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Money in Mono-Fractions

As purity standards rise, recyclers trending from mixed to mono-metal fractions for revenue boost

iStock-173926237_metal stock pile

Rising recycled metal quality standards. Stringent governmental material purity regulations. Once reliable global markets for recycled metal tougher to access.

Today’s scrap metal recycling facilities face multiple headwinds along the road to profitability. Market closures due to tightening purity standards plus an underdeveloped domestic recycling infrastructure have led an abundance of scrap metal, including metal fractions, in processors’ yards.

Material surpluses have driven down prices for recycled metal. “Over the last 18 months, since the implementation of National Sword, prices for general mixed metal products like Zorba have fallen,” comments Eric Thurston, sales manager, metals for TOMRA Sorting, Inc, headquartered in Charlotte for North American operations. Brian Gist, global sales director for TOMRA Sorting adds, “As a result, we are seeing a trend toward recycling facilities using advanced sorting techniques with sensor-based sorting to separate mixed materials into mono-fractions.”

While the headwinds are strong, some recycling companies see the new stringent quality standards as a way to separate themselves from other suppliers. This will, however, require upgrades to processing equipment. “Some customers are telling us that market conditions are right to upgrade their plants for processing the abundance of scrap metal available in North America to higher purity standards,” says Carlos Manchado Atienza, regional director Americas for TOMRA Sorting.

When it comes to sorting metal fractions, a company has options. Making the wrong decision between wet or dry for a market can have costly consequences.


Light/heavy dense sorting

Dense media, or wet sorting has been used by the scrap industry for decades to sort heavy metal fractions like copper, zinc and stainless steel from light fractions, such as aluminum. The process is a carry-over from the mining industry, where it was used to recover precious metals and coal fractions from tailings. At the surface, using water and a flocculant to float/sink the materials seems simple enough.

Beyond being a known commodity, initial capital outlays to build a wet plant is attractive to some scrap metal companies. It costs less to start up a wet plant vs a dry sorting plant.
However, this up-front savings comes at a long-term price. “Ferrosilicon costs can vary, ranging from $1,600 to 1,900 per ton at any given time,” comments Thurston.

Gist, who spent years operating a dense media plant, further explains that a well-run plant uses ferrosilicon at a rate of approximately 5.5 to 6.5 lb per ton of metal sorted. “However, the average plant uses roughly 17.5 to 20 pounds per ton of fine metals fraction separated,” he says.

Ferrosilicon creates the specific gravity (SG) range for which metal fractions are sorted into a light or a heavy product. The goal is to maintain between 1.8 to 2.2 SG for floating light material and 2.8 to 3.4 SG for the heavy product. 

While sounding simple, multiple factors influence targeted SG values, including material processed and water quality. “Stability is a constant battle in running a dense medial plant, making it difficult to obtain stability and repeatability in sorting,” continues Gist. “As material is floated, fine material settles in the water, and the dirtier the water the more ferrosilicon required to get the correct specific gravity for sorting the light or heavy package.”


Both Thurston and Gist caution scrap metal recycling facilities who consider investing in a wet plant to remember the sorting limitations, especially in today’s market. Flotation will only produce light (aluminum) and heavy packages. Unless mixed with a dry sorting circuit, wet plants cannot further sort the heavy metals into mono-fractions like copper, zinc, stainless steel or lead, which limits the plant’s flexibility to adapt to market conditions.

The average dense media plant is configured to process up to 20 tons per hour (TPH) of metal fractions. SG stability and recycled particle size will affect this rate. As SG instability occurs and particle sizes get smaller, production rate slows, often to as low as 7 TPH.

Dirt caught in the pores of scrap metal mixes with ferrosilicon and settles in the tanks, on the screens, and in lines and pumps. This filter cake must be cleared from the system, and depending location, it may be classified as hazardous waste, which makes disposal more difficult and costlier.

These items, plus the need to keep the tanks and lines from freezing during the winter in many markets, result in continuous care and significant long-term operating costs for a dense media plant. Operations must figure these costs into the equation when considering the type of sorting process for separating metal fractions.


Advanced Sensor-Based Sorting


While not available to the market for as long as wet sorting, metal recycling facilities have used dry sensor-based sorting for nearly three decades. “We began selling our optical sorting equipment in North America in the early 1990s,” mentions Manchado Atienza.

In addition to optical sorters, the metal industry also employs X-ray, electromagnetic and laser technologies to sort ferrous and non-ferrous metal fractions from impurities. Rather than water, short bursts of air are used to either eject detected feed material impurities and drop the desired product in a negative sort or eject the product and drop the impurities in a positive sort.

Whereas wet sorting provides simply a light or heavy product package, a dry system takes the sorting process a step further into mono-fractions. “Advanced optical sorting further separates the copper, nickel, stainless steel, lead and other metals from mixed metals like Zorba to deliver a higher quality aluminum product as well as other mono-fractional products,” explains Manchado Atienza.

In a market where mixed metals commodities are selling at a low price, dry sorting gives companies the flexibility to adapt to market conditions. “Zorba is currently selling at less than $0.50 per pound in many markets, but copper is selling at more than $2.00 per pound,” says Thurston. Optical sorters give companies the ability to change sorting processes and separate the more valuable fraction to meet market demands.

Changes to the sorting circuit are quickly made through the equipment’s control software package. TOMRA recently introduced its ACT operating system that allows operators to make simple product package sorting adjustments through a touchscreen. “It takes an operator less than two weeks to learn how to run a dry plant,” comments Thurston, “but running a wet plant is more of an artform and can take up to 18 months for an operator to run it at peak efficiency.”

Gist explains it’s the struggle to learn how to optimize SG in a wet plant to achieve maximum product recovery at a low flocculant usage rate. “If you have a good operator of a dense media plant, you need to retain him, as he will save the company on operating costs,” he says. “Whereas with optical sorters, the software program offers consistent and repeatable results at the touch of the screen, so it’s easier for the operator to learn and run.

Gist further details that wet plant operators are tied to the facility to keep a close eye on the floatation process. New technology available to the market, such as TOMRA Insight, uses the cloud to report critical operating data to companies using optical sorters, so the recycling circuit can be operated remotely, if desired.

Still, some metal recycling facilities point to a higher initial capital expenditure as a disadvantage to the dry sorting process. However, Thurston contends that long-term operating costs for running optical sorters are substantially less than operating dense media. “Operating costs are up to 90 percent lower with dry sorting,” he says, “and that’s one reason why a large Midwest metal recycling operation sold off its dense media plant in favor of a dry process. Plus, the uptime availability for optical sorters is around 95 percent verses approximately 75 percent with a dense media plant.”

Historically, sorting fine metal fractions of less than 0.4 inches is where wet separation held a distinct advantage, as the resolution on optical sorting equipment would be effective for 0.4-in fractions and above. Recent advancements in technology, however, has led to the introduction of the TOMRA X-TRACT X6 Fines package for its X-Ray sorting technology, recently launched at Aluminum USA in Nashville. “This package now allows us to effectively detect and sort fine metal fractions about 50 percent smaller than what was previously available to the market, while offering recovery rates of 95 percent and higher,” says Thurston.


The Right Mix


Thurston offers a consideration to companies currently operating dense media plants who want the flexibility of separating mixed metals into mono-fractions: sensor-based sorting add-on. Different types of dry sorting technologies can be added to the wet sorting process – either before or after the wet sort.

“Unlike a wet plant, dry sorting technology is scalable to meet the operation’s needs,” he says. “A dry sorting line can be cost-effectively added to the back-end of the process to sort mono-fractions, allowing a company to take advantage of market conditions.”

Whether going with wet or dry separation for metal fractions, Gist reminds companies that final product purity must be paramount, given today’s continually tightening regulations. “China’s implementation of National Sword and the many Southeast Asian markets following suit is an indicator that purity standards will only get more stringent. Therefore, a recycling operation must choose the right technology that will offer not only the product the company needs to sell to the market but also at the right purity levels.”

Topics: News, Metal