Tag Archives: density separation

Lost Dutchman Mine ready to tell its metal separation tale

A company out of Arizona, USA, believes it has come up with a density separation technology that could upgrade heavy metal concentrates without the need for water or chemicals.

Lost Dutchman Mine (LDM), named after the legend of a rich Arizona gold deposit discovered by an elusive Dutch prospector, never since located, is the company in question. Being supported along the way by the Centre for Excellence in Mining Innovation (CEMI) out of Sudbury, Ontario, the firm is looking to find a way into the mining sector at a time when environmental, social and governance (ESG) concerns have reached a new high.

Mark Ogram, one of three Co-founders of LDM, explained the company’s aim and name, saying: “We’ve been able to find gold where people could not find it.

“We have now come up with a solution that requires no chemicals or water to purify a gold ore.”

While gold is the company’s initial focus, the process can be applied to most heavy metals including silver, copper and tungsten, according to Ogram. Some encouraging results have also been seen removing sulphides from gold ore ahead of further processing, in addition to ‘cleaning’ coal, he added.

A gravity separation process that uses air flow rather than water to separate these materials by density, the obvious comparisons are with Knelson concentrators or other separation technologies – all of which tend to use water or another medium for their processes. Ogram says Knelson concentrators are also for free gold, not refractory gold, the latter of which the LDM technology can cope with.

allmineral’s allair® technology also comes to mind as a comparison. This is a process that leverages many of the functions of the water-operated alljig® technology but, instead, uses air as the pulsating medium. So far, allair’s applications have been confined to mostly coal and other minerals.

Like many of these technologies, it is feed preparation that will prove decisive for the application of LDM technology, with ore crush size and moisture content the two key factors.

“We don’t think we would need ball mills to get the feed down to the right size,” LDM Co-founder Ken Abbott said. “A standard crushing and screening setup should be suitable.”

While test work to date has been with material in the 30-60 mesh range, Abbott is confident the technology will work with material from 100-200 mesh.

“It will be a little more of a sensitive process, but it does work should people require it,” he said.

When it comes to moisture content, a drying process will most likely be needed ahead of feeding to the LDM unit.

“The material needs to flow freely to work well,” Abbott said.

In-field test work involved the company using a tumble-type continuous screener/dryer to reach the appropriate moisture content, but a more ‘industrial’ process will be required in commercial applications.

The best results are likely to be achieved when both factors are consistent, according to LDM.

“The system requires a steady and uniform distribution in the feed cycle that includes surge capacity and automated material flow to ensure a steady feed rate,” the company says.

Dale A Shay, a consultant with RIMCON advising LDM, said vat leaching operations were already producing material at the appropriate size for the LDM technology to be tested. “They are also reducing the moisture content to an appropriate level,” he said.

Despite this, the company feels tailings applications may be the most suitable place to start with. This harks back to the ESG concerns miners are feeling – some of which revolves around tailings impoundment areas – as well as the fact the ‘conservative’ mining industry is generally more comfortable testing new technologies on material they already consider to be ‘waste’.

For the technology to prove out, the company will have to scale up its testing.

LDM has, to date, carried out benchtop, laboratory scale and in-field tests on low-grade material, but it has only reached a 1 ton (0.9 t) per hour rate.

“We would put in a tonne and get a few grams out,” Ogram said. “That is how we developed the technology.”

Despite there being a linear progression of recoveries from benchtop to lab to the field, LDM will need to go bigger to find the widescale applications it is after.

Yet, its potential entry into the market is well timed.

Removing the use of chemicals and water in a process that will most likely come after initial crushing could prove cost-effective, as well as environmentally sound.

Yes, the air flow component and feed drying will consume power on mine sites, but this ‘upfront’ operating cost will pay off further downstream as not as much material will be transported to make its way down the process flowsheet. It is more likely to go straight to tailings or backfill material feed.

Abbott explains: “The technology drastically reduces the material that will move onto final concentration, which substantially reduces material movement on site.”

For new developments, there is a knock-on benefit for permitting; the regulatory boxes are much more likely to be ticked when the words ‘water’ and ‘cyanide’ are absent from applications.

LDM Co-founder, Wayne Rod, sums this up: “Although from a cost perspective, it is expected to be competitive with other concentration technologies, the real savings will come on the ESG front and being able to reduce any environmental issues you may have.”

This is a message Rod and the rest of the LDM team are taking to the headquarters of major mining companies, where executives and board members are treating ESG challenges like a ‘cost’ they need to reduce to stay viable.

“As that ESG issue becomes even more prevalent, I see technology becoming a much bigger focus area,” Rod says. “Taking water and chemicals out of the concentration process will help alleviate some of that pressure.”

Multotec keeps the ferrochrome flow going with new innovate spiral

Following years of detailed test work in the South Africa ferrochrome sector, Multotec says it has successfully developed and proven a spiral concentrator that eliminates beaching and enhances recoveries in the 1-3 mm fractions of high-density material.

Significantly, when compared with traditional spirals, the new spiral has shown extraordinarily higher metal recoveries, even for minus 1 mm fractions in ferrochrome slag, according to the company.

“Our SC25 spiral concentrator features steeper angles which facilitate the flow of material and increase separation efficiency,” Hlayisi Baloyi, Applications Engineer at Multotec, says.

“It also widens the particle size range that can be treated by the spiral. Traditionally, spirals would struggle to efficiently treat material above 1 mm in heavy mineral applications, but this spiral can go well beyond that. The spiral has been a game changer even for the minus 1 mm size range where higher separation efficiencies have been achieved on chromite ore.”

Baloyi says this innovation has provided the minerals processing sector with an exciting alternative to jigs in the “minus 3 to plus 1 size range”, which have been one of the conventional methods of separating larger particles. The solution is cost effective as spirals use no electricity and are also easy to maintain, Multotec says. “So attractive is the new model that the first order for the commercialised version has already been placed,” the company said.

Baloyi explained: “Taking ferrochrome samples from a number of mines over a period of two to three years, we conducted extensive test work on these at our well-equipped testing facility in Spartan, near Johannesburg,” he says. “Leveraging this data with our in-house engineering design capacity, we were able to develop the optimal solution and locally manufacture the new spiral concentrator.”

Multotec said: “The institutional knowledge within Multotec has been developed over more than four decades, including valuable expertise in fluid dynamics. Hands-on experience in test work and design allows the development of prototypes that solve customers’ specific challenges – followed by scaled-up local production of equipment to match market demand.”

The economic benefits of the Multotec SC25 spiral for ferrochrome producers are substantial, as some plants were losing the value of their 1 to 3 mm material to the tailings storage facility, according to the company. Many of those who used jigs to treat this fraction were also finding that efficiencies were low.

Refentse Molehe, Process Engineer at Multotec, said ferrochrome is not the only commodity the company has successfully tested.

“We have even seen improved recovery in heavy minerals below 1 mm size, alluvial chrome, manganese slag, and there is potential in industrial recycling,” Molehe said.