cyanide leach! cant get 99% Gold recovery

bee · May 16, 2013

recently i used the cyanide leach on gold plated pins the method is exactly described by GSP i set the ph to 12 and then add ZINC powder stir time by time after 24 hours i catch the black gold dust with zinc dust. problem is
on both two experiment its need too much zinc powder.
first batch of 13LB rams fingers i add 100 gram zinc powder and after 9 hours i got only 12 gram gold then add another 100 grams stir time by time after 24 hours get 6 grams. now add again 100 grams and stir 24 hours and get another 6 gram.
i donot have source of zinc powder so you cant imagine its a hard working i rub the zinc metal with a sharp rubbing tool i donot know the English name but i get 100 grams zinc powder into 9 hours. as English is not my first language.
so can i use zinc oxide instead of zinc powder?
why its taking so much zinc powder and giving only few grams of gold?
now i am tired and left the solution alone but i am 100% sure there is much gold left what is brown or gray fog which is so fluffy and fly all around when you add the zinc powder?
add about 300grams of zinc powder now how much its need more?
can GSP as he is expert enlighten me what is going wrong as he also add the the zinc powder i make the ph 12 with NAOH and try to follow him read all posts through google through this awesome forum but i am really confused the the liquid color is still brown type, the precipitate is black also the last two addition of 200 grams zinc powder given me only 12 grams gold which you can consider how hard is this when you add 50/50 HNO3 and yes i have very good hood setup and have chemistry back ground .also kindly do suggest me is zinc oxide can be used other than zinc powder?
thanks
bee

goldsilverpro · May 17, 2013

bee,

My guess is that the zinc is the problem. In my posts on the subject, I think I always said to use 325 mesh "zinc dust" (only by that name). In my experience, the gold tends to coat the zinc particles and this blocks the interior zinc from reacting. With coarse zinc, this can result in great inefficiency. The zinc powder you're producing is surely much, much coarser than 325 mesh (which is about 44 microns - .0017"). For example, if the powder you're producing is, say, 8 times larger (.013") than 325 mesh, the individual particles would weigh 500 times more.

Zinc dust, 325 mesh, is available on eBay, for about $4-$6/pound. The zinc dust tends to clump with moisture so run it through a fine sieve before using.

There is a zinc powder commonly available that contains a silica anti-clumping agent called Cab-O-Sil. It's not called "zinc dust". Most I've seen was 200 mesh. The silica tracks through the process and makes the gold refining more difficult. Don't buy any zinc powder with Cab-O-Sil in it.

Instead of zinc, I've first filtered the solution and then had good luck plating the gold out. Just rig up 2 electrodes made from stainless sheet. For a 5 gallon bucket, I would make the electrodes about 6" x 6" and use about 3 to 4 amps DC across them. If you clean the stainless before using, don't use anything even mildly abrasive. The passivated surface might be damaged and the gold will then stick to the cathode and be difficult to remove. Some of the plated gold might fall off the cathode and be on the bottom.

samuel-a · May 17, 2013

Instead of Zn dust, Steel wool is very cheap and very affective.

goldsilverpro · May 17, 2013

samuel-a said:
Instead of Zn dust, Steel wool is very cheap and very affective.

Have you ever tried this, Sam? I haven't, but I would question whether it would work. When I strip, I tumble it in a steel cement mixer and have NEVER had any gold deposit on the steel. The solution I use has a lot of cyanide and peroxide in it. In order to deposit gold on the steel wool, some of the steel wool would have to dissolve. I don't think that will happen by immersion in a simple cyanide solution. There are electrolytic processes that utilize steel wool cathodes to remove gold from cyanide but I've never seen one by simple immersion.

https://www.google.com/search?q=steel+wool+gold+cyanide&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US

fficial&client=firefox-a

samuel-a · May 17, 2013

Yes Chris

The cementation actually looks more like plating. It does take longer though, it took about 48 hours until the iron wire structure broke down and leave small wirs of gold.
I have pictures somewhere, i'll try to find them.

I believe the steel of cement mixer is different from the steel wool.

samuel-a · May 17, 2013

Found it in my phone.
The first one is the gold wires left after all the wool was gone.
The second picture is of the same solution but with Zinc ribbons cementing the gold.

bee · May 18, 2013

thanks so much Chris and Sam,
i think i should have use the electrolyte to plate out the gold.
Chris do i follow the same procedure like brought PH to 12 by NAOH and then use stainless steel two sheets?
what type of stainless steel sheet 304 or 316?
what is recommended thickness of sheet?
i ,ll use 12 vot 3 or 4 dc is this fast? i mean how much time it ,ll take to plate out a 5 gallon batch and how do i know the batch is empty and there is no gold left?
Sam kindly do give me a little more information about using the steel wool.
and yes you are right the problem is really Zinc because my zinc powder is about 200 mesh.
i am not able to use ebay as i am not into US i am far far away and if i try to buy zinc dust through ebay i ,ll face too much shipping cost.
thanks so much guys.
bee

samuel-a · May 26, 2013

I used same process as with zinc.
Add NaOH to ensure solution is basic and add steel wool.

Gratilla · May 27, 2013

For cyanidation to work, oxygen is necessary for the chemical process and air or oxygen is typically bubbled through the cyanidation tanks.

However ... cementation is a (partial) reduction process and is hindered by oxygen.

Cyanidation projects that use cementation (usually zinc) typically use a vacuum pump to extract oxygen from the pregnant cyanide solution prior to adding the zinc.

bee · May 28, 2013

How to vacuum pump to extract oxygen from the pregnant cyanide solution?
thanks
bee

samuel-a · May 28, 2013

Bee

Chemistry 101, if you reduce the pressure in the solution tank you will change the equilibrium.
Dissolved gases will strive to go back to the gas phase.

You could find more info on google using "Le Chatelier's principle".

Gratilla · May 28, 2013

You can also force out the oxygen (and other dissolved gases) by raising the temperature of the liquid (ie the solubility of gases in water usually decreases with increase in temperature). But the last time I looked at the solubility curve for oxygen in water, it still showed a decent amount of dissolved oxygen at 100 deg C (ie boiling point).

So a vacuum pump is the way to go.

bee · May 30, 2013

thanks guys.
sam this steel wool is easily available kindly correct me that this is working fine.
http://en.wikipedia.org/wiki/Steel_wool
thanks

samuel-a · May 30, 2013

Yes, plain steel wool.
Gentle heating, 40-50 °C will make things go faster of course.

bee · May 30, 2013

thanks sam i ,ll use and post the results
bee

goldsilverpro · Jun 1, 2013

Sam,

Good job. It certainly surprised me that the steel wool worked. If you don't mind, I have a few questions. What cyanide formula did you originally use? What was the source of the gold that was dissolved? Is all of the steel wool inside the gold dissolved? How did you test the solution to determine if all the gold was out?

samuel-a · Jun 11, 2013

Chris,

Sorry, i forgot to answer.
The starting material was solid crystals that were precipitated in an plating baths. I do not know the exact composition of the electrolyte nor the composition of the solids.
I have dissolved the crystals with dilute warm NaOH solution and placed the wool inside. Kept it warm for several hours.
The iron/steel from first addition of wool had been completely dissolved and the wire structure disintegrated. To test complete dissolution i turnd to the oldest trick - a magnet.
Then, the gold "wires" were filtered and new wool was added. The proces repeted two more times. The third time, the wire was coated with gold but magnetic after sveral days in solution, hinting there was no more cementation.

loghman1351 · Jul 28, 2013

What color is the deposition of gold in cyanide?
I deposited with aluminum foil.
White is the color of the precipitate.
Why
Sediment color is important?
Be black, or color does not matter deposition?

loghman1351 · Jul 28, 2013

I did 300 kg soil with cyanide. Poured sodium hydroxide solution, filtered
Aluminum foil and placed in a solution. The 0.5-inch foil
After 2 days, the white precipitate.
May be precipitated white gold?

chlaurite · Jul 28, 2013

Naive question...

I understand that, for most of the recoveries we do, we tend to use HCl/Cl because it counts as fairly safe (where "safe" means "causes instant burns on contact" as opposed to "one good whiff will destroy your lungs :shock: ); and AR works a good bit easier, though a lot more dangerous and (for most of us) both more expensive and harder to get the reagents.

But for what purposes would we ever intentionally choose cyanide over something safer? This one seems almost like a no-brainer.

/ Not even remotely interesting in trying it, only wondering out of intellectual curiosity.

cyanide leach! cant get 99% Gold recovery

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