Comminution Circuits Research Articles

Assessing the Impact of Surface Blast Design Parameters on the Performance of a Comminution Circuit Processing a Copper-Bearing Ore

Open-pit mining remains the dominant method for copper extraction in current operations, with blasting playing a pivotal role in the efficiency of downstream processes such as loading, hauling, crushing, and milling. This study assesses the impact of surface blast design parameters on the performance of a comminution circuit processing a copper-bearing ore. The analysis focuses on important design parameters such as burden, spacing, stemming, and powder factor, evaluating their influence on the fragment size distribution and downstream comminution circuit performance. Using the Kuz-Ram model, four novel blast designs are compared against a baseline to predict the size distribution of rock fragments (X80). Key performance indicators throughput and specific energy consumption are calculated to evaluate the comminution circuit performance. Results demonstrated that reducing the X80 from 500 mm to 120 mm led up to a 20% increase in throughput and a 29% reduction in total specific energy consumption. Furthermore, achieving finer particle sizes through more intensive blasting contributed to a reduction in total operating costs by up to 12%. These findings provide valuable insights for optimizing blast design to improve comminution circuit performance, contributing to sustainable mining practices by reducing energy consumption, operating costs, and the environmental footprint of mining operations.

Influence of blasting charge distribution on the energy required for communition of rock

The most energy-intensive process in the mining industry is particle size reduction - comminution. The first phase of this process is blasting to fragment the rock from the initial Boussinesq's half-space size. Scientific literature demonstrates that the output of a blast in terms of fragment size distribution can be manipulated by varying the specific charge (powder factor) and charge distribution. This study focuses on the influence of blasting on the internal resistance of the blasted fragments; in particular the influence of the spatial distribution of charges. Small-scale blasts were performed on 14 marble blocks using different powder factors and charge distributions. Three control blocks were fragmented by mechanical means for comparison. The results show the correlations between charge distributions and the specific energy of mechanical comminution. Opportunities for adjusting charge diameter and distribution in opencast blasts to improve the performancet of comminution circuits are discussed.

Integrating Underground Blast Fragmentation Modeling for Sustainable Mine-to-Mill Optimization: A Focus on Blast Fragmentation and Energy Efficiency in Comminution Circuits

Integrating Underground Blast Fragmentation Modeling for Sustainable Mine-to-Mill Optimization: A Focus on Blast Fragmentation and Energy Efficiency in Comminution Circuits

Application of Multibody Dynamics and Bonded-Particle GPU Discrete Element Method in Modelling of a Gyratory Crusher

The gyratory crusher is one of the most important mineral processing assets in the comminution circuit, and its production performance directly impacts the circuit throughput. Due to its higher energy utilisation rate for rock breakage than semi-autogenous (SAG/AG) milling, it is a common practice in operations to promote and optimise primary crushing before the downstream capacity can be enhanced. This study aims to develop a discrete element modelling (DEM) and multibody dynamics (MBD) cosimulation framework to optimise the performance of the gyratory crusher. An MBD model was initially established to simulate the gyratory crusher’s drivetrain system. A GPU-based DEM was also developed with a parallel bond model incorporated to simulate the particle breakage behaviour. Coupling of the MBD and GPU-based DEM resulted in a cosimulation framework based on the Function Mock-up Interface. An industrial-scale gyratory crusher was selected to test the developed numerical framework, and results indicated that the developed method was capable of modelling normal and choked working conditions. The outcome of this study enabled more realistic gyratory crusher improvement and optimisation strategies for enhanced production.

Discrete Element Modeling of the Breakage of Single Polyhedral Particles in the Rotary Offset Crusher

Innovation in comminution is expected to continue unabated to address the inefficiencies that are inherent in comminution circuits. The rotary offset crusher (ROC) is a new comminution device with a promising performance potential in terms of throughput due to the enhanced speed of transportation induced by the centrifugal force of the discs. However, the processes driving the comminution of particles trapped in the conical space between the two discs of the crusher are not fully understood. To gain a better insight into the comminution process in this device, discrete element modeling (DEM) simulations were conducted to study the breakage of a single particle for the crusher operated under two different dynamic conditions, i.e., (1) a stationary top disc and (2) both discs rotating at the same speed. For both scenarios, the speed of the discs was varied between 550 and 2350 rpm. Experimental testwork was also conducted with the laboratory prototype to generate the data that were used to calibrate the breakage parameters of the Ab × t10 breakage model. Simulations were performed using polyhedral UG2 ore particles that were generated with the in-built particle generator in the DEM simulator. The simulated ROC, which is operated with both discs rotating, outperformed the ROC with a stationary top disc in terms of the specific input energy and throughput. The crusher with a stationary top disc is characterized by high shear forces (suggesting a higher wear rate), specific input energies greater than 1 kWh/t, and low throughputs (<50 kg/h). The ROC operated with a stationary disc is not recommended for hard rock applications due to expected excessive wear of crushing surfaces and higher energy consumption. The freewheeling discs are recommended, but there is scope to optimize the crusher performance in terms of the power draw, size reduction, and throughput by manipulating the difference between the speeds of the discs. There is also scope to optimize the crusher performance when it is simulated with many particles. Once the full performance potential of the ROC is established, it will then be important to benchmark it against the existing crushers in the minerals industry as well as other industries where crushers are used.

A coupled CFD–DEM model for tumbling mill dynamics—Effect of lifter profile

In comminution circuits, grinding is the most energy-intensive process. Although significant work was focused on the charge particle dynamics via only DEM in the past, but lifter effects and slurry viscosity have often been overlooked. This work aims to develop a coupled CFD–DEM model to precisely predict mill dynamics involving slurry, charge, and air as free surface. The model uses the VOF method for the slurry–air interface and DEM for charge motion, connecting them through momentum exchange. Suitable slurry rheology and viscous drag sub-models are incorporated. Tumbling mill slurry and charge dynamics are simulated for varied lifter profiles, mill speeds, and slurry pulp conditions. Coupled CFD–DEM and only DEM models are validated against slurry-based Positron Emission Particle Tracking (PEPT) based data. Further, this coupled model is used to assess the effect of lifter face angles and slurry wt% solids on charge dynamics in terms of the mill’s power consumption and the kinetic energy spectra.

Modelling of Gyratory Crusher Liner Wear Using a Digital Wireless Sensor.

A gyratory crusher is a key mineral processing asset in a comminution circuit. Monitoring and predicting the crusher liner wear is essential to ensure the throughput and product quality are maintained during production. This study developed a digital sensor and a discrete element modelling (DEM)-coupled methodology to monitor and reconstruct the gyratory crusher concave liner wear pattern. The developed digital sensor was able to track and report the live thickness of the specific installation point on a concave liner during operation. A wear reconstruction model was then developed based on the wear intensity obtained using the DEM and digital sensor results. The wear reconstruction model predictive results were subsequently compared with site measurements after 95 days of operation. The results indicated that the wear reconstruction model showed good agreement with measured results in terms of wear zone distribution as well as quantitative wear rate prediction. The outcome of this study can be potentially utilised in the mineral processing industry for plant monitoring and automation.

A 3D cellular automata ore stockpile model – Part 2: Simulation and industrial validation of dynamic discharging and trajectory segregation mechanisms

This paper describes a 3D cellular automaton (CA) for dynamically modelling ore piles with continuous feeding and discharging and incorporating two separate size segregation mechanisms. Stockpiles are an integral part of materials handling and storage, and their operation plays an important role in the overall performance of the mineral processing plant. Size segregation can create fluctuations and cause processing units to receive uneven feeds. However, this issue has not received enough attention. Therefore, a three-dimensional dynamic stockpile model has been developed at the Julius Kruttschnitt Mineral Research Centre (JKMRC), which can model the dynamic response of a wide-size-range stockpile. A Continuous Cellular Automata was developed, dividing the volume of the stockpile into a three-dimensional grid of cells with each cell containing an independent set of properties that are tracked throughout the simulation. Modelling size segregation during material flow was presented in Part 1. The variation in the stockpile surface profile and size distribution of the stockpile can be predicted. In this paper, the stockpile model with size segregation extends to the discharging and migration for real-time simulation. The model structure and industrial validation are discussed in this paper, which will show the application of the dynamic model, including the particle size distribution and the height variation of the stockpile. The three-dimensional dynamic stockpile model can contribute to the control of the comminution circuit because different operational strategies can be predicted using the model.

Coupling of XGBoost ensemble methods and discrete element modelling in predicting autogenous grinding mill throughput

Autogenous Grinding (AG) is one the most important mineral processing assets in the comminution circuit, and its production performance directly impacts on the circuit throughput. Understanding the key parameters impacting the AG mill throughput is critical to reducing the operational variability and to improve throughput predictions. This study aims to develop a coupled discrete element modelling and machine learning ensemble method for AG mill throughput predictions. Discrete Element Modelling (DEM) was coupled to an extreme gradient boosting (XGBoost) decision tree method to construct an accurate mill throughput prediction model. Hyperparameter optimizations and model pruning were conducted to improve the generalized model prediction capability. A suite of operational data as well as DEM modelling results from a 32FT AG mill were used to train and validate the developed model. Results indicated that the coupled method showed good agreement with the validation dataset. The impact from each mill operational parameter on the mill throughput was also evaluated and ranked, from which the improvement strategy on mill operation can then be devised.

Performance Analysis of HRC™ HPGR in Manufactured Sand Production

The costs related to comminution in the mineral industry are significant, thus representing the main challenge for optimizing such a process. During the last few decades, the technology of High-Pressure Grinding Rolls (HPGR) has been consolidated as an important alternative for comminution circuits, due to the relatively low operational cost, as well as a relatively high energy efficiency. Due the initial high capital costs, HPGR applications are limited to high-capital projects. However, Metso Outotec has recently developed a relatively low-cost HPGR equipment mainly applied to aggregates segment. Accordingly, this work aims to evaluate the performance of HRC™ HPGR in the production of manufactured sand, based on surveys carried out in an existing industrial plant. The performance assessment indicates that the HRC™ was an adequate alternative for manufactured sand production. The analysis also includes the comparisons of the resulting products based on Brazilian Standards for sands used in concrete and filters.

Editorial for Special Issue “Comminution and Comminution Circuits Optimisation”

Comminution is the size reduction of rock particles from blasting during the mining stage to crushing and milling during the mineral processing stage [...]

Evaluating the performance of an industrial-scale high pressure grinding rolls (HPGR)-tower mill comminution circuit

This paper presents the commercial implementation of a novel comminution circuit with high pressure grinding rolls (HPGR) followed by tower mill in a copper–lead–zinc ore dressing plant. With a throughput of 650 t/d, the comminution circuit comprises three stages of crushing by a jaw crusher, cone crusher, and HPGR as primary, secondary, and tertiary crushers and one stage of grinding by tower mill. Closed with a flip-flow screen, the HPGR reduces the feed size from −12 to −1 mm, and the tower mill circuit produces a flotation feed with a fineness of 85 % passing 0.074 mm. This comminution circuit has HPGR for partial coarse grinding and uses tower mill to replace the energy-inefficient ball mill for primary grinding. The circuit has been operated for more than 7000 h without the replacement of rolls and is projected to reach its design service life of over 13,000 h. Compared with a conventional dressing plant handling similar ores using an SABC circuit, 20.16 % energy savings and improved separation are realised. Opportunities and considerations for this novel comminution configuration are discussed.

Ore hardness properties evaluation based on industrial comminution circuits surveys

The paper addresses determination of ore hardness and grindability parameters using the data obtained from the industrial comminutions circuits survey campaigns. The calculations use the earlier obtained relations between the high-energy impact fracture parameters A and b from JK DWT and SMC tests and the energy efficiency indices used in the Morrell method for the conventional grinding, coarse grinding and high pressure grinding roll milling. Using the simulation modeling of comminution circuits for two types of sulfide copper–nickel ore and one type of apatite–nepheline ore, it is shown that the relative error of the theoretical determination of the JK DWT and SMC testing data is never higher than 16.1%. The calculation method is recommended for application in design and optimization studies of process plants for various genesis minerals, including iron ore. The study was supported by the state contract for research activity in 2021, Grant No. FSRW-2020-0014.

Measuring and modelling the impact of primary crusher stockpiles on autogenous/semi-autogenous mill feed size

Comminution circuits generally have a coarse ore stockpile after the primary crusher to decouple the relatively uneven mined ore supply from the downstream comminution and concentrator circuits which require a stable feed. Whilst this assists with evening-out throughput disturbances, it can influence the size distribution presented to the downstream comminution circuits through size-segregation effects. This is particularly important in Autogenous (AG) and Semi-autogenous (SAG) circuits. What is not often considered, however, is that the stockpile may also cause size reduction. Size distribution data from stockpile feeds and stockpile products were collected from 13 different plants around the world. Analysis of these data supports the assertion that size reduction occurs in the stockpile. A simple power-based model is described which accurately predicts the degree of size reduction measured. Worked examples are provided which show how the model can be used to predict the stockpile product size given data on stockpile geometry and ore hardness.

Selective Comminution Applied to Mineral Processing of a Tantalum Ore: A Technical, Economic Analysis

There is an increasing demand to simulate and optimize the performance and profit of comminution circuits, especially in low-grade ore processing, as is the case with critical metals minerals. Recent research has shown that the optimization result is greatly influenced by quality aspects of the products, such as cost, profit, and capacity. This paper presents a novel approach to performing a multi-objective technical and economic analysis of tantalum ore processing to increase the production of critical metals minerals. The article starts with mineral composition analysis to highlight the potential of strategies for balancing the process layout for maximized production. The introduction of a combined technical and economic analysis presents the possibility of improving the profit by rearranging the mass flow given the rock’s mineral composition. Results show that selective comminution can improve process capacity by 23% and decrease production cost by 10% for the presented case.

A review of the influence of blast fragmentation on downstream processing of metal ores

Rock fragmentation is one of the most commonly optimized blasting outcomes due to its significant influence on the efficiency of downstream operations. This paper reviews the influence of blast fragmentation on processing of metal ores. Two aspects of rock fragmentation that influence downstream mineral processing operations include the particle size of the run-of-mine ore and the degree of internal microfracturing in the fragments induced by blasting. The main influences identified include productivity of comminution equipment, energy consumption in comminution equipment and mineral recovery. An increase in blasting energy results in higher throughput and energy reduction in comminution circuits. Increase in blasting energy results in energy savings in the overall mining operations. However, when increasing the blasting energy, the environmental and safety impacts must be taken into consideration. Blast-induced microfractures increase the permeability of the fragments, therefore enhancing mineral exposure to leaching reagents and consequently may lead to higher mineral recoveries, particularly in heap and dump leaching operations which employ-one-stage comminution. However, the textural characteristics of the ore also influence the mineral recovery. Further research should focus on establishing the relationship between blast intensity and mineral leaching recovery for metal ores of different textural properties.

A Methodology to Determine the Potential for Particulate Ore Sorting Based on Intrinsic Particle Properties

Sensor-based particulate ore sorting is a pre-concentration technique that sorts particles based on measurable physical properties, resulting in reduced energy consumption by removing waste prior to grinding. This study presents an integrated methodology to determine the potential for ore sorting based on intrinsic particle properties. The methodology first considers the intrinsic sortability based on perfect separation. Only intrinsically sortable ore is further assessed by determining the sensor-based sortability. The methodology is demonstrated using a case study based on a typical copper porphyry comminution circuit. The sorting duty identified for the case study was the removal of low-grade waste material from the pebble crusher stream at a suitable Cu cut-off grade. It was found that the ore had the potential to be sorted based on the intrinsic and ideal laboratory sensor sortability results but showed no potential to be sorted using industrial-scale sensors. The ideal laboratory XRF sensor results showed that around 40% of mass could be rejected as waste at copper recoveries above 80%. An economic analysis of the sortability tests showed that, at optimum separation conditions, the intrinsic, ideal sensor and industrial sensor sortability would result in an additional annual profit of ~$30 million, $21 million and $−7 million (loss), respectively.

Quantitative analysis of ore texture breakage characteristics affected by loading mechanism: Fragmentation and mineral liberation

• Iron ore textures were fragmented with compression mechanism. • Quantitative characterization of minerals breakage using mineralogical analysis. • Highlights the need for link the ore texture features to comminution process. • Comparison of high and low displacement rates showed more breakage on the later. Mineral liberation as the main purpose of comminution in ore beneficiation is not applied in the design of comminution machines or even often neglected in designing comminution circuits. In addition, other factors critical for comminution efficiency such as fracture energy, and particle fragmentation are rarely considered. The current study investigates the combined effects of particle textural properties and process operational conditions on the fragmentation of bed particle. In particular, the influence of ore texture and loading displacement rate (as the material and machine properties) on particle specific fracture energy, breakage mode, liberation, and fragmentation was studied. The results indicate that ore textures with coarsest grain sizes and lower quantities of cleavage minerals have the least amount of fracture energy. In terms of fragmentation, a lower displacement rates results in higher quantities of the fragmented particles compared to the higher displacement rate. Among studied ore textures, two types of hematite ore textures which had the coarsest grain sizes had lower liberation in finer size fractions. Overall, the outcomes show that the displacement rate and ore texture can affect the specific fracture energy, particle fragmentation, mineral liberation, and breakage mode at different degrees.

Keys to best practice comminution

Comminution circuits are composed of multiple unit operation, with the objective of reducing mined rock to a size where valuable minerals grains are liberated from gangue. Optimal comminution is critical to achieve efficient mineral separation. There are three reasons for writing this paper. For operators to manage good operations; for designers to produce workable designs; and for educators to provide useful education for mineral process engineers. In all cases, understanding of the transfer size (T80) between the SAG mill and the ball mill is critical to achieve best economics in a semi-autogenous mill (SAG) grinding plant. T80 is important to operators because when the SAG energy and the Bond Ball Mill Work Index on SAG ground ore are measured, accurate prediction of future throughput in any SAG circuit is possible. Without knowledge of the plant T80, it can take many months to figure out how to correct what is really a SAG mill grinding problem, because that problem is hidden if the T80 is not measured. Best Practice Comminution means running a SAG mill under optimal conditions, and avoiding overloading, overspeeding and using excessive steel additions, both during the design and operating stages of the plant. When normal limits for these parameters are exceeded in the design stage, production shortfalls will result, and operating costs will be high. While extra SAG mill capacity is a bonus, lack of capacity is a disaster. This paper shows how to design workable grinding circuits on a particular ore, using either single stage SAG milling, SAB grinding, SABC grinding, or HPGR pre-crushing followed by ball milling. There are many ways to set up a SAG plant, and future expansion should always be considered at the design stage. This opportunity can be overlooked if the designer does not understand the options available.

Helping to reduce mining industry carbon emissions: A step-by-step guide to sizing and selection of energy efficient high pressure grinding rolls circuits

• HPGR circuits can reduce the hard rock mining industry’s CO 2 emissions by up to 43.5% compared to SAG/Ball mill circuits. • Analysis of published data has confirmed that lower specific grinding forces result in an improvement in the comminution efficiency of HPGRs. • Equations have been derived which accurately reproduce HPGR throughput capacity, installed power and specific energy for a wide range of HPGRs. • Using a new equation that accounts for the influence of specific grinding force the “Morrell method” predicts HPGR circuit kWh/t to within 6.5%. • Analysis of data on the performance of ball mills in HPGR circuits indicates that the “Morrell method” predicts circuit kWh/t to within 3%. Comminution is a major contributor to the Mining Industry’s carbon footprint. As most of the world’s leading mining companies have formally committed themselves to having net zero scope 3 carbon emissions by at least 2050, the pressure to significantly improve comminution circuit energy efficiency over the next 25–30 years will be intense. High Pressure Grinding Rolls (HPGR) circuits have the potential to reduce the Mining Industry’s CO 2 emissions by up to 34.5 megatonnes/year, or 43.5% when compared to the established Autogenous (AG)/Semi-Autogenous (SAG)/Ball mill circuit alternatives. However, uptake of HPGR technology has been relatively slow. This may be due in part to the fact that costly and time-consuming pilot testing is still the norm for assessing, selecting and sizing HPGR circuits. This is in contrast to AG/SAG/Ball mill circuits where relatively cheap, fast and effective power-based methodologies are used. To combat this limitation and help accelerate the adoption of this technology a power-based methodology has been developed which can be easily used to assess, size and select HPGR closed circuits in hard rock mining applications. Equations are derived which, on the basis of published data from manufacturers and full-scale operating plants, are demonstrated to accurately reproduce HPGR throughput capacity, installed power and specific energy for a wide range of HPGRs. A number of worked examples are included which demonstrate how the methodology can be applied in practice.