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Grade Engineering® is focused on extracting metal more efficiently by separating ore from waste before it enters comminution. Early physical rejection of non valuable material through pre-concentration techniques before processing, decreases processing costs and importantly can significantly increase the life of a mine.
The minerals industry is facing a productivity and investment crisis. The ‘Millennium Super Cycle’ from 2003-11 was an unprecedented period of growth and investment resulting in increased throughput and development of lower grade resources to meet demand. During the boom quantity became more important than quality with throughput the key metric. This was accompanied by a general trend of decreasing feed grades across all commodities which was offset with higher production volumes.
Current industry perception is that declining feed grade is an unavoidable consequence of ore deposit geology and mass mining technologies for increasingly mature mining operations. In typical crush-grind-float operations value recovery only takes place at ~100-micron particle size involving 3-4 orders of magnitude size reduction compared to run of mine feed. For increasingly low grade deposits the cost of energy and capital intensity required to process and reject worthless material at micron scale drives poor productivity. An alternative is to deploy a range of coarse rejection technologies.
Grade Engineering® is an integrated approach to coarse rejection that matches a suite of separation technologies to ore specific characteristics and compares the net value of rejecting low value components in current feed streams to existing mine plans as part of a system-view.
Coarse rejection (~10-100 mm) can be used on size distributions ranging from run of mine to comminution mill discharge. Opportunity for Grade Engineering® is based on five rock based ‘levers’ linked to combinations of screening, sensor-based sorting and heavy media separation. These involve (scroll down to the bottom of the page for more information on these five levers):
Grade Engineering® is being developed and implemented by a consortium of over 30 mining companies, equipment suppliers and research organisations. Emerging results from collaborative site activities demonstrate potential for generating significant value which can reverse the trend of declining production due to declining feed grades.
Figure1: Vision for early measurement and separation
A focus on throughput as the main driver of revenue has led to a bulk average mentality with respect to in-situ cut-off grades. In many cases average grades used to define bench or stope scale processing destination decisions such as mill, dump leach, waste, etc. include significant sub-volumes of material outside cut-off specifications. An averaging approach ignores potentially exploitable grade heterogeneity below the scale of minimum mining unit even though significant localised grade heterogeneity is a dominant characteristic of many base and metal deposit styles and ore types.
Localised grade heterogeneity is typically overlooked in favor of maximising extraction rates and loading efficiency. This is coupled with a desire to blend ROM and produce steady state feed in terms of grade and physical properties to optimise and maximise recovery of saleable product particularly in crush-grind-float operations. Where blended supply of ‘averaged’ feed struggles to achieve steady state processing stability, this is a first order indication that significant heterogeneity exists within a resource that could be exploited rather than suppressed.
Grade Engineering® recognises that in many cases out of specification sub-volumes assigned to destinations based on bulk averages can be removed using efficient coarse separation techniques in the ‘dig and deliver’ interface. Coarse separation (~10-100mm) can be used on a range of particle size distributions ranging from ROM to SAG discharge. The earlier this occurs in the conventional dig and deliver mining cycle the higher the potential net value of removing uneconomic material.
Every handling and size transformation interface in the dig and deliver cycle should be considered an opportunity for applying coarse separation. ROM and post primary crushing are obvious intervention points with opportunity for separation conditioning during modified blast design. The decision to intervene is a function of grade heterogeneity in a given parcel of material; the yield-response of a separation device at a specific size reduction point; the ability to change a destination decision for one or more of the new streams following separation; and the net value of the new streams after handling costs.
Grade Engineering® outcomes do not create ‘new’ metal but rather exchange metal from separated components between existing destinations to create improved net value after cost of exchange is taken into account. This involves exchanging a component of separated mill feed with other destinations such as mineralised waste, stockpiles or dump leach with low recovery. The aim is to bring metal forward from destinations that are not delivering maximum current value.
Overall metal exchange balance can be modified to suit operational modes or bottlenecks. This can include keeping the concentrator full with improved grades or deferring the need for expanding installed capacity. Mass pull on separation devices can be used to control accept/reject tonnages and resulting upgrades. While Grade Engineering® does not create ‘new metal’, outcomes improve resource to reserve conversion by potentially separating economic parcels of ore from mineralised waste.
The concept of coarse separation or pre-concentration is not new and has been practiced from the beginning of mining as hand picking. The propensity of some ores to break preferentially during blasting and crushing leading to an increase of valuable phases in finer fractions has also been widely known but rarely exploited at production scale. A notable exception was pre-concentration carried out in the 1980’s at the Bougainville Copper Limited Panguna Cu-Au mine in Papua New Guinea. This involved a screening plant to upgrade marginal low grade ROM ores (0.22 Cu, 0.18 g/t Au) that exhibited preferential grade deportment into fines. The plant had a capacity of 35 Mt p.a. at a <32mm screening size, which produced a 50% Cu-Au upgrade in 38% retained mass.
Additional examples of production scale pre-concentration include the Dense Media Plant at Mount Isa Mines which removes ~35% of coarse and hardest Pb-Zn feed before the fine grinding treatment process. This increases throughput, reduces capital intensity in the comminution circuit, and reduces energy requirement per unit metal in the concentrator by >40%, together with a 15% improvement of grade in the retained stream.
While application of sensor-based sorting has found widespread application in industrial recycling and food quality management, there are limited examples of routine application to pre-concentration in the minerals industry. An exception is the Mittersill tungsten mine in Austria where in response to head grades falling from 0.7% to 0.2% since mining commenced in 1976, X-ray Transmission sensor-based particle sorting units were installed in 2008. The results significantly increased effective head grade and reduced energy intensity while allowing rejected waste to be sold as road aggregate.
Although there are global examples of coarse pre-concentration generating value for some base and precious metal mining operations, there is no coherent system-based industry approach or standard methodology to assess optimal configurations for selecting specific technologies or equipment to deliver maximum value for specific ores and operational constraints.
Grade Engineering® is the first large-scale initiative to focus on integrated methodologies to deliver maximum operational value. The prime aim for CRC ORE is to deliver Grade Engineering® as an industry standard methodology designed to improve productivity and value to mining operations which includes the ability to filter and rank individual operations for highest opportunity.
Within Grade Engineering®, five technology ‘levers’ are recognised that are capable of delivering coarse separation outcomes (>10mm).
1. Natural preferential grade by size deportment: the propensity for some ores to exhibit preferential breakage leading to concentration of minerals in specific size fractions. This typically involves an increase of valuable sulphide mineral phases in finer size fractions. Preferential grade deportment is an interaction function of rock mass properties, texture, ore paragenesis and mineralogy at a range of scales. There is typically no relationship between magnitude of response and head grade, with the main control being textural rather than absolute abundance. Physical separation is a function of screening employed after blasting or primary crushing.
2. Differential blasting for grade: involves conditioning of sub-volumes of material at bench or stope scale using customised blast designs that generate imposed size distributions with higher grade concentrated in finer fractions. Amenability is a function of exploitable grade heterogeneity at blast hole scale linked to the ability to impose and control different energy distributions within a blast design. As for Lever 1 physical separation is a function of screening.
3. Sensor based bulk sorting: involves use of a wide variety of electronic sensors capable of providing on-line information on grade in the dig and deliver material handling interface including shovel buckets, trucks and conveyors. There are many technologies capable of coarse rock sensing ranging from surface based to fully penetrative; and providing elemental to mineralogical resolution. Amenability is a function of the resolution and accuracy of individual sensors; rock interaction times and signal acquisition; and selected scale of resulting separation volume.
4. Sensor based stream sorting: while sensor based bulk sorting involves full particle size distributions, stream sorting involves a modified particle size distribution. This is driven by the requirements of some sensor technologies for a limited size distribution to improve rock interaction and enable individual particle separation using air jets or mechanical actuators. It is also driven by an option to use sensors as ‘cleaners’ on lower volume separated streams derived using other levers.
5. Coarse gravity separation: involves use of heavy media separation and in-line pressure jigs at coarse scale (>10mm) generating individual particle separations based on density. Amenability and separation outcomes are a function of texture and mineralogy at this scale. Compared to Levers 1 to 3, conditioning feed for coarse gravity separation typically requires secondary crushing and screening to deliver a carefully constrained particle size distribution. For this reason, coarse gravity separation in Grade Engineering® applications primarily operates as a ‘cleaner’ in combination with streams derived using other levers.
In order to assess relative merits and resulting value of coarse separation outcomes based on applying individual levers or sets of levers for specific ores and operations, it is necessary to define comparative response attributes through a process of physical testing and simulation.
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Integrated Extraction Simulator (IES)
The Integrated Extraction Simulator (IES) is a whole-of-mine optimisation simulator.
It is the next generation of fast, reliable and accurate simulation of the entire mining process - from the mine to the mill.
A cloud-based simulation and optimisation platform, mines use IES to predict and optimise mineral processing performance, engineers to compare and cost new flowsheet designs and researchers to prototype and refine new equipment models.
Integrating and optimising drilling & blasting, crushing, grinding and flotation, it provides mine managers with a cloud-based decision support platform that enables production departments to coordinate and optimise system value across all operational metrics.
Individual unit operations typically use individual process simulation and optimisation models which are not designed to interact. This restricts system integration.
The Integration Extraction Simulator (IES) is a major CRC ORE software development designed to overcome this problem and unlock system value.
IES is web-based cloud supported software designed to integrate existing simulation models through dynamic interaction links. This enables unit operations to be linked together for system optimisation simulations. IES supports Grade Engineering as well as offering next generation capabilities for process simulation.
The Integrated Extraction Simulator (IES) has been developed from the combined research of Cooperative Research Centre for Optimising Ore Extraction (CRC ORE), The Julius Kruttschnitt Mineral Research Centre (JKMRC) and AMIRA, and is available free to CRC ORE 1 Participants (term 2010-2015) and CRC ORE 2 Participants (term 2015-2021) when used in research projects and site based implementations.
Metallurgical Breakthroughs – new thinking in mining and metallurgical modelling
IES is the first platform to integrate all mining and mineral processing operations into one contiguous flow sheet environment, starting with drill and blast and stepping through each stage of haul, stockpile, blend and mix prior to crushing, grinding and flotation.
For the first time mining and mineral processing engineers can model the impact of every operation in the flowsheet on overall productivity. IES provides immediate response: change the blast design and seconds later see the impact on grinding throughput in the mill and concentrate recovery in the flotation plant.
Mining operations have to process multiple material types simultaneously in their operations – so their simulator platform should be able to as well. IES has been designed from the ground up as a platform for multi-component modeling and the new generation equipment models are responding to the challenge. Trusted models from years of research have been upgraded to “multi-component” capability and IES offers model developer’s sophisticated tools to facilitate multi-component processing.
Users can define expressions that calculate operating cost, power consumption, water usage and even CO2 emissions for each piece of equipment as well as the whole flowsheet. The optimisation function can be used to establish production targets that meet environmental and cost constraints.
Mill Performance Management (MPM) is a new module of IES that has all the functionality required to capture and process mill surveys in detail from the first stream sample to full flowsheet optimisation.
With MPM, the mill survey team can capture field observations, consolidate observations and laboratory assays into normalised flows and mass balance individual operations or subsets through to the entire flowsheet.
Once the flowsheet has been balanced, MPM facilitates calibration (model fitting) and automatically creates a new flowsheet with the calibrated equipment models.
The calibrated flowsheet can then be used to optimise the operator settings and flows of the mill to get improved operational performance.
Software Breakthroughs – better technology for improved productivity.
IES is a cloud-based subscription service - all the user needs is a browser and internet access to start building flowsheets. IES uses Amazon Web Services to provide safe, secure infrastructure with continuous backup and industrial grade data security. The design of IES allows the user to “scale up” and select the level of computing power to apply to mass simulation challenges.
Stand-alone deployment is available for times when where internet access is limited or when users with sensitive data require independent implementations.
Users can initiate multiple automated simulations from CSV files containing multiple flowsheet model parameters and material properties. The data in each row of the CSV file is mapped to the simulation engine and triggers a simulation.
Users can process entire geomet-enabled block models or mining extraction sequences in order to understand recovery and spot bottlenecks in long term mine plans. IES will map simulation results such as throughput and recovery back into the block model for use in downstream processes such as ultimate pit and optimised mine planning.
Mass simulation can also be used for setting up sensitivity analysis where multiple parameter ranges are tested against controls to understand performance relationships.
IES stores a record of each simulation performed on every flowsheet for future retrieval, modification and comparison. The database can be exported to a spreadsheet for further analysis and interpretation, including graphical representation for reporting.
Each simulation record contains sufficient data to completely rebuild the graphical flowsheet and all of its input parameters and material properties. The user is in complete control of the flowsheet development process and can easily go back and retrieve old flowsheets in order to create alternative processing options.
IES provides a model-scripting environment that allows mine operators and consultants to modify the standard models to suit site conditions as well as prototype completely new equipment models from scratch.
The user simply drags a special “BlackBox” model icon onto the flowsheet, opens it up and scripts a new piece of equipment with all of the facilities of sophisticated multi-component processing. The BlackBox can then be used together with tried and trusted industry standard models to get the best of both worlds – world’s leading technology modified to local conditions.
IES provides users with a platform to publish new models so other users can access their work or alternatively the user can choose to keep the model private.
Familiarisation training - web based or classroom tutorials:
Performance management – use flow sheet to improve performance
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Kalgoorlie-Boulder Mining Innovation Hub
CRC ORE and the Western Australia School of Mines has undertaken an initial study to assess the potential for creating an industry-led technology innovation hub in Kalgoorlie-Boulder to deliver value to Australian producers and METS in the Western Australian mining industry.
The key objectives of the hub are to address some of the mining industry challenges in the Goldfields region including:
The Western Australian School of Mines (WASM) has a long history of involvement with the mining industry, particularly through its Kalgoorlie campus and facilities. This includes state-of-the-art research laboratory facilities and experienced research academics in both mining and metallurgical engineering.
The Minerals Research Institute of Western Australia (MRIWA) is a statutory body that supports and encourages research for the Western Australian minerals industry. It is actively supporting a number of research projects via CRC ORE and other direct channels.
CRC ORE, a government and mining industry funded collaborative research centre, has a number of technologies it would seed into the hub, including Grade Engineering® technical capability. It also has a strong engagement model with the Mining and METS companies that would be embedded in the hub.
METS Ignited, an Industry Growth Centre funded by the Australian Government, supports the hub concept, which aligns closely with its Living Labs initiative to foster innovation and collaboration.
Initial industry engagement has been undertaken via a detailed consultation process with a range of regional Mining and METS companies. Overwhelmingly all parties supported the initial concept.
Other interested core collaborators include the Chamber of Mines and Energy, Central Regional TAFE and the City of Kalgoorlie-Boulder.
The hub provides an environment for focused collaboration between Researchers, METS and Miners. Possibilities exist to unlock significant additional value through technology to improve current operations, extend mine life and re-evaluate mothballed or undeveloped deposits. Projects can capitalise on opportunities identified in recent Grade Engineering® studies on mining operations across the world by CRC ORE. This work has identified significant economic benefits (∆NPV) in existing operations and greenfield projects.
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CRC ORE has developed a range of tests to predetermine the probability and extent of Acid Rock Drainage on a mine site. Failure to accurately predict acid rock drainage (ARD) leads to substantial financial consequences and reputational damage to operators.
Predicting the impact of acid metalliferous/mine drainage and metal leaching potential of waste rocks and ore to the local and wider environment is critical for all mining operations. Acid rock drainage represents a substantial liability for both industry and government.
There is currently a range of chemical static and kinetic tests used to evaluate the acid producing nature of materials, from which risk assessments are prepared and waste classification schemes designed. However, these well-established tests and practices have inherent limitations including:
Thus, accurate prediction is challenging because of the multifaceted processes leading to ARD. Hence, risk assessments need to consider mineralogical, textural and geometallurgical rock properties in addition to predictive geochemical test data.
A new architecture of integrative, staged ARD testing have been developed by CRC ORE. Better ARD prediction starts with improving the definition of geoenvironmental models and waste units. Then, a range of low-cost and rapid tests for the screening of samples should be conducted on site prior to the performance of established tests and advanced analyses using state-of-the-art laboratories. ARD prediction would support more accurate and cost-effective waste management during operation, and ultimately less costly mine closure outcomes.