Wills’ Mineral Processing Technology Wills’ Mineral Processing Technology An Introduction to the Practical Aspects of Ore Treatment and Mineral Recovery Eighth Edition Barry A. Wills Senior Partner, MEI, UK James A. Finch, FRSC, FCIM, P.Eng. Gerald G. Hatch Chair in Mining and Metallurgical Engineering, Department of Mining and Materials Engineering, McGill University, Montre´al, Canada AMSTERDAM ● BOSTON ● HEIDELBERG ● LONDON NEW YORK ● OXFORD ● PARIS ● SAN DIEGO SAN FRANCISCO ● SINGAPORE ● SYDNEY ● TOKYO Butterworth-Heinemann is an imprint of Elsevier Butterworth-Heinemann is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK 225 Wyman Street, Waltham, MA 02451, USA Copyright r 2016 Elsevier Ltd. All rights reserved. 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ISBN: 978-0-08-097053-0 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress For Information on all Butterworth-Heinemann publications visit our website at http://store.elsevier.com/ Preface The email came as a surprise: would I be interested in edit- teaching experience. By having students in the team, we ing the eighth edition of the classic Wills’ Mineral aimed to have illustrations that addressed the usual stu- Processing Technology? The book is the most-widely used dent questions. English-language textbook on the subject and the SME’s The next part of the plan was to use, as much as possi- ‘readers’ choice’, making it both an honor to be asked and a ble, the chapter structure that Barry had devised, but to daunting prospect. My old colleague, the late Dr. Rao, had number the sub-sections, as, according to the students, it always encouraged me to write another book, but after was sometimes difficult to know where you were. A team Column Flotation I vowed “never again”. Nevertheless, member read a chapter and made suggestions, in some cases after a career of more than 40 years, I was looking for new taking on the task of re-writing sections. All the chapters challenges, and with several day’s contemplation, I agreed. were finalized by me, including adding more example cal- This turned out to be the largest single professional task I culations, and then passed by Barry for a final review. have undertaken, consuming most of the last two years, and I appreciate the confidence Barry had that the book was in on several occasions I came to question my sanity. ‘good hands’. Chapter 3 became unwieldy, and we decided It was at that point that I seriously started to read whole to divide the contents between two chapters. To avoid alter- chapters of the seventh edition, as opposed to the odd sec- ing the numbering of the established chapters, a Chapter 17 tions I had consulted in the past. You have to admire that was inserted. Elsevier Americanized the English, although a Barry Wills wrote the first book, and the following 5 edi- few “sulphides” snuck through. This also meant that my tions, alone. As Tim Napier-Munn noted in the Preface to “tonnes” became “tons” and the reader should keep that in the seventh edition, a team is needed now, and for this edi- mind when working through the example calculations. tion the team, which included experts and recently gradu- I am proud of the final product, and grateful to Barry ated students, is recognized in the “Acknowledgments”. and Elsevier for giving me the chance to be part of this But what was the plan for the team? enterprise. Elsevier had hinted that the artwork could do with an upgrade, and we set about re-drawing the originals that James A. Finch were retained, and adding new artwork based on my July 2015 xi Acknowledgments Two people made the book possible and worked with Emad, M, Dr (Post-doctoral student, McGill me (JAF) throughout and thus deserve to be noted first: University): Chapter 2 Dr. Jarrett Quinn who handled much of the correspon- Flament, F (Triple Point Technology): Chapter 3, dence, as well as managing most of Chapters 6, 8, and “Mass Balancing” section 14 as well as the first draft of Chapter 3 and the Gilroy, T (student, McGill University): Chapter 4, “Flotation Machine” section of Chapter 12; and Dr. first draft Yue Hua Tan who contributed all the artwork, redraw- Grammatikopoulos, T (SGS Canada): Chapter 17, ing the originals and creating the new, and organized “Applied Mineralogy” section the supporting documentation and spreadsheets. My sin- Hart, B, Dr (Surface Science Western): Chapter 12, cere thanks to both individuals, who never doubted we “Diagnostic Surface Analysis” section would finish. Jordens, A (PhD candidate, McGill University): It was apparent from the start that assistance from Chapter 13 experts in the various aspects covered by the book Krishnamoorthy, N, Dr (Research assistant, McGill was going to be required for it to be brought up to University): Chapter 15, first draft date. Most of my requests for assistance were enthusi- Lotter, N, Dr (XPS Consulting & Testwork Services): astically met and knowing the time and effort involved Chapter 12, “High Confidence Flotation Testing” I am most grateful for the help, and the book has section benefitted accordingly. The contributions were edited Major, K (KMW Consulting): Chapters 6 and 8, ini- to bring some conformity to style, and any errors thus tial review incurred are mine alone. In alphabetical order the con- Maldonado, M, Prof (Universidad de Santiago): tributors are: Chapter 3, “Control” section Marcuson, S, Dr (Marcuson and Associates): Bittner, J, Dr (Separation Technologies): Chapter 13, Chapter 1, “Sustainability” section review of material McIvor, R, Dr (Metcom Technologies): Chapters 5, Bouchard, J, Prof (Universite´ Laval): Chapter 12, 7, and 9, initial review “Control” section Mitri, H, Prof (McGill University): Chapter 2, review Boucher, D (PhD candidate, McGill University): of material Chapter 17, “Machine Design” section Morrell, S, Dr (SMC Testing): Chapter 5, review of Brissette, M (Corem): Chapters 5 and 7, editing and material adding new material Nesset, J, Dr (NesseTech Consulting Services): Bulled, D (SGS Canada): Chapter 17, Chapter 2, “Self-Heating” section; Chapter 3, “Geometallurgy” section “Sampling” section; Chapter 17, “Design of Cappuccitti, F (Flottec): Chapter 12, editing the Experiments” section “Collector” section; Chapter 15, supplying chemical O’Keefe, C, Dr (CiDRA): Chapter 3, contribution to data “On-Line Analysis” section Cunningham, R (Met-Chem): Chapter 7, “Stirred Pax, R, Dr (RAP Innovation and Development): Milling” section Chapter 3, “Mineral/Phase Analysis” section Demers, I, Prof (Universite´ du Que´bec en Abitibi- Robben, C, Dr (TOMRA Sorting): Chapter 14, Te´miscamingue): Chapter 16 review of material Doll, A (Alex G Doll Consulting): Chapters 5 and 7, Schaffer, M (Portage Technologies): Chapters 6 and editing and adding new material 7, “Control” sections xiii xiv Acknowledgments Singh, N (Research assistant, McGill University): The book could not have been completed without Chapter 1, first draft financial and logistical support. Thanks go to the Natural Sosa, C, Dr (SGS Canada): Chapter 17, Sciences and Engineering Research Council of Canada “Geometallurgy” section (NSERC) for the funding to support the McGill team; and Sovechles, J (PhD candidate, McGill University): to McGill University for the time to devote to the book Chapter 9 and the use of the facilities. Smart, R, Prof (University of South Australia): Last but never least, JAF would like to thank his wife, Chapter 12, “Diagnostic Surface Analysis” section Lois, of 42 years for her support with what grew to Waters, K, Prof (McGill University): Chapters 10 occupy most of my time over the past 24 months. and 11, initial review Williams-Jones, A, Prof (McGill University): Appendices I and II, update Chapter 1 Introduction 1.1 MINERALS large parts of the earth’s crust. For instance, granite, which is one of the most abundant igneous rocks, that is, The forms in which metals are found in the crust of the a rock formed by cooling of molten material, or magma, earth and as seabed deposits depend on their reactivity within the earth’s crust, is composed of three main min- with their environment, particularly with oxygen, sulfur, eral constituents: feldspar, quartz, and mica. These three and carbon dioxide. Gold and platinum metals are found mineral components occur in varying proportions in dif- principally in the native or metallic form. Silver, copper, ferent parts of the same granite mass. and mercury are found native as well as in the form of Coals are a group of bedded rocks formed by the accu- sulfides, carbonates, and chlorides. The more reactive mulation of vegetable matter. Most coal-seams were metals are always in compound form, such as the oxides formed over 300 million years ago by the decomposition and sulfides of iron and the oxides and silicates of alumi- of vegetable matter from the dense tropical forests which num and beryllium. These naturally occurring compounds covered certain areas of the earth. During the early forma- are known as minerals, most of which have been given tion of the coal-seams, the rotting vegetation formed thick names according to their composition (e.g., galena—lead beds of peat, an unconsolidated product of the decomposi- sulfide, PbS; cassiterite—tin oxide, SnO2). tion of vegetation, found in marshes and bogs. This later Minerals by definition are natural inorganic substances became overlain with shales, sandstones, mud, and silt, possessing definite chemical compositions and atomic and under the action of the increasing pressure, tempera- structures. Some flexibility, however, is allowed in this ture and time, the peat-beds became altered, or metamor- definition. Many minerals exhibit isomorphism, where phosed, to produce the sedimentary rock known as coal. substitution of atoms within the crystal structure by simi- The degree of alteration is known as the rank of the coal, lar atoms takes place without affecting the atomic struc- with the lowest ranks (lignite or brown coal) showing lit- ture. The mineral olivine, for example, has the chemical tle alteration, while the highest rank (anthracite) is almost composition (Mg,Fe)2SiO4, but the ratio of Mg atoms to pure graphite (carbon). Fe atoms varies. The total number of Mg and Fe atoms in While metal content in an ore is typically quoted as per- all olivines, however, has the same ratio to that of the Si cent metal, it is important to remember that the metal is con- and O atoms. Minerals can also exhibit polymorphism, tained in a mineral (e.g., tin in SnO 2). Depending on the different minerals having the same chemical composition, circumstances it may be necessary to convert from metal to but markedly different physical properties due to a differ- mineral, or vice versa. The conversion is illustrated in the ence in crystal structure. Thus, the two minerals graphite following two examples (Examples 1.1 and 1.2). and diamond have exactly the same composition, being The same element may occur in more than one min- composed entirely of carbon atoms, but have widely dif- eral and the calculation becomes a little more involved. ferent properties due to the arrangement of the carbon atoms within the crystal lattice. The term “mineral” is often used in a much more 1.2 ABUNDANCE OF MINERALS extended sense to include anything of economic value that is extracted from the earth. Thus, coal, chalk, clay, The price of metals is governed mainly by supply and and granite do not come within the definition of a min- demand. Supply includes both newly mined and recycled eral, although details of their production are usually metal, and recycling is now a significant component of included in national figures for mineral production. Such the lifecycle of some metals—about 60% of lead supply materials are, in fact, rocks, which are not homogeneous comes from recycled sources. There have been many in chemical and physical composition, as are minerals, prophets of doom over the years pessimistically predicting but generally consist of a variety of minerals and form the imminent exhaustion of mineral supplies, the most Wills’ Mineral Processing Technology. © 2016 Elsevier Ltd. All rights reserved. 1 2 Wills’ Mineral Processing Technology Example 1.1 Example 1.2 Given a tin concentration of 2.00% in an ore, what is the A sample contains three phases, chalcopyrite (CuFeS2), concentration of cassiterite (SnO2)? pyrite (FeS2), and non-sulfides (containing no Cu or Fe). If the Cu concentration is 22.5% and the Fe concentration is Solution 25.6%, what is the concentration of pyrite and of the non- Step 1: What is the Sn content of SnO2? sulfides? 21 Molar mass of Sn (MSn) 118.71 g mol 21 Molar mass of O (MO) 15.99 g mol Solution Note, Fe occurs in two minerals which is the source of MSn 118:71 %Sn in SnO25 5 578:8% complication. The solution, in this case, is to calculate first MSn 123MO 118:7112315:99 the % chalcopyrite using the %Cu data in a similar manner Step 2: Convert Sn concentration to SnO2 to the calculation in Example 1.1 (Step 1), and then to cal- culate the %Fe contributed by the Fe in the chalcopyrite 2:00%Sn (Step 2) from which %Fe associated with pyrite can be cal- 52:54% SnO2 78:8%Sn in SnO2 culated (Step 3). 21 Molar masses (g mol ): Cu 63.54; Fe 55.85; S 32.06 Step 1: Convert Cu to chalcopyrite (Cp) 63:54155:851 ð2332:06Þ %Cp522:5% 565:0% 63:54 extreme perhaps being the “Limits to Growth” report to the Club of Rome in 1972, which forecast that gold would Step 2: Determine %Fe in Cp run out in 1981, zinc in 1990, and oil by 1992 (Meadows 55:85 et al., 1972). Mouat (2011) offers some insights as to the %Fe in Cp565% 519:8% 63:54155:851 ð2332:06Þ past and future of mining. In fact, major advances in productivity and technology Step 3: Determine %Fe associated with pyrite (Py) throughout the twentieth century greatly increased both the %Fe in Py525:6219:855:8% resource base and the supply of newly mined metals, through geological discovery and reductions in the cost of Step 4: Convert Fe to Py (answer to first question) production. These advances actually drove down metal 55:851 ð2332:06Þ prices in real terms, which reduced the profitability of %Py55:8% 512:5% 55:85 mining companies and had a damaging effect on economies Step 5: Determine % non-sulfides (answer to second heavily dependent on resource extraction, particularly those question) in Africa and South America. This in turn drove further improvements in productivity and technology. Clearly %non-sulfides51002ð%Cp1%PyÞ51002ð65:0112:5Þ mineral resources are finite, but supply and demand will 522:5% generally balance in such a way that if supplies decline or demand increases, the price will increase, which will motivate the search for new deposits, or technology to render marginal deposits economic, or even substitution by other materials. Gold is an exception, its price having not changed much in real terms since the sixteenth century, minerals in the future. Manganese nodules have been due mainly to its use as a monetary instrument and a store known since the beginning of the nineteenth century of wealth. (Mukherjee et al., 2004), and mineral-rich hydrothermal Estimates of the crustal abundances of metals are vents have been discovered (Scott, 2001). Mining will given in Table 1.1 (Taylor, 1964), together with the eventually extend to space as well. amounts of some of the most useful metals, to a depth of It can be seen from Table 1.1 that eight elements 3.5 km (Tan and Chi-Lung, 1970). account for over 99% of the earth’s crust: 74.6% is silicon The abundance of metals in the oceans is related to and oxygen, and only three of the industrially important some extent to the crustal abundances, since they have metals (aluminum, iron, and magnesium) are present in come from the weathering of the crustal rocks, but super- amounts above 2%. All the other useful metals occur in imposed upon this are the effects of acid rainwaters on amounts below 0.1%; copper, for example, which is the mineral leaching processes; thus, the metal availability most important non-ferrous metal, occurring only to the from seawater shown in Table 1.2 (Tan and Chi-Lung, extent of 0.0055%. It is interesting to note that the so- 1970) does not follow precisely that of the crustal called common metals, zinc and lead, are less plentiful abundance. The seabed may become a viable source of than the rare-earth metals (cerium, thorium, etc.). Introduction Chapter | 1 3 TABLE 1.1 Abundance of Metal in the Earth’s Crust Element Abundance (%) Amt. in Top Element Abundance (%) Amt. in Top 3.5 km (tons) 3.5 km (tons) 14 15 (Oxygen) 46.4 Vanadium 0.014 10 10 Silicon 28.2 Chromium 0.010 16 18 Aluminum 8.2 10 10 Nickel 0.0075 Iron 5.6 Zinc 0.0070 13 14 Calcium 4.1 Copper 0.0055 10 10 Sodium 2.4 Cobalt 0.0025 16 18 Magnesium 2.3 10 10 Lead 0.0013 Potassium 2.1 Uranium 0.00027 Titanium 0.57 Tin 0.00020 15 16 10 10 11 13 Manganese 0.095 Tungsten 0.00015 10 10 26 Barium 0.043 Mercury 83103 26 Strontium 0.038 Silver 7310 26 Rare earths 0.023 Gold ,5310 11 ,10 14 16 26 Zirconium 0.017 10 10 Platinum metals ,5310 TABLE 1.2 Abundance of Metal in the Oceans Element Abundance (tons) Element Abundance (tons) 15 16 9 10 Magnesium 10 10 Vanadium 10 10 12 13 Silicon 10 10 Titanium 12 13 Aluminium Cobalt 10 10 Iron 10 11 Silver 10 10 Molybdenum Tungsten Zinc Tin Chromium Uranium 9 10 Gold 8 10 10 ,10 Copper Zirconium Nickel Platinum both igneous and sedimentary rocks (i.e., those produced 1.3 DEPOSITS AND ORES by the deposition of material arising from the mechanical It is immediately apparent that if the minerals containing and chemical weathering of earlier rocks by water, ice, important metals were uniformly distributed throughout and chemical decay). Thus, when granite is weathered, the earth, they would be so thinly dispersed that their eco- cassiterite may be transported and redeposited as an nomic extraction would be impossible. However, the alluvial deposit. Besides these surface processes, mineral occurrence of minerals in nature is regulated by the geo- deposits are also created due to magmatic, hydrothermal, logical conditions throughout the life of the mineral. A sedimentary, and other geological events (Ridley, 2013). particular mineral may be found mainly in association Due to the action of these many natural agencies, with one rock type (for example, cassiterite mainly associ- mineral deposits are frequently found in sufficient ates with granite rocks) or may be found associated with concentrations to enable the metals to be profitably 4 Wills’ Mineral Processing Technology recovered; that is, the deposit becomes an ore. Most ores 1.5 THE NEED FOR MINERAL PROCESSING are mixtures of extractable minerals and extraneous “As-mined” or “run-of-mine” ore consists of valuable nonvaluable material described as gangue. They are minerals and gangue. Mineral processing, also known as frequently classed according to the nature of the valuable ore dressing, ore beneficiation, mineral dressing, or mill- mineral. Thus, in native ores the metal is present in the ing, follows mining and prepares the ore for extraction of elementary form; sulfide ores contain the metal as the valuable metal in the case of metallic ores, or to pro- sulfides, and in oxidized ores the valuable mineral may be duce a commercial end product as in the case of minerals present as oxide, sulfate, silicate, carbonate, or some such as potash (soluble salts of potassium) and coal. hydrated form of these. Complex ores are those containing Mineral processing comprises two principal steps: size profitable amounts of more than one valuable mineral. reduction to liberate the grains of valuable mineral (or Metallic minerals are often found in certain associations paymineral) from gangue minerals, and physical separa- within which they may occur as mixtures of a wide tion of the particles of valuable minerals from the gangue, range of grain sizes or as single-phase solid solutions or to produce an enriched portion, or concentrate, containing compounds. Galena and sphalerite, for example, are most of the valuable minerals, and a discard, or tailing commonly associated, as, to a lesser extent, are copper (tailings or tails), containing predominantly the gangue sulfide minerals and sphalerite. Pyrite is almost always minerals. The importance of mineral processing is today associated with these minerals as a sulfide gangue. taken for granted, but it is interesting to reflect that little There are several classifications of a deposit, which more than a century ago, ore concentration was often from an investment point of view it is important to a fairly crude operation, involving relatively simple understand: mineral resources are potentially valuable density-based and hand-sorting techniques. The twentieth and are further classified in order of increasing confi- century saw the development of mineral processing as an dence into inferred, indicated, and measured resources; important profession in its own right, and certainly with- mineral (ore) reserves are known to be economically out it the concentration of many ores, and particularly the (and legally) feasible for extraction and are further clas- metalliferous ores, would be hopelessly uneconomic sified, in order of increasing confidence, into probable (Wills and Atkinson, 1991). and proved reserves. It has been predicted that the importance of mineral processing of metallic ores may decline as the physical processes utilized are replaced by the hydro- and pyro- 1.4 METALLIC AND NONMETALLIC ORES metallurgical routes used by the extractive metallurgist Ores of economic value can be classed as metallic or (Gilchrist, 1989), because higher recoveries are obtained nonmetallic, according to the use of the mineral. Certain by some chemical methods. This may apply when the minerals may be mined and processed for more than one useful mineral is very finely disseminated in the ore and purpose. In one category, the mineral may be a metal ore, adequate liberation from the gangue is not possible, in that is, when it is used to prepare the metal, as when which case a combination of chemical and mineral pro- bauxite (hydrated aluminum oxide) is used to make alu- cessing techniques may be advantageous, as is the case minum. The alternative is for the compound to be classi- with some highly complex deposits of copper, lead, zinc, fied as a nonmetallic ore, that is, when bauxite or natural and precious metals (Gray, 1984; Barbery, 1986). Heap aluminum oxide is used to make material for refractory leaching of gold and oxidized copper ores are examples bricks or abrasives. where mineral processing is largely by-passed, providing Many nonmetallic ore minerals associate with metallic only size reduction to expose the minerals. In-situ leach- ore minerals (Appendixes I and II) and are mined and ing is used increasingly for the recovery of uranium and processed together. For example, galena, the main source bitumen from their ores. An exciting possibility is using of lead, sometimes associates with fluorite (CaF2) and plants to concentrate metals sufficiently for chemical barytes (BaSO4), both important nonmetallic minerals. extraction. Known as phytomining or agro-mining, it has Diamond ores have the lowest grade of all mined ores. shown particular promise for nickel (Moskvitch, 2014). One of the richest mines in terms of diamond content, For most ores, however, concentration of metals for Argyle (in Western Australia) enjoyed grades as high as subsequent extraction is best accomplished by mineral 2 ppm in its early life. The lowest grade deposits mined processing methods that are inexpensive, and their use is in Africa have been as low as 0.01 ppm. Diamond depos- readily justified on economic grounds. its are mined mainly for their gem quality stones which The two fundamental operations in mineral processing have the highest value, with the low-value industrial qual- are, therefore, liberation or release of the valuable miner- ity stones being essentially a by-product: most industrial als from the gangue, and concentration, the separation of diamond is now produced synthetically. these values from the gangue.