High Pressure Grinding Rolls Research Articles

Modeling of particle sizes for industrial HPGR products by a unique explainable AI tool- A “Conscious Lab” development

High-Pressure Grinding Rolls (HPGR), as a modified type of roll crushers, could intensively reduce the energy consumptions in the mineral processing comminution units. However, several problems counted for their operational modeling, especially in the industrial scales. Expanding a conscious laboratory (CL) as a recently developed concept based on the recorded datasets from the HPGR operational variables could be tackled those complications and fill the gap. Moreover, constructing such a CL base on explainable artificial intelligence (EAI) systems would be an innovative point for the digitalizing powder technology industries. Using a robust EAI model as a strategic approach could significantly improve system transparency and trustworthiness to convert any complicated black-box machine learning to a logical human basis system. This study introduced the SHapley Additive exPlanations (SHAP) and extreme gradient boosting (XGBoost) as the latest powerful EAI tool for the CL modeling of the particle sizes produced by an industrial HPGR (P80) in the Fakoor Sanat iron ore processing plant (Kerman, Iran). SHAP precisely assessed multivariable relationships between the monitored operational variables and correlated them with the HPGR P80. SHAP values showed relationship magnitudes among variables and ranked them based on their effectiveness on the P80 prediction. The working gap demonstrated the highest importance for the P80 prediction. XGBoost could precisely predict the P80 and showed higher accuracy than typical machine learning methods (random forest and support vector regression) for constructing the CL of HPGR. These significant outcomes would open a new window for robust consideration of the EAI models within powder technology.

Investigation of Lateral Confinement, Roller Aspect Ratio and Wear Condition on HPGR Performance Using DEM-MBD-PRM Simulations

It has been known that the performance of high-pressure grinding rolls (HPGR) varies as a function of the method used to laterally confine the rolls, their diameter/length (aspect) ratio as well as their condition, if new or worn. However, quantifying these effects through direct experimentation in machines with reasonably large dimensions is not straightforward, given the challenge, among others, of guaranteeing that the feed material remains unchanged. The present work couples the discrete element method (DEM) to multibody dynamics (MBD) and a novel particle replacement model (PRM) to simulate the performance of a pilot-scale HPGR grinding pellet feed. It shows that rotating side plates, in particular when fitted with studs, will result in more uniform forces along the bed, which also translates in a more constant product size along the rolls as well as higher throughput. It also shows that the edge effect is not affected by roll length, leading to substantially larger proportional edge regions for high-aspect ratio rolls. On the other hand, the product from the center region of such rolls was found to be finer when pressed at identical specific forces. Finally, rolls were found to have higher throughput, but generate a coarser product when worn following the commonly observed trapezoidal profile. The approach often used in industry to compensate for roller wear is to increase the specific force and roll speed. It has been demonstrated to be effective in maintaining product fineness and throughput, as long as the minimum safety gap is not reached.

An innovative flake graphite upgrading process based on HPGR, stirred grinding mill, and nanobubble column flotation

Physical upgrading of graphite is typically achieved with many stages of grinding and flotation to produce a concentrate with approximately 95% carbon grade. An innovative grinding and column flotation process has been developed for efficient graphite upgrading to substantially simplify the process flowsheet and reduce operating costs. In this process, a high-pressure grinding roller (HPGR) and a stirred mill were employed as primary comminution techniques and a nanobubble flotation column as a key separation process. The results obtained with a crystalline flake graphite sample with a carbon grade of 11.15% show that the novel process can produce a concentrate with 94.82% carbon grade and 97.89% recovery from an open circuit of one rougher and two cleaner flotation stages. Scanning electron microscope (SEM) microphotographs indicate that HPGR offers the advantage of more effective protection of graphite flakes during crushing. Grinding test results show that stirred mill could not only protect graphite flakes but also promote the efficient liberation of graphite. Compared with the traditional flotation process, nanobubble flotation can effectively recover ultrafine graphite. The new process possesses a number of important advantages over the traditional method, including substantially higher graphite recovery, greatly simplified process flowsheet, better protection of flake size, reduced reagent consumption and process costs, etc.

Fine milling of Stoilensky oxidized quartzite

The development and technological advance strategy of Stoilensky GOK (Mining and Processing Plant) includes modernization of crushing and milling facilities. The top-priority objective in this regard is resource-saving based on higher energy efficiency of ore pretreatment. The pretreatment process flow is added with high pressure grinding rolls (HPGR) manufactured by Köppern, Germany. The test subject is ferruginous quartzite from Stoilensky deposit. This is a finely disseminated and very strong rock. Dissociation of metal and nonmetal phases takes place in milling to the size of –0.045 mm. Milling was implemented in three stages, with preliminary size screening of stage III product, which offered a finely milled product with the weighted average size dav of 5.5 mm at the content of size +15 mm up to 2.5 %. Some aspects of the roller technology introduction are discussed, and the main stages of the technology application at the commercial scale are described. The informational measures are selected to compare ferruginous quartzite pretreatment circuits with and without HPGR. Fine milling enhances efficiency of processing by 8 % owing to the reduced size of feed of the head-end mills at the maintained iron ore concentration quality.

The Effect of Feed Characteristics on Particles Breakage and Weakening Behavior in High Pressure Grinding Rolls (HPGR)

ABSTRACT High Pressure Grinding Rolls (HPGR) is a high-energy efficiency device that has the ability to weaken the particle. This leads to lower energy consumption at subsequent grinding stages. Currently, no commonly used standard indices exist for predicting breakage, and weakening behavior of particles by HPGR. Accordingly, the current study mainly aimed at investigating the relationship between the common grindability/mechanical characteristics of rock (including work index, Brazilian tensile strength, elasticity module, and uniaxial compressive strength) and the breakage and weakening behaviors of HPGR products. For this purpose, six samples (pure calcite, pure magnetite, pure quartz, marmarite rock, travertine rock, and copper ore) with identical particle size distribution were comminuted by HPGR at three pressure force levels of 2.5, 4.5, and 7.5 MPa. Then, the breakage behavior of the samples was evaluated based on the size reduction ratio, followed by studying the weakening of particles by measuring changes in the fundamental breakage and deformation characteristics (mass-specific fracture energy and stiffness) by Impact Load Cell (ILC). The results revealed an excellent relationship between the breakage behavior of particles and their Brazilian tensile strength, as well as their weakening behavior and elasticity module. For particles with a higher module of elasticity (resistivity toward deformation), energy would be consumed for the formation of cracks and subsequently, particle weakening. In the case of particles with a lower module of elasticity, energy is probably dissipated as particle deformation, resulting in more cake formation and less weakening in particles.

Performance evaluation of the VSK separator for treating mineral fines

The separation process is an integral part of many industrial operations. Most of the present-day plants incorporate dry separation units compared to wet separators, due to scarcity of water and process needs. The VSK separator is a dynamic air classifier widely used in closed circuit with High-Pressure Grinding Rolls (HPGR). The HPGR-VSK separator circuit reduces the grinding energy consumption considerably compared to the conventional ball mill-classifier circuits. However, the fundamental principles of VSK separation and its applications in mineral classification/separation are not well reported in the literature. In the present investigation, pilot-scale experiments were carried out on VSK separator by varying feed rate, cage wheel speed, and blower speed to assess the classification and separation efficiency. The experimental results indicated that classification imparts 8.5–38.5% yield to the fines product with a d50 cut-size varying between 18 and 106 µm. Statistical analysis carried out to evaluate the separation efficiency indicated that the cage wheel speed and blower speed are having a prominent effect on the product yield, silica content, and d50 cut-size. The interaction effect between cage wheel speed and blower speed plays a vital role in product quality. The classification and separation efficiency of the unit was evaluated and discussed with respect to different operating parameters. Further, the size separation index (SSI) has been developed to quantify the separation efficiency, which is simpler than the conventional ways of assessments.

A methodology to predict the HPGR operational gap by using piston press tests

High-Pressure Grinding Rolls (HPGR) sizing requires conducting several pilot-scale tests with a large quantity of material and is costly for new projects. The University of British Columbia has developed a piston press test and models to predict the energy requirements and the size reduction capabilities for an HPGR. However, there is no small-scale test to predict either the throughput or the operational gap of the HPGR. For a given roll size, the throughput is a function of the gap between the rollers and the roll speed. This paper aims to present the concept for a novel gap-calibrated methodology that was developed to predict the operating gap by calibrating the piston press compressed bed thickness with the HPGR operational gap. On average, less than ±0.4% prediction errors have been obtained for the HPGR operating gap when validating using iron and copper ore. It is possible to predict the HPGR throughput with further calculations using the predicted gap. The proposed test and methodology are a first step towards calculating the HPGR throughput using small ore quantities.

Particle Size Effects on Selectivity in Confined Bed Comminution

Confined bed comminution in high-pressure grinding rollers (HPGRs) and vertical roller mills (VRMs) was previously used preferably for grinding comparably homogeneous materials such as coal or clinker. Meanwhile, it started to complement or even replace tumbling mills in ore beneficiation with ore and gangue particles of rather different breakage behaviors. The selectivity in the comminution of a mixture of particles with different strengths but similar particle size distribution (PSD) of the constituents in a particle bed was investigated earlier. The strength of a material is, however, also a function of particle size. Finer particles tend to be more competent than coarser ones of the same material. In industrial ore processing using confined bed comminution, this effect cannot be neglected but even be exploited to increase efficiency. This paper presents research results on this topic based on experimental investigations with model materials and with natural particles, which were stressed in a piston–die press. It appeared that the comminution result substantially depends on the material characteristics, the composition of the mixture and the PSD of the constituents. Conclusions will be drawn for the future applications of selective comminution in mineral processing.

Designs of new operating copper processing plants: process types, equipment selection, industry trends

The article describes the largest operating processing plants for lowgrade copper sulphide ores of our time: 10 plants using the semi-autogenous grinding (SAG) technology and 10 plants using high-pressure grinding rolls (HPGR), with the output of 18 to 100 Mtpa. The unfavorable natural and economic factors are balanced by improved ore preparation and concentration technologies and high-capacity equipment units, combined with cost-saving layout solutions. The ore preparation sector is currently divided between the competing technologies of semi-autogenous grinding and HPGR. The article contains an overview of their advantages and disadvantages. The world’s largest monosection with the capacity of 55.5 Mtpa, that uses the SAG technology, is described. The role of the Drop Weght Test JKSimMet (A×b) parameter in the selection of the ore preparation method and the trend for using HPGR in the processing of strong ores are shown. Examples are provided for the consequences of an inadequate assessment of the feed strength in SAG-based plant designs. Examples of ore preparation process intensification through the use of HPGR in semi-autogenous grinding circuits are also given. The volume of impeller flotation cells installed has reached 600 m3. An overview of the two largest processing plants of our time with the output of 88 and 100 Mtpa of ore is presented. The innovative technical solutions of a newest low-capacity copper plant are highlighted. Based on the results of the overview, a future processing plant is predicted to use ∅12.8–13 m SAG mills, HPGRs with the roll diameter of 3 m, vertical VTM-7000 mills in ore grinding cycles, large fine screens, large-scale impeller flotation cells, and staged SFR and DFR flotation reactors.

Relationships between particle breakage characteristics and comminution response of fine iron ore concentrates

Production of iron ore pellets typically requires regrinding of the iron ore concentrates. Although these concentrates are produced following close control of chemical composition, substantial differences may exist in their response to the size reduction operations that are used prior to pellet formation in the pelletizing disc or drum. Establishing relationships between some intrinsic characteristics of these concentrates and their response to size reduction is, therefore, worthwhile. Single-particle breakage testing has long been used to characterize the material intrinsic response to comminution. However, application of traditional breakage tests to iron ore concentrates is not possible, given their fine sizes. The present work analyzes the application of recent single-particle testing methods that are suitable for particles in the –150 µm size range to characterize breakage of four iron ore concentrates from Brazil. The response of particles when assembled in beds is then analyzed in great detail through piston-and-die testing, as well as by comminution tests in a bench-scale ball mill and high-pressure grinding rolls. Relationships between the results in the various devices, which represent the different levels of particle interaction, have been analyzed in light of their energy utilization. Furthermore, implications of differences in particle characteristics on the differences observed in breakage response are also analysed.

Investigation of Particles Breakage and Weakening Behaviors in Multi-Component Feed Grinding by High Pressure Grinding Rolls (HPGR)

ABSTRACT One of the main merits of using High Pressure Grinding Rolls (HPGR) is particle weakening, which leads to less energy consumption at downstream grinding processes. Normally, HPGR feed contains various minerals with different weakening behaviors. Therefore, understanding the difference between particle weakening behavior in pure and multi-component feed grinding by HPGR is very important. In the current study, the difference of particle weakening behaviors in pure and mixture feed grinding by HPGR was investigated. To this purpose, the pure and different mixture ratios of magnetite (hard component) and calcite (soft component) minerals were comminuted by HPGR under three different pressures. After grinding, particles breakage behavior was investigated based on the relation of consumed energy and the particle size distribution of products. Particle weakening was studied through measuring changes in fundamental breakage and deformation parameters by Impact Load Cell (ILC). It was concluded that, at pressures resulting in breakage saturation state, the weakening of soft component in mixture feed grinding is more than grinding alone, but the changes in weakening of hard component in the mixture and pure feed grinding are insignificant. It was observed that the weakening of soft component particles in pure feed grinding are 15%, and by increasing hard component to 50 V%, their weakening increases by 19%. It resulted that the presence of hard components led to more energy consumption in soft component breakage and decreased energy dissipation toward particles deformation, leading to an increase of induced damage to soft component particles.

Effect of the particle size and microstructure characteristics of the sample from HPGR on column bioleaching of agglomerated copper ore

High-pressure grinding rolls (HPGR) technology is a valuable way to improve the extraction efficiency of valuable minerals; however, the excessively fine particles of the HPGR products affect the heap permeability and limit its application in heap leaching. This study aims at investigating whether the HPGR products can still be leached efficiently after agglomeration to provide new guidance for the application of HPGR in heap leaching. In this study, the copper grain exposure of ores with different particle sizes was tested by X-ray microtomography (XMT), and the microstructure characteristics of the ore under different crushing methods were analyzed by stereomicroscope, scanning electron microscope (SEM), and nuclear magnetic resonance (NMR). The column bioleaching tests were carried out on the ores with different particle sizes and the agglomerates composed of fine-grained ores from different crushing methods. XMT, SEM, and NMR test results showed that copper grain exposure increases with decreasing particle size, and HPGR produces particles with more micro-cracks and higher porosity. The column bioleaching tests indicated that the copper extraction increased with the decrease of particle size, but excessive fine particles affected the heap's permeability in the column. After 66 days of column bioleaching, the copper extractions of agglomerates composed of fine-grained ores from HPGR and jaw crusher were 55.82% and 44.16%, respectively, while the copper extraction of 20–30 mm coarse-grained ores was only 28.54%. These results demonstrated that the increased copper grain exposure caused by the reduced particle size and the richer micro-cracks and higher porosity of the HPGR products could still significantly improve the leaching efficiency of copper ore after agglomeration.

Modeling comminution of iron ore concentrates in industrial-scale HPGR

High-pressure grinding rolls have an important role in several iron ore pellet feed preparation circuits. Modeling and simulation are potentially useful tools to improve their performance, but the applicability of mathematical models from the literature in this particular application has not yet been demonstrated, although the model by Torres and Casali has been identified as having good potential. The present work relies on several surveys on four HPGRs with variable diameters (1.4 to 2.25 m) and aspect ratios (0.88 to 1.45) operating in pelletizing plants to test the model originally proposed by Torres and Casali, as well as modifications proposed to it.Inadequacies have been found in the original model, which gave poor predictions of power, throughput and product size distribution along the roll's length. Modification of the power equation, incorporating a machine-dependent correction factor for the nip angle, as well as several modifications to the throughput model, including an expression meant to account for the ejection of material from the edge of the rolls and extrusion, resulted in very good agreement between data from surveys and the model. Finally, incorporation of an empirical correction equation to account for saturation and a more general expression for the roll profile led to good agreement between measured and predicted product size distributions, including their variation along the roll's length.

Axial pressure distribution, flow behaviour and breakage within a HPGR investigation using DEM

The pressure distribution between the rolls in a HPGR (High Pressure Grinding Rolls) is usually expected to vary significantly in the axial direction due to the end effects at the end of the rolls. This is based on the idea that particles near the ends of the rolls are less well confined which makes them more mobile with reduced ability to be trapped and crushed. This can reduce the performance efficiency of a HPGR quite significantly. Experimental measurement of this axial pressure distribution and its consequences for the breakage efficiency, particularly at industrial scale, is very difficult. So little is known about its nature or how this may change with choice of confining structures (such as cheek plates). This problem is tractable using DEM to predict the coupled flow and breakage of particles within the HPGR. A replacement strategy is used where particles are broken when the applied force exceeds a size dependent limit. This allows the DEM model to capture the fracture dynamics sufficiently to allow flow and load prediction. The model is calibrated against an experimentally measured product size distribution and predicts very close agreement across the entire resolved range of particle sizes. This model is used to explore the pressure distribution and how this, and the coarseness of the particles, changes along the rolls. Two mechanisms are identified for producing breakage in the HPGR. For a HPGR with cheek plates the discharge mass flow rate is found to be nearly independent of axial position with the product size distribution being axially invariant. The frictional effects of the cheek plates lead to a moderate axial flow towards each end of the rolls that balances the reduced vertical flow to give axially very uniform discharge behaviour. Finally, it is shown that only small changes in the confining cheek plate locations are needed to allow significant axial bypass, strong axial variation of discharge mass flow rate and a coarser product.

Modelling the product mass flow rate of high-pressure grinding rolls

Modelling the product mass flow rate of high-pressure grinding rolls

Advanced modeling of HPGR power consumption based on operational parameters by BNN: A “Conscious-Lab” development

This study, for the first time, is going to introduce the boosted neural network (BNN) as a robust artificial intelligence for filling gaps related to the modeling of energy consumption (power draw) in the industrial scale high-pressure grinding rolls (HPGR). For such a purpose, a new concept called “Conscious Laboratory (CL)” has been developed. CL would be the modeling of variables based on real databases that are collected from the industrial-scale plants. Although using HPGRs have been absorbed attention in many processing plants, a few investigations have been conducted to model the power draw of HPGRs. In this article, BNN was used for modeling relationships between HPGR operational variables, and their representative power draws based on an industrial database. This investigation indicated that the generated CL based on BNN could accurately assess the multivariable relationships between monitoring variables of an HPGR from an iron ore plant.

Modern trends in the design of comminution processes and equipment for non-ferrous metals ores

When designing new concentrator plants or revamping the existing ones, it is crucial to properly size and design the process equipment and choose the supplier. The comminution circuit is the most power consuming of all the processing stages. A variety of tests are usually performed to determine the physical and mechanical properties of ore, and the results of such tests serve as the basis for comminution circuit equipment sizing. Various computer simulation packages are used to find the best solutions in terms of process equipment and processes. Analysis of the in-house and public databases containing the test data helped obtain new relationships with regard to ore hardness. Having analyzed the public laboratory test data accumulated by Alex Doll, as well as the results of experiments conducted by the ore comminution laboratory of the Minerals Processing Department at Saint-Petersburg Mining University, the authors came up with a modern procedure to examine the physical and mechanical properties of ores for equipment sizing to implement a standard cycle of semi-autogenous grinding with further ball milling. Samples of copper-nickel ores were analyzed in this research study. The results of the analysis served as the basis to estimate the power consumption by the comminution circuit. The resultant figures were compared with the power consumption figures of a functioning concentrator plant that processes the studied copper-nickel ores. The estimated specific power consumption of the SAG mill deviated from the actual power consumption by –6.5%. In the case of the ball mills, the deviation was estimated at +14.4%. The total estimated specific power consumption of the entire comminution circuit exceeded the one of the functioning plant by +7.6%. The described approach is applicable to different comminution circuits, which include crushers, high pressure grinding roll, and tumbling mills. The resultant process parameters are necessary and sufficient for the comminution circuit simulation using the JKSimMet software and for crushing circuit simulation using the discrete element method in the RockyDEM software.This research study was funded by the Russian Foundation for Basic Research (Grant No. 20-55-12002 NNIO_a).

Enhancement of gold agitation leaching by HPGR comminution via microstructural modification of gold ore particles

A comparative study was carried out to investigate the effect of high-pressure grinding rolls (HPGR) comminution on agitation leaching of gold ore in comparison with the conventional jaw crusher (JC) comminution. The HPGR comminution products were evaluated in terms of particle size distribution, specific surface area and average pore volume, and the origin and density of micro-cracks. HPGR comminution produced finer particles with larger specific surface area and average pore volume, more surficial and internal micro-cracks. It was found that intragranular micro-cracks were dominant in JC products while intergranular micro-cracks were favored by HPGR products. Under optimum HPGR conditions (medium pressure of 5.5 N/mm2), gold metal recovery during agitation leaching was increased 6.79%–10.93% while cyanide consumption was reduced 5.82%–11.11%. These results suggest that more and narrower micro-cracks included in HPGR products may enhance contact between the leach solution and gold grains which contribute to the enhancement of gold agitation leaching. However, excessive grinding of HPGR products will moderate the advantage of HPGR comminution.

Confined Bed Breakage of Fine Iron Ore Concentrates

High-pressure grinding rolls (HPGR) have gained great popularity in the mining industry in the last 25 years or so. One of the first successful applications of the technology has been in iron ore pressing prior to pelletization. Piston-and-die tests can provide good insights on the material response in an HPGR. This work analyzed confined bed breakage of four iron ore concentrates under different conditions. Saturation in breakage of particles contained in the top size in the tests was observed to occur at specific energies of about 2 kWh/t, whereas full saturation in breakage, with no additional increase in specific surface area of the material, occurred at energies above about 6 kWh/t. An expression was proposed to characterize the propensity of a material to break under confined bed conditions. The phenomenology involved in confined bed breakage of such materials was then analyzed in light of the results.

Effect of HPGR comminution scheme on particle properties and heap leaching of gold

ABSTRACT The effect of high-pressure grinding roll (HPGR) comminution on the physical properties of ore particles and heap leaching of gold was investigated compared with that of conventional jaw crusher comminution. The comminuted products were evaluated in terms of particle size distribution, internal crack density, and saturated water content. Compared to conventional jaw crushers, the HPGR produced finer particles with more internal cracks. Moreover, the HPGR particles contained a higher water content in the ore heap. Under optimum conditions, the HPGR comminution scheme was found to significantly enhance the leach recovery of gold, in addition to reducing cyanide consumption. However, the fine particles generated during mini-column leaching, reduced the permeation velocity drastically for HPGR products.