Factors affecting the kinetics of froth flotation - White Rose Etheses

256 Pages·2012·24.25 MB·English

Factors affecting the kinetics of froth flotation
By
Jian-Guo Zhang
.,.-,-
Submitted in accordance with the requirements for
the degree of Doctor of Philosophy (ph.D)
Department of Mining and Mineral Engineering
University of Leeds
June 1989
To my grandmother
ABSTRACT
In this research work, three types of flotation models (discrete, mean rate and
the gamma function models) are modified based on the relationship between mass
recovery and recovery. The modified models can be used to calculate both the
recovery and grade of concentrate.
Experimental work was carried out by using three different samples, which are
chalcopyrite, coal and complex sulphide. In the chalcopyrite and coal flotation, air
flow rate (AFR) was varied and different size fractions were considered in coal
flotation. In complex sulphide flotation, the impeller speed (IPS) and air flow rate
were varied, different size fractions were also considered individually.
From the experimental results, the effect of air flow rate, impeller speed and
particle size on the recovery and grade of concentrate are obtained, it is shown that
an increase in air flow rate does not significantly increase recovery but reduce the
grade of concentrate. High impeller speed can increase the recovery of fine and
medium size, but it has very little effect on the coarse size. The effect of particle is
that the medium size has the highest recovery in Fe minerals but the fine has the
highest recovery in Zn and eu minerals.
The air flow rate, impeller speed and particle size affect on the kinetics of
flotation is discussed from the model results. Where the modified models are used,
the results show that an increase in air flow rate will increase the flotation rate of all
size fraction, but an increase in impeller speed can only increase the flotation rate
of the fine and medium size. The medium size has the highest flotation rate in most
of the case.
ACKNOWLEDGEMENTS
I would like to thank my project supervisor, Dr. A.C. Apling for his friendly
advice and English correction, for ideas and encouragement in this research work.
I would like to thank Professor P. A. Young (Head of Department) for all his help
during my research work.
Sincere thanks are due to Mr. A. Hanusch, M.Phil., for his friendly advice
and practical help in all the chemical analysis, in particular in his advice in the XRF
analysis techniques employed.
Thanks are also due to Mr. C. Farrar for his help and friendly advice during
the laboratory work.
Appreciation is also expressed to all members of the Department of Mining
and Mineral Engineering who have assisted me during my study, either by active
help or by stimulating discussion.
I also would like to thank the British Council and Chinese Ministry of
Education for their financial support for this project.
ABBREVIATION
CDM is Combined Discrete Model.
MCM is Modified Chen's Model.
GFM is Gamma Function Model (new).
AFR is Air Flow Rate.
IPS is ImPeller Speed.
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Table of Contents
Chapter One: Introduction ............................. .......... ................................. 1
Chapter Two: Literature review..... ...... ............ ...... ........ .... .... .... ...... ........... 4
2.1 Introduction...................................................................................... 4
2.2 Review of flotation models ............... .............................................. 4
2.2.1 Different flotation models ..................................................... 5
2.2.2 First order kinetic models ................... ........ .... .... ........ ........ ..... 8
2.2.3 Kinetic models with discrete rate constants ........................... 8
2.2.4 Kinetic models with continuous rate constant distribution ..... 10
2.2.5 The mean rate flotation model....... ...... ...... .... ................ ......... 11
2.3 Factors affecting flotation kinetics ................................................... 12
2.3.1 AFR affects on flotation ................................................... 12
2.3.2 IPS affects on flotation ........................................................ 19
2.3:3 Particle size effect on flotation ............................................... 23
2.3.4 The effect of other factors on flotation ................................... 25
Chapter Three: Development of Flotation Models .. ................ .......... .......... 26
3.1 Introduction ....................................................................................... 26
3.2 Development of Combined Discrete Model (CDM) ....................... 26
3.2.1 Mass and element recovery models ........................................ 26
3.2.2 The factors determining particle floatability...................... .... 27
3.2.3 General assumptions ............................................................... 29
3.2.4 Theoretical approach to Combined Discrete Model (CDM)
................ .................................................................................................................................. 30
3.2.5 Analysis ........ .... ...... ........ ...... .......... ...... ...... ...... .... ........ ........... 34
3.2.5.1 General conditions .......................................................... 35
3.2.5.2 The features of the CDM ................................................ 36
3.3 Development of Modified Chen's Model (MCM) .......................... 37
3.3.1 Chen'smodel ......................................................................... 37
3.3.2 The analysis of Chen's model................................................. 39
3.3.3 Modified Chen's Model ....................................................... 40
3.3.4 Analysis of MCM ....................................................... ............. 44
3.3.4.1 MCM and gamma function model ................................. 44
3.3.4.2 The features of MCM ..................................................... 45
3.4 Development on Gamma Function Model (GFM) .......................... 46
3.4.1 Gamma Function Model ......................................................... 46
3.4.2 Modified GFM ..................................................................... 47
3.4.3 Analysis of modified GFM ...................................................... 50
3.5 Summary ........................................................................................ 50
Chapter Four: Evaluation of Parameters by Computational Methods ......... 52
4.1 Introduction ............ ............ ...... .... .............. ............ .... ...................... 52
4.2 Start time and unfloatable fraction .................................................. 52
4.2.1 The effect of start time error ... .... .............. ...... ...... .... .... .......... 53
4.2.2 The effect of unfloatable fraction ............................................ 54
4.2.3 The methods of correcting errors . .... .... .... .... ........ .......... ....... 55
4.3 Computational method of the CDM ................................................ 58
4.3.1 Mathematical procedures ....................................................... 58
4.3.2 Computer program ................................................................. 60
4.4 Computer program of the MCM .................................................... 62
4.5 Computational method for GFM ..................................................... 63
4.5.1 Estimation of parameters ....................................... ............... 63
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4.5.2 Computer program ................................................... ........ ....... 66
4.6 Summary .... ...... ...... .... ........ ............ .............. .... ........ ...................... 67
Chapter Five: Experimentation One -- Preliminary test .............................. 69
5.1 Introduction ...................................................................................... 69
5.2 Bubble surface area measurement ................................................... 69
5.2.1 Bubble size measurement ........................................................ 69
5.2.2 The calculation of bubble surface area .......... ...... .............. .... 70
5.2.3 AFR and bubble surface area ................................................. 72
5.2.4 IPS and bubble surface area ................. .............. ...... .......... ...... 74
5.3 Power measurement ......................................................................... 74
5.3.1 Power input measurement ...................................................... 74
5.3.2 AFR and power input .............................................................. 76
5.3.3 IPS and power input .............................................................. 76
5.4 Water recovery measurment ............................................................ 78
5.4 ... 1 Method of water recovery measurement ................................. 78
5.4.2 AFR and water recovery ........................................................ 79
5.5 Chalcopyrite flotation ...................................................................... 81
5.5.1 Sample preparation .................................................................. 81
5.5.2 Grinding time test .............. 81
~.....................................................
5.5.3 Standardization of flotation .................................................. 82
5.5.4 AFR test ................................................................................. 86
Chapter Six: Experimentation Two -- Coal and complex sulphide
flotation ........................................................................................................ 88
6.1 Introduction ........................................................................ .............. 88
6.2 Coal flotation ................................................................................... 88
6.2.1 Sampling ................................................................................. 88
6.2.2 Preliminary tests of coal flotation . ........ .................. ........ ........ 89
6.2.3 AFR test .................................................................................. 90
6.3 Analyses of coal samples ................................................................. 91
6.3.1 Size analysis .......................................................................... 91
6.3.2 Ash analysis ... .... ................ ...... .... ........ .... ...... ...... ...... ........ ..... 94
6.3.3 Errors analysis ......................................................................... 95
6.4 Complex sulphide flotation ... ............ ............ ............ .......... ............. 96
6.4.1 Sampling .................................................................... ............. 96
6.4.2 Preliminary tests for flotation ....... .... .............................. ..... 97
6.4.3 AFR and IPS test .................................................................... 101
6.5 Analyses of complex sulphide samples ........................................... 102
6.5.1 Size analysis ........................................................................... 102
6.5.2 Analysis of Fe, Cu, Zn ............................................................. 104
6.5.2.1 Preparation of XRF discs ................................................ 104
6.5.2.2 XRF analysis .................................................................... 105
6.5.2.3 Calibration of XRF results ........... ...... ........ .... ...... ...... ..... 105
6.5.3 Error analysis ........................................................................... 106
6.6 Summary of experimentation .......................................................... 107
Chapter Seven: Discussion of Experimental Results ................................... 108
7.1 Introduction ........ .... .... ............ ........ ...... .... .... .... .......... .... ............ ...... 108
7.2 AFR effect on chalcopyrite flotation ............................................. 108
7.3 Coal flotation .................................................................... ............... 110
7.3.1 AFR effect on coal flotation ................................................. 110
7.3.2 The effect of particle size on coal flotation .............................. 113
7.4 Complex sulphide flotation ......... .... .... ........ ...... ............. ........... ..... 113
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7.4.1 The effect of AFR on complex sulphide flotation .............. 115
7.4.2 The effect of IPS on complex sulphide flotation ............. 120
7.4.3 The effect of particle size on complex sulphide flotation 128
7.5 Summary ........................................................................................ 133
Chapter Eight: Discussion of Model Results ... ...... .......... .... .... ...... .............. 135
8.1 Introduction ...................................................................................... 135
8.2 Result from CDM ........................................................................... 135
8.2.1 One mineral system .............................................................. 136
8.2.2 Multi-minerals system .............................................................. 140
8.2.3 The effect of AFR on the parameters of CDM ................. 140
8.2.4 The effect of IPS on the parameters of CDM ......................... 146
8.2.5 The effect of particle size on the parameters of CDM 146
8.3 The results from MCM .................................................................... 152
8.3.1 Parameters in the MCM ......................................................... 152
8.3.2 The effect of AFR on the parameters ofMCM ................... 153
8.3.3 The effect of IPS on the parameters of MCM ................. 157
8.3.4 The effect of size on the parameters of MCM ........................ 165
8.4 The result from GFM ...................................................................... 166
8.4.1 Parameters in the GFM . .................................................... 166
8.4.2 The effect of AFR on the parameters of GFM ................... 174
8.4.3 The effect of IPS on the parameters of GFM ...................... 179
8.4.4 The effect of particle size on the parameters of GFM ............. 183
8.5 Comparison between models ........................................................... 183
8.5.1 The errors in different models ................................................ 183
8.5.2 The difference between the CDM and MCM ........................ 185
8.5.3 The difference between the CDM and GFM .......................... 186
8.6 Summary ........................................................................................ 186
Chapter Nine: Conclusions and Suggestions for Further Research ............. 188
9.1 Conclusions of the research ............................................................. 188
9.1.1 The flotation models ... ................ ........ ...... ........ ........ .............. 188
9.1.2 The effect of AFR on flotation ....................................... ....... 189
9.1. 3 The effect of IPS on flotation ........ ................ ................... ...... 191
9.1.4 The effect of particle size on flotation .................................... 192
9.1.5 The difference between the flotaton of different minerals ....... 194
9.2 Suggestions for further research .................................................... 194
-- References 196
-- Appendixes .. .................................. .................... ...... ........................ ........ 206
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Chapter One
Introduction
With the increasing application of computers in the mineral industry, physical
and mathematical models of each operational circuit in the mineral processing plant
become ll!gently needed. Flotation, as an important process of mineral processing
has attracted much attention from researchers, and flotation models have been used
as early as the 1930's (Zuniga G. H. 193~, Morris T. M. 1952, Arbiter N. and Harris
C. C. 1962, King R.P 1974). However due to the complexity of the flotation process
and the limitations of the technology required to obtain the necessary infonnation,
most of the existing flotation models are still far from perfect.
Although the fundamentals of flotation models, i.e. the fIrst order kinetics,
have been developed, detailed infonnation about the factors which affect flotation
kinetics has still not been obtained. Remaining problems not only include the effect
of factors, such as reagent type and concentration, air flow rate and impeller speed
etc., on the parameters of flotation models, but also the flotation model itself, since
most of the models are not well constructed in representing true flotation behaviour.
In general, the models should follows the rules that the parameters in the model
should have physical signifIcance and the values of the parameters for one set of
flotation conditions should be consistent.
Flotation can be affected by many factors. Because of limited time, this
research work is only devoted to a small area of flotation kinetics. In order to obtain
an applicable flotation model, two major fIelds are selected in this research work.
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1. In order to overcome the problems of the inconsistency of the model
parameters and to enable the calculation of both the concentrate grade and recovery,
existing models are thoroughly analysed and three representative models, namely
discrete, mean rate, and gamma function models are modified and used in this thesis.
The modified models are developed based on the relationship between mass recovery
and recovery.
2. In order to explore the factors which affect model parameters, the factors
are separated into two major groups, which are the mineral properties and the
operating factors. The first group is further divided into two subgroups, one of which
is concerned with the chemical factors and the other with physical factors. The
chemical factors are the natural floatability and the floatability of the feed after
reacting with chemical reagents. As this subgroup is dependent on the individual
minerals, and sometimes even on the site where the minerals were formed, these
factors are beyond the scope of this research. The physical factors of minerals are
the specific gravity and the grain size of the valuable mineral in the surrounding
gaugue. This subgroup is considered here by floating coal and chalcopyrite. The
operating factors include the flotation solids concentration, the air flow rate, impeller
speed ( or power input to a unit pulp volume), the feed size (mechanically possible
to float), and the froth stability. Since the froth stability is closely related to the frother
type and frother dosage, it is not included in this research work. Therefore this
research work is devoted to find the effects of air flow rate (AFR), impeller speed
(IPS) and particle sizes on flotation kinetics as shown in the chart below.