# Does stannous chloride work on cyanide solution?



## kapasari (Aug 22, 2010)

Hello Everybody,

This is from a newbie trying to study.
I trying to leach sulfide ore with NACN. 

First I roast the ore to get rid of pyrite.
Then wash the grounded ore with 10% H2SO4
Wash with water.
Then use NaCN to leach the ore
After filtering, I got a yellow solution.
React that solution with stanous Cholride would give black color.

Does it mean the ore contains Gold ?

All of this is still using small quantity ore ( 100 gr) for testing purposes.
I also have sent the ore for fire assay test, but it would take 2 weeks.

Thank you.


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## Harold_V (Aug 22, 2010)

To my knowledge, stannous chloride does not react with base solutions. Could be wrong---I'm no chemist. 

It will be interesting to hear if the reaction you are getting is gold---but-- be advised----gold in cyanide is not yellow---it's clear of color. The crystals can be compared to something like baking soda in color (snow white) and appearance. 

Welcome to the forum.

Harold


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## nickvc (Aug 22, 2010)

I know we are only talking small quantities here but a warning over mixing acids and cyanide I feel must be posted! Please use a fume hood and if possible avoid mixing them at all , dropping the metals out of the cyanide solution with zinc dust washing and redissolving in AR then testing would give a better result in my opinion and be safer.


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## goldsilverpro (Aug 22, 2010)

> Then wash the grounded ore with 10% H2SO4
> Wash with water.
> Then use NaCN to leach the ore


This are the steps that scare me. If any traces of sulfuric are not rinsed out, the addition of NaCN would produce highly toxic HCN, hydrogen cyanide gas. After rinsing out the H2SO4, it would be wise to first adjust the pH to at least 10.5 with NaOH before adding the cyanide.

Stannous chloride won't detect gold directly in a cyanide solution.


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## kapasari (Aug 22, 2010)

Hi GSP,

Thank you for the reply.

Yes, I did add some NaOH and test the PH
to make sure that they are well above 12 with litmus paper.
I guess I forgot to include that step on my post.
( I'm also wearing a chemical fumes breathing filter)

If stanous Chloride does not work, how do we detect 
the gold concentrate on the solution?
I try to drop them using zinc, but as I only use 
small test sample, it is not very clear.
I did get some very fine brownish perticipation, 
but is not much.

Thank you.


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## goldsilverpro (Aug 22, 2010)

kapasari said:


> If stanous Chloride does not work, how do we detect
> the gold concentrate on the solution?
> I try to drop them using zinc, but as I only use
> small test sample, it is not very clear.
> ...


Stannous chloride won't test for gold in a cyanide solution because the gold has a valence of one (I). Using stannous chloride requires the gold to be valence 3 (III), which is the state of gold in a gold chloride solution

As far as I know, there is no simple method of detecting or analyzing gold directly from a cyanide solution. Exceptions would be the use of atomic absorption or ICP instrumentation.

Most all traditional analysis methods involve collecting the gold in lead and then using fire assay (there are 3 or 4 different ways to do this). An example would be to make a leak-proof box (or, boat) from lead foil and then slowly evaporate a sample (from 5ml to 50ml) of the solution in the box over gentle heat. When dry, the foil is folded up, with the dried residue inside, and then directly cupelled or fused/cupelled. A direct cupellation will "spit" some, but the losses should be minimal. I have used this method many times. If the NaOH is too high, though, it can attack the lead and the boat will leak. Instead of evaporating in the lead boat, the sample can be evaporated slowly in a small separate container (a watch glass can be used if the temperature is kept very, very low - otherwise, it will break). The residue can then be cooled, carefully and completely scraped out and collected, wrapped in lead foil, and cupelled. 

For quantitative results, the zinc method you are using may work, but I would use a larger sample - maybe a liter. Add enough zinc (325 mesh zinc dust is preferred) to barely make the precipitated powder gray colored. At first, the powder will be brown (gold and/or copper). When you've added enough zinc to produce a gray color, all of the gold should be precipitated out. The zinc tends to lump up in storage, so put some through a small fine flour sifter before using. Try not to use a great excess of zinc. It should take from 1 to 2 grams of zinc per gram of gold. Filter and rinse very well to remove all traces of cyanide. Under the fume hood, cover and leach the residue with 50/50 nitric for about 30 minutes - keep it hot. All of the zinc and copper, etc., should dissolve. A brown gold powder should remain. Filter, rinse well, dry, and weigh the powder.

If all you want to know is whether gold is present, or not, I would collect the brown powder that you say you already have (from zincing), rinse it well, leach out possible base metals with nitric, rinse, dissolve some of the residue in a few drops of aqua regia, and test this solution with stannous chloride. A white spot plate would work well for this. 

There is another colorimetric way I know of to convert the sodium gold(I) cyanide to a gold(III) chloride and then use stannous chloride to check for the presence of gold, but it is quite involved .

It is also possible to treat a sample of the cyanide solution directly with very hot concentrated H2SO4 plus a few drops of nitric acid (Under a very good fume hood!!!) for an extended period of time. This is called "wet ashing". The cyanide is destroyed and the gold comes down as a brown powder. The procedure has been covered somewhat on the forum. It is involved and can be quite dangerous if you don't know what you're doing.

If possible, I would send your solution samples to a qualified lab and let them do it.

Chris


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## kapasari (Aug 23, 2010)

Thank you GSP for the long and educational response.

I would try to :
wash the powder
Wash with 50% Nitric Acid
few drops of AR
test it with stannous chloride as suggested.

I read your posting about using m-NBSS, and a little 35% H2O2
in addition of using NaCN. Could you tell what are benefit of adding them ?

Thank you.


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## goldsilverpro (Aug 23, 2010)

kapasari said:


> wash the powder
> Wash with 50% Nitric Acid
> few drops of AR
> test it with stannous chloride as suggested.


In thinking more about this, to just test the powder you've already produced for the presence of gold, the nitric step wouldn't be necessary.



> I read your posting about using m-NBSS, and a little 35% H2O2
> in addition of using NaCN. Could you tell what are benefit of adding them ?


Sodium cyanide alone will not dissolve gold. An oxidizing agent is also needed. When leaching ore, very weak NaCN (about .02% or less - 0.2 g/l) is used and oxygen from the air is normally used as the oxidizing agent.

When stripping gold plating, more cyanide is used, along with a stronger oxidizer, in order to reduce the stripping time. Both m-NBSS and H2O2 are strong oxidizing agents. Either one or both can be combined with the cyanide. Please note that I have only used these on gold plated scrap, and not on ore. For use as a stripper for plated material, a combination of just m-NBSS (15-30 g/l) + NaCN (30-45 g/l) is usually heated to about 60C. When using H2O2 (about 6 ml/l of 35%) + NaCN (about 30 g/l), the solution will get hot by itself when these 2 chemicals are combined. The differences are that the use of H2O2 will tend to decompose the NaCN and the solution can only be used for one batch of stripping. Using only m-NBSS is slower but it doesn't appreciably decompose the cyanide and the solution can be re-used, for several stripping batches. However, once the solution has been zinced, it is spent and can't be used for further stripping. In some cases, for very thick plating, I have used both m-NBSS and H2O2 (in very small amounts) to speed things up a bit.


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## kapasari (Aug 25, 2010)

Hello GSP,

Thank you for your reply.

I have tested it as described and the result
was negative. So, no gold.. sigh..
This later confirmed by assay result.

However, this got me thinking.
Can I do AR directly on crushed ore,
without nitric wash, ect,
and then test it with stannous chloride 
to see if it contains gold ?
Would other dissolved metals give false positive?

Thank You.


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## qst42know (Aug 25, 2010)

Has your ore been fire assayed for gold content? 

Has the presence of gold been confirmed before you try to find a process.


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## rustyle (Jan 14, 2014)

goldsilverpro said:


> kapasari said:
> 
> 
> > wash the powder
> ...



GSP, 

You are pro of cyanide process on this site. Will you let us know more detail of drop gold out of gold cyanide solution? I did every step that you said under good fume hood, air supply mask and follow all safety guideline of cyanide. But come to drop gold out of solution, I didn't get all out as expected gold calculated. Will you help?

I did a 1 liter solution for 350 grs gold lids from cpu. Here's my solution: 20 grs m-NBSS + 35 grs NaCN + 1000 ml water

I add 30-35 ml H2O2 35% to kill cyanide after I dissolve all gold plated, then add KOH to adjust the pH to 12. I add 25-30 grams of 325 mesh Zinc powder to drop expecting gold of 11.5 grams Au. This number I get from sulfuric cell which I did the same amount and same type of gold lids from cpu.

After did the 40% nitric to clean up base metal and Zinc. The result is only 5.57 grams Au out of the solution. So in cyanide solution still have about half of the gold. 

I add more Zinc and nitric lean up but very little to nothing of Au. Where the rest of the gold? It should be still in solution. 

I had done with sulfuric cell/AR clean up of same amount and same type of 350 grams gold lids from cpu. All 3 batchs come out very much same number of 11.5 grams (+/- 0.6 grams)

Now I try with 1 liter cyanide solution to see any better result, but it's only 5.57 grams Au. 

Please help to save the rest of Au in the solution!

Thanks,


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## goldsilverpro (Jan 15, 2014)

rustyle said:


> goldsilverpro said:
> 
> 
> > kapasari said:
> ...



A couple of possibilities:

I would guess this is the problem. If these gold plated lids are typical, they have a band of gray colored 80gold/20tin braze around the edge on one side. On lids, about 50% of the gold is in the braze. In my experience, cyanide won't dissolve this braze. Check the stripped lids to see if there is still braze on them. If so, you possibly have no gold remaining in the solution. The sulfuric cell will strip the braze slowly but often incompletely. Actually, to process gold plated lids with gold braze on them, neither cyanide or the sulfuric stripper are good choices.

Why did you add the peroxide, after stripping and before zincing? You need cyanide available to complex the dissolved zinc. At room temp., it takes several hours to destroy the cyanide with H2O2 and therefore, you probably had some free peroxide in there when you zinced the solution. The oxidizing power of the peroxide may have hindered the reduction of the gold. Also, if the peroxide did destroy the cyanide, none would be available to complex the zinc.

If possible, find a lab with an atomic absorption unit (AA) and a gold lamp and have the solution checked for gold


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## Lou (Jan 15, 2014)

Chris,

Even if the CN- is destroyed, zinc should still drop it out and produce the corresponding sodium zincate [(Zn(OH)4)]2-, but then again, if all of the CN- ligand is gone, then your gold should be as sodium aurate. At that point, lowering the pH towards neutral will cause Au(OH)3 to precipitate, and that be melted straight as is.


Another option for gold determination is colorometric by extracting the Au(III) out with methyl isobutyl ketone, or even tributyl phosphate (preferable). In the case of the ketones, the extract can then be evaporated down and done gravimetrically or done straight with instrumentation. Using MIBK to extract out the gold is an option, if one is prepared to recover the solvent which has fairly high aqueous solubility, and a modicum of instability in strong base solutions.

I think the best way is to plate it, but there are other methods using NaOAc, N2H4, and dithionite.


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## jimdoc (Jan 15, 2014)

Can someone please fix the spelling in the title to this thread?

Jim

Thank You


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## goldsilverpro (Jan 15, 2014)

Lou,



> Even if the CN- is destroyed, zinc should still drop it out and produce the corresponding sodium zincate [(Zn(OH)4)]2-


I thought of that but didn't feel there would be enough NaOH in there to complex all the zinc needed to produce the zincate. If it takes an equal amount of zinc as you have gold (I know it's actually a little less), it would require at least 28g of NaOH. I doubt if he used that much to adjust the pH just to 12.


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## rustyle (Jan 15, 2014)

> A couple of possibilities:
> 
> I would guess this is the problem. If these gold plated lids are typical, they have a band of gray colored 80gold/20tin braze around the edge on one side. On lids, about 50% of the gold is in the braze. In my experience, cyanide won't dissolve this braze. Check the stripped lids to see if there is still braze on them. If so, you possibly have no gold remaining in the solution. The sulfuric cell will strip the braze slowly but often incompletely. Actually, to process gold plated lids with gold braze on them, neither cyanide or the sulfuric stripper are good choices.
> 
> ...



First,
Thank You for fast reply! and all other replies from other members

The sulfuric cell, GSP is right about the braze. There's still little bit but not much after stripping gold off. 
The cyanide, the braze are still there a lot more than sulfuric cell. But I don't think half of the gold is still on the stripped lids. 

As you said, I did wrong when add H2O2 before add zinc. So, correct way is not add H2O2. Just add around 28 grams of NaOH or KOH to adjust the pH to 12, then add the Zinc powder to drop the gold. Please confirm! 

I will try again with correct cyanide process on just clean gold pins. 

Also you said cyanide and sulfuric cell are not good process for these lids, what's best way to do these gold lids? I had done weak nitric before but I don't like to handle too much acid solution. 

I still have about 8-9 pounds of these cpu lids to process that I save from refining cpu and buy from junk yard. Mostly are Intel and Motorola.

Please advise! 

old but still in school....LOL.... I'll listen to all and learn.


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## rustyle (Jan 15, 2014)

goldsilverpro said:


> Lou,
> 
> 
> 
> ...



Yes you are right, I only add 15-20 grams of NaOH to adjust pH level. Should I add more NaOH or KOH and follow Lou's advice? 

Please advise of how to correct on this solution! 

Thanks,


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## rustyle (Jan 15, 2014)

Lou said:


> Chris,
> 
> Even if the CN- is destroyed, zinc should still drop it out and produce the corresponding sodium zincate [(Zn(OH)4)]2-, but then again, if all of the CN- ligand is gone, then your gold should be as sodium aurate. At that point, lowering the pH towards neutral will cause Au(OH)3 to precipitate, and that be melted straight as is.
> 
> ...



Lou,
What do I use to lower pH if there's no cyanide left in solution? 
Please advise!

Thanks,


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## goldsilverpro (Jan 15, 2014)

You're going in too many directions. 

The braze is 20-40 times thicker than the plating. I would bet that 90% of the gold in the braze is still there. I might also bet that no gold is in the solutions (there are always traces left, though). You might also find that the lids from the sulfuric stripper still have a lot more gold than you expect. The figure of 11.5g of gold/350 g of lids, about .5 oz/pound, seems low to me. A brand new 1/2"x1/2" lid, before sticking it on an IC package, will run about 1.0 tr.oz. of gold per pound. When brazed on the seal ring of an IC package and then removed by heat or, say, a chisel, about 1/2 of the braze will be on the lid and the other 1/2 will be on the seal ring of the IC package. Little lids are worth more money per pound than big lids.

You misunderstood about the 28 grams of NaOH. I didn't say to add it to the solution. If you added that much, you could have a pH way over 12. That's OK but it's a waste of chemicals.

About the only way to get 100% recovery is to dissolve them. There are 3 basic ways to do this.
(1) Dissolve the lids in some strength of hot nitric - 50/50 or weaker. 2 pounds of lids will dissolve in about 1 gallon of 70% nitric, before dilution. A heavy duty non-magnetic stainless pot will work well. It will go slow. The brown or black gold will settle to the bottom along with some pasty tin slime. After collecting the sludge and rinsing the nitric out of it, it is dissolved with aqua regia (AR).
(2) Dissolve everything in aqua regia. It's always faster than just nitric, as above, but there is a lot more fumes. You probably won't have to heat it because it makes its own heat. A gallon of AR will dissolve about 2 pounds of base metal. I would do about 2 pounds at a time in a bucket. Cover with HCl and dribble in a little nitric. When the reaction slows down, add a little more. Stop adding when an addition doesn't produce a reaction.
(3) This is more tricky. You do the same as (2) except you don't take it all the way. The lids want to dissolve before the gold. So, at first, only the base metals dissolves. At some point, when there is little base metals left, the gold will start dissolving. You want to catch it a little before this happens. You can do this with constant testing with stannous chloride. After you stop, you drain off the solution, start with fresh, ans dissolve everything that is left. The advantages are that it goes fast and that you end up with much less AR solution.


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## yasin1987 (Sep 8, 2021)

A very simple method that I think is mentioned in Hooke's book on page 93, but be sure to do it under the hood and do not forget the mask, because cyanide gas can poison you.

Take 10 drops of cyanide solution and pour 10 drops of hydrochloric acid into the test tube. Boil it for about 10 seconds.
Exhaust gases from the pipe contain cyanide gas. be careful.

Hydrochloric acid brings the solution to the acidic range, and the heat decomposes the cyanide complex with gold, placing the gold in solution.
Now pour a drop of your tin chloride solution into the test tube. If there is gold, the color of the solution inside the tube from pink - purple - pencil tip - black will represent your gold.
Other colors include reddish brown, which may indicate some iron minerals
Blue Maybe Arsenic And Copper

I found an image. Gold in solution at about 160 ppm. The ratio of soil to water is 1: 2

Welcome my bad English  :lol: 
Thanks


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