With a global push to reduce our carbon footprint and implement more effective environmental, social and corporate governance (ESG), Ausenco is leading environmentally conscious design solutions for the mining industry. According to McKinsey & Company, mining was responsible for 4 to 7% of greenhouse gas (GHG) emissions globally in 2020 (incurred through mining operations, processing and transportation). This figure grows to 28% of global emissions when indirect emissions such as the combustion of coal are considered.
Theoretically, the mining industry can significantly reduce carbon emissions (excluding indirect emissions) through operational efficiency, improvements in energy use, and the incorporation of renewable energy. Our objective is to help the mining sector reduce its carbon footprint through innovative flowsheet designs and process selection that provide higher energy efficiency, improved capital efficiency, and robust operating and maintenance practices.
In mining, it is well known that comminution is the most energy-intensive process in a processing plant, accounting globally for 3-4% of the total energy demand. This fact underscores that efforts to reduce GHG emissions from mining and mineral processing should focus on comminution efficiency, particularly when low-grade ores and more finer-grained deposits are targeted.
Traditionally, the selection of comminution circuit flowsheets is based on plant capacity, ore hardness and grades, all driven by the economic value of extraction. With sustainability in mind, incorporating energy and water efficiency into the mineral extraction value-driver challenges how we select and design circuits.
Based on the drivers of energy efficiency and water conservation, projects treating competent ores may favour selecting a multi-stage crushing circuit incorporating high pressure grinding rolls (HPGR). Although flowsheets incorporating HPGRs can provide lower energy consumptions, the capital cost can be higher than traditional circuits featuring semi-autogenous (SAG) and ball mills. Several new and emerging technologies can assist in the reduction of overall energy consumption associated with the comminution of ores. These include: the use of ore sorting, preconcentration and coarse particle flotation (CPF) before the energy-intensive grinding stages; the use of microwave or electrical pulse treatment to provide improved liberation at coarser grind sizes; and the use of stirred mills in regrind applications.
The site and plant layout significantly impact not only the installed cost of a processing plant but also the indirect GHG emissions. The general arrangement of equipment, the relationship between layout, earthworks requirements, bulk materials quantities and optimization of operational and maintenance all provide significant opportunities to maximize the value of a project. Hence, the installed capital costs can be related to the ESG drivers such as ‘carbon footprint’. For example, large processing plants with over-blown capital estimates can significantly affect the overall GHG footprint due to poor design and blindly following ‘standard layouts’.
There have been several attempts to generate ‘standard layouts’ for processing plants to reduce project schedule and contractor EPCM costs. This approach led to several inefficiencies in design due to the variation in ore competency across ore bodies and resulting compromises to the design. It can be argued that for highly variable ores, the inefficiencies in the design offset the performance efficiencies of the ‘standard design‘ due to the excessive bulk materials required for the generic layout. This, in turn, can result in higher GHG emissions throughout the life of the mine.
By challenging the ‘standard design’ convention from a technical, environmental, delivery, as well as operations and maintenance perspective, considerable project savings can be achieved by minimizing footprint and the associated bulk quantity requirements through a fit-for-purpose design approach.
Figure 1 (below) shows an example of reductions in concrete and steel quantities for a South American project where Ausenco successfully applied a fit-for-purpose design approach. Concrete and steel quantities were reduced by ~ 50%, which directly impacted the man-hours and schedule, resulting in a cost-effective comminution circuit design and indirect reduction in GHG emissions.
Figure 1. Reduction in bulk material quantities based on the paradigm shift in layout and design for a South American project
Key strategies for reducing the GHG emissions of a processing plant
- Consider an energy-efficient comminution flowsheet based on the measured ore breakage characteristics.
- Favour the selection of dry processing flowsheets or flowsheets that have a lower water footprint.
- Favour the usage of renewable energy sources where possible or types of fossil fuel that emit lower amounts of GHG.
- Understand the ore and its variability throughout the life of mine – use tools such as geometallurgy to predict processing performance when planning ore schedules to deliver a lower variability in energy usage.
- Consider innovative technologies in the flowsheet to reject waste as early as possible, reducing processing energy and water demand (e.g., ore sorting, preconcentration, CPF, pre-weakening treatment and stirred mills).
- Use a fit-for-purpose design approach for the processing plant that:
- has a reduced footprint,
- require lower bulk material quantities,
- allows for robust operating and maintenance practices, and
- delivers improved capital efficiency
For more information on how we can help you design a fit-for-purpose processing plant, contact Bianca Foggiatto.