Mineral Beneficiation - A Concise Basic Course PDF

cover_SubbaRao2.qxd 19-04-2011 16:12 Pagina 1 MINERAL BENEFICIATION – A CONCISE BASIC COURSE D.V. SUBBA RAO Beneficiation of run-of-m...

cover_SubbaRao2.qxd 19-04-2011 16:12 Pagina 1 MINERAL BENEFICIATION – A CONCISE BASIC COURSE D.V. SUBBA RAO Beneficiation of run-of-mine ore is a process of value addition through discarding the unwanted gangue bearing minerals from the wanted minerals. Owing to the mineral beneficiation tangible benefits are saving in freight and handling, loss of metal or values through slag etc. whereas mineral conservation, environment protection by filling the mine using gangue bearing minerals, energy savings etc. are intangible benefits. This concise basic book presents the rudimental knowledge on mineral beneficiation principles and its unit operations. It explains the definitions and techniques along with the basic formulas with practical examples. This book is designed for professionals in mining and mineral engineering (Geologists, Mining, Metallurgical and Chemical Engineers). It can be A CONCISE BASIC COURSE MINERAL BENEFICIATION used both as a simple reference guide and as a concise course in mineral beneficiation. MINERAL BENEFICIATION A CONCISE BASIC COURSE D.V. SUBBA RAO an informa business  Mineral Beneficiation 7007TS-SUBBARAO-0211-01_Book.indb i 4/19/2011 2:49:48 AM This page intentionally left blank  Mineral Beneficiation A Concise Basic Course D.V. Subba Rao Head of the department of Mineral Beneficiation S.D.S. Autonomous College Andhra Pradesh, India 7007TS-SUBBARAO-0211-01_Book.indb iii 4/19/2011 2:49:48 AM CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2011 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20111129 International Standard Book Number-13: 978-0-203-84789-3 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the valid- ity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or uti- lized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopy- ing, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http:// www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com  Dedication Late Seth Sriman Durgaprasadji Saraf Founder, M/s Ferro Alloys Corp. Ltd, Shreeramnagar, A.P. India who has given me the great opportunity of serving students of Mineral Beneficiation in particular and the Mineral Engineering Profession in general 7007TS-SUBBARAO-0211-01_Book.indb v 4/19/2011 2:49:49 AM This page intentionally left blank  Tributes to Sri A.L. Mohan Director, Infronics Systems India Ltd., Hyderabad, A.P. India who lay the foundation for my professional growth 7007TS-SUBBARAO-0211-01_Book.indb vii 4/19/2011 2:49:49 AM This page intentionally left blank  Contents Preface xv Foreword xvii Acknowledgements xix List of tables xxi List of figures xxiii 1 Introduction 1 1.1 Minerals 2 1.2 Important Terminology 3 1.3 Beneficiation 4 1.4 Mineral Beneficiation 4 1.5 Mineral Beneficiation Operations 6 1.6 Unit Operations 7 1.7 Technology 7 2 Ore formation, identification and analysis 9 2.1 Ore Formation 9 2.2 Identification of Minerals 9 2.3 Mineral Analysis 10 3 Sampling 13 4 Size 17 4.1 Sieve Analysis 21 4.2 Testing Method 22 4.3 Presentation of Particle Size Distribution Data 24 4.4 Applications of Particle Size Distribution Data 25 4.5 Sub-Sieve Sizing 25 7007TS-SUBBARAO-0211-01_Book.indb ix 4/19/2011 2:49:49 AM  x Contents 5 Screening 27 5.1 Purpose of Screening 27 5.2 Screen Surfaces 27 5.3 Screen Action 29 5.4 Types of Screens 29 5.5 Factors Affecting the Rate of Screening 32 5.6 Screen Efficiency 32 6 Liberation 35 7 Comminution 39 7.1 Fracture 39 7.2 Laws of Comminution 40 7.3 Objectives of Comminution 42 7.4 Types of Comminution Operations 42 8 Crushing 43 8.1 Jaw Crushers 44 8.2 Gyratory and Cone Crushers 45 8.3 Roll Crushers 46 8.4 Impact Crushers 47 8.5 Bradford Breaker 47 8.6 High Pressure Grinding Rolls (HPGR) 48 8.7 Crushing Operation 48 8.8 Open Circuit and Closed Circuit Operations 49 9 Grinding 51 9.1 Ball Mill 52 9.2 Rod Mill 53 9.3 Tube or Pebble Mill 55 9.4 Autogenous Mill 55 9.5 Wet and Dry Grinding 55 9.6 Grinding Circuits 56 10 Separation operations 57 10.1 Separation of Ore Particles According to their Size 57 10.2 Separation of Ore Particles According to a Property Where Valuable Mineral Particles are Different from Gangue Mineral Particles in that Property 57 10.3 Separation of Ore Particles from the Mixture of Solids and Fluids 58 7007TS-SUBBARAO-0211-01_Book.indb x 4/19/2011 2:49:49 AM  Contents xi 11 Density 59 12 Settling of solids in fluids 63 12.1 Principles of Settling 63 12.1.1 Free settling 65 12.1.2 Hindered settling 66 12.1.3 Equal settling particles 66 12.1.4 Settling ratio 66 13 Classification 71 13.1 Classifiers 71 13.1.1 Sizing classifiers 73 13.1.2 Sorting classifiers 74 13.1.3 Centrifugal classifiers 76 14 Beneficiation operations 79 15 Gravity concentration 83 15.1 Float and Sink 84 15.2 Heavy Medium Separation 85 15.2.1 Chance cone process 86 15.2.2 Centrifugal separators 87 15.3 Jigging 88 15.4 Flowing Film Concentration 93 16 Froth flotation 99 16.1 Contact Angle 100 16.2 Flotation Reagents 101 16.3 Types of Flotation 104 16.4 Flotation Machines 105 16.5 Flotation Operation 106 16.6 Column Flotation 106 16.7 Flotation Practice of Sulphide Ores 107 17 Magnetic separation 109 17.1 Magnetism 109 17.2 Electro-Magnetism 111 17.3 Types of Minerals 114 17.4 Magnetic Separators 114 17.4.1 Tramp iron magnetic separators 115 17.4.2 Concentrators 115 7007TS-SUBBARAO-0211-01_Book.indb xi 4/19/2011 2:49:49 AM  xii Contents 17.4.2.1 Dry magnetic separators 116 17.4.2.2 Wet magnetic separators 117 18 Electrical separation 121 18.1 Charge and Charge Interactions 121 18.1.1 Conductors and insulators 122 18.1.2 Polarization 122 18.2 Methods of Charging 123 18.3 Electrostatic Separation 125 18.4 Electrostatic Separator 126 18.5 High Tension Separator 126 19 Dewatering 129 19.1 Thickening 129 19.2 Filtration 132 19.2.1 Types of filters 133 20 Materials handling 135 20.1 Properties of Bulk Solids 135 20.1.1 Size of the particles 135 20.1.2 Shape of the particles 136 20.1.3 Surface area of the particles 136 20.1.4 Particle density (Density of the bulk solids) 136 20.1.5 Bulk density 136 20.1.6 Compressibility 137 20.1.7 Cohesion and adhesion 137 20.1.8 Angle of repose 137 20.1.9 Angle of fall 138 20.1.10 Angle of difference 138 20.1.11 Angle of spatula 138 20.1.12 Angle of surcharge 139 20.1.13 Angle of slide 139 20.1.14 Tackiness 139 20.1.15 Abrasion 140 20.1.16 Corrosion 140 20.1.17 Friability (Degradation) 140 20.1.18 Dispersibility 140 20.1.19 Moisture content and hygroscopicity 140 20.2 Storage 140 20.3 Conveying 141 20.4 Feeders 142 20.5 Disposal of Products 142 7007TS-SUBBARAO-0211-01_Book.indb xii 4/19/2011 2:49:49 AM  Contents xiii 21 Beneficiation of minerals 143 21.1 Agglomeration 146 21.2 Mathematical Model 146 21.3 Simulation 147 21.4 Automatic Control 147 22 Applications 149 22.1 Assay Value and Grade 149 22.2 Sieve Analysis 150 22.3 Distribution of Metal Values 151 22.4 Efficiency of the Screen 152 22.5 Laws of Comminution 155 22.6 Reduction Ratio 156 22.7 Size of Roll in Roll Crusher 157 22.8 Crushing Circuits 157 22.9 Critical Speed 158 22.10 Grinding Circuits 160 22.11 Density and % Solids 161 22.12 Settling Velocities 163 22.13 Recovery, Grade, Loss of Metal etc 165 References 169 Further readings 171 Subject index 173 7007TS-SUBBARAO-0211-01_FM.indd xiii 4/19/2011 3:29:08 AM This page intentionally left blank  Preface This book is the essence of thirty years of my experience as a teacher of undergraduate students of Mineral Beneficiation and ten years as a trainer of working Engineers of Kutch minerals, Essar Steels, Tega Industries, and Trimex Sands. During the first fifteen years, I experienced the difficulty of injecting the basic principles of Mineral Beneficiation into the minds of the students. I consulted with my colleagues and many engineers working in mineral beneficiation plants in search of a way out. I found that the explanation of basic principles given in various books available on the market lacks clarity in concepts because they were not written for this purpose. Then a thought came into my mind to prepare notes exclusively on basic princi- ples. An attempt was made in 1994, when I prepared the notes and conducted a short term course for my own students where all the basic principles were explained in just four days. The response was very good. During later years, the notes were revised by adding few additional points and conducting the course for five days for students as well as working engineers. The response was very encouraging. Many engineers of mineral industries went through my notes, courtesy of my former students, and they were well appreciated. It was suggested that I should pub- lish the book for the benefit of the Mineral Industries at large. This led me to write this book. It is hoped that this small book will be of great use, not only for beginners but also for working engineers, erection engineers, designers, researchers and those who attend an interview at all levels. Any suggestions for improvement of this book will be appreciated, acknowledged and implemented in the right spirit. D.V. Subba Rao Head of the department of Mineral Beneficiation S.D.S.Autonomous College Shreeramnagar, Garividi – 535 101 Vizianagaram District Andhra Pradesh India e-mail: [email protected] 7007TS-SUBBARAO-0211-01_Book.indb xv 4/19/2011 2:49:50 AM This page intentionally left blank  Foreword I have great pleasure in writing the foreword for this book. Mr. D.V. Subba Rao and I are professional colleagues and have known each other for several years. His passion for Mineral Processing, in general, and teaching the fundamentals of the subject, in particular, are evident every time he steps into the classroom. I have had the opportunity to see his teaching in action on several occasions. In fact, I attended a full training course given by him to the engineers of Tega Industries limited, Kolkata. The way the participants responded to him is amazing. He has an uncanny ability to break down complex concepts into easy-to-understand lessons. In his book “COAL – ITS BENEFICIATION” (Subba Rao, 2003) he presents the concepts in simple way and includes lots of exercises to bring all the relevant concepts into one book to help students to grasp the principles and practicing engineers to apply the same for plant improvement studies. The present book is his second book. I applaud the author for creating such a book, trying to bring out the fundamentals in the area of Mineral Beneficiation. In this book, Mr. Subba Rao has included everything he has learnt, whilst teaching and conducting short courses for plant engineers, and created an easy-to-understand way of presentation with illustrations which will provide proper fundamentals of the subject not only to the students but also to the practicing engineers. Throughout the book, an emphasis on making the mineral engineering a specialized subject in its own right is the central theme. I am sure that this book will win the approbation of stu- dents, practicing engineers, researchers, and all associated with mineral development including legends in the subject. I compliment Mr. Subba Rao for his dedicated service to the field of Mineral Processing. If you are a student or practicing engineer searching for the fundamentals of Min- eral Beneficiation/Processing to learn in the right way, this book is for you. Dr. T.C. Rao Formerly Director Regional Research Laboratory, Bhopal Professor and Head of the Department of Fuel and Mineral Engineering Indian School of Mines, Dhanbad 7007TS-SUBBARAO-0211-01_Book.indb xvii 4/19/2011 2:49:50 AM This page intentionally left blank  Acknowledgements I am grateful to Dr. T.C. Rao, former Director, Regional Research Laboratory, Bhopal, and Professor and Head of the Department of Fuel and Mineral Engineering, Indian School of Mines, Dhanbad for continuous encouragement in writing this book. I sincerely thank Prof. Kal Sastry, University of California, for his comments and suggestions on the contents of this book. I am indebted to my colleagues Sri Y. Ramachandra Rao and Sri K. Satyanarayana, who helped me in various ways, including subject discussions and critical analysis and Sri A.K. Shrivastav and Sri K. Ganga Raju for their precious and supreme services rendered in bringing out this book. I am thankful to FACOR management, in particular Sri R.K. Saraf (CMD), Dr. V. Subba Rao (Principal) and several other colleagues, both teaching and non- teaching, of S.D.S. Autonomous College for extending their cooperation in preparing this book. Special thanks go to Sri C. Raghu Kumar, one of my former students, who has taken lot of pains to help with this book. It has been a pleasure to work with Taylor & Francis group and the cooperation of the editorial and production staff is much appreciated. Finally, my deepest gratitude to my wife Mrs. Krishna Veni and daughters, Mrs. Radha Rani and Ms. Lalitha Rani for their unfailing emotional support in bringing out this book. I gratefully acknowledge the following organizations for permitting me to use respective photographs: Jayant Scientific Industries, Mumbai Table Model Sieve Shaker Maharashtra, India Ro-tap Sieve shaker Mogensen, Grantham, Divergator Lincolnshire, England Vibrating grizzly Deister Concentrator LLC, USA Sieve Bend Qingzhou Yuanhua Machinery Trommel Manufacture Co. Ltd., China Robert Cort Ltd., Reading, England Vibrating Screen 7007TS-SUBBARAO-0211-01_Book.indb xix 4/19/2011 2:49:50 AM  xx Acknowledgements FLSmidth Pvt Ltd, Kelambakkam, Cut section of Fuller-Traylor Tamilnadu, India Gyratory Crusher Pennsylvania Crusher Corporation, USA Bradford Breaker Metso Minerals Industries, Inc Cut section of Cylindroconical Ball Mill www.mine-engineer.com Cut section of Cylindrical Ball Mill Outotec (USA) Inc., Jacksonville, Humphrey Spiral 7007TS-SUBBARAO-0211-01_Book.indb xx 4/19/2011 2:49:50 AM  List of tables 1.1 Abundance of chemical elements in the Earth’s crust 1 1.2 Metallic minerals 2 1.3 Non-metallic minerals 3 3.1 Particle size and minimum weight of the sample 15 4.1 Comparison of test sieves of different standards 19 4.2 Particle size distribution data from size analysis test 23 4.3 Calculated values for particle size distribution 24 4.4 Size analysis methods for sub-sieve sizing 26 5.1 Types of screen surfaces 28 14.1 Beneficiation operations and basis of separation 79 15.1 Concentration criterion of minerals separated by gravity separation from a gangue of density 2.65 gm/cc 84 15.2 Organic liquids and their specific gravities 85 15.3 Medium solids 86 16.1 Quantities of flotation reagents 104 20.1 Flowability character 138 20.2 Inter-relationship between angle of repose, surcharge and flowability 139 22.1 Sieve analysis data 150 22.2 Calculated values for determination of average size 150 22.3 Calculated values for drawing graph 151 22.4 Size analysis data 152 22.5 Calculated values 152 22.6 Size analysis data 155 22.7 Plant performance data 166 7007TS-SUBBARAO-0211-01_Book.indb xxi 4/19/2011 2:49:50 AM This page intentionally left blank  List of figures 1.1 The major steps in processing of ores 5 3.1 Sampling process 14 4.1 Spherical and cubical particles 17 4.2 Test sieve 18 4.3 Table model sieve shaker 21 4.4 Ro-tap sieve shaker 21 4.5 Sieve analysis at the end of sieving 22 4.6 Graphical presentation of particle size distribution data 24 4.7 Plot for determination of 80% passing size D80 25 5.1 Simplified screen 29 5.2 Grizzly 30 5.3 Divergator 30 5.4 Sieve bend 30 5.5 Trommel 30 5.6 Vibrating grizzly 31 5.7 Vibrating screen 31 6.1 A particle of an ore containing A, B and C minerals 36 6.2 Liberation methods 37 6.3 Typical comminution product 38 7.1 Compressive forces 39 7.2 Mechanism of fracture 40 8.1 (a) Single toggle jaw crusher; (b) Double toggle jaw crusher 44 8.2 Types of jaw crushers 44 8.3 Cut section of Fuller-Traylor gyratory grusher 45 8.4 Types of crushing chambers 46 8.5 Roll crusher 47 8.6 Angle of nip of roll crusher 47 8.7 Hammer mill 47 8.8 Bradford breaker 48 8.9 High pressure grinding rolls (HPGR) 48 8.10 Crushing circuits 49 9.1 (a) Cylindroconical ball mill; (b) Cylindrical ball mill 52 9.2 Motion of the charge in a ball mill 52 9.3 Zones in a ball mill 53 9.4 Grinding action of rods 54 7007TS-SUBBARAO-0211-01_Book.indb xxiii 4/19/2011 2:49:50 AM  xxiv List of figures 9.5 Types of rod mills according to method of discharge 54 9.6 Open circuit grinding 56 9.7 Closed circuit grinding 56 12.1 (a) Free settling; (b) Hindered settling 65 12.2 Free settling of (a) Fine particles; (b) Coarse particles 67 13.1 (a) Free settling; (b) Hindered settling 72 13.2 Principle of a mechanical classifier 73 13.3 (a) Spiral classifier; (b) Rake classifier 73 13.4 Principle of sorting classifier 74 13.5 Hydraulic classifier with sorting effect 75 13.6 Hydraulic classifier with sizing effect 75 13.7 Hydrocyclone 76 13.8 Hydrocyclone operation 77 14.1 Flow sheet of three stage treatment 82 15.1 Chance cone separator 87 15.2 Settling velocities of six particles 89 15.3 Jigging process 90 15.4 Stratification of equal size particles due to jigging action 90 15.5 Stratification of different size particles due to jigging action 90 15.6 Basic construction of a hydraulic jig 91 15.7 Harz jig 92 15.8 Baum jig 92 15.9 Flow of water on sloping deck 93 15.10 Particles’ drift in flowing water 93 15.11 Forces of flowing water on particle 94 15.12 Arrangement of particles over a deck of flowing film 94 15.13 Pinched sluice 95 15.14 Reichert cone 95 15.15 Humphrey spiral concentrator 95 15.16 Effect of riffle over a deck of flowing film 96 15.17 Stratification of particles due to the shaking motion 96 15.18 Comparison between tabling and sorting followed by tabling 97 15.19 Wilfley table 98 16.1 Process of rising air bubbles and forming froth 100 16.2 Contact angle 101 16.3 Denver sub-aeration cell 105 16.4 A typical flotation circuit 106 16.5 Flotation column 107 17.1 Magnetic lines of force 111 17.2 Types of solenoid 112 17.3 Magnetic circuit 112 17.4 Magnetic circuit with air gap 113 17.5 Tramp iron magnetic separators 115 17.6 Dry magnetic drum separators 116 17.7 Induced roll magnetic separator 117 17.8 Low-intensity wet drum magnetic separators 118 17.9 Wet high-intensity magnetic separator 118 7007TS-SUBBARAO-0211-01_Book.indb xxiv 4/19/2011 2:49:50 AM  List of figures xxv 18.1 Classification of materials based on conducting ability 122 18.2 Charging by induction with negatively charged object 123 18.3 Charging by induction with positively charged object 124 18.4 Charging single sphere by induction 124 18.5 Electrostatic separator 127 18.6 High tension separator 127 18.7 Multi-pass electrostatic separator 128 19.1 Batch sedimentation test 130 19.2 Dorr thickener 131 19.3 Mechanism of filtration 132 19.4 Rotary vacuum drum filter 133 19.5 Rotary vacuum disc filter 134 19.6 Sector 134 20.1 Angle of repose 138 21.1 Model flow sheet for beach sands beneficiation plant 144 21.2 Model flow sheet for chromite ore beneficiation plant 145 21.3 Model flow sheet for iron ore beneficiation plant 145 22.1 Graph to determine 80% passing size 151 22.2 Closed circuit crushing 158 22.3 Path of a ball 159 22.4 Forces on a ball 159 22.5 Closed circuit grinding 161 7007TS-SUBBARAO-0211-01_Book.indb xxv 4/19/2011 2:49:50 AM This page intentionally left blank  Chapter 1 Introduction The Earth’s Crust is the topmost solid layer of the Earth which has a thickness of 30–35 km in the continents and 5–6 km in the oceans (the Mantle and the Core being the other two inner parts of the earth). According to F.W. Clarke, the abundance of Chemical elements in the earth’s crust is shown in Table 1.1. The chemical elements that occur in the earth’s crust in compound forms are known as minerals. However, certain elements like Gold, Silver, Platinum and Copper often occur in native form. The use of minerals has been instrumental in raising the standard of living of mankind. The sophisticated world of today is largely the result of the enlarged use of minerals for various purposes. All engineering and structural materials, machinery, plants, equipments and anything from a pin to a plane are manufactured from metals extracted from minerals. Some minerals form the starting point for basic industries like cement, fertilizer, ceramic, electrical, insulating, refractory, paint and abrasive materials and a host of chemicals. There is not a single industry which can do without minerals or their products. Minerals, thus, form part and parcel of our daily life. Table 1.1 Abundance of chemical elements in the Earth’s crust. Chemical elements Percentage Oxygen 46.46 Silicon 27.61 Aluminium 8.07 Iron 5.06 Calcium 3.64 Sodium 2.75 Potassium 2.58 Magnesium 2.07 Titanium 0.62 Hydrogen 0.14 Phosphorus 0.12 Manganese 0.09 Carbon 0.09 Sulphur 0.06 Barium 0.04 Flourine 0.03 Strontium 0.02 All other elements 0.50 7007TS-SUBBARAO-0211-01_Book.indb 1 4/19/2011 2:49:50 AM  2 Mineral beneficiation 1.1 MINERALS As defined by Dana, a well known physicist: Mineral is a substance having definite chemical composition and internal atomic structure and formed by the inorganic processes of nature Minerals are broadly classified into two types: 1 Metallic minerals. 2 Non-metallic minerals. Metallic minerals are the minerals from which a metal is extracted. A few metallic minerals, their chemical formulae, metal extracted and the percent metal present in the mineral are shown in Table 1.2. The minerals of Uranium and Thorium are also called atomic minerals. Non-metallic minerals are the minerals used for industrial purposes for making cement, refractories, glass and ceramics, insulators, fertilizers etc. These minerals are also called industrial minerals. Metals are not extracted from these minerals. Some metallic minerals are also used for industrial purposes like Bauxite, Chromite and Zircon for the refractory industry, Pyrolusite for dry battery cells and Ilmenite for the pigment industry, etc. A few non-metallic minerals with their chemical formulae are shown in Table 1.3. The third type, coal, is considered a mineral and is sometimes spoken of as min- eral coal in trade, industry and legal affairs. But in a restricted technical sense, coal is not a mineral. It is organic in composition and formed from decaying vegetation and mineral matter. As it is a useful part of the earth’s crust and requires treatment before use, it can be classed as third type of special significance. Table 1.2 Metallic minerals. Mineral Chemical formula Metal extracted % metal Hematite Fe2O3 Iron 69.94 Magnetite Fe3O4 Iron 72.36 Bauxite Al2O3.2H2O Aluminium 39.11 Braunite 3Mn2O3 MnSiO3 Manganese 63.60 Pyrolusite MnO2 Manganese 63.19 Chromite FeO Cr2O3 Chromium 46.46 Galena PbS Lead 86.60 Sphalerite ZnS Zinc 67.10 Chalcopyrite CuFeS2 Copper 34.63 Ilmenite FeO TiO2 Titanium 31.57 Rutile TiO2 Titanium 59.95 Zircon ZrSiO4 Zirconium 49.76 Pitchblende U3O8 Uranium 84.80 Monazite (Ce,La,Th)PO4 Thorium – 7007TS-SUBBARAO-0211-01_Book.indb 2 4/19/2011 2:49:50 AM  Introduction 3 Table 1.3 Non-metallic minerals. Mineral Chemical formula Andalusite Al2SiO2 Apatite Ca4(CaF)(PO4)3 Asbestos (Crysotile) Mg3Si2O5(OH)4 Baryte BaSO4 Bentonite (Ca Mg)O SiO2 (Al Fe)2O3 Calcite CaCO3 Corundum Al2O3 Diamond C Diaspore Al2O3H2O Dolomite CaMg(CO3)2 Feldspar (Na,K,Ca) AlSi3O8 Fluorite CaF2 Garnet (Almandine) 3FeO Al2O3 3SiO2 Graphite C Gypsum CaSO4.2H2O Kaolinite (China clay) H4 Al2Si2O9 Kyanite Al2SiO5 Limestone CaCO3 Marble Chiefly CaCO3 Magnesite MgCO3 Mica (Muscovite) KAl2(AlSi3O10)(OH,F)2 Phosphate rock Ca3(PO4)2 Pyrite FeS2 Pyrophyllite H Al(SiO3)2 Quartz SiO2 Sillimanite Al2O3 SiO2 Talc H2 Mg3(SiO3)4 Vermiculite 3 MgO(FeAl)2O3 3SiO2 1.2 IMPORTANT TERMINOLOGY Minerals do not occur singly in the earth’s crust. They occur in association with sev- eral other minerals. The following important terminology is used in describing the mineral deposits and related terms. Rock is an aggregation of several minerals as occurred in the earth’s crust. Ore is also an aggregation of several minerals from which one or more minerals can be exploited/separated at profit. All Ores are Rocks, but all Rocks are not Ores An Ore at one place may be a Rock at other place Ore Minerals or Valuable Minerals are those minerals which contain an economically exploitable quantity of some metal or non-metal. Gangue Minerals are usually the non-metallic minerals associated with ore minerals which are worthless as a source for that metal or otherwise. These are usually 7007TS-SUBBARAO-0211-01_Book.indb 3 4/19/2011 2:49:50 AM  4 Mineral beneficiation unwanted, waste or useless minerals. These gangue minerals occasionally find use as source of by-products. For example, pyrite present in Lead and Zinc ores is a gangue mineral but it is separated as by-product for extraction of sulphur after the lead and zinc minerals are separated. Ore Deposits are the natural deposits of ore minerals. Ore is an aggregation of valuable and gangue minerals. Simple Ore is one from which a single metal can be extracted. For example, only Iron is extracted from Hematite ore, Aluminium is extracted from Bauxite ore, Chro- mium is extracted from Chromite ore, etc. Complex Ore is one from which two or more metals can be extracted. Lead, Zinc and Copper metals are extracted from Lead-Zinc-Copper Ore. Metal Content of a mineral is generally expressed in percent of metal present in the mineral. It is calculated by taking the atomic weights of the elements present in the mineral. Let us consider Hematite (Fe2O3) Atomic weight of Iron = 55.85 Atomic weight of Oxygen = 16.00 Molecular weight of Hematite = 55.85 × 2 + 16 × 3 = 159.7 55.85 × 2 Percent Iron = × 100 = 69.94 159.7 Assay Value or Tenor is the percent metal, percent valuable mineral, or ounces precious metal per ton depending upon the type of ore involved. Grade is a relative term used to represent the value of an ore. High Grade Ore is an ore having a high assay value and Low Grade Ore is an ore having a low assay value. The Ore having an assay value between that of high and low value is called Medium Grade Ore. Rich Ore and Lean Ore are the other terms of common usage where an ore with a high assay value is rich ore and an ore with low assay value is lean ore. 1.3 BENEFICIATION Separation of the wanted part from the aggregation of wanted and unwanted parts by physical methods is termed as Beneficiation. Separation of rice from the mixture of rice and stones is the example known to everyone. 1.4 MINERAL BENEFICIATION As defined by A.M. Gaudin Mineral Beneficiation can be defined as processing of raw minerals to yield mar- ketable products and waste by means of physical or mechanical methods in such a way that the physical and chemical identity of the minerals are not destroyed. 7007TS-SUBBARAO-0211-01_Book.indb 4 4/19/2011 2:49:50 AM  Introduction 5 Geological survey Mining BENEFICIATION Smelting or Industrial use Figure 1.1 The major steps in processing of ores. It follows that mineral beneficiation is a process designed to meet the needs of the consumer of minerals. Run-of-mine Ore is an ore directly taken from the mine, as it is mined. Figure 1.1 shows the successive major steps involved in processing the ores. Geologists conduct a geological survey and estimate the ore reserves, their quality and tenor. Mining engineers mine the ore and bring it to the surface of the earth. Min- eral Engineers beneficiate the ore to higher tenor. Thus beneficiated ore, if it is metallic ore, is smelted and the metal is extracted which is further utilized for the production of alloys. If the ore is non metallic, beneficiated ore is directly utilized for the produc- tion of various products like cement, fertilizers etc. Smelting operation, for the extraction of a metal, requires: Uniform quality of the ore. Appropriate size of the ore. Minimum tenor of the ore. Beneficiation of run-of-mine ore is done to achieve the above. The primary object of Mineral Beneficiation is to eliminate either unwanted chemical species or particles of unsuitable size or structure. During beneficiation, much of the gangue minerals, usually present in large quan- tities in many ores, are eliminated or removed. The benefits are: 1 Freight and handling costs reduced. 2 Cost of extraction (smelting) reduced. 3 Loss of metal in slag reduced. By doing beneficiation, lean ores can be made technically suitable for extraction of metal. Mineral Beneficiation is usually carried out at the mine site. The essential reason is to reduce the bulk of the ore which must be transported, thus saving the transport cost. 7007TS-SUBBARAO-0211-01_Book.indb 5 4/19/2011 2:49:50 AM  6 Mineral beneficiation The reasons for the increasing importance of Mineral Beneficiation are: 1 Reserves of good quality ore (high grade ore) are depleting day by day as much of such ore is continuously mined and utilized for extraction of metal and hence it is unavoidable to use low grade ores (which need beneficiation) for metal extraction to meet the demands. 2 In order to use un-mined reserves of a particular mine, switching over from Selec- tive mining to a cheaper mining method, Bulk mining, is found to be more eco- nomical wherein beneficiation is a must. 3 When compared to metallurgical processes Mineral Beneficiation is inexpensive. 1.5 MINERAL BENEFICIATION OPERATIONS The following are some of the synonymous terms used for Mineral Beneficiation: Mineral Dressing Mineral Processing Ore Dressing Ore Processing Ore Preparation Ore Concentration Ore Upgradation Ore Enrichment Milling Even though the individual terms have their own significance and meaning, it can be taken that all the terms are alike as far as simple understanding is considered. The principal steps involved in beneficiation of Minerals are: 1 Liberation: Detachment or freeing of dissimilar particles from each other i.e. val- uable mineral particles and gangue mineral particles. Operations: Crushing Grinding 2 Separation: Actual separation of liberated dissimilar particles i.e., valuable min- eral particles and gangue mineral particles. Operations: Gravity concentration Heavy Medium Separation Jigging Spiraling Tabling Flotation Magnetic separation Electrical separation Miscellaneous operations like hand sorting 7007TS-SUBBARAO-0211-01_Book.indb 6 4/19/2011 2:49:51 AM  Introduction 7 Supporting Operations: Preliminary washing Screening Classification Thickening Filtration Handling of materials Storage Conveying Feeding Pumping Pneumatic and Slurry transport Supporting operations (one or the other) are essential operations of any plant without which no plant exists. A road metal crusher, for example, can perform its job only when proper arrangements are made to feed the metal to the crusher and to convey the crushed metal for separating it into different sizes. 1.6 UNIT OPERATIONS The operations conducted on any material that involve physical changes are termed as Unit Operations. The various operations performed for the beneficiation of minerals are all unit operations as the changes in these operations are primarily physical. The basic principles involved in Unit Operations are independent of the material treated. In designing a treatment method, it is essential to recognize the unit operations to be performed. 1.7 TECHNOLOGY The term technology is used in the sense of the application of technical skills along with the economic justification of the operations. A sound knowledge of basic sciences such as chemistry, physics and mathematics as well as engineering crafts required in the handling of large tonnages of ore and fluids, is of prime importance in the study of this technology. Experience and judgment play an important part in the application of theoretical principles. 7007TS-SUBBARAO-0211-01_Book.indb 7 4/19/2011 2:49:51 AM This page intentionally left blank  Chapter 2 Ore formation, identification and analysis 2.1 ORE FORMATION Ores in the earth’s crust have been formed by several processes. These ore-forming processes have been classified from time to time by several workers. However, in 1950, Bateman proposed a classification of the processes as shown below : 1 Magmatic concentration. 2 Sublimation. 3 Contact metasomatism. 4 Hydrothermal processes. 5 Sedimentation. 6 Evaporation. 7 Residual and mechanical concentration. 8 Oxidation and supergene enrichment. 9 Metamorphism. According to the manner of formation, ore deposits are divided into three great types as given below: 1 Igneous. 2 Sedimentary. 3 Metamorphic. 2.2 IDENTIFICATION OF MINERALS The following are the some of the physical properties of minerals through which min- erals can be identified before they are put to use: 1 Characters dependent upon light a Colour b Streak c Lustre d Transparency 7007TS-SUBBARAO-0211-01_Book.indb 9 4/19/2011 2:49:51 AM  10 Mineral beneficiation e Phosphorescence f Fluorescence 2 Taste, odour and feel 3 State of aggregation a Form b Habit c Pseudomorphism, Polymorphism and Polytipism d Cleavage e Fracture g Hardness h Tenacity 4 Specific gravity (density) 5 Magnetic susceptibility 6 Electrical conductivity 7 Radioactivity 8 Surface property The identification of minerals by their physical properties is termed as Megascopic Identification. Minerals are also identified by their optical properties under a micro- scope. Transparent minerals are identified under a Petrological or Mineralogical microscope whereas opaque minerals are identified under an Ore microscope. This microscopic examination, carried out for thorough understanding of the mineralogy of ore, determine the mineral species present in the ore and their relative abundance. Texture of mineral occurrences is an important property useful for separation of valuable minerals from their ores. Textures are mainly of three types: Fine-grained 5 mm 2.3 MINERAL ANALYSIS Minerals are analyzed by conventional chemical analysis. Two types of chemical anal- ysis are: 1 Qualitative Analysis, in which elements present in the sample are identified. 2 Quantitative Analysis, in which the quantity of elements, or compounds, present in the sample is estimated. In a few instances it may be possible to calculate the mineral proportions of a sam- ple specimen from the results of a chemical analysis. More usually, chemical analysis can, at best, only provide a rough estimate of the mineral content of an ore or plant product. The combined information on mineral identities, mineral compositions and mineral proportions, will establish how the various chemical elements are partitioned 7007TS-SUBBARAO-0211-01_Book.indb 10 4/19/2011 2:49:51 AM  Ore formation, identification and analysis 11 (or shared) among the various minerals. This information can then be used to estimate both the quantities and the qualities of the various products that may be obtained from an ore. Several varieties of instrumental methods are also available for analysis of ores and minerals. The three following points are to be noted carefully in case of metallic ores: 1 The grade or quality of an ore is represented by its metal content. 2 The minerals are separated during beneficiation. 3 The metal is extracted through metallurgical operations. 7007TS-SUBBARAO-0211-01_Book.indb 11 4/19/2011 2:49:51 AM This page intentionally left blank  Chapter 3 Sampling A Mineral Beneficiation plant costs thousands of dollars to build and operate. The success of the plant relies on the assays of a few small samples. Representing large ore bodies truly and accurately by a small sample that can be handled in a laboratory is a difficult task. The difficulties arise chiefly in collecting such small samples from the bulk of the material. The method or operation of taking the small amount of material from the bulk is called Sampling. It is the art of cutting a small portion of material from a large lot. The small amount of material is called Sample and it should be representative of the bulk in all respects (in its physical and chemical properties). More precisely, sampling can be defined as the operation of removing a part, convenient in quantity for analy- sis, from a whole which is much greater, in such a way that the proportion and distri- bution of the quality to be tested are the same in both the sample and the whole. Sampling is a statistical technique based on the theory of probability. The first and most obvious reason for sampling is to acquire information about the ore entering the plant for treatment. The second is to inspect its condition at selected points during its progress through the plant so that comparison can be made between the optimum requirements for efficient treatment and those actually existing, should these not coin- cide. The third is to disclose recovery and reduce losses. The prerequisite for the development of a satisfactory flowsheet is the acquisition of a fully representative ore sample, even though, in respect of a new ore-body, this sample may have to be something of a compromise. A bad sample will result in wast- age of all test work and can lead to a completely wrongly designed mill. A sample can be taken from any type of material dry, wet or pulp. But, in each case, the method of sampling and the apparatus necessary for them are different. A sample is collected from huge lot of dry material in stages. At first, a large quantity sample is collected from a lot, known as primary sample or gross sample, by means of various types of sampling equipment such as mechanical or hand-tool samplers using appropriate sampling methods and techniques. The two methods used to obtain a gross sample are Random sampling and Sys- tematic sampling. The various hand-tool samplers used are Drill, Shovel, Scoop, Auger, Pipe and Slot samplers. The gross sample is reduced to a quantity that can be handled with ease by alternate shoveling or fractional shoveling in stages depending upon the quantity of the gross sample. It is essential that the gross sample be thoroughly mixed before reduction in order to obtain a representative sub-sample or laboratory sample. 7007TS-SUBBARAO-0211-01_Book.indb 13 4/19/2011 2:49:51 AM  14 Mineral beneficiation Such reduced samples are called secondary sample and ternary sample depending upon the number of stages used. Figure 3.1 shows the stages of sampling. Reduction of this reduced sample to a quantity necessary for analysis, known as final sample or test sam- ple, is called sample preparation. It is the process of reducing the quantity by splitting. Sample preparation is done by Coning and quartering or by using paper cone splitter, riffle splitter, rotary cone splitter, rotary table splitter or micro splitter. The sampler’s knowledge, experience, judgment and ability are of greater value because instructions cannot cover every point or combination of circumstances encountered on each preparation. When it is required to collect samples from streams of solids and/or pulps, man- ual or mechanical sample cutters are employed to cut and withdraw small quantities from a stream of traveling material at predetermined frequencies and speeds to form a gross sample. The sample cutter should travel across the material stream and intersect the stream perpendicular to the flow so that the material from the entire width of the stream is collected. The cutter width should be 3 times the top size of the particle and should travel at constant speed. A common falling ore sampling device is the Vezin sampler. Sampling devices called poppet valves are used for pulp sampling in pipes. These are typically used in pipes where the flow is upward. The procedure to be adopted for taking a sample and the amount of the sample depends on the size of the original material, particle size of the material, the method of sampling and the purpose for which the sample is taken. Table 3.1 is one of the early sampling studies that proposed to relate the particle size of the material being sampled to the sample size required for a representative sample. The basis for the sample for this theory was 100 tons of ore. As one can see, the finer the material being sampled, the smaller the size of sample required. Owing to the statistical fact that the finer particles have many more individual particles per pound than the coarser particles do and, since ore is made up of many different materials, Figure 3.1 Sampling process. 7007TS-SUBBARAO-0211-01_Book.indb 14 4/19/2011 2:49:51 AM  Sampling 15 Table 3.1 Particle size and minimum weight of the sample. Particle size Minimum weight of the sample, inches pounds 0.04 0.0625 0.08 0.5 0.16 4 0.32 32 0.64 256 1.25 2048 2.50 16348 the finer particles are much more likely to contain all of the individual elements of the whole sample. When a sample is to be taken for chemical analysis to determine the assay value of the ore, the sample should be re-crushed sufficiently between each cutting down of the sample so that the ratio of the diameter of the largest particles to the weight of the sample to be taken shall not exceed a certain safe proportion. It is to be noted that no amount of mixing and careful division can make the sample and reject alike in value when the lot before division contains an uneven number of large high grade ore particles. In a process plant, or mine, the preferred method of obtaining a sample, is from a moving stream, such as a conveyor belt, a slurry pipe line, or perhaps from a chute that a stream of ore flows through. The material collected each time is called an increment. How the sample is obtained, the number of increments and the size of each increment, will often determine the degree of probability that a sample is indeed representative. The sampling ratio, which is defined as the ratio of the weight of the sample taken by the sampling system to the weight of the lot from which that sample is taken, is the most important indicator of the performance of the sampling system. When the sample is taken, and subjected to analysis, there exists some chance of error in a single sample. One must take the number of samples to reduce the error and to keep the overall error within the tolerable working limits. 7007TS-SUBBARAO-0211-01_Book.indb 15 4/19/2011 2:49:52 AM This page intentionally left blank  Chapter 4 Size Size of the particle is an important consideration in Mineral Beneficiation because of the following main reasons: Energy consumed for reducing the size of the particles depends on size. Size of the particles determines the type of size reduction equipment, beneficiation equipment and other equipment to be employed. The size of the particle of standard configuration like sphere and cube can easily be specified. For example, the size of a spherical particle is its diameter (d) and that of a cubical particle is the length of its side (l) as shown in Figure 4.1. As the mineral particles are irregular in shape, it is difficult to define and deter- mine their size. A number of authors have proposed several empirical definitions to particle size. Feret , in 1929, defined the size of an irregular particle as the distance between the two most extreme points on the surface of a particle. Martin , in 1931, defined the length of the line bisecting the maximum cross-sectional area of the particle. During later years, the size of a particle is defined by comparison with a standard configuration, normally a spherical particle. Equivalent size or equivalent diameter of an irregular particle is defined as the diam- eter of a spherical particle which behaves similar to an irregular particle under specified conditions. Surface diameter is defined as a diameter of a spherical particle having the same sur- face area as the irregular particle. Volume diameter is defined as the diameter of a spherical particle having the same volume as the irregular particle. Figure 4.1 Spherical and cubical particles. 7007TS-SUBBARAO-0211-01_Book.indb 17 4/19/2011 2:49:52 AM  18 Mineral beneficiation Figure 4.2 Test sieve. It is obvious that each definition has its own limitations. In mineral industry, the side of a square aperture through which a particle just passes is taken as the size of the particle even though little or no importance is given to its shape. Standard Test Sieves are used in the mineral industry to measure the size of the small and the fine particles, usually down to 74 microns. Test Sieve is a circular shell of brass having an 8 inch diameter and being about 2 inch high as shown in Figure 4.2. Sieve cloth is made of wire, woven to produce nominally uniform cloth apertures (openings). The sieve cloth is placed in the bottom of the shell so that material can be held on the sieve. Aperture (or Opening) is a distance between two parallel wires. Mesh number is the number of apertures per linear inch. Sieves are designated by mesh number. Mesh size is the size of an aperture i.e. the distance between two parallel wires. As mesh number increases, mesh size decreases. Sieve Scale is the list of successive sieve sizes used in any laboratory, taken in order from coarsest to finest. Standard Sieve Scale is the sieve scale adopted for size analyses and general testing work to facilitate the interchangeability of results and data. In this standard sieve scale, the sizes of successive sieves in series form a geometric progression. For a standard sieve scale, the reference point is 74 microns, which is the aperture of a 200 mesh woven wire sieve. The ratio of the successive sizes of the sieves in the standard sieve scale is 2 , which means that the area of the opening of any sieve in the series is twice that of the sieve just below it and one half of the area of the sieve above it in the series. In general, mesh number × mesh size in microns ≈ 15,000. For closer sizing work the sieve ratio of 4 2 is common. The different standards in use are: American Tyler Series American Standards for Testing and Materials, ASTM E-11-01 7007TS-SUBBARAO-0211-01_Book.indb 18 4/19/2011 2:49:52 AM 7007TS-SUBBARAO-0211-01_Book.indb 19 Table 4.1 Comparison of test sieves of different standards. U.S.A. BRITISH INDIAN FRENCH AFNOR GERMAN TYLER ASTM E-11-01 B.S 410-2000 I.S. 460-1962 NFX-11-501 DIN 3310-1 :2000 Sieve Mesh Sieve Sieve Sieve Sieve Sieve designation Width of double designation Width of designation Width of designation Width of designation Width of designation Width of mesh aperture tyler mesh aperture mesh aperture mesh aperture mesh aperture mesh aperture no. mm series no. mm no. mm no. mm no. mm no. mm – – – – – – – – – 38 5.00 5.00 4 4.75 – 4 4.75 3½ 4.75 480 4.75 – – 4.50 – 4.00 5 5 4.00 4 4.00 400 4.00 37 4.00 2E 4.00 6 3.35 – 6 3.35 5 3.35 340 3.35 – – – – – – – – – 3.15 320 3.18 36 3.15 3.15 – 2.80 7 7 2.80 6 2.80 280 2.80 – – 2.80 8 2.36 – 8 2.36 7 2.36 240 2.39 35 2.50 2.50 – 2.00 9 10 2.00 8 2.00 200 2.00 34 2.00 3E 2.00 10 1.70 – 12 1.70 10 1.70 170 1.70 33 1.60 1.60 – 1.40 12 14 1.40 12 1.40 140 1.40 – 1.40 1.40 – – – – – – 1.25 – – 32 1.25 1.25 14 1.18 – 16 1.18 14 1.18 120 1.20 – – 5 1.20 – 1.00 16 18 1.00 16 1.00 100 1.00 31 1.00 6 1.00 20 0.85 – 20 0.850 18 0.850 85 0.850 – – – – – – – – – 0.800 80 0.79 30 0.800 0.800 – 0.710 24 25 0.710 22 0.710 70 0.710 – 0.710 0.710 – – – – – – 0.630 – – 29 0.630 0.630 28 0.600 – 30 0.600 25 0.600 60 0.600 – – 10 0.600 – 0.500 32 35 0.500 30 0.500 50 0.500 28 0.500 12 0.500 35 0.425 – 40 0.425 36 0.425 40 0.425 – – – – – – – – – 0.400 – – 27 0.400 16 0.400 – 0.355 42 45 0.355 44 0.355 35 0.355 – 0.355 0.355 – – – – – – 0.315 – – 26 0.315 0.315 48 0.300 – 50 0.300 52 0.300 30 0.300 – – 20 0.300 – 0.250 60 60 0.250 60 0.250 25 0.250 25 0.250 24 0.250 65 0.212 – 70 0.212 72 0.212 20 0.212 – – – (Continued ) 4/19/2011 2:49:53 AM 7007TS-SUBBARAO-0211-01_Book.indb 20 Table 4.1 (Continued ). U.S.A. BRITISH INDIAN FRENCH AFNOR GERMAN TYLER ASTM E-11-01 B.S 410-2000 I.S. 460-1962 NFX-11-501 DIN 3310-1 :2000 Sieve Mesh Sieve Sieve Sieve Sieve Sieve designation Width of double designation Width of designation Width of designation Width of designation Width of designation Width of mesh aperture tyler mesh aperture mesh aperture mesh aperture mesh aperture mesh aperture no. mm series no. mm no. mm no. mm no. mm no. mm – – – – – – 0.200 – – 24 0.200 30 0.200 – 0.180 80 80 0.180 85 0.180 18 0.180 – 0.180 0.180 – – – – – – 0.160 – – 23 0.160 0.160 100 0.150 – 100 0.150 100 0.150 15 0.150 – – 40 0.150 – 0.125 115 120 0.125 120 0.125 12 0.125 22 0.125 50 0.125 150 0.106 – 140 0.106 150 0.106 10 0.106 – – – – – – – – – 0.100 – – 21 0.100 60 0.100 – 0.90 170 170 0.090 170 0.090 9 0.090 – 0.090 70 0.090 – – – – – – 0.080 – – 20 0.080 0.080 200 0.075 – 200 0.075 200 0.075 8 0.075 – – 80 0.075 – – – – – – 0.071 – – – 0.071 0.071 – 0.063 250 230 0.063 240 0.063 6 0.063 19 0.063 0.063 – – – – – – 0.056 – – – 0.056 110 0.056 270 0.053 – 270 0.053 300 0.053 5 0.053 – – – – – – – – – 0.050 – – 18 0.050 120 0.050 – 0.045 325 325 0.045 350 0.045 4 0.045 – 0.045 0.045 – – – – – – 0.040 – – 17 0.040 0.040 400 0.038 – 400 0.038 400 0.038 3 0.038 – – 130 – 4/19/2011 2:49:53 AM  Size 21 British Standard Sieves, BSS 410-2000 French Series, AFNOR (Association Francaise de Normalisation)NFX 11-501 German Standard, DIN (Deutsches Institut fur Normung) 3310-1 : 2000 The Indian Standard (IS) sieves, however, follow a different type of designation. For an IS sieve, the mesh number is equal to its aperture size expressed to the nearest deca-micron (0.01 mm). Thus an IS sieve of mesh number 50 will have an aperture width of approximately 500 microns. Such a method of designation has the simplicity that the aperture width is readily indicated from the mesh number. For most size analyses it is usually impracticable and unnecessary to use all the sieves in a particular series. For most purposes, alternative sieves are quite ade- quate. For accurate work over certain size ranges of particular interest, consecu- tive sieves may be used. Intermediate sieves should never be chosen at random, as the data obtained will be difficult to interpret. In general, the sieve range should be chosen so that no more than about 5% of the sample material it retained on the coarsest sieve, or passes the finest sieve. These limits may be lowered for more accurate work. Table 4.1 shows the comparison of test sieves of different standards. 4.1 SIEVE ANALYSIS It is a method of size analysis. It is performed to determine the percentage weight of closely sized fraction by allowing the sample of material to pass through a series of test sieves. Closely sized material is the material in which the difference between maximum and minimum sizes is less. Sieving can be done by hand or by machine. The hand sieving method is considered more effective as it allows the particles to present in all possible orientations on to the Figure 4.3 Table model sieve shaker. Figure 4.4 Ro-tap sieve shaker. (Courtesy Jayant Scientific Industries, Mumbai). (Courtesy Jayant Scientific Industries, Mumbai). 7007TS-SUBBARAO-0211-01_Book.indb 21 4/19/2011 2:49:53 AM  22 Mineral beneficiation sieve surface. However, machine sieving is preferred for routine analysis as hand sieving is long and tedious. Table model sieve shaker and Ro-tap sieve shaker (Figures 4.3 and 4.4) are the two principal machines used in a laboratory for sieve analysis. Owing to irregular shapes, particles cannot pass through the sieve unless they are presented in a favourable orientation, particularly with the fine particles. Hence there is no end point for sieving. For all practical purposes, the end point is considered to have been reached when there is little amount of material passing through after a certain length of sieving. Sieving is generally done dry. Wet sieving is used when the material is in the form of slurry. When little moisture is present, a combination of wet and dry sieving is per- formed by initially adding water. 4.2 TESTING METHOD The sieves chosen for the test are arranged in a stack, or nest, starting from the coars- est sieve at the top and the finest at the bottom. A pan or receiver is placed below the bottom sieve to receive the final undersize, and a lid is placed on top of the coarsest sieve to prevent escape of the sample. The material to be tested is placed on the uppermost coarsest sieve and closed with lid. The nest is then placed in a Sieve Shaker and sieved for certain time. Figure 4.5 shows the sieve analysis at the end of the sieving. The material collected on each sieve is removed and weighed. The complete set of values is known as Particl