Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

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Black layer attached to Dore bar (2 replies)

J
Jeffreybch
5 years ago
Jeffreybch 5 years ago

Hi,

We normally reduce our loaded electrowinning Steel Wool with Sulphuric acid, then the acid is removed and the remaining materials are washed and dried.

Later the dried materials are mixed with the following flux:
60% Borax, 20 Niter, 5% Soda Ash, 15% Silica.  (we tried several other combinations with similar results).

The problem is that the resulting dore bar (after removing the slag), always has a hard black layer attached to the top.  This "matte" bar seems fused to the dore, and it is very hard to remove it.  The material smells like sulphure and it is soapy if you touch it, but extremely hard.  We XRF a chip of the "matte" (the xrf only reads for metals) and it is basically 85% silver 1% gold 11% iron.

I am looking for ideas on how to improve my procedure or flux formula, please.

Thanks in advanced,

 

J.

J
Jeffreybch
5 years ago
Jeffreybch 5 years ago
Like

I forgot to mention that this layer is in the range of 1-2 millimeters.

 

A
AJ
5 years ago
AJ 5 years ago
Like

Hi Jeffrey

We occasionally see this black material too...

I would suggest that it is an excess of iron from your cathodes, a solution for this problem would be to allow more time (or acid) for your cathode digestion, this will reduce the amount of iron going into the smelt. You could also change your flux mix to the following:  Borax 40%, Nitre 30%, Silica 20% and Soda ash 10% and this should remove any remaining iron from the steel wool.

Regards

Andrew J

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