Checking black sand for Au

[tlcarrig]

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.

 

[Smitty]

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.

 

[tlcarrig]

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.

 

[Lou]

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


Lou

 

[tlcarrig]

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.

 

[Irons]

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.

 

[Anonymous]

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.

 

[Lou]

Think mercury would do the trick?

 

[Platdigger]

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

 

[Lou]

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

 

[Irons]

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.

 

[Irons]

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

 

[OMG]

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.

 

[ChucknC]

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

 

[zauggart]

). 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

 

[Baja Bob]

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

 

[eagle2]

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.

 

[OMG]

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?

 

[tlcarrig]

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.

 

[eagle2]

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