread on Goldex a few times, including the post showing the constituents and came away with that it's just fancy marketing. Buy the potassium ferrocyanide and move on with life. Put in a bubbler, keep that pH at 11, and go to town.

Like MM said though, we're a little bit off from that step yet.

Found a way to destroy the cyanide when we are done with it. Limit on discharge of cyanide is at 1 ppm. This process reliably reduces the discharge to 0.1 ppm. I'll send you a pm on it tommorrow, I need some sleep.

 

[kurtak]

Found a way to destroy the cyanide when we are done with it. Limit on discharge of cyanide is at 1 ppm. This process reliably reduces the discharge to 0.1 ppm. I'll send you a pm on it tommorrow, I need some sleep.

Mad Machinist

Per the underlined - I assume you mean a PM to SaltwaterServr - I am interested in what you came up with as well - I am wondering if its a different method then what I am aware of or not - so do you mind sharing what you came up with on the open forum --- it would be good for others following along to know as well

I am aware of two methods of destroying cyanide - one is chemical destruction the other uses an electrolytic cell

The chemical destruction uses sodium hypochlorite (bleach) in the first step which converts (oxidizes) the more toxic cyanide to less toxic cyanate & then sulfuric acid is used in the second step to oxidize the cyanate to carbon dioxide and nitrogen - pH plays a part in each step along with specific ORP being maintained for a specific time at each step

Destruction using an electrolytic cell has some real benefits because you use the same electro cell that is used as a winning cell to win your gold back from the cyanide solution

Its a "flow through" cell meaning the solution is pumped through the cell - first to win your gold - then to destroy your cyanide

The other benefit is that when you use it as a winning cell - once the gold is won back from the solution - it frees the cyanide (to a point) that it can be reused again for leaching --- I say to a point because depending on various factors depends on how much reuse of the cyanide (after winning your gold) you get before needing to destroy the cyanide

With out going into to much detail on the actual design/set up of the cell - the basics of it are that you first run it as a winning cell wherein you pump the solution through the cell with your positive lead hooked to the anode & your negative lead hooked to the cathode --- then to use it to destroy the cyanide you simply reverse the polarity - so what was the anode becomes the cathode - & what was the cathode becomes the anode - & you run the solution back through it to destroy the cyanide

So the up side of the electro cell is (1) winning your gold back from solution (2)to a point reuse of your cyanide solution (3) destruction of the cyanide when needed

The down side to the electro cell is initial cost of set up (its not cheap)

So though it may not be in your starting budget of what you & SaltwaterServr are working on - it is certainly worth looking into for future plains

The cell can be used for winning from acidic solutions as well as from cyanide solutions

Kurt

 

[Mad Machinist]

Kurt.

The electrowinning cell was food for thought at a later date. Would be a nice addition I think.

For the cyanide destruction, it is as follows.

Solution pH is raised to a specified pH. Sodium hypochlorite is added to achieve a specific ORP and reacted for a specified period to oxidize the cyanide to cyanates.

Solution pH is then lowered to a specific level and additional sodium hypochlorite is added to achieve a specific ORP. Solution reacts forward a specified time and oxidizes the cyanates to potassium bicarbonate and nitrogen.

Method is commonly reputed to drop cyanide levels to less than 0.1 ppm.


As you can see, I am very hesitant to post specifics due to the fact people cannot follow directions and this stuff is nothing to goof around with. If you want I'll pm you the link where I found this.

 

[SaltwaterServr]

Yeah, I've got some links too, but I'll shoot them via PM.

***FOLKS, DO NOT EFF AROUND WITH THIS STUFF***


You make a mistake with hydrochloric acid and peroxide, you'll end up hurting yourself and others pretty severely. You make a mistake with cyanide you end up killing people. With cyanide there is no middle ground and no second chances.

 

[kurtak]

SaltwaterServr

Thanks for the PM & link

Mad Machinist

Yes - please send me a PM - IMO the more info one is armed with the better !!!

Kurt

 

[kurtak]

Mad Machinist

In the last PM I sent you I wanted to proved I picture of the Hydroxocobalamin & EDTA I talked about - but there was no option to post a pic

So here is a pic of those supplements - the brand name is Source Naturals - you can order them on line

Kurt