EPA-600/1-77-001
January 1977
Environmental Health Effects Research Series
LIBRARY
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ASHKV
CP 600/1
77-001
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Research Triangle Park, North
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application
of environmental technology Elimination of traditional grouping was con-
sciously planned to foster technology transfer and a maximum interface in
related fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS
RESEARCH series. This series describes projects and studies relating to the
tolerances of man for unhealthful substances or conditions. This work is gener-
ally assessed from a medical viewpoint, including physiological or psycho-
logical studies. In addition to toxicology and other medical specialities, study
areas include biomechcal instrumentation and health research techniques uti-
lizing animals—but always with intended application to human health measures.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/1-77-001
January 1977
AMPHIBOLE MINERAL STUDY
To Complement the Ongoing Characterization of
Fine Particulate Environmental Contaminants
for Biological Experimentation
by
Paul C. Siebert and Colin F. Harwood
IIT Research Institute
10 West 35th Street
Chicago, Illinois 60616
Contract No. 68-02-1687
Project Officer
David L. Coffin
Health Effects Research Laboratory
Research Triangle Park, N.C. 27711
V .TP.T? A T> V
' ..-v«.l.^,. • J3*..'.. '.I X,
•!. S. E;i •.":,... ..:. . PROTECTION AGEHCY
y ' ">;/';;7
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
HEALTH EFFECTS RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, N.C. 27711
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DISCLAIMER
This report has been reviewed by the Health Effects Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
11.
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FOREWORD
The many benefits of our modern, developing, industrial society are
accompanied by certain hazards. Careful assessment of the relative risk
of existing and new man-made environmental hazards is necessary for the
establishment of sound regulatory policy. These regulations serve to
enhance the quality of our environment in order to promote the public
health and welfare and the productive capacity of our Nation's population.
The Health Effects Research Laboratory, Research Triangle Park
conducts a coordinated environmental health research program in toxicology,
epidemiology, and clinical studies using human volunteer subjects. These
studies address problems in air pollution, non-ionizing radiation,
environmental carcinogenesis and the toxicology of pesticides as well as
other chemical pollutants. The Laboratory develops and revises air quality
criteria documents on pollutants for which national ambient air quality
standards exist or are proposed, provides the data for registration of new
pesticides or proposed suspension of those already in use, conducts research
on hazardous and toxic materials, and is preparing the health basis for
non-ionizing radiation standards. Direct support to the regulatory function
of the Agency is provided in the form of expert testimony and preparation of
affidavits as well as expert advice to the Administrator to assure the
adequacy of health care and surveillance of persons having suffered imminent
and substantial endangerment of their health.
This report details the work and results of a program concerned with
the collection of amphibole mineral samples from the Reserve Mining taconite
mine in Babbitt, Minnesota. A profile of the ore body was performed by
means of petrographic examination of speciments obtained from multiple sites on
the rock face. These specimens contained amphibole, magnitite, hornblende,
and other minerals. The amphibole fibers were found to have many properties
similar to amphibole asbestos types. A large amount of a representative
specimen was prepared, blended and placed in vials for animal inoculation.
John H. Knelson, M.D.
Director,
Health Effects Research Laboratory
111
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ABSTRACT
This report details the work and results on a program
concerned with the collection of amphibole mineral samples
from the Reserve Mining taconite mine in Babbitt, Minnesota
and the preparation of highly characterized amphibole fibers
from these samples. A profile of the ore body was compiled
after a petrographic examination of mineral samples.
Various separation and sizing techniques for the fibrous
material present in the ore were investigated. Air jet:
milling of ground and sieved fibrous rock was used to pre-
pare samples for biological experimentation. This material
was characterized by optical microscopy, electron microscopy,
electron diffraction, x-ray spectroscopy, x-ray diffraction,
atomic absorption spectrometry, B.E.T. surface area, and
benzene extraction. The fibers were found to have many
properties similar to amphibole asbestos types. Vials of
weighed amounts of product sample were prepared and purged
with nitrogen.
IV
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CONTENTS
Page
Abstract iv
List of Figures vi
List of Tables
Acknowledgements
Sections
1 Summary 1
2 Conclusions 8
3 Recommendations 10
4 Introduction 11
5 Ore Sample Collection 13
6 Ore Body Profile 16
7 Fibrous Sample Preparation 33
8 Characterization of Fibrous Samples 45
9 References 78
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FIGURES
No. Page
1 Reserve Mining Company 19
2 Selected Fiber-Bearing Thin Sections 30
3 Optical Microscope Photomicrographs 49
4 Electron Microscope Photomicrographs 56
5 Electron Diffraction Patterns of Ground and
Sieved Material 62
6 X-ray Spectrographs 66
7 B.E.T. Surface Area Analysis 76
VI
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TABLES
No. Page
1 The Chemical Composition of Amphiboles 14
2 Mineral Occurrence Based on 25 Thin Sections 29
3 Jet-Mill Operating Conditions 43
4 Jet-Milled Samples Particle Counts; Optical
Microscope, 625X 46
5 Size Distribution by Number of Fibers and Non-
Fibers; Optical Microscope at 400X 47
6 Size Distribution by Number of Fibers and Non-
Fibers; Transmission Electron Microscope at 10,OOOX 52
7 Electron Diffraction and X-ray Spectroscopy
of Particles 61
8 Chemical Analysis by X-ray Spectroscopy 65
9 X-ray Diffraction Lines Present in Samples 68
10 X-ray Diffraction Lines Present in Samples of
Ground and Sieved Fibrous Rock 69
11 X-ray Diffraction Lines in Some Inorganic Minerals 71
12 X-ray Diffraction Lines in Main Asbestos Types 72
13 Summary of X-ray Diffraction Results 73
14 Atomic Absorption 74
15 Benzene Extraction of Organics 74
VI1
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ACKNOWLEDGEMENTS
The cooperation of the Reserve Mining Company in
allowing us free access to their mine in Babbitt, Minnesota
is gratefully acknowledged. We would in particular like to
thank the President, Mr. Woodle, and the Research Director,
Mr. K. Haley.
Dr. Bertram Woodland of the Chicago Museum of Natural
History provided invaluable consultancy services in performing
the geological survey. We are also grateful to Dr. Arthur
Langer and other staff members of the Mount Sinai Environmental
Laboratory for general consultancy on the mineralogy of the
fibers and rock fragments.
Our efforts were stimulated and encouraged by the
enthusiasm and interest by the EPA personnel, including
Dr. David Coffin, David Oestreich, and Vandy Duffield, and
also by Dr. L. Palekar of Northrup Services.
IITRI personnel contributing to the program were:
Dr. Colin F. Harwood, Project Leader; Paul C. Siebert,
Principle Investigator; Dr. Anant Samudra and George Yamate,
electron microscopists; M. Lai, analytical services;
Erdmann Luebcke, sample collection; and Hubert Ashley,
technician. The project was administered out of the Fine
Particles Research Section, Manager, Mr. J. D. Stockham.
Vlll
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SECTION 1
SUMMARY
This program involved the collection of amphibole min-
eral samples from Reserve Mining's Peter Mitchell Pit near
Babbitt, Minnesota. A geological profile of the ore body
was prepared by an examination of ore samples taken from
various sites at the mine. Highly characterized amphibole
fibers for biological experimentation were prepared from
selected mineral samples.
Taconite ore, from which magnetite is extracted, is
mined from the Peter Mitchell Pit. The magnetite occurs
associated with quartz and various amphiboles, particularly
those in the cummingtonite-grunerite series. Amosite is re-
garded as the fibrous modification of the grunerite (iron
rich) end of the series. As amosite asbestos is a health
hazard, one of the objectives of this program was to pre-
pare and characterize amphibole fibers for biological exper-
imentation so that it can be determined whether fibers chem-
ically similar to amosite are also a health hazard.
The Peter Mitchell Pit is located at the eastern end
of the Mesabi Range in northeastern Minnesota. It has
been excavated in the Biwabik Iron Formation of Middle
Cambrian age, which trends northeast to southwest and dips
gently to the southeast. The formation is subdivided into
four members: Lower Cherty, Lower Slaty, Upper Cherty, and
Upper Slaty. The pit is mainly in the Upper Cherty, which
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is about 140 feet thick, but a little of the Upper Slaty
Member is also worked. The formation is truncated east of
the pit by the Duluth Gabbro complex. The close proxi-
mity of the gabbro is responsible for the high metamorphic
grade of the rocks exposed in the pit. The mineralogy of
this highgrade zone is distinct from the lower-grade rocks
to the west and is characterized by the appearance of am-
phiboles (grunerite, cummingtonite, hornblende), pyroxenes
(hedenbergite, ferrohypersthene), and fayalite.
The pit extends for about eight miles along the strike
of the horizon. Nearly 100 specimens were collected on July
1, 1975, from nine localities over a distance of approxi-
mately six miles. The specimens, which were selected from
broken rock lying at the base of the face and on the quarry
floor, include what appeared to average ore types from each
locality, but are biased towards samples having layers or
masses of iron silicates.
The specimens were examined using a binocular micro-
scope (30x) and 25 thin sections from 24 specimens were
prepared and examined by microscope. These 24 specimens
were chosen particularly for study of the iron silicate
layers and masses, although layers of typical ore are also
included in most of the sections. Fibrous to prismatic
amphibole, belonging to the grunerite-cummingtonite series,
is common and occurs in every thin section. With fine-
grained material it is difficult to determine optically
whether the amphibole is cummingtonite or grunerite, so
this material was referred to as cummingtonite. However,
the Mg content of the amphibole has been known to increase
toward the contact of the Duluth Gabbro.
Grain size varies considerably. Magnetite occurs as
dust, as grains 20-200 ym in diameter, and as large dense
aggregate masses and layers. Grunerite-cummingtonite
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varies from fibers (less than 1 ym wide and 25-270 ym long),
needles (20 ym wide and 170-770 ym long), small blades or
prisms (10-40 ym wide and 50-230 ym long), to larger blades
(100 ym wide and 2040 ym long). Garnet grades from grains
of 50 ym to several centimeters in diameter. Quartz occurs
in grains varying from 20-4650 ym. Fayalite varies from
approximately 100-1000 ym. Hedenbergite ranges from grains
of 50 ym to 2.5 cm. Hornblende, including actinolite, varies
from tiny grains (80 ym) to prisms commonly intergrown with
cummingtonite (120-870 ym in length) to coarser prismatic
grains (5-7 mm long). Ferrohypersthene occurs in irregular
or prismatic grains up to 1.6 mm long. Calcite is not com-
mon, but is usually coarse-grained (up to 6.0 mm diameter).
Biotite is rare and has a maximum length of 290 ym. Magne-
tite and quartz were found to be abundant; cummingtonite-
grunerite and hornblende (actinolite) ranged from sparse to
abundant, and calcite from rare to sparse.
An additional 750 Ibs. of high fibrous content ore were
located and collected on October 2, 1975, for preparation
of fibrous material for biological experimentation. Ore
containing rich fibrous veins were available only near the
incursion of the Duluth Gabbro and occured only in two very
localized areas within approximately 100 m of each other.
The fiber separation and sizing techniques that were
investigated, in the literature and/or experimentally were:
1. Jaw Crushing
2. Roll Crushing
3. Ball Milling (wet)
4. Air Jet Milling
5. Magnetic Separation
6. Sieving
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7. Sedimentation
8. Felvation
9. Serial Filtration by Nuclepore Filters
10. Magnetic Alignment of Fibers
11. Dielectrophoresis
12. Stirred Screening
13. Vertical Spinning
14. Combinations of the Above
Jaw crushing and roll crushing, and mechanical sieving were
found to be unnecessary when the material from fibrous veins
was used. Wet ball milling could be used to reduce size
to the micron and sub-micron ranges; however, this technique
introduces the possibility of leaching of the material by
the liquid. Air jet milling was found to be successful in
first breaking up the bundles into individual fibers and
second in reducing the length of the fibers. Magnetic sep-
aration would be useful in preparing samples from taconite
in that the non-magnetic fraction was more fibrous (85%)
than unseparated crushed taconite; however, only a small
portion of the crushed taconite was non-magnetic. Sedimen-
tation separated., by diameter, fibrous or non-fibrous par-
ticles in fair agreement with theory; however, sedimentation
has the disadvantage of not being able to separate fibrous
and non-fibrous particles, or by length of fiber, and of the
possibility of leaching of the settling material. Felvation
has similar disadvantages to sedimentation with the added
drawback that it is extremely time consuming and has low
productivity due to the low free area and high pressure drop
of micron pore sized sieves. Serial filtration by Nuclepore
filters could prove useful in separating fibrous and non-
fibrous material (of diameter greater than the fiber diam-
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eter) however, this technique does not separate by length
of fiber and requires aerosolization of a fiber rich sample.
Magnetic alignment of fibers was not investigated, as an
electromagnet of suitable size and strength was not avail-
able and because most amphibole fibers align in two frac-
tions perpendicular to each other. No conclusive separation
of fibrous and non-fibrous material was achieved using
dielectrophoresis. Stirred screening and vertical spinning
have been used with only limited success with chrysotile by
Johns-Manville, and thus were not attempted for this material,
Fibers were separated from fiber-rich rocks using
several methods. Both hand and vibratory cobbing were
used to separate fibrous material (^1.5kg) in veins. Sev-
eral rocks were found to consist almost entirely of soft,
light green or brown fibrous material. These rocks were
crushed, ground, and sieved (<35 mesh) to produce a material
( a,3kg) with a high fibrous-to-non-fibrous ratio.
These separated fibrous materials are not necessarily
representative in all respects of the majority of the fibers
in the ore in the Reserve Mine or in the tailings from the
magnetite extraction at Silver Bay, Minnesota. However, this
method was used as large quantities of materials with a
large fibrous fraction could be produced more easily than
by separating fibers from the ore or the tailings.
Jet milling runs, each of lOOg of ground and sieved
material were successful in producing material that was
mostly less than 30 pm in size (length of fiber or diameter
of particle) and with a large fibrous fraction. A spinning
riffler was used to reduce the sample size to amounts
suitable for various types of characterization.
Jet-milled sample #14 was chosen as the product sample
after this characterization. This sample was found to be
36.4% (No.) fibrous with 98.5% of the fibers and 99.5% of
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the total particles less than 35 ym in major dimension by
optical microscopy-(400x). The fibers ranged in length from
approximately 1.5 to 40.0 ym. Electron microscopy (10,000x)
showed this sample to 13.2% fibrous by number. The
fibers ranged in length from approximately 0.2 to 32.0 Mm,
with 99.0% less than 30 ym and 93.9% less than 15 Urn. The
higher proportion of non-fibrous particles counted by this tech-
nique is due to the large number of non-fibrous particles of
diameter less than 0.38 ym. Electron diffraction of sele-
cted particles showed all of the fibers examined to be am-
phibole and all of the non-fibrous particles to be crystal-
line. Chemical analysis by X-ray spectroscopy showed that all
of the fibers and non-fibrous particles examined contained
magnesium, silicon, and iron. All of the fibers and 64% of
the non-fibers contained calcium while 30% of the fibers
and 36% of the non-fibers contained manganese. Aluminum
and potassium were present in 9% of the non-fibrous parti-
cles. X-ray diffraction analysis of the sample showed that
cummingtonite, riebeckite and richerite were present.
Tremolite and crocidolite were present as trace materials.
Atomic absorption spectroscopy was undertaken for manganese,
nickel, chromium, and cobalt which were found in amounts of
11.2 mg/g, 224, 34, and 22 yg/g, respectively. The benzene
extractables were determined as 2.22 mg/g. The B.E.T.
2
surface area was determined as 34.1 m /g.
The electron diffraction results show that the fibers
are amphibole. The presence of magnesium, silicon, and es-
pecially iron suggest similarity to amosite or crocidolite
with some similarity to anthophyllite. The trace quantities
of nickel, chromium and cobalt are common to asbestos, while
the quantities present suggest anthophyllite as the most likely.
The large amount of manganese present is typical of amosite.
The X-ray diffraction results indicate the presence of cum-
mingtonite, tremolite-actinolite or crocidolite. The
surface area is high for any asbestos type except chrysotile,
however, this may be due in part to. the size reduction and pre-
sence of small non-fibrous particles. Analysis for aluminum,
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which was too weak to be detected, and for sodium, which is
at the limit of detection for the X-ray spectroscopy equip-
ment used, would be useful in further characterizing the
sample.
No definite conclusions can be reached as to the
positive identification of this material; however, it has
been shown to be similar to different asbestos types with
regard to different characteristics.
The sample was reduced in size to amounts of approxi-
mately 75 mg which were then put in 30 ml hypo-vials, closed
with a resealing silicone rubber septum, purged with nitrogen
for at least 10 minutes, and capped with an aluminum seal.
Two hundred of these vials have been prepared. The remain-
ing material of this sample and the other separated fibrous
material will be stored in case of further requirments at a
later date.
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SECTION 2
CONCLUSIONS
The Peter Mitchell Pit of the Reserve Mine has been
surveyed. The pit is 10 miles in length and about one mile
wide at its widest point. It contains a rich variety of
minerals including many different amphiboles and pyroxenes,
and also magnetite, quartz, fayalite, garnet, calcite, and
other mineral species.
Fibrous to prismatic amphiboles pervade the mine and
are readily seen in thin sections of rock taken from loca-
tions throughout the mine. Fibrous particles are commonly
found to belong to the cummingtonite-grunerite series as
determined by optical microscopy. As such, they have a
variable chemical composition. The chemical structure is
further confused by the fact that the cummingtonite-
grunerite fibers are commonly intergrown with hornblende and
actinolite.
Although numerous methods were considered and tested
for the removal of fibers from crushed rock, none were
found to be successful. They resulted in a very high
(about 90%) proportion of non-fibrous rock. The most satis-
factory method of separating out the fibers was to hand-cobb
that portion of the rock which was seen to be rich in fibers.
The separated fibers could not be classified using
classical techniques such as sedimentation. It was found to
be most satisfactory to use an air-jet mill to classify the
fibers. The air-jet mill had the combined action of reducing
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the fibers to below 30 ].im, breaking up fiber bundles and
long fibers, and separating out much of the very fine
(sub-micron) gangue material.
The fibers collected were characterized using the opti-
cal and electron microscopes, x-ray diffraction, atomic
absorption, surface area, x-ray probe, and electron diffrac-
tion techniques. A benzene extraction was used to determine
the oil content of the fiber. The fibers which have been
prepared may be regarded as typical of the type of amphibole
fiber which may be found in the mine, but they are not rep-
resentative of the whole mine.
Small, 75 mg portions of the fibers have been accurately
weighed into injectable rubber seal vials. They have been
purged with nitrogen prior to shipment.
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SECTION 3
RECOMMENDATIONS
Extraction of fibers from crushed rock is extremely
difficult. It is recommended that the best approach is
to hand-cobb fiber-rich rock and then subject it to air-
jet milling to break it down.
Fibers are required which are more representative of
the fibers which reach the ambient air of Silver Bay. It
is recommended that air samples be taken at Silver Bay.
Knowing the fiber characteristics to be sought, rock
samples containing these fibers may be collected and sub-
jected to the already developed separation methodology.
All fibers or other particulates should be characteri-
zed to a degree far above that commonly applied. As a
minimum, the fibers should be analyzed by:
• Transmission electron microscope for size and the
presence of other particulates
• Selected area electron diffraction
• X-ray probe elemental analysis
• X-ray diffraction
• Surface area
• Pore volume
• Trace element analysis
• Organic extractable content
10
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SECTION 4
INTRODUCTION
Amphlbole rocks are very widespread and form the base
rock of about one-third of the United States. It has been
realized recently that these rocks may contain appreciable
quantities of fibers which have a close similarity to com-
mercial asbestos fibers. Only five amphibole minerals are
actually given the name asbestos, and they are:
amosite
actinolite
crocidolite
anthophyllite
tremolite
The criteria for inclusion of a fibrous rock in the asbestos
list is based on their commercial viability and not on their
adverse health threat. To be commercially viable, the fibers
have to have a long length to breadth ratio and they have to
be easily separated from the ore.
The basis of the defense in the EPA versus Reserve
Mining case hinged upon whether the fibers in Reserve's ore
tailings was asbestos. Reserve claimed that although the
fibers had a similar chemistry to amosite asbestos, they
were not amosite asbestos. Strictly, amosite asbestos comes
from Penge, South Africa, and takes its name from the
Asbestos Mines of South Africa; however, it is a common
practice to name all rocks of a particular group after a well
11
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established source of such rocks. Thus, cummingtonite rock
is named after Cummington, Massachusetts, although the
rock is found in many parts of the world. Reserve also
claimed that the fibers were too small to be regarded as
asbestos fibers and that there was insufficient medical data
for the fibers to be regarded as a health threat.
This program was concerned with the collection of amphi-
bole minerals samples from the Reserve Taconite Mine in
Minnesota and the preparation of highly characterized amphi-
bole fibers from these samples. From an examination of ore
samples taken from various sites at the mine, a geological
profile of the ore body was prepared. This profile was made
by a detailed petrographic examination of thin sections pre-
pared from 24 samples. The 24 samples were chosen from the
ore samples taken xising a binocular microscope at 30-50X.
Fibrous particles were then separated from the fiber-
rich rock, reduced in size, and characterized by size,
chemistry, electron and x-ray diffraction, surface area, and
trace metal and organics content. As the preparation process
was dry, there was no problem with leaching of the samples.
The separated fibers were then weighed and sealed into hypo-
vials in amounts sufficient for one dose for a group in the
biological experimentation, sealed and purged with nitrogen
prior to shipment.
12
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SECTION 5
ORE SAMPLE COLLECTION
Taconite ore is mined by the Reserve Mining Company
from the Peter Mitchell pit near Babbitt, Minnesota. The
magnetite that is extracted occurs associated with quartz
and amphiboles in the cummingtonite/grunerite series. The
amphibole rocks have the general formula (MgFe)ySio022(OH)21.
Cummingtonite is the magnesium rich end member with the
theoretical formula MgySig022(OH^, while grunerite is the
iron rich end member with a theoretical formula Fe-,Sig022 (OH)2 •
Amosite is regarded as the fibrous modification of the
minerals on the grunerite end of the series; it has a Fe:Fe+Mg
ratio of 0.87:I2. The chemical composition of several
amphibole minerals is given in Table 1. It can be seen that
the amosite has a higher Fe20o content than grunerite and it
has been suggested, but not substantiated, that this results
from oxidation as a result of igneous activity which is also
responsible for recrystallization of grunerite as fibers3.
The Peter Mitchell pit has been geologically surveyed
and has been shown to consist of some 22 layers of rock1*.
The picture is made more difficult by folding, shearing, and
faulting throughout the region, and by the presence of an
igneous intrusion (the Duluth Gabbro) in the northern part
of the pit. However, the area from which the ore is taken
consists essentially of three layers. It is upon these
layers that this study was concentrated.
13
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On July 1, 1975, more than 100 samples weighing some
300 Ibs were collected from the Peter Mitchell Pit at
Babbitt, Minnesota by Drs. Harwood and Woodland and
Mr. Luebcke. The samples for geological examination were
collected at widely different sites within the mine. Samples
of the rock tailings after the removal of magnetite at the
Reserve Mining plant at Silver Bay, Minnesota, were also col-
lected. Large quantities of samples were taken from the
northeast corner of the mine, near the Duluth Gabbro, where
veins containing obvious fibers were located. These samples
were collected for testing of methods of separating and
sizing of fibrous material.
On October 2, 1975, approximately 750 Ibs of high fib-
rous content ore were located and collected. It was found
that the ore containing rich fibrous veins was a very
localized phenomenon. Such samples were available only near
the incursion of the Duluth Gabbro and occurred only in two
very localized areas within approximately 100 m of each
other. Several samples were also collected of "typical"
taconite ore and cummingtonite, chosen by Reserve Mining's
geologist who was assisting in the sample collection.
15
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SECTION 6
ORE BODY PROFILE
The Peter Mitchell Pit is located near Babbitt, at the
eastern end of the Mesabi Range in northeastern Minnesota.
It has been excavated in the Biwabik Iron Formation of
Middle Cambrian age. The Iron Formation trends northeast
to southwest and dips gently to the southeast. It is sub-
divided into four members: Lower Cherty, Lower Slaty,
Upper Cherty, and Upper Slaty. The pit is mainly in the
Upper Cherty, which is about 149 feet thick, but a little of
the Upper Slaty Member is also worked. The Iron Formation
is truncated east of the pit by the Duluth Gabbro complex,
the contact of which swings away from the top of the Biwabik
Formation and then approximately parallels it to the south-
west at a distance of about one to one and a half miles;
south of Mesaba it turns sharply southward away from the
Iron Format ion.
The close proximity of the Gabbro is responsible for
the high metamorphic grade of the rocks exposed in the pit
and also approximately southwestward to the vicinity of
Mesaba. The mineralogy of this highgrade zone is distinct
from the lower-grade rocks to the west, and is characterized
by the appearance of amphiboles (grunerite, cummingtonite,
hornblende), pyroxenes (hedenbergite, ferrohypersthene), and
fayalite 5'6.
The pit extends for about eight miles along the strike
of the ore horizon, and samples were collected on July 1,
1975, from nine localities over a distance of a little more
16
-------
than six miles. The working face of each bench is approxi-
mately 35 feet high, that is, over a quarter of the thick-
ness of the total exploited thickness of ore beds. Nearly
100 specimens varying in size from about three inches on a
side to over six inches were collected. The specimens were
selected from broken rock lying at the base of the face and
on the quarry floor. They include what appeared to be
average ore types from each locality, but are biased towards
samples having layers or masses of iron silicates.
GENERAL MICROSCOPIC DESCRIPTION
A total of 25 thin sections from 24 specimens were pre-
pared and examined. These specimens were chosen particularly
for study of the iron silicate layers and masses, although
layers of typical ore are also included in most of the
sections.
Fibrous to prismatic amphibole is common and occurs in
every thin section; it belongs to the grunerite-cummingtonite
solid solution series. The division between grunerite
2+
[(Fe Mg)7Sig022(OH)2J, the iron-rich end of the series, and
cummingtonite, [(MgFe )mSig022(OH)2] is arbitrary, as there
is no natural gap in the series. It is commonly taken that
2+
707o or more of the Fe molecule is called grunerite and,
conversely, that more than 30% of the Mg molecule is cumming-
tonite7 . Optically this approximates to the change of 2V
from negative (grunerite) to positive (cummingtonite).
With fine-grained material, however, it is difficult to
determine; in this report the amphibole of this series is
referred to as cummingtonite, although some may actually be
grunerite. The Mg content of the amphibole increases towards
the contact of the Duluth Gabbro. French (1968) indicates
that it is cummingtonite that is present within one and a
quarter to one and a half miles of the contact, and grunerite
beyond. The Mitchell Pit's collecting localities A and B
17
-------
lie within this distance, and localities C, D, and E just
beyond (see Figure 1) .
Grain Size
Grain size varies considerably. Magnetite occurs as
dust, as grains 0.02-0.2 mm in diameter, and up to large,
dense aggregate masses and layers. Grunerite-cummingtonite
has considerable variation in both grain size and habit,
from fibers (25 ym long and less than 1 ym wide; or longer --
up to 0.08-0.27 mm), needles (0.17-0.77 mm long and 0.02 mm
wide), small blades or prisms (0.05 mm long and 0.01 mm wide
up to 0.23 mm long and 0.04 mm wide), to larger blades
(2.04 mm long and 0.1 mm wide).
Garnet grades from grains about 0.05 mm in diameter to
masses several centimeters across. Quartz occurs in very
fine grains (0.02 mm), medium-sized grains (0.4-0.8 mm),
and very coarse (up to 4.65 mm in some sections). Fayalite
varies from approximately 0.1-0.96 mm.
Hedenbergite, similarly, grades from very fine grains
(0.05 mm) through medium grains (0.03-3.3 mm) to coarse
grains (9.3 mm) and very coarse (2.5 cm). Hornblende,
including actinolite, varies from tiny grains (0.08 mm) to
prisms commonly intergrown with cummingtonite (0.12-0.87 mm
in length) and to much coarser prismatic grains 5.0-7.0 mm
long. Ferrohypersthene occurs in irregular or prismatic
grains up to 1.63 mm long.
Calcite is not common, but is usually coarse-grained
(up to at least 6.0 mm in diameter). Biotite is rare; maxi-
mum grain size is about 0.29 mm in length.
LITHOLOGIC AND MICROSCOPIC DESCRIPTIONS
The following is a brief lithologic description of the
specimens based on their examination under a binocular micro-
scope (X30), together with a microscopic description of the
thin sections.
18
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19
-------
Locality A. N.
Working face, north side of the pit, in the lower part
of the Upper Cherty Member, nearly due north of crusher #1
(Figure 1), that is, about one mile from the easternmost
extent of the workings and close to the Gabbro contact to
the southeast; 11 specimens, four thin sections.
Lithology -
Banded ore: fine-grained, dense magnetite in layers
4-10 mm thick, intercalated with layers of coarse-grained
magnetite and quartz; coarse-grained iron silicates with
quartz and magnetite in layers up to 50-60 mm thick and in
masses; garnet, amphibole, and fibrous amphibole associated
with garnet.
Micro-lithology -
Dense, fine-grained magnetite bands and band rich in
quartz and magnetite grains. In one slide (AN8), the granule
structure of the magnetite is evident within the mosaic of
recrystallized quartz together with a little garnet, horn-
blende, calcite, arid fibrous cummingtonite, partly in
radiating clusters. Ferrohypersthene is common in two other
slides; it has fringes of fibrous cummingtonite (less than
2 ym wide) which partly replaces the ferrohypersthene.
Hedenbergite occurs in the same sections (AN3, AN7); in AN7
it is associated with patches of blue-green hornblende.
Cummingtonite, with typical lamellar twins, is found in
magnetite-rich bands, and green hornblende in magnetite-
poor bands. One slide (AN12) has abundant fayalite together
with green hornblende and cummingtonite. Hisingerite veins
and patches occur in two of the thin sections.
20
-------
Locality A. S.
Working face, due south of Locality A. N. and towards
the upper part of the Upper Cherty Member, the closest
locality to the Gabbro; 28 specimens, four thin sections
(three specimens).
Lithology -
Six of the specimens are from irregular sheets or veins
composed of quartz and matted fibrous amphibole (identified
microscopically as cummingtonite-grunerite) stained by iron
oxide from weathering. These sheeted veins apparently cut
the ore layers in irregular fashion and are relatively com-
mon at this locality. The banded ore is typical: fine- and
medium-grained quartz and magnetite in bands varying from
5-100 mm thick; prismatic amphibole prominent in some
magnetite-rich layers; iron silicate layers and masses with
garnet, epidote, biotite, and prismatic amphibole identified
in some specimens; calcite vein in one specimen. A prominent
constituent of some specimens is fibrous amphibole; it occurs
in association with magnetite, quartz, and other iron silicates
as veins cutting magnetite-quartz layers and in masses on and
penetrating magnetite layers.
Micro-lithology -
Cummingtonite is common in all four sections; in one
(ASl4c), it is abundant, prismatic to fibrous in habit, in
part yellow-brown due to alteration, and intergrown with
hornblende; magnetite is disseminated throughout. In
another slide (ASl7ca), magnetite-rich bands have lenses
of quartz with acicular fibrous masses of cummingtonite,
and other layers have abundant light green hornblende (or
actinolite); plagioclase occurs sparingly. The other two
thin sections (ASl7cb; AS20c) are rich in magnetite, have
common acicular to prismatic cummingtonite, coarse
21
-------
plagioclase and biotite, full of tiny grains or dusty
magnetite, and quartz.
Locality Bi
Working face, in the upper middle portion of the Upper
Cherty Member, 1.5 miles west of Locality A (the 11,500 foot
mark on the pit reference line, Figure 1); five specimens,
one thin section.
Ljithology -
Fine-grained, dense magnetite layers alternate with
medium-grained quartz and magnetite; fibrous amphibole
masses and layers with other iron silicates in four of the
five specimens.
Micro-lithology -
Magnetite shows a granule structure in a quartz mosaic,
in part with aggregates of prismatic to fibrous cummington-
ite in patches and also needles of cummingtonite in the
quartz. There are bands rich in dense magnetite. Aggregates
of blue-green hornblende intergrown with cummingtonite are
abundant. There is also a little chlorite, calcite, and a
vein of yellow-brown hisingerite.
Locality Bii
Working face, near Locality Bi but in the middle part
of the Upper Cherty Member; 11 specimens, three thin sections,
Lithology -
Typical ore is composed of alternating dense magnetite-
rich layers and medium-grained quartz-magnetite layers;
green silicate layers; garnet in some; prismatic pyribole
(amphibole or pyroxene) disseminated throughout the quartz-
magnetite layers and silicate layers in a number of specimens,
22
-------
Micro-lithology -
One section (BM26b) has a large mass of garnet and
large aggregates of hedenbergite intergrown or altering to
acicular to fibrous cummingtonite; fayalite with hedenbergite,
prismatic cummingtonite, and a little magnetite; prismatic
and fibrous cummingtonite in patches and in part light brown
due to alteration.
In the other two slides (BM27b; BM27e), magnetite in
granule structure is present; acicular cummingtonite abun-
dant in the granules and also in aggregates and surrounding
area with granule structure. One of the sections (BM27b)
has a little hedenbergite and hornblende.
Locality C
Working face, in the middle of the Upper Cherty Member,
approximately 1.5 miles west of Locality B (about the
19,600 foot mark on the pit reference line, Figure 1);
12 specimens, four thin sections.
Lithology -
Alternating dense magnetite and coarse quartz-magnetite
layers the most common; silicate layers include masses of
fibrous amphibole in radiating clusters and in seams up to
17 mm thick; calcite with coarse-grained amphibole, quartz,
and magnetite.
Micro-lithology -
In section CM28c, magnetite occurs in a granule struc-
ture in a mosaic of quartz with abundant needle and fibrous
cummingtonite and some pleochroic brown to very dark brown
mineral, which is either hisingerite or nontronite; aggrega-
tes of hedenbergite have fringes of cummingtonite and are
cut by veins of hisingerite.
23
-------
Section CM28e has a dense aggregate of blue-green horn-
blende, in part plumose, with fringes of fine needle to
fibrous cummingtonite; magnetite has a granule structure,
and there are ovoid areas of plagioclase with hornblende
surrounding and grown into them and containing acicular
cummingtonite.
Section CM28g has both dense magnetite-rich bands and
bands with granule structure, the latter with abundant fibers
and prismatic grains of cummingtonite. Another band is dense
with needle and fibrous cummingtonite in radiating clusters.
The fourth section (CM28d) contains considerable calcite
and quartz; acicular cummingtonite occurs in the calcite;
hornblende is common and partly intergrown with cummingtonite.
Locality D
Working face, in the upper portion of the Upper Cherty
Member, about a quarter of a mile southwest of Locality C
(near the 20,500 foot mark on the pit reference line,
Figure 1); 10 specimens, three thin sections.
Lithology -
Fine-grained, dense magnetite layers intercalated with
fine- to medium-grained silicate layers with calcite, quartz,
and magnetite; garnet-rich layers with associated green
pyribole; layer with fibrous amphibole in radiating groups;
sulfide streaks in some of the dense magnetite layers;
hematite in some specimens together with magnetite, quartz,
jasper, and stellate fibrous amphibole.
Micro-lithology -
Section DU30c has a zone with magnetite grains and dust
in fine-grained quartz; a mass of poikilitic garnet with
quartz, a little cummingtonite, brown-colored alteration
material, and some hedenbergite altering to brownish-yellow
hisingerite.
24
-------
Section DU30a has, in addition to magnetite-rich masses,
quartz, and calcite, abundant hedenbergite with intergrown
cummingtonite. The hedenbergite exhibits varying styles of
alteration to brown hisingerite. A little blue-green horn-
blende is also present.
The third section (DU30e) has bands of varying composi-
tion; much coarse magnetite with interstitial quartz and
abundant fine needles of cummingtonite and green hornblende
in some bands; bands and lenticles rich in fibrous cumming-
tonite; quartz with abundant cummingtonite needles; another
band has common green-brown biotite, abundant cummingtonite,
some in radiating clusters, and a little chlorite (after
biotite?).
Locality Ei
Working face, in the lower middle part of the Upper
Cherty Member, about half a mile west of Locality D (about
the 22,750 foot mark on the pit reference line, Figure 1);
five specimens, two thin sections.
Lithology -
Calcite veins and quartz veins with sulfides cut layers
of fine-grained, dense magnetite and coarser layers of quartz
and magnetite with iron silicates, including green prismatic
and fibrous amphiboles. One specimen has thin layers of
green fibrous amphibole.
Micro-lithology -
Section ELM32a has abundant magnetite in dense bands
and in bands with granule structure; in the dense bands
there are lenses of fibrous or needle cummingtonite and a
little green hornblende. There is also a band of fine-
grained, green, prismatic hornblende with a little cumming-
tonite, a band of matted cummingtonite with a little horn-
blende, magnetite grains, and green clots. A band rich in
25
-------
magnetite has abundant brown hisingerite (or nontronite?).
The granule zone has much quartz, fibrous cummingtonite in
stellate bunches, and some hornblende. There is a band of
cummingtonite fibers in stellate of plumose structure, and
another with much magnetite and a mass of fibrous cumming-
tonite with green or greenish-brown alteration product of
hisingerite. A quartz-rich zone has cummingtonite fibers
penetrating it as a fringe.
The other section (ELM32e) has coarse calcite, coarse
prismatic hornblende (or actinolite), a little plagioclase,
quartz, and a little fibrous cummingtonite; hornblende
intergrown with cummingtonite. Aggregates of prismatic
cummingtonite occur with patches of cummingtonite fibers,
brown-colored because of alteration; some fine-grained
cummingtonite has a plumose structure and grades into an
area with laths of green hornblende.
Locality Eii
Working face, in the lower part of the Upper Cherty
Member, adjacent to Locality Ei; seven specimens, two
thin sections.
Lithology -
Fine-grained, dense magnetite with coarse quartz and
magnetite, green pyribole, and sulfides; silicate layers
with magnetite and prismatic amphibole. One specimen has
a mass of fibrous green amphibole, and another has a brown
vein of partly radiating fibrous amphibole with quartz.
Drusy purple quartz is present on fine-grained magnetite
with disseminated green iron silicate.
Micro-lithology -
Section EL33e has bands rich in magnetite grains with
interstitial fibrous cummingtonite in some and dark green
hornblende in others; other bands are rich in fibrous
26
-------
amphibole --an intergrowth of cummingtonite and hornblende --
with a little magnetite. Another band has magnetite, quartz,
and needle to fibrous cummingtonite, partly in stellate
clusters, and rare hornblende and plagioclase. There is also
some brown to green-brown hisingerite (or nontronite?) as an
alteration product.
The other section (EL33f) has a magnetite-rich zone with
aggregates of intergrown hornblende-cummingtonite needles,
quartz with needles of amphibole, blue-green hornblende, and
prismatic cummingtonite. There is an area of coarse quartz
with prismatic to needle intergrown hornblende-cummingtonite.
In another zone, quartz and magnetite occur with needle
cummingtonite in stellate patterns and a little hornblende.
Locality F
Working face, in the upper part of the Upper Cherty
Member, one and a half miles west of crusher #2, a little
over two and a half miles west of Locality E (at the
36,500 foot mark on the pit reference line, Figure 1), and
less than two miles from the westernmost limit of the pit
(the westernmost collecting locality); nine specimens, two
thin sections.
Lithology -
Hematite with jasper and magnetite; garnet conspicous
in several of the specimens with green iron silicates; green
fibrous amphibole associated with garnet in one specimen;
layers rich in fibrous amphibole in another specimen.
Alternate layers of fine-grained, dense magnetite and
coarser-grained quartz plus magnetite with iron silicates
are common with blotches and patches of hematite. Coarse-
grained calcite together with garnet, prismatic amphibole,
and fine-grained magnetite layers make up another specimen.
27
-------
Micro-lithology -
Section FU34e has dense magnetite bands with inter-
stitial cummingtonite and a little garnet; abundant needle
dimmingtonite in matted layers with fine-grained magnetite
and common tiny garnet. Some bands with magnetite in granule
structure also have cummingtonite, common blue-green horn-
blende, and a little garnet. Quartz has dense inclusions of
fibrous aggregates of cummingtonite.
The other section (FU34a) has a large area of abundant
quartz and aggregates of needle to fibrous cummingtonite with
"frayed-out" ends; also aggregates of hedenbergite and cum-
mingtonite, the hedenbergite having intergrown cummingtonite;
sparse occurrence of fine-grained magnetite in granule
structure distributed throughout the quartz mosaic; large
garnet, partly anisotropic, has inclusions of hedenbergite
and cummingtonite; another large garnet has a fringe of
matted cummingtonite fibers with some hedenbergite, a little
blue-green hornblende, and a very small amount of calcite,
and, in places, a very narrow outer rim of hisingerite, A
vein-like aggregate of fibrous cummingtonite and hedenbergite
cuts a sinuous path across the slide. The cummingtonite
in this thin section has a very pale green color and is,
thus, probably iron-rich or grunerite.
SUMMARY OF MINERAL OCCURRENCES
The approximate mineral abundances for the different
zones of the Upper Cherty Member and averaged from the
25 thin sections are shown in Table 2. Sample photomicro-
graphs of thin sections are shown in Figure 2.
28
-------
o
LU
to
LA
CM)
Q
LU
00
<
CO
o
o
CM
0>
«J
Plagio-
clase
a
4-1
•r-
4J
0
•r
«
0)
4J
C.
r-
n
u
j-
n
n)
PK
Garnet
Hornblende
(Actinolite)
Ferro-
hypersthene
Hedenbergite
Gumming t oni te-
Grunerite
Quartz
Magnetite
>,
4J
-------
AS I4e - Aggregate of Acicular to Fibrous Cummingtonite-Grunerite
(Yellow by Alteration; Some Isotropic Yellow-Brown Substance)
A Little Intergrown Hornblende (kx)
BM 27e - Magnetite and Quartz in Granule Structure, with Acicular
to Fine Needle and Fibrous Cummingtonite and Grunerite (Ax)
Figure 2. Selected fiber-bearing thin sections
30
-------
CM 28c - Magnetite and Quartz in Granule Structure; Abundant
Needle to Fibrous Cummingtonite-Grunerite, with a
little Hedenbergite largely altered to inter-
grown with Cummingtonite-Grunerite
DU 30e - Dense Aggregate of Matted Needles and Fibers of Cum-
mingtoni te-Gruner i te, with a fringe of Fibrous, Radiating
Cummingtonite-Grunerite; Biotite at lower border (4x)
Figure 2. (continued)
31
-------
ELM 32a - Stellate Aggregates of Cummingtonite-Grunerite and
Hornblende, Set in Quartz Matrix with Magnetite Grains (Ax)
Figure 2. (continued)
32
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SECTION 7
FIBROUS SAMPLE PREPARATION
In order to prepare fibrous samples suitable for bio-
logical experimentation from the ore samples collected at
the Peter Mitchell Pit, Babbitt, Minnesota, several processes
were required. The fibrous material had to be separated from
the non-fibrous gangue, ground or fractionated into the des-
ired sizes, divided into amounts suitable for use, and seal-
ed into vials. During these processes, the fibrous samples
were, as much as possible, to be representative of those
fibers present throughout the ore body, unchanged chemically
and not contaminated by other substances.
FIBER SEPARATION AND SIZING TECHNIQUES
Many types of fiber separation and sizing techniques
and equipment were investigated. Those that were consid-
ered are:
1. Jaw Crushing
2. Roll Crushing
3. Ball Milling (wet)
4. Air Jet Milling
5. Magnetic Separation
6. Sieving
7. Sedimentation
8. Felvation
33
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9. Serial Filtration by Nucleopore Filters
10. Magnetic Alignment of Fibers
11. Dielectrophoresis
12. Stirred Screening
13. Vertical Spinning
14. Combinations of the Above
These techniques were investigated in the literature and, if
promising, experimentally to determine their applicability
to this particular separation and sizing problem. Depending
on the success of the various techniques under different
operating conditions and whether the ore or the fibrous
veins in the ore were used as raw material, a separation
and sizing process was to be developed from the above tech-
niques. In the following paragraphs, the above techniques
will be discussed.
A jaw crusher is available at IITRI that will accept
pieces of rock of 4 in. major diameter and break them to
approximately % in. pieces. This equipment simulates the
operation of industrially used crushing equipment. The pro-
duct size distribution is also similar to those produced
industrially.
A roll crusher is also available at IITRI that will
accept the product of the jaw crusher and will break it to
9070 less than 10 mesh. This has to be accomplished at var-
ious gap settings of the roll crusher alternated with
screen sieving. This equipment also simulates the operation
and size distribution of industrially used crushers.
A ball mill is available that simulates industrial
operation. If used, it would have been operated wet to
maximize preservation of the fibers' crystal structure.
Almost any size distribution can be attained by controlling
the time and conditions of operation.
34
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Air jet milling uses centrifugal forces to break up
particles. The particles of the desired size then escape
through a cyclone type exit. This type of sizing has been
used by Johns-Manville in the preparation of asbestos fiber
samples. A Jet Pulverizer Model 04-503 4" Micron-Master
air jet mill with a capacity of 30-50 Ib/hr at an air flow
of 50 scfm at 100 psig was obtained to test its suitability
for this type of fibrous sample. The jet mill consists of a
4in. diameter, shallow, circular grinding chamber with four
angled nozzles equally spaced around the chamber periphery.
These nozzles discharge a high energy fluid, such as air
or steam, imparting turbulence and a circular motion. The
feed particles are impacted upon each other causing breakage,
The fine fragments are carried out with the discharged air
and collected in a cyclone. The coarse particles are thrown
toward the wall and are further ground. Thus, air jet mil-
ling accomplishes size reduction with no contact of the
material being ground by any other substance except filtered
air. A final filter capable of holding 4-8 in. x 10 in.
filters was constructed. Nuclepore 0.8 ym pore size filters
were used to maximize the capability of recovering the
fine fraction that escapes from the jet mill cyclone. Pre-
liminary test runs showed that the length of almost all
the fibers was reduced to less than 200 ym with most of
the fibers less than 30 ym.
Magnetic separation is one of the steps used in the
industrial processing of t.aconite to iron ore at the Reserve
mine. It is used to separate the iron fraction from the
tailings. Examination by optical microscope of minus 325
mesh (< 44 ym) hammer crushed taconite before and after
electromagnetic separation showed that the total size fra-
tion was approximately 60% fibrous, the magnetic fraction
approximately 20% fibrous, and the non-magnetic fraction
approximately 85% fibrous. Thus, magnetic separation would
35
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be a useful step in sample preparation from the raw taconite
ore in that it enriches the fibrous fraction and simulates
the production of tailings in the actual operation. However,
this may have to be done for a larger size fraction as the
iron content of the amosite-like fibers may cause them to
exhibit magnetic properties when in small sizes. This was
somewhat confirmed as the magnetic fraction for the mag-
netic field used was much larger than the non-magnetic
fraction.
Mechanical sieving is used to separate the product
after roll crushing and ball milling. The smallest size
mesh practical for moderate amounts to be practicable is
a 325 mesh (<44 ym). Therefore, this would be an intermed-
idate step if sample preparation is started with the tacon-
ite ore.
Sedimentation may be used to separate particles by
their terminal settling velocity. Stoke's Law applies for
spherical particles at Reynold's Number £ 1.0. For fibers
settling with their axis normal to their velocity, the re-
lationship is more complex, involving an iteration on the
Reynold's Number for Re <_ 0.5. The settling velocities of
both spherical particles of the density of cummingtonite
3
(p = 3.1 g/cm ) and fibrous particles of the density of
3
amosite (p = 2.8 g/cm ) have been calculated. The settling
velocity of a fiber is greater than that of the same dia-
meter spherical particle and the difference increases as
the diameter decreases.
Sedimentation experiments were conducted to determine
the accuracy of the theory for the particles involved.
Hammer crused taconite of minus 325 mesh was sedimented to
take the fine fraction. Theoretically, this fraction should
consist of fibers less than 3.3 ym diameter and particles
less than 9.6 yin in diameter. This method separated diameter
36
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fairly well both for fibers and particles; however, many
non-fibrous particles were present in both the coarse and
fine fractions. Some agglomeration took place in the fine
fraction during its separation from the fluid. Also, the
sedimentation technique is maninly insensitive to fiber
length. Sedimentation of hand-cobbed fibers into three size
fractions was also investigated. As hand-cobbed fibers con-
tain much less gangue material, further separation is not
as critical or necessary. Sedimentation was performed for
the theoretical fiber diameters of D* _> 3.3 ym,
3.3 ym > D^ >_ 1.0 ym, and D^ <1.0 ym (equivalent to spher-
ical particle diameters of D >_ 9.6 ym, 9.6 ym > D ^ 4.5 ym,
and D <4.5 ym). Optical microscope examination of the sized
fractions showed the actual separation by fiber diameter to
be nearly that predicted; however, aspect ratios varied from
the minimum of three to nearly fifty. The majority of fibers
ranged in aspect ratio from three to ten, but the mass dis-
tribution would be greatly skewed by the few fibers of much
greater length present. Therefore, sedimentation was shown
to be a reasonable method of sizing fibers by diameter in
large quantities. However, sedimentation has the disadvan-
tages of not being able to separate by shape or length of
fiber and of the possibility of leaching of the settling
material by the sedimenting fluid.
Felvation is a technique developed at IITRI for frac-
tionating powders. It was initially developed by Kaye and
Jackson8 and since has been modified by other workers to
overcome some of the practical operating difficulties. The
technique involves aspects of fluidization, elutriation and
sieving to separate powders into size fractions between
sieves. This technique has, to our knowledge, never been
attempted for fibers. An additional complication is that
sieves as small as 10 ym are difficult to obtain. For fibers
elutriating with their axis normal to the flow as would
37
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normally be expected for micron size fibers, the cut size
for felvation would be the length. Thus, the non-fibrous
particles of diamter less than the fiber length required
will also pass through the sieve. In the case of a 10 ym
sieve, felvation would have approximately the same effect
as sedimentation as fibers of length 10.0 ym by 3.3 ym are
settled in the same time as 9.6 ym diameter particles.
Thus, the fibers can be sized by either of these methods,
but only separated from a portion of the non-fibrous
particles present. Felvation of the fine sedimented fra-
ction hammer crushed taconite using both Nuclepore filters
and 10 ym sieves was investigated. The Nuclepore filters
could not withstand the suction necessary to draw the
particles through the filter. The sieve method did very
little to improve separation of fibers from gangue mater-
ial or to improve sizing of fibers and was extremely time
consiming. Felvation of the finer fractions of sedimented
hand-cobbed fibers using a 5 ym sieve was found to be even
slower than when a 10 ym sieve was used. The amount of mat-
erial passing through the sieve was of almost negligible
mass, while the degree of separation from the gangue was
not appreciable. Therefore, felvation was found to be of
very low productivity and very time consuming. However, it
might prove of some value in removing the longer fibers or
in separating the smaller diameter fibers from the gangue
if magnetic alignment of fibers is found to be feasible.
Serial filtration of asbestos fibers by Nuclepore fil-
ters is a technique developed by Spurny9. This technique
uses a 8.0 or 5.0 ym Nuclepore filter to separate the larger
particles and a 0.2 ym Nuclepore filter to collect the
asbestos fibers. In air, the fibers tend to align with the
flow and pass through the larger pore size filter. However,
this technique has only been used for separation of fibers
from ambient air and does not separate by length of fiber.
38
-------
The additional problem of aerosolizing a fiber-rich sample
for separation is also posed.
The magnetic alignment of asbestos fibers has been in-
vestigated by Timbrell10. He has found that all types of as-
bestos fibers of respirable size align in response to a mag-
netic field when settling in a fluid. Amosite fibers in
particular align in two fractions parallel and normal to the
field and of generally differing size. Thus, the fibers in
sedimentation, felvation, or serial filtration could be al-
igned for one fraction to be parallel or normal to the flow.
This technique could prove of great value in combination
with other techniques.
This technique was not investigated as an electromag-
netic of suitable size and strength was not available and
because amosite fibers align in two fractions perpendicular
to each other.
H.A. Pohl11'12'13 is the major investigator of dielect-
rophoresis as a technique for separation of particles. Di-
electrophoresis employs the effect of a non-uniform electric
field on the polarity induced on particles of high dielect-
ric constant. The particle will move toward the stronger
region of the non-uniform field. This effect can be util-
ized to separate particles of differing dielectric constants
by setting up an apparatus such that a constant force is
put on the particle throughout the non-uniform field. The
apparatus is then tilted such that the particles in a
fluid flow down the length of the apparatus and the force
of the field opposes the gravitational force across the
width. Thus, the particles of higher dielectric constant
are preferentially taken to the high side of the apparatus.
Such an "isomotive cell" was constructed, and some exper-
iments run to test the separation of fibers from rock. No
effective separation was achieved with the apparatus as
used.
39
-------
Stirred screening is a method developed with some suc-
cess by Johns-Manville11* . The purpose of this technique is
to keep the fibers parallel to the screens (10 ym - 44 ym)
in order to segregate by length; however, limited success
was achieved in that separations could only be made less
than 5 ym and greater than 10 ym. There was also some over-
lap of lengths in the separations. This technique was used
on ground chrysotile fibers of industrial purity.
Another possible method is that of spinning a test tube
full of fibers in suspension at low speed to separate by
length. In preliminary studies with carbon fibers11* the
longer fibers came out over the top of the test tube while
the shorter ones remained. The mechanism and parameters in-
volved are unknown, so it is unknown whether this method
might be suitable for fractionating asbestos fibers by
length.
Many combinations of the above methods are possible,
depending on the applicability of the various techniques
and whether the starting material is the ore itself or
only the fibrous veins. A possible process for the sep-
aration and sizing of fibers from the raw ore would in-
volve the following techniques:
1. Jaw Crushing to reduce size
2. Roll Crushing to reduce size
3. Ball Milling (wet) to reduce size
4. Magnetic Separation to remove the magnetic,
fiber-lean fraction
5. Sedimentation to remove the larger diameter
fibers and particles
6. Serial felvation by Nuclepore filters using mag-
netic alignment of fibers to separate first by
diameter and to remove non-fibrous particles and
then by length.
40
-------
A possible process from the fibrous vein material would in-
volve the following techniques:
1. Air Jet Milling to reduce size and allow only the
fines by aerodynamic diameter to escape
2. Serial filtration by Nuclepore filters using mag-
netic alignment to fractionate by length
3. Sedimentation to fractionate by diameter in each
length fraction (2 and 3 could be reversed)
Another possible process would be sedimentation of the tail-
ings material produced at Silver Bay, Minnesota, after the
extraction of magnetite from the taconite ore. One of the
techniques suggested above would have to be used to sep-
arate the fibers from the other gangue material. These
sample process give some idea of the complexity of the pro-
blem and of the number of techniques and steps that may have
to be involved to produce samples of acceptable characteri-
zation. These problems are separate from but relate to those
of the quantity of sample that can reasonably be produced
in a given time from a quantity of ore.
FIBER SEPARATION AND SIZING
Fibers were separated from rocks containing large num-
bers of fibers in significant veins both by hand and by
mechanical vibrator. Both methods were found to bring about
a major reduction in the amount of non-fibrous gargue present
from the amount present in crushed fiber bearing rock. Size
of the fibers was dependent on the method used and whether
large agglomerates were further reduced in size mechanically.
Approximately 1.5 kg of this material was produced; however
the process was very time consuming due to the low bulk den-
sity of the material of 0.65g/cc (40.6 lb/ft3).
Several rocks were found to consist almost entirely of
soft, light green or brown fibrous material. Crushing, gri-
nding, and sieving (< 35 mesh) of these rocks produces a
41
-------
material that has a very high ratio of fibrous to non-fib-
rous material. Approximately 3 kg of this fine fibrous
material was produced. The obviously different types of
fibers were kept separate by physical characteristics and
separation technique as much as practicable.
These separated fibrous materials are not necessarily
representative in all respects of the majority of the fibers
present in the ore in the Reserve mine or of the fibers in
the tailings from the processing at Silver Bay, Minnesota.
However, as these materials consist of mostly fibrous mat-
erial and could be produced much more easily than by attemp-
ting to separate the fibrous and non-fibrous fractions from
the ore or the tailings, this method was used to produce a
large quantity of material with a large fibrous fraction.
Jet milling was conducted for a series of six 100 g
samples of ground and sieved material in order to determine
optimum operating conditions. The operating conditions of
the tests are given in Table 3. Due to the number of para-
meters involved and possible problems with sample represen-
tativeness, the optimum operating conditions were not read-
ily apparent. However, several of the runs had little or no
material larger than 100 ym and most of the material smaller
than 10 ym.
It was then decided in a meeting with Dr. Coffin that
approximately 15 g of fibrous material of 0-30 ym length
would be satisfactory. Therefore, more detailed characteri-
zation of the two 100 g samples (No.'s 12 and 14) found most
promising by optical microscopy and of the unmilled material
was undertaken. For this more extensive characterization, a
spinning riffler was used to successively reduce sample
sizes for representative analysis. After this characteri-
zation, consisting of optical and electron microscopy,
X-ray spectroscopy, electron and X-ray diffraction, atomic
42
-------
Table 3. JET-MILL OPERATING CONDITIONS
Sample
No.
9
10
11
12
13
14
Feed
Setting
9
9
9
8
8
10
Pressure (psig)
Feed
50
65
70
4o
45
60
Mill
40
65
75
40
60
65
43
-------
absorption for some trace elements, B.E.T. surface area, and
solvent extraction for organics. After this characterization
the "best" material (No. 14) was chosen for biological
experimentation. The other fibrous material is being retain-
ed in case of further requirements at a later date.
PREPARATION OF SAMPLES FOR SHIPPING
The sample for biological experimentation was then
successively reduced in size using a spinning riffler to
200 approximately 75mg representative amounts for shipment.
The 75mg amounts were used as that is the amount needed
for one dose for a group of animals in the biological
experiment. Each representative amount was weighed out to
the nearest O.lmg and placed in a 30ml hypo-vial. Each
vial was then sealed with a resealing silicone rubber sep-
tum and purged with nitrogen for at least 10 minutes, at a
pressure of at least 2 in. Hg. An aluminum seal was then
fastened over the top of each vial for shipping.
44
-------
SECTION 8
CHARACTERIZATION OF FIBROUS SAMPLES
OPTICAL MICROSCOPY
Samples were counted by optical microscope using phase
contrast and a Porton graticule at 400 or 625X. The counting
procedure used was that of the Joint AIHA-AICGIH Aerosol
Hazards Evaluation Committee15 . In the first series of
counts of the six jet-milled samples of the ground and sieved
material, at least 100 particles were counted to deter-
mine the sizes of the fibrous and non-fibrous fractions and
their approximate size distributions. The results of these
counts are shown in Table 4. From these results, it was
concluded that samples 12 through 14 might be satisfactory
for biological experimentation. A spinning riffler was used
to reduce the sample to representative portions for further
analysis. Counts of at least 100 fibers were then conducted
of the unmilled material (1 and 2) and samples 12 and 14 at
400X. The results of these samples (see Table 5) show that
the jet-milled samples (12 and 14) have a reduction in the
length of fibers (to 10070 <_ 70 ym) and the amount of non-fib-
rous material (from ^ 80-90% to 60-70% non-fibrous). Sample
photomicrographs are shown in Figure 3. The jet-mill seems
to be effective in breaking up bundles of fibers into indi-
vidiual fibers, reducing their length, and reducing the size
of many of the non-fibrous particles so that they are too
small to be collected in the cyclone. The results of this
analysis suggest the use of sample 14 for biological exper-
45
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48
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(a) Unmilled Ground & Sieved Material (Sample #2; 65X)
(b) Milled Ground & Sieved Material (Sample #14; 65X)
Figure'3. Optical microscope photomicrographs
49
-------
(c) Unmilled Ground & Sieved Material (Sample #1; *407X)
(d) Milled Ground & Sieved Material (Sample #14; 407X)
Figure 3. (continued)
50
-------
imentation as this sample has the least amount of fibers
greater than 35 Mm in length (1-670) and greater than
4.4 pm in diameter (0.370).
ELECTRON MICROSCOPY
Samples were sized by electron microscopy using the
JEOL-100C electron microscope in the transmission mode.
Counts were made at 10,OOOX. Approximately 100 particles
including at least 10 fibers were counted to determine the
relative numbers of fibrous and non-fibrous particles.
Approximately 100 fibers were then counted to determine
their size distribution. The results of these counts are
given in Table 6. Sample photomicrographs are shown in
Figure 4. These counts of the four ground and sieved samples
show that at least 8570 of the particles are non-fibrous and
consist largely of particles less than 0.38 ym in diameter,
which are not visible at 400X. However, the results show
again that sample 14 has greater size reduction than
sample 12. (It should be noted that many visibly large par-
ticles did not remain suspended in the unmilled samples
(1 and 2) when the suspended sample was taken to place on
the electron microscope grid).
ELECTRON DIFFRACTION
Electron diffraction was also accomplished using the
JEOL 100C. Early analysis showed all of the fibers both from
fibrous veins in the ore and from the ore itself were amphi-
bole in structure. As shown in Table 7, all of the fibers in
the four analyzed samples were also found to be crystalline.
Of the 43 non-fibrous particles analyzed in the four samples
only one was found to be non-crystalline. Therefore, both
the fibrous and non-fibrous material is almost totally
crystalline. Samples of electron diffraction patterns are
shown in Figure 5.
51
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(a) UnmMled Ground & Sieved Material
Sample /M (1000X)
-
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(a) Unmilled Ground & Sieved Material (cont)
Sample ft] (5000X)
ifSr^i
Sample #1 (10.000X)
Figure 4. (cont inued)
57
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(b) Mi 1 1 ed Ground & Sieved Material
Sample #12 (1000X)
Sample #12 (5000X)
Figure k. (continued'
58
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(b) Milled Ground .S Sieved Matt-rial
V
Sample /O 4 (1000X)
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Figure 4. (continued)
59
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(b) Milled Ground & Sieved Material (cont)
Sample #]k (lO.OOOX)
Sample #14 (10.000X)
Figure 4. (continued)
60
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LU
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(b) Unmilled Fiber (Sample #2; 26.000X)
Figure 5. Electron diffraction patterns of
ground and sieved material
62
-------
(c) Milled Particle (Sample #12; 26,OOOX)
(d) Milled Fiber (Sample #14; 26.000X)
Figure 5. (continued)
63
-------
X-RAY SPECTROSCOPY
The chemistry of the particles was analyzed by x-ray
spectroscopy using the Kevex Energy Dispersive X-ray Spectro-
meter. Analysis of fibers from fibrous veins and from the
ore showed that nearly all of the fibers were silicates with
high iron content and with significant amounts of magnesium
and calcium (see Table 8). The x-ray spectroscopy results
of fibrous and non-fibrous particles in the four samples are
given in Table 7. Sample spectra are shown in Figure 6. All
of the fibers examined were found to be iron silicates, most
of which contained magnesium and calcium and some containing
manganese. Most of the non-fibrous particles were iron
silicates, many of which contained magnesium and calcium
while a few contained aluminum, potassium, and manganese.
Sample 14 is again outstanding as all of the fibers examined
were silicates containing iron, magnesium, and calcium,
while most of the non-fibrous particles examined were similar
to the fibers in that all were silicates with iron and
magnesium and most contained calcium. The high iron content
shows that the fibers are chemically similar to either
amosite or crocidolite. However, no aluminum or sodium is
present in most of the fibers as they should be in
corcidolite.
X-RAY DIFFRACTION
Bulk samples of approximately 5 g were analyzed in the
x-ray diffractioner. The results of the analysis for various
ore and fibrous samples are given in terms of relative
intensities (the intensity of the strongest line = 100) and
spacings of the diffraction lines are given in Table 9.
The results for the four samples are presented in Table 10.
64
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. fl&fr ,ti8ICi¥/CH
1. 88IICIV* 28.
Kfi K
2. 6S 4, 8:
(a) Fiber (0.7x4.0 ym); Sample #1
Mg, Si, Ca, Fe Present
(b) Particle (0.5 ym) ; Sample
Mg , Si, Fe Present
Figure 6. X-ray spectrographs
66
-------
PHftli fi&O ,8i8KE¥/CM 41. SEC.
BUG* .228KEV, I,
1.26
(c) Fiber (2.0x12.0 ym); Sample #14
Mg, Si, Ca, Mn, Fe
(d) Particle (1.7 ym) ; Sample
Mg, Si, Ca, Mn, Fe
Figure 6. (continued)
67
-------
Table 9. X-RAY DIFFRACTION LINES PRESENT IN SAMPLES
Hand-Cobbed
F i bers
1
33
5
5
14
36
5
7
7
7
100
5
7
33
5
7
12
12
d(nm)
0.84249
0.45753
0. 42302
0.33264
0.31644
0.28400
0.27303
0.26180
0.25218
0.20490
0.18953
0.18022
0.17760
0.16556
0.16327
0.15418
0.15234
Vibratory-
Cobbed Fibers
1
57
5
5
5
5
70
10
10
10
10
8
18
8
5
5
13
100
5
5
5
40
8
15
13
25
8
5
d (nm)
0.84249
0.48216
0.45753
0.42302
0.33022
0.31534
0.29592
0.28225
0.27385
0.27223
0.26143
0.25218
0.24169
0.23441
0.21834
0.20941
0.20490
0.19863
0.19065
0.18344
0.17744
0.1636?
0.16078
0.1518?
0.14796
0.14547
0. 14079
Fiber-Bearing
Rock w/Fibers
1
42
6
16
23
23
10
10
100
10
8
35
52
6
10
10
16
42
8
52
10
10
13
d (nm)
0.83065
0.48216
0.31377
0.30582
0.29592
0.28139
0.27223
0.25218
0.23500
0.2)885
0.20918
0.20490
0.19852
0.19294
0.17744
0.17098
0.16104
0.16027
0.14817
0.14547
0.14250
0.14079
F i ber-Bearing
Rock w/Fibers
< 147 Vim
1
43
15
11
7
7
37
33
7
100
18
7
26
78
9
11
11
56
52
7
11
11
7
1 1
d (nm)
0.83456
0.48087
0.45063
0.41520
0.32903
0.31425
0.29497
0.27143
0.25218
0.24169
0.22405
0.20895
0.20490
0.17776
0.17068
0.16612
0.16104
0.14796
0.14467
0.14192
0.13440
0. 13021
0.12780
Taconi te
1
42
>100
10
3
7
1 1
12
9
8
4
52
17
31
13
16
14
3
22
5
4
19
25
5
2
5
5
5
8
8
6
d (nm)
0.42402
0.33325
0.31865
0.29592
0.25286
0.24551
0.22813
0.22325
0.21246
0.20941
0.20381
0.19811
0.18156
0.17744
0.17680
0.16695
0.16078
0.15395
0.14817
0.14507
0.13786
0.13733
0. 12854
0. 12839
0. 12549
0.12521
0.12276
0.11993
0.11786
0.1 1521
F iber-Bear ing
Rock w/o
Fibers
I
89
7
11
4
16
100
7
9
7
9
7
7
7
7
4
44
44
4
7
4
7
7
38
4
4
9
9
11
d (nm)
0.84089
0.47958
0.45521
0.38667
0.33022
0.31480
0.29592
0.28312
0.27223
0.26069
0.25355
0.24044
0.23982
0.23559
0.21859
0.20446
0.20359
0.19689
0.19160
0.19064
0.18413
0.18207
0.17744
0.16584
0.16340
0.15234
0.15144
0.14527
Cummingtoni te-
Rich Taconite
1
26
6
14
5
6
4
70
20
50
12
12
8
10
6
6
6
100
6
4
12
64
4
4
12
12
6
16
d (nm)
0.83456
0.45521
0.42704
0.39001
0.36776
0.36187
0.33448
0.32549
0.30685
0.27466
0.26217
0.25149
0.24584
0.22758
0.21910
0.21270
0.20381
0.19852
0.18643
0.18173
0.17744
0.16751
0.16584
0.15395
0.15144
0.14041
0.13741
68
-------
Table 10. X-RAY DIFFRACTION LINES PRESENT IN SAMPLES
OF GROUND AND SIEVED FIBROUS ROCK
Sample No. 1
Unmi 1 led
1
100
7
7
b
9
82
7
9
11
7
5
7
9
9
5
5
7~
7
d (nm)
0.850
0.1)82
0.1(57
0.3^"
0.333
0.315
0.296
0.28*4
0.273
0.262
0.255
0.2^0
0.236
0.218
0.166
0.160
0.1148
0.11*5
Sample No. 2
Unm t 1 1 ed
1
100
8
3
" 8
11
7^
8
8
16
"8
11
5
8
8
8
11
d(nm)
0.843
0.1479
0.1(52
0.3146
0.331
0.315
0.295
0.282
0.273
6.262
0.255
0.2142
0.235
0.218
0.166
0.1<(5
Sample No. 12
Jet-Mi 1 led
1
100
1 1
9
9
14
14
9
67
7
11
18
9
11
9
9
1 1
7
d (nm)
0.838
0.1(77
0.457
0.1(52
0.31(2
0.337
0.330
0.311(
0.295
0.282
0.273
0.262
0.25l(
0.21(0
0.235
0.218
0.1149
Sample No. 1 ^
Jet-Mi I led
1
100
6
10
16
81
6
10
29
10
16
13
10
10
d(nm)
0.81(2
0.1482
0.339
0.330
0.315
0.296
0.282
0.273
0.262
0.255
0.236
0. 166
0. 145
69
-------
Standard X-ray diffraction lines of some inorganic materials
and asbestos types are given in Tables 11 and 12. A summary
of observations made from these results are given in Table
13. It should be noted that many other materials could be
present; there is some inaccuracy in the method; concen-
tration effects may mask the presence of some materials and
identification of the materials present is somewhat sub-
jective and only within reasonable accuracy. Cummingtonite
or grunerite and amosite or crocidolite may be present in
all of the samples analyzed except the typical taconite. The
analysis of the four ground and sieved samples are nearly
identical. They all appear to contain cummingtonite, rie-
beckite and richerite with significant trace amounts of
tremolite and crocidolite. This suggests that at least the
ground and sieved material is structurally more similar to
crodidolite than amosite. As no sodium or aluminum was found
to be present in the fibers as would be in crocidolite and
the amount of calcium was found to be higher than normally
found in the grunerite-cummingtonite series of which amosite
is member, the results suggest that the fibers are in the
tremolite-actinolite series.
ATOMIC ABSORPTION
Atomic absorption analysis was conducted on approxi-
mately 0.1-0.2 gamounts of the ground and sieved samples
for four trace metals (Mn, Ni, Cr, Co) using a Jarrell-
Ash Model 82-528 Maximum Versatility Atomic Absorption-
Flame Emission Spectrophotometer. The results are presen-
ted in Table 14. Manganese was found to be present in fairly
large quantities (on the order of 10 mg per gram of sample)
while nickel, chromium, and cobalt were present in smaller
quantities. All of these elements are present in trace
quantities in many types of asbestos.
70
-------
Table 11. X-RAY DIFFRACTION LINES IN SOME INORGANIC MINERALS
Nickel
Holder
I
100
42
21
dCnmJ
0.203
0.176
0.125
Quartz
JL
35
100
17
Aimi
0.426
0.334
0.246
0.228
0.224
0.213
0.198
0.182
0.167
0.154
4LJJS.
0.137
0.129
0.126
0.123
0.120
0.115
Grunerite i
100
Id
30
35
40
50
55
50
80
40
90
60
30
40
20
15
10
10
35
25
20
10
35
19
20
atna;
0,833
0.484
0.468
0.458
0.416
0.383
0.347
0.328
0.307
0.300
0.277
0.251
0.241
0.230
0.153
0.152
Q.151
0.148
0.141
0.139
0.137
0.133
0.131
0,128
0.119
umminatonite
70
-
60
80
60
100
6f
60
40
40
30
40
oiruu
0.838
0.326
0.307
0.299
0.275
0.262
0.251
0.229
0.218
0.203
0.165
40
0.140
i«b«ckite
00
20
16
55
20
50
45
16
10
10
0.840
0.451
0.342
0.311
0.298
0.273
0.253
0.232
0.226
0.218
renollte
00
10
20
20
35
16
0.838
0.487
0.476
0.451
0.420
0.387
40 0.378
75J0.327
100l0.312
10
40
45
16
0.303
0.294
0.280
0.273
90 0.270
30 0.259
40J0.253
i
810.241
30 0.238
I
1
i
i
lie «rice Fa
" V*»J — 1
0.338
0.315
0.294
0.271
0.253
0.216
t
v lite
1.282
1.250
;
i
0.178
•
i
i
i
i
Paragonite
a.ic Na-Al-Silicate
I d Cnml
0.439
0.318
0. 303
0.251
I
0.241
0.208
i
i
'
0. 148
1-Montmoi
I
1
-illonite
-Silicate
d(nin)
1
1
i
0.317
0.199
0.186
I
71
-------
Table 12. X-RAY DIFFRACTION LINES IN MAIN ASBESTOS TYPES
Amosite
1
100
36
52
^3
d(nm)
0.82fc
0.327
0.307
0.277
Anthophyl 1 i te
1
100
26
56
V
??
Ik
d (nm)
0.950
0.840
0.458
0.325
0.3'3
0.306
Crocidol i te
1
100
26
26
41
50
20
36
d(nm)
0.81(3
0.451
0.343
0.3H
0.272
0.261
0.254
Rhodes ian
Chrysot i le
1
100
29
51
27
20
d (nm)
0.738
0.455
0.366
0.246
0.154
Canad ian
Chrysot i le
1
100
27
57
24
21
d (nm)
0.738
0.455
0.366
0.246
0.154
72
-------
00
LU
CC
O
O
<
LL.
O
z
o
CO
XI
ro
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=«=
CSI
CNJ
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cn ' "
C j. -C •—
— •" o c
!§=§
0 ^ I—
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1- c .* XI
o> T o —
XI O LU
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0
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4->
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r— 4-t
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1- — 4-J
o • — • —
c ^* *~~
4-1 w x: o
c 4-> a. -a
o — o —
Z 1/1 x: o
i 0 *-• O
< 5 < <->
z •z.
•z. ~z
•z. ~z.
•z. 'z.
z z
z z
z z
z z
•Z. 'Z.
z z
z -z.
0)
— 0)
4-1 —
O *->
i/i O
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l_ >*
x: v-
o x;
o
c
ra c
•— ra
in •—
0) -o
TJ ra
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x: ra
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C
01
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a.
>-
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01
4-1
• —
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a
i
ra
L.
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XI
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ra
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1
4-1
C
0)
I/I
0)
L-
a.
4-J
O
1
73
-------
Table 14. ATOMIC ABSORPTION
Sample
No.
#1
#12
#14
Sample
Wt (g)
0.1 464
0.1140
0.1337
Weight (yg)
Mn
1900
1650
1500
Ni
37.5
50.0
30.0
Cr
6.0
4.5
4.5
Co
3.75
3.00
3.00
Metal Wt/Sample Wt (ug/g)
Mn
12980
16670
11220
Ni
256.1
438.6
224.4
Cr
40.98
39-47
33.66
Co
25.61
26.32
22.44
Table 15. BENZENE EXTRACTION OF ORGANICS
Sample
No.
#1
#12
#14
Sample
Wt (g)
0.4933
0.4035
0.4503
Weight Organics
(mg)
1 .0
1.7
1 .0
Organics Wt/Sample Wt
(mg/g)
2.03
4.21
2.22
74
-------
B.E.T. SURFACE AREA
B.E.T. Surface Area Analysis was conducted using a
Micromeritics Model 2100D Orr Surface-Area Pore-Volume Ana-
lyzer. The results of four point B.E.T. surface area analysis
for the four ground and sieved samples are shown in Figure
7. The experimental points lie almost exactly on the regre-
ssion lines in all cases (correlation coefficients >_0.9999).
There is.^little variation in surface area between the un-
milled and milled samples as the surface area-to-volume ratio
is independent of the fiber length and inversely propor-
tional to diameter which is only slightly reduced by break-
ing of bundles. Thus, the surface area of the milled sam-
2
pies ranges from 30.7 to 34.1m /g, while that of the un-
milled samples ranges from 28.9 to 31.3m /g showing that
only bundles are broken up to increase the area exposed for
absorption slightly and that they are reduced in length
while not in the diameter of individual fibers. The B.E.T.
surface areas measured are significantly higher than those
measured for UICC amphibole asbestos samples. Timbrell16
measured values of 5.7 + 0.3, 11.8 + 1.0, 8.3 + 0.5m /g for amosite,
anthophyllite, and crocidolite, respectively. Chrysotile
has a surface area closer to those measured (Rhodesian
Chrysotile 21.3 + 1.5m /g; Canadian Chrysotile 26.8 +
2
0.7g/m ). Samples of tremolite and actinolite have been
o
measured as having surface areas of 6.2 and 11.6m /g,
respectively. The high surface areas values obtained for
these samples may indicate the small size of the ground
material or the large amount of small, non-fibrous par-
ticles.
75
-------
Figure 7. B.E.T. surface area analysis
Surface Area Sw
0.2687 s
(Slope + Intercept)
0.035
0.030 -
E
o
\
en
0.025 -
in
a.
i/i
a.
0.020 -
ro
0.015 -
0.010 -
0.005 -
0.000
0.00
0.05
0.10
0.15
Unmilled #1
Unmilled #2
Unmilled #1
Unmilled #1
0.20
Sw=28.9m /g
2
Sw=31,3m /g
Sw=30.7m2/g
Sw=3i».lm2/g
0.25
O.j
76
-------
BENZENE EXTRACTION
Soxlet extraction of benzene soluble oils was conducted
for at least four hours. The results are shown in Table 15.
The values of oil content measured ranged from 2.0 to 4.2 mg/g
of sample. These values are approximately fifty times greater
than those measured for UICC samples of amosite, anthophyllite,
and crocidolite, and approximately ten times greater than
those measured for UICC chrysotile 16.
77
-------
SECTION 8
REFERENCES
1. Vermas, F.H.S., "The Amphibole Asbestos of South
Africa", Trans, and Proc. Geological Society of South
Africa, 55, 199-299, 1952.
2. Champness, P.E., Lorimer, G.W., Richards, A.L., and
Zussman, J., "Electron Optical Analysis of Particulate
Matter in Six Water Samples", Report presented as
evidence at EPA vs. Reserve Mining, 1973.
3. Zussman, J., Transcripts of the EPA vs. Reserve Mining,
Vol. 39, p. 5378-5548, September 28, 1973.
4. Langer, A., Private Communication, January 1975.
5. Gundersen, J.N., and Schwartz, G.M. , the Geology of the
Metamorphosed Biwabik Iron-Formation, Eastern Mesabi
District, Minnesota: Minnesota Geol. Survey Bull., No.
43, 139 p., 1962.
6. French, B,M., 1968, Progressive Contact Metamorphism of
the Biwabik Iron-Formation, Mesabi Range, Minnesota:
Minnesota Geol. Survey Bull., No. 45, 103p.
7. Deer, W.A., Howie, R.A., and Zussman, J., 1963, Rock-
forming Minerals, v.2, Chain Silicates: London, Long-
mans, Green, and Co., Ltd., 379 p.
8. Kaye, B.H. and Jackson, M.R., "A New Technique for
Fractionating Powders", Powder Technology, 1(1967),
43-50.
9. Spurny, K.R., et. al., "A Note on the Sampling and
Electron Microscopy of Asbestos Aerosol in Ambient Air
by Means of Nuclepore Filters", Paper 74-47 presented
at 67th Annual Meeting of APCA, Denver, Co., June 9-
13, 1974.
78
-------
10. Timbrell, V., et.al., "Alignment of Asbestos Fibers by
Magnetic Fields: Biophysical Applications", 3rd Inter-
national Conference on the Physics and Chemistry of
Asbestos Minerals, August 1975
11. Pohl, H.A. and Plymale, C.E., "Continous Separations
of Suspensions by Non-Uniform Electric Fields", Elec-
trochemical Society Journal, 107:390-6, May 1960
12. Pohl, H.A., "Non-Uniform Electric Fields", Scientific
American, 203:106-12+, December 1960
13. Pohl, H.A., "Theoretical Aspects of Dielectrophoretic
Deposition and Separation of Particles", Electro-
chemical Society Journal, 115:sup!55c-61, June 1968
14. Presnar, P.V., Ed., "Fibers for Biological Experiments'
Transcript of the IOEH Conference, October 1973
15. Joint AIHA-ACHIH Aerosol Hazards Evaluation Committee,
"Recommended Procedures for Sampling Counting As-
bestos Fibers, AIHA Journal, 36, (2): 83-90, Feb. 1975
16. Timbrell, V., "Characteristics of the UICC Standard
Reference Samples of Asbestos", in H.A. Shapiro (Ed)
Pneumoconiosis, Proc. International Conference,
Johannesburg, 1969, Oxford University Press, Capetown,
1970, p.28
79
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/1-77-001 _
4. TITLE AND SUBTITLE
AMPHIBOLE MINERAL STUDY - to complement the oingoing
characterization of fine participate environmental
contaminants for biological experimentation
7 AUTHOR(S)
Paul C. Siebert and Colin F. Harwood
3 RECIPIENT'S ACCESSION NO.
5 REPORT DATE
January 1977
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
IIT Research Institute
10 West 35th Street
Chicago, IL 60616
1AA6Q1
11. CONTRACT/GRANT NO.
68-02-1687
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory
Office of Research and Develpment
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report details the work and results of a program concerned with the
collection of amphibole mineral samples from the Reserve Mining taconite mine
in Babbitt, Minnesota and the preparation of highly characterized amphibole
fibers from these samples. A profile of the ore body was compiled after a
petrographi.c examination of mineral samples.
Various separation and sizing techniques for the fibrous material present in
the ore were investigated. Air jet milling of ground and sieved fibrous rock
was used to prepare samples for biological experimentation. This material
was characterized by optical microscopy, electron miscroscopy, electron
diffraction, x-ray spectroscopy, x-ray diffraction, atomic absorption spectrometry,
B.E.T. surface area, and benzene extraction. The fibers were found to have many
properties similar to amphibole asbestos types. Vials of weighed amounts of
product sample were prepared and purged with nitrogen.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
*Amphiboles
*0re sampling
*Taconite
Mining
Asbestos
b.IDENTIFIERS/OPEN ENDED TERMS
Sample Preparation
Biological Experimentatic
c. COSATI Field/Group
08 G
06 A
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFT|rn
8 SECURITY
2(5
CLASS (This page)
21. NO. OF PAGES
_88
22. PRICE
EPA Form 2220-1 (9-73)
80
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