Sort It and Save

Mine and project owners are increasingly interested in accurate, rapid sorting of ore from waste rock at the earliest possible flowsheet step

By Russell A. Carter, Contributing Editor

Potential solutions offering better, quicker separation of valuable material from waste have always been high on the mining industry’s ‘want’ list. One particularly tantalizing technology has been ore sorting – either of individual particles or bulk materials – but its degree of success within the industry has wavered over the years. In the nearly century-long history of sensor-based ore sorting, for example, new sensor technologies have emerged, been tried in various applications and rejected due to a variety of factors. Failure modes have included the inability to successfully adapt to more than one type of ore or mineral commodity, or to expand pilot-plant ore-sorting setups to full-scale production-scale systems. Even when testing provided positive results, the sorted material sometimes simply wasn’t compatible with an existing plant’s flowsheet; or adequate performance hinged on separating only the largest chunks of ore-bearing material from waste, leading to unacceptable losses of valuable minerals to the tailings stream. 

Ore sorting is part of a larger assortment of technologies known as preconcentration, which also includes coarse particle recovery, dense media separation and gravity or magnetic separation. As the saying goes, a rising tide floats all boats, and the surging economic waters that are currently pushing the global mining industry to achieve better overall productivity, energy conservation and process automation are also raising its interest in preconcentration, including a range of emerging ore sorting technologies and new applications from both long-established providers and more recent mining tech startups. Also driving heightened interest is the use of mining methods such as block and panel caving, which are attractive to miners faced with developing low-grade, deeply buried deposits, but are generally hampered by reduced grade selectivity and offer a prime opportunity to use ore sorting for achieving higher mill feed quality. Higher prices for reagents, construction materials and increases in general operating expenses also makes the potential cost-saving advantages of ore sorting an appealing option for projects under development as well as mature operations.

However, even the most ardent advocates of ore-sorting technology will agree that it’s not suitable for every site. Structured, extensive testing of increasingly larger ore samples is highly recommended before making a purchase decision, and the fact that ore characteristics, flowsheet design and even financing arrangements often change during the early stages of project planning and development means that an ore-sorting method that initially tests well and seems suitable for purpose might not be the ultimate best choice. Prospective customers often have questions about system throughput capacity, the specific strengths and weaknesses of the various sensing technologies and the actual benefits available given their site requirements.  

To get a better understanding of the market for ore-sorting solutions, we asked Lutke von Ketelhod, business development manager-mining, at sorting-system specialist Steinert to comment on some of the broader issues and trends accompanying the rise of interest in ore-sorting tech.

E&MJ: Should new mine projects be designed from the start to consider or implement ore-sorting technology when appropriate to site geology and mineralogy? What benefits can be gained by early inclusion of ore sorting systems? In general, what practical aspects need to be considered before a mature operation can efficiently adopt ore-sorting in the process stream?

von Ketelhod: The industry is showing great interest in testing the sortability of their ore at a very early stage when developing a mine. Steinert provides amenability test work services for clients who only have limited drill-core material available to evaluate the processing flow sheet for their ore deposit. Some engineering and consulting houses are striving to have ore sorting evaluation as a standard for new projects. 

Ore sorting is the link between the mine and the processing plant. If ore sorting can prove to be an option early in the project, it can also open opportunities to evaluate ore zones which may be below cut-off grade, but due to beneficiation by ore sorting can now be included in the ore reserve. This can have important implication in extending the life of mine calculation, mining methods, down-stream milling capacities, and wet processing, etc. 

Implementing ore sorting in mature or existing operations can also have a significant impact in improving their operation. Below cut-off grade ore zones could now become part of the ROM mix, extending the LOM. Apart from the economic advantages, beneficiation of coarser size fractions provides several factors enhancing a mine’s ESG portfolio. The more waste rock that is removed before the mill, the more energy is saved and with feed-grade improved and controlled, vastly improving downstream wet processing.

E&MJ: Traditional ore-sorting technologies have typically been used in mostly high-value, low-volume applications in the past, but as an expanding number of high-tonnage mineral producers strive to reduce processing costs while raising throughput, they are showing greater interest in ore-sorting tech that works at higher process stream speeds and volumes. What benefits can Steinert’s products offer users with high-throughput requirements right now, and what remains to be done to make ore-sorting even more adaptable to high-volume process streams?

von Ketelhod: Steinert is continuously developing techniques to achieve higher throughput rates for our ore sorting equipment. For large particles, for instance, a combination of sensors (XRT and laser) has been applied to provide accurate detection data to distinguish between coarse chromite ore particles and waste. This was not possible with a single sensor. 

High capacities are very important in the finer size ranges of -50 mm – +10 mm when the sorting efficiencies on liberated particles are better than large particles containing lock-up mineralization within the particles. Steinert has made significant progress in increasing throughput rates, which are mainly dependent on belt speed, belt coverage, sensor data processing/sorting software and valve response time. 

Other factors, such as material characteristics, operational conditions, feed preparation, and plant design will also influence the capacities of ore sorting. Test work is essential in determining to what extent the throughput rates can be pushed. Applications with clear-cut heterogeneous ores are usually easier to run at high capacities.

E&MJ: Sensor fusion – involving an array of sensors offering different methods or levels of particle analysis – seems to be of interest as a way of improving run-of-mine ore input data to make that information more timely, accurate and useful for plant operators and process-parameter refinement. What is the level of industry interest in the concept, and how far along the path towards full commercialization is the industry right now?

von Ketelhod: Steinert launched its Kombination Sensor Sorting (KSS) concept in 2017. Since then, significant advances have been made in finding solutions for complex ore sorting applications. For example, in a quartzite/sulphide vein-type gold deposit, gold is found in dense sulphides as well as in less-dense quartzite. XRT is utilized to detect dense gold-bearing sulphides and a laser to detect brightly reflecting gold-bearing quartzite. The sorter is thus able to produce a product of dense sulphides and less-dense bright quartzite, and a waste stream of less-dense waste rock. 

At Steinert, sensor fusion is referred to as multi-sensor sorting. Up to four sensors can be incorporated into one sorter machine. For example, the KSS CLI XT incorporates XRT, induction, color and laser sensors in one sorter. Steinert is experiencing a high level of interest for the industry for multi-sensor applications. Numerous Steinert sorters are operational in various ore sorting plants around the world, providing excellent results on complex applications. A multi-sensor sorter also provides the mine flexibility for further opportunities to adjust the sorting program to adapt to changing conditions.

Sorting It Out

Mine project owners are finding that as the availability of different sorting technologies increases, they have more latitude to test and adopt the most appropriate technology for their project requirements.

For example, in May, Canadian Critical Minerals announced that it had secured a Steinert KSS 100 X-Ray Transmissive ore sorter for upgrading of mineralized copper-bearing material currently stockpiled on surface at its Bull River mine (BRM) project near Cranbrook, British Columbia. The sorter will be leased for a period of 12 months during which time the company plans to screen, crush and sort the entire stockpile of approximately 180,000 metric tons (mt) of mineralized material. CCM said it intends to pre-screen the entire stockpile, thereby removing approximately 25% of the mineralized material as fines. The remaining oversize material will be crushed to minus 3 in. and this material will report to the sorter.

After investigating sorting systems based on XRT and XRF technologies provided by other suppliers – and finding that OEM lead times for delivering new  sorting systems could be as long as 46 to 50 weeks – CCM concluded that leasing an available Steiner XRT ore sorting system could provide certain benefits, including a lowering of operating costs on a unit basis, a reduction in the volume of fine tailings created through the milling process and the overall volume of material transported to the tailings storage facility, a reduction in power consumption particularly in the grinding circuit, and a lower overall environmental impact. By pre-concentrating higher-grade material, the company said it also will have flexibility to ship that material to another permitted milling facility, thereby generating early revenues.

Norway-based sorting systems supplier TOMRA recently highlighted its progress on design and implementation of what it describes as the industry’s largest lithium sorting plant, at a mine operated by Pilbara Minerals in Western Australia. 

The Pilgangoora hardrock mine produces a spodumene and tantalite concentrate. With 50 years’ experience in sensor-based sorting technologies and having designed and having built some 90% of the world’s large-scale mining sorting plants with a capacity above 300t/h, TOMRA told the client it could offer effective ore-sorting solutions with high sensor resolution and ejection accuracy that ensure high lithium recovery and waste removal with a stable and consistent performance at high capacity.

The TOMRA team conducted a geological assessment of sample ores supplied by Pilbara and found that the pegmatite deposit did have non-lithium bearing host rock intrusions with a high density like that of spodumene, which meant that it would also be concentrated when using heavy media separation (HMS) which, in turn, would reduce flotation efficiency and contaminate the final product. Sensor-based sorting technologies, however, could measure the color, density, and mineralogical variations in individual particles, enabling accurate detection and removal of the barren material.

TOMRA conducted extensive testwork at its testing center in Sydney. The samples were run at capacity on production sorters and included repeatability and variation testing. The test work benchmarked the expected performance of the sorters and was used to establish the sort quality on each of the ore types that will be fed through the plant. TOMRA reported that the sorting plant’s installation was underway and is expected to be completed later this year.

In February, the Australian company NextOre announced that it had completed assembly and factory testing of a magnetic-resonance truck load analyzer. The unit, measuring 7 m in diameter and designed to be suspended 10 m over 180-mt trucks, was put into service at a large copper mine in March. The analyzer will be used to detect copper as chalcopyrite. 

The company said the truck analyzer will be used to enable real-time, quantitative mine control, detecting the quality of ore carried in trucks as it is mined, eliminating both accidental losses of valuable minerals to waste and the processing of barren material. In addition to improving the efficiency of metal production from copper mines, NextOre said it also enables significant reductions in fuel, water, electricity and reagent consumption while also reducing the quantity of wet tailings produced for each ton of copper.

Products based on an open geometry magnetic resonance sensor make up a second core product line offered by NextOre – an on-conveyor version of the magnetic resonance analyzer. On-conveyor units have been deployed to mines in Australia, Africa, Philippines, Chile and Mexico. 

Around the Industry

If industry news announcements are any indication of an emerging technological trend, the outlook seems promising for integration of various types of ore-sorting systems into current and future mining projects. Here’s a sample of developments reported during just the past few months:

Osisko Development, a Montreal-based gold mining company, recently reported that it intends to employ ore sorting during phased development of its Cariboo underground mine project, targeted to produce approximately 1.87 million oz of gold over a 12-year mine life. In the first phase, ore will be initially pre-concentrated using mobile crushing and ore sorting, after which the ore will be trucked to the company’s Quesnel River mill for further comminution, leaching, and refining. 

In the second phase, a crushing facility will be constructed underground with ore subsequently brought to surface using a conveyor system. Crushed material will be screened to separate fine material, below 10 mm, and coarse material 10 to 25 mm. The coarse material will go to ore sorting, where gold-bearing material will be separated from waste. Fines and coarse particles will then go through a grinding circuit. Ground material will be sent to flotation for the last stage of pre-concentration. Ore sorting, grinding and flotation processing activities will be conducted in a service building at the mine site complex. The facility will serve as a pre-concentration step to reduce the overall operation and transportation costs producing a concentrate of approximately to 25 to 33 g/mt gold.

Toronto, Ontario-based Doré Copper also announced positive results from ore sorting test work in April for its flagship Corner Bay high-grade copper-gold project located approximately 55 km by road from the corporation’s Copper Rand mill, near Chibougamau, Québec. Steinert was commissioned to complete ore sorting tests at their facility in Kentucky, using a XRT sensor (X-ray transmission) and a laser sensor on a spatially diverse sample from the Corner Bay deposit. 

The company explained that sorting, in addition to reducing operating costs for milling, flotation and tailings management due to a significant rejection of low-grade material, is expected to decrease the hardness of the ore sent to the mill (lower Bond Work Index of the sorter pre-concentrate product compared to the feed), resulting in potential energy savings. The commensurate increase in the head grade of the ore that will report to the flotation circuit has the potential to result in improved metallurgical recoveries in the flotation circuit and higher concentrate grades.

Another Canadian company, Laurion Exploration, reported that the Saskatchewan Research Council completed test work earlier this year using a 2-mt sample of 20- to 60-mm sized material sourced from the stockpile at its Ishkoday project in northwestern Ontario, to simulate a sensor-based sorting (SBS) operation and develop a sorting algorithm for future pilot plant work. 

The results of the test work, said the company, demonstrated that SBS laser and color sorting methods were successful in removing a significant proportion of vein host rock while still efficiently recovering small, fragmented quartz particles that are often associated with gold. Specifically, the SBS laser threshold setting could remove an estimated 92.6% of host rock (compared to vein material), while the SBS color and optical tests removed an estimated 89.6% of host rock, with efficient recovery of the quartz fragments often associated with gold.