Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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High Silver in Dore' (2 replies and 1 comment)

Japhet
9 months ago
Japhet 9 months ago

Hi Team,

I getting trouble to improve fineness on Dore' as most of the time i am getting more  50%+ Ag, Is there a specific flux recipe or extra additive that has been tested to improve the fineness of the gold bars? 

Greg Henderson
9 months ago
Greg Henderson 9 months ago
1 like by David

Japhet

I'm not clear on why you want to improve the gold purity as the gold refinery would pay out on silver anyway, less processing costs.  Silver is valuable to refineries as they make 1000 oz bars using for sale.  They separate out the silver during refining using the Miller Process (chlorine gas injection) or electrolysis.

If you are really keen on removing silver on site you could try nitric acid digestion of your precious metals cell muds or filter cake prior to smelting in a plastic vat.  This will also remove copper, zinc and most other base metals, leaving only gold.  You will need good fume extraction and gas scrubbing as toxic nitrogen dioxide fumes are generated.  After leaving it to stew overnight, decant off the silver nitrate solution and do several rinses of the solids prior to filtering to remove free acid.  You don't want any acid in your crucible! 

The silver nitrate solution can be treated with lime to drop out the metals as a mixed hydroxide which may have some commercial value.  Have fun, this takes me back to my days at the Old Perth Mint!

Greg h

David
9 months ago
David 9 months ago

Tor Danielsen told me this: Pour molten au Ag into water bath to granulate product, then treat using hot nitric acid to dissolve the silver, then add chlorine as HCl to produce AgCl precipitate. If the process is carefully executed you will end up with Au and Ag in the high nineties eg 99% plus.

To be certain to obtain the above the result, a higher ratio of Ag to Au than 50:50 is envisaged. An increased inventory of silver in the dore smelt before granulation will result in higher gold percentage in the final product. Optimum silver addition before granulation needs to be determined in each case, but as the silver needed is recovered after the operation it can be reused perpetually.

 

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.999
7 months ago

The process David is referring to is called " inquarting " or " quartering." It's when refiners lower the percentage of gold to 25% by the addition of silver or a base metal such as copper. 3 parts silver to 1 part gold. You can then remove the unwanted metals with nitric acid and washing with water. The silver can be dropped from the nitric acid with copper as elemental silver or it can be dropped as a chloride with salt or hcl. With the proper procedures and washes it's possible to get 99% plus gold or silver.

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