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LIBS vs XRF: comparing two technologies

Handheld scrap analyzers are an essential tool for today's scrap and recycling yards

Hitachi High-Technologies’ Vulcan LIBS analyzer employs advanced data management for logging of both results and images.
Hitachi High-Technologies’ Vulcan LIBS analyzer employs advanced data management for logging of both results and images.

For recyclers who sort metals and alloys, in applications where precise understanding of content and composition is paramount, X-ray fluorescence (XRF) based handheld analyzers have been the main tool employed for over a decade. In recent years, however, laser-induced breakdown spectroscopy (LIBS) technology has been used increasingly in metal recycling applications, especially with aluminum and other nonferrous metals, and for light elements. XRF is still considered by most to be the best option for applications in stainless steel and heavy metals, or for recyclers focused on plastics and e-waste sorting.

To put it most simply, XRF technology uses X-ray radiation to determine metal and alloy content and composition, while LIBS uses low-energy lasers and optical technology, providing analysis without radiation concerns. 

Overall, advances in handheld analyzers for scrap mean recyclers can now identify and sort a wider range of elements and alloys, including light elements, in the yard or in their facilities, with high speed, accuracy and safety. Both LIBS and XRF, now feature smart, reliable connectivity to data analysis tools, and are designed to be lightweight, rugged and ergonomically friendly for users.
Recycling Product News asked some of the industry's leading manufacturers to provide insight on how the two technologies compare.

The Bruker S1 TITAN Handheld XRF Spectrometer is among the lightest tube-based handheld XRF analyzers on the market today.

Bruker: A tale of two technologies
Bruker, a leading U.S.-based manufacturer of both XRF and LIBS handheld analyzers, describes XRF technology on their company website as a completely non-destructive process whereby electrons are displaced from their atomic orbital positions, releasing a burst of energy that is characteristic of a specific element. This release of energy is then registered by a silicon detector in the XRF handheld instrument, which in turn categorizes the energies by element.

With LIBS technology, Bruker's site describes the concept as follows. "With LIBS, a laser pulse strikes the surface of the sample and ablates an amount of material and generates a plasma plume (partially ionized gas). The energy of the laser is low, but is focused to a microscopic point on the sample to generate the plasma. In this plasma, emitted light is transmitted through optical fibres and the polychromatic radiation is dispersed in one or more spectrometers and detected by CCD chips." (CCD is an acronym for "charge coupled device", an image sensor technology that converts light into electrical charges, as used in most digital cameras.)

In a 2015 white paper, by John I.H. Patterson, Phd., a consultant for Bruker and expert on the topic of metals analysis, he compares the two technologies in detail. He writes: "For fast sorting of aluminum alloys based upon light elements, LIBS is clearly the best alternative, as well as for separating many magnesium and titanium grades. When precision and accuracy matter more, as in PMI (positive material identification) analysis and quality control or when price figures are required in scrap trading (Ni, Mo, etc.), or if your application is measuring stainless steel, high-temp alloys or other heavy metal alloys, then XRF is the still the method of choice." 

Bruker: S1 TITAN (XRF) The S1 TITAN Handheld XRF Spectrometer is among the lightest tube-based handheld XRF analyzers on the market today, according to its manufacturer Bruker, at 1.5 kg, including battery. Fast analysis speed and exceptional accuracy are two key attributes that help define the S1 TITAN. Other innovative features include an integrated touch-screen colour display, 50 kV X-ray tube, SMART Grade timing, SharpBeam optimized X-ray geometry, Silicon Drift Detector (SDD), and an extremely tough housing that is sealed against humid and dusty environments. 

The S1 TITAN series is available in five configurations: models 800, 600, 500, 300 and 200. All models use Bruker's SharpBeam technology. The S1 TITAN 800 and 600 use a large area CUBE SDD detector to provide incredibly fast analysis times, while the S1 TITAN 500 is configured with a fast, accurate, and affordable standard SDD detector. The S1 TITAN 200 and 300 are configured with an economical Si-PIN detector. In addition, the S1 TITAN can be configured with calibrations that are optimized for a variety of sample materials, including a wide range of alloys, a variety of mining and environmental samples, as well as restricted materials.

Bruker: EOS 500 - Handheld (LIBS)
Bruker's new EOS 500 is a handheld Laser Induced Breakdown Spectroscopy (HH-LIBS) system. The EOS 500 is based on laser excitation of a metal sample followed by quantitative analysis of the light generated in the plume. This technology provides quick (3 to 5 seconds) analysis of alloys including aluminum, titanium and magnesium.

The EOS is especially well suited to scrap sorting of these alloys because of its quick and user-friendly operation. In addition to common elements detectable with XRF technology, the EOS is capable of measuring very light elements such as Li, Be and B, as well as laser-fast analysis of Mg, Al and Si.

TSI’s ChemLite LIBS analyzer provides high accuracy and speed for light metals.

TSI: LIBS provides speed, ease of use and low cost of ownership
Todd Hardwick is the global marketing manager for TSI Incorporated, a company focused on the manufacture of LIBS handheld analyzers."XRF cannot compete with LIBS when it comes to speed, ease of operation and cost of ownership," says Hardwick. "Our ChemLite LIBS analyzers precisely identify metals in one to two seconds, much faster than with XRF."Hardwick says that because there are no radiation concerns and their units use an eye-safe Class 1M laser, ChemLite "gun" owners avoid regulatory hassles - such as radiation licensing and the paperwork that comes with it.  

"LIBS requires no special training or storage and ChemLite LIBS guns do not need argon gas to operate," he continues. "When you add up the extra time, fees, training and supplies that XRF requires, the cost of ownership is often lower for LIBS." 

Hardwick adds that when it comes to accuracy, LIBS is a clear improvement over XRF for light metals. "LIBS allows better, faster aluminum alloy separation," he says. "Our ChemLite LIBS guns have limits of detection as low as 1 ppm."Overall, for Hardwick, LIBS is the tool of choice for nonferrous recycling yards and aluminum scrap sorting. 

"Our engineering teams at TSI-ChemLogix patented a LIBS sensor for in-line metals analysis a few years ago," he says. "Our customers have deployed these sensors successfully for high-volume automatic aluminum scrap sorting as well as part of a Zorba/Twitch sorting system." 

Hardwick does add though that LIBS is not a viable option for plastics recycling or e-waste applications according to their experience, whereas XRF technology is a viable tool for use in these applications. 

TSI: ChemLite Plus (LIBS)
ChemLite Plus is TSI's newest handheld LIBS metals analyzer. Units are designed to be accurate and fast, with 1 to 2 second readings and eye-safe, Class 1M lasers. Because there's no radiation, there are no regulation requirements, and compared to XRF units, ChemLite is easy and safe for any operator. Additionally, ChemLite analyzers have the largest laser spot size available, and a built-in cleaning mode.

ChemLite guns identify Al, Mg, Ti, Fe, Ni, and Cu alloys, and are able to separate close Al alloys that XRF cannot. TSI LIBS technology can also detect tramp elements, like Li and Be, down to 1 ppm and can measure Be copper alloys. 

Olympus’ Vanta handheld scrap analyzer on the job.

Olympus: Each has its place
According to Ted Shields, portable products manager, analytical instruments division, Olympus Scientific Solutions Americas, LIBS is best viewed as a complimentary technology to more traditional handheld XRF, and each type of technology does certain things well. 

"The most intriguing thing about LIBS is the ability to measure elements that you cannot measure with XRF," says Shields. "Carbon, beryllium and lithium are all possible, and recent advances are making carbon in L-grades achievable for some LIBS analyzers." 

He says however that LIBS technology struggles with some elements that XRF excels at. Most notably, he says, these include refractory metals, such as Cr, Zr, Mo, Ta and other common and commercially important alloying elements. "LIBS has a much smaller spot size than XRF," continues Shields. "This is good in the sense that the burn mark left behind is small. But it makes it much harder to get the same answer when you test twice in a row. This is because the sample varies across the small scale of the LIBS spot." 

He says some LIBS analyzer manufacturers compensate for this by recommending users take several shots at different places (called rastering the laser). But this adds to the test time. "Variations in sample geometry effect the results to a much larger degree for LIBS," he continues. 

"LIBS is also more sensitive to moisture and surface contamination. Some manufacturers try to address this by recommending users perform a cleaning pre-burn with the laser, again adding time to the analysis." 

Shields continues by adding that while LIBS calibrations are empirical, XRF metal calibrations are Fundamental Parameters (FP). "FP lets the XRF instrument calculate the effect of every element on every other element," he says. "This calculation lets one XRF calibration be remarkably accurate for a wide range of samples. On the other hand, empirical calibrations are only as broad as the samples used to create them. If you analyze something outside of the range of calibration samples, the results can be dramatically wrong. This is why LIBS analyzers require users to choose among several calibrations, and why making the right choice is critical to achieving reasonable results." 

Shields also emphasizes that knowledge about what materials are being dealt with is critical to achieving higher purity standards, especially in light of increased global standards for end materials, including those recently established by China. 

"One sample with a high concentration of an undesirable element can contaminate an entire batch of metal," he says. "The only way to know is to test. And the test needs to be quick and portable - like it is with handheld XRF technology," which he adds "are faster and more sensitive than ever before, making it possible for recyclers to meet higher purity standards."

Olympus: VANTA (XRF)
The Vanta analyzer is Olympus' most advanced handheld X-ray fluorescence (XRF) device and provides rapid, accurate element analysis and alloy identification to laboratory-quality results in the field. Units are military-standard drop tested, IP64 or IP65 rated, and designed with a large, gesture-capable touch screen, wireless communication, access to the Olympus Scientific Cloud, and direct PDF creation. They are also designed to be easy to use with minimal training, and to provide high throughput. 

The latest Vanta VMR model analyzers' come with a graphene detector window making them even more sensitive for magnesium, aluminum and silicon. Units provide very fast grade identification and are combined with Axon technology for high x-ray count. Other key features include: SmartSort and Grade Match Messaging; IMX processor; a metal detector shutter; intuitive navigation and configurable software

Hitachi High-Technologies’ X-MET8000 XRF-based analyzer features calibration options that suit various recycling applications.

Hitachi High-Technologies: speed vs range of application
For Hitachi High-Tech's latest LIBS analyzer (the Vulcan) speed is the biggest asset to scrap metal recyclers as this maximizes their operational efficiency during metal sorting. According to Sean McKernan of Non-Destructive Testing (NDT) Products, an Ontario-based distributor for Hitachi High-Technologies analyzers; "by employing point and shoot operation, Hitachi High-Tech's Vulcan LIBS technology, creates a simple, fast routine for recyclers which eliminates user related errors and ensures consistency of results.  

"Our Vulcan is able to provide an accurate alloy ID, often sufficient for most scrap metal recyclers," says McKernan. "And Vulcan's advanced data management allows logging both results and pictures to make reporting easy and complete." He adds that as a laser analyzer, there are no requirements for operator certification and licensing, which is required for XRF operation in Canada." 

Hitachi High-Tech's latest XRF analyzer, the X-MET8000, is typically used in metal recycling and scrap yards when accurate on-site alloy identification and chemistry are required. 

"The optimized combination of a high performance X-ray tube and large area silicon-drift detector (SDD) delivers the results required in even the most demanding metals applications," says McKernan. "The X-MET8000 is used for analysis of light elements (Mg to S) and most commercial alloys, including aluminum, titanium, bronze and high temperature alloys. The low limits of detection provide accurate grading and determination of impurities and penalty elements." 

McKernan adds that unlike Hitachi-High Tech's LIBS model (Vulcan), its X-MET8000 HH-XRF analyzer is available with calibration options that suit various recycling applications. The X-MET8000's plastic FP calibration, for example, is optimized for the determination of a wide range of elements (Cl, Cd, Hg, Pb and many others).  "In instances where separation of chlorinated from non-chlorinated plastics is required, The X-MET8000 can be used to ensure that materials such as PVC are not incinerated, preventing damage to the incinerator's masonry as well as the release of harmful dioxins into the atmosphere," explains McKernan. 

"HHXRF is also often used at e-waste recycling facilities to quickly check for the presence of precious metals such as gold (Au), as well as toxic elements such as lead (Pb), to decide the next best processing step," he says. "In automobile scrap yards, Hitachi High-Tech X-MET8000 with Car Catalyst calibration is used in the determination of platinum, palladium and rhodium at various stages in the recycling and refining process of automotive catalytic converters.  "Empty exhaust converter cans, manifolds and pipes can also be sorted on-site using the X-MET's alloy calibration," he says, "adding further value to the recycling process." 

Hitachi High-Technologies: Vulcan (LIBS)
Hitachi High-Tech's Vulcan (LIBS) analyzers are among the fastest in the industry, taking just one second to identify and analyze a wide range of alloys. Designed to be rugged and durable, the latest models, including the Vulcan Smart and Vulcan Expert, are IP54-certified and comply with MIL-STD-810G military-grade standards. These LIBS-based analyzers feature measurement optics protected by tough, sapphire glass, with a single battery charge lasting up to eight hours when analyzing one sample every five seconds. Units also include intuitive user interface and point-and-shoot analysis to reduce the chance of user-related errors. Additionally, Vulcan features advanced reporting tools, allowing results to be shared via mobile phone or securely stored through Hitachi cloud-based service. 

Hitachi High-Technologies: X-MET8000 (XRF)
The X-MET8000 handheld XRF analyzer is available in three configurations, offering both fundamental parameters (FP) method and empirical calibrations (traceable to CRMs) for superior precision and accuracy. The X-MET8000 series' intuitive, icon-driven user interface minimizes operator training, while a customizable results screen accelerates decision-making. The latest models are lightweight (as low as 1.5 kg) and feature an ergonomic design, comfortable for daily use. A 4.3-inch colour touchscreen is easy to use and read, and no tool is required to change a quick-swap analysis window when broken or dirty. These analyzers also have an automatic sample size compensation for accurate testing of cables, wires, fasteners, turnings, chips, etc. Data can be store on-board the X-MET8000, exported to USB flash drive, PC or the Hitachi High-Technologies cloud-based service. 

SciAps: Z-200 (LIBS)
SciAps offers both LIBS and X-ray technologies. The Z-200 LIBS model uses a pulsed laser, 5-6 mJ/pulse, with a 50 Hz repetition rate. According to SciAps, it is the world's only handheld LIBS capable of carbon analysis, and the only handheld technology with integrated argon purge, allowing for operation in both air-based analysis for quick screening, or argon-purge for highly sensitive, precise measurements. The Z model is ideal for analysis of aluminum scrap, particularly where low concentrations of Li, Be and/or B are important, for upgrading stainless into low-carbon or straight grades, and for sorting carbon steels.  

Complementing the LIBS model, SciAps' latest XRF model is the X-250, which provides quick analysis of stainless, high temperature- and red metals. The X-250 also excels in the analysis of aluminum alloys, in four seconds, including Al alloys that historically get mixed by other X-ray guns. Additionally, the X-250 offers leading performance on other light elements including S, P, Al and Si. 

This article was originally published in the March 2018 edition of Recycling Product News, Volume 26, Number 2.

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