Ore Comminution Research Articles

Influence of HPGR operation on the reduction of Bond’s working index of crushing product

Article concerns the issues of ore comminution in HPGR. A series of laboratory tests were carried out for three lithologic types of sulphide ore. Four values of operating pressing force were accepted. Bond’s index value, determined with using a standard Bond method, was also determined for all HPGR products. There were also determined functional relationships between Bond index and operational pressure. Results of investigation showed, that application oh HPGR for that type of feed resulted in lowering the value of Bond index. The relationship between the pressing force and Bond index can be approximated with hyperbolic function.

The effects of microwave irradiation on the floatability of chalcopyrite, pentlandite and pyrrhotite

Research into the application of microwave irradiation in the comminution of ores has made great progress in recent years, creating a demand to understand the effects of this technique on downstream processes, especially flotation. The present work investigated the floatability of untreated and microwave-treated chalcopyrite, pentlandite and pyrrhotite samples using potassium amyl xanthate and sodium oleate as collectors. The effects of the exposure time on each mineral’s recovery at different concentrations, pH and particle sizes were studied through microflotation, and the adsorption of the collectors was analyzed by electrophoretic zeta potential measurements. Microwave irradiation led to the decrease in the floatability of chalcopyrite and pyrrhotite in the presence of xanthate, at the pH values investigated, whereas no significant change was observed for pentlandite. The flotation of the microwave-treated minerals required greater sodium oleate concentration. The treated and non-treated pentlandite and pyrrhotite samples did not float at pH 10. Although the treated chalcopyrite and pentlandite displayed low recoveries at all pH values, the treated pyrrhotite displayed high floatability at acidic and neutral pH. The recovery of the microwave-treated sulphide minerals was more affected by the particle size in the tests with potassium amyl xanthate than with sodium oleate. The overall results presented by this work indicate potential conditions to achieve selectivity between the microwave-treated chalcopyrite, pentlandite and pyrrhotite.

Comparison of ore comminution technologies using SAG mill and roller-press for Udokan copper deposit ores

Comparison of ore comminution technologies using SAG mill and roller-press for Udokan copper deposit ores

Influence of Copper Ore Comminution in HPGR on Downstream Minerallurgical Processes

AbstractCrushing processes taking place in high-pressure grinding rolls devices (HPGR) are currently one of the most efficient methods of hard ore size reduction in terms of the energy consumption. The HPGR products are characterized by a fine particle size and the micro-cracks formation in individual particles, which appears in downstream grinding processes, decreasing their energy consumption. The purpose of the paper was to analyze the effectiveness of a ball mill grinding process and flotation operations depending on the changeable conditions of run of the HPGR crushing process. The research programme carried out included crushing tests in the laboratory scale HPGR device at various settings of the operating pressure volume and selected qualitative properties of the feed material (i.e. particle size distribution). On the basis of obtained results the models, defining the grinding process effectiveness as a function of changeable conditions of HPGR process run, were determined. Based on these models the optimal grinding time in a ball mill was specified which is, in turn, the basis for optimization of operation the technological comminution circuits for a given material type. The obtained results proved that the application of HPGR devices in given copper ore comminution circuit may improve the effectiveness of downstream grinding process what leads to improvement of the entire circuit work efficiency through decreasing the process energy consumption and enhancing the product size reduction.

Empirical Determination of the Effect of Lifter Wear in Mill Power for Dry Grinding

Grinding stage has one of the highest production costs in mining operations due to the intensive use of energy needed for the comminution process. Hence, any improvement in the energy use of this process will have an important impact on production costs. Paper presents the results of an extensive testing program to determine the effect of lifter wear on the power demanded by the grinding mill. Selected power–speed curves covering up to 110% of critical speed are reported. Using these results, a lifter wear factor is proposed to include this effect on the power demand expressions of grinding mills. Results show that for dry grinding, as the lifters wear, the power needed for a specific operating condition increases. Using these results, mill operators will have an important piece of information to set the best operating point for an efficient ore comminution and efficient energy consumption. It will also help to define the appropriate date for a liner change.

The efficiency of copper ore comminution: A thermodynamic exergy analysis

This study analyzes the exergy efficiency of comminution using a laboratory sized dry ball mill and a copper mineral ore from central Chile. In this research, we develop a minimum work index from uniaxial compression tests results on the ore fitted to Morrell’s comminution energy equation using Hukki’s constant mineral parameter. An exergy analysis is then performed on a laboratory sized dry ball mill by considering the surface energy variation for different ore sizes, the obtained Hukki-Morrell fitted relationship from the compression tests of the ore and the minimum inertial energy required during a dry-ball milling process. The theoretical minimum work needed to crush the rock is first calculated by comparing the difference in surface energy between the incoming ore and the outgoing crushed rock. However, this analysis (based on the creation of new surfaces) suggests an impractical low minimum work of little use as a benchmark. Instead, use of the Hukki-Morrell relationship evaluated at the resulting ore particle sizes suggests a practical benchmark. Using this benchmark for the laboratory’s dry ball mill process renders an efficiency of approximately 3%. One could use the heat from the outgoing crushed ore to, theoretically perform work, but the heat flows through at a low temperature that this change would only increase the efficiency to 3.1%. We also consider the inertial energy needed to drive the ball mill employing it as a new benchmark for our efficiency calculation. The latter raises the efficiency of the dry ball milling to an average 23%. Finally, electrical energy measurements and inertial calculations on operating an empty versus loaded ball mill suggest that the efficiency could be increased by ensuring correct machinery scaling (diameter of the drum shell), ball load and a properly maintained transmission system.

Erratum: Evaluation of HPGR and VRM for dry comminution of mineral ores (2016, vol. 52, no. 1, pp. 11-25)

Erratum: Evaluation of HPGR and VRM for dry comminution of mineral ores (2016, vol. 52, no. 1, pp. 11-25)

Study of the effect of ultrasonic treatment on mineral materials of different morphologies

Coal, iron and manganese ore samples were exposed to different ultrasonic intensities of 250, 300 and 350 W/L for five minutes and to an ultrosonic intensity of 270 W/L for different time durations of 3, 5 and 7 minutes. The ultrasonically treated samples showed reductions in D80 particle diameters of 6 percent for the coal samples, 5.95 percent for the iron ore samples and 35.63 percent for the manganese ore samples during grinding. The ultrasonic treatment was also observed to assist in reducing ash content in the coal product by 8 percent and to reduce manganese losses in rejects by about 5 percent. Ultrasonic treatment was concluded to be capable of assisting in the comminution of friable ores more prominently than the hard and porous materials.

Truths and misconceptions in the ore comminution

Inventions and now widely applied machines for ore comminution dated back to the second half of the 19th century. For the past 150 years, much theoretical knowledge was accumulated in the field of physics the solid bodies, physics of fracture, the theory of shock, etc., but they did not significantly affect the development of machines and technologies of comminution. Their development had a high­lighted the empirical flow in the direction of increasing the unit sizes and capacities, while the main deformation mechanisms and technological principles remained unchanged. Development on practical experiences and insufficient physical justified hypothesis of the solid state physics inevitably had to result in some misconceptions that, despite recent theoretical knowledge and proven facts, continue to exist in practice. This paper just wants to point out some of these misconceptions.

Evaluation of HPGR and VRM for dry comminution of mineral ores

The mining industry is searching for more energy efficient and dry comminution equipment as an alternative to conventional crushing followed by wet grinding circuits. This is a result of growing challenges associated with the increasing energy cost, scarcity of water resources and stricter environmental legislation. Dry comminution technologies, such as High Pressure Grinding Rolls (HPGR) and Vertical Roller Mills (VRM), have been successfully used in other industries such as cement and coal for decades, and the literature claims that these technologies are more energy efficient than conventional comminution practices. Pilot scale testing was conducted for each of these technologies using rock with properties similar to many mineral ores to test the claims in the literature and evaluate the applicability for hard rock mining operations. Whilst the test results for the HPGR and VRM are not directly comparable (due to different degree of size reduction), both demonstrated the potential for considerable energy savings compared to conventional ball milling. The HPGR and air classification circuit used 20 - 30 % less energy than the HGPR, screen, ball mill circuit. While VRM was estimated to use 10 - 30 % less energy (depending on the type of VRM) than a ball mill circuit for a similar degree of comminution.

Influence of type of lining in high-pressure grinding rolls on effectiveness of copper ore comminution

Comminution in a High-Pressure Grinding Rolls (HPGR) device is considered as one of the most efficient method to break particles, in terms of the energy utilization. Two main types of the rolls linings are applied in hard ore grinding: studded and hexagonal, which show varied characteristics of operation and have different lifetime of service. The article concerns the analysis of HPGR device operation for various linings of the rolls. Two pilot-scale test programmes were run and performance of both types of rolls was tested in terms of energy consumption, technological effects measured by means of comminution ratio, lifetime service as well as economic aspects. Results of investigation show, that much longer lifetime service was obtained for the studded rolls, while hexagonal ones are more favourable from economic scope. The feed material for the HPGR comminution tests was Polish copper ore from two divisions of processing plants of KGHM Polska Miedz S.A. Taking into account that industrial comminution operations in mining and mineral processing sector consume over 50% of total energy utilized for ore treatment operations, the problem is of a major significance, especially in terms of optimization of hard ore crushing and grinding circuits.

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.

Testing of Ore Comminution Behavior in the Geometallurgical Context—A Review

Comminution tests are an important element in the proper design of ore beneficiation plants. In the past, test work has been conducted for particular representative reference samples. Within geometallurgy the entire ore body is explored in order to further identify the variation within the resource and to establish spatial geometallurgical domains that show the differential response to mineral processing. Setting up a geometallurgical program for an ore deposit requires extensive test work. Methods for testing the comminution behavior must therefore be more efficient in terms of time and cost but also with respect to sample requirements. The integration of the test method into the geometallurgical modeling framework is also important. This paper provides an overview of standard comminution test methods used for the investigation of ore comminution behavior and evaluates their applicability and potential in the geometallurgical context.

Research of iron ore grinding in a vertical-roller-mill

The total energy consumption for ore comminution will further increase within the next decades. One contribution to minimise the increase is to use more efficient comminution equipment. Vertical-roller-mills (VRM) are an energy-efficient alternative to conventional grinding technology. One reason is the dry in-bed grinding principle. Results of extensive test works with two types of magnetite iron ores in a Loesche VRM are presented here. Within these test works, mill parameters like grinding pressure, separator speed and dam ring height were varied, following a factorial design of the experiments. The effects of the grinding parameters on the liberation of valuable minerals are characterised using mineral liberation analysis (MLA). It is shown how the different mill parameters influence important performance values like energy consumption, production rate and mineral liberation. Via multiple regression analysis, an optimal parameter range can be modelled for both ore types. The parameter predictions have been successfully verified in practical test works.

Benchmarking comminution energy consumption for the processing of copper and gold ores

A survey of the comminution energy requirements of gold and copper producing mines has been conducted to provide reliable benchmarking data which can be used to compare comminution energy consumption across different mine sites. The total gold and copper production of the mines included in the study equated to 15% and 24% respectively of global production and all of Australian production. The comminution energy per unit metal product has been presented in a graphical form similar to a cost curve. This simple technique allows individual mines to be ranked with respect to energy consumption and clearly displays the potential energy and cost benefits of moving down the graph into more efficient operating regimes. Assuming similar specific energy requirements for other sites, comminution of gold and copper ores can be expected to consume about 0.2% of global, and 1.3% of Australia’s electricity consumption. Efforts to reduce this figure should be aimed at the top third of consumers as they are responsible for 80% of the total consumption. Analysis of the contribution of circuit efficiency, ore competence, grind size and ore grade showed that ore grade was the greatest determinate of specific comminution energy. Therefore, concentrating the ore via gangue rejection or grade engineering prior to grinding is likely to achieve the largest positive effect on comminution energy efficiency.

MODELAMIENTO MATEMÁTICO APLICADO A CONMINUCIÓN

El modelamiento matemático aplicado a equipos destinados en el proceso de conminución de minerales (chancado, molienda), suelen ser herramientas tan importantes para llegar a simular y luego optimizar procesos metalúrgicos continuos (a nivel industrial); vale decir llegar a predecir el producto granulométrico de un cierto mineral tratado, conociendo tan solo lo del alimento (simulación). Obviamente el modelo almacenará intrínsecamente, inherentemente las características físicas del mineral (dureza, fractura) y operativas del equipo (abertura- CSS).Consiguiendo de esta manera mejorar el rendimiento del equipo en cuestión y que ciertamente contribuirá en la buena repercusión en los procesos posteriores del tratamiento del mineral.

Grade control based on economic ore/waste classification functions and stochastic simulations: examples, comparisons and applications

Grade control and ore/waste delineation in open pit mining operations was traditionally based on the comparison of estimated grades with an economic cutoff. In the 1990s, an alternative approach to ore selection was applied and established, taking into account financial indicators through the so-called economic classification functions in combination with grade uncertainty assessment. Grade uncertainty is assessed using multiple grade realisations from geostatistical or stochastic simulations. Ore/waste selection integrates and is supported by the evaluation of economic consequences of sending a block of mined material to a processing facility or to the waste dump, and the related asymmetric financial implications.The benefits and practical implications of this efficient alternative framework are best illustrated by comparing the performance of three economic functions when combined with three commonly used stochastic simulation methods under different conditions. The latter conditions include a sparse and a dense blasthole sampling patterns and three cutoff grades. A general observation is that the minimum loss classification function combined with the indicator sequential simulation presents the most consistently better performing combination. This observation is reinforced in an application at a gold mine where the above combination outperforms the already well reconciling conventional grade control approach of the mine. The extension of the framework of economic functions to account for geometallurgical properties follows. This extension shows the integration of ore and waste grindability, a key aspect of ore comminution. Finding shows the improvements that could be made over current best practice when grindability is considered, and suggests how other geometallurgical attributes may be further integrated into grade control, as long as economic classification functions and orebody uncertainty models are considered.

A developed approach based on grinding time to determine ore comminution properties

In this paper, iron ore sample from the Chadormalu was investigated to determine some comminution properties. Chadormalu deposit is one of the largest iron ore mine in Iran, which is located in Yazd province. The representative ore sample contained 57%Fe, 0.9%P and 0.17%S. The sample was crushed; afterward, it was ground in various grinding times according to the Bond Ball mill approach to specify the work index values. Based on different grinding times and the obtained results, a new work index equation was then simulated through which grinding time was considered as the main variable. The relationships between work index, the work input and P80 were then concluded. In addition, the results of tests were then used to estimate the selection function parameter. A new equation was applied to determine energy efficiency which could be implemented for energy consumption calculation. Two equations for EB and EB/Elimit were then obtained, where EB is the efficiency of comminution, and the ELimit is the maximum limiting energy efficiency for particle fracture under compressive loading. These equations could estimate the parameters of the iron ore would be precisely estimated. Indeed, by means of work index value; some crushing and grinding characteristics of the taken sample were assessed by which comminution circuit would be designed much better.

MATHEMATICAL MODELS OF PARTICLE SIZE DISTRIBUTION IN SIMULATION ANALYSIS OF HIGH-PRESSURE GRINDING ROLL OPERATIONS

The high-pressure grinding roll (HPGR) technology is currently one of the most efficient methods of hard ore comminution from the scope of the energy consumption. Throughput and energetic models of performance are quite well developed, but technological models predicting the comminution effects still needs an in-depth research. In the paper author presents the method of modeling of HPGR products' particle size distribution by using suitable mathematical models. A basis of the HPGR perfor- mance assessment and HPGR-based crushing circuits design is a product's particle size distribution. In order to precisely determine the particle size distribution of a HPGR product, parameters of product's particle size distributions should be conditional on the main technical parameters of the roller press like operating pressure and the speed of rolls. The most accurate approximation of a distribution of size parti- cle appears to be Weibull's truncated distribution and it is possible to obtain significant relationships between the approximation formula and the value of operating pressure, or feed characteristics. It makes possible a determination of mass recoveries of the product's respective size fractions and the productivity planning. Instead of pressure, the other HPGR operating parameters can be applied, but the pressure value appears to produce the most relevant relationship. A determination of HPGR product's particle size dis- tribution is a basis of the press operation simulation analysis.

Optimizing The Performance Of High-Pressure Grinding Roll Based Ore Enrichment Circuits / Optymalizacja Pracy Układów Przeróbki Mechanicznej Rud Opartych Na Wysokociśnieniowych Prasach Walcowych

This article concerns the issues of modeling and the optimizational approach for the performance of ore comminution circuits. A typical, multi-stage comminution circuit was analyzed with the high-pressure grinding rolls unit operating at a fine crushing stage. The final product of the circuit under investigation was, at the same time, a flotation feed in which particle size distribution initially determined the effectiveness of flotation operations. In order to determine the HPGR-based comminution circuit performance, a suitable mathematical model was built wherein the target function was linked directly with the effectiveness of the flotation processes. The target function in the presented model considers the issue in terms of the flotation operation’s effectiveness. The particle size distribution of individual comminution products and resulting from the weight recoveries of individual size fractions were criteria determining the quality of the comminution product. Weight recoveries of individual size fractions, in turn, were tied with the technical operating parameters of individual comminution devices. In the first model, profit maximization was the target function, while the second variant of the model took into account maximization of the useful mineral weight recovery in the concentrate. The HPGR application into ore processing circuits also results in energy saving benefits which were presented in a comparative analysis of the energy consumption of two comminution circuits - the first based on conventional crushing devices, and the second on the HPGR unit application which replaced the rod mills. The main benefit of such a modernization was almost two times lower energy consumption by the fine crushing stage and a decrease in the ball mills’ grinding operations load through bypassing a part of the material directly for the rough flotation operations.