acid/clorox leach

[Traveller11]

I tried to leach a test sample of sand today. It had been part of a cemented gravel and sand deposit; largely cemented with what seems to be iron. I ran it in a cement mixer and then classified it through a 30 mesh screen. Repeated washings seemed to remove the majority of the iron leaving only sand.

I covered a small sample with 20% muriatic acid and then added an equal portion of 6% Clorox. It fizzed up, settled down and then bubbled away for a couple of hours.

At first, the liquid turned that nice golden brown auric chloride is supposed to turn. When all action stopped, it had changed to a very yellow colour like strong lemonade.

I had prepared a small amount of stannous chloride at the same time by snipping bits of lead free solder into a small amount of 20% muriatic acid. I dipped a Q-tip into the leach solution and put a drop of it on a paper towel. I then dipped another Q-tip into the stannous chloride and added it to the other drop.

No purple reaction. Did I make a mistake here? If the yellow coloured solution was not gold, what was it?

Bob

 

[nickvc]

It sounds to me like you started to dissolve your gold,supposing it's there, and then your solution started to weaken before all the metals dissolved and the gold cemented back out onto your base metals. Try a small sample and test the solution when it's fully active with your stannous,this might confirm you have gold there but it's never easy to treat ores or sands with acids due to their complex chemical natures and removal of base metals is your first objective not going for the gold.

 

[geonorts]

carbonates in the sand could explain the fizzing and the weakening of the acid, try a HCL wash first, also you will need to remove the heamatite "iron" as well.

 

[dtectr]

manganese can cement sands in deposits, as well. And since it dissolves readily in HCl, coloring the acid, that may be some of what you're getting. Good news is a little manganese goes a long way, so it may be worth attacking it with HCl 1st.
Have you had even a rough assay done on this material?

 

[Anonymous]

removal of base metals is your first objective not going for the gold.

it may be worth attacking it with HCl 1st.

carbonates in the sand could explain the fizzing and the weakening of the acid, try a HCL wash first, also you will need to remove the heamatite "iron" as well.

The first,and MOST important objective,is to establish that you in fact have gold in your material.There is nothing to be gained by removing base matals,and iron,if there are no values to be recovered.
You need to start by determining that you have the precious metal(s) you desire first.A small test with AR will determine that.
You stand to gain nothing from wasting chemicals,simply to dissolve trash metals.

 

[Traveller11]

Yes the objective of my experiment was to try to establish if there was any gold in this material. It was a very small sample, less than a teaspoon.
I would assay the material but, with assays in this part of Canada costing $50 each for Au (plus shipping costs to a lab) and there being quite a number of sites I'd like to test, the economics of multiple assays are just not within my budget. (or so my wife tells me anyways)

Mic, you mentioned AR. Would it not get caught up in the base metal problem too? The nitric acid part of AR is a problem as well. I live in a remote part of Canada's northwest coast and, as anything coming to our islands must come by ferry or aeroplane, I can't find a shipper that will transport it for me; assuming that I could get past the retailer's gruelling anti-terrorist questionnaire.

There is no shortage of manganese here. I operate our town's water system and dealing with manganese and iron in our groundwater is a major problem.

As this is only an experiment in miniature and not a full scale recovery operation, I am willing to devote more time and resources to unlocking this sample, although I agree with Mic that establishing the presence of gold first is paramount.

As to washing with HCl prior to leaching; when I first covered this sample with HCL, nothing appeared to be happening. If the HCl was dissolving base metals, would there not be some physical activity visible?

Bob

 

[nickvc]

Traveller use the search function and look up poor mans AR,I think that will tell you how to make your own nitric,if not there have been plenty of posts covering it.
When you first posted I assumed wrongly you had buckets of material you were treating hence the suggestion to remove the base metals first but as you are doing small samples I would certainly try to dissolve everything to determine if there's gold in your sands, while it might not tell you how much it should give an indication as to wether it's worth proceeding to a larger test batch to see what values you can recover and wether it would be economically worth it.
Try hot hcl on your sands first that might remove some of the unwanted materials but to be fair many have tried to refine this material and few if any have succeeded to do it in their back yards due to the complexity of the metals and the sulphides etc. It's way over my head but I wish you luck and hope you find your pot of gold.

 

[dtectr]

In my very limited experience, I didn't get a "active" reaction to the manganese - it simply dissolved & went into solution. The brown part of your initial dissolution sounds more like that than gold, frankly.

I was thinking more about treatment of the sands - we had a lengthy thread here just a week or so ago about processing black sands. If you can find that thread, there was some great info. A preliminary roast in either a mild steel skillet or any other kind with some nails thrown in was reccomended, I believe. This would convert any sulfides to oxides, helpful as sulfides tend to trap values.

Others here with much more experience than me can contribute much to this discussion, & I'm sure they will.

good luck & hang in there.

 

[Traveller11]

I returned to the yellow coloured solution I ended up with after attempting to leach an iron cemented material. Considering what one poster mentioned about the gold possibly precipitating back out once the leach ran out of oxidizer, I introduced more Clorox into the solution. Once again, it foamed up and overflowed the jar. This time, it did not change colour but stayed yellow.

I am rapidly losing interest in creating my own leach for the sole purpose of doing a crude assay on my material. I was standing ten feet away from the solution, supposedly upwind, and I got a whiff of chlorine gas. An hour later, I was still coughing up phlegm.

There is a website called Goldmine World. They market a gold test kit based on what they claim is their exclusive sodium thiosulphate leach. From what I have read here and other places, many people have tried using sodium thiosulphate as a leach but have found it difficult to regulate. Goldmine World claims to have perfected the process and are now actively marketing it. They also claim thio leach ignores base metals and only dissolves PM's.

Does anyone have any experience with Goldmine World and their sodium thiosulphate based leach? It would be great if it did all the things they say it does. I have used bulk sodium thiosulphate in burlap sacks in our water system to neutralize chlorine in drinking water before it goes into a fish creek. It's about as cheap and non-toxic as you can get.

Bob

 

[Anonymous]

I returned to the yellow coloured solution I ended up with after attempting to leach an iron cemented material. Considering what one poster mentioned about the gold possibly precipitating back out once the leach ran out of oxidizer, I introduced more Clorox into the solution. Once again, it foamed up and overflowed the jar. This time, it did not change colour but stayed yellow.

I am rapidly losing interest in creating my own leach for the sole purpose of doing a crude assay on my material. I was standing ten feet away from the solution, supposedly upwind, and I got a whiff of chlorine gas. An hour later, I was still coughing up phlegm.

There is a website called Goldmine World. They market a gold test kit based on what they claim is their exclusive sodium thiosulphate leach. From what I have read here and other places, many people have tried using sodium thiosulphate as a leach but have found it difficult to regulate. Goldmine World claims to have perfected the process and are now actively marketing it. They also claim thio leach ignores base metals and only dissolves PM's.

Does anyone have any experience with Goldmine World and their sodium thiosulphate based leach? It would be great if it did all the things they say it does. I have used bulk sodium thiosulphate in burlap sacks in our water system to neutralize chlorine in drinking water before it goes into a fish creek. It's about as cheap and non-toxic as you can get.

Bob

Every one to a TEE, that has used thiosulfate, iodine, super special chemical T-6, X, or green magic, whatever you want to call them has had large problems and from what I have seen no success, even when there is known gold in the sample.

I would first take a small sample 30 grams or so and roast it with some plain old everyday salt (2 grams), I would do this in a old small stainless steel or cast iron pan, stir it around and let it oxidize and react with the salt.

Next let this cool then rinse with HCL that is dilutes with 5 times the amount of water until not more fizzing, or color changes.

Then use the HCL leach that you spoke of. But use the diluted HCL to cover and add only a few drops of chlorox cover with a lid that seals but is not tight enough to build large pressure. I use a old babyfood jar with a cork lid so I can see whats going on, shake this side to side to stir in the chlorine gas with the hcl and leave this sit for a mininum of 48 hours. After this time has passed rinse the material well with water and filter, evaporate this water down to just a milliliter or so, then test the concentrate with stannous.
Remember evaporate not boil down.

Jim

 

[Harold_V]

I am rapidly losing interest in creating my own leach for the sole purpose of doing a crude assay on my material.

That may be a good thing. At best, it won't be much of an assay, reflecting, more than anything, that your ore may or may not contain values, depending on if the process you chose works, or not, and if it contains gold, how much is recovered in the process. That would be relatively meaningless unless you understood how much the ore contains. Hardly an assay, in my estimation, but I think you already know that. Not trying to be rude, just trying to have you understand that your attempt isn't going to provide answers that are of value. You are far better served to pay for an assay by those with experience and the proper equipment. An assay should be reliable, not something that hints at content.

I was standing ten feet away from the solution, supposedly upwind, and I got a whiff of chlorine gas. An hour later, I was still coughing up phlegm.

Most unfortunate. A good reason to always work in a fume hood, for sure. Chlorine does serious damage to lungs. Be careful! (I know you were trying to be).

Harold

 

[Traveller11]

Harold
Thank you for the words of wisdom. The ironic thing is, my intended method of recovery for this area has nothing to do with leaching but rather involves a careful gravity separation followed by direct smelting.
Imagine how frustrating it is to be working with a placer deposit in a remote location where the largest particle of gold (flaky too) can likely pass through a 150 mesh or smaller screen. The old method of panning a scoopful down to see colours does not produce much as this stuff is so fine and flaky it almost floats. Also, not all parts of this placer are rich, or even contain gold at all. This is why I was experimenting with the acid leach, and also why I was asking about these gold test kits marketed online.
A "go/no go" test just for the rough indication of gold's presence and light enough to be carried in the field would save a lot of time and effort ultimately.
Bob

 

[qst42know]

If it wants to float why not help it?

You may want to explore froth flotation as a means of concentrating.

 

[Chumbawamba]

Wait a second: how do you know your "lead-free" solder has any tin? Is it possible you were not getting any results because you didn't have stannous chloride? This is what you need to figure out before you move forward. You need to test your stannous with a known gold-pregnant solution. Once you get positive results, then move on to testing the sand.

 

[butcher]

yes fine gold can float, and will, but even fine gold can be panned.panning should be fruitful (fine gold left after black sand panned off) if you are actually panning fine gold and not pyrite, are you sure this is not just pyrite? and how about your panning, how you use the pan is very important to first getting fine gold to the bottom of the pan and then kepping it there after all the gravel is panned off, how good are you at panning?

sometimes really fine gold in black sands, can be a hassel to seperate, here a blue bowl or shaker table is handy, but if it is pyrite it will float away anyway.
dish soap can help stop fine gold from floating on tension of waters surface.
the black sand can be concentrated, seperate magnetic, roast , and leached.
this fine gold does it smash flat or crumble? does it melt together or just oxidize under the torch smlling like SO2 gas as it burns away? basically are you after fools gold?
a common mistake for new miners.
you can do your own assay melt to see if this is gold or pyrite, using a lead collector and cupelling button. it may not be as good as a paid for assay but can give give you some idea.

 

[Traveller11]

Chumbawumba
I used "Silver Bearing Lead Free Solder". Before I cut it up into the HCl, I looked up this classification on the net. It is defined as 96% tin and 4% silver and is the most commonly used solder by plumbers these days.
Bob

 

[Traveller11]

HaroldV
Good news...I visited a metal detecting site and the good people there introduced me to the Falcon MD20 Gold Probe. It is a specialized type of metal detector; designed not to detect very far (under an inch) but able to locate even the tiniest specks of gold; even those hidden within a rock. It has a feature that distinguishes black sand from gold, as well. Hopefully, it will tell me which parts of the clay hardpan the "invisible" gold is hiding in.
That being said, I will leave the acid leaches to those, like yourself, with the experience to handle them safely.
Thank you again.
Regards
Bob

 

[Harold_V]

Bob,
That sounds interesting. Be certain to share the results with us!

Harold

 

[dtectr]

HaroldV
Good news...I visited a metal detecting site and the good people there introduced me to the Falcon MD20 Gold Probe. It is a specialized type of metal detector; designed not to detect very far (under an inch) but able to locate even the tiniest specks of gold; even those hidden within a rock. It has a feature that distinguishes black sand from gold, as well. Hopefully, it will tell me which parts of the clay hardpan the "invisible" gold is hiding in.
That being said, I will leave the acid leaches to those, like yourself, with the experience to handle them safely.
Thank you again.
Regards
Bob

Bob,
It seems this thread has strayed a little from the "chemical" but here goes - Please note that the "Gold Probe" is just that - a probe that has to be able to probe into the material in question & must come into contact or very-near contact with material being checked. You cannot just move it over the samples as with a conventional metal detector, but properly used, it can be helpful. Be sure to loosen material at least to gravel before attempting to probe.

As far as detecting "even those hidden within a rock", I'd be dubious for the reasons stated above. Probe technology isn't new - its been available for over a decade, & IMHO they can make them more durable or put better discriminating circuits but magically looking through rock sounds a little like necromancy.

Re: "panning", as discussed earlier:
"A skilled panner can quite literally find a needle in a haystack - in such hands, the process is almost incredibly fast and accurate. The author saw Robert W. Roots, Jr., at about 75 years of age, win the world's panning championship at Sacramento by recovering all 20 flakes of gold, the size of pinheads [italics mine], from 1 ton of crushed rock in less than 20 minutes. Many women have the dexterity to give much the same performance, and some have won the international championship." - Handbook for prospectors by Richard M. Pearl, p. 113.

I guess the point is - there is no quick, effortless way to attempt this, as many (not all) detector sites & detectors themselves like to imply. Remember, the purpose of most detector sites is to help sell detectors. They can be an invaluable tool in locating possible sites that are amenable to finding gold, but once that is done, the real, fairly physical aspect, in some cases the drudgery, is required to extract your values.

Keep your eyes on the prize, so to speak, roll your sleeves up & make your own luck.

just my dos centavos.

 

[patnor1011]

http://metaldetectorreviews.net/detectors/196-1-falcongoldprobemd20.html

As to that probe. It can detect metal in rock. Not in boulders but it will scan few centimeters in. That gold probe is sufficient for what he intend to use it for and much safer to use in remote locations than experimenting with acids there to determine if gold is there or not. It can be adjusted and set up using samples which have gold in. I am using similar probe when detecting (well not very often in these days to be honest)