Maximising diamond recovery while optimising costs: this is the priority at the top of the list of every diamond producer. With TOMRA’s holistic approach and cutting-edge technologies, both can be achieved to deliver outstanding results.

The company is a leading supplier of X-Ray Transmission (XRT) diamond recovery technology, having recovered some of the largest and rarest gemstones in history.

This article first appeared in Mining Review Africa Issue 10, 2020
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TOMRA’s promise to customers is simple – 100% detection in the specified range, irrespective of luminescence profile or coating, and a guaranteed diamond recovery greater than 98%.

Advanced technologies add value at various stages of the process

TOMRA’s XRT technology recognises and separates materials based on its specific atomic density. It uses a cutting-edge X-Ray camera with DUOLINE sensor technology to measure spectral absorption information. TOMRA’s proprietary high-speed X-Ray processing unit uses the data to produce a detailed ‘density image’ of the material.

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The result is a high level of purity in sorting materials, irrespective of size, the degree of moisture or surface pollution present. TOMRA’s XRT high-capacity sorters are incredibly effective in the recovery of free, liberated diamonds at high feed rates up to 300 tph.

TOMRA’s NIR sorters recognise and separate kimberlite and waste rock based on their chemical composition. This technology is useful in upgrading lower grade ROM and stockpiles, producing a Kimberlite concentrate for further processing.

Marie-Claude Hallé had first-hand experience of how TOMRA’s solutions can add value to diamond mining operations when she held the role as marketing operations manager for leading Canadian diamond exploration and producing company Stornoway Diamonds:

“You have to really envision that TOMRA has actually changed the game in terms rough diamond recovered around the world and allowed producers to access large exceptional quality goods that perhaps in the past would be crushed to pieces.”

Customised solutions for Kimberlite, Lamproite and Alluvial applications

With its customised approach, TOMRA can deliver on its promise of guaranteed results both in hard rock kimberlite/lamproite, and alluvial deposits – each of which presents their specific challenges.

In Kimberlite, the challenge is to recover ‘needle in a haystack’ diamonds, which requires controlled crushing of kimberlite ore to avoid damaging or breaking the diamonds. High waste dilution impacts the crushing energy needed and further increases diamond breakage risk.

Utilising TOMRA NIR technologies the company is able to remove non-diamond bearing material, not only improving the crushing profile of the ore, but also increasing the value of each ton of ore processed. TOMRA NIR waste sorting technology can make diluted marginal kimberlite deposits economic.

Additionally, complex, energy and water intensive kimberlite liberation processes, and the cost of transportation for crushing and processing are challenges facing modern diamond miners today.

TOMRA’s XRT and NIR technologies, which offer extremely high concentration factors, allow the production of hand sortable, ultra-high grade concentrates in as little as two stages compared to up to seven in traditional methods.

The challenge of economically mining low-grade alluvial deposits is due to their typically lower grade and the sporadic nature of the deposits. The high recovery performance of TOMRA’s XRT technology enables single-stage or double-stage diamond recovery, offering a drastically lower operating cost and capital investment so that mining marginal deposits becomes economically viable.

Another advantage of TOMRA’s XRT solution is that it can operate as a dry process, which dramatically reduces its environmental impact and operational complexity.

Besides, it opens the door to new opportunities, making it possible to mine deposits in arid areas where water access is minimal.

TOMRA XRT machines have proved effective in alluvial operations. One such case is that of the Lulo mine in Angola operated by Lucapa Diamond Corporation, where TOMRA XRT technology is used to process material between 18 and 55 mm in size and allows the recovery of diamonds up to 1 100 carats – and where it has recovered Angola’s second-biggest diamond on record in 2017, a 227-carat stone.

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“The recovery of the 227-carat diamond using the new XRT circuit justifies our investment in TOMRA’s large diamond recovery technology, which has more than paid for itself with the recovery of this one stone alone,” comments Stephen Wetherall, Lucapa Diamonds MD at the time of the recovery.

Optimised flow sheet redefined

TOMRA is in the unique position of being able to offer diamond operations a full XRT recovery flow sheet to 2 mm that delivers concentration factors up to 1 million with a much-reduced number of concentration stages.

“TOMRA XRT technology replaces multiple stages of diamond concentration by virtue of its ability to concentrate diamonds to a hand sortable product after only a single step,” explains Geoffrey Madderson, diamond segment manager for TOMRA Sorting Mining.

“This concentration factor allows for the removal of multiple recovery steps, drastically reducing both the capital investment and operational costs to recover diamonds.”

TOMRA’s XRT technology can replace traditional methods such as Dense Media Separation (DMS), wet magnetic separation and XRL final recovery with single-stage solutions for +8 mm and double-pass for -8mm +4mm particles.

This solution eliminates up to seven concentration stages, dramatically reducing the complexity of the supporting plant and infrastructure. This results in significantly lower power and water consumption, which not only reduces costs, but also the environmental impact of the recovery process.

An additional benefit of TOMRA’s solution is that it is a fully automated process, so that there is no manual handling during pre-concentration and recovery, which has positive implications on security and eliminates human error resulting in greater accuracy.

High recovery rate

TOMRA’s sorters not only stand out for their high capacity, they process these large volumes with great efficiency, finding more diamonds than other, traditional separation methods – including coated and low- or non-luminescent diamonds.

The performance of its XRT sorters is independent of the heavies content in the feed, and is ideal for processing high-yielding ores unsuitable for DMS.

The result is an exceptionally high recovery rate: “TOMRA guarantees >98% recovery: that is how confident we are in our technology,” states Madderson.

Large diamond recovery

With TOMRA’s sorting solutions, diamond producers can install large diamond recovery systems with a small capital investment and operate with a fraction of operating expenditures per tonne compared to traditional recovery methods such as DMS and XRL.

In addition, the economic recovery of ultra-low-frequency exceptional diamonds of +32 mm is now possible.

TOMRA’s XRT technology has exceeded all expectations at Lucara Diamond Corporation’s Karowe mine in Botswana with a string of record-breaking diamond recoveries.

TOMRA’s large diamond recovery circuit was installed in 2015 and Eira Thomas, Lucara Diamond CEO is fully satisfied:

“We felt, certainly, that the technology that TOMRA offered was the best. But, more importantly, I think it was really around the approach, the attitude of collaboration and willingness to actually work with Lucara as we undertook to solve this problem.”

 “TOMRA’s ability to deliver not only a technology that can detect such large diamonds but also an economical process solution for the recovery of ultra-rare, exceptional diamonds, is what sets us apart from its competitors. 

“This is the reason that to date, TOMRA XRT has become synonymous with the recovery of extraordinary diamonds from all around the world,” concludes Madderson.