Dealing with low-grade ore

by Mark Cooksey

Reducing the handling and processing of sub-economic ore

Mining, handling and processing low-grade ore in mining and mineral processing operations is resulting in higher costs and lower profits. While this is a widely acknowledged issue, solutions have so far been limited.

New technologies now being developed are giving operators options to divert low-grade ore at multiple stages of their operation.

By removing low grade ore prior to processing, operations can minimise energy use and increase plant profitability. Some of these technologies are already being tested at demonstration scale.

Existing approaches are proving unsustainable

In almost all mining operations ore is moved to the surface. The priority is to optimise the mining location and schedule.

Most operations conduct extensive sampling of ore deposits, but ore grade varies even over small scales, sampling is expensive and it takes time to obtain sampling results. It is common for a significant percentage of the mined ore to be sub-economic.

Some operations blend higher and lower grade ore to ensure grade consistency. This can be beneficial for process stability and performance, but does not change the amount of sub-economic material being processed.

This becomes increasingly problematic, as mining and processing sub-economic material results in:

• high consumables costs, e.g. energy and water. Energy consumption can increase exponentially with decreasing ore grade. A 2016 study calculated that energy required to produce 30% Cu concentrate increased from 60 MJ/kg for 0.5% Cu up to 450 MJ/kg for 0.3% Cu
• high capital costs, due to the need for a larger plant
• high waste generation (e.g. tailings), and
• lower profit.

In an environment of increasing cost and environmental pressures, and decreasing ore grades, reduction of material handing and transport is one of the few ways that could potentially deliver a step change increase in performance and value.

Multiple opportunities for alternative solutions exist

Theoretically, it would be best to remove sub-economic material as early as possible during mining and processing. The theoretical options for achieving this are:

• in-situ recovery, where metals are extracted from ore via solution, with the bulk ore never moved
• optimised mining, where the ore is well characterised and areas of low-grade ore are not mined
• conducting some processing underground, e.g. crushing, to reduce the amount of ore transported to the surface, and
• ore sorting, at various stages of the process, where ore quality is measured and sub-economic material is diverted away from further processing

These options show that each step of the process provides an opportunity to divert lower-grade ore,  and reduce the amount of material transported to produce a given quantity of metal.

To make these theroretical options possible, new technologies that allow for the practical implementation of these options are being developed and tested.

Explore and implement alternative characterisation processes with the help of CSIRO

Advanced technologies to reduce the amount of low-grade ore being fed to downstream processing operations are currently being established and tested at length.

Partnering with suppliers and R&D providers to implement these technologies can help operators take long-held theoretical solutions and make them feasible at an operating scale.

We have been heavily involved in the research and development of technologies that can be implemented at different stages of the mining process to discover and remove low-grade ore, including:

• fast-tracking sample grade measurement
• in-situ leaching: extracting valuable minerals from ore while it’s in the ground, avoiding transport of ore altogether. In collaboration with Mining3, we are currently coordinating projects to reduce barriers to in-situ leaching.
• ore-sorting: technology to measure the concentration of valuable minerals in ore on conveyor belt so that ore can be separated based on grade. We developed the world’s first sensor system for large-scale sorting, NextOre technology.

If you’re interested in reducing costs and energy consumption in your operation, we are uniquely positioned to assist you and add value to your project. Contact the team on +61 8 9334 8094 or email me, mark.cooksey@csiro.au, to discuss how our expertise and experience can help you.

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