Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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Optimise Merril Crowe Process and reduce base metal in the dore (11 replies and 6 comments)

Alex Loutou
3 months ago
Alex Loutou 3 months ago

Currently our Merril Crowe running with 2.5 ppm Au, 5 ppm Ag, zinc consumption 5kg/hrs (more than 20x stoichiometry) and 100 ppm PbNO3. So the base metal content in dore consist of 17% zn, 8% Pb and less Cu, Fe. Smelting ratio 1:1 cake: flux (15% silica : 50% borax : 35% Soda ash).

Can I increase the smelting ratio to 1:2 cake flux, or only Silica, borax, soda ash? whats the negative effect of excess flux?  or need borate or KNO3 or something?

Any response will appreciated.

Thank you,

Alex

David
3 months ago
David 3 months ago

Keep adding flux. you are pretty low now. 

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Richard S
3 months ago

David, I received your friendship request and I think that I have tried to OK that. I went to the membership directory and clicked on the friendship request button. If I need to do something else, please let me know as I am new to the site and haven't done that before. Regards, Richard Kunter

Richard S
3 months ago
Richard S 3 months ago
1 like by David

You can treat the precipitate with sulfuric acid to remove the excess zinc and the copper from the precipitate prior to smelting.  Alternatively or additionally you can calcine the precipitate at about 600C to oxidize the metal content making it easier to flux and take the base metals into the slag.  Increasing the flux ratio to precipitate amount will also help as suggested by David.

Alex Loutou
3 months ago
Alex Loutou 3 months ago

Thanks a lot David and Richard,

I have to increase flux ratio.

Treatmment by sulfuric acid is last option. Considering to handling sulfuric acid with cyanide in Merill-Crowe process.

Best,

Alex

 

 

Richard S
3 months ago

Adding an oxidant such as niter to your flux will help oxidize the base metal content and make it more amenable to staying in the slag. Increase the niter content of the flux with a small amount initially until you see how it reacts. Too much niter can make the reaction very active. You can experiment with gradually increasing amounts of niter until you have more of the base metal oxidized and not a too violent smelting condition. Addition of a small amount of flurospar, calcium fluoride, will help increase the fluidity of the slag if it becomes too viscous. Don't over do the fluoride as it can increase metal loses if you have too much.

sarchery
3 months ago

Richard S
I've added 20% (of calcine mass)potassium nitrate to try and get copper into the slag, it didn't work. I m going to now try a bit more potassium nitrate with a bit of manganese dioxide. What is the maximum potassium nitrate one can add without it being violent?

Richard S
3 months ago

I think that you are going to have to experiment to find out the maximum amount of niter by continuing to add some additional niter percentage to a new batch. You can observe the reaction to determine if that becomes too violent. I would also consider adding some additional borax and silica to the flux mix. Report on how it went please. Treating the precipitate with sulfuric acid carefully in a controlled gold room is still an excellent way to put the copper and remaining zinc into solution and out of the precipitate. Calcining at 600C prior to smelting would also be helpful as it oxidizes the base metals so they prefer to be in the silica based slag.

Alex Loutou
3 months ago
Alex Loutou 3 months ago

I have increase the quantity with same formula of flux but it didn't work. The base metal not decrease. Atleast I know that excess of flux not affect for melting and pouring.

Due to the the base metal containing is Zinc dominant and less copper. Consider to sulfuric treatment but the first is looking for reduce zinc dust in Merril Crowe.

 

David
3 months ago
David 3 months ago

By how much did you increase the flux?

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Alex Loutou
3 months ago

50%

David
3 months ago
David 3 months ago

That' still low. A friend was guiding me on this. He was saying you could 2x it. It really is not my strong point. I'll let others help you out. 

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Alex Loutou
3 months ago

Ok thanks alot David,
I try to reduce Zn duct to precipitated in MC.

David
3 months ago
David 3 months ago

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Richard S
3 months ago
Richard S 3 months ago
1 like by David

Alex:  Make sure you check your PLS barrens for both gold and silver if you are reducing zinc dust (and lead nitrate or lead acetate at 1:10 zinc ?).  If you reduce too much you fail to precipitate all of the metal in solution.  Drop your zinc amounts until you start to see a rise in barren metal content (likely silver first), then up it a small amount.  You will need to adjust if your feed to leaching changes significantly so that your PLS loading increases.

I agree with David's comment about upping the flux ratio more.  I also left you a comment on your other question about gold and silver ratios using MC.

Richard

Alex Loutou
3 months ago
Alex Loutou 3 months ago

Thanks David and Richard,

Yes, reducing Zinc if posibble without sacrife the precipitate efficiency, controlling on barren solution should intens as long as trial.

Aim to reduce the zing is the best way I thought to decrease the base metal in dore which is zinc dominantly. Increase more flux as David suggested will applied in the future opportunity, beacuse from the first I have trial increase 50% flux gave no significant effect.  I point that take long time to smelting (qty increase) beside increase flux consumption itself.

Thank you,

Alex 

max skinner
3 months ago
max skinner 3 months ago
1 like by David

Alex, here is some information that I received, when at the Mackay school of mines, from my metallurgy professor who had lots of experience smelting zinc ppt. I hope this will help you. 

hammond formulas
https://www.911metallurgist.com/wp-content/uploads/2017/04/hammond-formulas.jpeg
David
3 months ago
David 3 months ago

I just uploaded this long and extensive history paper. I think it would help you. It reviews an example goldroom refining practices https://www.911metallurgist.com/gold-refinery/

https://www.911metallurgist.com/gold-silver-refinery/

https://www.911metallurgist.com/fine-gold-recovery-refining/

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