Using SSN Leach--ORP Levels?

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GoldHappy
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Using SSN Leach--ORP Levels?

Post by GoldHappy » September 6th, 2013, 4:41 pm

We're leaching ore (ground down to 100-200 mesh) that came from a volcanic mud flow and using SSN/butyl/oxalic for leach/recovery. We sent a 3 lb sample to a company in Idaho that leaches/extracts/tests for large companies to see if any gold could be recovered. They sent results back and said SSN was the best leach to use for our ore and they did recover gold. We've had poor results, but recently discovered the ORP is supposed to stay above 800 and preferably above 900 to put the gold into solution and keep it there. We checked and the ORP was around 600+, but never above 700. In doing a little more research we've discovered a pre-leach/pre-wash with HCL might be beneficial and enable us to get the ORP up where it needs to be. We're going to do the pre-wash today.

Has anyone had experience with getting the ORP up on SSN and keeping it up? We'd love to hear any other comments/suggestions you might have on using SSN. Thanks!

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Re: Using SSN Leach--ORP Levels?

Post by Gratilla » September 6th, 2013, 6:46 pm

1) First (if you haven't already done so) get yourself a copy of the standard SSN PDF available at a number of locations on this site, including here:

http://goldrefiningforum.com/~goldrefi/ ... 38#p123484

If you look at the graphs verrry carefully, you can see residual shaded patches of the "sweet spot/area" for Eh(ORP)/Ph for most of the PGMs. Although these areas are verrry indistinct, you can generally work them out by cross-referencing with the text.

2) I believe Eh decreases with time (and use), so instead of making your SSN in bulk, mix up a fresh batch each time you need it.

3) Do a search of SSN on this site using the GRF (Google Custom) Search ie NOT the standard forum search (which doesn't work for TLA's - Three Letter Acronyms). Lots of good stuff.

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Re: Using SSN Leach--ORP Levels?

Post by GoldHappy » September 6th, 2013, 9:13 pm

Thanks so much. We've read the PDF a couple of times in the past as well as doing a lot of research other places. From what we've discovered, for gold ORP/Eh needs to be above 800 and the pH at around .8. Our problem in the past has been getting the ORP up to the 800+ mark. We'll see what happens this time after doing a pre-wash with HCL, and if it improves the ORP I'll post an update.

Yes, we agree. We never mix SSN in advance, always only when we need it, but thanks for the reminder.

I didn't know about the Google search on the forum. I've been trying to use the standard forum search with little to no results, so I very much appreciate your instruction on that aspect.

Thanks for chiming in!!
Gratilla wrote:1) First (if you haven't already done so) get yourself a copy of the standard SSN PDF available at a number of locations on this site, including here:

http://goldrefiningforum.com/~goldrefi/ ... 38#p123484

If you look at the graphs verrry carefully, you can see residual shaded patches of the "sweet spot/area" for Eh(ORP)/Ph for most of the PGMs. Although these areas are verrry indistinct, you can generally work them out by cross-referencing with the text.

2) I believe Eh decreases with time (and use), so instead of making your SSN in bulk, mix up a fresh batch each time you need it.

3) Do a search of SSN on this site using the GRF (Google Custom) Search ie NOT the standard forum search (which doesn't work for TLA's - Three Letter Acronyms). Lots of good stuff.

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Re: Using SSN Leach--ORP Levels?

Post by Gratilla » September 7th, 2013, 12:48 am

If you look at the Pourbaix diagram on page 6 of the PDF, you'll see a minimum Eh of 0.89 (at a pH of between around 0.1 and 1.6) is required to "encourage" Au into solution. At a lower pH, a higher Eh is required.

IMO, it's well worth the learning curve time to get your head around Pourbaix diagrams.

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Re: Using SSN Leach--ORP Levels?

Post by golddigger2 » December 31st, 2013, 8:01 am

With the SSN document you are referring to it also states that the most gold they obtained in their experiments 1600 mg was at a ph of 0.8 and at a temperature of 80 degrees celcious. Are you heating your leech solution?. Just a thought :mrgreen:

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Re: Using SSN Leach--ORP Levels?

Post by GoldHappy » January 9th, 2014, 10:53 pm

golddigger2 wrote:With the SSN document you are referring to it also states that the most gold they obtained in their experiments 1600 mg was at a ph of 0.8 and at a temperature of 80 degrees celcious. Are you heating your leech solution?. Just a thought :mrgreen:
We were heating it to 120 to 130 F....we got that suggestion from a scientist who actually works for the company who makes Butyl Diglyme and has done a lot of work with SSN, recovering with Butyl and then oxaylic acid.

It was mentioned here by Gratilla that the Eh should be .89....we're more familiar with ORP numbers....so is .89 similar to 890 ORP, or something else entirely? Everything we've read has said the ORP must be above 800 while keeping the pH down to under 1 (around .8) also stated by the chemist from the Butyl company. It's been impossible to have the ORP up while keeping the pH that low. That's what we're hoping someone can help us figure out how to do.

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Re: Using SSN Leach--ORP Levels?

Post by Platdigger » January 10th, 2014, 1:02 am

What ratio of nitric to saturated salt water are you starting with? Looks like the orp should go up as well as the ph going down with additions of nitric.

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Re: Using SSN Leach--ORP Levels?

Post by GoldHappy » January 10th, 2014, 1:28 am

Platdigger wrote:What ratio of nitric to saturated salt water are you starting with? Looks like the orp should go up as well as the ph going down with additions of nitric.
7 to 1, which is supposed to be the optimum ratio. We've tried adding more nitric but it doesn't bring the ORP up enough to help, and you don't want to add to much, or it alters the ratio to where it's not working as effectively. The only thing we've found that works at all is hydrogen peroxide, but even it won't get the ORP up to anywhere near 600, much less 800.

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Re: Using SSN Leach--ORP Levels?

Post by Platdigger » January 10th, 2014, 2:21 am

I am curious if sodium bromide or even iodine would help.

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Re: Using SSN Leach--ORP Levels?

Post by Lou » January 10th, 2014, 9:17 am

I doubt you'll get over 800 mV with any SSN leach unless pH is very low.
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Re: Using SSN Leach--ORP Levels?

Post by nickvc » January 10th, 2014, 10:38 am

I,ll ask the idiot question Lou, is this a leech that basically needs a full lab to make it work efficiently or can any fairly well informed refiner get this working in their shed?

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Re: Using SSN Leach--ORP Levels?

Post by GoldHappy » January 10th, 2014, 11:46 am

Yes, iodine will bring it up if you can get your hands on the real thing. We've only been able to purchase the weak, regulated version that's on the market now. If anyone knows where to find the old iodine that is strong, we'd love to know.

Nickvc--we have made it work but it's tricky and not consistent. We've felt that the ORP being too low might be the main issue. We've had it up to 650 before.

As to dropping the pH lower, we've had it down to .2 and still not been able to get the ORP above 700.

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Re: Using SSN Leach--ORP Levels?

Post by nickvc » January 10th, 2014, 11:58 am

I have tried to search for stateside manufacturers or suppliers but I'm not sure I'm searching the right thing but there must be suppliers there, you just need to find them. Surely the chemical supply houses would have it or could get it.

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Re: Using SSN Leach--ORP Levels?

Post by Platdigger » January 10th, 2014, 12:07 pm

I found it was cheap when I was in Mexico.

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Re: Using SSN Leach--ORP Levels?

Post by solar_plasma » January 10th, 2014, 4:22 pm

In former times, 18th and 19th century, they made iodine from the ashes of kelp.Those ashes contain 0,1-0,5wt% iodine, bound as iodide and iodate. I will have eyes open if I can find an old book with descriptions, - could be a nice experiment, if one lives near the sea.
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Re: Using SSN Leach--ORP Levels?

Post by GoldHappy » January 10th, 2014, 5:18 pm

nickvc wrote:I have tried to search for stateside manufacturers or suppliers but I'm not sure I'm searching the right thing but there must be suppliers there, you just need to find them. Surely the chemical supply houses would have it or could get it.
Everyone we called said it's been banned due to meth labs using it to make illegal drugs. It can now only be sold super diluted, at least here in the states. Getting it in Mexico would be a great option if you lived near the border.

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Re: Using SSN Leach--ORP Levels?

Post by eastky » January 10th, 2014, 6:55 pm

99.9% ACS grade elemental iodine crystals. 250 grams for $125.00 on ebay. Would that work?

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Re: Using SSN Leach--ORP Levels?

Post by GoldHappy » January 10th, 2014, 9:41 pm

eastky wrote:99.9% ACS grade elemental iodine crystals. 250 grams for $125.00 on ebay. Would that work?
Whew! I'm sure it would, but that's spendy! Thanks for finding it. Nice to know there's an option. Just a little richer than I want to spend not knowing for sure it's going to work after the ORP goes up.

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Re: Using SSN Leach--ORP Levels?

Post by Lou » January 11th, 2014, 12:09 pm

I would avoid buying the iodine--not necessary and not even worth getting put on The List.

Suggestion: forget the SSN.

I'd like to know where all these ore processing companies in Idaho or Utah or Nevada are coming up with their suggestions. For small operators, if it doesn't pan, it doesn't pay.

Nick,

I think the leach is acceptable for dilute amounts of PMs when there are special circumstances (like a really clean feed on silica or ceramic). But even then, I'm not a big believer in using lots of solution for little amount of values on material that's in a porous substrate. Can you say solution volume escalation?

To be honest, I really believe that physical/mechanical upgrading (milling, floatation, etc) and pyrometallurgy (smelting) are the best ways to do ore. Otherwise you're making a bunch of kitchen sink solutions containing dilute amounts of precious metals as well as nasty base metals...just a mess. It really shouldn't be done on complex ores.
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Re: Using SSN Leach--ORP Levels?

Post by nickvc » January 11th, 2014, 12:26 pm

Thanks Lou that's what I thought.
To paraphrase what your saying, this is a total waste of time on most material.
I'm with you on low level concentrations of values in big volumes, a pain to recover all the values and a headache to safely treat for disposal.
I'm sure the big boys are playing with various ideas to recover values more efficiently but physical concentration of the values first is almost mandatory to make recovery and eventual refining possible and economical.

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Re: Using SSN Leach--ORP Levels?

Post by GoldHappy » January 11th, 2014, 3:12 pm

That's the conclusion I've come to, as well....I originally posted this before getting interested in and researching froth flotation as the best means for concentration since we have a sulfide ore. Trying to learn more about the process, chemicals, etc., but there's not a lot of super specific info out there.

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Re: Using SSN Leach--ORP Levels?

Post by eastky » January 11th, 2014, 3:23 pm

Goldhappy I don't know anything about ores so I cant help you on that. If I understand you right you want to collect small particle gold after you crush it to a fine powder? Is that right or are you trying to get the gold into solution to recover.

I got interested in recovering fine gold from mud and did some searching on the net to see how people were collecting flour gold.

If you do a search for " micro flood gold " on the net you will find a post on a gold prospecting forum. The post is quite long 17 pages. There is a guy that posted in that topic that uses fish oil to recover fine gold from dirt gravel sand and such. Might point you in the right direction.

He doesn't give out the whole setup details but he gives out enough that you should be able to figure it out through trial and error.

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Re: Using SSN Leach--ORP Levels?

Post by bmgold2 » January 11th, 2014, 5:09 pm

From what I understand about sulfide ore (which isn't much), the gold is locked up as sulfides and not as "free gold". A quick Google search for "concentrate sulfide ores" got me http://electrochem.cwru.edu/encycl/art-m02-metals.htm that gives different methods of extracting metals from sulfide ores. I don't know if it might help any but thought I'd post it just in case it might be useful.

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Re: Using SSN Leach--ORP Levels?

Post by Gratilla » January 12th, 2014, 8:40 pm

I've just been wading through one of the Intec patents:

http://www.google.com/patents/US7858056 - Recovering metals from sulfidic materials

and came across this:

"To achieve a higher solution Eh ..., it may be necessary to add additional oxidant such as oxygen, air, chlorine gas, hydrogen peroxide etc

FWIW.

Hmmm.

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Re: Using SSN Leach--ORP Levels?

Post by Lou » January 12th, 2014, 11:16 pm

If you have to add more oxidizer, why not just skip this lixiviant all together?
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Re: Using SSN Leach--ORP Levels?

Post by Gratilla » January 13th, 2014, 5:17 am

Lou wrote: If you have to add more oxidizer, why not just skip this lixiviant all together?
In preference to what, exactly? A little extra air/oxygen sparging (if necessary) is hardly excessive.
Lou wrote: Suggestion: forget the SSN.
Is it just SSN you're against or is it all halide leaches?
Lou wrote: To be honest, I really believe that physical/mechanical upgrading (milling, floatation, etc) and pyrometallurgy (smelting) are the best ways to do ore.
The mining industry as a whole, though, disagrees. Over 90% of ore is (cyanide) leached; the vast majority of low grade ores is (cyanide heap) leached - much without any preprocessing apart from possibly milling

Moves against cyanide though are turning to other leaches with the current favourite being halide leaches - for many reasons - not least of which are their ability to handle refractory ores (including sulfides, arsenates, etc), with the possible exception of high-carbon preg-robbing ores (for which preprocessing would be necessary).

If you add solvent extraction (SX) to leaching, you have the minimum number of unit processes from ore to high-purity metals. And a number of large names in the industry are already predominantly using SX (for which a pre-leach is necessary) for all their PGMs (except Rhodium).

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Re: Using SSN Leach--ORP Levels?

Post by Lou » January 13th, 2014, 9:37 am

In preference to not doing it on the small scale.

I'm against halide leaches for reducing ores (all of the chalcogenides). I'm against them for ores containing larger quantities of heavy elements. I'm against them for amateur use. We're talking context here.
Agreed that air is cheapest (I meant that more in the sense of peroxide). That's why it's used in mass to roast ores and why most of the large players in SA have sulfuric acid plants integrated with the refinery.


FYI, the cyanidation was implied as that happens after comminution but before smelting of the Merril-Crowe cementate.

As for SX...I've used pretty much all of them. Only one I've ever been impressed with are the carbitols and the longer chain alcohols favored by Mintek.
They all have issues and are really specific to the feed you're running.

Don't fool yourself into thinking you're going to load up a lixiviant and pull out the PMs in pure form and have not a care in the world. It might be possible to get 4N Pd/Pt out of such a leach, but unless you have dedicated recycle loops, it will not be profitable.
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Re: Using SSN Leach--ORP Levels?

Post by Gratilla » January 14th, 2014, 8:51 am

Obviously we disagree on a number of points (but not all).

The main significant difference between small and large scale is attention to detail. Large Scale needs it to be viable; Small Scale too often unrealistically expects to be fed a by-the-numbers optimum process.

Case in point is SX where an understanding of partition coefficients is in order. And sometime back I uploaded a graph to show exactly this. Appreciation of the "sweet spot" for optimum partitioning and again for the acid scrub CAN successfully produce high quality separations.

BTW, Mintek's favourite organic solvent as used in their flagship Minataur process is neither a carbitol/diglyme nor an alcohol. It's an ester.

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Re: Using SSN Leach--ORP Levels?

Post by Lou » January 14th, 2014, 9:21 am

It's OK to disagree--I'm interested in your thoughts on why SSN or halide leaches should be used. My thoughts on reducing ores would be that you'd have too much gas formation. Not sure that we're entirely on the same page.

Sure it's not a long chain alcohol? I would have guessed it would be ethylhexanol or something like that, but please enlighten me.

I guess my concern really is the waste volume produced from leaching. Sure, all of it is surmountable, but I think for the small operator it's too easy to get mired in getting the value out without looking down stream to all the raff treatment.


As for the SX, yes, you can scrub out a lot of the junk but it requires some pretty advanced technology (i.e. continuous, counter-current centrifugal separation--Rousselet Robatel is one manufacturer whose components are in common employ). Certain conditions must be employed given different contaminant levels. One thing I've noticed with the carbitols--high iron/selenium, you're going to have a lot of scrubbing. Sure, that waste acid can be re-used but you're just moving contaminants around at that point and have to deal with them eventually.
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Re: Using SSN Leach--ORP Levels?

Post by Gratilla » January 16th, 2014, 10:51 pm

My thoughts on why halide leaches should be used?

A major reason is that they're "broad spectrum". That is, they can (potentially) dissolve pretty much all the metals etc in the ore (if it has been properly preprocessed) as opposed to, say, cyanide, which is more targetted - towards gold (and silver). Some may consider this a disadvantage, but with available ores becoming increasingly low grade and increasingly contaminated, I believe a "cover all" leach is attractive, particularly if viable separation technologies are available at the preprocessing and post-refining stages. (see Intec [Refractory] Gold Process at http://www.intec.com.au and patent US7858056.)

This makes possible additional income streams from sale of commodity "contaminants" and can decrease tailings disposal costs by converting toxic products to inert minerals.

In addition hydrometallurgical pre/leach/post processing make synergies possible where (particularly halide leach) processes can be combined (ie run in parallel).

In short, a totally hydro process makes for potentially elegant solutions BUT a broad appreciation of the science is vital.

SX techniques (if you're familiar with the background) are fairly straight-forward and needn't be technologically advanced. For example, centrifugal separation is only really necessary where the densities of the organic solvent and aqueous fraction approach each other; if they are equal, separation becomes pretty much impossible. The Minataur solvent doesn't have this problem!

Ethylhexanol is a good guess. It is superior to DBC (see patent WO2011/154603A1) in that:
- the [Au loaded] DBC phase settles very slowly from the aquaeous phase,
- the solubility of DBC is extremely high (approx 3 g/l @25 deg C), leading to reagent losses [to the aqueous fraction],
- the flashpoint of DBC is relatively low
- etc

Mintek's organic solvent has all these advantages, plus one virtually unique one, which they let slip in their Minataur description, namely it does not suffer from phase inversion. The answer should now be easy to determine for those with a reasonable grasp of chemistry. I won't post the answer on a public forum, but will let you (ie Lou) know, if necessary <g>, in PM.

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