Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-03-23T09:55:18+00:00
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Panning of gold containing borax slag (5 replies)

8 months ago
kannan 8 months ago

I wonder how to increase the panning of gold containing borax slag?

Is the particle size affect the panning yield?


8 months ago
inOr 8 months ago
1 like by Bob Mathias

You want to grind to the size of the gold particles you are going to pan.  Too large, and the gold will be mixed with other material (eg. undissolved borax) and the particles of mixed composition won't have the specific gravity of pure gold.  That will make it harder to separate the gold from lighter materials.  On the other hand, if you grind it too small, the gold can "float" and be discarded together with the light materials.  You need to experiment to determine the optimum particle size. BTW, if the borax slag still contains borax (sodium borate), then the borax can be removed in water, since it is quite soluble in water.  

7 months ago
kannan 7 months ago

How to improve the yield in the smelting stage itself? without giving out the gold to the borax.

Is there any special method available to do so.

Jorge Ganoza
7 months ago
Jorge Ganoza 7 months ago

If you want to recover gold from slags, you should evaluate the effect of the particle size on the recovery. It is necessary to perform several tests in the met lab using a shaking table. Try to study if the gravity recovery is very important or not to get an acceptable gold recovery.

Other option is to recycle the slags to the leaching process. For example, after crushing, slags could be placed in the heap leaching process. 

You should be aware that some operations installed a gravity recovery circuit to treat slags. but the results were very variable and decision was to close the circuit.

Finally, try to evaluate different fluxes to get an indication of the optimal charge in the smelting process.   


7 months ago
Colette 7 months ago

Hi Kannan

If I understand your query in the comments correctly, you are also keen on reducing the amount of gold (or shot) in the slag?

The presence of gold in your slag is commonly due to two things - too short a smelt time or too viscous a slag. Most gold smelts run around 1.5 to 2 hours from a cold start, but they do tend to be very temperamental, and you almost need an "eye" for when it is ready. Using electric arc furnaces I was taught that when you start seeing sparks fly out of the furnace that have a comet like tail the pot is "ready" - it might be better to be a bit more scientific about things :-), and run your smelts at increasing times - add 10 to 15 minutes per smelt, and see if there is a difference in the yield?

Viscosity can be a bit trickier to sort out. Fluorspar and silica both can reduce viscosity in the slag if you increase their relative ratios in your flux recipe. If you have a silicaeous slag already (glassy streamers when you pour are a good indication of this), then consider adding a bit more Na2CO3. Fiddling with flux ratios tends to be a bit empirical, just remember to write down what you have done so that you can go back to it if things go wrong!

7 months ago
kannan 7 months ago

Which flux is more oxidizing potassium nitrate or sodium peroxide? for smelting with borax.

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