Wills Wills' Mineral Processing Technology

An Introduction to the Practical Aspects of Ore Treatment and Mineral Recovery
7. Auflage 2011
ISBN: 978-0-08-047947-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 456 Seiten

Wills' Mineral Processing Technology provides practising engineers and students of mineral processing, metallurgy and mining with a review of all of the common ore-processing techniques utilized in modern processing installations.
Now in its Seventh Edition, this renowned book is a standard reference for the mineral processing industry. Chapters deal with each of the major processing techniques, and coverage includes the latest technical developments in the processing of increasingly complex refractory ores, new equipment and process routes. This new edition has been prepared by the prestigious J K Minerals Research Centre of Australia, which contributes its world-class expertise and ensures that this will continue to be the book of choice for professionals and students in this field.
This latest edition highlights the developments and the challenges facing the mineral processor, particularly with regard to the environmental problems posed in improving the efficiency of the existing processes and also in dealing with the waste created. The work is fully indexed and referenced.
·The classic mineral processing text, revised and updated by a prestigious new team
·Provides a clear exposition of the principles and practice of mineral processing, with examples taken from practice
·Covers the latest technological developments and highlights the challenges facing the mineral processor
·New sections on environmental problems, improving the efficiency of existing processes and dealing with waste.

Autoren/Hrsg.

Wills, Barry A.

Inhaltsverzeichnis

1;Front Cover;1
2;Title Page;4
3;Copyright Page;5
4;Table of Contents;6
5;Preface to 7th Edition;10
6;Contributors;11
7;Acknowledgements;12
8;Chapter 1 Introduction;14
8.1;Minerals and ores;14
8.2;Mineral processing methods;20
8.3;Efficiency of mineral processing operations;27
8.4;Concentration;29
8.5;Economics of tin processing;33
8.6;Economics of copper processing;36
8.7;Economic efficiency;39
8.8;References;41
9;Chapter 2 Ore handling;43
9.1;Introduction;43
9.2;The removal of harmful materials;43
9.3;Ore transportation;45
9.4;Ore storage;47
9.5;Feeding;49
9.6;References;51
10;Chapter 3 Metallurgical accounting, control and simulation;52
10.1;Introduction;52
10.2;Sampling and weighing the ore;52
10.3;Slurry streams;64
10.4;Automatic control in mineral processing;68
10.5;Neural networks;75
10.6;Circuit design and optimisation by computer simulation;76
10.7;Mass balancing methods;77
10.8;Introduction to mass balances on complex circuits;88
10.9;Design of experiments and plant trials;99
10.10;References;99
11;Chapter 4 Particle size analysis;103
11.1;Introduction;103
11.2;Particle size and shape;103
11.3;Sieve analysis;104
11.4;Sub-sieve techniques;110
11.5;References;120
12;Chapter 5 Comminution;121
12.1;Introduction;121
12.2;Principles of comminution;122
12.3;Comminution theory;123
12.4;Grindability;124
12.5;Simulation of comminution processes and circuits;125
12.6;References;128
13;Chapter 6 Crushers;131
13.1;Introduction;131
13.2;Primary crushers;132
13.3;Secondary crushers;139
13.4;Crushing circuits and control;152
13.5;References;156
14;Chapter 7 Grinding mills;159
14.1;Introduction;159
14.2;The motion of the charge in a tumbling mill;160
14.3;Tumbling mills;162
14.4;Grinding circuits;183
14.5;References;195
15;Chapter 8 Industrial screening;199
15.1;Introduction;199
15.2;Performance of screens;199
15.3;Factors affecting screen performance;201
15.4;Screen types;204
15.5;References;215
16;Chapter 9 Classification;216
16.1;Introduction;216
16.2;Principles of classification;216
16.3;Types of classifier;219
16.4;References;236
17;Chapter 10 Gravity concentration;238
17.1;Introduction;238
17.2;Principles of gravity concentration;238
17.3;Gravity separators;239
17.4;Jigs;240
17.5;Pinched sluices and cones;246
17.6;Spirals;249
17.7;Shaking tables;251
17.8;Pneumatic tables;254
17.9;Duplex concentrator;254
17.10;Mozley Laboratory Separator;255
17.11;Centrifugal concentrators;255
17.12;Gold ore concentrators;256
17.13;References;257
18;Chapter 11 Dense medium separation (DMS);259
18.1;Introduction;259
18.2;The dense medium;260
18.3;Centrifugal separators;264
18.4;DMS circuits;267
18.5;Typical dense medium separations;268
18.6;Laboratory heavy liquid tests;270
18.7;Efficiency of dense medium separation;273
18.8;Construction of partition curves;274
18.9;Organic efficiency;277
18.10;References;278
19;Chapter 12 Froth flotation;280
19.1;Introduction;280
19.2;Principles of flotation;280
19.3;Classification of minerals;282
19.4;Collectors;283
19.5;Frothers;289
19.6;Regulators;290
19.7;The importance of pH;295
19.8;The importance of pulp potential;296
19.9;The role of bubble generation and froth performance;298
19.10;Entrainment;299
19.11;The engineering of flotation;300
19.12;Electroflotation;328
19.13;Agglomeration-skin flotation;329
19.14;Flotation plant practice;329
19.15;Reagents and conditioning;332
19.16;Control of flotation plants;333
19.17;Typical flotation separations;340
19.18;Flotation of copper ores;340
19.19;Oxidised copper ores;345
19.20;References;357
20;Chapter 13 Magnetic and electrical separation;366
20.1;Introduction;366
20.2;Magnetic separation;366
20.3;References;385
21;Chapter 14 Ore sorting;386
21.1;Introduction;386
21.2;Electronic sorting principles;386
21.3;Examples;387
21.4;References;390
22;Chapter 15 Dewatering;391
22.1;Introduction;391
22.2;Sedimentation;391
22.3;Filtration;403
22.4;Drying;410
22.5;References;411
23;Chapter 16 Tailings disposal;413
23.1;Introduction;413
23.2;Methods of disposal of tailings;413
23.3;References;420
24;Appendix 1 Metallic ore minerals;422
25;Appendix 2 Common non-metallic ores;434
26;Appendix 3 Excel spreadsheets for formulae in Chapter 3;441
27;Index;450

Leseproben

2 Ore handling Introduction
Ore handling, which may account for 30–60% of the total delivered price of raw materials, covers the processes of transportation, storage, feeding, and washing of the ore en route to, or during, its various stages of treatment in the mill. Since the physical state of ores in situ may range from friable, or even sandy material, to monolithic deposits with the hardness of granite, the methods of mining and provisions for the handling of freshly excavated material will vary extremely widely. Ore that has been well broken can be transported by trucks, belts, or even by sluicing, but large lumps of hard ore may need individual blasting. Modern developments in microsecond delay fuses and plastic explosive have resulted in more controllable primary breakage and easier demolition of occasional very large lumps. At the same time, crushers have become larger and lumps up to 2 m in size can now be fed into some primary units. Open-pit ore tends to be very heterogeneous, the largest lumps often being over 1.5 m in diameter. The broken ore from the pit, after blasting, is loaded directly into trucks, holding up to 200 t of ore in some cases, and is transported directly to the primary crushers. Storage of such ore is not always practicable, due to its “long-ranged” particle size which causes segregation during storage, the fines working their way down through the voids between the larger particles; extremely coarse ore is sometimes difficult to start moving once it has been stopped. Sophisticated storage and feed mechanisms are therefore often dispensed with, the trucks depositing their loads directly into the mouth of the primary crusher. The operating cycle on an underground mine is complex. Drilling and blasting are often performed on one shift, the ore broken in this time being hoisted to the surface during the other two shifts of the working day. The ore is transported through the passes via chutes and tramways and is loaded into skips, holding as much as 30 t of ore, to be hoisted to the surface. Large rocks are often crushed underground by primary breakers in order to facilitate loading and handling at this stage. The ore, on arrival at the surface, having undergone some initial crushing, is easier to handle than that from an open pit mine and storage and feeding is usually easier, and indeed essential, due to the intermittent arrival of skips at the surface. The removal of harmful materials
Ore entering the mill from the mine (run-of-mine ore) normally contains a small proportion of material which is potentially harmful to the mill equipment and processes. For instance, large pieces of iron and steel broken off from mine machinery can jam in the crushers. Wood is a major problem in many mills as this is ground into a fine pulp and causes choking or blocking of screens, etc. It can also choke flotation cell ports, consume flotation reagents by absorption and decompose to give depressants, which render valuable minerals unfloatable. Clays and slimes adhering to the ore are also harmful as they hinder screening, filtration, and thickening, and again consume valuable flotation reagents. All these must be removed as far as possible at an early stage in treatment. Hand sorting from conveyor belts has declined in importance with the development of mechanised methods of dealing with large tonnages, but it is still used when plentiful cheap labour is available. Crushers can be protected from large pieces of “tramp” iron and steel by electromagnets suspended over conveyor belts (Figure 2.­1). These powerful electromagnets can pick up large pieces of iron and steel travelling over the belt and, at intervals, can be swung away from the belt and unloaded. Guard magnets, however, cannot be used to remove tramp iron from magnetic ores, such as those containing magnetite, nor will they remove non-ferrous metals or non-magnetic steels from the ore. Metal detectors, which measure the electrical conductivity of the material being conveyed, can be fitted over or around conveyor belts. The electrical conductivity of ores is much lower than that of metals and fluctuations in electrical conductivity in the conveyed material can be detected by measuring the change that tramp metal causes in a given electromagnetic field. Figure 1.1 Conveyor guard magnet When a metal object causes an alarm, the belt automatically stops and the object can be removed. It is advantageous with non-magnetic ores to precede the metal detector with a heavy guard magnet which will remove the ferromagnetic tramp metals and thus minimise belt stoppages. Large pieces of wood which have been “flattened out” by passage through a primary crusher can be removed by passing the ore feed over a vibrating scalping screen. Here the apertures of the screen are slightly larger than the maximum size of particle in the crusher discharge, allowing the ore to fall through the apertures and the flattened wood particles to ride over the screen and be collected separately. Wood can be further removed from the pulp discharge from the grinding mills by passing the pulp through a fine screen. Again, while the ore particles pass through the apertures, the wood collects on top of the screen and can be periodically removed. Washing of run-of-mine ore can be carried out to facilitate sorting by removing obscuring dirt from the surfaces of the ore particles. However, washing to remove very fine material, or slimes, of little or no value, is more important. Washing is normally performed after primary crushing as the ore is then of a suitable size to be passed over washing screens. It should always precede secondary crushing as slimes severely interfere with this stage. The ore is passed through high-pressure jets of water on mechanically vibrated screens. The screen apertures are usually of similar size to the particles in the feed to the grinding mills, the reason for which will become apparent. In the circuit shown in Figure 2.­2 material passing over the screen, i.e. washed ore, is transported to the secondary crushers. Material passing through the screens is classified into coarse and fine fractions by a mechanical classifier or hydrocyclone (Chapter 9) or both. It may be beneficial to classify initially in a mechanical classifier as this is more able to smooth out fluctuations in flow than is the hydrocyclone and it is better suited to handling coarse material. Figure 1.2 Typical washing plant flowsheet The coarse product from the classifier, designated “washing plant sands”, is either routed direct to the grinding mills or is dewatered over vibrating screens before being sent to mill storage. A considerable load, therefore, is taken off the dry crushing section. The fine product from classification, i.e. the “slimes”, may be partially dewatered in shallow large diameter settling tanks known as thickeners (Chapter 15) and the thickened pulp is either pumped to tailings disposal or, if containing values, pumped direct to the concentration process, thus removing load from the grinding section. In the circuit shown, the thickener overflows are used to feed the high-pressure washing sprays. Water conservation in this manner is practised in most mills. Wood pulp may again be a problem in the above circuit, as it will tend to float in the thickener, and will choke the water spray nozzles unless it is removed by retention on a fine screen. Ore transportation
In a mineral processing plant, operating at the rate of 400,000 t d-1, this is equivalent to about 28 t of solid per minute, requiring up to 75 m3 min-1 of water. It is therefore important to operate with the minimum upward or horizontal movement and with the maximum practicable pulp density in all of those stages subsequent to the addition of water to the system. The basic philosophy requires maximum use of gravity and continuous movement over the shortest possible distances between processing units. Dry ore can be moved through chutes, provided they are of sufficient slope to allow easy sliding, and sharp turns are avoided. Clean solids slide easily on a 15–25° steel-faced slope, but for most ores, a 45–55° working slope is used. The ore may be difficult to control if the slope is too steep. The belt conveyor is the most widely used method of handling loose bulk materials. Belts now in use are with capacities up to 20,000 t h-1 and single flight lengths exceeding 15,000 m (“­Bulk Materials Handling”­, 2005), with feasible speeds of up to 10 m s-1. The standard rubber conveyor belt has a foundation of sufficient strength to withstand the driving tension and loading strains. This foundation, which may be of cotton, nylon, or steel cord, is bound together with a rubber matrix and completely covered with a layer of vulcanised rubber. The carrying capacity of the belt is increased by passing it over troughing idlers. These are support rollers set normal to the travel of the belt and inclined upward from the centre so as to raise the edges and give it a trough-like profile. There may be three or five in a set and they will be rubber-coated under a loading point, so as to reduce the wear and damage from impact. Spacing along the belt is at the maximum interval which avoids excessive sag. The return belt is supported by horizontal straight idlers which overlap the belt by a few inches at each...