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By W. L. Maxson

GRINDING is one of the major problems in present-day milling practice, and in many cases, it represents one of the main items of expense. It becomes necessary from time to time, to compare grinding practice in one plant with that in another plant, and in making such comparisons, it would be very desirable were there available accepted standards of grinding resistance for the materials involved. Such a set of grinding constants would also be of considerable value in planning new grind-ing installations. There have been some tests published, notably those of Lennox,1 which have been generally cited as a basis for such comparisons. Most of the tests made have been based upon open-circuit grinding, in which a weighed sample of the ore was crushed to pass a certain mesh, and was .then ground under certain conditions, either wet or dry. Grinding was continued until a certain desired fineness was attained, and the compari-sons based on the grinding time, or the samples were all ground for a certain specified length of time and comparison based upon the screen analysis of the products. Such methods have been acceptable where the ore was to be ground in open circuit. However, in modern milling practice, many grinding problems involve closed circuits wherein the oversize returns to the mill and a large circulating, load builds up. A method of testing that does not take the circulating load into consideration might yield results quite different from those to he expected in practice, because the minerals in the ore that offer maximum resistance to grinding will accumulate in the circulating load up to an equilibrium value. Thus the nature of the ore charge in the mill at any instant may differ greatly from that of the new feed, with a consequent error in the rate of grinding determined by such a method.

Jan 1, 1933

By C. H. Rawlins

The total amount of ferrous slag generated in the U.S. is about one-third the amount of iron ore mined, thus ferrous slag can be considered a significant mineral body for processing. Steelmaking slag contains up to 30 wt.% metal of which only the >25mm fraction is commonly recovered. A grinding study was conducted of BOF, EAF, and LMF slags using the Bond Work Index method to determine grindability to 106µm. Work Index values obtained were 13.8-24.9 kWh/ST, depending upon the slag type and composition. Steel particles were magnetically recovered from the crushed and ground samples for size-by-size analysis, yielding up to 18 wt.% of the slag weight recovered as magnetic. The recovered material, as characterized by inert gas melting, was found to be 61-96 wt.% metallic.

Jan 1, 2008

By J. W. Leonard

One of the more obvious phenomena which relate to coke formation is that soft coals of low volatile matter content tend to yield hard or high strength cokes while hard coals of high volatile matter content tend to yield soft or low strength cokes. This observation led researchers of the Coal Research Bureau of West Virginia Univ. to study the possibility of using Hardgrove grindability as a supplemental rank indicator for coking properties. Grindability has been used for many years as a means to measure the resistance of coal to comminution but it has rarely if ever been considered for evaluating coals for carbonization. The coal proper- ties which are measured by grindability are complex, but recent work with the difficult-to-correlate high volatile coals has demonstrated that a 93% correlation exists between grindability and the total petrographic rnicrinites, exinites, and resinites. This work demonstrated that inherent ash had no apparent effect on the grindability of high volatile coals, suggesting that the coal substance is apparently harder than the associated ash. These observations, together with the patented Burstlein process," indicate that the distribution of hard and soft components in the individual high volatile coals and blends of coals may be quantitatively interrelated to coke stability through selected ranges of coal volatile matter. The objective of this progress report is 1) to demonstrate the statistical relationships which exist between coal grindability and the numerous coal petrographic entities and 2) to present the results of initial studies concerning the correlation of the coke physical strength index of stability with coal volatile matter and grindability.

Jan 3, 1964

In terms of throughput, product size and power draw, grindcurves provide a measure of the response of the mill performance to changes in mill operating parameters ? usually mill filling. Since presenting the principle in 2006, grindcurves have been applied to a wide variety of AG and SAG mills. Mill response has been carefully measured for variations in: mill fillings from 15% to 40%; throughput by a factor of two; power by 50%; feed blends; liner profile; and mill speed from 65% to 80%. The outcomes of this extensive program of work are presented as the measured grindcurves. How they have enhanced our understanding of mill operation and how they may be applied to practical daily mill control is discussed. It is proposed that this technique provides a viable and valuable mill control tool that may find extensive application in the industry.

Jan 1, 2012

In terms of throughput, product size and power draw, grindcurves provide a measure of the response of the mill performance to changes in mill operating parameters – usually mill filling. Since presenting the principle in 2006, grindcurves have been applied to a wide variety of AG and SAG mills. Mill response has been carefully measured for variations in: mill fillings from 15% to 40%; throughput by a factor of two; power by 50%; feed blends; liner profile; and mill speed from 65% to 80%. The outcomes of this extensive program of work are presented as the measured grindcurves. How they have enhanced our understanding of mill operation and how they may be applied to practical daily mill control is discussed. It is proposed that this technique provides a viable and valuable mill control tool that may find extensive application in the industry.

Jan 1, 2012

Contents

Jan 1, 1985

Grinding and Beneficiation Characteristics of a Low-Grade Haematite Ore

Sep 13, 2010

By W. H. A. Timm

Lake Dufault Mines, Limited, is located ten miles north of Noranda, Quebec. Following discovery of a copper-zinc orebody late in 1961, metallurgical investigations of diamond drill core were conducted by Lakefield Research Limited during 1962 and 1963. These were followed by pilot-plant tests in May and June of 1964, utilizing underground development ore. Milling operations commenced on August 16, 1964, and reached rated capacity of 1,300 tons per day by October 1, 1964 (Figure 1). Since that time, tonnage was gradually increased to a maximum of 1,400 tons per day and since January 1, 1968, gradually decreased to the present rate of 1,100 tons per day due to an increase in the hardness of the ore. The ore milled from start-up until January, 1968, was mainly massive sulphides, consisting of a complex mixture of iron, copper, zinc and minor amounts of lead sulphides with important associated values in gold, silver and cadmium (aver- age specific gravity 3.8). From January, 1968, until the present, the ore being processed is described geologically as a boxwork of sulphide stringers of chalcopyrite, pyrite and pyrrhotite and some local dissemination in siliceous rhyolite (average specific gravity 2.9) supplemented by the massive copper-zinc ore. The limited size of the orebody and the mining method employed (open stoping by blasthole and slash and bench methods) would have made grade control from the mine difficult and expensive. It was decided to try to cope with grade variations in the mill. The resulting rapid and wide swings in mill heads, hardness and specific gravity have presented many and varied challenges for the mill personnel.

Jan 1, 1970

By J. W. Keck

Pilot plant grinding and concentration test results indicate that conglomerate native copper ore can be ground and concentrated using conventional techniques. Single stage autogenous grinding and rod mill-ball mill grinding required the same amount of energy far the required comminution. Metallurgical results were comparable for both types of grinding investigated.

Jan 1, 1973

By O. A. Bascur

In recent years, metal-producing companies have increased their investment in automation and technological innovation, embracing new opportunities to enable transformational change. Transformation to a digital plant can fundamentally revolutionize how industrial complexes operate. The abundant and growing quantity of real-time data and events collected in the grinding and flotation circuits in a mineral processing plant can be used to solve operational issues and optimize plant performance. A grade recovery model is used to identify the best operating conditions in real time. A strategy for increasing the value of instrumentation in current plants is reviewed. An optimal Gaudin size distribution model provides augmented information from traditional sensors to find the optimal grind cut size to reduce metal losses in the flotation circuits. Sensors in flotation circuits enable an estimate of the recovery and determination of the optimal froth depth and aeration using an air hold up flotation model. A strategy of classifying data for online generation of insights to using operational intelligence tools is described. The implementation of a recovery/grind strategy with industrial examples in nonferrous mineral processing is presented.

By O. A. Bascur

In recent years, metal-producing companies have increased their investment in automation and technological innovation, embracing new opportunities to enable transformational change. Transformation to a digital plant can fundamentally revolutionize how industrial complexes operate. The abundant and growing quantity of real-time data and events collected in the grinding and flotation circuits in a mineral processing plant can be used to solve operational issues and optimize plant performance. A grade recovery model is used to identify the best operating conditions in real time. The strategy for increasing the value of instrumentation in current plants is reviewed. An optimal Gaudin size distribution model provides augmented information from traditional sensors to find the optimal grind cut size to reduce metal losses in the flotation circuits. Sensors in flotation circuits enable an estimate of the recovery and determination of the optimal froth depth and aeration using an air hold up flotation model. A strategy of classifying data for on-line generation of insights to using operational intelligence tools is described. The implementation of a recovery/grind strategy with industrial examples in non-ferrous mineral processing is presented.

Grinding and Flowing Investigation on Dry Stirred Ball Milling in Order to Determine the Influence of Grinding Aids Huge difficulties of the great ultra fine ground material production in dry stirred ball mill are the cohesion and agglomeration of the particles. During grinding the material stick on the grinding wall and the grinding media furthermore the grinds start cohere, making aggregation and agglomeration to appear. Due to these effects the particle size will not decrease after a certain value during grinding and the energy demand increases significantly. According to experience on fine grinding in ball mill, it is well known that these effects can be reduced with the use of grinding aids. The influence of grinding aids has three different effects: due to the adsorption strength reduction (Rebinder effect) the grinding resistance of the material decreases; the surface energy diminishes and the agglomeration liability decreases; and the flow properties of material improve. The aim of this study is to investigate the flow properties of fine grinds and the effect of grinding aids on flow properties in case of dry stirred ball milling. In addition, the influence of grinding aids was investigated based on the particle size distribution and specific surface area of grinds and the specific energy demand of grinding. The examinations were carried out with three different model materials (limestone, clinker, quartz) using the usually applied grinding aid. The flow properties were measured by the Jenike shear cell; the particle size distribution and specific surface area were measured by laser particle size analyser (Fritsch Analysette 22), grinding energy demand was measured with microcomputer controlled digital energy meter. It can be said that under certain measuring circumstances the influence of grinding aid on flow properties can be demonstrated by Jenike shear cell, so the grinding result is in correlation with the flow properties of grind.

Sep 13, 2010

By Steve Kral

The success of the industrial minerals end of the mining industry is often overshadowed by the high price of copper, the glamour of gold, and the nation's huge reserves of coal. Those three segments of the industry, however, along with every other business in the world, could not function without the products that are composed of a variety of industrial minerals. And, according to Haydn H. Murray, past president of SME, the value of industrial minerals in the United States is more than triple that of metals, about $19 billion a year versus $6 billion. In the developed countries of the world, he said, the value of industrial minerals is nearly always greater than the value of metallic minerals. Murray, also a professor of geology at Indiana University, was the luncheon speaker at the SME-sponsored Grinding of Industrial Minerals conference held in Asheville, NC this past September. Producers of industrial minerals know they must squeeze the maximum value out of the industrial mineral being mined and processed, Murray told the audience of about 100 people. Grinding and particle size, then, are vital to a commodity's profitability.

Jan 1, 1990

By J. F. Myers, F. M. Lewis

The paper reports the development of a large, slow speed ball mill closed circuited with a hydroscillator. This increased grinding efficiency 28 pct over conventional units.

Jan 1, 1950

By W. M. Lupton

"Internal grinding mill entries are routinely done by mill personnel during scheduled maintenance periods. Reasons for entry include mill liner life profiles, liner inspcections and replacement and grinding media investigations. These entries require employees to adhere to safety regulations and policies including special permitting, testing, procedure-following practices and the wearing of proper personal protective equipment.A realized semi-autogenous mill entry safety hazard is the unpredicted breakage and occasional shattering of large diameter grinding media while personnel are inside. This was a concern to both media user and supflier. American Barrick's Holt McDermott Mine has improved mi l operational procedures and the media manufacturer has assisted by their developments to essentially eliminate this problem.This paper presents the improvements instituted; and the author's wish to communicate this potential hazard to other large diameter SAG ball users or potential users.INTRODUCTIONAmerican Barrick' s Holt McDermott mine is situated on Highway 101, some 70 kilometers northeast of Kirkland Lake, Ontario, 120 km east of Timmins and 90 km northwest of Rouyn Noranda, Quebec. The mine draws 160 employees from these surrounding areas to extract and process the underground ore, and recover near 60,000 ounces of gold per year. The mill department is completing it's fifth year of operation this spring.The company and the employees are proud of the safety improvements realized over the short history of the mine. Post accident/incident reviews and pro-active safety awareness programs have substantially reduced the mine's accident frequency and severity to date.One of the mill department's objectives is to provide a safe working environment for mill personnel, which includes the interior of the grinding mills."

Jan 1, 1993

By Walter L. Crow

MUCH has been published on highly technical phases of grinding. Very little has been written on how a mill man can improve his operations by determining the optimum size assortment of grinding balls that should be added as a makeup charge. This ball rationing is not to be confused with the ball ration used as an initial charge when the mill is started up. Ball rationing is considered for one or more of the following purposes: 1) to increase throughput of the mill, 2) to reduce the power required per ton of ore ground to the desired size, 3) to reduce steel consumption per ton of ore ground, 4) to improve product size, and 5) to lower retention time of ore in the mill.

Jan 7, 1957

By Fred C. Bond

SIZE of grinding media is one of the principal factors affecting efficiency and capacity of tumbling-type grinding mills. It is best determined for any particular installation by lengthy plant tests with carefully kept records. However, a method of calculating the proper sizes, based on correct theoretical principles and tested by experience, can be very helpful, both for new installations and for guiding existing operations. As a general principle, the proper size of the make-up grinding balls added to an operating mill is the size that will just break the largest feed particles. If the balls are too large the number of breaking contacts will be reduced and grinding capacity will suffer. Moreover, the amount of extreme fines produced by each contact will be increased, and size distribution of the ground product may be adversely affected.

Jan 5, 1958

By Arthur Taggart

FOREWORD THE tests herein described are part of an extended series of experiments, performed by the authors together with J. F. McClelland and L. W. Bahney, on the reclamation of metallics from foundry and manufacturing-plant scrap. The most obstinate problem encountered was the proper cleaning of the metal. INTRODUCTION In the manufacture of brass and brass products the weight of the finished product leaving the plant is much less than the total weight of copper and zinc entering. A small part of this discrepancy is due to the unavoidable oxidation of the metals in melting, but by far the largest part of the loss is in the form of metallic particles of copper, zinc, and brass. These losses occur principally at three points in the process: (a) in the casting-shop ashes; (b) in the slags from furnaces melting scrap brass; (c) in material spilled on the floor throughout the manufacturing process. The amount of these products in some plants is nearly 100 tons per 24 hours. Casting-shop ashes contain the metal spilled from the crucibles during melting and pouring, and the metal included in the slags formed in the melting process. The ashes also contain pieces of broken crucibles with adhering metal; 20 to 30 per cent. of unburned coal is also present. The metal in casting-shop ashes contains clean pieces of zinc or copper ingots weighing 1 to 2 lb., jagged pieces of metal of all shapes ranging in size from several inches down to the finest dust, and shot and botryoidal shapes ranging in size from 2 or 3 in. down to 0.01 mm. or less in diameter. Slags from furnaces melting scrap brass contain metal in the form of small shot.

Jan 2, 1916

By C. A. Rowland Jr

"I. INTRODUCTIONFred C. Bond's ""Third Theory of Comminution"" (1) was published in 1952. The mathematical statement of the Third Theory is the well-known Bond Formula:where W - Kw H per short tonWl - Work IndexP - Product size in microns which 80% passesF .. Product size in microns which 80% passesWork Index, as defined by Fred Bond, "" ... is the comminution parameter which expresses the resistance of the material to crushing and grinding. Numerically, the Work Index is the KwHrs per short ton required to reduce the material from theoretically infinite feed size to 80% passing 100 microns."" (2)Work indices for grinding can be obtained tram Bond grindability tests and can be calculated from plant grinding mill operating data when power consumed per ton of ore ground, the feed size analysis and the product size analysis are known.Work indices obtained tram Bond grindability tests, having been obtained from standard and controlled laboratory procedures, are reproducible and for the sample tested are accurate. The degree of accuracy relative to plant mill operation depends upon how representative the sample is of the total mill feed.The results of the Bond closed circuit rod and ball mill grindability tests (3) are given in grams of product sized material produced per revolution of the test mill. In developing a method to evaluate plant operating data and results from his grindability test, Fred Bond developed the ""Third Theory of Comminution."" In the process formulae were developed for converting grams per revolutionobtained from grindability tests to work index.The standard feed sizes for the Bond grindability tests are:Rod Mill Test ore crushed to minus 1ll inchBall Mill Test ore crushed to minus 6 mesh (Tyler)The formulae for converting grams per revolution to work index incorporate the 80% passing sizes for the feed to and the product produced in the specific test. Therefore, accurate work indices can be obtained from Bond grindability tests when the feed size is finer than standard. To obtain accurate test results, the ratio of reduction should be greater than 6 to 1."

Jan 1, 1972

Grinding with an electrochemically inert grinding media (i.e. high chrome white iron, or Magotteaux’s Duromax® alloys) shifts the pulp potentials to more oxidising conditions, increases the dissolved oxygen content and reduces the EDTA extractable iron concentration when compared with milling with electrochemically active grinding media (forged steel). These changes in pulp chemistry produce cleaner particle surfaces, reduce reagent consumption and increase concentrate grades and recoveries. This paper presents a robust laboratory test program that is able to not only demonstrates these effects but also provide an indication of the magnitude of the improvements that are possible. While laboratory studies are interesting, the proof is in the pudding! So, the paper provides an overview of plant trials conducted at a number of operations around the world, including: Newcrest’s Cadia Operation, Oz Minerals’ Prominent Hill Mine and Glencore’s Ernest Henry Mine. These successful plant trials clearly demonstrate that selection of the right grinding media alloy will yield savings in grinding media consumption and reagent consumption as well as increases in revenue through improved copper, gold and molybdenum recoveries. INTRODUCTION The key to a successful separation in mineral processing is the preparation of particles with adequate liberation under the correct pulp chemical conditions. While the importance of liberation on flotation separations is generally understood and well documented in the literature (Johnson, 1987; Jackson, Sutherland, Gottlieb & Quittner, 1989; Young, Pease, Johnson, & Munro, 1997; Greet and Freeman, 2000), the importance of pulp chemistry is more nebulous, particularly with regard to the impact of grinding media. Extensive work examining the electrochemical interactions between grinding media and sulphide minerals has been completed (for example, Iwasaki, Reid, Lex & Smith, 1983; Natarajan and Iwasaki, 1984; Yelloji Rao and Natarajan, 1989(a); Yelloji Rao and Natarajan, 1989(b)). Broadly, these studies indicate that most sulphide minerals are more noble than the grinding media used during comminution, therefore a galvanic couple between the media and the sulphide mineral(s) exists, which increases the corrosion rate of the grinding media. The corrosion products of the grinding media, iron oxy-hydroxide species, invariably precipitate on to the surfaces of the sulphide minerals thereby affecting their floatability (Johnson, 2002).

Jan 1, 2019