Flowsheets attended the 52nd national meeting of the CMP in Ottawa in January 2020. Delegates from most segments of the profession were present – operations, academics, researchers and laboratories. What stood out from the technical sessions was the section on ore sorting. Due to the lower metal grades of the future ores, mines and mills will have to treat more tonnage to produce the same amount of metal, unless a waste portion of the mined ore can be identified in the Run-of-Mine and rejected ahead of the grinding circuit. Our industry has been aware of this problem for a while, but despite pursuing the idea of ore sorting for approximately twenty years, it is only in 2020 that we now see practical proofs of concept at a pilot scale.
The session saw the following papers presented:
McCarthy, R.J. et al., The Bulk Sorting Potential of the Cumo Deposit in Idaho, USA.
Plugatyr, A., et al., Application of Bulk Ore Sensing and Sorting for Optimal Allocation of Mined Material: a Techno-Economic Case Study.
Bobicki, E., et al., Canmicro: Scaling up Microwave Technology for the Mining Industry.
Xu, M., et al., Value Recovery from Waste Ore Stockpiles.
McGrath, T.D.T., et al., Application of the Gangue Rejection Amenability Test (GRAT) for Gold Ores.
Campbell, M., et al., Preliminary Evaluation of Neutron Activation for Gold and Silver Analysis using a Medical Cyclotron.
NRCan is leading a research competition called “Crush It!”, with a $5 million prize for the winning technology. Of course this has spurred much activity and development.
Of great interest was Erin Bobicki’s paper, which showed the practical use of microwaves to heat the ore, causing micro-fracturing along grain boundaries, thus reducing ore hardness. At the same time, a thermal signature is generated that allows the physical sorting of the ore into waste and payable ore grades. The potential energy saving in grinding was estimated at up to two-thirds of present untreated ore hardness. This project is sponsored by the Canada Mining Innovation Council, and enjoys the support of industry professionals.
From an equivalent angle, Tracey Holmes, of Jenike and Johannson, is making progress with her Selective Heat Ore Treatment (SHOT). Together with Richard Wagner of SGS, this project was also updated at the conference. They have set a target of 20% energy savings with this technology. Their application also uses microwave treatment of the broken ore, and have so far demonstrated the development of micro-fractures in the ore that soften the material in excess of the NRCan competition requirement of 0.3 to 3.0 Kwh/t. So far this has only been proven on copper porphyry ore, with project plans to test other ore types in the near future.
Dr. Manqui Xu, of Vale’s Sheridan Park research laboratory, presented some good practical work on the use of differential breakage in the retreatment of a Sudbury waste stockpile, to provide make-up tonnage for the Clarabelle Mill. There are many such stockpiles in the Sudbury area, and apart from the economic benefit of viable reprocessing in the Clarabelle mill, such a solution would also offer an environmentally cleaner outcome. The process involved the bulk sizing and crushing of the waste material, allowing the differential breakage characteristics of the ore to concentrate the higher grades into the smaller size classes.
A pilot trial using 300 tonnes of the waste stockpile was performed, using screens and crushers to produce -0.5”, -3+1.5”, -1.5+0.5” size classes. The -0.5” fines bypassed the XRT sorting unit process. Both the -3+1.5 and -1.5+0.5” size classes were separated into “Accept” and “Reject” Streams. The Rejects graded lower in Ni and Cu (0.06 and 0.09% respectively) than Clarabelle’s flotation tailings. The upgraded “Accept” product carried 86 and 85% of the original Ni and Cu respectively.
Although differential breakage has been known about for a long time, this was a practical demonstration of the principle that has turned out to be sustainable. Clarabelle Mill has been retreating this stockpile as part of its daily duty since early 2019.
On a separate note, two remarkable papers on other topics were presented:
Fleming, C., et al., Development of Process Options to Treat Oxiudised Mineralisation Containing a Very High Concentration of Cyanide-Soluble Copper.
Van Wyk, A., et al., Pilot Testing Pressurised Flotation Systems for Froth-Free Concentrators.
Chris Fleming’s paper discussed the flowsheet development for the Emipa deposit in Bolivia, which contains 6-8 kg/t of cyanide-soluble copper, thwarting conventional cyanidation for the gold present. The conventional process consumes 16-18 kg/t of cyanide, making the treatment cost and associated cyanide destruction uneconomic. This was solved by introducing the SART process that converts the copper cyanide to saleable copper sulphide, releasing free cyanide for the gold leach, mking treatment of this ore viable.
The Woodgrove paper, presented by Gerard Rowe, announced the development of the Direct Flotation Reactor (DFR), to take over from the earlier Staged Flotation Reactor (SFR), so that a froth-free flotation system could operate under pressure to provide higher recoveries than are seen in the SFR and the conventional flotation cell with a froth bed, wherein fall-back by the hydrophobic particles in the froth causes recovery losses. As a result, the cell footprint is smaller and cheaper than the conventional cells, and produces better metallurgical performance. This cell design is challenging old conventions, and presents an interesting future for the industry.
The organising committee, contributing authors are to be congratulated on a great conference.