# Checking black sand for Au



## tlcarrig (Mar 21, 2008)

I'm hoping this is the best place to put this. Apologies if it is not. Please follow me through on this. I am in the process of checking my black sand to see if there is gold in it. Here are the steps I have done so far:

1. Vinegar soak for 24 hours
2. Water (home supply, chlorinated) washed 5 times
3. Roasted with NON iodized salt and dropped into cold water
4. Washed 5 times with water to remove the salt
5. Washed 3 times with HCl (so far)

Here is my quandry. My HCl washings are yellow. See attached picture. Should I keep washing until they are clear before adding Colorox or should I just go ahead and add the colorox and hope to form AuCl3? Realise that I am just checking a sample (2 Tbsp.) before I consider any serious processing of my cons. I have my stannous chloride ready to go but do not have SMB yet 'cause no need for it if my cons don't have any Au.


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## Smitty (Mar 22, 2008)

Hello Terry. I've tried what you are about to attempt. Someone told me that the yellow is from iron. I tried to dissolve all of the black sand with hcl and could never get it to totally disapper. Try crushing the black sand with a hammer of sort as small as you can and use a 10x loupe to see if any gold is present that way. There is a thread on separating pyrite from gold under the prospecting category. In that thread I actually had Pyrite in with black sand.


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## tlcarrig (Mar 22, 2008)

Thanks Smitty. I kinda thought that It might be iron but I have not seen that mentioned in any of the sands processing threads. I know that is the primary make up of the sand though. I guess I'll roast some more and give a good soak in CLR and try that. I was thinking that the vinegar soak before roasting was supposed to take care of that though. I'm going to try some more HCl rinses, maybe even hot to see if I can get a clear one before I colorox it. I dont want to use up all my HCl though. I might be butting my head against a wall though. I'll also try what you said on a sample too.


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## Lou (Mar 22, 2008)

I wonder if hot sulfuric acid treatment would get rid of most of the iron contamination.


Lou


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## tlcarrig (Mar 22, 2008)

Don't know Lou. I don't recall having seen that mentioned anywhere on the forum. I'm hoping that lasersteve or some of the other wizards will see this and chime in.


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## Irons (Mar 22, 2008)

Lou said:


> I wonder if hot sulfuric acid treatment would get rid of most of the iron contamination.
> 
> 
> Lou



I prefer Sulfuric because it usually won't attack any PMs and it doesn't give off a lot of corrosive fumes like HCl.
It's still a good idea not to do this indoors as many black sands also contain Arsenic compounds. 
I was almost killed last fall by Arsenic poisoning from a sample that gave off Arsine gas.

The scientist who discovered Arsine (AsH3) was killed by it when he accidentally inhaled a large bubble of it. Levels over about 135 PPM can kill you instantly. Lower levels can build up in your system can cause chronic Arsenic poisoning. That's what happened to me.


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## Anonymous (Mar 22, 2008)

I now have black sand concentrates that have been soaked and are still soaking in HCL for over a month. Every time I change and wash then add new acid more of the iron dissolves. I have changed and washed once a week. I intend to do more when it no longer reacts with the HCL
but nothing until then. This stuff is very heavy or would dense be a better word. I have repanned the concentrates to remove new blond sand but have not had any gold show in the pan - maybe its too small to see or maybe when I orginially panned it I got all I could get and the smaller stuff sluffed off.

Hoping that the black sand itself is something that is why I am waiting untill all of the iron stops showing. I am going to run it in my hammer mill this weekend and retreat with new acid.

I have saved all of the acid washed and I am going to drop them with Aluminum to see what I get.


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## Lou (Mar 22, 2008)

Think mercury would do the trick?


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## Platdigger (Mar 22, 2008)

Nope. Not for what they are talking about here. Thing about these iron oxides is they are not easily attacked (chemically) until they are first reduced back to elemental iron.

One way to do that, is in the presence of carbon at high temps.
And of course there are others.
Randy


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## Lou (Mar 22, 2008)

Ah, so if you melted them cupola style with charcoal, you'd have a ton of iron to dissolve once solidified. 


I still wonder if mercury wouldn't just amalgamate all of the gold and silver from the ''concentrate''.

Another option is to chlorinate the gold and PGMs away. They have volatile chlorides, could you not just pack a couple kilograms of black sand conc. and then blow chlorine through it at high temp?


Lou


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## Irons (Mar 22, 2008)

From what i've seen of microscopic analysis of so called 'black sands', the values tend to be dispersed as a solid suspension where you have ferroplatinum with discrete crystals of other PGMs or Gold dispersed much like gravel in concrete. To allow dissolution, the values have to be exposed by completely breaking down the matrix, whatever it is, precipitating everything out and starting from that point, otherwise it's just a waste of time.

Every 'black sand' is different and even in a given area, the composition will change with depth and location.

Until you know exactly what you are dealing with, it's anybody's guess as to what is there and how to attack it.


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## Irons (Mar 22, 2008)

A common contaminant of 'Black Sands', is composed of manganese Dioxide, MnO2. When combined with HCl, it liberates Chlorine Gas.


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## OMG (Mar 22, 2008)

I've been working on black sands too for a few months. The yellow liquid is iron. From my calculations, I figure it would take about a gallon of 32% HCl to dissolve 1kg of Fe203 into FeCl3 (under perfect circumstances). I've been trying ways of reusing the dissolved chlorides to make more HCl. Right now I'm doing this by a two cell electrolytic setup which bubbles chlorine into the dissolving tank and precipitates the Fe(OH)'s in the precipitating tank. The chlorine readily dissolves into the HCl and FeCl mix. The issue I will have is the amount of chlorine that has to be absorbed back into the dissolving tank. I would need to push through about 100 amps and even at that speed it would still take something like 10 days to dissolve all the iron in a gallon of concentrates. I am also having problems using carbon electrodes. They degrade too quickly, I sure wish I could find some titanium to try out.


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## ChucknC (Mar 22, 2008)

Hot sulphuric will digest silver and palladium into tough as can be to recover compounds. The best way I've found to pre-treat black sands is to heat them to red heat for at least an hour, in the presence of oxygen, and when cooled, give them a soak in dilute nitric acid. This will free up more fine gold from the black sand particles than you realize.

Another idea is to concentrate the material as far as possible gravimetricly. How much blacks sands do you have? How much material did you start with? Where are these blacksands from? What mesh are you working? All these questions will have a bearing on what the ultimate answers could be.

I posted this vid link before, but it will give you an idea of how to economically concentrate material down to where it is in an economically workable amount.

http://www.youtube.com/watch?v=KdikUKNLCHY

Pay special attention to the cleanup sluice used after the crusher.
Here is another. Once again, pay special attention to the cleanup sluice. It's very informative.

http://www.youtube.com/watch?v=0jXGbp8KJAo&feature=related

That'd give you an idea of how to concentrate placer material, and free milling hard rock material, to where it is much more economical to leach or fire.

Oh, and just to let you know, Hg is only partially effective at amalgamating 50 mesh gold and finer. I've seen clean Hg flow right over 100 mesh gold and ignore it. The only thing that changes that is charged Hg. A whole nother animal. I don't use Hg even though I have access to it.

Chuck


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## zauggart (Mar 22, 2008)

OMG said:


> ). I am also having problems using carbon electrodes. They degrade too quickly, I sure wish I could find some titanium to try out.


hi there
i have a piece of a titanium hip joint would that help you?
Ian


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## Baja Bob (Mar 23, 2008)

if your are only checking for gold can you do the stannous chloride test.
Baja Bob


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## eagle2 (Mar 23, 2008)

No engineering process is feasible trying to get rid of the black sand first. You`re trying to dissolve 90+% of the solids!! 

Just roast it and set up a heap bleach leach, with a circulating pump. Most engineers are happy if they get 50% recovery.

Most Black sands may not have any PM`s in them anyway. Did you have yours assayed? 

Also Look into the Sulfite or Thiourea processes.


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## OMG (Mar 23, 2008)

I'm going for 95%+ recovery of the gold from the black sands. Just cause I'm stubborn and will keep trying until I learn enough that I realize it's stupid. But who knows I might learn something unique along the way. I've got it so it dissolves so much that what was once rather coarse sand is now very fine silt/mud. Just the silicates are left I imagine. (as a side note I am also trying to find a way to make the process re use all the chemicals, so nothing additional has to be put in- except some electricity for the electrolysis. And I've been thinking of ways to use the precipitated/plated iron and other metals to make other saleable products.)

eagle2, do you have any good references for the sulfite and thiourea processes?


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## tlcarrig (Mar 23, 2008)

ChucknC, realize that this is only an experiment. Basically to see if my sand contains any locked up Au. My sample size is probably a tablespoon. This is sand straight from the pan. It has a minimal amount of blonds. Probably -5% but it does definately have some garnet sand in it. It still has magnetics. I probably did not heat it enough as I only have a small propane torch and had it in a lead ladel which would soak up a lot of heat. I have not decreased mesh size yet. Right now its at least -20. I have no way to measure smaller that that but can hand crush it smaller. I still have plenty to work with. 

OMG, with your figures, how muct HCl do you think it would take to clean the Fe from my tablespoon size sample? I think my muratic is 28 Baum.


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## eagle2 (Mar 23, 2008)

Hi: You can Google your keywords and get tons of info. I saw a thread on this forum, where Steve, Harold, and GSP discussed Sodium Thiosulfite/Sulfate leaching. I can`t find it, it might not have been in the right category.

Its great to experiment. You will learn the fastest, but read the work of the scientists first. You`ll get more ideas. 

Here`s a Website with a lot on leaching: www.e-goldprospecting.com 

A lot of mining info also.

Almost always you should roast the ore or black sands, Roasting is done at 500 -900 C. for about an hour. Then a leach will work. Some engineers are claiming 80-90% recovery, but every ore is different as Irons points out. 

If you have a big steady supply of the same ore, you want to have an assay so you know what your trying to get and how much!

A tablespoon size sample will have so little in it you just can`t tell what there is. Ores are like 0.5 - 5 oz Gold per ton. Black sands might have more, but there is so much iron, the only reasonable method is a leach.

I remember panning around out West years ago, in places that had been worked by the old miners,that used Mercury. At the bottom of the pan, you could many times see fine silvery grains, looking like sand, only it was heavier than the magnatite. If you used Nitric acid on these it would dissolve the Mercury and leave fine gold flour to see. 

Al


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## OMG (Mar 23, 2008)

tlcarrig, from the pic I would say thats enough. The thing is it takes a long time for it to get all the iron, because the iron is locked up as well. You should grind the concentrates to as fine as possible so they react as quickly as possible. Also if you put a bit of peroxide in it dramatically increases the speed. I had some sitting for about 4 hours and I added a bit of peroxide and within minutes It dissolved more that it had in the 4 hours.
When its done, all you should see is a bit of slimy mud in extremely yellow liquid. The sand should get broken up so fine that it will stay suspended for quite a while before it eventually settles. You will probably have a hard time filtering. I'm just learning this stuff myself from experiments, this site and wikipedia, but thats what I would suggest - grind the concentrates to a powder to start with, and use a bit of peroxide. (hcl and peroxide can dissolve gold but very slowly, and all that iron will probably also prevent it from dissolving).
I'm finding it is quite the task to dissolve ALL of the metals in a bunch of black sand so the gold can be gotten to. Although like you, I want to see how much 'invisible' gold there actually is - and I'm not going to pay for an assay on a bunch of sand.


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## tlcarrig (Mar 23, 2008)

Thanks OMG. I'll probably try the peroxide as I have 3 gallons of 27%. We use it in our pool. This should get rid of the base metals so I can get to the gold, if any. A ml or two in the volume I have should do it. I am going to run another sample after I smash it down fine. I'll roast longer too. Again with non iodized salt? Still can't figure out what that does. The salt seems to pop out like popcorn. I don't know if I can keep up that kind of heat for that long though. Will keep everyone posted


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## OMG (Mar 23, 2008)

The salt makes the sands fracture into smaller pieces.


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## Brandt (Mar 24, 2008)

Processing black sands grind down fine soak in muratic acid for couple days and wash verry good. then use some sodium thiosulfate leach which ignores the iron an base metals. Brandt


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## Anonymous (Mar 24, 2008)

placed aluminum in my acids from the black sand - this was just HCL so I do not expect any gold in them - I got a white precip and some black dust that I am going to test. I thought it could be iron but if I had iron this fine I think it should rust and be reddish.


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## OMG (Mar 25, 2008)

There are many forms of iron oxides. I get lots of black precip that is iron. I don't know what exactly happens when you use aluminum to cement out chlorides, but from my experience it reacts very vigorously and takes a long time to complete fully. I think the aluminum takes the chloride from the iron (or whatever) to form AlCl3, but AlCl3 apparently reacts with water to release HCl and Aluminum (hydr)oxides. Some of the HCl would get absorbed back into the water, and would react with the metals again until more aluminum pulls it out as well.
Sooo, I think what happens in the end is the higher metals will drop out and eventually all of the Cl's will get removed (as HCl gas) so you'll have just the metals and hydr(oxides) left. I think it takes a long time to get rid of all the Cl's though because I've had some going for a month, and If I shake it bubbles still come up out of the black and grey particles.
But. I'm not sure because I tried to bubble the gas emitted back through water - If it was HCl(g) it should dissolve and make HCl(aq). It didn't work. It might just have been my mickey mouse setup, but I think a lot of H2 gets emitted too.


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## Anonymous (Mar 25, 2008)

Mine has been working for a while and I made sure and put extra aluminum in. I will work on figuring out what it (the black powder) is this weekend.


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## Traveller11 (Jan 17, 2009)

Could someone give me elaboration and instruction on the sodium thiosulfate leach method for recovering gold from black sands? As Brandt points out in his post, it might make more sense to use a selective leach rather than trying to remove the iron and base metals prior to employing Cl/HCL.
Also, how do the two methods compare in cost?


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