ABSTRACT
Mining operations globally face a looming critical minerals crisis. Demand for resources is rapidly increasing due to a growing global population, rising living standards and increased prevalence of technology (Ali, et al., 2017). Whilst contending with this, the industry struggled against significant headwinds due to declining ore grades, increasing waste production and complex deposits, and addressing societal expectations for more sustainable operating practices (Gorain, 2016). Drastic increases in mining efficiency, productivity and sustainability will be required to meet the projected resource forecasts.
It has long been established that blasting is the most effective means of size reduction for ore, particularly compared to traditional grinding processes such as the Semi Autogenous Ball Mill Crushing comminution circuit (Eloranta, 1997). In addition, high brisance explosives can create microfractures which improves the grindability of the ore and the performance of lixiviants employed to extract the resource (Kinyua, Jianhua, Kasomo, Mauti, & Mwangangi, 2022). However, the use of ‘ultra-high’ powder factors of >2.0 kg/m3 in conventional blast designs typically results in disastrous blast outcomes, including flyrock, excessive vibration and misfire.
UltraBlast is a revolutionary suite of blasting methods developed by Orica to optimise the fragment size distribution of blasted rock to maximise mine productivity, minimise the energy intensity of resource production, and seek to reduce customer carbon footprint (Brent, Dare-Bryan, Hawke, & Rothery, 2013; Hawke & Dominguez, 2015; Howe & Pan, 2018). The design of these methods varies but they all employ a thick layer of blasted rock to safely confine a lower horizon which is designed with an ‘ultra-high’ powder factor. UltraBlast provides a necessary pathway for drastic improvements to mine productivity and sustainability without compromising on safety.
BLASTING FOR SUSTAINABILITY
Mining is a significant contributor and necessary solution to climate change. Napier-Munn (2015) estimates that comminution alone consumes nearly 2% of global energy production. This is troubling as the demand for resources is increasing due to global population growth, rising living standards and growing demands for critical minerals. Ali et al. (2017) and Herrington (2021) argue that primary production of resources through mining is the only viable pathway for society to produce the necessary raw materials required for a renewable energy transition and decarbonisation. The only other viable alternative to mining would be increased reuse of materials, also termed as secondary production. Whilst efforts to transition to a circular economy and boost secondary production are necessary and noble, primary production of metals through mining is expected to be necessary for the indefinite future to achieve sustainable development goals (Charpentier Poncelet, et al., 2022). At present, substantial progress is needed to develop a circular economy. Many resources are not recycled, and resource losses throughout the metal cycle are inevitable (Figure 1). Once we add to this increased resource demand through population growth and rising standards of living, sustainable solutions for boosting mining productivity will be required for the indefinite future.
Figure 1: Metal losses in a circular economy (Charpentier Poncelet, et al., 2022):
Contending with these issues is challenging and becoming increasingly difficult due to a range of other factors troubling the industry. Some of the most concerning challenges are declining head grades, declining rates of new deposit discovery and increasing demands for improved social licences to operate (Batterham & Robinson, 2019). Declining head grades is a particularly pernicious problem as this results in increases to waste handling, energy intensity of mineral processing and potentially the presence of deleterious minerals that may impact resource recovery. At the heart of all these issues is a requirement for mining operations to improve efficiency.
It becomes essential then, to determine how to both reduce the CO2e emissions of mining operations and boost productivity through improvements to operational efficiency. Assessments of carbon emissions produced by the mining process have identified two key areas that account for most of a mining operation’s carbon footprint - diesel combustion and comminution (Figure 2). Comminution alone is estimated to consume 40% of mine electricity usage in the United States (Department of Energy, 2007). Likewise, a study on Australian copper and gold operations determined that 36% of mine energy was attributable to comminution (Ballantyne, Powell, & Tiang, 2012). Mining operations treating drill and blast and mineral processing as independent silos are lamentable as there are well-established linkages between blast outcomes and mill performance. Throughput increases of 10-30% and mill power reduction of 30% have been achieved by increasing the powder factor applied during blasting (Kanchibotla, 2014; Gorain, 2016; Seccatore, 2019; Lastra, Jokovic, & Kanchibotla, 2021).
Figure 2: Energy consumption in Chilean Copper Operations (COCHILCO, 2017).
However, the above figures on improved mill performance do not consider impacts on the ‘hidden’ energy entrained in mill components, known as indirect energy consumption. Examples include the mill liners and grinding media used in SAG milling operations; manufacturing these components requires a considerable amount of energy. Material properties of the blasted material feeding into the mill is known to impact the rate that these components wear out. Studies have determined that indirect energy may be as much as 30-50% of direct energy consumption (Ballantyne, Powell, & Tiang, 2012; Musa & Morrison, 2009). Therefore, the benefits of improving mill performance through higher intensity blasting as reported in prior studies may be understated.
Another well-established but often overlooked factor in mine-to-mill optimisation is microfracture, also known as fragment conditioning. It has long been known that explosives not only generate macrofractures that form fragment boundaries but also microfractures, that is, fractures within the blasted rock fragments (Jern, 2002). These microfractures not only soften the ore, which improves the efficiency of milling, but also provide additional surface area for the lixiviant to contact resource bearing minerals, which improves resource recovery (Fribla, 2006; Parra, Onederra, & Michaux, 2014; Parra, et al., 2015; Khademian & Bagherpour, 2017; Kinyua, Jianhua, Kasomo, Mauti, & Mwangangi, 2022). From the literature, it is clear that microfracture generation is influenced by both the powder factor and the brisance of the explosives used.
In summary, increasing the powder factor leads to increased mine productivity, increased efficiency of beneficiation processes, and resource recovery, whilst also decreasing the emissions intensity of production. It should be noted that there are limits to how far powder factors can be practically increased in conventional blast designs, as explosive energies increase, so too do the risks of negative blast outcomes such as dynamic pressure, vibration, airblast, flyrock and wall control. To safely unlock the value offered by ultra-high powder factors, an alternative blast design methodology is needed.
ULTRABLAST
UltraBlast is a revolutionary suite of blasting methods developed by Orica to optimise the fragment size distribution of blasted rock to maximise mine productivity, minimise the energy intensity of resource production, and seek to reduce customer carbon footprint (Brent, Dare-Bryan, Hawke, & Rothery, 2013; Yuill, Hawke, & Dominguez, 2013; Hawke & Dominguez, 2015; Howe & Pan, 2018; Mansfield, 2020). The paper outlining the original variant of this method was awarded the 2014 CEEC medal for its innovative approach to improving the efficiency of resource extraction. Since then, it has been implemented at several mining operations, and variants of the technique have been developed. This article will consider two novel methods of implementing ultra-high powder factors.
Ultra-High Intensity Blasting (UHIB) is a decked blast design method that utilises a high precision electronic blasting system to initiate a blast comprising of two sections, an upper layer which is designed at a standard powder factor and a lower, ultra-high powder factor layer. The upper layer is initiated first and subsequently there is a long delay before the initiation of the lower layer. This delay provides sufficient time for the rock in the upper horizon to fragment, heave and settle to provide an effective blanket to contain the ultra-high energy lower layer before it initiates (Figure 3). This method typically produces a bimodal fragmentation distribution due to the two-layer approach, which may be attractive to customers with mills employing autogenous grinding.
Figure 3: UHIB Firing Sequence (Yuill, Hawke, & Dominguez, 2013).
Precondition Blasting is a variant of UHIB that eliminates the need for decking. For this method, a substantial amount of subdrill is added to the bottom of production holes, roughly equivalent to the length of the stemming region for the underlying, unblasted bench (Figure 4). When this blast is excavated, the material is only extracted to the target bench height, leaving a thick layer of preconditioned material overlying the subsequent bench which can then be safely loaded and fired using ultra-high powder factors. Movement of heavy machinery over this broken material, such as trucks, shovels, and drill rigs, provides sufficient compaction so that holes can be drilled through the preconditioned material and minimal fall back is experienced. This method provides an even distribution of energy through the rock, which is desirable for customers that require a more consistent and finer fragmentation distribution.
Figure 4: A diagram of the Precondition Blasting concept (Hawke & Dominguez, 2015).
To date, trials of these techniques have been conducted at many customer sites and several continue to use them in production. These trials have consistently demonstrated that ultra-high powder factors can be applied safely and effectively using these techniques. Both modelling and trial work have indicated that using the technique substantially improves the granulometry of the blasted material, mill performance, operation productivity and sustainability (Howe & Pan, 2018).
However, UltraBlast is only suitable for some mining operations. These methods are designed to maximise mill throughput; if the operation is not limited by mill throughput, then the technique will not be appropriate. Likewise, the implications of increasing mill throughput should be considered through mill modelling packages such as the Integrated Extraction Simulator (IES) to ensure that bottlenecks will not occur elsewhere in the mineral processing operation.
To achieve ultra-high powder factors, it is necessary to employ aggressive blast design parameters, including large diameter boreholes and tight hole spacings. To sustainably implement UltraBlast, the operation will likely need to optimise drill availability and usage, provide sufficient drilling capacity to support the technique or increase the size of the drilling fleet. One option for destressing drill utilisation is the application of high brisance explosives such as Fortis™ Extra, Vistis™ or 4D™. These products could be combined with a design featuring ultra-high powder factors to minimise the need for tight hole spacings. Many prior studies have noted that the siloed nature of many mining operations makes it difficult to implement and sustain mine-to-mill initiatives (Nielsen & Kristiansen, 1996; Lastra, Jokovic, & Kanchibotla, 2021). Ultra-blast suffers from the same pitfall, as drill and blast expenditures are expected to increase, with the considerable value of the technique only realised downstream in mineral processing. Therefore, it is essential to integrate technologies with UltraBlast techniques that can characterise and track material flows to fully demonstrate the value delivered. Such technologies include RHINO™, ORETrack™, FRAGTrack™ and IES. In prior trials of the technique, a common issue was poor data density and availability. These are problems that can be rectified using the commercially available technologies listed above. Operations can be optimised for the higher drilling intensity required and the processing of finer mill feeds.
Application of these techniques provides an effective means to tackle the increasing demand for critical minerals and reduce the carbon intensity of production. Improved particle size distribution and microfracture content not only substantially increase mill throughput, but also reduce energy intensity of resource production and improve resource recovery by improving contact between the lixiviant and resource bearing minerals. There are likely other benefits, such as reductions to the indirect energy usage. Intelligent use of preconditioned material ensures that the risks associated with ultra-high powder factors can be safely controlled whilst achieving substantial productivity and sustainability gains.
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