FLS crushing station with an indirect feed Eccentric Roll Crusher. (Image: FLSmidth)

According to Jonas Olsson, Director for Strategy and Business Development at Sandvik Rock Processing Solutions, there is a huge potential to save energy by rethinking the comminution process. “We have made it our mission to help our customers find the best sustainable solution in terms of financial savings, energy efficiency and climate gains throughout the lifecycle of the plant,” said Olsson in a recent blog post.

Improvements in energy efficiency can be made at every step of the process of turning solid rock into a valuable product size fraction, or into a liberation size where metals like iron, gold or copper can be extracted. Significant savings can, for example, be achieved by extending the crushing process which generally ends when the rock has reached a top size of 12- 14 millimeters. “Move that limit down to 8 or 6 millimeters and there are significant amounts of energy, as well as water, to be saved,” explained Olsson. “Our stationary crushers have an energy efficiency of 50%. That means that, for every ton you convert to crushing instead of grinding, you’ve saved 90% of the energy.”

A big challenge is making the industry aware of how much there is to gain from shifting towards energy-efficient rock processing solutions, although Sandvik said that recent high energy prices have led to increased interest in its solutions. “There’s generally always an improvement potential of 10%-15% that can be reached through configuration and customization of the equipment that’s already in use,” said Marcus Johansson, global application development Manager at Sandvik Rock Processing Solutions. “We look at the entire process to identify the true bottlenecks, as well as areas with the best improvement potential.”

It’s becoming increasingly important for mine operators to demonstrate to regulators and stakeholders that they’re using the most sustainable extraction methods. Johansson said that more and more are turning to OEMs, like Sandvik, to find solutions. “It’s no longer enough to only be price competitive, and we do have a unique knowhow based on decades of processing experience,” he added.

Sandvik is placing a big focus on knowledge transfer surrounding best operating practices for processing plants and equipment. The company’s customized performance optimization program starts with characterizing the customer’s material in a test lab. This provides information which, in combination with software tools, such as Sandvik’s PlantDesigner, are used to maximize the value of Sandvik rock processing equipment.

“Thanks to our decentralization strategy we can provide certified expertise regardless of where our customers are located,” added Johansson.

Operating Practices for Max Efficiency
Jaw crushers are often used as primary crushers where the main duty is to produce a material that can be transported by conveyor to the subsequent stages of the plant. They crush material via compression, squeezing it between a moving piece of steel and a stationary piece of steel. One of the main benefits of jaw crushers compared to other types of primary crushers has to do with the wearing components — wear is typically limited to the jaw plates and side plates. Additionally, these plates can be reversible, allowing for double the wear life.

In a recent blog post, the team at McLanahan explained that to further increase the wear life of these components, proper feeding practices should be followed. “Properly feeding the crusher not only increases component wear life, but it also improves the efficiency of the jaw crusher itself,” they stated.

Their first suggestion is to observe in-line feeding; jaw crushers should only be fed in line with a feeder or scalping screen. This means the discharge end of the feeder should align with the feed opening or gape of the crusher. This limits opportunities for the material to clog the crusher.

Properly feeding a jaw crusher not only increases component wear life, but
it also improves the efficiency of the crusher itself. (Photo: McLanahan)

Material that exceeds the size of the feed opening can clog jaw crushers and reduce their efficiency or block production altogether. Removing oversize ahead of the jaw crusher will help to avoid this. “A good rule of thumb is that the maximum feed size should be 80% of the crusher opening. If the crusher opening is 30 in., a 24-in. feed top size is recommended,” McLanahan stated. Fines in the feed can limit production for several reasons: they can clog the crushing chamber, reducing the tons per hour and machine efficiency. They can also prevent even distribution of particle sizes and generate an inconsistent product shape.

“Fines can also create unnecessary wear on crusher components,” the team stated. “Scalping out this material ahead of time will help to prolong the life of wear components (jaw dies and side plates), as well as help to reduce the downtime required to changeout worn components.” Another best practice for feeding jaw crushers is to blend the feed material ahead of the crusher to ensure a well-graded feed. This will produce steady, consistent tons per hour out of the crusher and will also promote inter- particle crushing to break any flat or elongated material. “A well-graded feed for a jaw crusher includes material larger than the closed-side setting but no larger than 80% of the feed opening,” McLanahan said. “Remove oversize, fines and material equal to the product size ahead of time for optimum operation.”

Jaw crushers can handle a wide variety of materials, including hard, abrasive, non-friable and even some wet materials. However, they are not suited to handling sticky or lightweight materials. These are best avoided. The team added that, while jaw crushers can handle some tramp metal, if equipped with an automatic tramp relief system, it’s best to limit the amount metal that enters the crusher to avoid costly repairs and downtime.

“If the crusher does not feature a tramp relief system, the toggle that maintains the closed-side setting can break, potentially damaging other components in the plant as it falls out of the crusher as well as causing unplanned downtime to replace the toggle,” they stated. “It’s always best to remove as much steel as possible via a hydraulic breaker, shear or concrete processor before feeding into the jaw crusher.”

Unlocking Complex/ Low-grade Deposits
As mines become deeper and ore grades deplete, more material must be crushed to maintain production levels. Newer, more efficient comminution technologies are helping to unlock deposits that were considered uneconomic 20-30 years ago thanks to material characteristics such as, hardness and wear rates, and the throughput capacity required to make these lower yield ores commercially viable. Primary gyratory crushers are one such technology; new designs and features now offer high capacity and cost-effective operation with low servicing and maintenance costs.

Bill Malone, vice president and global product group manager for crushing and screening at FLSmidth told E&MJ: “FLS MkV Gyratory Crushers are designed to work on the toughest rock and deliver higher capacities that, in the past, were only possible by using two older technology machines. Also, being equipped with the additional power handling capability to cope with these extreme demands, newer models allow the delivery of the same product size as the older models, but at a much-increased capacity, i.e., one machine instead of two, with no compromise on output gradation and the same footprint as the older type machines.”

FLS gyratory crushers are designed to work on the toughest rock and deliver high
capacities. (Image: FLSmidth)

“The capability to also switch-out existing older generation machines with units that are twice as powerful and do not require any major structural changes to existing stations also makes this a very attractive option in terms of investment and installation times,” added Malone.

In September 2023, FLSmidth announced it will deliver three Top Service Design (TSUV) gyratory crushers to a long-standing copper customer in South American. Under the agreement, FLSmidth will replace three existing gyratory crushers (originally supplied by FLSmidth) with its more efficient TSUV gyratory crushers. It said that the customer will benefit from increased efficiency as well as safer and simpler maintenance. Two of the crushers will be installed in the existing foundations of the old crushers. This will minimize construction costs, while also limiting environmental impacts from the replacements.

Following its 2022 acquisition of tk Mining, FLSmidth’s portfolio also now boasts the Eccentric Roll Crusher (ERC) which, it said, currently has no competitor. Released in 2019, the ERC fits between FLS’ range of jaw crushers and large gyratory crushers.

“These can accept large rocks and produce a suitable size for conveying and secondary crushing or directly to tertiary crushing, if applicable,” Malone explained. “The ERC has a built-in static grizzly screen situated before the crushing zone. Fine material is discharged directly and not passed through the crushing chamber, lowering power consumption and reducing the risk of material compaction and overloading the machine. This also minimizes wear on the crushing elements.”

Internal studies have shown that the use of the ERC brings process advantages thanks to its product size distribution which allows optimization of the entire comminution circuit. This can be reflected in lower investment costs and low operating costs through the entire cycle.

Malone said: “These process advantages were confirmed by the first industrial tests. The type of ore being processed will dictate the selection of comminution equipment. However, we have observed significant energy reductions of up to 30% in the lithium/ spodumene flowsheet that we are currently developing. We are looking at using a stacked ABON sizer system in conjunction with our OK mill technology, and we believe that the energy consumption could be further reduced by adding the ERC crusher to the circuit.”

Generating New Value From Mine Waste
The availability of methods and technologies which offer better recoveries than in the past are also allowing for the recovery of materials and metals that were previously considered waste. Indeed, recovering saleable material from legacy mine dumps is fast becoming an emerging trend across the mining industry.

Weir Minerals recently supplied a bespoke two-stage crushing and screening plant for a stockpile recycling project at an iron-ore mine in South Africa. Gravmax Africa, a specialist in minerals processing and metal recovery plant design, construction and operating services, was subcontracted by steel producer, Phoenix Global, to design, execute and operate the process plant.

This project is primarily focused on the production of fine, saleable iron ore from a banded iron stone formation. The hematite occurs in layers sandwiched with gangue minerals, and the plant supplied by Weir Minerals forms the first step of the beneficiation process, liberating the iron ore from the gangue.

The two cone crushers are coupled with a surge bin tower and a Trio EF pan feeder to guarantee adequate surge capacity to ensure adequate choke feeding conditions. This also protects the crusher from intermittent feeding which reduces equipment reliability. The plant is unique in that it crushes the ore down to a minus 5 mm product size using a dry process.

Phoenix is responsible for all materials handling on the plant. Ore is fed into a 15 m3 live volume capacity feed bin using wheel loaders. The bin was supplied with a static grizzly with a fixed 130 mm aperture. Ore is extracted from the bin at a controlled rate by means of a Trio EF3606 pan feeder. From there, material is fed into an Enduron DHG24/48 double deck horizontal secondary screen. The undersize product is taken directly to the final product radial stockpile.

Oversize material from the screen is redirected to the secondary crushing station, consisting of a Trio TC51 live-shaft cone crusher fed by a 16-m3 surge bin tower coupled with a Trio EF3606 pan feeder. Crusher product recirculates back to the Enduron DHG 24/48 screen to form the first closed loop of the crushing circuit. Mid-size material from the DHG screen is sent to the tertiary screen, an Enduron DHG21/54 double deck horizontal screen, while the oversize and midsize materials are mixed and sent to the tertiary crushing station. The undersize product is again sent to the final product radial stockpile.

Product from the tertiary crusher is recirculated back to the Enduron DHG 21/54 tertiary screen, the second closed loop of the circuit. The final product is loaded to the radial stockpile by means of a 24 m Trio radial stockpile conveyor.

The different components of the two-stage crushing and screening plant are interconnected by means of a modular Trio conveyor system. The ore at the mine is abrasive and difficult to handle due to the high moisture content as a result of the naturally weathered state of the dumps, so Weir Minerals used a combination of material- on-material ledged chutes for the oversize screened material transfers, as well as specialized low-friction liners in chutes and underpans for handling the sticky fines and to prevent any unwanted fines build-up.