Shrinking the Waste Line
Producers and service providers are mapping out pathways to more eco-friendly handling of mining’s solid-waste materials ranging from tires to trash

By Russell A. Carter, Contributing Editor

The number of mining tires scrapped
annually is a tiny fraction of the total
volume of scrap tires, but they carry
disproportionate weight-to-numbers:
In the U.S., for example, OTR tires
account for about 1% of scrap tires
by number, but 15% by weight.
Mine operators expect to encounter unanticipated incidents throughout the life of a project. It could be an outcome of a bad decision in an early stage of development, an unexpected natural event, or a shift in the regulatory framework. Maybe the drilling contractor pulled cores that were too small in diameter to provide valid crushing samples during the testwork phase. Or, years of unprecedented drought shrink a once abundant water supply to a trickle. Changes to mining taxes and royalties can hinge on the outcome of an election. That’s why risk management advice is an industry growth sector.

The flip side of this coin represents project “constants” — expectations of continuity, such as processes that might be tweaked but not abandoned, steady increases in haulage fuel burn as mining goes deeper, or an inevitable rise in process-energy demands as ore grade diminishes. One of the most tenacious constants is waste generation: Where there is mining, there will be waste. It can take the form of waste rock, tailings, water, sludges or slurries, and discarded consumables ranging from worn-out conveyor belts or giant equipment tires to pallets, drums and miscellaneous trash. The corollary to this constant is that pressure on mineral producers to reduce, control and even profit from waste is only going to get stronger.

The rising tide of mining-related waste generation stemming from growing world demand for mineral commodities, coupled with declining ore grades, also has lifted waste management into the category of growth sector. Market studies predict — albeit with sometimes wildly differing figures — steady increases in the global mine waste-management market size. One recent study estimated that the waste-management market size just for rock and tailings will rise to almost 18 billion tons worldwide between 2018 and 2022, with growth accelerating at a Combined Annual Growth Rate (CAGR) of 5% during that period. Another predicts a CAGR of 6.1% with a total market size of more than 233 billion tons by 2022.

How closely the industry actually follows those predictions remains to be seen. Teck Resources, for example, is Canada’s largest diversified mining company, with copper, zinc, metallurgical coal and oil sands operations located in Canada, Chile, Peru and the U.S. According to the company, its operations produced about 917,000 metric tons (mt) of mineral waste in 2017, most of it coming from ore and coal extraction. In 2018, that amount increased to roughly 928,000 mt, a gain of slightly more than 1% over the course of a year.

Although the production and primary handling and storage of rock waste and tailings accounts for the lion’s share of tonnage and attention from large producers, that topic is beyond the scope of a single article. This month, E&MJ looks at a few facets of the “re”-segment of mine waste management — as in recycling or reuse of once-discarded materials. And yes, it too represents a modest but increasingly significant growth sector, as part of the “circular economy” model that’s driving commercial interest in this area.

A Circular Approach
The main premise of a circular economy involves minimizing waste and obtaining maximum value from resources, and recycling is a major foundation block in the model. Teck, for example, noted in its 2018 Sustainability Report that it recycles waste materials, buying certain types of e-waste such as cathode ray tubes and alkaline batteries for processing at its Trail, British Columbia, smelting/refining complex. And it recycles its water — up to four times at some operations.

Other producers pursue similar strategies. Rio Tinto said its Kennecott Copper operation in Utah has, since 2012, added recycled scrap metals such as old copper wiring into the smelting process. In 2017, Kennecott processed 2.8 million lb of copper from recycled scrap metal. Its Oyu Tolgoi operation in Mongolia currently recycles more than 80% of its water, which, in terms of water-per-ton-of-ore processed, means it uses less than half the global average of similar mines, according to the company.

In Sweden, Boliden has recycled waste at its Rönnskär smelter since the 1960s. The refinery, outside Skellefteå, has an annual capacity for recycling electrical material of 120,000 mt, including circuit boards from computers and mobile phones sourced principally from Europe, reportedly making it one of the world’s largest recyclers of metal from electronic material.

Programs like these shift the industry a small step closer to the concept of urban mining — recovery of valuable metals from e-waste — and also have the potential benefit of positioning mining as an active player in seeking solutions to some environmental problems that its critics blame it for: e.g., digging up metal-bearing ores in remote and often environmentally sensitive sites, only to have those metals, once made into salvageable components, eventually buried again in landfills.

There’s also a financial aspect. Recent studies indicate that recovery of copper and gold from recycled CRT tubes, for instance, costs 13 times less than extracting the same amount of metal from virgin ores. An organization called StEP (Solving the E-waste Problem), formed as a partnership between the United Nations and academic and business organizations, reported recently that the annual production of electronic goods worldwide required 320 tons of gold and more than 7,500 tons of silver, with a combined value of $21 billion.

At present, just 15% of that is recovered, according to StEP, and much of it is processed in less-than-ideal circumstances involving unscrupulous or technically unsophisticated operations that potentially create as many environmental problems as recycling is intended to solve. The situation seems to offer mine operators, with vast experience in finding, handling and processing sometimes difficult-to-handle materials, an opportunity to apply their expertise.

As shown above, some mining companies are already established as fringe players in the recycling sector, and many are adopting life-of-project strategies for waste management. Anglo American, for example, explained its policy on its sustainability webpage: “We’re finding new ways to cut waste by re-mining or reusing it. We apply the ‘avoid, reduce, reuse and recycle’ management hierarchy to ensure the least possible impact on human health and environment during both the operational and post-closure phases. Once waste-reduction opportunities are exhausted, we actively explore the reuse of byproducts.”

Some common aspects of mining make recycling and reuse difficult. Barrick Gold noted that “A number of non-process wastes are generated each year at our operations. These wastes may differ by country and by operation, but typically include scrap metals, waste oils, cans and bottles, spent tires, and office and camp waste. While we try to recycle these wastes as much as possible, this is not always feasible at some of our remote sites or at operations located in countries where recycling is not available. Non-hazardous waste that is not recycled is usually landfilled (either in municipal landfills or landfills constructed on the mine property) or incinerated, on or off the site.

Increasingly, less-waste-to-landfill provisions are becoming part of a mine’s basic permitting package. At the $6.7 billion Donlin gold project in Alaska — a joint venture between Barrick and Nova- Gold — the mine’s Integrated Waste Management Plan stipulates that in accordance with state law, management decisions that may affect waste generation at the proposed project would be made by considering, in sequence, options starting with waste source reduction and/or recycling, followed by waste treatment or disposal. In order to accomplish this, Donlin said its plan will ensure that:
• Operations that generate wastes would be reviewed to identify opportunities for reducing waste, and these opportunities would be implemented whenever possible.
• The properties of materials would be reviewed prior to purchase and an effort made to minimize the use of hazardous materials and those classified as hazardous wastes once they can no longer be used for their intended purpose.
• Methods for reusing and recycling materials would be promoted and implemented whenever possible.
• Non-hazardous solid wastes that are permitted for disposal on site would be disposed of at on-site, permitted, solid waste inert landfills, regulated by the state.
• Materials that cannot be managed on site would be sent off site to appropriate facilities for recycling, reuse, treatment and/or disposal.

Another aspect of the circular economy model that could increasingly affect disposition of mining-related consumables is Extended Producer Responsibility (EPR), informally referred to as the “producer pays” approach in which manufacturers become accountable for the treatment or disposal of post-consumer products, with producers or importers assigned responsibility for organizing and financing waste management. EPR laws have gained momentum in Europe and Latin America. Legislation (Law No. 20.920) that has gone into effect in Chile, for example, applies to processing oils, electronics, packaging, tires of all sizes and batteries — foreshadowing possible future legislation in other nations where mining activities are extensive.

Giant Tires, Giant Problem
Disposal of large and giant-sized tires used on haulage and loading equipment is one of the principal ongoing challenges for both surface and underground mine operators. Giant OTR tires pose a number of problems for recyclers, which makes them up to a hundred or more times more expensive, per tire, to process than the dollar or so it generally costs a recycler to completely reduce a car tire to rubber crumbs.

Salvadori says its MT-REX recycling equipment can downsize 7,000 or more giant tires per year, providing
about 35,000 t/y of tire chunks suitable for shredding.
OTR tires’ physical characteristics also make them bad choices for landfill disposal. Their low density and hollow centers allow them to “float” upward in landfills, disrupting compaction efforts. Scrapped and buried OTR tires also pose additional problems in case of fire. Once ignited, they’re extremely difficult to extinguish and can release pyrolytic oil, ash and smoke, which contain carcinogens, heavy metals and other toxic compounds.

They carry the burden of requiring specialized treatment, with per-tire shipping and handling costs that can amount to thousands of dollars each, along with the hazards they present to workers during the course of loading, unloading and processing, and the need for extra heavy-duty equipment to cut, cull individual tire components such as the steel bead bundles, and shred the tire chunks.

Because of the low volume of OTR tires available at any single site and the stress they put upon conventional tire recycling equipment, many recyclers are reluctant to process giant tires with existing equipment. And, with estimated capital costs in the $2 million to $4 million range for a tire size-reduction and shredding facility capable of handling giant OTR tires, many also aren’t eager to invest in systems that are expensive yet may be used only intermittently. Under these circumstances, both mining clients and contract recyclers are looking for equipment flexibility, efficiency, and transportability to service widely scattered sites and minimize shipping and handling costs.

If not repairable or retreadable, often the first step in reducing a giant OTR tire prior to shredding is to remove the bundles of steel cables that form the tire’s bead. Nebraska, USA-based Eagle International’s OTR tire bead remover is a transportable, automated unit that cleanly cuts the steel bead bundles from the tire, simplifying downstream handling and adding value to the wire scrap. The bead remover is part of a transportable, three-stage OTR recycling product line that includes a tire cutter unit that slices OTR tires in half — like splitting a bagel — to reduce the weight and size of giant tires to a more manageable size. As in other areas of mining and heavy industry in general, automation and energy efficiency are becoming strong selling points for OTR tire recycling equipment. For example, Italy-based Salvadori Srl offers the MT-REX system, claimed to be the first fully automated solution capable of handling tires up to 63-in.-rim diameter and providing a continuous flow of consistently sized tire chunks. It can be operated by a single operator using a forklift. No overhead crane is necessary.

The MT-REX system weighs about 42 tons and has a footprint of 7 m x 14 m. According to the company, its modular design makes teardown and installation at another site just a two-day operation — one day for disassembly and one day for reassembly. Last year, Eldan Recycling introduced a new version of its Super Chopper “pre-chopper” designed to more economically handle mining tires that have been cut into segments with an industrial shear. The Super Chopper shreds the segments and liberates the wire strands within the tire, which are then recovered by a high-powered magnet. The machine is now available with a variable frequency drive, as well as in the original hydraulic- drive configuration. According to the company, the frequency drive-equipped Super Chopper provides low startup power demand and cuts overall power consumption by 50%-60%. It is capable of handling tires up to 157 in. in diameter and weighing up to 6 tons.

Although cutting, shredding and grinding has been the conventional industry path for responsible disposal and processing of OTR tires, yielding marketable end products such as crumb rubber and steel scrap, several companies have or are in the process of implementing other physical or thermal conversion technologies to recover even more useful materials. Titan Tire Reclamation, a subsidiary of Titan Tire International, opened a thermal vacuum pyrolysis recovery plant in Fort McMurray, Alberta, in 2016. The plant was damaged by a fire in 2017, but at the plant’s inauguration event, a company executive estimated that on a daily basis the operation would be capable of converting 240,000 lb of scrap tires to approximately 13,600 gallons of oil, 52,800 lb of steel and 76,800 lb of carbon black. The system uses 85% of the gas it generates to heat up the vessel containing the scrap tires.

Kal Tire has been actively involved in tire recycling, first partnering with another company to shred up to 6,000 tires annually, including mining-class tires up to 63 in. in diameter, at a facility in Alberta near oil sands mining operations. In Chile, the company is working toward completion of a thermal conversion plant that will reduce tires to their original components — carbon black, steel, fuel oil and gas — with the latter also being used to fuel the process. It also provides comprehensive tire repair services. Most notably, its proprietary Ultra Repair technology, which was developed to patch and return deeply damaged but expensive OTR tires to service instead of consigning them to the scrap pile.

In some cases, the technology doesn’t require size reduction of large tires prior to intake. In Australia, a collaboration between the Tytec Group and Green Distillation Technologies Corp. is working toward commercialization of a thermal process that is claimed to reduce earthmover tires to their basic components in a single step, without need of cutting or shredding. In an interview with an Australian trade publication in early 2018, CEO of GDT Trevor Bayley said the privately held company was finalizing arrangements to build a commercial plant at a site in Queensland that would be capable of handling 19,000 mt of tires annually to produce about 7.3 million gallons of oil derived from the process.

Although the actual technical details of the process are skimpy, Bayley explained that during processing, heat is applied in a controlled manner to induce a reaction that reduces the rubber and other nonsteel compounds in the tire to their molecular state. Some of these molecules interreact and form new hydrocarbon compounds, which are extracted as vapor and condensed into crude oil. Once all the susceptible molecules have recombined, the process ceases and the remaining carbon is extracted together with the steel skeleton of the tire, which is unchanged.

And in Belgium, an enterprise called Big Tyre Recycling Co. (BTRC) reportedly has developed an Ultra High Pressure (UHP) water jet system capable of demolishing tires up to 4 m diameter. The patent-pending process, which slices and pulverizes the tires using only UHP jets, does not require any form of mechanical shredding or grinding, and produces rubber powder, clean steel and textile fluff for other industrial uses, according to the company.

As featured in Womp 2019 Vol 04 -