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By G Johnson, S Michalek, N Redman

As the modification of the 2009 Mill OperatorsÆ Conference theme from æmilling through the boomÆ to æthe boom û experience gained and lessons learnedÆ exemplifies, comminution practitioners are facing a series of challenges in the dramatically changing mining environment. One of the main problems plant managers have been facing during the boom times has been the severe metallurgy skills shortage and high staff turnover, both factors that can cause difficulties in mill liner management. Many of todayÆs mill managers are now also more than ever faced with the need for cost-cutting in order to continue operating viably. Amongst other potential target outcomes such as maximised throughput, MillMapperÖ, a tool for mill condition monitoring and mill performance optimisation, can be utilised to address these issues. This paper demonstrates how MillMapperÆs quantifying decision making tools can serve to be in control of managing mill liner and production issues, and how it can form the basis for mill cost savings without the risks normally associated with conventional methods or the lack of using any condition monitoring methods. MillMapperÖ is currently being referred to at a rate of approximately 150 surveys and associated reports per annum at processing plants in Australasia, South America and Africa. Examples throughout the paper provide insight into how the presented sample set of users have extracted benefits that could have otherwise not been safely or at all achieved.

Jan 1, 2009

By R. S. Rickard

Chemical processing of ores has gained new im¬petus in recent years. The reasons are many. They range from the need to process ores that are difficult to beneficiate to the avoidance of pollution. Although many think of chemical processing as a hydrometallurgical operation there are other techniques. An example is chlorination. Chlorination, although examined and discarded by many investigators, is again being considered as a means of extracting uranium1, treatment of silver-lead ores2, and the recovery of base metals from pyrite cinder and ores3. Segregation roasting of copper and nickel ores, a process similar to chlorination, is another chemical treatment being revived.

Jan 1, 1970

By Ivan Caetano Machado

Good morning ladies and gentleman. During 1995 Prof. R. P. King (University of Utah Comminution Center) presented 2 papers on new horizons in comminution: "Comminution Research in the United States " was presented at the 1995 Meeting of the National Mining Association, while "Comminution: Meeting the Needs of Fundamental Research in the Mineral Industry" was presented at the 2nd SME Research Forum - 1995. In both papers a very interesting graph named "Energy usage for various comminution schemes" illustrated some poignant issues proposed by Prof. King. We do think that some of Prof. King's ideas might very well serve as "warm-ups" for this Comminution Panel Discussion, which are ultimately the goals to be reached by the 3-minute presentations. Thus, we shall be addressing in the sequence Prof. King's most relevant ideas (as well as introducing his graph), intending therefore show how important creative and state-of-the-art Mill Modeling is, if it is to become a Tool to Effective Cost-Saving Optimization Strategies.

Jan 1, 1996

By E A. Gunn, J Zhou

In this paper a project to develop a joint optimisation/simulation model for production planning in a mine-mill complex is presented. The system involves a mill receiving ore from a number of different locations, each with a unique mineral composition. The mill consists of several crushing and grinding circuits that function in series and parallel. Scheduling the flow of materials through the mill is complex due to constraints on throughput imposed by the millÆs design, the length of time material can be stockpiled on the surface, varying input mineral composition, and throughput targets for a range of output products.An optimisation model is used to create a set of campaigns (ore feed rates) over a given planning horizon under the assumption of deterministic mill throughput. A simulation model is used to evaluate the production plan under assumptions of stochastic machine failure and operational losses created by the need to cycle between input feeds. Campaign scheduling has two important implications for the simulation. First, during any campaign, multiple ore types may need to flow through the mill. However, the mill must be controlled to ensure that only one type of ore can be in a crusher, a grinder or a storage bin at any point in time. Second, as the mill switches from one campaign to another, the set of ores being processed may differ. Thus, the flow of ore through the equipment during a campaign changeover must be controlled to ensure that one or more of the ores from the current campaign can be completely eliminated before the ores from the new campaign are introduced.The simulation architecture employed for this project is Visual Basic for Applications (VBA) combined with MS-Excel as a user interface. A fixed step discrete event orientation is assumed as the simulation framework. A set of model constructs was built for the project with a specific Canadian milling operation in mind, but was designed to be representative of a broad class of milling operations. The constructs are implemented as class objects within the VBA structure, each with a number of properties and methods. The collection of VBA objects forms a composable modelling toolkit. These objects can be linked together by users, via MS-Excel, to represent a broad range of milling operations.

Sep 26, 2011

By L. S. Urbanoski

This presentation describes a major modernization project at the Geco concentrator. The objectives of the program were to replace obsolete flotation equipment and upgrade process controls.Noranda Minerals Inc. — Gecc Division is located at Manitouwadge in Northern Ontario. The community is situated north of Lake Superior approximately equidistant from Thunder Bay and Sault Ste. Marie.Milling operations began in September, 1957. The mill processes a complex base metal ore by differential flotation techniques to produce copper, lead and zinc concentrates. To date some 43 million tons have been milled, qualifying Geco as a rather major base metal deposit.II. BACKGROUND:The Geco concentrator was designed and constructed in the mid 50's. A number of features specific to a concentrator of that vintage provided the justification for the modernization efforts described herein.Firstly, the mill was constructed without any instrumentation, not even pneumatic controls. Solid state electronics, computers and related instrumentation were unheard of, or rather primitive by today's standards.Secondly, some of the major equipment, in particular the flotation equipment, did not compare favourably to that in use today. MacIntosh flotation machines (more commonly known as Mac cells) were installed at Geco. These cells were prevalent in a number of concentrators built by Noranda, including Quemont Mining Corporation Limited, Gaspe Copper Mines Limited and Noranda — Horne Division. The Mac cells were used for copper and zinc rougher and scavenger operations. Some units were also installed for a pyrite recovery circuit that was never operated. In total, 104 Mac cells were installed in the main flotation area of the concentrator.

Jan 1, 1987

By Nathaniel Herz

IN the operation of any ore processing plant, no matter what beneficiation process or combination of processes may be used, certain fundamental figures are regularly needed for essential records and accounting. These include amounts of ore treated and products made, with their assays, as well as quantities of labor and supplies used, with their cost. Usually labor and supplies are broken down and allocated to certain operations by the accounting department, and resulting tabulations are available for study by the milling plant management. However, to avoid too many minor details that would make these reports cumbersome and involved, much information that could be useful to the plant operator is often consolidated in such a manner as to have lost a considerable part of its value. To clarify this point, it may be stated that top management is most concerned with production figures and cost of production, while the plant operator is also interested in quantities of labor in man- hours and amounts of supplies used. Due to varying unit prices of labor and supplies, comparisons on a dollar basis alone are often misleading. With rising unit costs of the past few years now about twice as high as they were a few years ago, constant study of quantities involved is required to improve efficiency and productivity.

Jan 6, 1957

By P. R. Richardson

"Milling is the weak link in the process chain of many mineral operations. While this activity accounts for only a relatively small proportion of the direct costs of most mineral processing complexes, there are intangible and indirect costs associated with milling which are extremely large. For example, significant opportunity costs are associated with the relatively low yields which characterize this stage of the process.There are changes abroad in the world which I believe are going to cause us to reformulate the whole concept of milling. Increased competition in mineral markets are going to force managers to look anew at the high mineral values reporting to tailings which are a high opportunity cost for many operations. Tailings recovery plants are not the ultimate solution to this problem. Greater environmental concerns are going to increase the costs associated with tailings disposal and force the mining industry to look for other ways to dispose of waste products. Technology changes currently underway in manufacturing and other process industries, such as the automated 'lights-out' plant are going to be brought into this industry, and the changes will be dramatic.These are major long term changes which probably seem rather remote to many managers and professionals in existing operations which are faced with much more mundane challenges arising from day-to-day operations. However, I believe that milling is increasingly a 'lean and keen' operation involving fewer and fewer people, but who are increasingly skilled and professional. Traditional cost management approaches are no longer adequate and the industry has to take a new look at the nature of cost reduction in this core activity. This stage in the mineral process provides opportunities for value creation leading to a significant unit cost advantage for the corporations willing to adopt a total cost approach."

Jan 1, 1988

By Wheeler North

THE United Eastern Mining Co.'s property is located in the Oatman, Gold Roads mining district of Mohave County, Ariz. The mine and mill are some 26 mi. (41.8 km.) southwest of Kingman, the nearest railway connection. The ore consists of a mixture of calcite and quartz with some andesite. The values, which are mainly gold, alloyed with approximately 34 per cent., by weight, of silver, are extremely fine so that fine grinding is a most important factor in extraction. The milling process, briefly, consists of single-stage, coarse-crushing, two-stage ball milling in cyanide solution, followed by combined mechanical and air agitation, and by straight counter-current decantation. The Merrill zinc-dust precipitation method is used to recover the values, and is preceded by the Crowe vacuum treatment of the solution. The most notable features of the plant are the absence of filters, and the use of short peb mills loaded with steel balls, for fine grinding. As originally designed, the capacity of the mill was to be 200 tons per day, although the grinding end was to be capable of handling double that amount. By adding extra agitators and thickeners and by some alterations to the grinding end, the daily capacity has been raised to 285 tons. This, it is hoped, may be increased to 300 tons during the warm months of the present year. TONNAGE MILLED PER DAY 1917 average 234 Maximum month 272 Minimum month 146 1918 average 253 Maximum month 276 Minimum month 217 As this article primarily deals with plant operations, those interested in the mechanical description are referred to the article by Mr. Otto Wartenweiler,1 the designing engineer, which gives the details and costs of design and construction. The following changes have been made since that article was published:

Jan 8, 1919

LUTHER B. EAMES, Pueblo, Colo. (written discussion*).-In reading Mr. North's interesting paper, several points have been noted that appear to warrant discussion. With a feed all through 20 mesh, I feel inclined to question the use of steel balls as large as 2 in. in a tube mill. I have seen balls as small as-3/4 in. used for the dry grinding of cement clinker, and surely many more points of contact would result from smaller balls. This would seem to be desirable in a mill as short as 6 ft. The heavy load in the classifiers would also indicate a high proportion of returned pulp. I hope that some discussion by Mr. North -and others may develop this point. The flow sheet on page 1181 shows the solution returning from the dam valued at 40 c. per ton being added to the last decantation tank. Theoretically, this solution should not be added to that of a lower value. As I calculate it, if this solution were added to tank X the solution finally discharged from tank Z would be reduced in value by nearly 4 c. per ton.

Jan 10, 1919

G. M. TAYLOR,* Colorado Springs, Colo.-The ore treated at the United Eastern is primarily a gold one and is cyanided-the counter-current decantation method being employed. One of our employees visited this plant a few months ago and, on his return, reported that the moisture in the tailing was carrying 20 c. per ton, which would appear to be somewhat high. As this type of plant has been advocated by one of the recognized cyaniding engineering firms in the country, and a number of these plants are in successful operation, it does not seem to me that the dissolved loss could be so high, and I would like to know if any one can give any definite information on this point? J. V. N. DORR, New York, N. Y.-I am very glad that Mr. Taylor has raised this question. When I first read Mr. North's paper and saw his statement, that they had an actual dissolved loss of 21.5 c. per ton, I was very much puzzled at this high loss which appeared avoidable by another decantation or the addition of a rotary filter. Reading it again, however, I noted that the actual dissolved loss of 21.5 c. given was evi-dently obtained by multiplying the assay of solution discharged from Z. thickener by the tonnage. On the basis of 283 tons milled per clay, this means $56.54 going to the clam. He states, however, that he returns from. the dam into the system, 70 tons daily assaying 40 c. per ton or $28 per day, so it would seem reasonable, unless I have overlooked something to regard the actual dissolved loss as $56.54 less $28 or $28.54, equaling 10.8 c. per ton. Even this loss, however, is much higher than good practice elsewhere, and can be accounted for largely by the tonnage being handled, which I believe is 30 per cent. above the capacity planned.

Jan 12, 1919

By Andre Vien, D. H. Hendriks, D. Willet, B. C. Flintoff

"For many years the training of mill operators was an informal process which involved senior operators training junior operators on an as-needed basis. Recognizing the needs and benefits of better training some companies, and even some provinces through legislation, have moved to ensure that a formalized training program exists in the plants. These programs tend to focus on basic safety and operations. Much remains to be done. With the more rapid incorporation of new processing and information technologies, and the goal to keep labour costs to a minimum by doing more with less, operator training has become a critical issue. This paper briefly examines the evolution of training programs, provides some measure of their effectiveness, and explores some recent developments which could have a very significant impact on the industry.PreambleOne can draw an analogy between operator training and the mechanical support of production equipment. When we buy a piece of process equipment it is critical that the mechanical installation be done properly to ensure that the device will operate at peak performance on start-up. Once the equipment is running, some form of preventive maintenance is required to ensure continued efficient operation. The operators and the equipment are both elements of the processing system, yet the former do not seem to get the same ""start-up"" or ""operating"" support. Are they not seen as critical to efficient operation? Why is this so? What impact does it have? How can we improve?These are all very logical and important questions, although the answers are not nearly so obvious. In the mineral processing industry, progress in operator training over the past thirty years has been limited and quite variable. To address the perceived need for a more coherent and consistent approach, some provinces have moved to incorporate basic training requirements in their legislation. Some plants have gone a few steps further by building integrated training programs into their operating culture. One conclusion which can be easily reached is that there are no standards, and that the range of training activity is great. In other words, a flotation operator is not a flotation operator is not a flotation operator. Their knowledge and skills are very much a function of training and experience, which are clearly corporate and site specific."

Jan 1, 1994

By P D. Munro

On the occasion of the 14th Mill Operators’ Conference and marking 40 years since the first one was held in Mount Isa in 1978, it is fitting to review the history of the Conference and its development over that time.The first 10 Conferences were irregularly held at three to four year intervals, with 9 of these in regional centres of Australasia. It is only since 2012 that the Mill Operators’ Conference has become a regular biennial event, alternating with the MetPlant Conference.The number of people attending the Conference has more than doubled to 470 delegates at the 13th one in 2016. It has outgrown its regional beginnings.Papers presented to the previous Conferences have been analysed according to commodity, country of origin, technology and theme plus the affiliation of the authors to discern any trends that may assist in planning the future events.Suggestions are made as to how the AusIMM might wish to arrange its mineral processing/metallurgical conferences.Recent changes to the structure of the Conference providing a more meaningful experience for the delegates and increasing their interaction and involvement should be vigorously pursued.CITATION:Munro, P D, 2018. Mill Operators’ conferences – a 40-year retrospective and a vision for the future, in Proceedings 14th AusIMM Mill Operators' Conference 2018, pp 5–14 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 29, 2018

By L. G. Austin

Using an instrumented laboratory high-pressure grinding rolls mill, the grinding force, gap dimension, mass flow rate and net mill power were measured for six coals and a crystalline quartz. A technique was developed to estimate the compressive stress-strain curves for compression of the materials in the mill plus the effects of elastic decompression. To reconcile the mill power and grinding pressure results, it was necessary to allow for the energy recovery on decompression. No clear correlation was obtained between the form of the stress-strain curves or the variation of specific mill power factor with the Hardgrove grindability index (HGI), although coals with the lowest and highest HGIs (i.e., 44 and 106) gave results significantly different from the other coals. Feeds below 140 mesh (105 µm) flowed more rapidly than coarser feeds and would not build up high grinding pressures. This indicated shearing and fluidlike properties rather than compression as a locked bed.

Jan 1, 1998

By Steve Hubbard, Brad Marchant, Rolando Cuadra

"Triton Mining Corporation acquired the rights to Mina El Limon in Nicaragua in 1993 by international bid. The bid included the gold operations at Limon and an exploration concession of approximately 4000 km2. Triton assumed control of operations and exploration in May 1994.The Limon mine is located in west-central Nicaragua, approximately 100 kilometers northwest of Managua. The climate is tropical, characterized by a wet season from May through October, and a dry season November through April. Gold at Limon is associated with both banded quartz and silicified breccia veins in Tertiary volcanic rocks, belonging to the lower Coyol Group. Mining is from two open pits and one mechanized underground operation. A second underground mine is currently under development for production during 1997.This paper describes the expansion of the milling facility at El Limon from a nominal capacity of 400 tonnes/day, producing approximately 20,000 ounces of gold annually, to the existing 900 tonne per day mill operation. Engineering of the new mill facility was initiated in September 1994 and construction was completed a year later."

Jan 1, 1997

By P Rubie, B Morgan, J Russell, C Stewart

The relationship between efficient liner exchange, concentrator availability and concentrator profitability is well documented. Russell Mineral Equipment’s (RME) relationship with OZ Minerals’ Prominent Hill site personnel enabled sound collaboration between the two parties. Both parties worked together to identify the sources of productivity and efficiency loss and developed solutions to reverse them.This paper chronicles the identification of production inefficiencies and the resulting removal of mill relining from the critical path through the materialisation of mill relining optimisation strategies. Furthermore, this paper outlines other recent mill relining optimisation strategies developed by RME and tested at Prominent Hill, to demonstrate and achieve further productivity, efficiency and safety improvements.CITATION:Rubie, P, Russell, J, Morgan, B and Stewart, C, 2017. Mill relining optimisation – a story of collaboration, in Proceedings MetPlant 2017, pp 335–345 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 11, 2017

By Peter Rubie, John Russell

"For many years, optimizing the relining of hard rock grinding mills has been complicated by the large number of variables, the low frequency of relines (resulting in a slow relining experience assessment and review cycle), and the potential economic risk associated with some changes to relining equipment or work practices. A technology that has its roots in the automotive manufacturing industry is being utilized to construct a statistically accurate, configurable, and dynamic simulation of the mill relining process. The detailed effects of various mechanization and process changes can be rapidly modeled and compared. Application of this discrete event analysis technology in the mineral processing industry delivers a range of benefits to many industry stakeholders. For example, mill maintenance managers and contract relining companies can embrace the opportunity to benchmark current performance against world’s best practice. Concentrator plant designers and mill manufacturers, informed by this technology’s scientifically defensible data set, can accurately plan for maximum plant efficiency when designing an infrastructure and equipment combination that truly maximizes annual plant availability. Time-motion studies of grinding mill reline data at mills of varying dimensions, liner configurations, mill relining equipment, operator and tool variables, have been integral to the development of this dynamic simulation tool and its associated data set. Access to mill relining simulation technology will enable mineral processing industry professionals to take advantage of an increased capacity to develop mineral concentrator performance optimisation initiatives within the given financial, physical and technological constraints of the individual concentrator plant."

Jan 1, 2014

By Mishra BK, Agrawala S

The traditional method of scale-up uses the population-balance model. In particular, the selection function values for a material are determined in a laboratory mill and a variety of correlations are used to scale these values to plant scale mills. For example, the factor D2-5L (D-mill diameter, L-mill length) appears in many power correlations. The number of collisions is proportional to the number of balls (aD2L), the frequency of mill rotation ((x 1/4D-) and effectiveness of impact ((XD), which gives rise to the 'D2.5L' expression. However, what is lacking in this expression is that it does not throw light on the intensities of collisions. In other words, the collision intensities in both laboratory and plant scale mills are implied to be identical. This fact has been very limiting. Alternatively, the collision frequencies and intensity of impacts can be computed with the discrete element code. This code computes the motion and collision of each individual ball in the ball charge. Therefore the number of collisions and the fraction of collisions in the energy range Et, E2.òòE. (collision energy density) are calculated for a given mill size and operating conditions. Then, using the breakage function determined in drop-weight experiments, the evolution of size distribution is computed for a lab mill. The collision frequency and energy density for larger mill sizes are shown. The fundamental theory outlined for the calculation of size distribution is equally applicable for the large mill, which is the basis for scale-up.

Jan 1, 1993

By K. A. Brame, L. G. Austin, R. S. C. Rogers

The breakage parameters of phosphate ore were determined by batch first-ordering grinding studies in a laboratory ball mill according to the Austin, Klimpel, and Luckie procedures. The results were scaled to five larger mills of 0.56, 0.82, 8.36, 4.41, and 5 m in diameter assuming equilibrium ball charges for the full-scale mills. The results were used to predict product size distributions and capacities for batch grinding in the smaller mills and open-circuit grinding in the larger mills. The predicted capacities were in approximate agreement with experimental values except for the 5-m diam mill. The Bond method gave capacity predictions that were 4570 to 150% too high.

Jan 1, 1987

By Reed S. C. Rogers

The breakage parameters of phosphate ore were determined by batch first-order grinding studies in a laboratory ball mill according to the procedures described in the text by Austin, Klimpel and Luckie, using a slurry density of 70 weight percent. The results were scaled to five larger mills of 0.56 m diameter by 0.91 m length (2 ft. by 3 ft.), 0.82 m by 1.52 m (3 ft. by 5 ft.), 3.36 m by 7.90 m (11.5 ft. by 25 ft.), 4.41 m by 9.10 m (14.5 ft. by 30 ft.), and 5 m by 11.1 m (17 ft. by 36 ft.), assuming equilibrium ball charges for the full-scale mills. The results were used to predict product size distribustions and capacities for batch grinding in the 0.56 m and 0.82 m diameter mills and open circuit grinding in the 0.82 m diameter and larger mills using a one-large/two-small reactors in series model fitted to the residence time distribution measured in the 4.41 m diameter mill. The simulated results were compared to plant data for ranges of mill capacities. It was found that the simulated product size distributions were in good agreement with the experimental values below the 70% passing sizes, but did not agree so well in the top sizes. The predicted capacities were in approximate agreement with experimental values for the pilot-scale mills, were about 7 percent too high for the 3.36 m and 4.41 m diameter mills and about 25 percent high for the 5 m diameter mill. Use of the Bond method with the measured Work Index of the phosphate ore gave capacity predictions that were 45 to 150 percent too high.

Jan 1, 1985

By V. K. Gupta

"Effect of mill speed on grinding kinetics has been investigated with a view to using mill speed as a manipulated variable for control and optimization of the grinding circuit performance under variable ore hardness conditions. Dry and wet batch grinding tests were carried out for quartz, limestone and cement clinker in a 29 cm x 18 cm laboratory ball mill. Mill speed values selected were 55 and 70% critical. In the case of dry grinding operation, with an exception of quartz, for all materials studied the effect of mill speed on grinding rate was found to be insignificant for sizes finer than about 35 mesh. In the case of wet operation, grinding rates were found to be approximately proportional to the mill speed. The implications of these results are discussed.INTRODUCTIONIt is well known that mill speed has a considerable effect on the grinding rate of the ore particles l-3 For particles of a given size there is an optimum speed at which mill grinding efficiency is maximum (i.e. specific energy consumption is minimum) 3•4. Mill speed can, therefore, be effectively used as a manipulated variable to deal with the disturbances arising from changes in the size and hardness (grinding rate) of the ore being fed to the grinding circuit. Though, it has not been the case so far, with recent developments of ring motors2 and frequency inverters5 a continuous variation of mill speed has now become feasible, and it is expected that mill speed control will soon be a regular feature of plant operation2,6."

Jan 1, 1985