Autogenous Mills Research Articles

Heterarchical modelling of comminution for rotary mills: part II—particle crushing with segregation and mixing

In granular media, the crushing of individual particles is influenced by the number of contacts with neighbouring particles. This well-known phenomenon of “cushioning” shields the individual particles from crushing when the number of contacts is high. However, in open systems that involve extensive granular flow and bulk motion, like those found in industrial mills, the neighbouring particles continually exchange positions due to segregation and mixing, thereby altering the number of neighbouring contacts and their sizes, affecting the crushing of individual particles. Therefore, a critical challenge for properly modelling comminution in such systems lies in tracking the fluxes of the various particle size classes. Here, we explore the physics that governs the mechanisms of segregation and mixing within the multiscale heterarchical modelling paradigm. Building upon the framework developed in Part I, which integrated the heterarchical aspects of the physics of crushing along streamlines, we further account for segregation and mixing, and demonstrate their impact on the comminution efficiency of autogenous grinding mills. In particular, segregation is shown to greatly enhance the extent of particle crushing within the mill. Accordingly, we posit that this mechanism cannot be ignored. In summary, the new model sheds light on previously obscured dynamics within industrial mills, as well as enables the field to predict the time evolution of the particle size distribution at any point in the mill domain. This modelling capability opens the doors to new developments for estimating and improving milling efficiencies.Graphical

Heterarchical modelling of comminution for rotary mills: part I—particle crushing along streamlines

Rotary mills aim to effectively reduce the size of particles through a process called comminution. Modelling comminution in rotary mills is a challenging task due to substantial material deformation and the intricate interplay of particle kinematics of segregation, mixing, crushing, and abrasion. Existing particle-based simulations tend to provide predictions that cannot cope with the large number of particles within rotary mills, their wide range of sizes, and the physics dictating the crushing of individual particles. Similarly, there is currently no deterministic modelling means to determine the evolving population of particle sizes at any point in time and space within the mill. The aim of this two-part contribution is to address these gaps by advancing a framework for a novel stochastic comminution model for rotary mills, which has a well-defined deterministic continuum limit and can cope with arbitrarily large numbers of particles. This work describes the basic physics and structure of the new model within a heterarchical framework for ball and autogenous grinding mills. The primary focus of this Part I paper is to develop a computational model for the integration of motion of material along streamlines inside a mill. Coupled to this process is the kinetic physics dictating particle crushing. In a subsequent work, Part II, segregation and mixing will be added to this model such that realistic behaviour from the mill can be observed.Graphical

Polygenic gold mineralization in quartz-pebble formations on the Takyr-Kaljir site of the Southern Altai, East Kazakhstan Region

Purpose. The research purpose is to study the forms of gold occurrence in the Takyr graben alluvial-proluvial deposits in order to develop a low-waste resource-saving processing technology. Methods. At the first stage, in the course of field studies, the geological structure of the site is specified, samples are taken for mineralogical-technological analysis, which includes the following procedures: studying granulometric and mineral composition of detrital material; fractional gravitational beneficiation of the source material; fractional beneficiation of material pre-processed in the autogenous mill (AG mill); studying free (native) and bound gold in beneficiation products, their quantitative assessment. The samples are processed under the three-stage scheme using an autogenous mill for sample preparation. Findings. For the first time, the geological structure of the site has been specified with the identification of the deposits in the Turangi and Tuzkabak suites within its boundaries, as well as granulometric and petrographic composition of gold-bearing deposits, and the specifics of gold bearing. The detrital material, represented by quartz with a sharply subordinate amount of quartzite, quartz diorites and jasperoids, is practically identical in all fractions. Originality. For the first time, various types of gold mineralization have been identified in placer sands: clastogenic, newly-formed hypergene, newly-formed hydrothermal and residual. Fractional beneficiation makes it possible to estimate the gold content in each fraction and gravitational beneficiation products, as well as the ratio of free and bound native gold in different fractions. The largest amount of free native gold has been revealed in fractions of -0.25 + 0.1 mm (60%) and -0.074 + 0.044 mm (~40%). Gold is high-grade (96.5%) with an admixture of silver and iron. Together with gold, ilmenite, zircon, scheelite, native bismuth, as well as barite, galena, sphalerite, and dolomite have been identified. Practical implications. The research results make it possible to reassess the prospects of similar objects, to adjust the scheme and methodology for processing stream-sediment samples, to solve the issues of productive sand processing technology, as well as to improve the efficiency of geological exploration and eliminate the “underestimation” of gold deposits. The results obtained can be recommended for implementation by both domestic and foreign organizations specializing in the exploration and mining of gold deposits.

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.

АНАЛИЗ ЭНЕРГЕТИЧЕСКИХ ХАРАКТЕРИСТИК ОТДЕЛЕНИЯ ИЗМЕЛЬЧЕНИЯ ОБОГАТИТЕЛЬНОЙ ФАБРИКИ

For processing plants of mining and processing plants, an important and urgent issue is a comprehensive analysis of the energy characteristics of the most energy-intensive equipment. Such an analysis is necessary to identify the potential for energy savings and reduce energy costs per product cost. In the presented work, on the basis of data on the power consumption of a large processing plant, an analysis of the energy characteristics of autogenous grinding mills was carried out. Based on the data on the power consumption of the processing plant departments, statistical estimates were obtained: average (estimation of the mathematical expectation); standard (unbiased estimate of standard deviation). The technological process of grinding separation is given, the regime map of the technological process of the self-grinding body is shown. The utilization factors for active power, the forms of the load schedule, the filling of the load schedule are determined. The dynamics of change in the power value during the hours of the evening maximum of the power system over the decades of the month under study is given...

Integrated analysis of electric energy demand of autogenous grinding mills at concentration factories

Integrated analysis of electric energy demand of autogenous grinding mills at concentration factories

Self-adjusting filling control system forself-grinding drum mills

Purpose of work isan improvement of the controlling efficiency for the processes of self-grinding ores in drum mills by using adaptive settings for the perimeters of the control part of the system. Methodology. For the self-grinding process, the degree of filling of the mill drum is a critical technological variable, i.e. this parameter not only has a direct impact on the efficiency of the grinding unit in terms of the newly formed finished product, but also determines the trouble-free operation of the mill.It is known from the referenced literature that during thedecay time of the autocorrelation function for the processes of original ore’s main characteristics change is on the order of several hours or more. At the same time, the inertia of the crushed aggregate is measured in tens of minutes. Under such conditions, one should assume that quasi-stationarity and the rational use of the control system for a wide scope of self-grinding take place. Research results. Using the method of auxiliary operators, the law for setting the parameters of the main circuit of the self-adjusting system was generated, and the block diagrams of the adaptive control system for filling ore self-grinding mills were determined. The transient processes in the control system are calculated, which proves the expediency and effectiveness of the proposed approach. Scientific novelty. A new approach is proposed using an adaptive control system to regulate the degree of filling of autogenous ores mills, based on the use of the method of auxiliary operators. Practical significance. While calculating the tuning processes in the control system for the filling degree of the mill, it was found that even with a simultaneous abrupt change in the object’s parameters K0,T1,T2to the maximum value, the adaptive system completes tuning the parameters of the controllerC1, C2, C3 for a time of about 230 ÷ 270 minutes, which indicates the practical feasibility and effectiveness of this approach to control the filling level of ore self-grinding mills.

Investigation of the effects of rock dynamic hardness on the energy consumption in the crushing unit, case study: Midouk copper mine

ABSTRACT The mounted semi autogenous (SAG) mill in the processing unit of the Midouk copper mine which consumes 35% of operational costs has a critical size within the range of 2.5–5 cm. To optimize the energy consumption in the milling unit of the mine, the data have been collected from 36 blast blocks. These blocks are selected in the main ore body area to monitor their effects on energy consumption in the milling unit. Owing to the dependence of mill energy consumption on the feed strength properties, a criterion for mill performance (MPC) has been defined and compared with the obtained dynamic hardness of seven specific blasting blocks. The results show a linear relationship with the accuracy of R 2 = 0.91 between the dynamic hardness and the MPC. For mines that use SAG or AG mills, the energy consumption for crushing the unit weight of feed depends on their dynamic stiffness.

Current status in the copper ore processing (review)

The article provides the analysis of process flows used for sulfide and oxidized copper ore treatment, reagent schemes, process equipment, indicators of flotation concentration at a number of domestic and foreign concentrating mills and plants. Autogenous and semi-autogenous grinding mills are widely used at the ore preparatory processing at the first stage of grinding to eliminate medium and fine crushing stages. An alternative is the use of high pressure grinding rolls that can reduce electricity consumption as compared to autogenous and semi-autogenous grinding. There is an increase in the use of large-volume and high-performance ore-preparation and flotation equipment for maintaining the quality and quantity of the product. In addition to ball mills, fine and ultrafine regrinding mills of various configurations are widely used at the stage of rougher flotation concentrate regrinding. The analysis of flotation reagents used to improve separation process efficiency was conducted with domestic and foreign approaches to flotation reagent selection shown. It is noted that foreign concentrating mills often use a combination of main and additional collectors. The paper provides the data on flotation reagents used in the copper sulfide and oxidized ore concentration, and their consumption. A combined diagram of flotation-hydrometallurgical processing of mixed copper ore from the Udokan deposit is considered. Conclusions are drawn about current trends in the processing of copper ores including the choice of equipment.

Autogenous grinding mill process control practices

This paper considers pre-requisite conditions for developing grinding mill control systems and describes the main problems of control and existing constraints. The author selected a set of grinding equipment that consists of autogenous grinding mills and ball mills. The paper considers the selected mill types as control objects. It is shown that there exists a good correlation between the mill charge and its acoustic and vibration noise. The paper examines the relationship between the level of vibroacoustic noise and the mill motor power draw and defines what can be considered an extreme dependence, as well as the conditions in which a stable operation of the automatic system can be maintained excluding the mill overload mode. The paper specifies what hardware and software means would be necessary to implement such system and describes the mill charge analyzer VAZM-1M developed by Soyuztsvetmetavtomatika that was selected for this application. The author looks at certain downsides typical of the conventional control scheme when the head mill feed rate changes as the mill motor power draw changes without allowing for changing physical and mechanical properties of the ore material. The author also considers the capability of the VAZM-1M analyzer in terms of mill load estimation accuracy. This laid the basis for developing mill protection and optimization algorithms for the AG and Ball Mill comminution circuit. The paper features a block diagram of the control algorithm and its brief description. The algorithm consists of blocks, which are responsible for the following actions: they receive key process parameters from the process control system database, check them for validity, perform initial processing and filtering; after that they analyze the trends of the measured parameters and analyze if an overload condition is probable. As decided by the mill operator, the ore flow rate can be adjusted. The paper describes a case study of running an AG mill control system on the basis of the above described algorithm and using the VAZM-1M analyzer. It is noted that this algorithm can be implemented both as an adviser for the operator and for automatic control of the mill when running in overload mode.

Comparing strategies for grinding itabirite iron ores in autogenous and semi-autogenous pilot-scale mills

High grade iron ore resources are becoming depleted in Brazil, with relatively low-grade ores requiring more intensive comminution for proper liberation of iron minerals, followed by upgrading. Comminution circuits that have been frequently used in the Brazilian iron ore industry in preparation of high-grade iron ores consist of multiple crushing stages followed by ball milling and are known for being highly complex and capital-intensive installations. This work assesses the potential suitability of autogenous (AG) and semi-autogenous (SAG) milling through an extensive pilot plant campaign carried out with itabirite iron ores. The effects of ore type, feed size distribution, circuit configuration (open or closed-circuit and two-stage or single-stage), mode of grinding (AG or SAG), ball load, use of pebble crushing as well as of full secondary pre-crushing have been investigated. The results demonstrate both the technical feasibility and energy efficiency of such an alternative for itabirite comminution circuits.

The performance improvement of a full-scale autogenous mill by setting the feed ore properties

The feed ore properties can seriously affect the success of autogenous (AG) mill operation in terms of many criteria such as production rate, product quality and energy consumption, since the grinding media in an AG mill derive from the feed ore itself. In this research, the feed ore properties including hardness and particle size distribution was applied in order to improve the AG mill operation. In the regard of particle size distribution, the amount of materials coarser than 200 mm in the feed of a full-scale AG mill was increased by direct addition large lumps of ore (200–500 mm). Accordingly, the mill power consumption decreased from 8.4 to 5.16 kWh/t (a nearly 40% reduction), and the fresh feed flow rate increased from 515 to 615 t/h (a nearly 20% increase in the mill throughput) by increasing the amount of materials coarser than 200 mm in the AG mill feed from less than 10 wt% to about 30 wt%. In the regard of feed ore hardness, the blending of two hard and soft iron ores was performed at various blend ratios. Tracking the mill performance showed that the mill power consumption decreased from 9.49 to 6.63 kWh/t (a nearly 30% reduction), P80 of the mill product decreased from 611 to 355 μm, and the mill fresh feed flow rate increased from 511 to 521 t/h by decreasing the feed ore hardness from 112 min to 58 min based on SAG power index (SPI). Finally, a model was developed for the prediction of mill power consumption.

Modeling and optimization of complex ore pretreatment by disintegration in autogenous mills

Modeling and optimization of complex ore pretreatment by disintegration in autogenous mills

АНАЛИЗ ВЛИЯНИЯ КИНЕМАТИЧЕСКОГО НЕСООТВЕТСТВИЯ ВЕТВЕЙ ЗАМКНУТОГО КОНТУРА НА УДЕЛЬНУЮ ЭНЕРГОЁМКОСТЬ В МЕЛЬНИЦЕ СИСТЕМЫ «МКАД»

The necessity of improving technological operations in the processing of mineral raw materials and the use of energy-efficient grinding equipment is substantiated. The technical and technological benefits of vertical dynamic autogenous grinding mills are given. They are based on a method of self-grinding of the material, which allows to reduce the specific energy consumption. The technical advantages of the MKAD system mills, the structural schemes of which have an indifferent group are explained. Since the mills of this system additionally use so-called “circulating” energy, depending on the degree of deformation of the drive motor shaft, it is necessary to study the effect of kinematic mismatch of closed-circuit branches on the specific energy consumption of grinding. The graphic dependences of kinematic discrepancy effect on the specific energy consumption of grinding in the MKAD system mills are presented.

Dynamic modeling and simulation of a SAG mill-pebble crusher circuit by controlling crusher operational parameters

A semi-autogenous (SAG) or autogenous mills (AG) circuit commonly comprises a pebble (cone) crusher to deal with the critical size particles. The pebbles crusher is often oversized, and thus not fully utilized. The hypothesis put forward in this paper is that active control of the cone crusher’s eccentric speed and closed side setting (CSS) can increase throughput and/or energy efficiency of the SAG circuit. To verify this hypothesis, a dynamic model of a SAG mill-pebble crusher circuit was implemented. The dynamic unit models are based on results presented by several different researchers, whose results here have been combined and implemented in Matlab/Simulink.Previous research shows that by controlling the cone crusher operational parameters, the product particle size distribution (PSD) can be altered during operation. However, few papers have been published about whether the changes of the pebbles crusher’s product PSD, lead to a higher performance of the SAG circuit. This paper examines the relations between the SAG mill and the pebble crusher in closed circuit while putting emphasis on controlling the pebble crusher in order to optimize the circuit throughput.

Predicting the Operating States of Grinding Circuits by Use of Recurrence Texture Analysis of Time Series Data

Grinding circuits typically contribute disproportionately to the overall cost of ore beneficiation and their optimal operation is therefore of critical importance in the cost-effective operation of mineral processing plants. This can be challenging, as these circuits can also exhibit complex, nonlinear behavior that can be difficult to model. In this paper, it is shown that key time series variables of grinding circuits can be recast into sets of descriptor variables that can be used in advanced modelling and control of the mill. Two real-world case studies are considered. In the first, it is shown that the controller states of an autogenous mill can be identified from the load measurements of the mill by using a support vector machine and the abovementioned descriptor variables as predictors. In the second case study, it is shown that power and temperature measurements in a horizontally stirred mill can be used for online estimation of the particle size of the mill product.

Evolution of AG mill shell liner design at Gol-E-Gohar concentration plant

Liner design is becoming an increasingly more important tool for the AG/SAG mill performance optimization. The Gol-E-Gohar iron ore concentration plant uses three 9 m × 2.05 m autogenous mills (AG) in parallel in a dry operation. Due to large variations in feed characteristics and inadequate blending, the performance of AG mills has been lower than the target value. In order to increase the circuit throughput while maintaining the desired product size, based upon physical and numerical simulations, it was proposed to convert the AG mills to SAG mills. Simulation of the charge trajectory indicated that increasing the liner lifter face angle from 7 to 30° could provide an appropriate charge trajectory in the SAG mode. Installation of the new liners and conversion of AG mill No. 2 to SAG mill, by adding 5% (v/v) balls, resulted in an overall increase of 31% in throughput (from 419 to 548 t/h). Measurement of the wear profiles of shell liners indicated that the wear along the liner length was not uniform. In order to arrive at a uniform wear profile, a new liner design was proposed. Installing the second liner design in AG mill No. 1 and converting it to SAG mill increased the mill throughput by 18% (from 413 to 489 t/h), while the liner life showed a 7% increase. Measurement of the wear profiles of the second liner set indicate that the maximum wear occurs in the centre of the mill. A new liner design was then designed by increasing the width of the lifter top from 12.5 to 15 cm and increasing the lifter height from 16 to 26 cm to enhance the liner life.

Analytical solution for the dynamic model of tumbling mills

Optimisation of grinding circuits is invariably dependent on sound process models together with process simulators that can solve the process models accurately. Most of the process models are solved numerically because analytical solutions are not available, which can lead to errors in the results due to the numerical approximation of mathematical equations. Whiten [1], and Valery Jnr & Morrell [2,3] have developed a dynamic model with numerical simulation for autogenous and semi-autogenous mills, and validated the model with dynamic response of mills in terms of power draw, grinding charge level, slurry level and product size distribution to changes in feed rate, feed size, feed hardness and water addition [2,3]. In this work, an analytical solution for their dynamic model of tumbling mills has been developed based on the knowledge of solutions to the first-order nonhomogeneous linear differential equations. Two algorithms, Direct Single Time method (DST) and Direct Multiple Time method (DMT), were applied to obtain the analytical solutions respectively. It was found that analytical solutions are more accurate than the traditional finite difference numerical methods. However, the DST analytical method has a drawback of numerical instability due to the accumulation of round-off errors which are amplified by exponential functions, whilst the DMT method can provide stable solutions. To test the DMT analytical method, two cases of SAG mill dynamic operation were studied with both the traditional numerical method and the newly developed analytical method, further proving the robustness and feasibility of the analytical solutions.

An experimental study on the relation between input variables and output quality of a new concrete recycling process

Enormous amount of Construction and Demolition Waste (CDW) are yearly generated in Europe and the predominant material constituent is concrete. Despite the urgency of creating a sustainable solution for End Of Life (EOL) concrete waste treatment, there has not been a large driving force for recycling it into prime grade materials. The C2CA concrete recycling process aims at a cost effective system approach to recycle EOL concrete to hardened cement and clean aggregates. This recycling process consists of a combination of smart demolition, gentle grinding of the crushed concrete in an autogenous mill, and a novel dry classification technology called Advanced Dry Recovery (ADR) to remove the fines. The main factors in the C2CA process which may influence the properties of Recycled Aggregates (RA) or Recycled Aggregate Concrete (RAC) include the type of Parent Concrete (PC), the intensity of autogenous milling (changing the amount of shear and compression inside of a mill) and the ADR cut-size point (usage of +2mm or +4mm RA in the new concrete). This study aims to investigate the influence of implied factors on the quality of the RA and RAC. To conduct the study, first of all, three types of concrete which are mostly demanded in the Dutch market were cast as PC and their fresh and hardened properties were tested. After nearly one year curing, PC samples were recycled independently varying the type of PC and intensity of the autogenous milling. Experimental variables resulted in the production of eight types of RA. The physical, mechanical and durability properties of the produced RA were tested and the effect of the experimental variables on their properties were investigated. According to the results, the type of PC is a prevailing parameter for the final properties of RA, in comparison with the milling intensity. Moreover, it is observed that a variation in the milling intensity mostly influences the properties of RA produced from a lower strength PC. Furthermore, the performance of the RA in the new concrete was studied. Four types of RAC were produced based on the modified recipe of their corresponding PCs. For the modification of the recipes, water absorption and density of RA were taken into account while the amount of applied cement and consistency class was kept similar to the corresponding PC. Experimental results show that the RAC samples compare favourably with PC. Among various autogenous milling intensities, milling at medium shear and compression delivers better properties for RA and RAC. Good performance of RAC with the incorporation of 2–4mm ADR fines and RA, confirms the possibility of setting ADR cut-size point on 2mm.

Dynamic image analysis of differently milled talc particles and comparison by various methods

ABSTRACTIn this study, particle shapes of talc mineral ground by various types of mills were determined using automated dynamic image analyzer by counting averagely 19,000 particles for each mill product. The results were expressed in terms of circularity (C) and bounding rectangle aspect ratio (BRAR). It was concluded that particles created by rod mill had the highest BRAR and the lowest C, while the particles having the highest C and the lowest BRAR were obtained by autogenous milling. The statistical significance of mean shape values of different milled particles was also tested by using one way analysis of variance (ANOVA) and post hoc Tukey test. The ANOVA results showed that there are significant differences among C and BRAR mean values of particles produced by autogenous, ball, and rod mill at 99% level of confidence. The results were in good agreement with the results obtained by other techniques employed previously. Thus, the result of dynamic image analysis (DIA) can be used for quality control of the products of talc mineral as the morphology decides whether specific talc is appropriate for a specific application or not.