High Pressure Grinding Rolls Research Articles

Influence of HPGR operating parameters on the edge and centre product – an industrial trial

ABSTRACT High pressure grinding rolls has been widely used in mineral industries as energy-efficient equipment. During the working life of an HPGR mill, the rolls’ surface wears out, and a concave wear profile (maximum wear in the middle) occurs on the rolls. As a result, a difference between HPGR discharge particle size from the middle and edges is also expected that has yet to be quantified. On the other hand, many operational variables affect the HPGR performance; however, there is an interaction between the operational variables and worn rolls. This work studied the effect of operational variables such as hydraulic pressure, rolls’ rotation speed, level of material in the hopper, and operational gap on the HPGR performance on an industrial scale. In addition, the particle size of HPGR discharge from the middle and edges of the rolls is also investigated. Results indicated that HPGR discharge from the middle of the rolls is always finer than discharge from the edges, while the difference between the discharge size from the middle and edges depended on the other variables. Furthermore, it was concluded that deeper material levels in the hopper and lower rotation speed of the rolls resulted in a finer HPGR discharge. This finding is crucial in optimising the HPGR performance and modifying the design of HPGRs to regulate the distribution of material on the rolls.

Impact of the feed particle size distribution and its packing characteristics on compression comminution

Due to its lower energy consumption than a conventional grinding circuit, there is an increased interest in the mining industry in the High-Pressure Grinding Rolls (HPGR) technology. Despite the benefits, the high quantity of material required to size the HPGR makes it difficult for new mines to consider this technology. The piston press test has been used at The University of British Columbia to predict the behavior of the HPGR. It is possible to predict energy requirements, size reduction, and throughput by utilizing a small amount of material to size the HPGR. The bulk material’s particle size distribution (PSD) plays an important role in how the particle bed will pack. This study investigates the differences in compressing three different sample PSDs obtained from the same copper ore crushed to −12.5 mm. The first PSD corresponds to the natural distribution resulting from the crusher. The second is created artificially to match the Fuller curve PSD, which theoretically should have the highest packing density. The third corresponds to a truncated feed produced by removing the fines (−300μm) from the natural feed. Tests were performed using a piston-and-die press test apparatus to compress the samples at different force levels. Entirely different behaviors are obtained while compressing the same material with different PSDs. Particularly, the Fuller curve PSD achieves a 31%–40% higher grinding rate than the natural feed, while the truncated feed achieves a 9%–30% higher grinding rate than the natural feed. Differences in the specific energy consumption, grinding efficiency, and final compacted densities highlight the critical influence of feed particle size distribution on the energy usage and generation of fine particles, underscoring the importance of optimizing these parameters for energy-efficient mineral processing. The overall findings indicate that an HPGR feed particle size distribution that matches the Fuller curve and, therefore, has a maximum packing density, results in the most energy-efficient comminution.

The Diatomite Grinding Technology Concept for the Protection of Diatomite Shells and the Control of Product Grading.

Diatomite deposits in Poland are located in the Podkarpackie Voivodeship, and the only active deposit is in Jawornik Ruski. Therefore, it is a unique material. Improved rock processing methods are constantly in demand. In the research presented here, we have used research methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), particle shape analysis, and appropriate sets of crushing machines. Diatomite comminution tests were carried out on test stands in different crushers (jaw crusher, hammer crusher, high-pressure roller press, ball mill) using different elementary crushing force actions: crushing, abrasion, and impact, occurring separately or in combination. The machines were tested with selected variable parameters to obtain products with a wide range of grain sizes ranging from 0 to 10 mm. The ball mill (yield 87%, system C3) and the hammer crusher with HPGR (high-pressure grinding roller) (yield 79%, system D2 + D3) have the greatest impact on diatom shell release and accumulation in the finest 0-5 μm and 5-10 μm fractions. For commercial purposes, it is important to obtain very fine fractions while keeping the shells undisturbed.

Critical Assessment of Novel Developments in HPGR Technology Using DEM.

Advances in high-pressure grinding roll (HGPR) technology since its first commercial application in the cement industry include new roll wear protection techniques and new confinement systems. The latter contribute to reductions in the edge effects in an attempt to reach a more homogenous product size along the rolls. Additional advances in this technology have been made in recent years, while modeling and simulation tools are also reaching maturity and can now be used to subject such novel developments to detailed scrutiny. This work applies a hybrid approach combining advanced simulations using the discrete element method, the particle replacement model and multibody dynamics to a phenomenological population balance model to critically assess two recent advances in HPGR technology: spring-loaded cheek plates and the offset roller press. Force and torque controllers, included in the EDEM 2022.1 software, were used to describe the responses of the geometries in contact with the granular material processed. Simulations showed that while the former successfully reduced the lateral bypass of the material by as much as 65% when cheek plates became severely worn, the latter demonstrated lower throughput and higher potential wear but an ability to generate a finer product than the traditional design.

Investigating the benefits of using HPGR prior to cyanidation of low grade gold ore

AbstractIt is known that the cracked structure of the particles has positive effects in leaching processes. In this respect, high pressure grinding rolls (HPGR) provides some advantages such as increasing leaching efficiency and reducing leaching time by creating more cracked particles compared to other crushers. Although there are studies on the advantages of HPGR on different ores, these have not been fully demonstrated in low grade gold ores, and leaching kinetics have not been examined in detail in the studies conducted in this context. In this study, first of all, crack formation in a low grade gold ore by crushing with HPGR and jaw crusher was investigated. Then, bottle roll tests were performed in different size fractions and different cyanide concentrations along with column leaching of the pelletized ore in a single test condition. As a result of the studies, it was determined that 2–3 times more cracked particles were formed in HPGR depending on the particle size. It was shown that the modified Kelsall model explains the kinetics better than other kinetic models tested. In summary, it was revealed that maximum gold extractions are almost same for HPGR and jaw crushers. However, the fast dissolution kinetic constant was found to be around 25% higher for HPGR than for the jaw crusher in bottle roll tests while this ratio was approximately 30% higher in column leaching tests, suggesting a distinct influence of the crushing method on the dissolution kinetics.

A quantitative study between HPGR and cone crusher aided ball mill grinding: mathematical modeling by evaluating the possible microfracture effect produced by HPGR technology and cone crusher

High Pressure Grinding Rolls (HPGR) have been used in the mining industry for decades. However, there are limited quantifications of the particle properties after comminution. Furthermore, the influence of microcracks in grinding provided by this technology has not been extensively quantified. In the recent work, there were two comminution paths tested: 1 (Jaw crusher + cone crusher + ball mill) and 2 (Jaw crusher + HPGR + ball mill). The possible weakening effect aiding ball mill grinding due to microcracks of HPGR path was shown via specific energy, fines generation and breakage rate measurements. To achieve a quantification about the impact of microcracks and the high rate of reduction rate of HPGR technology, first the product was reconstructed using Rosin Rammler's Weibull double formula and the similar particle size distribution was obtained by a conventional cone crusher. By this way the feed size distribution to the grinding stage remained constant regardless of the type of crushing process (HPGR or cone crusher). The results showed that the microfractures generated by the HPGR technology influence the specific energy consumption, fines generation and breakage rates. Ball mill after HPGR consumed 12.46 kWh/t of specific energy, however ball mill after cone crusher consumed 14.36 kWh/t of specific energy. The experimental methodology proposed in this paper maintains a consistent feed size range (-1500 to +41.31 µm) to show that the size reduction observed in the sample undergoing HPGR grinding is not the primary factor contributing to reduced energy consumption and increased fines generation. Instead, it is predominantly associated with the microfractures generated through the compression in HPGR technology; the energy reduction (optimization) of a grinding path is shown in the study.

Effect of material bed compression on white fused corundum product particle shape and bulk density

Comminution of corundum is a challenging task, as it has outstanding mechanical strength and is highly abrasive and is consequently applied as a blasting and polishing agent in the abrasive industry. Thus, the selection of the best comminution methods to achieve the required dispersity properties has great importance. For this, first we must understand the effects of different type of stresses and their influence on the corundum particle fractions. Laboratory scale material bed compression experiments in a piston press were carried out to examine the effect of the pressure and material bed height on the product's particle size distribution, bulk density, and particle shape. The results showed that outstanding yield, high bulk density, and spherical particle shape can be achieved by particle bed breakage in a piston press, so the high-pressure grinding roll (HPGR) technology is a promising comminution method for corundum.

The Effect of HPGR and Conventional Crushing on the Extent of Micro-Cracks, Milling Energy Requirements and the Degree of Liberation: A Case Study of UG2 Platinum Ore

Comparative high pressure grinding rolls (HPGR) and cone crusher pilot-scale tests were conducted using Upper Group 2 (UG2) platinum-bearing ore in order to determine the impact of micro-cracks in HPGR products toward energy requirements in ball mills and the degree of liberation. The ball mill was fed with HPGR and cone crusher products of similar particle size distributions (PSDs). Qualitative analysis of the degree of micro-cracking on the HPGR and cone crusher products performed using scanning electron microscope (SEM) and image analysis software showed that an HPGR product had more micro-cracks than the equivalent cone crusher product. Milling energy requirements were evaluated using size-specific energy consumption indices calculated based on three grind sizes of 300 µm, 150 µm and 75 µm. The effect of residual micro-cracks in the products of HPGR and cone crusher on the milling size-specific energy requirement is inconclusive. The kinetic parameter k in the cumulative rate kinetic model for ball milling cone crusher products and for ball milling HPGR products were similar. Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) was used to determine the degree of liberation of various mineral phases in the mill products. At a coarser grind size (P80 of 300 µm), the sulfides in the mill products pre-crushed using the cone crusher have consistently poorer liberation than in the equivalent HPGR pre-crushed sample. However, at a finer grind size (P80 of 75 µm), the sulfides in the mill products pre-crushed using the cone crusher and using an HPGR showed similar liberation.

Commercialisation pathway for low energy wet/dry gyratory rolls crusher comminution technology

Comminution for mining and cement industries accounts for over 2 % of global energy consumption and an innovative Gyratory Rolls Crusher (GRolls®) technology has been developed in South Australia to reduce energy and water consumption, providing dry and wet crushing from ∼ 20 mm to 20µm fractions without media, replacing up to two stages of size reduction. The GRolls® is a compression based particle size reduction device, designed to generate fine and ultra-fine products from coarse feeds, by simultaneously applying pulsed compression and shear forces to a packed particle bed. The breakage mechanisms initiated by these forces include compression breakage, inter-particle compression, induced tensile failure and particle shear forces generated by a gyrating roll.The paper presents the commercialisation pathway of the GRolls® technology, from “proof of concept” laboratory scale Alpha prototype and concept design of an upscaled Beta prototype for a pilot plant. A systematic progression of laboratory scale testing of a wide range of feed materials through the Alpha prototype was undertaken to confirm the ‘”proof of concept” design and identify the many design variables and operational configurations that affect the GRolls® crushing and energy performance. The test results were evaluated against currently available comminution solutions such as the High Pressure Grinding Rolls (HPGR) and Vertical Rolls Mill (VRM) in which the mining section is moving towards to provide more economical dry comminution and a progression towards partial to full dry process flowsheets.The commercialisation pathway has confirmed the broad performance range and energy consumption of the GRolls® which could be modularised in the near future to support new and existing low grade mining operations in remote areas restricted by limited water and power infrastructure.

DEM analysis of wear evolution and its effect on the operation of a lab-scale HPGR mill

Wear due to compression and abrasion from particles is a critical issue for high pressure grinding rolls (HPGR) mills. Understanding the evolution of wear provides useful insight on its mechanisms and helps to mitigate the issue so mills are operated at their optimal states. This work presented numerical simulations based on the discrete element method (DEM) to analyse the formation and evolution of wear of a lab-scale HPGR mill and to investigate how wear affects mill performance and particle breakage. By coupling the DEM model with the Archard wear model and surface re-meshing, the simulated wear patterns were comparable with those observed in practice, showing a parabolic wear profile wear along the rolls with more severe wear in the centre. In addition, the rear part of the stud, compared with the middle and front parts, experienced more significant wear due to the combined effect of compression and abrasion. While increasing wear had no visible effect on throughput, it reduced mill power draw due to weaker compressive force from the rolls to particles. Furthermore, analysis on particle breakage showed that increasing wear reduced particle breakage and produced coarser products. Increasing wear also caused less damage to particles, suggesting more cycles are required to achieve targeted products.

Influence of magnetite concentrate morphology on oxidation and sintering rates of pellet during induration

This study investigates the influence of the morphology of concentrate on the oxidation and sintering rates of magnetite pellets during induration and its impact on the indurated pellets' quality. Various morphologies of concentrates were obtained by ball milling (BM) and high-pressure grinding rolls (HPGR). Pelletizing and induration processes were carried out at different temperatures and times. After a comparative study of the physical characteristics of concentrate powders, the effect of morphology was evaluated through thermal behavior during induration. The physical, microstructural, and strength properties of pellets were also investigated. The HPGR concentrate had angular and elongated-shaped particles with a broad particle size distribution, while the BM particles had a more rounded morphology, and their size distribution was narrower. Results showed that BM and HPGR magnetite pellets are oxidized between 270 and 950 °C. HPGR pellets oxidize slower than BM pellets. Cold compressive strength (CCS) was increased by induration time, although porosity was reduced. HPGR pellets had less porosity than BM pellets; however, their CCS was significantly higher. For pellets indurated at 1200 °C, the difference in CCS between HPGR and BM pellets increased with an increment in the induration time and reached 80 kg/pellet in 20 min. The microstructural analysis took place on the concentrate powder and pellets fracture surface. It was found that HPGR powder sinters faster than BM powder due to its angular shape and broad particle size distribution.

Online prediction of pressing iron ore concentrates in an industrial HPGR. Part 2: Digital assistant

Besides the recent advances in high-pressure grinding rolls (HPGR) technology, the good track record demonstrates the potential growth in its applications in the future. In this regard, challenges are emerging driven by technology improvements and the increasing demand for a proper understanding of the operation and optimization of the grinding process in different scenarios. To fill this gap, new dynamic modeling and simulation approaches have been evolving to capture information of the process in real-time using online tools. However, proper application of these models as online digital assistants is still missing. The present work applies the online modeling approach proposed by the authors in the first part of this series as a digital assistant. The digital assistant receives real-time information of an industrial-scale HPGR pressing of iron ore concentrates and uses the Modified Torres and Casali model to predict the main HPGR performance variables. At first, a quantitative description of the HPGR hydro-pneumatic pressurizing system is calibrated and validated describing the relationship between hydraulic pressure and gap in the industrial machine. Feasibility of applying the online model as a digital assistant was demonstrated from two simulation case studies by providing setpoints of hydraulic pressure based on real-time changes in HPGR feed BSA, with the aim of reducing the variabilities of the HPGR product BSA and absorbing a coarser feed BSA.

Enhancement of the quality of marketable iron ore products of Kryvyi Rih iron ore basin

The main indicators of the iron ore quality are the content of iron, silica, phosphorus and other components. It is ascertained that the quality of ore depends on its grain-size composition. The article proves that when crushing 16-0 mm fraction ore to 5-0 mm, Fe content is reclassified by sizes due to liberation of both martite and hematite at this grain size. To reduce energy consumption during grinding, it is recommended to install high pressure grinding rolls for crushing the 16-1 mm fraction and consider this operation as the first stage of grinding. Martite liberation in the -1.0+0.0 mm material shows that significant predominance (87.0 vs. 13.0%) of free grains over aggregates is observed in the -0.071+0.05 mm fraction material. Free martite aggregates make 57.12% in the -0.16+0.071 mm material. Complete (100%) liberation of martite is observed in the -0.05 mm material. Sieve analysis of the A56 sinter ore sample crushed to 5-0 mm in the industrial roll crusher enables ascertaining that the greatest increase in recovery (Fetot = 60.05%) of sinter ore occurs at the -0.16+0.071 mm grain size.

An Energy Efficient Advanced Comminution Process to Treat Low-Grade Ferrochrome Slag Using High-Pressure Grinding Rolls

The present research aims to analyze the comminution behavior of ferrochrome slag using high-pressure grinding rolls. The laboratory bench scale high-pressure grinding rolls were used to study the three significant variables on the grinding efficiency of ferrochrome slag. The Central Composite Design was used to study the process variables, such as roll gap, applied load, and roller speed. The grinding efficiency was evaluated based on the product size and the energy consumption. The results showed that the increased gap between the rolls and roller speed decreases the product size with increased energy consumption. The results also found that an increase in applied load decreases the product fineness with increased energy consumption. The models were developed for the responses of P80 (size of 80% mass finer) and Ecs (specific energy consumption). Both the responses show high regression coefficients, thus ensuring adequate models with the experimental data. The minimum values of the P80 size and specific energy were determined using quadratic programming. The optimum values of the roll gap applied load and roll speed were found to be 1.43 mm, 16 kN, and 800 Rpm, respectively. The minimum values of P80 and the specific energy consumption were found to be 1264 µm and 0.56 kWh/t, respectively.

Understanding the mechanism of microcrack-enhanced bioleaching of copper

Investigations on the microcrack distribution characteristics and bioleaching behaviors of particles were conducted to obtain better bioleaching efficiency and deepen the mechanism understanding. Results indicate that comminution by high-pressure grinding roll (HPGR) is the desirable method for obtaining particles with more abundant and wider microcracks. Fixing the HPGR pressure at 4 MPa results in the highest bioleaching efficiency for copper extraction, namely 86% for the shaking flask bioleaching (particle size: <1.7 mm) and 52% for the column bioleaching of particles (particle size: 3.35–6.7 mm). The suggested model for reaction kinetics of microcrack-containing particles implies that more abundant and wider microcracks can promote the exposure of both Cu-containing phases and ferrous iron as well as solution infiltration, as evidenced by the COMSOL simulation results and bacteria proliferation analysis. The results highlight the importance of microcracks for enhancing the bioleaching process and provide insights for the mechanism understanding.

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.

Comparing economic model predictive control to basic and advanced regulatory control on a simulated high-pressure grinding rolls, ball mill, and flotation circuit

Mineral processing plants remain nowadays infamous for their low energy efficiency. Economic model predictive control (EMPC), by directly considering the energy costs, could possibly help reduce their footprint, but its environmental benefits are yet to be clearly quantified. In an attempt to cast some light on this topic, this paper compares the response to a given ore feed size and hardness disturbance sequence of an EMPC to that of basic and advanced regulatory control systems using the profits and the specific energy (power draw/ore feed rate) as metrics. The simulated circuit comprises a high-pressure grinding rolls (HPGR), a ball mill, and a flotation circuit. It is based on population balance modeling and is an extension of previous works. The basic regulatory control (BRC) system comprises only single-input–single-output control loops with proportional–integral (PI) controllers and operates at a fixed feed rate. The advanced regulatory control (ARC) system consists of PI controllers maximizing the plant feed rate with override constraint handling. The results show that (1) ARC generates more revenue and maintains a lower circuit specific energy consumption than BRC, (2) ARC can produce the same economic performance as EMPC because the constraints of the system define the economic optimum, and (3) EMPC can trade revenues for a lower circuit specific energy with a hybrid criterion that penalizes power draw.

A Hybrid PBM-DEM Model of High-Pressure Grinding Rolls Applied to Iron Ore Pellet Feed Pressing

Mathematical models of high-pressure grinding rolls (HPGR) have attracted great attention, owing to their role in optimization of operating machines as well as in the design and selection of new ones. Although population balance models (PBM) and the discrete element method (DEM) have been used in this task, both suffer from important limitations. Whereas PBMs have challenges associated to the prediction of operating gap and to the validity of several of its assumptions in different formulations in the literature, application of DEM has its own challenges, in particular when fed with distributions containing large amounts of fines. This work proposes a hybrid approach in which the coupling of DEM to particle replacement models and multibody dynamics is used to predict operating gap, throughput and power, as well as providing information along the rolls length that is used in PBM to predict the product fineness. The hybrid approach is then compared to both DEM and a PBM (Modified Torres and Casali), demonstrating similar results to the later when applied to simulating a pilot-scale machine operating under different conditions, but improved prediction when applied in scale-up to an industrial-scale HPGR.

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&ndash;nickel ore and one type of apatite&ndash;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.