The Differences Between XRF & ICP and How They Affect The Value of Your Converters

When you ship your converters to a toll refiner, the assay analysis determines the precise composition of platinum, palladium, and rhodium in your lot. To carry out this analysis, toll refiners mainly use two technologies: XRF and ICP.

But what sets these two analysis methods apart? Is one superior to the other? To answer these questions, let's examine how these tools work.

What Is XRF?

An X-ray fluorescence benchtop machine is a non-destructive method used to analyze the elemental composition of your material.

How Does XRF Work?

In the machine, a source produces an X-ray, which then enters your sample by a few micrometers. As a result, the atom in the sample is excited, causing an electron to be expelled from its inner shell.

This forces all the other electrons to rearrange themselves, filling the void left by the ejected electron. By changing places and moving around, the electrons release energy in the form of fluorescence. This creates a unique fingerprint or signal for each element, whether it’s platinum, palladium, or rhodium.

The energy signal is measured to determine the concentration of each precious metal. Greater fluorescence indicates higher concentrations, while lower fluorescence indicates lower concentrations. A report is then generated, highlighting the elements detected within the sample.

What Is ICP?

The Inductive Coupled Plasma machine, otherwise known as ICP, measures a sample using light intensity to determine the platinum, palladium, and rhodium concentration in your converters.

How Does ICP Work?

The sample taken from your converter load is turned into a liquid. Then, it’s aspirated by a pump until it reaches a nebulizer, where it mixes with argon gasses to create small droplets. From the nebulizer, the droplets move into the spray chamber, where the finest droplets are separated from the rest and sent into the plasma, which burns at 10,000 degrees Celsius. At this incredibly high temperature, the atoms in the sample absorb huge amounts of energy. And when the energy is expelled from the plasma, it releases light. Depending on the element that’s being measured, the light emitted will be on different wavelengths.

To determine the concentration of each element, we measure the intensity of those wavelengths and voila, we’ve got the concentration of PGMs in your load!

But how do these methods differ in terms of determining the value of your sample? And which instrument provides more accurate material analysis?

The Differences Between XRF & ICP

XRF and ICP machines differ in three aspects: accuracy, time, and investment. Before we dive in, remember that the first step in getting accurate results is preparing a proper sample.

How Should Samples Be Prepared?

For accurate results, samples must be ground into fine particles with a consistent mesh rate to ensure appropriate particle size and homogeneity. It’s also important to measure humidity and carbon content, since  they can impact the material's weight and analysis results. Now that we know what the ideal sample looks like, we can see how the different methods for analyzing it compare.

Time

XRF machines require significantly less time to analyze a sample compared to ICP, which requires a huge time investment. However, both methods require proper sample preparation and machine calibration beforehand, which takes a lot of time as well.

Accuracy

While XRF machines can complete an analysis pretty quickly, this method isn’t as accurate as ICP. It’s important to note here that accuracy depends heavily on proper sample preparation, so with a correct sample, XRF analysis can still be very precise.

On the other hand, ICP has excellent accuracy. There’s a reason why it’s considered the industry standard!

Capital Investment

In terms of financial investment, XRF machines require a lower capital investment compared to ICP machines. However, this does not imply that XRF machines can’t produce accurate results that you can rely on. With proper sample preparation, XRF machines can be incredibly precise in their analysis. On the other hand, ICP machines require a significant capital investment, but they consistently deliver accurate results.

So, XRF or ICP?

In the processing industry, it’s always better to go the extra mile. We saw above that the first step in getting the most accurate results possible is proper sample preparation. Without a correct and thorough sample preparation method, the analysis will be inaccurate, and the declared value of your material won’t reflect what it’s actually worth. So, make sure your toll refiner has the proper sample preparation method.

With a properly prepared sample, the next step is using both the XRF benchtop machine and the ICP machine to analyze your material. That’s because your bottom line relies on the accuracy of your results, so when both analysis methods are used, maximum accuracy is achieved. But not all processors use both, so remember to stay informed and ask your processor what their analysis methods are.

At PMR, we use both XRF and ICP methods. This means that we can provide you with the most accurate and reliable information, allowing you to determine your material’s true value. If you’d like to learn more about our processing methods, please visit our Toll-Refining page to stay in the loop.

For more information on evaluation and processing, visit PMR’s Resource Center.