I'm an analytical chemist with experience in graphite exploration, and field sample analysis. The method we use is: precisely weigh a powdered sample (0.1 to 1 gram aliquot); leach with dilute HCl to remove carbonate carbon; roast in Leco furnace at 425 C until weight is stable (removes organic carbon); ash the residue and detect graphitic carbon-derived CO2 by IR.

Is it possible to determine by controlled weight loss on ignition, perhaps done in several steps?

Try the flotation method. See the paper by

T. Wakamatsu & Y. Numata'

Flotation of graphite'

In: Minerals Engineering Volume 4, Issues 7–11, 1991, Pages 975-982

Another possibility for the quantitative determination of the graphite content is the use of the point counter method on polished thick sections. To this end, the graphite-bearing rock powder needs to be embedded in synthetic resin. The grains on the polished surface are then counted in terms of the graphite content under reflected light bright field microscope.

Dear Mr. Spürgin,

you refer to C powder. With this in mind the common laboratory-based mineralogical and industrial means of benefication or mineral processing, such as flotation, do no longer work. I have had problems to get minerals separated from coal samples ranking from lignite to anthracite which comes close to semigraphite and last-but-not least passes into graphite. I suggest to take a closer look at the plasma pyrolysis a more highly sophisticated but not-out-of- the-ordinary technique which is going to be used in ore processing (e.g. ilmenite). In the afore-mentioned case of mine it worked perfectly well. And I assume that there is also potential for your issue. It will still take some preparatory work for sure.

Best regards

H.G.Dill

there is a very useful BGS Technical Report (No. WG/92/30) by CJ Mitchell, 'Industrial Minerals Laboratory Manual - Flake Graphite'. It is accessible at  www.bgs.ac.uk/research/international/dfid-kar/wg92030_col.pdf.

On pages 25ff, this manual has recipes for graphite assay / determination of flake graphite contents in samples. May be this will help.

Depending on the (silicate? carbonate?) matrix of the graphite, other options would be calorimetric determination of graphitic carbon in a bomb calorimeter, or, alternatively, gravimetric determination of graphite residue after dissolution of matrix minerals in a classical HF-HCl acid digestion procedure. Graphite should end up in the insoluble residue, and in many rocks graphite will be the only insoluble residue so that simple gravimetry may directly yield graphite contents  

Dear colleagues, thanks for the suggestions how to solve the problem. I guess, as you mentioned very different methods, I will find a way to quantify graphite contents (in silicic matrix with minor calcite, btw.). The contents vary roughly between 0 and some 20 (?) wt%, and the grain size is from µm-mm. Next step for me is to do some laboratory tests to find out which method works for my materials.

Asking the experts: Isn't there any "standard" analytic procedure designed in the exploration industry for graphite deposits?

Please don't hesitate to add other ideas/methods to the discussion!

Simon

Dear Johannes, the BGS report is quite interesting, although the methods described definitely need some "customizing".

Dear Mathias, no, it's nothing to be produced. It's "just" a task of quantitative phase analysis (QPA) on bulk powders which I routinely do with XRD, but this method fails in this case.

One can first take up XRD analysis of samples for the quantity of graphite present. Then samples can be analysed for graphitic carbon on Leco CS 230 carbon-sulphur analyser.  In this method components like total carbon, inorganic carbon and organic carbon can be used for graphitic carbon determination.

Graphite flakes may be very common in palynological residues after HCl and HF etching of Palaeozoic fine-grained sediments. You can quantify the graphite content by weighting the remaining residue after separation by heavy liquids (remove the pyrite, zircons and other minerals not destroyed during the etching) and separation of the “lighter” organic remains (e.g. acritarchs, spores…)

Thanks to all your suggestions, showing very different methods to solve the issue!

Simon

I'm an analytical chemist with experience in graphite exploration, and field sample analysis. The method we use is: precisely weigh a powdered sample (0.1 to 1 gram aliquot); leach with dilute HCl to remove carbonate carbon; roast in Leco furnace at 425 C until weight is stable (removes organic carbon); ash the residue and detect graphitic carbon-derived CO2 by IR.

I agree with Larry but we need to have some assurance about hexagonal Carbon contents rather that total Carbon. Some electrical conductivity is perhaps better answer if someone can elaborate

I am retired and I was not expert in graphite. However, when I was active as a palynologist I sorted graphite from palynological residues including organic walled palynomorphs mixed with graphite flakes. This residue was obtained by dissolving weighted fragmented rock samples (Palaeozoic mudstones or siltstones) with HF (70%) and HCL. After the bleaching of the residue with Shultz solution (fuming HNO3+KClO3) and sifting, I hand-sorted the graphite flakes with a micropipette under a microscope binocular. I used this technique for the preparation of "clean" samples for D13C investigations. It is of course possible to weight the sorted graphite in order to get its percentage in the rock sample.

I noted high differences between the D13C of the graphite and those of my palynomorphs, at least enough to preclude the use of the bulk residue for such investigations

It is also possible to separate the graphite from the organic walled microfossils using the heavy liquid technique (centrifugation in bromoforme ethanol or any other heavy liquid with the right density).