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Pilot Crushtec Iron Ore Case Study

Companies who thrive in the African Mining Industry are the ones that learn how to turn extremely difficult conditions into lucrative opportunities. This takes levels of insight, vast amounts of practical experience and perseverance that are not easy to achieve. We spoke to Franco Le Roux Mining (FLRM) who have managed to find success in an application which would intimidate most mining contractors to see what separates them from the rest.

The opportunity was a contract for remining of an old, untouched ROM stockpiles at a large Iron Ore Mine. The contract was initially drawn up based on a few assumptions regarding the material properties, which were later proven to be quite far from reality. This could easily have spelled disaster for the project as it so often does, but some inspired thinking, along with the adaptability of Metso Lokotracks, helped FLRM navigate these obstacles seamlessly.

The assumption made regarding the material properties were that amongst the ROM stockpiles meant for remining, there would be an average of 37% natural fines (below -8mm) that could be recovered and sent directly to the smelter. With this initial material description, the client specified a 3-Tier approach to the project; phase 1 would involve recovery of just the natural fines through the use of a mobile scalper, phase 2 would incorporate a mobile jaw crusher to increase the fines generated for recovery by the mobile scalper and phase 3 would add two mobile cone crushers as well as a mobile sizing screen to ensure all material would pass -8mm.

Shortly after implementation of phase one, it became clear that the working assumptions from which the job was specified were just not the facts of the material properties. Instead of 37% natural fines on the product, the stockpiles were proving to contain between 17-22% of fines, about half of what was expected. Such a massive difference between the initial specification and reality would most often spell disaster for the viability of the contract due to the large tonnages which required crushing, but thanks to some foresight by the engineers who had already specified the process capabilities, a solution was already in the works, which meant that they would have to immediately
skip to phase 3, a fully mobile 3-Stage crushing and screening plant to achieve the required tonnages of end-product.

Fortunately, due to Pilot Crushtec’s high level of experience, planning and equipment stock holding, the full complement of machinery required; one mobile jaw crusher (Metso Lokotrack LT106), two mobile cones crushers (Metso Lokotrack LT200HP and LT200HP Short Head), and a triple deck mobile screen (Metso Lokotrack ST4.8) were deployed to site within a few weeks of the problem being identified on-site. A crisis was swiftly averted, and Franco Le Roux Mining got back to doing what they had to do, putting -8mm crushed iron ore on the ground.

However, mining in Africa is never predictable nor simple and it did not take long for the ghost of the initial assumptions to come back and challenge FLRM Mining once again. Not only were there fewer natural fines in the ROM stockpiles than expected, but the concentration of iron within the ore was also proving lower than expected. This meant that many of the 170ton stockpiles produced would not be accepted by the smelter, making all the crushing and screening being done on-site was not producing sellable product. The solution this time would be even harder to find; no amount of further crushing could make up for a lack of richness in the ore. Some other, more creative solutions would have to find their way to the mind of both Pilot Crushtec and the client FLRM.

After a few days of consultation, proposals, internal meetings and site visits, a unique idea was exposed by one of the site operators. They noticed that the natural fines being scalped out from the rest of the material looked to have a slightly more ‘reddish’ tint. This pointed to the possibility that the natural fines in the ROM were richer in Iron than the rest of the ROM stockpiles. If there was some way to blend the richer material with the less rich, crushed ore, each 170ton stockpile could be brought to a level of concentration that would be accepted by the client.

With its industry-unique two-way split, it could be used to provide a consistent supply of Iron-rich natural fines which could be blended into stockpiles wherever needed. Suddenly a few thousand tons of useless material was available for sale at full contract price once again.

Averting two disasters may have been enough for some, but the determined people at FLRM felt there was more progress to be made. Production figures were good, an average total of 150 tonnes per hour of -8mm product meant that only the most advanced fine-tuning would yield improvements. They turned to the experts yet again for some assistance and ideas. Pilot Crushtec International’s 30 years of experience, with the help of Metso’s well trusted process simulation software, Bruno, led FLRM towards further 10-15% gains in production. Average hourly production increased up to 205 tonnes per hour at peak with the plant averaging about 175tph throughout the day.

How did they do it? The following tweaks were made to the process.
The standard course liner in the secondary cone crusher, the Metso LT200HP, was changed out for a standard medium liner. The optimized liner profile helped to increase the reduction ratio in the second stage of crushing, ensuring a better distribution of reduction across all three crushing stages.

The 28mm diamond mesh on the top deck of the ST4.8 was replaced with a 30mm square mesh which marginally improved throughput on this deck. The bottom deck also had a 5mm piano wire replaced with a more conventional 10mm square mesh which helped to control the final product and made sure there were no large pieces of flaky material finding its way into the product stockpiles. And finally, a controversial decision was made. They would “split the train”. This essentially meant that most of the material would be subject to double handling, an issue not taken lightly by anyone involved in crushing and screening due to the high costs involved. A safety stockpile was created by the first half of the train which consisted of the mobile jaw, scalper and cone crusher (LT106, ST2.8, and LT200HP), which meant that the second train of an additional cone crusher and triple deck sizing screen (LT200HP Short Head and ST4.8) always had material to crush, even when the first mobile train was not available. When the second section of the mobile train would have to be stopped, the first section could carry on crushing material to be stockpiled and then fed into the second section of the train.

Many operators want to link as many mobile units as possible to try to optimize production but often, by separating the crushing stages, there are many operational benefits in terms of maintenance time and continuing crushing when unplanned downtime occurs. Separating the process also meant that the first two stages of crushing, which are able to run at an average of 220tph, while the tertiary stage was capable of up to 200tph at most, were able to crush at full capacity. This made quicker work of the material processing and in doing so, decreased the cost of production. The first two stages of crushing could finish daily production targets in a shorter time instead of being bottlenecked by the tertiary crushing and screening stage. This translated into less fuel and wear costs, while also increasing the residual value in the equipment in the first half of the train by ensuring the units run less hours to process the same amount of material. This is often never considered by site operators but can be a smart strategy which in many situations, can benefit breaking the process into two sections, which ultimately, easily outweighs the costs of double handling.

What FLRM Mining has experienced is that a world of increasing uncertainty, the plans that we put so much effort and research into, can be turned on their heads at a moments’ notice when working with raw materials. If we want to remain efficient and profitable, we need to adapt at quick notice and be willing to innovate, even the tiniest details, which make the difference between success and failure.