Tag Archives: sensor-based sorting

TOMRA’s XRT solution creates value from waste at Mina Esperanza de Caravelí in Peru

The integration of TOMRA’s ore sorting technology at the Mina Esperanza de Caravelí mine in Peru has helped the polymetallic miner produce more metal as well as clean up its legacy tailing operations.

The close collaboration between two companies emphasises a shared philosophy, that of making the most of natural resources and embracing a circular economy.

Mina Esperanza de Caravelí, owned by MTP and operated by Minera Croacia, is a polymetallic vein deposit with a mining rate of 150 t/d. It is located in the district of Atico, in the Nazca-Ocoña geological gold belt in the southern part of Peru, and contains narrow veins with a rosary formation, of which over 30 have been discovered so far. The mineralisation is located in vein fill fractures of hydrothermal origin and are mesothermal in appearance.

In 2019, Minera Croacia contacted TOMRA to explore a solution to extract value from low-grade material previously deemed uneconomical, and to address the environmental issue of metals left in the dumps.

Marco Fernandez Concha, Senior Geologist to Minera Croacia, said: “Mining operations need to find ways to optimise the use of natural resources while reducing waste and their impact on the environment as much as possible. With TOMRA’s ore sorting technologies, this is possible.”

A sensor-based ore sorter represents a significant investment for a mine the size of Minera Croacia, according to Emilio Uribe, Senior Metallurgical Advisor at Minera Croacia.

“When we purchase important equipment, we need to analyse the solution in great detail because we can’t afford to make mistakes,” he said. “We need it to work and deliver the results we want from the start. TOMRA has adapted to our needs as a small business with limited resources. They have been an important advisor, giving us all the support we needed with highly qualified and knowledgeable staff. They have really committed to the project and found the solution that meets our operational needs and is financially viable for us.”

The teams from TOMRA and Minera Croacia worked closely to precisely analyse the requirements and identify the best solution. TOMRA’s Test Center in Wedel, Germany, conducted three series of tests on samples from the mine to narrow down the requirements. A technical team from Minera Croacia attended the final session, which gave them a better understanding of what TOMRA’s XRT technology could do for their operation.

Christian Korsten, who at the time was the Test Center’s Manager, said: “This project stands out for presenting different types of ores from different locations. Usually we test one or two different ores for a customer, but, with Minera Croacia, we had different metallogenic veins. They were all a little bit different in mineralogy, sensor response and in the customer’s objectives for each.”

Strong communication between the two companies’ teams was crucial to the successful outcome – especially since COVID-19 travel restrictions limited the opportunities for face-to-face meetings.

Mathilde Robben, TOMRA Key Account Manager, said the company ensured Minera Croacia received the support and advice they needed throughout the process.

“We did it all through online meetings,” she said. “The management team and staff at Minera Croacia were always to the point and friendly, and together we completed this fast-track project.”

Korsten agreed: “Minera Croacia had very clear objectives. All our questions were answered in a perfect, fast and professional manner, and the same applies to the discussion of the test results. This project was one of my favourites in almost 10 years in the Test Center.”

Following the detailed analysis of the test results and Minera Croacia’s requirements, Robben proposed the use of a TOMRA COM Tertiary XRT sorter as the solution: a machine suited to the particle size range of the dump material (-25 mm/+ 10 mm and -40 mm/+ 25 mm) and an investment that fitted Minera Croacia’s budget.

The test results made a clear business case for the sorter, showing that out of 1,300 t of run of mine material containing gold and copper, 21% are fines (-10 mm) and screened out. This results into a concentration of gold and copper in the fines and, therefore, this material does not need to be sorted. Of the rest of the material, 34% is enriched, going from a grade of 2.7 g/t gold-equivalent to 5.12 g/t gold-equivalent – almost double.

This leaves 45% of the material discarded as waste with very low metal content, 0.41 g/t gold-equivalent, which addresses the environmental issue, as it contains virtually no contaminants. This also shows that maximum value has been extracted from the material, as there is virtually no gold left, TOMRA said.

Uribe said: “The test has shown that TOMRA’s sorter can create value from material that would have gone to the waste dump, from 33% of the run of mine that is too low-grade for processing to be financially viable.”

The TOMRA COM Tertiary XRT sorter is now installed and has been operating since December 2021 re-processing the mine’s 800,000 t of historic dumps. It is delivering on all counts for Minera Croacia: now able to increase the grade of the dump material that was not considered economic, it has reduced freight costs of the operation as it is now transporting less low-grade material to its processing plant, and it has successfully addressed the environmental impact of its waste materials.

Uribe concluded: “All the calculations we made when we evaluated this investment are being fulfilled. The sorter’s performance is perfectly consistent with the test results, and we expect it to pay for itself as planned within two years – including the other components and infrastructure of the circuit.”

The company’s management is so impressed with the results achieved that it is considering investing in further sorters for low grade run of mine ore with the aim of extracting value from mineral that is currently considered marginal, according to TOMRA.

TOMRA Mining’s ore sorting solution helps Renison tin mine do ‘more with less’

TOMRA Mining and its X-ray Transmission (XRT) technology has, the company says, provided an effective solution for the extreme conditions at the Bluestone Mines Tasmania JV (BMTJV) Renison tin mine in Tasmania, Australia, with sensor-based ore sorting solution unlocking significant value and delivering environmental benefits.

The Renison mine is 50% owned by Metals X through the BMTJV, and is the only major tin mine in production in Australia with a mining rate of close to 1 Mt/y, according to TOMRA. While slated capacity is 1 Mt/y, the concentrator is restricted to 750,000 t/y.

The mine’s extreme humidity and highly acidic processing water (pH around 4.5) create unique challenges for the sorting process, the equipment and waste management, according to TOMRA.

A complex flowsheet

The underground mine operates a primary crushing system before the material is transported to the surface through a shaft. Once there, it enters the pre-concentration plant, where it undergoes a three-stage crushing, screening and cleaning process. The particles are split into two fractions – 10-25 mm and 25-60 mm – which are fed into two TOMRA XRT sorters. The output consists of two streams: the product, which is transferred to the wet plant, and the waste, which is fed into a TOMRA EM sorter to separate acid-forming sulphides from this waste stream.

In the wet plant, the product goes through primary grinding followed by bulk sulphide flotation. The tailings are processed downstream to concentrate the cassiterite tin mineral through gravity concentration; gravity tails are further treated via desliming and tin flotation. The combined concentrates are fed to a leaching circuit to remove carbonate minerals. After a final wash stage, the concentrate is de-watered and dispatched.

BMTJV approached TOMRA to address two key requirements at the plant. The first was the need to upgrade the tin feed to the plant, as Ben Wraith, Principal Project Metallurgist at BMTJV (pictured below), explained: “The Renison tin operation wanted to achieve economies of scale, putting more tonnes through the front end of the plant without upgrading the back end downstream – we wanted to do more with less.”

The second requirement was to address the environmental issue of removing acid-forming sulphides from the waste.

Following site visits and extensive discussions with BMTJV’s teams, TOMRA proposed a solution that addressed the tin feed quality with two COM Tertiary XRT 1200 sorters and the waste issue with a COM Tertiary EM 1200 sorter. A team from BMTJV visited the TOMRA Test Center in Sydney, Australia, where they observed what the XRT sorter operating at capacity is capable of.

Gavin Rech, Technical Manager at TOMRA, said: “Our XRT stands out for the high spatial and density resolution and its ability to do contrast sorting, identifying fine high-density tin inclusions in the ore with an accuracy that has no equal on the market. On top of that, it can separate it from the acid-forming sulphides, so that we have the ability of pulling the tin into the first product and sending the rest to the EM sorter.”

Gavin Rech, Technical Manager at TOMRA

The two COM Tertiary XRT 1200 sorters went into operation in 2018. Initially, BMTJV’s strategy focused on low reject grades, devoting less focus to achieving the mass reject rate and overall process plant throughput. However, the specific conditions at the Renison mine affected the results achieved. The large variance in run of mine (ROM) particle size distribution resulted in insufficient stability in the feed to the circuit. In addition, the extremely wet conditions in west Tasmania and consequent high ambient moisture content, combined with the high moisture of the ore delivered from underground, further affected the sorting process.

In 2019, a new investigation was conducted into the ore sorting performance and led to a change of direction, where the operation shifted away from targeting low reject grades, towards sorting as aggressively as possible, according to Wraith, moving from a “tin recovery-based” operating strategy to a “mass reduction” one.

“We are getting 20-25% mass reduction, so 75-80% of the materials are going into the wet plant, and we are still achieving 97-98% tin recovery overall across the crushing circuit,” he said. “Pre-concentration didn’t materially impact overall recovery because the tin in the material that is rejected as waste is extremely fine grained and a proportion is associated with sulphides, so it wouldn’t have been fully recovered in the downstream wet plant and would have been lost to tailings.”

This approach, he said, is best for Bluestone’s application as it provides the ability to process 15-20% more tin units without having to upgrade the downstream concentrator.

Wraith added: “Operating the sorting circuit has slightly increased our overall processing cost, but this is more than offset by the large increase in ROM throughput by 15-20% and, thus, tin production, so the unit cost per tonne of tin produced is reduced by almost 10%. We’ve broken multiple production records in the last year in tin units, and this gives us confidence in what we can achieve because the machine performs over and over again if you treat it right and if you prepare your feed correctly.”

TOMRA XRT success leads to upgrade decision

In view of the results achieved with the two TOMRA XRT sorters, BMTJV decided to upgrade the ore sorting circuit with two new, recently launched XRT models with stainless steel internal parts and advanced features such as the TOMRA ACT user interface and the TOMRA Insight cloud-based platform, according to TOMRA.

“The decision to buy new machines was easy,” Wraith said. “The stainless steel will assist prolonging the TOMRA sorter’s life by protecting the unit from our high-moisture and corrosive environment. The more ergonomic design will help our maintenance teams, which is particularly important for machinery operating in these harsh conditions.”

Wraith said the use of TOMRA Insight, the ore sorting company’s subscription-based service that relays and analyses machine data, will “enhance everybody’s understanding and experience of the machines”.

He added: “It will be more of an analytical platform for our metallurgy and maintenance staff, providing ample opportunity to gain valuable information that can be analysed and optimised over time. The one feature I am personally interested in is the particle size monitoring through the machines, which will enhance our overall circuit performance because we have an integrated circuit with the crushing and screening plant. Feed preparation is key to maintain a consistent performance – knowing how well you’re preparing your feed in a live fashion can only end up with a better result.”

TOMRA will also be able to log into the machine and check the daily reports generated by TOMRA Insight, so its technical teams will be prepared ahead of site visits for maintenance or optimisation.

Wraith concluded: “TOMRA has been working with the site maintenance team to tailor solutions to our operating environment, which has been invaluable. TOMRA supported me through site visits, which included equipment inspections, site-based training of our personnel, and an openness to continually improving the technology and finetune it to our site-specific requirements. They assisted the site with troubleshooting, optimisation, discussing the nuts and bolts of the issues as they arose, and finding a solution that works.”