As the demand for recycled products continues to increase, it is imperative that the technology associated with the industry continues to evolve. These technologies must be cognizant of the changing environmental issues and economic advantages that affect businesses associated with the circular economy.
By Martin Weiss and Tina Keough

The principles of X-Ray Fluorescence (XRF) have been known since the early 20th century, but it was not until the development of modern X-ray detectors in the mid-20th century that XRF began to be widely used for elemental analysis. In the 1940s and 1950s, physicist Bruno Rossi and his colleagues developed the first portable X-ray fluorescence spectrometers capable of analyzing a wide range of materials. In the decades since, XRF has become a valuable tool for elemental analysis and metal sorting in a variety of fields, including materials science, geology, environmental science, and industrial quality control.

In the recycling industry, XRF has become a respected and appreciated tool for accurately sorting materials based on their chemical elements. By exciting the sample with X-rays, which causes the atoms in the sample to emit energy specific to each element, XRF can analyze various materials such as metals, alloys, or glass to determine the exact chemical composition. During the sorting process, this allows for individual metals to be separated from a larger pile at higher speeds—up to 10 metric tons (11 U.S. tons) per meter sorting width.


REDWAVE XRF machines awaiting shipment.
Photos courtesy of REDWAVE.

The separation velocity of XRF has become increasingly important since the “China Green Fence” policy was implemented. This policy created stricter standards for the import of recycled materials, including tighter contamination limits and complete bans on certain types of waste. The policy has had a significant impact on global recycling markets as China, who was importing 50 percent of US scrap metal in 2018, was a major destination for recycled materials. As a result, U.S.-based metal recyclers have had to search for alternative outlets. This quest has aided in the recovery of the U.S. scrap metal market while allowing many recyclers to gain domestic distribution for their material.

Sorting Options
As with any industry, recycling technologies are developed to face economic requirements and environmental needs to quickly overcome challenges. The three main platforms, XRF, XRT and DMS, are used to separate materials based on their physical and chemical properties, but there are differences in their sorting principles. For example, XRF and XRT are faster and can detect elements in smaller concentrations, whereas DMS is more effective at sorting larger, or denser, materials. Let us compare the three main sorting technologies.

Dense Media Separation (DMS)
Quite simply, Dense Media Separation (DMS) uses density to separate materials. Heavy items sink to the bottom while lighter items float to the top. DMS is the most efficient and accurate method for recovering aluminum from heavy metals as it uses the density and size of the pieces in juxtaposition against ferrosilicon media. This process, despite its dynamic ability to isolate aluminum, is limited when distinguishing between distinct types of metals. Also, DMS tanks are relatively large, as they require enough space to accommodate the dense media suspension. If not properly managed, the tanks are subject to contamination and the mandatory water purification systems can potentially be hazardous to the environment. Although the suspension solution for DMS can be expensive to maintain, the system itself, unlike XRF or XRT which require upgrades, can last for decades and be a significant boon for sorting facility owners who do not want to replace their technology every few years.

XRT Sorting
XRT sorting is a method used to separate materials based on their absorption characteristics. It works by directing an X-ray beam through a sample and measuring the amount that is absorbed by the material. Elements with high atomic numbers—heavy metals for example—will absorb more X-rays. This is the reason for wearing lead gowns while having a body scan as the dense lead will shield you from potentially harmful X-rays. Commonly used in the mining and metal industries, automated XRT machines tend to be large, use costly belt conveyor systems to move materials through the machine, but are known to be quick, precise, and non-destructive to the material. Versatile as these machines can be, the moving parts associated with the belt system can be prone to breakdown and carry heavy maintenance requirements. Also, XRT may experience interference from the X-ray absorption spectra that can overlap between samples. For example, a thin piece of zinc and a thick piece of aluminum can absorb the same amount of energy resulting in a significant quantity of aluminum to settle with heavier metals. Although XRT has been used for many years to separate aluminum from the load, it is similar to DMS in limitation, as it cannot further sort the produced heavy metals into individual elements and alloys. It is important to remember that XRT can remove lighter elements that elude DMS and XRF: magnesium for example.

ZORBA input material waiting to be sorted.

XRF Sorting
XRF sorting uses X-rays to “excite” the electrons in the materials’ atoms, causing them to emit secondary X-rays. These X-rays are characteristic of the elements present in the material, and the intensity of the emitted X-rays can be used to determine the composition of the object. Scrapyards will often use handheld XRF, or Niton Guns, whose accuracy depends greatly on the load and user experience. These versatile machines have a minimal footprint and use cameras in conjunction with X-ray detectors to reliably distinguish alloys. XRF machines use a chute design, which allows customers to determine pass and eject materials while eliminating moving parts and lessening maintenance downtime. Although XRF may have difficulties with light metals, such as silicon and magnesium, it excels at rapid identification of metals, alloys, ceramics, polymers, and glass. XRF is the only available technology to be used to sort heavy metals into individual high purity products: copper, brass, zinc, stainless steel, and precious metals, for example. Over the last 10 years a unique order for sorting heavy metals has been developed. This format yields the greatest purity while using the least amount of sorting steps, minimum machine time usage and highest possible recovery output. This ensures an increased profitable result, overcoming the initial higher cost of putting the system into operation. As the XRF is versatile in application, it is recommended for use in the metal, glass, plastic, and mining industries.

All three technologies, DMS, XRT, and XRF, are admirable methods for separating scrap metals. Whichever application the facility intends to pursue will determine the better method for accurate sorting. At the end of the day, the system that yields the purest product and generates the highest profit while offering maximum flexibility and versatility, will be the best solution for the facility.

Future Advancements
Economic and environmental changes constantly urge sorting manufacturers to improve available technologies. For example, in 2022, new XRF machines use 20 percent less electricity, yield 15 percent increased ejection power, and have a 75 percent higher scan capacity than XRF predecessors. Internal designs have been modified to allow for easier accessibility, and with no moving parts, maintenance is minimal. In an effort to combat rising inflation and supply chain shortages, most sensor systems and sorting software have been brought in-house allowing for more timely and cost-effective production. Enhanced spectral analysis also makes new applications possible. These upgrades, coupled with the existing advantages of XRF machines’ robust free-fall principles, create the opportunity for future expansion as the technology grows.

Smaller materials have always been a hurdle for accurate sorting. Spacing requirements for each individual air jet nozzle allow smaller materials to pass unimpeded between them yielding a less pure final product. For entrepreneurs, this means that measures must be put in place beforehand to ensure an accurate sort. In order to shrink the quantity of smaller material from sneaking through the system, and to aid facility owners in maximizing profits, new XRF machines, scheduled to be released in April 2023, have been designed to detect smaller pieces of material, and will revolutionize the scrap metal industry. | WA


Capability comparison for XRF, XRT and Dense Media



As the demand for recycled products continues to increase, it is imperative that the technology associated with the industry continues to evolve. These technologies must be cognizant of the changing environmental issues and economic advantages that affect businesses associated with the circular economy. REDWAVE recognized this need and developed its first XRF machine. The environmental benefits reaped by these machines became evident in 2022 when figures, stemming from the Bureau of International Recycling’s annual report calculating both CO2 and electric kilowatt hours savings in the U.S., using REDWAVE XRF sorting machines to recover copper, aluminum, and zinc scrap were released. With only 15 REDWAVE XRF machines, and facilities using secondary sources of scrap versus primary sources as basis, U.S.-based recyclers annually saved $881 million (5.9 million electric kilowatt hours), reduced the CO2 output by 1.7 million tons and averted an estimated 306,000 tons of mixed scrap metal from landfills. For reference, to capture 1.7 million tons of CO2, approximately 85 million trees will need to grow undisturbed for one year. Multiply these figures across the world, and using 100 REDWAVE XRF machines as basis, the electricity savings increased to $5.9 billion (39 billion kilowatt hours), a CO2 reduction of 11.2 million tons was attained and 2 million tons of mixed scrap was averted from landfills.

Economically, recycling scrap metal generates billions of dollars in export sales every year. As developing nations grow and modernize, the global marketplace for scrap metal continually expands, pushing resellers to seek new outlets for scrap material. Since pre-sorted metal brings a higher monetary return, many savvy entrepreneurs are investing in sorting machines to facilitate the process. Machines with advanced software optimization, adjustable sorting capacities and widths, such as the REDWAVE XRF, become instrumental when choosing between the three main sorting technologies: XRF, XRT (X-Ray Transmission), and DMS (Dense Media Separation).








Martin Weiss is COO of REDWAVE Solutions US LLC. After working for BT-Wolfgang Binder GmbH, a leading general contractor specialized in mineral and environmental technology, first in R&D, then in Product Management, he soon moved to sales where he was Global Sales Management for the product group REDWAVE XRF. During his times as Global Sales Manager Martin Weiss travelled to the U.S. on a regular basis to lead Product Development and Sales of the same product group.During his +12 years employment at BT Wolfgang Binder Marting gained knowledge and experience in many different areas such as R&D, Project Management, Application Management, Solution Selling, Negotiation, Sales Management and Leadership. Tina Keough is U.S. Marketing Manager for REDWAVE Solutions US LLC.

REDWAVE Solutions US LLC, based in Alpharetta, GA, is a world leader in XRF sorting technology. With more than 25 years of plant building experience, their engineers are facility centric and capable of completing projects from design concept and construction through to operational status. For more information, For more information, e-mail [email protected] or visit