Wills' Mineral Processing Technology, Seventh Edition: An Introduction to the Practical Aspects of Ore Treatment and Mineral Recovery

450 Pages·2006·40.12 MB·English

by  Barry A. Wills

Mineral Processing Technology
An Introduction to the Practical Aspects of Ore Treatment and Mineral
Recovery, by Barry A. Wills, Tim Napier-Munn

• ISBN: 0750644508
• Publisher: Elsevier Science & Technology Books
• Pub. Date: October 2006
Preface to 7th Edition
Although mining is a conservative industry, economic drivers continue to encourage innovation and
technological change. In mineral processing, equipment vendors, researchers and the operations them-
selves work to develop technologies that are more efficient, of lower cost and more sustainable than
their predecessors. The results are apparent in new equipment and new operating practice. Any textbook
needs to reflect these changes, and Barry Wills' classic is no exception.
It is nearly 30 years since Mineral Processing Technology was first published, and it has become the
most widely used English-language textbook of its kind. The sixth edition appeared in 1997 and Barry
and his publishers felt that it was again time to bring the text up to date. They approached the Julius
Kruttschnitt Mineral Research Centre at the University of Queensland to take on the challenging task.
My colleagues and I agreed to do so with some trepidation. The book's well-deserved reputation and
utility were at stake, and the magnitude of the task was clear. Revising someone else's text is not an
easy thing to do successfully, and there was a real danger of throwing the baby out with the bath water.
The value of Mineral Processing Technology lies in its clear exposition of the principles and practice
of mineral processing, with examples taken from practice. It has found favour with students of mineral
processing, those trained in other disciplines who have converted to mineral processing, and as a reference
to current equipment and practice. It was important that its appeal to these different communities be
preserved and if possible enhanced. We therefore adopted the following guidelines in revising the book.
The 7th edition is indeed a revision, not a complete re-write. This decision was based on the view
that "if it ain't broke, don't fix it". Each diagram, flowsheet, reference or passage of text was considered
as follows. If it reflected current knowledge and practice, it was left unchanged (or modestly updated
where necessary). If it had been entirely superseded, it was removed unless some useful principle or
piece of history was being illustrated. Where the introduction of new knowledge or practice was thought
to be important to preserve the book's currency, this was done. As a consequence, some chapters remain
relatively unscathed whereas others have experienced substantial changes.
A particular problem arose with the extensive references to particular machines, concentrators and flow-
sheets. Where the point being illustrated remained valid, these were generally retained in the interest of
minimising changes to the structure of the book. Where they were clearly out of date in a misleading sense
and/or where alternative developments had attained the status of current practice, new material was added.
It is perhaps a measure of Barry Wills' original achievement that it has taken more than a dozen people
to prepare this latest edition. I would like to acknowledge my gratitude to my colleagues at the JKMRC
and elsewhere, listed below, for subscribing their knowledge, experience and valuable time to this good
cause; doing so has not been easy. Each chapter was handled by a particular individual with expertise in
the topic (several individuals in the case of the larger chapters). I must also thank the editorial staff at
Elsevier, especially Miranda Turner and Helen Eaton, for their support and patience, and Barry Wills for
his encouragement of the enterprise. My job was to contribute some of the chapters, to restrain some of
the more idiosyncratic stylistic extravagancies, and to help make the whole thing happen. To misquote
the great comic genius Spike Milligan: the last time I edited a book I swore I would never do another
one. This is it.
Tim Napier-Munn
December 2005
Contributors
Chapters 1, 4, 9, 11, 14 Prof. Tim Napier-Munn (JKMRC)
Chapters 2 and 16 Dr Glen Corder (JKTech)
Chapter 3 Dr Rob Morrison (JKMRC) and Dr Michael Dunglison (JKTech)
Chapters 5 and 6 Dr Toni Kojovic (JKMRC)
Chapter 7 Dr Frank Shi (JKMRC)
Chapter 8 Marko Hilden (JKMRC) and Dean David (GRD Minproc, formerly with
JKTech)
Chapters 10, 13 and 15 Dr Peter Holtham (JKMRC)
Chapter 12 Dr Dan Alexander (JKTech), Dr Emmy Manlapig (JKMRC), Dr Dee
Bradshaw (Dept. Chemical Engineering, University of Cape Town) and
Dr Greg Harbort (JKTech)
Appendix III Dr Michael Dunglison (JKTech)
Acknowledgements
Secretarial assistance Vynette Holliday and Libby Hill (JKMRC)
Other acknowledgements Prof. J-P Franzidis (JKMRC) and Evie Franzidis for their work on an
earlier incarnation of this project.
Dr Andrew Thornton and Bob Yench of Mipac for help with aspects
of process control.
The Julius Kruttschnitt Mineral Research Centre, The University of
Queensland, for administrative support. The logos of the University
and the JKMRC are published by permission of The University of
Queensland, the Director, JKMRC.
Table of Contents

1 Introduction 1
2 Ore handling 30
3 Metallurgical accounting, control and simulation 39
4 Particle size analysis 90
5 Comminution 108
6 Crushers 118
7 Grinding mills 146
8 Industrial screening 186
9 Classification 203
10 Gravity concentration 225
11 Dense medium separation (DMS) 246
12 Froth flotation 267
13 Magnetic and electrical separation 353
14 Ore sorting 373
15 Dewatering 378
16 Tailings disposal 400
App. 1 Metallic ore minerals 409
App. 2 Common non-metallic ores 421
App. 3 Excel spreadsheets for formulae in chapter 3
Introduction
Minerals and ores lattice. The term "mineral" is often used in a
much more extended sense to include anything
Minerals of economic value which is extracted from the
earth. Thus, coal, chalk, clay, and granite do not
The forms in which metals are found in the crust
come within the definition of a mineral, although
of the earth and as sea-bed deposits depend on
details of their production are usually included in
their reactivity with their environment, particularly
national figures for mineral production. Such mate-
with oxygen, sulphur, and carbon dioxide. Gold and
rials are, in fact, rocks, which are not homoge-
platinum metals are found principally in the native
neous in chemical and physical composition, as
or metallic form. Silver, copper, and mercury are
are minerals, but generally consist of a variety
found native as well as in the form of sulphides,
carbonates, and chlorides. The more reactive metals of minerals and form large parts of the earth's
are always in compound form, such as the oxides crust. For instance, granite, which is one of the
and sulphides of iron and the oxides and silicates of most abundant igneous rocks, i.e. a rock formed by
aluminium and beryllium. The naturally occurring cooling of molten material, or magma, within the
compounds are known as minerals, most of which earth's crust, is composed of three main mineral
have been given names according to their composi- constituents, feldspar, quartz, and mica. These
tion (e.g. ga lena- lead sulphide, PbS; sphalerite - three homogeneous mineral components occur in
zinc sulphide, ZnS; cassiterite- tin oxide, SnO2). varying proportions in different parts of the same
Minerals by definition are natural inorganic granite mass.
substances possessing definite chemical compo- Coals are not minerals in the geological sense,
sitions and atomic structures. Some flexibility, but a group of bedded rocks formed by the accu-
however, is allowed in this definition. Many mulation of vegetable matter. Most coal-seams
minerals exhibit isomorphism, where substitution were formed over 300 million years ago by
of atoms within the crystal structure by similar the decomposition of vegetable matter from the
atoms takes place without affecting the atomic dense tropical forests which covered certain areas
structure. The mineral olivine, for example, has of the earth. During the early formation of the
the chemical composition (Mg, Fe)2 SiO4, but the coal-seams, the rotting vegetation formed thick
ratio of Mg atoms to Fe atoms varies in different beds of peat, an unconsolidated product of the
olivines. The total number of Mg and Fe atoms decomposition of vegetation, found in marshes
in all olivines, however, has the same ratio to and bogs. This later became overlain with shales,
that of the Si and O atoms. Minerals can also sandstones, mud, and silt, and under the action
exhibit polymorphism, different minerals having of the increasing pressure and temperature and
the same chemical composition, but markedly time, the peat-beds became altered, or metamor-
different physical properties due to a difference in phosed, to produce the sedimentary rock known
crystal structure. Thus, the two minerals graphite as coal. The degree of alteration is known as
and diamond have exactly the same composi- the rank of the coal, the lowest ranks (lignite or
tion, being composed entirely of carbon atoms, brown coal) showing little alteration, while the
but have widely different properties due to the highest rank (anthracite) is almost pure graphite
arrangement of the carbon atoms within the crystal (carbon).
2 Wills' Mineral Processing Technology
Metallic ore processing These large fluctuations in oil prices have had
a significant impact on metalliferous ore mining,
Metals
due to their, influence both on the world economy
The enormous growth of industrialisation from the
and thus the demand for metals, and directly on the
eighteenth century onward led to dramatic increases
energy costs of mining and processing. It has been
in the annual output of most mineral commodi-
estimated that the energy cost in copper produc-
ties, particularly metals. Copper output grew by a
tion is about 35% of the selling price of the metal
factor of 27 in the twentieth century alone, and
(Dahlstrom, 1986).
aluminium by an astonishing factor of 3800 in the
The price of metals is governed mainly by
same period. Figure 1.1 shows the world produc-
supply and demand. Supply includes both newly
tion of aluminium, copper and zinc for the period
mined and recycled metal, and recycling is now
1900-2002 (data from USGS, 2005).
a significant component of the lifecycle of some
All these metals suffered to a greater or
me ta l s - about 60% of lead supply comes from
lesser extent when the Organisation of Petroleum
recycled sources. There have been many prophets
Exporting Countries (OPEC) quadrupled the price
of doom over the years pessimistically predicting
of oil in 1973-74, ending the great postwar indus-
the imminent exhaustion of mineral supplies, the
trial boom. The situation worsened in 1979-81,
most extreme perhaps being the notorious "Limits
when the Iranian revolution and then the Iran-Iraq
to Growth" report to the Club of Rome in 1972,
war forced the price of oil up from $13 to nearly
which forecast that gold would run out in 1981, zinc
$40 a barrel, plunging the world into another and
in 1990, and oil by 1992 (Meadows et al., 1972).
deeper recession, while early in 1986 a glut in the In fact major advances in productivity and tech-
world's oil supply cut the price from $26 a barrel nology throughout the twentieth century greatly
in December 1985 to below $15 in 1986. Iraq's increased both the resource and the supply of
invasion of Kuwait in 1990 pushed the price up newly mined metals, through geological discovery
again, from $16 in July to a peak of $42 in October, and reductions in the cost of production. This
although by then 20% of the world's energy was actually drove down metal prices in real terms,
being provided by natural gas. which reduced the profitability of mining compa-
In 1999, overproduction and the Asian economic nies and had a damaging effect on economies
crisis depressed oil prices to as low as $10 a barrel heavily dependent on mining, particularly those
from where it has climbed steadily to a record in Africa and South America. This in turn drove
figure of over $60 a barrel in 2005, driven largely further improvements in productivity and tech-
by demand especially from the emerging Asian nology. Clearly mineral resources are finite, but
economies, particularly China. supply and demand will generally balance in such
Figure 1.1 World production of aluminium, copper and zinc for the period 1900-2002
Introduction 3
a way that if supplies decline or demand increases, Table 1.2 Abundance of metal in the oceans
the price will increase, which will motivate the
Element Abundance Element Abundance
search for new deposits, or technology to render
in sea-water in sea-water
marginal deposits economic, or even substitution
(tonnes) (tonnes)
by other materials.
Magnesium 1015-1016 Vanadium } 109_1010
Interestingly gold is an exception, its price
Silicon 1012-1013 Titanium
having not changed much in real terms since
Aluminium Cobalt }
the sixteenth century, due mainly to its use as
Iron 101~ Silver 1012_1013
a monetary instrument and a store of wealth
Molybdenum Tungsten
(Humphreys, 1999).
Zinc Chromium /
Estimates of the crustal abundances of metals are
Tin Gold <10 8
given in Table 1.1 (Taylor, 1964), together with the Uranium Zirconium
actual amounts of some of the most useful metals, Copper 109-10 l~ Platinum
to a depth of 3.5 km (Chi-Lung, 1970). Nickel
The abundance of metals in the oceans is related
to some extent to the crustal abundances, since
silicon and oxygen, and only three of the industri-
they have come from the weathering of the crustal
ally important metals (aluminium, iron, and magne-
rocks, but superimposed upon this are the effects
sium) are present in amounts above 2%. All the
of acid rain-waters on mineral leaching processes;
other useful metals occur in amounts below 0.1%;
thus the metal availability from sea-water shown in
copper, for example, which is the most important
Table 1.2 (Chi-Lung, 1970) does not follow
non-ferrous metal, occurring only to the extent of
precisely that of the crustal abundance. The sea-
0.0055%. It is interesting to note that the so-called
bed may become a viable source of minerals in the
common metals, zinc and lead, are less plentiful
future. Manganese nodules have been known since than the rare-earth metals (cerium, thorium, etc.).
the beginning of the nineteenth century (Mukherjee It is immediately apparent that if the minerals
et al., 2004), and recently mineral-rich hydrothermal containing the important metals were uniformly
vents have been discovered and plans are being made distributed throughout the earth, they would be
to mine them (Scott, 2001). so thinly dispersed that their economic extraction
It can be seen from Table 1.1 that eight elements would be impossible. However, the occurrence of
account for over 99% of the earth's crust; 74.6% is minerals in nature is regulated by the geological
Table 1.1 Abundance of metal in the oceans
Element Abundance (%) Amount in Element Abundance (%) Amount in
3.5km of 3.5 km of crust
crust (tonnes) (tonnes)
(Oxygen) 46.4 Vanadium 0.014 1014-1015
Silicon 28.2 Chromium 0.010
Aluminium 8.2 1016-1018 Nickel 0.0075
Iron 5.6 Zinc 0.0070
Calcium 4.1 Copper 0.0055 1013-1014
Sodium 2.4 Cobalt 0.0025
Magnesium 2.3 1016-1018 Lead 0.0013
Potassium 2.1 Uranium 0.00027
Titanium 0.57 Tin 0.00020
Manganese 0.095 1015-1016 Tungsten 0.00015 1011-1013
Barium 0.043 Mercury 8 • 10 -6
Strontium 0.038 Silver 7 • 10 -6
Rare earths 0.023 Gold <5 x 10 -6 /
Zirconium 0.017 1014--1016 Platinum metals <5 • 10 -6 <1011
4 Wills' Mineral Processing Technology
conditions throughout the life of the mineral. A certain contained value which is dependent on the
particular mineral may be found mainly in asso- metal content and current price of the contained
ciation with one rock type, e.g. cassiterite mainly metal. For instance, at a copper price of s
associates with granite rocks, or may be found asso- and a molybdenum price of s a deposit
ciated with both igneous and sedimentary rocks containing 1% copper and 0.015% molybdenum
(i.e. those produced by the deposition of material has a contained value of more than s The
arising from the mechanical and chemical weath- deposit will be economic to work, and can be clas-
ering of earlier rocks by water, ice, and chemical sified as an ore deposit if:
decay). Thus, when granite is weathered, cassiterite
Contained value per tonne > (total processing costs
may be transported and re-deposited as an alluvial
deposit.
+ losses + other costs) per tonne
Due to the action of these many natural agencies,
mineral deposits are frequently found in sufficient A major cost is mining, and this can vary enor-
concentrations to enable the metals to be profitably mously, from only a few pence per tonne of
recovered. It is these concentrating agencies and the ore to well over s High-tonnage operations
development of demand as a result of research and are cheaper in terms of operating costs but have
discovery which convert a mineral deposit into an higher initial capital costs. These capital costs are
ore. Most ores are mixtures of extractable minerals paid off over a number of years, so that high-
and extraneous rocky material described as gangue. tonnage operations can only be justified for the
They are frequently classed according to the nature treatment of deposits large enough to allow this.
of the valuable mineral. Thus, in native ores the Small ore bodies are worked on a smaller scale, to
metal is present in the elementary form; sulphide reduce overall capital costs, but capital and oper-
ores contain the metal as sulphides, and in oxidised ating costs per tonne are correspondingly higher
ores the valuable mineral may be present as oxide, (Ottley, 1991).
sulphate, silicate, carbonate, or some hydrated form Alluvial mining is the cheapest method and, if
of these. Complex ores are those containing prof- on a large scale, can be used to mine ores of very
itable amounts of more than one valuable mineral. low contained value due to low grade or low metal
Metallic minerals are often found in certain associ- price, or both. For instance, in S.E. Asia, tin ores
ations within which they may occur as mixtures of a containing as little as 0.01% Sn are mined by allu-
wide range of particle sizes or as single-phase solid vial methods. These ores had a contained value
solutions or compounds. Galena and sphalerite, for of less than s but very low processing costs
example, associate themselves commonly, as do allowed them to be economically worked.
copper sulphide minerals and sphalerite to a lesser High-tonnage open-pit and underground block-
extent. Pyrite (FeS2) is very often associated with caving methods are also used to treat ores of low
these minerals. contained value, such as low-grade copper ores.
Ores are also classified by the nature of their Where the ore must be mined selectively, however,
gangues, such as calcareous or basic (lime rich) as is the case with underground vein-type deposits,
and siliceous or acidic (silica rich). An ore can be mining methods become very expensive, and can
described as an accumulation of mineral in suffi- only be justified on ores of high contained value.
cient quantity so as to be capable of economic An underground selective mining cost of s
extraction. The minimum metal content (grade) would obviously be hopelessly uneconomic on a
required for a deposit to qualify as an ore varies tin ore of alluvial grade, but may be economic on a
from metal to metal. Many non-ferrous ores hard-rock ore containing 1.5% tin, with a contained
contain, as mined, as little as 1% metal, and often value of around s
much less. In order to produce metals, the ore minerals must
Gold may be recovered profitably in ores be broken down by the action of heat (pyromet-
containing only 1 part per million (ppm) of the allurgy), solvents (hydrometallurgy) or electricity
metal, whereas iron ores containing less than (electrometallurgy), either alone or in combination,
about 45% metal are regarded as of low grade. the most common method being the pyrometallur-
Every tonne of material in the deposit has a gical process of smelting. These chemical methods