Testing the amount of Gold dissolved in Thiosulfate solution

[yasin1987]

Hi...

I think there are many articles about sodium thiosulfate that some of you have read.
Usually the first thing to do to test minerals is to know how much gold and silver there is in them.
I want to do a few things and since I'm not a chemist I want my friends to help me.
Suppose we have 100 ppm of gold per kilogram of ore.
Now we want to know how much of this gold is dissolved in the solution. Is all the gold dissolved or is there some left?
Usually in cyanide solutions we use Hoke's and measure the exact amount of gold in the solution with stannous chloride. This is needed to determine the amount of cyanide needed as well as the activated carbon needed to extract the gold.
Now I want to discuss whether this is possible for thiosulfate solution...

 

[Yggdrasil]

Stannous can't give an exact amount of gold in any solution.
And stannous has to be acidic and acid and cyanide do not mix well.
That means you have to make sure the cyanide is properly destroyed first.

For ores one usually use fire assays or similar.

 

[Yggdrasil]

For thiosulfate I don't know.
But still it will not be quantitative.
It will however if acidified tell whether or not there are gold in solution.

 

[yasin1987]

Stannous can't give an exact amount of gold in any solution.
And stannous has to be acidic and acid and cyanide do not mix well.
That means you have to make sure the cyanide is properly destroyed first.

For ores one usually use fire assays or similar.

Pages 90-91 of Hoke's book:

TESTING FOR GOLD IN ALKALINE OR CYANIDE SOLUTION
The test with copperas works only in acid solutions; it will not work at all in alkaline or cyanide solutions until the alkalinity is destroyed.
Thus, suppose you have an old cyanide gilding solution, and wonder if it might contain dissolved gold. Take about five drops of the suspected liquid in a small test tube or tiny beaker, stand near a window or an exhaust fan, and add four or five drops of hydrochloric acid. The fumes evolved are extremely poisonous— hence the need for working near an exhaust. Bring the mixture cautiously to a boil; this drives off the cyanide. Let it cool, and you can now test with copperas as usual.

Well now you use stannous chloride solution instead of copperas, one drop or two drops. If gold is present, the pink-purple-black color spectrum will indicate gold in solution. Experience can show how much gold is in solution.

 

[Yggdrasil]

We do not support all things in Hokes book. They had a completely different view on safety in those days. And she is referring to Copperas (FeSO4) not Stannous.

But my post is still valid.
It is not quantitative, one can on the other hand make up known solutions and compare them to a unknown sample, but I still would not call that quantitative.
For analysing during leaching one need some kind of spectrographic machine.

I do not know if one can do some analytic titration, I hope some of our gurus can chime in.

 

[yasin1987]

Although cyanide is not an issue for this part, in my experience, aluminum performs better than zinc and activated carbon does better.
But in sulfide or carbon ores, cyanide will not work. I want to learn about thiosulfate, which may be useful to others.

I think the mixture of cyanide solution with hydrochloric acid will be like this.
Of course, cyanide killer gas is very dangerous and you must observe all safety conditions.
AuCN + HCl = HCN + AuCl

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Combination of hydrochloric acid with thiosulfate
Na2S2O3 (aq) + 2HCl (aq) → S (s) + SO2 (g) + 2NaCl (aq)
Well, this compound cloud the solution with sulfur. And apparently a very pungent odor will come out of the sulfur dioxide gas.
I do not know where I read that the mixture of chlorine gas in thiosulfate solutions with ammonia causes an explosion? Or it was something else, I do not remember.
From friends who know to guide us in this matter.

 

[Yggdrasil]

Sulfur dioxide will precipitate any gold in a solution, that is how SMB works.
Still if you want to know how much gold in solution neither Copperas or Stannous will be the solution.
You need proper analysis done.

 

[yasin1987]

Sulfur dioxide will precipitate any gold in a solution, that is how SMB works.
Still if you want to know how much gold in solution neither Copperas or Stannous will be the solution.
You need proper analysis done.

Dear friend, you have not read my content correctly.
First of all, you say that Stannous chloride cannot determine the amount of gold!
If you mean the exact amount of gold in a ore, you are right.
But if you mean the exact amount of gold in a "solution" (like cyanide), you are wrong.
I can show you the exact amount of gold in solution with the same Stannous chloride. An issue that even Hoke has mentioned.
In fact, a way must be found
1. Give you the exact amount of gold or silver etc. in the ore (or anything else).
For example, in the cyanide method, you need it to get the amount of cyanide and activated carbon, and so on.
2. When you have the exact amount of gold, you should get the same amount of gold in your solution. Otherwise you will suffer financial loss.

 

[yasin1987]

And you say:

Sulfur dioxide will precipitate any gold in a solution...

No. Sulfur dioxide will not work in every solution. An example is thiosulfate solution.
If you mean SMB of sodium metabisulfite, as far as I know, in the presence of hydrochloric acid, it produces sulfur dioxide, Which causes gold to fall, for example in AR, (where nitric acid is destroyed by heat or sulfamic acid).
Na2S2O5 + hcl> 2 SO2 + 2 NaCl + H2O

 

[yasin1987]

Well, we are very far from our discussion.
There are many articles that discuss sodium thiosulfate or ammonium thiosulfate.
Many methods have been used for cementation of this solution. But in general, cementation also depends on the amount of thiosulfate and ammonia consumed. Like cyanide solution, the aluminum, zinc, and copper methods also work on thiosulfate. Of course, other materials such as steel wool have also been used. But apparently the role of copper in cementation is not good and part of the gold always remains in the solution.

1. Leaching Behavior of Gold and Silver from Concentrated Sulfide Ore Using Ammonium Thiosulfate

2. Gold Cementation from Ammonium Thiosulfate Solution

 

[orvi]

Dear friend, you have not read my content correctly.
First of all, you say that Stannous chloride cannot determine the amount of gold!
If you mean the exact amount of gold in a ore, you are right.
But if you mean the exact amount of gold in a "solution" (like cyanide), you are wrong.
I can show you the exact amount of gold in solution with the same Stannous chloride. An issue that even Hoke has mentioned.
In fact, a way must be found
1. Give you the exact amount of gold or silver etc. in the ore (or anything else).
For example, in the cyanide method, you need it to get the amount of cyanide and activated carbon, and so on.
2. When you have the exact amount of gold, you should get the same amount of gold in your solution. Otherwise you will suffer financial loss.

And you say:

No. Sulfur dioxide will not work in every solution. An example is thiosulfate solution.
If you mean SMB of sodium metabisulfite, as far as I know, in the presence of hydrochloric acid, it produces sulfur dioxide, Which causes gold to fall, for example in AR, (where nitric acid is destroyed by heat or sulfamic acid).
Na2S2O5 + hcl> 2 SO2 + 2 NaCl + H2O

Analytical measurements shoud be taken. In clandestine conditions, i bet only partly reliable method is gravimetry. Just process bulk sample, you will get an ammount of gold, which could be reliably weighed... With that rich ore, 100ppm... It takes few kilos to get solid result with low error.
Then get the ore properly fire-assayed. Compare the yields, you will know losses.

Issue with stannous for quantification of gold in solution is - it produces particles of gold, thus not homogenous mixture, which is not transparent. Grain size of gold particles differ from experiment to experiment - depend on how precisely the two are mixed. Nephelometry would be used with great difficulty here.
With that small ammounts in lixiviant, any spectroscopic or colourimetric measurements would be nearly impossible to perform reliably due to contaminants, unless very sensitive instruments are used.
AAS is conveniently used for this kind of stuff for these exact reasons.

Big boys are fire-assaying and bulk processing to know the yields. Maybe some companies use some new tech to resove this, but quantitative testing for gold in solution is not trivial.

 

[yasin1987]

Big boys are fire-assaying and bulk processing to know the yields. Maybe some companies use some new tech to resove this, but quantitative testing for gold in solution is not trivial.

Usually everyone has an extraction system for themselves.
Well, after Fire assaying, we have to measure the same amount in our solution. One of our main methods for measuring gold in solution, which I think is the fastest and cheapest, is tin chloride and iron sulfate.
In addition, the solution test should be performed after the addition of activated carbon or zinc or aluminum, etc.
Our method is to dilute the solution to 50 ppm.
Then we use iron sulfate or tin chloride.
Mercury and molybdenum can usually disrupt this system in many cases, but iron sulfate is a great option.

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TESTING PRECIOUS METALS Gold, Silver, Platinum Metals
By G. M. HOKE :

TESTING ALKALINE SOLUTIONS
You will observe that in the tests so far described, the solutions have been mildly acid or neutral. Never strongly acid—excess acid will weaken or even ruin most of them—nor alkaline, except in those cases where an ammoniacal solution was used. Testing Solution A will not work at all in alkaline or cyanide solutions, until the alkalinity is destroyed. Thus, suppose you have an old cyanide gilding solution, and wonder if it contains dissolved gold: Take about five drops of the suspected liquid in a small test tube or tiny dish, stand near a window or an exhaust fan, and carefully add four or five drops of hydrochloric acid. The fumes evolved are extremely poisonous—hence the need for working near an exhaust. Bring the mixture cautiously to a boil; this drives off the cyanide. Let it cool, and you can now use Testing Solution A or ferrous sulphate the same as usual.
Success with all these tests calls for practice, patience, and a good light. It also requires keeping your spot plate clean.

Well this is my main question. we know that stannous chloride does not work in an alkaline environment and must be in an acidic environment.

Now my question is, can such a thing be done in gold thiosulfate solution?
Given that by adding hydrochloric acid in thiosulfate solution the solution is filled with sulfur? Will gold chloride be formed in this medium for measurement with Stannous chloride?

 

[butcher]

I can't be of much help here.
I would do some controlled experiments.

You may find this helpful.

A test they used in determining the gold content in a gold cells electrolyte solution.

Solution strength is made up of ferrous ammonium sulfate, where 1cc of solution will precipitate 27.5 grams of gold from the solution...

A test that used for testing gold in a chloride solution (acidic).
Using Fe(NH4)2(SO4)2 ferrous ammonium sulfate.

To a liter is added 3.5cc of Fe(NH4)2(SO4)2, which is capable of precipitating 96.25 grams of gold from solution (more gold than our gold chloride solution sample being tested has gold ions involved).

With an excess of the ferrous salts which was then to be determined. they then used potassium permanganate by titration with a solution where 1cc of K2Mn2O4 would oxidize 1cc of Fe(NH4)2(SO4)2 where drops of the solution would destroy the purple color as long as ferrous salt remains, till the endpoint.

 

[yasin1987]

I would do some controlled experiments.

Thank you for this useful article. I will definitely order these materials for use.
......................
I have a question that a chemist has to answer.
if
Na2S2O3 (aq) + 2HCl (aq) → S (s) + SO2 (g) + 2NaCl (aq)
so:
[Au(S2O3)2]3- + HCl → ?

 

[orvi]

Usually everyone has an extraction system for themselves.
Well, after Fire assaying, we have to measure the same amount in our solution. One of our main methods for measuring gold in solution, which I think is the fastest and cheapest, is tin chloride and iron sulfate.
In addition, the solution test should be performed after the addition of activated carbon or zinc or aluminum, etc.
Our method is to dilute the solution to 50 ppm.
Then we use iron sulfate or tin chloride.
Mercury and molybdenum can usually disrupt this system in many cases, but iron sulfate is a great option.

---

TESTING PRECIOUS METALS Gold, Silver, Platinum Metals
By G. M. HOKE :


Well this is my main question. we know that stannous chloride does not work in an alkaline environment and must be in an acidic environment.

Now my question is, can such a thing be done in gold thiosulfate solution?
Given that by adding hydrochloric acid in thiosulfate solution the solution is filled with sulfur? Will gold chloride be formed in this medium for measurement with Stannous chloride?

This is certainly not my field of chemistry, but i used to work a lot with thiosulfate while quenching iodination reactions. It is excellent scavenger for bromine/iodine.
Suggestion: add iodine to the gold bearing solution in form of KI/I2 - this will kill thiosulfate (oxidize it) and mutually /should/ form a iodoaurate anions in exchange reaction. Excess iodine should not be used, hence it colour the solution, but slight excess could be killed by stannous itself easily.
If this happen as it should, you will be left with convenient solution of gold to manage. Adjusting pH with some "inert" acid near neutral and then testing with stannous.
But I never tested this, so just my assumption.

But with 50 ppm, it is quite challenging to measure gold content. I would be interested in how you quantify the gold with SnCl2 approach aside of gravimetry. Just visually observing the colour, some optic instruments involved ? Would be dirt cheap/easy to perform if it is reproducible enough.

Some sort of back titration could be of some help, but sensitive indicators should be used. With that low concentrations... Tricky to perform reliably

 

[orvi]

I can't be of much help here.
I would do some controlled experiments.

You may find this helpful.

A test they used in determining the gold content in a gold cells electrolyte solution.

Solution strength is made up of ferrous ammonium sulfate, where 1cc of solution will precipitate 27.5 grams of gold from the solution...

A test that used for testing gold in a chloride solution (acidic).
Using Fe(NH4)2(SO4)2 ferrous ammonium sulfate.

To a liter is added 3.5cc of Fe(NH4)2(SO4)2, which is capable of precipitating 96.25 grams of gold from solution (more gold than our gold chloride solution sample being tested has gold ions involved).

With an excess of the ferrous salts which was then to be determined. they then used potassium permanganate by titration with a solution where 1cc of K2Mn2O4 would oxidize 1cc of Fe(NH4)2(SO4)2 where drops of the solution would destroy the purple color as long as ferrous salt remains, till the endpoint.

Nice method, i was thinking of something similar. Permanganate/manganate is a lot easier to standardize than iodine, good technique

 

[yasin1987]

Suggestion: add iodine to the gold bearing solution in form of KI/I2 - this will kill thiosulfate (oxidize it) and mutually /should/ form a iodoaurate anions in exchange reaction. Excess iodine should not be used, hence it colour the solution, but slight excess could be killed by stannous itself easily.

Iodine itself, due to its color in contact with chloride, can confuse the tin chloride test. The purple color it produces is exactly the same as the purple gold color in the tin chloride drop test. And this can confuse a person.
In my opinion, adding some lead nitrate in the presence of gold thiosulfate and hydrochloric acid can reduce sulfur and sulfur dioxide pollution. The condition is that gold chloride is formed in it.

But with 50 ppm, it is quite challenging to measure gold content. I would be interested in how you quantify the gold with SnCl2 approach aside of gravimetry. Just visually observing the colour, some optic instruments involved ? Would be dirt cheap/easy to perform if it is reproducible enough.

More experience is the criterion of work. At the end we do fire assaying and the result is what we want.
I must also say that the consumption of cyanide and even activated carbon is considered as the amount of solution. While the consumption of cyanide and activate carbon, on the other hand, depends on the amount of gold in the ore. Makes distilling and diluting the experiment easier.

 

[Yggdrasil]

Destilling what???

First and foremost stannous will not be precise enough to be considered quantitative. It can get in the neighbourhood of guesstimate with experience, thats it.

Why not look for a proper method as Orvi and Butcher is sketching for you? AAS, ICP and such is what the big guys use.