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Grinding Mill Operation and Maintenance - Central to Asset Management Since 2005, RME has pursued a vision for a new grinding plant operational paradigm, made possible by RME's latest Mill Relining Systems. At some sites, new liners degrade SAG mill performance. The variables include mill volume loss, rotational speed limitations (ball strike) and liner designs developed for longer and longer life but without a backward glance at metallurgical consequences of whole plant performance. Freshly relined mills can initially deliver as little as 80 per cent of their maximum throughput, that maximum occurring toward the end of the liners' wear life. RME's proposition is to see new liners designed for maximum commercial performance. This may mean more frequent mill relines but with liners designed to yield optimum grinding, metallurgical and profitability performance, not maximum life. In other words, mill liner profiles and relining speed become key profitability contributors and not simply 'must do' maintenance functions and costs. This paper includes a short history of RME's Mill Relining System development (Appendix A). These are the enabling technologies which permit more frequent liner exchange without incurring additional downtime imposts. The body of this paper outlines RME's vision of a 'liner profile vs. profitability' commercial model, underpinned by the rigour of PAS 55-1:2008 Asset Management Part 1: Specification for the optimised management of physical assets. The technical elements can be developed either intuitively (based on plant experience) or by using a combination of new measurement and modelling technologies. These new measurement and modelling tools provide the opportunity to predict the optimum technical solution for the maximum commercial outcome. Much of this can be modelled off-line, in the virtual world, before asking senior management to commit to an expensive liner experiment. The potential benefits are compelling.

Sep 13, 2010

By S. McTavish

Since mechanically suitable grinding mills were available in 1908, mill operators have been searching for the best material and design with which to line the mills. These liner systems had to fulfill several criteria. First and foremost they had to last long enough in an operating mill to protect the mill structure from the abrasive wear of the ore and the grinding media. In addition they had to be able to efficiently transfer the energy from the mill to the mill charge in order to facilitate the grinding process. The liners also had to be easily attached to the mill when new and removed from the mill when worn out. The first liners used were generally made of cast white iron, Hadfield manganese, unalloyed high carbon steel and composites of steel and concrete or cemented in flint blocks or natural stone. 1

Jan 1, 1989

By N. Arbiter, C. C. Harris

The economic advantages of large diameter ball mills can be compromised by unexpected capacity limiting conditions. These arise because media rotational flow to ore axial flow ratios, and the number of mill revolutions that ore is subjected to during residence, are both inversely proportional to mill diameter. Because of this, mixing efficiency and grinding kinetics may decrease and become capacity limiting when mill diameters reach a critical range. There are two possible scale-up problems involved in the design and use of mineral processing machinery: • Selecting the size and operating conditions for available larger equipment, to insure that operating results will match those obtained with smaller units; or •Extending the size ranges of equipment beyond existing limits. Previous research at Columbia University into flotation machine hydrodynamics has demonstrated the importance in scale-up of internal flow relationships; these perform a similar role in grinding (Arbiter and Harris, 1980).

Jan 1, 1982

By C. G. McLachlan

Laboratory flotation tests carried out on massive sulphide ores may not be reproduced in plant practice, and when this occurs the discrepancy can be the result of differences between laboratory and plant grinding. Results of parallel flotation tests are given to support this contention, and data show how tailing losses are affected in corresponding size zones.

Jan 4, 1951

By J. George Gregr

"This paper gives a brief review of grinding mills installation procedures with special emphasis on future maintenance. The importance of cooperation between the customer, construction contractor and manufacturer's representative is discussed, as well as the imparlance of complying with standards, specifications and the keeping comprehensive installation records.Fundamentals of mill maintenance are explained with the aim being to maximize the equipment availability and to minimize unscheduled downtime. The paper also includes development of wear items design, based on operating conditions, drive components and bearings, and how to keep large gears healthy thus eliminating surprise failures.Experience with installation of a large gear on a 34-foot diameter mill in Lornex and successful application of a computer program for the gear alignment on the mill are given.IntroductionSuccessful operation of a concentrator begins with the engineering of the project and continues through selecting the right equipment, its installation , start-up period, and ends with final tuning of the process. machinery and the human factor into an efficient and viable industrial complex.The following is a brief review of grinding mill installation procedures with special emphasis on future maintenance. Fundamentals of mill maintenance are discussed with the aim being to maximize the equipment availability and to minimize unscheduled downtime, with some specific points on key grinding mill components such as bearings and drives.Finally, the experience is recounted with the installation of a large ring gear on a 34-foot diameter mill at Lornex, and the successful application of a computer program for the gear alignment on the mill."

Jan 1, 1985

"The first 90 years of the last century generated a considerable volume of technical literature on the subject of grinding mill power and its prediction. It is therefore surprising that during this time there were no published models for predicting grinding mill power draw which were validated using a wide range of comprehensive industrial scale data.Notwithstanding this lack of data, the majority of models placed limited emphasis on the internal dynamics of mills and relied on simple assumptions which considered the charge to take up a fixed position and shape.Laboratory based studies (Liddell, 1986), and industrial data (Morrell, 1993), showed that these assumptions did not hold over a wide range of operating conditions, and brought into doubt the ability of the (then) existing models to accurately predict grinding mill power draw. Furthermore no model treated AG,SAG and ball mills as a single class of devices whose power draw could be predicted with the same equations.Through a detailed investigation of the charge dynamics, coupled with a large data base of industrial mill power draws, this situation was rectified by the end of the century, by which time a model had been developed and validated, which accurately predicted the power draw of all wet tumbling mills. This paper describes this model and reviews some of the earlier attempts at mill power modelling.INTRODUCTIONThe early 1900?s saw the beginnings of published papers which tackled the problem of what influenced the power draw of tumbling mills and what equations (models) were suitable for predicting power draw. This interest continued for the rest of the 20th century and the literature contains many papers that attempted to satisfactorily answer these questions. A common and disappointing theme in the majority of them, however, is the distinct lack of suitable experimentally derived power draw data. This deficiency consequently limited the practical application of many of the attempts at modelling mill power draw. Prior to the early 1990?s some limited data on the power draw of grinding mills in the literature can be found, but as Harris et al (1985) remarked they are ?... too frequently unusable simply because one or more essential variables have been omitted?. The absence of published results, from vigorous experimental testing of the various models, has resulted in a general lack of evaluation of the validity of assumptions and hypotheses that such models contain. Harris et al (1985) however, did make some efforts in attempting to evaluate the performance of various power prediction equations and in so doing further developed a semi-empirical one of their own. However, in using manufacturers? published data, which themselves were undoubtedly generated by proprietary equations of unproven validity, they probably succeeded in generating little more than a consensus of the various errors in these models."

Jan 1, 2003

"The first 90 years of the last century generated a considerable volume of technical literature on the subject of grinding mill power and its prediction. It is therefore surprising that during this time there were no published models for predicting grinding mill power draw which were validated using a wide range of comprehensive industrial scale data.Notwithstanding this lack of data, the majority of models placed limited emphasis on the internal dynamics of mills and relied on simple assumptions which considered the charge to take up a fixed position and shape.Laboratory based studies (Liddell, 1986), and industrial data (Morrell, 1993), showed that these assumptions did not hold over a wide range of operating conditions, and brought into doubt the ability of the (then) existing models to accurately predict grinding mill power draw. Furthermore no model treated AG,SAG and ball mills as a single class of devices whose power draw could be predicted with the same equations.Through a detailed investigation of the charge dynamics, coupled with a large data base of industrial mill power draws, this situation was rectified by the end of the century, by which time a model had been developed and validated, which accurately predicted the power draw of all wet tumbling mills. This paper describes this model and reviews some of the earlier attempts at mill power modelling."

Jan 1, 2003

By Rene Cane, V. I. Lakshmanan, John Starkey, Richard May

"The Agrium Kapuskasing Phosphate Operation mines and processes up to 6,000 t/d of phosphate ore. Run-of-mine crushing to minus 6 inches is done in a toothed roll-crusher, while grinding is done in a SAG/ball mill circuit with no coarse recycle classification of the SAG mill discharge. The primary grinding mill is an 18 ft. diameter x 9 ft. EGL, 1500 HP variable speed SAG mill and the secondary mill is a 13 ft. diameter x 21 ft. long, 2000 HP fixed speed, ball mill. When hard ore was treated, the SAG mill restricted the tonnage that could be ground. When soft ore was treated, the ball mill and spiral classifier overloaded and restricted throughput.Recommendations from a plant benchmark and an ore hardness testing program, on how to better utilize installed energy in the Agrium SAG mill when treating soft ore, and how to obtain best results when treating hard ore, were checked in a pilot plant investigation in the 3 ft. diameter Starkey-PRO Pilot SAG Mill. Correlation between the ore hardness testing and the results from the 3’ Pilot SAG mill was very good. In addition, the work indicated the results that could be expected for the different ore types when using either smaller SAG discharge grates and/or a vibrating screen with 10 mesh square opening cloth.INTRODUCTIONAgrium Kapuskasing Phosphate Operation consists of a 6800 t/d open pit mine and a concentrator, near the Town of Kapuskasing in Northern Ontario. The two major ore types are sandy ore and cemented ore. Sandy ore is fine, soft and easy to grind in the SAG mill while cemented ore is harder, more blocky and difficult to grind in the SAG mill. The ratio of sandy to cemented ore in the deposit is thought to be in the order of 80:20 but can range as high as 5050, so it was important for the grinding circuit to have the ability to treat sandy ore alone."

Jan 1, 2002

By C. H. Frick

BEFORE presenting the main topic, as indicated by the title, this paper will give some of the high-spot history of the anthracite industry. INTRODUCTION The earliest recorded use of anthracite was in the year 1762, when a company of Connecticut pioneers discovered anthracite near the present city of Wilkes-Barre, Pennsylvania. In the early days of the industry, the coal was used only in large pieces, the smaller pieces being discarded to waste piles. As the output of the industry increased during the nineteenth century, uses were developed for somewhat smaller sizes down to and including pea coal. Early in the twentieth century, sizes smaller than pea, such as No. I and No. 2 buckwheat, were developed and used. Accu¬mulations of piles from current mining operations were still increasing; that is, the smaller sizes were still being discarded. It was not until after World War I that preparation of the so-called steam sizes began commercially. This was largely No. 3 buckwheat, which is screened through a 3f 6-in. round-hole screen and over a 332-in. or a M 6-in. round-hole screen. USE OF SMALLER SIZES The earliest recorded experience in burning the small sizes of anthracite for steam production, other than in a previous small experiment, was in the year 1913, when a size known as "boiler fuel" was introduced-a mixture of rice and barley (No. 2 and No. 3 buckwheat). At that time, there was still no method known for burning the still smaller sizes. TABLE I.-Screen Sizes Used for Small Sizes of Anthracite [ ] At the present time, various sizes down to and including No. 5 buckwheat are being prepared (Table I) from current mining and bank-reclaiming operations. The sizes of No. 4 and No. 5 buckwheat and smaller are generally being used for steam production in large boilers. The Pennsylvania Power and Light Co., following World War I, used 680,000 tons of anthracite per year, burned largely on stokers for production of steam, whereas for the year 1943 it used 1,940,000 tons of stoker sizes and 400,000 tons of smaller sizes for grinding and burning in pulverized form. This company has taken a very large part in the research and development of ways and means of burning these smaller sizes of anthracite, including the grinding of the very small sizes. This paper is particularly concerned with the latter feature.

Jan 1, 1946

By D. W. Fuerstenau, G. S. Sudhir, P. C. Kapur

Quartz-limestone feed mixtures were ground in a laboratory-size, choke-fed, high- pressure roll mill. As compared to individually ground minerals, the harder component (quartz) in the product mixture is coarser, and the softer component (limestone) is finer. An energy split index is introduced for quantifying the disproportionate split of the mill energy between the feed constituents. This index is incorporated into a grinding kinetic model for simulation of the product size distributions of the mineral components as a function of energy input to the mill. The self-similar character of the size distributions is analyzed and an energy-size reduction relationship for the roll mill is highlighted.

Jan 1, 1992

By V. G. Cawagdan, E. M. Sacris

The performance of the grinding circuit, from the initial stages of operation to the present, is discussed. The mill efficiency as measured by the Bond (Bond and Maxson, 1943) grindability data and the operating work index is presented. The objective was to produce a sand cyclone overflow containing not more than 6% 210 µm (+ 65 mesh). This has never been attained, even at low milling rates. Significant improvements in throughput were achieved by instituting equipment changes and process modifications within the grinding circuit. Grind improvements were achieved with enlargement of cyclone spigots, grinding at reduced densities, and decreasing the opening of the ball mill discharge. Additional grinding capacity was realized by converting the concentrate regrinding mill into a secondary ball mill. The previous 20% 210 µm (+ 65 mesh) grind improved to under 15% 210 µm (+ 65 mesh). The latest approach to solving the coarse grind problem is also discussed.

Jan 1, 1985

By F. M. Lewis, J. E. Goodman

TENNESSEE Copper Co. operates two ore concentrators, the London and Isabella mill. Copperhill, Tenn. In 1948 and 1949 the small ball mills and rake classifiers in the London concentrator were replaced by one large ball mill and one hydraulic classifier. This new ball mill was designed oversize so that it could be operated at slower than normal speed. The proper operating conditions were established and the results published.1 Later it was found that this mill operated more efficiently with a small ball charge.2 While this London grinding practice was being developed, the Isabella grinding circuit was not changed in any way. It remained a conventional two-stage rod mill-ball mill combination, the rod mill in open circuit and the ball mill in closed circuit with a rake classifier. Study of the data indicated that grinding cost could be lowered by converting to the London practice, but not enough would have been saved to warrant the expense of converting. No plan for improving this grinding operation could be developed.

Jan 11, 1957

By G. A. Frame, J. G. Patterson

The 24,000-tpd Frood-Stobie mill grinding circuit operation and control are described. Changes implemented during the past three years to improve grinding efficiency and capacity are discussed.

Jan 1, 1971

By T. H. Yang, Q. K. Wang, T. Song, J. W. Zhou

The grinding circuit can be one of the most important mineral processing circuits in plants. Along with the application of large-scale milling machines, the design and optimisation of the operation strategy for grinding circuits is more complicated. An in-house grinding process simulation tool was developed to mass balance, model fit and simulate crushing, grinding and classification circuits. An industrial grinding and classification circuit in a copper mine was modelled, and the modelling parameters were verified by a particular group of plant survey data. To justify the prediction ability of the fitted models, the model predictions under different operation conditions were compared with another group of plant survey data. Then the model predicted the effects on the circuit of changing operating conditions. Circuit analysis of the comminution process for water feed to a SAG mill, water feed to sump, the rolling speed of a SAG mill and the percentage of ball filling in a SAG mill was put into practise, based on the simulation results. The simulation results can be used to help plant operators understand the features of the comminution process and may help to build a knowledge library for process control. Keywords: Process modelling, grinding, comminution, circuit analysis

Jan 1, 2020

By L. F. Moran

Rod Mill Grinding is an important and fundamental step of the concentrating process in Marcona Mining Company's plants at San Nicolas Bay, Peru. This Paper summarizes experience in regard to consumption and specifications of grinding rods based on twelve years operation of the grinding circuits. Marcona operates a Plant complex producing 10 million tons per year of beneficiated iron ore products including pellets, sinter feed concentrates, high grade concentrates as slurry and filter cake. Processing capacity is 15 million tons per crude ore per year of which 13 million are around in rod mills. A continuous testing program was carried out over the years. Initial studies of daily production operations gave indications of poor grinding rates in relation to mill size and power consumption, with a high rate of broken liners and rods. The broken nieces of rod were not automatically expelled and further interfered with grinding efficiency, while replacement of liners caused unwarranted do n tire. Objectives were to improve all phases of the Process by studying the effects of changes in rod diameter, length, alloy constituents, and volume and weight of rod charge.

Jan 1, 1975

By R. del Villar, A. R. Laplante

"This article presents four grinding simulation programs, written in Applesoft BASIC. The firs t two calculate residence time distributions (RT Ds) for open and closed loops mills. The third program calculates the select ion functions from the RTD, breakage function and particle size distribution (PSD) o f the feed and discharge. Two linear regression programs are also included to calculate the breakage function. These results are used in the fourth program to simulate continuous or batch grinding kinetics.The modelling approach presented is the size discrete, time continuous matrix formulation presented by Reid (1965) from concepts originally proposed by Epstein (1948). It is at the present time the most widely accepted phenomenological model of grinding kinetics and is standard textbook material (Austin et 01., 1982; Kelly and Spottiswood, 1982, p. 152). The concepts of RTDs and tracer testing originated from chemical engineering theory and practice, and are well presented in Leven spiel (2n d Ed . 1972 , Ch. 9) .Applesoft* was chosen because it is compatible with many micro computers. It is also one of the simplest and least powerful BASIC versions. Thus it can easily be adapted to other more complex BASIC versions.Open Loop Residence Time Distributions (Program RTDOPEN)As mixing, channelling, stagnation and short-circuiting all affect slurry motion in tumbling mills, transport characteristics are very complex an d cannot be derived from fundamental principles. Fortunately , as grinding follows first order kinetics, transport characteristics for the purpose of grinding simulation ca n be represented by the RTD of the slurry phase . It is normally determined using liquid tracers, as it has been demonstrated and is commonly accepted that in industrial ball mill s, the RTD of the so lid phase is particle size independent and equal to that of the liquid phase."

Jan 1, 1985

By Norbert Patzelt, Johann Knecht

Future ore reserves of major gold producers in North America and elsewhere will consist of refractory gold ores. About 60 % of the current U.S. gold production is mined in Nevada. Several of the large gold operations in this state indicate that 40 to 90 % of their future ore feeds will contain refractory gold. To com­pound problems, average head grades for refractory U.S. gold ores had fallen from 8 - 9 g/mt to about 4 g/mt by 1991. In Latin America, 52 % of the gold operations will require milling for optimal recovery. Deeper reserves are, like in North America, refractory. Therefore a special treatment process is needed in order to allow for the gold ore to be leached downstream in a conven­tional cyanidation process for a high gold recovery. There are several options available for this oxidation process like treat­ment of the gold bearing ore in pressure oxidation, in a biooxi­dation or in a roasting plant depending on the reason for the refractoriness. If organic carbonaceous matters and sulfides are the prima­ry reasons for the refractoriness, whole ore roasting is a pre­ferred method for the treatment of this type of ore. Since dry ore is to feed to the roaster, a dry grinding mill is advantageous. For the dry grinding system, the moisture content and the ore char­acteristic is of importance. Those parameters decide the mode of the grinding system. For autoclave systems common wet grind­ing systems can be applied. This paper deals with technical aspects for dry grinding plants and gives an outlook on and pos­sibilities for new grinding systems.

Jan 1, 1996

By Bernardo Siqueira

This paper presents a unique stirred milling technology, Outotec HIGmill™, a modern, flexible and energy efficient grinding solution for fine and ultra fine grinding being tested in an industrial scale level. The test was performed at an iron ore pellet producing plant in Sweden (for confidentiality reasons, it will be referred to only as “the client”) where a pilot HIGmill™ unit (HIG25) was installed parallel to a conventional regrind circuit to compare its performance to the existing ball mill. By using a continuous test run procedure and evaluating the parameters of F80, P80, mill shaft rotation speed and power drawn it was determined its grinding capabilities, operational flexibility and energy efficiency. Outotec HIGmill™ outperformed the existing ball mill in the plant proving its capabilities to grinding finer, with steeper particle size distribution (PSD) and much higher energy efficiency. The tests performed showed that, with further refining of its operation, it is capable of consistently deliver the required PSD with up to 30% higher grinding efficiency.

Aug 16, 2017

By Jack White

This paper gives details of the results of careful testing carried out on two types of ball mills, conical trunnion overflow and cylindrical grate discharge, on identical ore. The object of the test work was to determine which ball mill was the most economical to install for future extensions to the Mufulira concentrator.

Jan 1, 1950

By Jack White

This paper gives details of the results - of careful testing carried out on two types of ball mills, conical trunnion overflow and cylindrical grate discharge, on identical ore. The object of the test work was to determine which ball mill was the most economical to install for future extensions to the Mufulira concentrator.

Jan 1, 1950