The Role of the Collector in Froth Flotation

275 Pages·011.06 MB·English

by  Htin, Kyaw

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THE ROLE OE THE COLLECTOR IN EROTH FLOTATION
- ~ '■ ..
Being a thesis submitted by
Kyaw Htin, B.Sc», A.R.T.C», A.R.I.C.
to the University of Glasgow in fulfilment of
the requirements for the Degree of Doctor of
Philosophy in Applied Science.
— -------- 0O0O0-----------
Technical Chemistry Department,
Royal Technical College,
Glasgow. November , 1950
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ACKNOWLEDGMENTS.
The author wishes to acknowledge his indebtedness
to Professor W.M. Cumming, O.B.E., D.Sc., F.R.I.C., M«I. Chem.
E., F.R.S.E., and to Professor P.D. Ritchie, B.Sc.:, Ph.D.,
F.R.I.C., for providing all the necessary facilities and for
their continued interest in the investigations; to Professor
G. Hibberd, Ph.D., A.R.T.C., M.I. Min. E., for his kindness
in obtaining the required minerals; to W. Gibb, B.Sc., Ph.D.,
A.R.T.C., A.R.I.C., for his constant help, guidance and useful
criticisms throughout the course of this work; to A.B.
Crawford, B.Sc., Ph.D., A.R.T.C., F.R.I.C., for the spectro­
scopic analyses of the barytes samples; and to T.J. Mitchell,
Ph.D.,A.R.T.C•, F.R.I.C., A.M.I. Chem. E., for his helpful
criticisms•
Thanks are also due to Mr. R. Barbour for making
the various glass apparatus, to the Workshop of the Technical
Chemistry Department for the Permeability Cells used for
surface area measurements, to Mr. J. Donald of the Geography
Department,’ Glasgow University, for the micro-photographs of
barytes powders, and finally to the Government of the Union of
Burma for the award of the scholarship which made this research
possible.
C O N T E N T S.
Chapter. Subject. Page Kb
Acknowledgments.
Contents.
Summary.
Introduction. 1*
I. Collectors - " - 5
Role of Collector 5
Wetting and Contact angle o
Polar-N on-Polar structure 8
Classification of collectors 12
II. Theories on Collection 15
. „ Reaction versus Adsorption Theory 15
vlA Recent theory on collection 2b
III. Reagents J2
Purification of fatty acids 32
Purity of acids 32
Sodium soaps 33
Inorganic reagents 54*
IY. Frothing Properties of The Lower Fatty Acids 35
Theory of Froth Formation 35
Adsorption at liquid surfaces 37
Experimental 4-0
Frothing apparatus IfO
Frothing tests 4-5
Results 4 8
Discussion of results 49
Concentration of the surface film 50
Y. A Standardised Flotation Test 56
Laboratory flotation cells 56
Flotation cell (A) 57
Reproducibility of results 65
Effect of Sintered Disc 0
Flotation cell (B) 64
Hallimond Tube 65
YI. Flotation Tests 69
Flotation variables 69
Preliminary tests J1
Purification and purity of barytes J1
Flotation with frothers only 73
Temperature 75
C O N T E N T S .
Chapter. Subject. Page No.
Time of collection of floated ore 75
Pulp density 7°
Hate of air flow oO
Particle size ”1
VII. Flotation with Patty Acids and Soaps. 83
Preparation of solutions 83
Effect of mode of preparation of solutions 85
Effect of age of solutions 87
Texts with fatty acids 88
Tests with soaps 93-
Discussion of results 91
Adsorption and collector requirement 93
Effect of pH 9®
104
VIII. Effect of Anions and Cations on Flotation of Barytes
with Sodium Laurate 104
Activation and depression 104
Experimental 10 J
Effect of anions 107
Hydroxyl ions 10J
Carbonate ions 110
Sulphate ions 112
Effect of cations 113
Barium ions 113
Ferric ions 116
Triangular diagrams 120
Adsorption of Ferric ions on barytes 123
Variation with pH 123
Adsorption with varying ferric ion
concentration and pH 128
Comparison of natural barytes and
pure barium sulphate 129
Preparation of pure barium sulphate 129
Comparison of Flotation of pure barium 130
sulphate and natural barytes
Adsorption tests 132
IX. Surface Area of Powders 139
Rigden's (Liquid) Permeability Method 141
Discussion 245
Lea and Nurse Air Permeability Apparatus I47
Density of barytes 145
Discussion of Results 150
Gas Adsorption Method 151
Discussion of results 158
Adsorption of The Lower Fatty Acids on Silica,
Barytes and Pyrites 163
Experimental 164
Chapter. Subject. Page N o.
Purity of Minerals l&f
Purification of Minerals 1&5
Silica 165
Pyrites 3.66
Adsorption tests 166
Acid-alkali titration 166
Conductivity measurements 167
Results 172
Adsorption of silica 3-7*1-
Discussion of results 175
pH measurements and potentiometric 183
titrations
Discussion of Results 187
Flotation Tests 188
XI. Discussion and Suggestions for Further Work I90
Bibliography. 196
fforco.i-or; soo id of of acid ardton 000
olio .0: barium salt of too' acid la responsible fit c.
K-.yvf, al of soi'pi loii of of a fix tty acid aaicm tat os pj,
tfcs ’oooro ,0-0 loos as oco>otor lone, The afloat of r,
ffotosios wx'tib e&prylic seld* audios eapryl&ee, os.d
0 o'louito., preaexRof ni the anions * hydroxyl* c-
• j.or*;5 f is . found to dapre?aa ito flotation
Summary of Thesis.
The importance of the polar-non-polar structure in
the collector molecule is explained and a review is made of
the present state of knowledge regarding the mechanism of
collection in froth flotation. Using the bubble column, the
froth stabilities of the lower fatty acids, which possess low
collecting power, are compared and the results discussed with
respect to the concentration at the air-liquid interface.
Preliminary flotation tests are carried out on the variation
in recovery of barytes with time of collection, rate of air
flow, pulp density, and particles size, in a laboratory
flotation cell to obtain the optimum conditions for later
experiments. Tests on flotation of purified natural barytes
with fatty acids and sodium soaps indicate that a complete
monolayer of the collector is not necessary for maximum
flotation and that adsorption of acid anion and not the forma­
tion of barium salt of the acid is responsible for collection.
Physical adsorption of the fatty acid anion takes place with
the hydrogen ions as counter ions. The effect of pH on
flotation with caprylic acid, sodium caprylace, and lauric acid,
is studied. The presence of the anions, hydroxyl, carbonate,
and sulphate ions, is found to depress the flotation while the
cations, barium ions, bring about activation. Hydrogen and
ferric ions, however, depress the flotation. The part played
by these ions is discussed. An investigation is made of the
adsorption of ferric ions on natural barytes and pure barium
sulphate. Prom the findings, a hypothesis on the mode of the
adsorption and its relation to the depressing action, is
put forward. Flotation of pure barium sulphate with sodium
laurate is compared with that of natural barytes using the
Hallimond Tube. Exploratory tests are done oil the adsorption
of the lower fatty acids on pyrites, silica, and barytes.
The pH and the potentiometric titration methods indicate
unimolecular adsorption of these acids on pyrites and barytes.
The nitrogen adsorption method, Rigden's water permeability
method, and the Lea and Nurse air permeability method are used
for measuring the surface areas of the powders tested. The
applicability of these three methods to flotation research is
discussed.
rap:-! pai prx« to the pro sent s tag© of applia. .. j
ft' v,e,axp ax fha of the present aeaturp ■-
t’ — -. h-pp-p to he paid to the fundamental aspects of x
flit preaapt intensive research* being carried xap :!.a
ssa aa.o del pea ta make the subject bopo o ' -
v as a preat amount of fxipdaiEental work rem&ipx; to he tap-
■■■ xaifexlyixiy baeie principles *
(1)
I N T R O D U C T I O N .
Froth flotation may he defined simply as the
science of separating particles from each other in a liquid
suspension by means of air bubbles. As implied in this
definition, one of the first uses of flotation was to separate
'solids' from 'solids' as in the flotation of useful minerals
from the unwanted gangue particles. Now, however, froth
flotation is also a recognised process for removing solids
from liquids, and research is under way to apply it to the
separation and reclamation of liquids from liquids.
Even although ninety years have elapsed since the
first patent in i860 by William Haynes (l), the froth flota­
tion process is still largely an art as far as plant practice
is concerned. Empirical research has been largely responsible
for its rapid progress to the present stage of application*
It was only at the beginning of the present century that atten­
tion began to be paid to the fundamental aspects of the process.
The present intensive research,, being carried out in America
and Australia, has helped to make the subject more of a science
but a great amount of fundamental work remains to be done on
the -underlying basic principles.
The realisation that air bubbles may become
attached to some minerals and not to others brought about a
revolution in flotation research. Investigators at once
tried to enhance the differences between the minerals by the
empirical method of adding to the pulp any substance in solid,
(2)
liquid or gaseous state which might possibly have some effect
on the separation. That this trial and error method was
successful is evident from the citation of over two thousand
flotation reagents in Taggart's Handbook of Ore Dressing (2).
The next notable step forward was the classification
of these reagents into different groups according to their
functions in flotation. Out of several suggestions made by
various authors, the following four are now recognised as the
main types used in the process:- frothers, collectors,
activators and depressants.
These are defined according to Wark (3 ) as:-
(i) Frothers:- A "frother" is a substance which, when
dissolved in water, enables it to form a more or less stable
froth with air.
Collector:- a "collector” for any mineral is a substance
(generally organic),which induces it to float at the air-water
interface, and in the presence of a frother to form a more or
less stable mineralised froth.
(3) Activators:- An "activator” for any mineral is a substance
(generally inorganic), the addition of which induces flotation
in the presence of some collector that is otherwise without
effect on the mineral o
(*!•) Depressants:- A "depressant" for any mineral is a substance
(generally inorganic), the addition of which prevents a
collector from functioning as such for that mineral.
The role of the collector is obvious from the above
definition. A frother is necessary to provide the large