# Refining silt from mining machinery



## froot (Sep 8, 2011)

Hi, great site, first post. 
I'm part owner in a company that manufactures and refurbishes machinery for the gold and platinum mines and I have questions in more than one area of refining pm's. For now I would like some advice from the know-hows on how to refine any pm's from silt that I've removed from a piece of equipment from a gold mine that was obviously left in an area underground where water collected. It has been proven that sediments that have been transported by water underground have incredibly high gold content. This silt is a yellow/orange/brown colour. 
How would you go about testing a sample for gold?

Sorry about the abrupt post, rushing around.
Thanks in advance.


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## martyn111 (Sep 8, 2011)

Get an assay on the material, the colouration could be iron oxide from the machinery being in water and is no guide as to what the material contains


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## Harold_V (Sep 9, 2011)

The advice to get an assay is sound, but if you feel there's free gold in the sample and you'd like to investigate before paying for an assay, you might try giving the material a prolonged boil in HCl. That should eliminate iron, leaving behind material that lacks the staining. If there's free gold present, it should be obvious. 

Alternately, you might try panning the material. Again, if there's free gold, it may be visible. 

I'm assuming that the gold in question would be large enough to be seen. If it's extremely fine, you may not have success with either of these processes. In that case, the HCl wash, followed by a dissolution of a small sample with aqua regia may reveal the presence of gold. You'd test the resulting solution with stannous chloride. 

You'd have to use good judgment if you go the AR route. Too much free acid would not yield a result with the stannous chloride test, even if there was gold present. 

You'd be well served to read Hoke's book, which will help explain these things.

Harold


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## froot (Sep 9, 2011)

Thanks for the replies. Any gold present would be in it's mineral form. 
Apart from any values there will be a large amount of iron and it's oxides/hydroxides from the rusting machinery in the mix as well as Silicon oxides/quartz type solids. I'm also expecting Calcium compounds from concrete that's used underground to anchor the machinery. 
Boiling in 30%HCl sounds like good advice, thanks. Will give it a try and report back.


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## froot (Sep 19, 2011)

As I go along more and more questions occur to me. I have downloaded the book by CM Hoke and read through it, it does mention catagorically however that it does not encompass the refining of PM's from ore, which is basically what I'm trying to do but it has been nonetheless very interesting. 

Ok progress so far is that I have cooked about 100g of silt in HCl for an hour and filtered out the HCl + solubles. I then washed the silt with purified hot water by pouring it on the silt while still in the filter paper over and over for 3 times. The silt now has a white - greyish appearance. I have not proceeded with the silt yet until I am comfortable with the AR procedure that I'm going to use. The silt would contain considerably less Au than jewellry/dental/electronic scrap so it's inevitable that I'll exceed the stoichemetry of HNO3 based on Au. I need to distinguish the least amount if AR to use while making sure it is in contact with all particles in the silt and the maximum possible dilution of AR with water while still remaining effective in order to ensure all the silt is wet and treated. After treatment I wish to add enough water to mobilise the mix and filter out the liquids with washing. Then concentrate the liquids by boiling down, testing with stannous chloride and If I get a +ve, I'll store it and do more batches until I have enough to make it viable to precipitate the Au. If anybody has suggestions please don't hesitate to mention them, and if any can point me to a procedure for AR preparation for this sort of thing I would be truly greatful. 

Now here's something else I pulled out of a winch from a Platinum mine:





I am assuming it's a chunk of chromite from either the Merensky or UG2 platinum reefs in the Bushveld complex here in South Africa. It's heavy compared to an average rock that size, it crumbles easily and has a nice glitter about it. 
Here's a closeup of the grain: 





If anybody here is familiar with this material how would you go about turning it into shiny metal, assuming it is bearing?

My thoughts at the moment are to crush it fine in a bar mill I'm building, dissolve the prospective PM bearing matrix in molten NaOH to form soluble products (FeCr2O4 + NaOH + O2 -> NaCr2O4(sol) + Fe2O3 + H2O. I would then dissolve the solubles and seperate this from the insolubles. The insolubles would then be washed and treated with HCl to remove Fe and other unwanted metals. Filter, wash then treat as per Hoke for multiple PGM with hot AR. Make sense?

Thanks in advance.


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## Palladium (Sep 19, 2011)

The best man to answer that question is Rick. He goes by the name Rock man here on the forum. If you want to know about rocks he is your man. Post your question again here http://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=5588&p=108063&hilit=the+rock+man#p108063 and he will answer it. welcome to the forum.


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## froot (Sep 20, 2011)

Thanks, will do.


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