Comminution Circuits Research Articles

The wear pattern in high pressure grinding rolls

ABSTRACTThe use of high pressure grinding rolls (HPGR) is growing in iron ore processing. Because of the high technology of this kind of crusher, optimum utilization requires a thorough understanding of the effect of parameters on their operation. An important factor for consideration in the operation of these crushers is wear. Failure to control wear, in addition to incurring heavy costs, decreases the efficiency of the machine and, subsequently, the efficiency of the comminution circuit. Hence, it is necessary to control the wear rate of rolls by readjusting the machine. In this study, the wear of HPGR rolls in the fourth line of concentrate production at the Golgohar Mining and Industrial Company, Iran, was investigated. The wear rate at different times was measured and the wear pattern was determined. The pattern was concave and the wear on the centre part of the rolls was greater than that at the edges. The wear rate on the tyre surface was higher than on the stud surface. Solutions for maintaining the efficiency of the HPGR due to wear have been proposed.

Optimizing Performance of SABC Comminution Circuit of the Wushan Porphyry Copper Mine—A Practical Approach

This research is focused on the Phase I SABC milling circuit of the Wushan porphyry copper mine. Improvements to the existing circuit were targeted without any significant alterations to existing equipment or the SABC circuit. JKSimMet simulations were used to test various operating and design conditions to improve the comminution process. Modifications to the SABC comminution circuit included an increase in the SAG mill ball charge from 8% to 10% v/v; an increase in the mill ball charge from 23% v/v to 27% v/v; an increase in the maximum operating power draw in the ball mill to 5800 kW; the replacement of the HP Series pebble crusher with a TC84 crusher; and the addition of a pebble bin. Following these improvements, an increase in circuit throughput, a reduction in energy consumption, and an increase in profitability were obtained.

Process development testing for comminution circuit design

Metallurgical process development in greenfield projects must define the comminution flowsheet and establish the equipment sizes that are required to deliver the project design criteria. These are critical steps that heavily influence the financial performance of the project, requiring a detailed understanding of the ore properties of the project resources and the best practice methods to size comminution machines. This paper reviews current practices for determining the ore characteristics relevant to comminution circuit design. Particular attention is given to the design of sampling and testing programs, and the methods commonly applied to size crushers and mills for conventional size reduction applications in mineral processing.

Limitation of HPGR application

Many researchers have discussed the advantages of the pressure breakage mechanism and the importance of high-pressure grinding rolls (HPGR) in the hard minerals industry but the impact of this machine on the final product of the comminution circuit at an industrial scale has been less studied. In this research, the influence of HPGR utilisation on the comminution circuit of the 4th line of the iron ore concentrator at the Golgohar Mining and Industrial Complex, Iran, was investigated. Two series of experiments were carried out: the first was performed with the HPGR in the circuit (ON) while the other was conducted with the HPGR out of the circuit (OFF). The results show that the HPGR had no significant effect on the final product of the comminution circuit from the point of view of particle size. The trommel screen overflow rate decreased by 5.1% of the fresh feed rate when the HPGR was ON. To determine the probable reasons, X-ray computed tomography analyses were carried out. These showed that cracks in the particles entering the grinding circuit were caused not only by the HPGR since some small cracks were present in the HPGR feed. It was also found that coarse particles are more susceptible to failure in the HPGR and that soft materials, such as talc, reduce the HPGR performance.

Comminution circuits for compact itabirites

In the beneficiation of compact Itabirites, crushing and grinding account for major operational and capital costs. As such, the study and development of comminution circuits have a fundamental importance for feasibility and optimization of compact Itabirite beneficiation. This work makes a comparison between comminution circuits for compact Itabirites from the Iron Quadrangle. The circuits developed are: a crushing and ball mill circuit (CB), a SAG mill and ball mill circuit (SAB) and a single stage SAG mill circuit (SSSAG). For the SAB circuit, the use of pebble crushing is analyzed (SABC). An industrial circuit for 25 million tons of run of mine was developed for each route from tests on a pilot scale (grinding) and industrial scale. The energy consumption obtained for grinding in the pilot tests was compared with that reported by Donda and Bond. The SSSAG route had the lowest energy consumption, 11.8kWh/t and the SAB route had the highest energy consumption, 15.8kWh/t. The CB and SABC routes had a similar energy consumption of 14.4 kWh/t and 14.5 kWh/t respectively.

Towards dynamical profit optimization of comminution circuits

There is an increasing demand to optimize performance and profit of comminution circuits. Research in this area has resulted in the development of numerous optimization tools, and recent research has shown that the quality aspects of the production have a great influence on the optimization results. The quality, cost, profit and capacity of a product are influenced by several parameters, and in order to control all of these parameters it is necessary to use some sort of optimization algorithm. In this paper, a novel approach to apply e.g. cost, revenue, capacity and quality in order to perform a multi objective optimization with the ability to handle dynamic variations of a comminution is presented. The problem with optimizations in general is that the objective function used for optimization is reduced in complexity in order to save computational time. In a comminution process performance varies with time and in order to perform a correct optimization the objective function used must be able to handle this type of dynamic behavior. The process has a given set of constraints that represents the conditions normal in these type of comminution applications. The first step in this paper is to identify if the range of the constraints can cause undesirable production costs when reaching for a given product property. In this step a dynamic response model is described that will be able to address the difficulties with optimizing dynamic systems. The next step in the optimization is the definition of the multi-objective optimization formulation including constraints for the optimization. Evaluating the result of the optimization in combination with a strategy for relaxing constraint can show how to increase overall productivity and still reach certain product properties. The conclusions made in this work are that multi objective optimization is essential when optimizing a comminution circuit against multiple objectives.

Unlocking additional value by optimising comminution strategies to process Grade Engineering® streams

Grade Engineering® comprises a range of techniques aiming to reject low grade uneconomic material (preconcentration) as early as possible within the mining value chain. It has been identified as an effective and feasible operating strategy whereby mining unit metal productivity can be significantly increased. Two Grade Engineering (G.E) levers have been assessed in a copper porphyry deposit: preferential grade by size response, and differential blasting for grade. Those are exploited through a modified blasting fragmentation coupled with screening based process on run-of-mine material to recover upgraded undersize fractions. Application of G.E inevitably alters comminution circuit typical feed particle size distributions, and consequently impact semi-autogenous (SAG) milling performance. A factorial design approach has been employed to assess the extent of this effect. A wide range of different operating scenarios, representing the possible G.E strategies and dynamic processing rock attributes, were simultaneously assessed using the Integrated Extraction Simulator (IES), a new cloud-based process simulator. This enabled the development of a G.E throughput improvement model as function of blasting fragmentation, impact hardness (Axb) and grindability (BMWi), which can be employed to conduct more detailed process modelling as well as resource optimisation.Improvements up to 14% in throughput due to changes in mill feed particle size distributions were observed under the conditions examined. The impact of this effect upon the proportion of material that is amenable to G.E is also discussed.

Study on the Selection of Comminution Circuits for a Magnetite Ore in Eastern Hebei, China

Standard drop weight, SMC, and Bond ball work index tests have been conducted to investigate the comminution circuit of a magnetite ore located in Eastern Hebei, China. In addition, simulations based on JKSimMet and Morrell models have been performed to compare the specific energy consumption of various comminution circuits. According to the desired capacity and the ore communition characteristics observed, a simulation was conducted to determine the size and driving power of the grinding mills. The SMC and Bond ball work index experiments as well as the Morrell model indicated that the order of the specific energy consumption of comminution was “Jaw crusher + HPGR mill + ball mill” < “Jaw crusher + ball mill”< “SAG mill + ball mill”.

A Modular Dynamic Simulation Model for Comminution Circuits

Abstract: Properly controlling comminution circuits is generally acknowledged to be highly profitable for any mining site’s bottom line. On the other hand, the process control problem of comminution circuits is challenging due to circulating loads and non-linear transport/transformation rates. As the performance and robustness of the control system highly rely on a good understanding of the process dynamics, characterizing the deterministic behavior requires a certain level of operation disruption (bump tests). For a grinding circuit, it implies affecting the throughput and product size distributions. The management team can be reluctant to risk obvious consequences on downstream processing stages i.e. inadequate mineral liberation, reduction of product quality, and perhaps even recovery losses. Process simulation becomes in this case an attractive tool to design, assess, and pre-commission advanced control strategies. This paper presents a phenomenological dynamic simulator for comminution circuits developed in Matlab/Simulink®. The block model programming allows changing plant layout or control loops easily, and is flexible for future extensions or model upgrades as any block can be simply added to the library or replaced with its updated version. The flexibility of the modular approach allows testing any control system, from basic PID loops to advanced control schemes. A simulation case study shows how the simulation model can capture the behavior of an actual circuit once properly calibrated.

Plant-wide control of grinding mill circuits: Top-down analysis

A generic top-down control structure is proposed for the optimal steady-state operation of a grinding mill circuit. The economic cost function of the grinding mill circuit is defined with reference to the final product of the larger mineral processing plant. A mineral processing plant in this study consists of a comminution and a separation circuit. The comminution circuit’s operational performance primarily depends on the mill’s performance. Since grindcurves define the operational performance range of a mill, the grindcurves are used to define the setpoints for the economic controlled variables for optimal steady-state operation. For a given metal price, processing cost, and transportation cost, the proposed structure can be used to define the optimal operating region of a grinding mill circuit for the best economic return of the mineral processing plant.

Microdiamond analysis - a method for estimating the size frequency distribution of the macrodiamonds

��69*3<3 Estimating the size frequency distribution of the macrodiamonds on a new deposit is important for both economic reasons and for the design of the processing plant. Millions of dollars can be lost due to incorrectly sized comminution circuits. This report analyses an alternative methodology for macrodiamond grade estimation using the cumulative results from small parcels of microdiamonds and plotting them on a log-log scale. The method was first evaluated mathematically for diamond populations to assess the confidence for data extrapolation. Macrodiamond size distributions and grades were predicted using microdiamond data from three kimberlites, and the actual macrodiamond grades compared to the the predicted grades. The predicted grades were found to replicate the actual grades closely, showing that a high degree of confidence can be ascribed to the results from this method of analysis. This analysis can be used both for resource estimates and for predicting the diamond size distribution information needed for designing a new operation.

Simulation and Optimization of the SABC Comminution Circuit

Simulation and Optimization of the SABC Comminution Circuit

Analysis of the criticality of flaws found in trunnion of grinding ball mills used in mining plants

Abstract The grinding ball mills are equipments present in mining plants, being important in the ore comminution circuits. Depending on numerous factors, such as, for example, inappropriate design, manufacturing, overloads, poor maintenance and inadequate operating procedures, flaws are developed in the structural components of this equipment. The structural components of a mill, basically, shell, heads and trunnions, besides high costs, have lead times that might reach three years, according to market demand. Therefore, it becomes increasingly necessary that any flaws in those components to be properly evaluated. This paper analyzed the fracture mechanics of flaws, such as cracks observed in a ball mill trunnion and compared the theoretical values of growth rate of these defects with actual values obtained through periodic inspections performed in this component. The cracks nucleation was caused by lack of lubrication in the trunnion bearings, generating circumferential thermal stresses, thus the estimated temperature of the trunnion and bushing contact achieved 150 °C. The lack of lubrication was originated by a logic failure which allowed the mill to start and run over the trunnion bearing bushing without the lubrication system to be turned on, that is, without oil film. The logic failure was caused by an operator fault. During the analyzed period, the results obtained by the standard BS7910 proved to be closest to the actual values than the standard ASME, Section XI, Appendix A.

Simulation-Assisted Evaluation of Grinding Circuit Flowsheet Design Alternatives: Aghdarreh Gold Ore Processing Plant / Ocena Alternatywnych Schematów Technologicznych Procesu Rozdrabniania W Zakładach Przeróbki Rud Złota W Aghdarreh, Z Wykorzystaniem Metod Symulacji

Abstract The run of mine ore from Aghdarreh gold mine must be comminuted to achieve the desired degree of liberation of gold particles. Currently, comminution circuits include a single-stage crushing using a jaw crusher and a single-stage grinding using a Semi-Autogenous Grinding (SAG) mill in closed circuit with a hydrocyclone package. The gold extraction is done by leaching process using cyanidation method through a series of stirred tanks. In this research, an optimization study of Aghdarreh plant grinding circuit performance was done to lower the product particle size (P80) from 70 μm to approximately 40 μm by maintaining current throughput using modeling and simulation approach. After two sampling campaigns from grinding circuit, particle size distribution data were balanced using NorBal software. The first and second data sets obtained from the two sampling campaigns were used to calibrate necessary models and validate them prior to performing simulation trials using MODSIM software. Computer simulations were performed to assess performance of two proposed new circuit flowsheets. The first proposed flowsheet consists of existing SAG mill circuit and a new proposed ball mill in closed circuit with a new second hydrocyclone package. The second proposed flowsheet consists of existing SAG mill circuit followed by a new proposed ball mill in closed circuit with the existing hydrocyclone package. In all simulations, SAGT, CYCL and MILL models were selected to simulate SAG mill, Hydrocyclone packages and ball mill units. SAGT and MILL models both are based on population balance model of grinding process. CYCL model is based on Plitt’s empirical model of classification process in hydrocyclone units. It was shown that P80 can be reduced to about 40 μm and 42 μm for the first and second proposed circuits, respectively. Based on capital and operational costs, it can be concluded that the second proposed circuit is a more suitable option for plant grinding flowsheet modification.

Modelling SAG milling power and specific energy consumption including the feed percentage of intermediate size particles

Comminution, particularly milling, is on average the largest consumer of energy in mining. Actual comminution circuits consist in most of the cases in coarse crushing, SAG milling, pebble crushing and secondary ball milling. In these circuits the SAG mill is the largest energy consumer. In many engineering projects either a power equation and/or a specific energy equation are used for the designing of these mills but not always with acceptable results. In general these equations are used to predict power consumption as a function of mill size, level and density of the internal charge and % of critical speed. Almost none of these equations (with the notable exception of the Morrell’s model) consider explicitly the effect that the feed particle size has on the mill performance, particularly on the power and on the specific energy consumption of the mill. To address this fact new models are developed in this work able to predict power or specific energy consumption, including the usual design variables, but adding a variable that represents the feed size distribution. Operational data from 4 grinding circuits corresponding to 3 Chilean copper concentration plants are used and the % −6″ +1″ (−152 +25mm) is selected as independent variable. The results indicate that both models are able to estimate the required variables for all data sets. In the first model (power equation) the average error obtained was 3.7% and in the second model (specific energy) the average error was 6.8%. These models would be useful for performance optimisation of the test case mills and should be fitted (parameters values) again for other mills.

Size specific energy (SSE)—Energy required to generate minus 75 micron material

This paper explores the relationship between energy and the generation of minus 75 micron material. Rittinger's law of comminution states that the energy input is proportional to the generation of new surface area. An accurate and consistent measurement of surface area, applicable across multiple size ranges, is required to apply this practically. The amount of new −75μm material generated has previously been proposed as a proxy for surface area. This has been demonstrated to some extent on a range of different laboratory equipment, but not in a manner suited to equipment-independent ore characterisation. To this end the JK Rotary Breakage Tester (JKRBT) and Schönert breakage device have been used to measure the progressive production of fines from cumulative single impacts starting with 37.5mm particles down to 250μm. As per expectation, the generation of −75μm material was found to be proportional to the specific energy, but there was a secondary influence of size. A model was developed to describe the breakage and it was found that the standard t10 relationship could be used to effectively calculate the size specific energy. Measuring the intrinsic competence of an ore in this way can then be used to assess the energy efficiency of full-scale mills in relation to a lab scale test. It is envisaged that this relationship also has the potential to be used in the design of new comminution circuits. The methodology and the results from its application are presented for discussion and review.

A semi-mechanistic model of hydrocyclones — Developed from industrial data and inputs from CFD

The flow behavior in hydrocyclones is extremely complex, leading the designers to rely on empirical equations for predicting cyclone performance. A number of classifying cyclone models have been developed and used in mineral comminution circuit simulators in the past. The problem with these empirical cyclone models is that they cannot be used outside the range of conditions under which they were developed. A semi-mechanistic hydrocyclone model is developed using the dimensionless approach based on both the fluid mechanics concepts from Computational Fluid Dynamics (CFD) simulations and the wide range of industrial cyclone performance data. The improved model consist a set of equations for the water split to underflow (Rf), reduced cut-size (d50c), throughput (Q) and sharpness of the separation (α). The model for Rf, d50c, Q gives a very good fit to the data. The alpha model shows reasonable correlation for the cyclone design and operating conditions. Additional data sets were used to validate the new hydrocyclone model by comparing the predictions of the model equations with the experimental results.

An Efficient and Simple Multiple Criteria Model for a Grinding Circuit Selection Based on MOORA Method

The comminution process, particularly grinding, is very important in the mineral processing industry. Some characteristics of ore particles, which occur as a product of grinding process, have a significant impact on the effects of further ore processing. At the same time, this process requires a significant amount of energy which significantly affects the overall processing costs. Therefore, in this paper, we propose new multiple criteria decision making model, based on the Ratio system part of the MOORA method, which should enable an efficient selection of the adequate comminution circuit design.

A FRAMEWORK FOR COMMINUTION CIRCUITS DESIGN EVALUATION USING GREY COMPROMISE PROGRAMMING

Comminution process, particularly grinding, is very important in the mineral processing industry. Some characteristics of ore particles, which occur as a product of grinding process, have a significant impact on the effects of further ore processing. At the same time, this process requires a significant amount of energy and also significantly affects the overall processing costs. Therefore, in this paper, we propose new multiple criteria decision making model based on grey compromise programming for adequate comminution circuit design selection. Although it is based on a simple procedure, we consider that the proposed model is efficient and flexible, and that it also represents the basis for forming more sophisticated models for comminution circuit design selection, as in addition, many other decision making problems in business environment, which is characterized by predictions and uncertainty.

Effects of tramp grinding steel and iron fines on comminution, flotation and cyanidation

Comminution circuits are widely used in nonferrous and precious metals milling. Steel crushers, grinding mills and grinding media are typically used in comminution circuits. Comminution circuit wear products, in the form of metallic iron (steel) fines, are unavoidably produced and report to undersize products in the classification circuit, i.e., flotation or leach feed, while tramp grinding steel (TGS) reports to classification oversize products and returns to the grinding mill, building up in the circulating load. In laboratory studies, TGS reduced grinding efficiency significantly, the impact being dependent upon the size of the TGS present in the mill. Because iron fines adsorb flotation reagents effectively, iron fines increase reagent consumption and reduce flotation recovery. Iron fines are also capable of reducing gold recovery in cyanidation circuits via a cementation reaction. When using filtered gold solution from the cyanidation circuit of an Alaskan gold mine, the gold concentration in solution was reduced by 0.2 to 2.6% over various reaction periods when iron fines were present in the solution.