The Use of Ore Sorting to Improve Resource Efficiency
What is Ore Sorting?
Against a backdrop of increasing energy prices and ever more stringent environmental regulations, coupled with the rising cost of materials, sensor-based ore sorting has become a significant consideration for projects looking to optimise resource efficiency.
While different types of sensor-based ore sorters exist, they all work on the same basic principle: that different particles trigger different responses in the sensor and can be separated accordingly, often through the use of high-pressure air jets. For a sample to be amenable to ore sorting it needs to exhibit heterogeneity. This could be as simple as optical sorting, where particles are separated based on visible differences, such as colour, to XRT sorting, where particles are separated based on differences in their atomic densities.
Ore sorting allows for a more streamlined operation and, through the accurate rejection of low-grade waste at an early stage in the process, produces higher, more stable feed grades, optimises mill throughput, and reduces the capacity of downstream tailings storage facilities. This has the dual benefit of yielding significant cost savings, while simultaneously reducing the environmental impact of the project.
(Photographs clockwise from top): COM Tertiary XRT Sorter, TOMRA Mining Test Center in Germany; Sorted Product Fraction from a Polymetallic Cu-Pb-Zn-Ag Project; Crushing and Screening Equipment at WAI’s Mineral Processing Laboratory
What does WAI have to offer?
Over recent years, Wardell Armstrong International (WAI) has built a close working relationship with TOMRA Mining, an industry leader in ore sorting. TOMRA offers a wide range of high-capacity sensor-based sorting systems, which can be deployed to meet the requirements of a variety of mining applications including metalliferous ores, industrial minerals, and diamonds. Through this partnership, TOMRA and WAI have helped numerous clients to maximise resource efficiency and reduce their environmental footprint.
WAI’s role in the process can vary from full project management and flowsheet development to simple preparation and analysis of the sorted products, entirely dependent on the needs of the client. Sorter tests themselves can range from analysis of individual particles to processing of multiple tonnes of material, which in turn yields several tons of sorted products.
WAI’s primary role in this process is, in the first instance, the preparation of suitably sized particles for ore sorting to be undertaken on. This is achieved through a combination of crushing and screening; areas that WAI has invested in heavily in recent times. Once the prepared material has been shipped to TOMRA, sorted, and returned to WAI, of utmost importance is the representative and efficient sub-sampling of the bulk ore sorter products, and the subsequent fast and accurate analysis of those samples.
The products of ore sorting tests can weigh several tonnes and crushing these in their entirety can be a laborious and expensive endeavour. By applying the principles of sampling theory, WAI can minimise these crushing requirements, thus providing time and cost savings for the client. Key to this is a combination of the modern crushing equipment employed by WAI and a sound understanding of sampling theory, which dictates the minimum weight sub-sample that can be removed from a bulk sample while still providing a high degree of representativity.
Recent Project Examples
One client with whom WAI has recently worked with is Vedra Metals, a joint venture between Appian Italy B.V and Altamin (formerly Altazinc). Altazinc had previously demonstrated that ore sorting could be used successfully as a preconcentration stage at their Gorno Pb-Zn-Ag project in Italy, achieving a mass rejection of some 50% of the sorter feed with associated metal losses of less than 5%. WAI then assisted in a programme of further confirmatory testing to validate the previous findings and to continue flowsheet development. This involved the preparation and analysis of over 11 tonnes of ore sorter products which will ultimately be subjected to pilot plant testing.
Geraint Harris, Managing Director of Altamin said:
“Our Alta team have worked very successfully with WAI to further develop the Gorno flowsheet, optimise the metallurgy, and understand any variability in our mineralisation. WAI offering the ability to sub-sample and assay our ore-sorted bulk sample was extremely convenient and efficient for us, as it has allowed us to progress immediately to pilot plant work. The WAI metallurgical team have proven themselves as a trusted, efficient and high-quality partner to Altamin, and this is just another example of the comprehensive service they can offer from their UK facility”.
WAI was also able to work closely with TOMRA to deliver PFS-level metallurgical testing services for Europa Metal’s polymetallic Toral deposit in Spain. Following a successful investigation demonstrating that ore sorting could be used to reject almost half of the sample mass while recovering >95% of the contained lead and zinc, a programme of metallurgical testing was undertaken on ore sorter products to confirm the grades and recoveries that could be expected from a flowsheet including ore sorting.
Myles Campion, acting CEO and Executive Chairman of Europa Metals, said:
“We have been busy so far this year on all fronts, including the recent completion of our metallurgical testwork campaign with WAI which achieved excellent results from both the upper siliceous zone and the lower carbonate zone.
“Lead and zinc recoveries to respective concentrates are very good. Ore sorting has played a part in lifting these recoveries (zinc to zinc concentrate by approximately 4 percentage points and lead to lead concentrate by approximately 3 percentage points, versus the previous results on unsorted ore) which is highly encouraging. The grades achieved for both zinc and lead are better than previous results, with the siliceous showing that the upper levels can also produce a high-grade concentrate.”
