Industrial Minerals Laboratory Manual. Kaolin

80 Pages·4.491 MB·English

by  Bloodworth A.J., Highley D.E., Mitchell C.J.

British Geological Survey cna4
TECHNICAL REPORT WG/93/1
Mineralogy and Petrology Series
Industrial Minerals Laboratory Manual
KAOLIN
A J Bloodworth, D E Highley and C J Mitchell
Mineralogy and Petrology Group
British Geological Survey
Keyworth
Nottingham
United Kingdom NG12 5GG
British Geological Survey
TECHNICAL REPORT WG/93/1
Mineralogy and Petrology Series
Industrial Minerals Laboratory Manual
KAOLIN
A J Bloodworth, D E Highley and C J Mitchell
A Report prepared for the Overseas Development Administration under the
ODA/BGS Technology Development and Research Programme, Project9 1/1
ODA Classrfication:
Subsector: Geoscience
Theme: G 1 - Promote environmentally sensitive
development of non-renewable resources
Project title: Mineralsf or Development
Reference number: R554 1
Bibliographic reference:
Bloodworth, A J, D J, Highley, D E & Mitchell, C J
Industrial Minerals Laboratory Manual:
Kaolin
BGS Technical Report WG/93/1
Subject index:
Industrial minerals, kaolin, laboratory techniques
Cover illustration:
Transmission electron micrographo f
well-formed hexagonal crystals of kaolinite
from Uganda (X 75000). The crystals
have been metal-shadowed to allow
measurement of thickness and aspect ratio.
0 NERC 1993
Keyworth, Nottingham, British GeologicalS urvey, 1993
CONTENTS
Page
1. INTRODUCTION 1
2. GEOLOGICAL OCCURRENCE 2
3. MINING AND REFINING 5
4. INDUSTRIAL APPLICATIONS 10
5. LABORATORY ASSESSMENT OF KAOLIN 20
REFERENCES 53
APPENDICES:
1. Dispersion and wet screeninogf kaolinite-bearing rock 55
2. Kaolinite grade and recovery calculation 57
3. Sub-sieve particle size analysis 58
4. Iron oxide/oxyhydroxide removalb y sodium dithionite bleach 64
5. Brightness determination 65
6. Viscosity measurement 67
7. Preparation of test pieces for moduluso f rupture determination 7 1
8. Determinaptiroonp oefr tfiierse d 72
Preface
Industrial mineral raw materials are essential for economic development.
Infrastructure improvement and growothf the manufacturing sector requires
a reliable supply of good quality construction minerals and a wide rangeo f
other industrial mineral raw materials.
Although many less developed countries have signlficant potential industrial
mineral resources, some continue to import these materials supply their
industries. Indigenous resources may not be exploited (or are exploited
ineffectively) because they do notm eet industrial specifications, and
facilities and expertise to carry out the necessary evaluation and testwaroer k
unavailable. Unlike metallic and energy minerals, the suitability of
industrial minerals generally depends on physical behaviour, as well as on
chemical and mineraiogcai properties. Laboratory evaluation often involves
determination of a wide range of inter-related properties and mubset canied
out with knowledge of the requirements of consumingi ndustries.
Evaluation may also include investigation of likely processing required to
enable the commodity to meet industry specifications.
Over the last 10 yearsf, undingf rom the OverseasD evelopment
Administration has enabled the British Geological Survey to provide
assistance to less developed countries in the evaluation of their industrial
mineral resources. This series of laboratory manuals sets out experience
gained during this period. The manualsa re intended to be practical bench-
top guides for use by organisati.ons such asG eological Surveys and Mines
Departments and are not exhaustive in their coverage of every test and
specification. The following manuals have been published to date:
Limestone
Flake Graphite
Diatomite
Kaolin
Bentonite
Construction Materials
A complementary series of Exploration Guides is also being produced.
These are intended to provide ideas and advicfeo r geoscientists involvedi n
the identification and field evaluatioonf industrial minerais in the developing
world. The following guide hasb een published to date:
Biogenic Sedimentary Rocks
A J Bloodworth
Series Editor
D J Morgan
1
Industrial Minerals Laboratory Manual
Kaolin
1. INTRODUCTION
Kaolin is a commercial term used to describe white clay composed
essentially of kaolinite, Al&010(OH)g. The term is typically usedt o
refer to both the rawc lay and the refined commercial product. This
manual describes the laboratory assessmeonf t‘ non-plastic’ kaolin
(sometimes known as china clay); plastic kaolinitic clays (or ball clay)
are dealt with elsewhere in this serioefs manuals. Although originally
valued for use in the manufactureo f whiteware ceramics, the principal
use of kaolin is now in thef illing and coatingo f paper. The minerali s
also used to a lesser extenta s a filleri n paint, rubber and plastics,a s
well as in a wide rangeo f other applications. Kaolins are distinguished
from other claysb y whiteness, and finec, ontrollable particle size. Iti s
generally necessary to process kaolifnro m the crude state in orderto
optimise these highly commercial properties.
This manual is oneo f a series produceda s part of the BGSDDA R&D
Project ‘Minerals for Development’.
Mineralogy and PetrologyG roup, British Geological Survey 0 NERC 1993
2
Kaolin
2. GEOLOGICAL OCCURRENCE
Kaolin deposits are generally classifieads either primary (residual) or
secondary (sedimentary)T. he mode of formationo f the kaolin may have
considerable influence on the mineralogy, chemistry and morphologoyf
the clay and mayd ictate the type of mining and beneficiation process
employed to achievea commercial product.
2.1 Primary kaolins
Primary deposits of kaolin are generally formedb y in situ alteration of
aluminosilicate-rich parent rock (such as granitoer granitic gneiss) by
weathering, hydrothermal,a nd, more rarely, volcanic processes. The
nature of the parent rock mayb e critical in determining the qualityo f the
kaolin; the abundance and natureo f iron-bearing minerals is particularly
important. The kaolinite content of primary kaolins may vary, though
20-30% is not untypical.
Humid tropical weathering of granitic rockiss a major process in
kaolinite formation through the intense leachinogf alkalis from
aluminosilicate minerals. Kaolin deposits form as residual mantles at or
near the surface. Occasionally theym ay occur in association with
bauxite deposits.
Hydrothermal alteration of aluminosilicate-bearing rocks iasn important
kaolinisation process. The host rock must be sufficiently fractured to
allow the circulation of hot groundwater. High-heat-flow granites may
provide optimum thermal condtions required to drive groundwater
convection cells. High-quality kaolins are producedfr om granitic host
rocks which are relatively lowi n iron-bearing minerals such as biotite.
The kaolin resources of south west England are regarded as typical
primary deposits (Bristow, 1987). These world class deposits are
developed within high-heat-flow granites rich in radiogenic elements
such as U, Th and K. High-temperature hydrothermal circulation
associated with a relatively early phaseo f mineralisation is thought to
have increased the permeability of the granite and reduced its iron
content. Thisw as followed by the main phase of kaolinisation, carried
out by low-temperature convection cells of meteoric groundwater. This
process was augmented bya n intense periodo f deep tropical weathering
during the Palaeogene. The intensityo f kaolinisation is controlledb y the
joint patterns within the granite. Kaolinised zoneasr e funnel or trough-
shaped, narrowing downwards (Figure 1). Sodium feldspars are
preferentially alteredt o kaolinite in these granites.
Mineralogy and Petrology Group, British Geological Survey 0 NERC 1993
3
Figure 1. Idealiseds ection of ak aolin pit in southw estE ngland
(AfteBr ristow, 1969)
lnwnton Sand Member
Sand. conrans malls and
C\vrredwta-cde) ous beds . . tahsm h lragyee rcso 0m1 mkaeorclmia la ksa wolelnll
deo0SlS
Kaoh
Figure 2. Generalisedg e ologicasl e ctiont h roughk aolin-bearing
formationsG, eorgia, USA (AfterP atterson & Murray, 1984).
Mineralogy and Petrology Group, British Geological Survey 0 NERC 1993
4
Kaolin
2.2 Secondary kaolins
Kaolin deposits occurring in sedimentaroryc ks are generally classified
as ‘secondary’ or ‘sedimentary’. Some may have formed by the
transportation and depositiono f kaolinite formed elsewhere. However,
diagenetic and weathering processes appteoa pr lay an important role in
the in situ formation andm odifcation of sedimentary kaolins. Deposits
often contain ine xcess of 60% kaolinite. Lower concentrations occuri n
kaolinitic sand,f ormed by the in situ alteration of feldspathic
sandstones.
The extensive sedimentary kaolin depositosf the south-eastem United
States occur in a belt extending over so4m-0e0 km. Economic deposits
occur within Upper Cretaceous and Palaeogene intertidal sedimeanst s
lenses and tabular bodieosf kaolin (Figure2 ). The clays contain 90-
95% kaolinite, with quartz, ilmenite anadn atase being the main
impurities (Patterson& Murray, 1984).
Mineralogy and Petrology Group, British Geological Survey 0 NERC 1993
5
Kaolin
3. MINING AND REFINING
The techniques used in mining and refining (beneficiatioofn p) rimary
and secondary kaolins are reviewed in this section. An understanding
of the processing methods used in the refrnoifn gco mmercial kaolinsi s
essential for effective laboratory appraisaolf these raw materials. A
more comprehensive discussiono f commercial kaolin mining and
processing techniques canb e found in Highley(1 9 84) and Pemberton
(1 989).
3.1 Mining
In south-west England the kaolinised granite is strippofe do verburden
and the clay matrix mined with high-pressure water monitors, which
disintegrate the friable, kaolinised granite and disptehres ek aolinite into
suspension. Hard, unkaolinised granities left behind and is removed by
truck and shovel. In order to maintaina consistent blend froma variable
clay matrix, up to twelve ~ferenpto sitions may be worked
simutaneously. The slurry collecitns the pit bottom and is then pumped
to the refining system.
The exploitation of secondary kaolins shows many differencferso m
primary deposits. Theya re worked by conventional strip mining
methods with overburden thicknesses of up to 45 m. In the south-
eastern USA the clay is excavated from widely-dispersed pits and the
clay transferred to a central refining plant. Thec lay may be moved in
the raw state, or itm ay be blunged (dispersed) to produce a slurry
which is then pumped to the refining plant. After degritting to remove
quartz, the kaolinite content mayb e sufficiently high not to require
further refining, subsequent processing principally being dedicated to
improving the brightness and particle-size distributioonf the clay.
3.2 Refining
The two principle objectiveso f kaolin refininga re the removalo f
impurities and the productioonf the desired particle-size distribution.
Air-floated kaolinsa re produced in theU SA for low-grade applications.
However, most kaolini s refined by wet classification involvingt he
separation of fine platy kaolinite from coarser quartz, feldspar and mica
using the different settling velocities associated with parstiiczlee as
governed by Stokes' Law. Kaolinite is generally concentrated int he
fine fraction, therefore beneficiation cabne achieved by simple size
separation (Figure3 ). A cut at between 10 and 20 pm removes all of
the quartz and most of the mica anfdo r many years thisw as the only
form of beneficiation used by the industry.
Mineralogy and Petrology Group, British Geological Survey 0 NERC 1993
6
Kaolin
100
80
60
kaolinite
mica
srnectite
40 I feldspar & qut artz
20
0
.1 100 1 10
Equival spherical diameter (pn)
Figure 3. Variationi n m ineralogy of ak aolin from south-westE nglandw ithp article
siz(Ae fter Jepson,1984).
The wet refining of primary and secondary kaolins followssi milar
routes and the south-west England operations wiblle used to illustrate
the main techniques. A generalized flowsheet of the process route
followed in south-west England is shownin Figure 4.
Spiral classifiers or bucket wheel classifiers form the first stoafg teh e
separation process, the objectivoef which is to removea ll material
coarser than 250 pm (mainly quartz and feldspar). Followings and
removal, the <250 pm clay slurry is pumped to hydrocyclones for the
next stage of refining. The <53 pm ‘overflow’ (fine fraction)f rom the
hydrocyclones is thickened prior tob eing fed to the hydroseparation
system. This consists of circular tanks where the suspension is allowed
to settle under gravity to remove th>e1 5 p.m fraction. A fine saleable
product is recovered (45% <2 pm), suitable for papefr iller purposes
(see Section 4.2). High-performance, small-diameter hydrocyclones are
now replacing hydroseparators with savings ocna pital costs. The use of
hydrocyclones dispensesw ith the need to chemically deflocculatthee
clay.
Clays used for paper-coating purposes must havfien er particle sizes
(see Section 4.2). This is achieved by using continuous centrifuges that
Mineralogy and Petrology Group, British Geological Survey 0 NERC 1993