Best methods of gold concentrate analysis

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S

sar

Active member
Joined
Jan 29, 2021
Messages
28
Hi everyone
We have a concentrate of gold and silver, it has about 35 % Au and 50 % Ag rough estimate . The rest is Zn Cu Fe and other base metals and very low content of other precious metals.
What method or methods do you recommend for complete analyzing of elements?
 
I would start with a basic fire assay. From that you will determine Gold Silver and total
Precious metals (not specific just total). From there you can determine what specific PGM’s are there by either gravimetric methods or ICP analysis. But a good, get started result can be had by fire assay.
 
How the base metals are determined?
I need complete analysis of concentrate
 
The fire assay will give you the high dollar metals in your concentrate but none of the base metals as they are absorbed into the cupel during the cupellation. For an analysis of all metals you will need to ship a sample of the raw concentrate to a lab for an instrumental analysis.
 
4metals said:
Do you really think this kind of response is helpful?
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sar said:
“I need a full analysis of the concentrate”

This formulation of the question excludes any help other than:
(a) advice to find a professional lab
(b) find all the necessary information in ONE source.

I only have this book in paper version, so I uploaded the cover so that people can find it themselves in the electronic version.

Giving direct links to any electronic copies of the books under copyright I consider unethical.
This is a internal choice of each person to try or not try to find the electronic version.

Why did you find my answer useless, please explain your reasons?
 
The members of this forum come to us from all walks of life. Some are chemists. But most are not. On top of not knowing the background of members who post questions, we have to deal with descriptions that are usually lacking in detail. When a member posts a question I try to go back and read a few of their earlier posts or questions. Based on this I tried to provide the OP with a simple answer that he or she can work with. While the reference book you posted could likely provide the correct answer to the question, I question the ability of someone not trained or experienced in chemistry to understand it. It is simply too much information that cannot be easily used.

It's almost as if someone asked a question about planets, I posted a book on the complete history of the universe. Most of our members will get more value out of brief explanations and follow up questions. Please understand this is only my opinion and I will gladly entertain other opinions.
 
You are right, in most cases, I share the approach in which a simple and concise explanation is better than a reference to complex literature.

But in this particular case, the question was asked in a form that suggested that the most complete answer was required.

And you have provided the correct advice - "contact a professional laboratory".

I provided the only possible alternative (from my point of view) in this case - read one textbook on this topic (and this is a specific textbook for students) which will allow completely answer the question of the author of the topic.

Our responses are always an attempt to achieve a balanced compromise between the level of understanding of users and the level of our competence.

Nevertheless, the answer to the biggest question about Life, the Universe, and Everything will always be 42 :)
 
One thing I try to do on this forum is encourage discussion. In the 14 years since I joined this forum it has certainly grown. In the beginning most members were looking to process jewelers scrap and karat gold with a little sprinkling of e-scrap. I remember having some excellent discussions on threads with Chris Owen (GSP) about things like fire assay techniques and other detailed process descriptions. These discussions are always helpful to some and if we were having a discussion today about fire assays I think the greater diversity we have today amongst our members would provide an better learning experience because of the diversity.

Along these same lines, in a thread like this the OP were to say "I've no experience running a fire assay but would love to learn" I would gladly launch into a discussion on fire assay, welcoming all of the different perspectives we now enjoy on the forum. And by starting out with the basics and working our way through the process, it would produce, or should I say it would have the potential to produce, a much easier to digest process for our members to follow and learn. And at the same time allow members to interject questions which will make it even easier to understand by more of our members.

In essence, what I have just described is what I think my responsibility as a moderator on the forum is. To provide useful information in a way that it can be utilized by our members while at the same time being open to input from others who can provide different perspectives.
 
Ultrax said:
Also you can try to find this book and read it.
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Actually this book will be helpful. I'll try to find it.
I draw your attention to this point that I said "what methods",
Some instruments have some limitations. But a total of several devices can cover each other limitations.
As 4metals said fire assay is a good start method to collect precious metals in one button, But it is not enough for complete analyzing. So in the continual some other methods like XRF or ICP should be applied to detect a precise analysis.
I should decide which tests in what order should be done. These experiences are not always written in the books.
That's why I asked the question and it's better to say: what order of methods should be done to test that typical gold concentrate for all elements ?
 
sar said:
Hi everyone
We have a concentrate of gold and silver, it has about 35 % Au and 50 % Ag rough estimate . The rest is Zn Cu Fe and other base metals and very low content of other precious metals.
What method or methods do you recommend for complete analyzing of elements?
Click to expand...
Depends on how you want to use that information, and what purpose it will serve.

If you produce such concentrate, you can be looking for buyers, or assess the profitability of your operation. Depending on how accurate you want to present the cons or assess the viability of the mine/plant, you can seek professional lab which will perform fire assay or some sort of ICP and other stuff to precisely measure the content of high and low value metals. Here you are in the right place to ask very experienced guys - who can help you decide what test best suit your needs, as they have more than century of combined experience in this area.

If you indeed want to sell the cons to the bigger buyer, you would need to claim what you have - and thus pro results will come in handy - serving as good proof of what you have.

On the other hand, if you just need some approximate numbers regarding your cons and also setup used for the recovery of metals, other thing you can do is process a larger sample by a viable method (like smelting the cons in induction furnance+graphite crucible to reduce everything from noble metals down to iron into one metallic puddle), which will give you pretty good numbers on how much of what metal you have in the cons. It also tells you what you can recover with your methods - and thus what is real "yield" from the ore/placer you have. Zinc won´t be captured by this procedure well. Best is to have process sample combined with also pro lab results to compare these two - and assess the losses on particular elements. But metallic product you obtain can be analyzed with good quality XRF to give you quite usable and reliable numbers. And this is cheaper than sending samples for pro ICP + fire assay.

However, I need to say, if you do not have experience with advanced smelting techniques and lack proper equipment, I would strongly advise going with pro labs. Yeah, it can cost quite a bit of money, but you will have certified results, on which you can further build your setup/operation/calculations, or negotiate with potential buyer from stronger, more credible position.
 
sar said:
it has about 35 % Au and 50 % Ag rough estimate . The rest is Zn Cu Fe
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Has this concentrate been melted into a bar?

The high Silver will prevent a complete dissolution for instrumental analysis. With the high Silver and Gold (85% of total) you should be able to cupel a doré bead and flatten it out for an XRF result. The fire assay parting on the cups with added Silver will tell you the Gold accurately. The parting solutions will yield Palladium results with Dimethylglyoxime and the XRF should indicate Platinum Palladium Gold and Silver on the doré bead. The total sample with base metals will require 2 analyses. One from a nitric digestion to determine all of the nitric soluble elements, and the balance of the insolubles from the nitric digestion need to be digested in aqua regia for the balance of the metals. It is possible that Platinum will dissolve with nitric if the Silver content is high enough so look for it in both fractions.

The book suggested by Ultrax was published 70 years ago, when I was 2, so the preferred methods undoubtedly have changed. That said, the older gravimetric methods were excellent, just more tedious than the newer instrumental methods.
 
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The issue is that even average-top-level XRF can produce incorrect results when analyzing complex rare earth and PM concentrates.

Of course, if you don't have access to atomic absorption spectroscopy (AAS).

But usually, in most cases, it is much cheaper and simpler to use a 100-year-old :) standard methods of analytical chemistry, starting with the removal of carbonates, water, quantitative analysis of base metals, and so on... up to silver, gold and platinum group metals. The results will be good enough.

P. S. Moved my comments to a separate post below.
 
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Ultrax said:
The issue is that even average-top-level XRF can produce incorrect results when analyzing complex rare earth and PM concentrates.

Of course, if you don't have access to atomic absorption spectroscopy (AAS).

But usually, in most cases, it is much cheaper and simpler to use a 100-year-old :) standard methods of analytical chemistry, starting with the removal of carbonates, water, quantitative analysis of base metals, and so on... up to silver, gold and platinum group metals. The results will be good enough.
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That is why I suggest pro analysis as my first bet. Pricey, but in early stages of setting up operation, paired with lack of proper skills and apparatus, it is probably well worth it.

I will disagree with you (just partially), that XRF cannot give good results. Yup, on raw cons, of course it would be unusable. But cleverly melting/smelting them, followed by some easy workup/parting, actual results for PM and base metals can be quite accurate (analyzing solid metal samples in the end).
I won´t sell the truckloads of cons based on these, but not knowing his situation and actual purpose of these tests, maybe some informative result will suffice.

There are multiple options, and every one of them have it´s own drawbacks. To perform classic analytical chemistry on complex sample require well established/geared lab and skilled chemist to do it (if you want to trust the obtained results in the end). And at the end of the day, sending sample for ICP+fire assay can prove cheaper than undergoing your own tedious analytical venture.

I have no doubt you can perform such analysis yourself. And I am pretty confident I would also be able to. But we do not know if he is in our position.
 
orvi said:
I have no doubt you can perform such analysis yourself. And I am pretty confident I would also be able to. But we do not know if he is in our position.
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Exactly!

And, so far on this thread, we do not know if the cons he is holding have been melted into a bar or if they're loose cons off of a gravity table or what they are. As I've said before, and it is applicable here, details matter.
 
P. P. S. I can say this with complete certainty since our ores in Ukraine are very rich in gold with a huge amount of rare earth impurities, uranium, and thorium. Almost all spectrographic methods provided incorrect results, but 100-year-old methods of analytical chemistry showed results with an error of less than 0.1% per ton of concentrate (deviation from the calculated theoretical quantity)

The main reason for errors in spectrographic methods when working with complex concentrates is the encapsulation of precious metals in solid solutions of other elements.

It’s easy to analyze only bars and nuggets, and when it comes to microparticles of gold in a crystal lattice, for example, with bismuth, vanadium, etc. covered with a film of organic petroleum and coal polymers, in a fossilized shell of limonite 10,000 years old, then only analytical methods will help since you first need to chemically separate all these substances for further analysis...
 
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In order not to theorize further pro/vs XRF, let the author of the topic decide personally what is best for :)
 

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