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Sulphide-sulphur and carbonate-carbon sampling (10 replies)

Ace Levy
8 months ago
Ace Levy 8 months ago

I'm looking for some opinions and experiences as to the most reliable methods of determining sulphide-sulphur (in pyrite, arsenopyrite and so as opposed to sulphate sulphur) and carbon in carbonate versus organic carbon in rock materials. What sampling and analytical methods work best for complete mapping of samples in a mineral deposit? Which methods can you consider total and which partial?

8 months ago
Obersturmbann 8 months ago

I am also pursuing similar topics, though' it is still in the initial stage. Some possible help / info may come from:

Sulfur / sulfite in wines.
A USGS person, in a talk to the Geol Society of Nevada a few months back, said he is working on a fast technique to have more than 40 elements values in under an hour; I'm still trying to find the abstract on it.
Some instant S values using calometric paper strips (used in quick medical applications) .

Would appreciate developments info on this matter.

John Koenig
8 months ago
John Koenig 8 months ago

You could do that with a LECO CS844 instrument. Assay total S. Second sample weak acid strip sulfate, also run by leco. Difference will tell Sulfide vs sulfate assay total C. Second sample weak acid for carbonate. Difference will tell organic C from carbonate. I'd start with that.

8 months ago
Standartenfurer 8 months ago

A quick comment a lab that can do a LECO test and DTA (differential thermal) TGA (thermogravimetic) should be able to handle whatever you want along these lines. The lab could design the optimum protocol for your materials, goals and budget.

For example, by combining various tests, the various forms of S and C can be determined by difference:
An LOI test (loss on ignition) at the right temp will drive off everything except sulphate typical LECO machine gives total sulphur. etc.

Bill Rico
8 months ago
Bill Rico 8 months ago

OK folks here are a dilemma that I would like an answer to. I'm a prospector who was asked to do soil sampling over a known graphite deposit trouble is this: the carbon footprint of the graphite is muddled with the carbon in re-crystallized limestone that the graphite forms in. Can there be an easy assay for total carbon with just the graphite alone? Or how does one differentiate between the total carbon of the limestone & that of the graphite. Thanks for all of everyone's input ahead of time.

8 months ago
Oberfuhrer 8 months ago

One thing to bear in mind is that data from different laboratories are not generally equivalent. This is especially so for partial carbon analyses and is due to slight variations in acid used acid concentrations, reaction temperatures and operator skill.
Partial carbon assays are hideous for QAQC!

With the partial sulphur assays you need to be aware of where the 'native' sulphur is reporting. Some methods the 'native' sulphur reports with the sulphide and other methods it reports with the oxidised fraction. So you really need to know the exact method, rather than just being told that the results are 'sulphide' sulphur.

An IR analyser such as Leco machines are the only reliable total methods for both C and S. ICP is OK for S up to about 5% sulphur, but ICP starts to underestimate total S above this for reasons I forget (interference?).

Google returns lots of useful papers and laboratories should provide background material as well. As always, talk to your lab.

Bill Fraser
8 months ago
Bill Fraser 8 months ago

A Ferric leach for sulphide sulphur is also an option.

Ace Levy
8 months ago
Ace Levy 8 months ago

Thanks all for you very helpful replies. A couple of follow-up questions

What LOI temperature would you suggest?
What acid would you use and what (weak) concentration would you recommend?

Your comment regarding different results from different laboratories is relevant - how would you make a standard for carbonate carbon versus organic carbon?

8 months ago
Standartenfurer 8 months ago

Since the carbonate calcines at about 600 deg C, LOI at 550 represents losses not related to carbonate. Typically for cement raw materials the lab uses 950 deg C for LOI that represents all losses, including carbonate.

Victor Bergman
8 months ago
Victor Bergman 8 months ago

Upper limit for S on ICP-OES from typical commercial labs is somewhere between 5 and 10%, depending on exact method, i.e. typically open vessel acid digest. Much higher limits (30%) can be achieved with closed vessel MW digest but you'll get precipitation if Ba, Pb, etc are present as sulphates.

The major reason why the QC is hideous is because the sample weights for the combustion IR instruments (especially LECO), are so tiny, i.e. <0.1g for material with typical p80 of 75um. The higher the value of S or C, the lower the sample weight. 🙁

For the digest hit the sample with 50% HCl in Leco crucible, over several hours at 100 C. Technically this is the non-carbonate carbon. Carbonate is calculated by difference and is prone to error.

If the intention for speciation is resource definition and not exploration, I would suggest the most reliable method would be quantitative mineralogy, through SEM, at least for the sulphide/sulphur mineralisation. This would also give you the specific mineralisation of your arsenic, i.e. tennantite or arsenopyrite and provide critical insights into process flow sheets, etc.

Marshal Meru
8 months ago
Marshal Meru 8 months ago

By reading the various comments I didn't read a mention to the theory and practice of sampling by Pierre GY.

Least of you certainly have heard or read some sampling documents.
Nets about what Pierre GY has done in theory and practise.

This is the only theory recognised on a worldwide basis. In his book you have a way to find a solution to your problem of sampling.

Personally I happened to know and work sixth apierre GY and I can give lectures ent the theory and practise.

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