Checking black sand for Au

[OMG]

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.

 

[tlcarrig]

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

 

[OMG]

The salt makes the sands fracture into smaller pieces.

 

[Brandt]

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

 

[Anonymous]

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.

 

[OMG]

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.

 

[Anonymous]

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.

 

[Traveller11]

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?