Iridium ore or XRF error

[tomrod]

I have an ore sample that reads 6 percent gold, 37 percent silver and 39 percent iridium with a Bruker XRF. I see a lot of silver but the the iridium content seems incredibly high. Is there a good place to get this tested?

 

[Lou]

It's in error.

 

[goldandsilver123]

It's in error.

We get a lot of people coming to us thinking that their material is high in precious metals because they made a XRF analysis.

Do you know why the XRF is so off? I know that without the precious metals software, handheld Thermo sees gold as tungsten. Is it a software "problem" or does it need something like more photon energy?

They do not believe that the analysis is wrong, so we just say we're not interested..

 

[anachronism]

We use XRF a lot. Lou's points are extremely valid because from experience you have to ensure that the conditions are right to give you a correct reading. for example there are a lot of items that only read "true" if you keep a 100 percent copper base behind it to remove a lot of the spurious readings. Otherwise it is easy to get all excited over nothing.

 

[nickvc]

The key to using an xrf gun or xrf analysis well is to understand its limitations and plenty of practice on known materials which the xrf can and does get wrong, having said this they are a fantastic tool if used correctly.

 

[Lou]

I'm probably a broken record like usual but analytically speaking....context context context. It's all what's in the sample and how it's prepared.

As for XRF, it can be any number of things:

1. The instrument isn't calibrated or warmed up properly,
2. The analyte of interest is much less in concentration (o not present to detection limit) relative to a matrix or bulk contaminant that has a similar spot in the fluorescence spectrum. Most handhelds use algorithms designed for standard materials (i.e. Karat or regular old copper alloys) and operate in modes. If the energy-dispersive instrument is in the precious metals analyzing mode, it can attribute W as Au or Ta (or Se) as Pt.





On their wavelength dispersive freezer-sized instruments, a well known smelter uses copper disks samples from heats (while taking a shot sample for fire assay) that have been milled flat so that an irregular surface doesn't goof up the results.

 

[Connie Saxe]

Our lab refines and tests Iridium ores and there have been XRF's done that registered Iridium Oxide as Titanium Oxide - guessing, most probably because the two share the same unique molecular morphology - featuring six coordinate Iridium (Titanium) atoms and three coordinate oxygen atoms. Most XRF people shy-away from calibrating their devices to accurately detect Iridium. ICP Analysis is currently the analysis of choice for Iridium.

 

[Marcel]

XRF is only one of several available methods. While it is widely accessible and provides an initial indication, it is prone to errors and primarily examines only the surface. Therefore, it should be considered merely a preliminary step. To achieve a reliable assessment of an object's material composition at an affordable cost, especially for amateurs, it would be sensible to establish a series of tests—including chemical, optical, magnetic, and other measurement methods.

There is no single non-destructive method that can definitively identify the metallic composition of an object in 3D. (Although some studies use advanced techniques like MRI, these are generally beyond the budgets of most users.) Imagine scanning a thin vein exposed by a crack: if only the 0.2 mm surface is analyzed, the remainder of the material goes unchecked.

I want to address the ongoing criticism on this board regarding the use of XRF. I see it as one of many testing methods that provide a directional hint toward the true composition. After conducting an XRF analysis, one should follow up with chemical tests on pulverized material to further narrow down the composition. Advanced methods like fire assay or comprehensive laboratory analyses are costly and not feasible for everyone; they should be reserved as the final step in a thorough assessment. Preliminary techniques like XRF can help determine whether further testing is necessary and worthwhile.

I have always regarded this forum as a space for amateur enthusiasts rather than for industrial users with unlimited budgets. In that spirit, we need to incorporate all feasible testing methods while being mindful not to overestimate their individual outcomes.

So, I suggest to develop and establish a chain of tests or a process chart (which may incorporate XRF) for such tasks as "gold standard" or "best practice" in this forum —one that is both affordable and doable without fancy equipment. This approach serves both the holder of an unknown material and the users who are asked to comment on the findings, allowing them to provide their assumptions or assessments based on a more comprehensive set of data.

 

[Yggdrasil]

XRF is only one of several available methods. While it is widely accessible and provides an initial indication, it is prone to errors and primarily examines only the surface. Therefore, it should be considered merely a preliminary step. To achieve a reliable assessment of an object's material composition at an affordable cost, especially for amateurs, it would be sensible to establish a series of tests—including chemical, optical, magnetic, and other measurement methods.

There is no single non-destructive method that can definitively identify the metallic composition of an object in 3D. (Although some studies use advanced techniques like MRI, these are generally beyond the budgets of most users.) Imagine scanning a thin vein exposed by a crack: if only the 0.2 mm surface is analyzed, the remainder of the material goes unchecked.

I want to address the ongoing criticism on this board regarding the use of XRF. I see it as one of many testing methods that provide a directional hint toward the true composition. After conducting an XRF analysis, one should follow up with chemical tests on pulverized material to further narrow down the composition. Advanced methods like fire assay or comprehensive laboratory analyses are costly and not feasible for everyone; they should be reserved as the final step in a thorough assessment. Preliminary techniques like XRF can help determine whether further testing is necessary and worthwhile.

I have always regarded this forum as a space for amateur enthusiasts rather than for industrial users with unlimited budgets. In that spirit, we need to incorporate all feasible testing methods while being mindful not to overestimate their individual outcomes.

So, I suggest to develop and establish a chain of tests or a process chart (which may incorporate XRF) for such tasks as "gold standard" or "best practice" in this forum —one that is both affordable and doable without fancy equipment. This approach serves both the holder of an unknown material and the users who are asked to comment on the findings, allowing them to provide their assumptions or assessments based on a more comprehensive set of data.

It would be nice if we can establish a minimal set of tests that can either confirm or rule out the need for proper testing.
And we don not have anything against XRF as a tool.
What we try do is to emphasize for the ones with "precious metal fever" from ores, what a XRF can and can not do.

 

[Crudmudgeon]

I guess this is still an issue!!!
The prospect of 3.6% Rhodium is exciting... but I'm not sure I'll find a lab capable of verifying it.

 

[galenrog]

The problem with nearly XRF model is that if it does not have a detected material in its onboard library, it will default to a material in its library.

A frequent example is an XRF, when arsenic is detected, will default to iridium or rhodium if arsenic is not part of its library.

XRF is a good tool, if used properly, but has limitations.

Time for more coffee.

 

[Yggdrasil]

View attachment 67212
I guess this is still an issue!!!
The prospect of 3.6% Rhodium is exciting... but I'm not sure I'll find a lab capable of verifying it.

As Galenrog says, all testing equipment has their limitations and that goes for XRF too.
Her one telltale information is the notion on top.
"Not in Library"

 

[Alondro]

The problem with nearly XRF model is that if it does not have a detected material in its onboard library, it will default to a material in its library.

A frequent example is an XRF, when arsenic is detected, will default to iridium or rhodium if arsenic is not part of its library.

XRF is a good tool, if used properly, but has limitations.

Time for more coffee.

If it's a metal alloy, then arsenic isn't likely. Arsenic makes many alloys brittle, one exception being arsenic bronze, which made casting easier and the result was stronger. But that isn't used in electronics, and it's a primarily copper alloy.

Ores are the things that give many many misleading results!

Even so, the XRF has to be properly calibrated, or the measurements are simply useless.