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Bauxite Laboratory Analysis (7 replies)

John Koenig
8 months ago
John Koenig 8 months ago

I'm interested to hear from fellow members on the type/manufacturer of XRF instrumentation that are in use for the determination of the following bauxite parameters: Total Al2O3, Available Al2O3, Total SiO2, Reactive SiO2 and Fe2O3. We have a PIMA MACHINE in use, but too inaccurate when results are compared against CRM's. Any suggestions how to replace PIMA MACHINE with and why?

Right now I'm considering the purchase of a BRUKER S8 Tiger or the Axios-Max Minerals XRF unit from Analytical. In conjunction with this, I also have rutile, gold and diamond exploration projects. Ideally, 1 XRF unit that can handle my entire project samples with the wide range of commodities.

8 months ago
Oberfuhrer 8 months ago

The PIMA is collecting IR spectra of the minerals and is not capable of giving you quantitative analysis unless you have a chemo metric program set up for quantifying minerals present. The XRF systems on the other hand are giving you elemental data and you will need to convert these into mineral data using modal calculations based on stoichiometric data for the minerals present - BQUANT is one program that used to be available. We have done this for bauxite, but usually need XRD backup to ensure we are getting all the minerals present.

Maya Rothman
8 months ago
Maya Rothman 8 months ago

For the melange of commodities you mentioned, I suspect you are in West Africa. Depending on your projects stage of development I recommend for early stage bauxite as well as gold assaying: ALS (Bamako).
For rutile (+/- ilmenite) I recommend MSA SA, or any Canadian outfit.

I would like to discourage you from endeavoring to create your own Lab because it will have to be certified in order for the analysis and the assay results to be compliant.
Hope it helped.

Sachin Prakash
8 months ago
Sachin Prakash 8 months ago

I would like to know how sampling and anlytical suitable choosing methods are justified and how it changes preferences from one ore mineral to other.

Marshal Meru
8 months ago
Marshal Meru 8 months ago

First, you must first separate lab XRF from field XRF. Both are complementary methods and do not replace each other.

Second, field XRF (or pXRF) is extremely sensitive to sample preparation and to adequate site-specific calibration. Taking this into account is much more important than selecting the right machine.

Do not forget that Al and Si are the most difficult elements to analyze properly with a pXRF, and that you cannot achieve anything like CRMs comparison by plain point and shoot. Analyses are easier with lab XRF, but it still needs attention to preparation, calibration and specific standards. A careful elaboration of your site-specific protocol with an experienced pXRF specialist is mandatory for your plans. XRF will be great for rutile projects as it deals easily with Ti analyses.

For gold projects, it will be project-dependent, as XRF requires a lot of replicate shoots in order to get rid of nugget effects - and its sensibility is better in the ppm range than in ppbs. If you have any pathfinder element such as As, XRF may do wonders.
Your PIMA machine is not necessarily useless: it might find new applications in mineralogy control. 

8 months ago
Obersturmbann 8 months ago

Your sample preparation is critical. May I suggest that you visit the IMP website, they offer a mill and press combination machine model HPMP that will give you excellent reproducibility. For fusion there are also several solutions available.

Bob Mathias
8 months ago
Bob Mathias 8 months ago

My experience with PIMA is also disappointing and would recommend that you use XRF combined with some sort of 'met digest' method (like a bomb digest) for available alumina and reactive silica (usually read by ICPOES).

These pseudo met-tests can be tricky to get reasonable precision due to the many difficult to control factors but at least give results that can be calibrated to process plant data (or at least expectations).

As a general rule I'm usually more concerned about the sample preparation and quality of the fusion and/or met-test preparation than the actual read machines.

I would expect most new machines read the full suite of analyses concurrently these days but I expect others in the group are better qualified to comment about the hardware.

Ace Levy
8 months ago
Ace Levy 8 months ago

The comments on the importance of sample preparation for accurate XRF analysis are well placed. The entire process chain can be considered, finding the right balance between material type, sample size, sample preparation, analytical method and desired accuracy.