Reducing Mine Water & Waste Through Preconcentration

Preconcentration offers miners the opportunity to address some of the operational, environmental and CSR-based challenges that lie ahead.

This is an excerpt from an Engineering and Mining Journal article (March 2020), written by Carly Leonida, European Editor.

Preconcentration, as a concept, is not new. It is a commonly used process in base metals, coal, iron ore and phosphate operations, and selective ore sorting in the form of hand picking has been employed since the birth of mining to optimize processing.

At a commercial scale, processes such as gravity concentration, heavy media separation and ore sorting have been used, where cost effective, since the 1970s. However, there is renewed interest in preconcentration due to technological advances and shifts in the monetary and social costs of two key inputs to ore processing — energy and water. In line with this, there has been an increase in the number of patents registered for preconcentration technologies, particularly those targeted at reducing water consumption and improving tailings deposition as a result of benefication of valuable minerals at coarser particle sizes.

Preconcentration is vital to the future of the mining industry as it has the potential to lower the cost and risk associated with mineral transportation, processing and tailings disposal. It also cuts energy and water use and minimizes the environmental footprint of operations.

Reducing the amount of energy required for comminution by discarding waste material prior to grinding lowers greenhouse gas emissions and will be key in helping many mining companies realize their long-term goal of carbon neutrality. Lowering the quantity of fine material sent to tailings also reduces net water consumption and lessens the impact of operations on local communities, which is especially important in arid environments and remote areas, for example in high altitude South American locations.

“Preconcentration can potentially offer a higher rate of return, enabling new projects with low ‘in-ground’ grade to secure funding,” said Greg Lane, director at the Coalition for Energy-Efficient Comminution (CEEC). “For existing projects, there are opportunities to retrofit in order to improve processing efficiency. In some cases, resource recovery can increase if the processing of previously sub-economic resource is enabled.”

The CEEC is an independent organization dedicated to driving advances in mineral processing.

“Our focus is on highlighting existing and emerging technologies and processes that are practical, reduce energy and/or water consumption, and have potential for a favorable economic outcome,” CEO Alison Keogh said. “Operators, researchers and collaborative groups are working with mining suppliers, services and software groups to develop and trial advanced preconcentration technologies. The rate of uptake will depend on the success of these technologies in the field.”

In 2019, the CEEC Medal for Technical Research was awarded to Laureate Professor Graeme Jameson and Dr. Cagri Emer for Coarse Chalcopyrite Recovery in a Universal Froth Flotation Machine. The paper documents a novel flotation device, the NovaCell (more on this later), which features a fluidized bed for coarse particle collection and a high shear aeration zone for ultra-fines separation.

CEEC Director Joe Pease explained: “Coarse flotation is an important development that links with and amplifies the economic impact of preconcentration. For example, HydroFloat technology is being trialed to evaluate the possibility of improving metals recovery at Rio Tinto’s Kennecott Copper operation in Utah, U.S., and to improve copper and gold recovery from tailings at Newcrest’s Cadia Valley operations in New South Wales, Australia. HydroFloat developer, Eriez, is also sponsoring The University of Queensland’s Julius Kruttschnitt Mineral Research Centre (JKMRC) in the formation of a Collaborative Consortium for Coarse Particle Processing Research.”

The development of sophisticated, precise sensors is opening up opportunities for preconcentration in commodities such as gold and base metal sulfides using time tested techniques such as dense media separation, gravity concentration and in bulk sorting — the latter is already being used in a semi-commercial application for sulfide ores at several sites, and there are a number of others implementing testing. CRC ORE is currently funding sensor development and demonstrations with groups including CSIRO, the University of Adelaide and the National Research Council in Canada.

Additionally, data science and integrated modelling approaches are enabling the assessment of which orebodies are amenable to upgrades using preconcentration and helping to quantify the benefits and impact of preconcentration.

“These types of collaboration help produce data that supports wider awareness and adoption of new preconcentration technologies,” Lane added.


Engineering Grade

CRC ORE is a Cooperative Research Centre focused on Optimizing Resource Extraction for the mining sector. It is jointly funded by participants including mining and METS companies, research organizations and the Australian government, and is an independent technology broker and facilitator.

“We are working to minimize the impact of declining grades and improve the productivity, energy and water signatures of mining operations,” CEO Ben Adair, explained. “We do this by enabling mining operations to reduce the amount of waste they process and identify increases in overall value. Operators can decrease their use of energy and water, leading to increased sustainability, greater profitability and a smaller environmental footprint.”

Preconcentration is core to the work that CRC ORE is doing. Grade Engineering, one of its signature innovations, employs a combination of techniques to reject low-value material early in the mining process.

Adair said, “Preconcentration is important to the future of the mining industry as it enables operations to work smarter by processing less barren waste and instead focus on maximizing the processing of target minerals. This is particularly important as deposits are becoming increasingly difficult to mine, which in turn drives up capital expenditure. Any improvements that can be made to optimize resource extraction are extremely beneficial.

“Collaboration across our participant cohorts has been critical to the development of Grade Engineering. It is only through collaboration that we have been able to design, test and assess improvements that have resulted in preconcentration outcomes at sites.”


Adding Value at San Cristóbal

A successful full-scale production trial of Grade Engineering was recently demonstrated at Sumitomo Corp.’s Minera San Cristóbal (MSC) operation in Bolivia.

The CRC ORE and MSC teams conducted site studies and analysis in 2017 to determine the level of opportunity available and a full-scale production trial using a Metso Lokotrack ST2.8 mobile screening plant began in 2018.

The trial focused on upgrading mineralized waste from the pit to determine if Grade Engineering could produce a new economic stream of valuable material that could then be combined with ROM feed through to the concentrator to produce a positive net smelter return.

Adair said the results are impressive: “The production trial resulted in a 75% rejection of barren material from sub-economic mineralized waste,” he said. “The ‘accepts’ fraction, representing 25% of the mass has been upgraded to more than twice the grade of the traditional feed stock.”

CRC ORE said this result is of significance to the operation, with work to date extending the life of mine by at least two years. Additional work is now being undertaken that will further extend this time considerably.

“The Minera San Cristóbal engagement has been an outstanding success where the intrinsic culture of the site has facilitated the rapid testing and deployment of the technologies,” Adair said.

“We currently are engaged at several site trials nationally and internationally on behalf of our participants. This includes a number of Western Australian gold and base metal operations. These trials are focused on a number of gangue rejection techniques and are showing highly promising results for those involved.”

Click to read the full Engineering and Mining Journal article.

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