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Strategic University Programme at Department of Geology and
Mineral Resources Engineering. ”THE VALUE CHAIN FROM MINERAL
DEPOSIT TO BENEFICIATED PRODUCT WITH EMPHASIS ON QUARTZ” Background
for the programme The production and value of industrial minerals
in Norway has increased considerably in the last years. The
Norwegian industrial mineral production is both characterised by
the variety of different minerals and mineral products, and by the
fact that Norway is the major producer in the world of some
minerals such as olivine, nepheline and beneficiated carbonates
(GCC) used in paper. In addition Norway produces quartz/quartzite,
graphite, talc, anorthosite, feldspar, mica, dolomite and ilmenite.
The production value of mineral resources in Norway , except for
oil/gas, was about 7,5 thousand millions NOK in 2003. Of this, 2,6
thousand millions NOK came from the industrial minerals, 2,5
thousand millions from crushed rocks/aggregates, 1 thousand
millions from natural stone and only 0,5 thousand millions NOK from
metallic ores. The rest is from an increased coal production at
Svalbard. The growth in industrial mineral production exceeds the
decline in metallic ores, and it is recognised that there is a
considerably future growth potential in industrial mineral
production in Norway. The value of industrial minerals is in high
degree created during the beneficiation and the production of
special products, which need both competence and high technology.
For instance, crushed carbonate may be priced at 35 – 40 NOK/t,
while beneficiated carbonate filler used in paper may reach prices
up to 1000 NOK/t. There is a gradual transition from mineral
beneficiation to material technology. In accordance with
recommendations given by the “National Working Group” a close
co-operation with staff at the Department of Materials Technology
is strongly emphasised in this project. The research activity in
industrial minerals has been fairly low in Norway. Most of the
research is carried out by the industry itself, and the results are
generally kept in secret. However, to produce valuable and special
products reaching high prices in the marked, there is a
considerable need for skill and competence. Being the only
university in Norway responsible for research and teaching in
mineral production, the research programme is of major importance
including five doctoral students and one post.doc. The programme
comprises three areas of research:
• Genesis of industrially applicable high purity quartz in
igneous and metamorphic environments
• Beneficiation of quartz • Advanced characterization of
industrial minerals and beneficiated products.
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It is collaboration with other universities as well as with
industrial partners which also give financial support to the
project. Following departments and institutions collaborate in the
programme:
The department of Geology and Mineral Resources Engineering,
(IGBt), NTNU The Department of Materials Technology, NTNU SINTEF
Civil and Environmental Engineering, Department of Rock and Mineral
Engineering The Geological Survey of Norway (NGU) The Department of
Geology, The University of Oslo (UiO)
Industry partners: TITANIA A/S Hustadmarmor A/S Norwegian
Crystallite North Cape Minerals Elkem A/S
Time plane: 5 years, from 01.01.2001 to 31.12.2005 Financial
support: NFR 11,8 mill. NOK. In addition financial support from the
industry and field contribution from researchers at NGU. Staff: 5
dr. candidates. 1 postdoc. Researchers at NTNU and NGU. Description
of the research areas Research area: Genesis of industrially
applicable high purity quartz in igneous and metamorphic
environments Supervisors: Rune B. Larsen, Objective Our primary
goal is to study the element exchange processes in quartz from
igneous and sedimentary environments that are exposed to multiple
episodes of high-grade metamorphic re-crystallisation. Theoretical
considerations and laboratory experiments imply that this type of
quartz may obtain qualities commensurable with industrially
applicable high purity quartz (HPQ). South Norway comprises an
excellent natural laboratory for this character of studies, because
quartzites and acid meta-igneous rocks covering large areas
experienced different degrees of granulite facies metamorphism.
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Background High purity quartz, i.e. quartz with extremely low
concentrations of impurities, is a rare commodity that only forms
under geological conditions where a narrow set of chemical and
physical parameters is fulfilled. When identified, HPQ obtain very
attractive prices and is applied in the communications industries
and other high-technology sectors that currently are under rapid
expansion. Examples of end products where HPQ is the main raw
material includes photovoltaic solar cells for environmentally
sound energy production, silicon metal-oxide wafers in the
production of ever-faster computer chips and long distance optical
fibres that are extensively used in communication networks. Marked
considerations Industrial agencies forecast a solid 5-20 % annual
growth in the demand for high purity granular quartz and predict a
near exhaustion of raw materials. Together with environmental
problems in the main quartz producing districts, a coming shortage
in the supply of HPQ is implied. By far the largest proportions of
HPQ (maybe as much as 90 %) come from granite pegmatites in the
Spruce Pine district, North Carolina. The quality of quartz from
Spruce Pine is steadily decreasing and, having an arid climate with
limited water supplies, the processing of quartz is difficult and
costly. Adding to these challenges are environmental concerns
because the endangered species the 'Appalachian Elktoe Mussel',
habit the few fresh water resources that are exploited by the
mining industry. Parallel with foreseeable production shortages of
HPQ, the semi-conductor industry plans at least 15 more years of
development of more powerful silicon chips that depends on the
productions of thicker thus more HPQ demanding silicon metal-oxide
wafers. Also imposing higher demands is the fact that the
production of HPQ-demanding photo voltaic devices, i.e. solar cells
is forecasted to expand rapidly in the future. Geology of quartz
The high-purity silica glass sector require that HPQ contain very
low concentrations of structural impurities, i.e. foreign
substitutional elements or charge compensator elements that are
integrated as a part of the atomic lattice structure of quartz.
Being bonded by the lattice structure of quartz, structural
impurities are nearly impossible to remove with conventional
dressing technologies. Particularly for the lighting and optical
fibre industries, HPQ is required to contain very low
concentrations of fluid inclusions because, expansion during
melting of the fluid inclusions will generate vesicles in the
silica glass melt that may be incorporated in the optical fibres.
Therefore, good qualities of HPQ must crystallise under anhydrous
conditions and must incorporate a minimum of structural impurities.
The most important structural impurities that are easily
accommodated by the quartz crystal structure includes Al, Ti, Fe,
Ge, Li, Na, K, B, P, Ca and H. With lower abundance but still well
accommodated we have Cr, Cu, Mg, Mn, Pb, Rb and U. For some
industrial applications, low Fe and B contents are imperative (e.g.
in photovoltaic cells for solar panels) whereas some Ti may be
tolerated. Other applications primarily require low
Ti-concentrations and yet other applications are mostly concerned
with low concentrations of Li. As with many other minerals, the
concentration of structural impurities rise with temperature.
Quartz from diorites and monzonites, for example, comprise much
higher concentrations of structural impurities than quartz from
evolved granites and granite pegmatites. Recent studies of the
trace element distribution in granite pegmatites in Evje-Iveland,
South Norway, demonstrate that the speciation and concentration of
structural impurities also depends on the degree of differentiation
of
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the igneous melts (Larsen & Polve 1998, Larsen et al. 1998a,
Larsen 1999, Larsen & Lahaye, 1999, Larsen 2000, Larsen et al.
2000). Incorporation of fluid inclusions in quartz is primarily a
function of the amount of volatiles in the quartz-forming
environment. Diorites and monzonites largely form under volatile
undersaturated conditions whereas granite pegmatites at least
partially form during volatile oversaturation. Also, the speciation
of volatiles may be important for the manufacture of silica glass.
H2O, for example, has a much higher solubility in the silica glass
melt (several percents) than CO2, CH4 and N2 (a few hundred ppm).
Dissolution of aqueous fluid inclusions during silica glass melt
production may therefore hinder vesicle formation, however, being
an excellent solvent, may contribute with Na, Fe, Mg, Li and
several other electrolytes that are dissolved in the aqueous phase.
Scope of work From the above considerations it appears that igneous
quartz that formed at low temperatures may provide excellent HPQ
raw materials in having low concentrations of structural
impurities, but may be void because oversaturation of volatile
fluids cater for high fluid inclusion abundances. Igneous quartz is
not attractive because it formed at high temperatures that strongly
enhances the incorporation of structural impurities HPQ with good
melting behaviour, i.e. low fluid inclusion contents, is therefore
very difficult to form in igneous and hydrothermal environments
thus the so-called long-distance optical fibre industries where
vesicle free silica glass is imperative, largely have to rely on
extremely expensive man-made silicon compound glass. Granulite
facies terrains Probably the only geological environment that on a
large scale may produce quartz with low abundances of fluid
inclusions and low concentrations of structural impurities is
high-grade metamorphic terrain's and in particular, granulite
facies terrain's. Factors during granulite facies metamorphism that
influences the purity and quality of quartz includes: • Repetitive
and massive re-crystallisation of quartz • Low density of lattice
defects because of slow re-crystallisation of quartz •
Homogenisation of the impurity distribution in the quartz-bearing
host lithology • Continuous decrepitation of fluid inclusions •
Hydrous leaching of quartz during low- to high-grade metamorphism •
Regional depletion of LIL-elements during peak granulite facies
metamorphism • Anhydrous conditions during peak metamorphism •
Volatile fluids during peak metamorphism mostly comprises CO2, N2
and CH4 It is beyond the scope of the present proposal to discuss
all these points in detail. Important for the formation of HPQ is
the fact that quartz will re-crystallise repetitively during
prograde and retrograde metamorphism. During prograde metamorphism,
pre-metamorphic fluid inclusions will efficiently decrepitate but
because metamorphic volatiles are common from diagenetic to
amphibolite facies conditions, new fluid inclusions will be
generated and incorporated in quartz. However, during granulite
facies re-crystallisation metamorphogenic fluid inclusions will
also decrepitate and because peak granulite facies metamorphism
occur under anhydrous conditions, new fluid inclusions with aqueous
solutions will not form. There may be CO2, CH4 and N2 fluids (or
other C-O-H-N compounds) present in the system (e.g. Touret &
Dietvorst, 1983; Andersen et al., 1993; Larsen et al., 1998b)
however, they are rather harmless when compared to aqueous
inclusions because they are easy to extract during industrial
dressing processes.
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The behaviour of structural impurities in quartz is not quite as
predictable as the faith of fluid inclusions. During
re-crystallisation at low temperatures, quartz with high
concentrations of impurities may indeed be significantly more pure
as the impurities will partition in favour of other minerals or
aqueous fluids. Experiments synthesising sequential
re-crystallisation of autoclave quartz at 345-380oC demonstrated
5-10 times reduction in the concentration of Al, Li, Na, K and Fe
during four episodes of re-crystallisation (Armington and Balsacio,
1984 in Jung, 1992 p.194). At higher temperatures some impurities
may again be incorporated, however, this depends on the
availability of impurities and the distribution coefficients
between fluids, quartz and other phases. Impurities that partition
into fluids may no longer be available. For example, peak granulite
facies metamorphism is commonly associated with pronounced
LIL-element depletion enforced by a combination of metamorphic
dehydration, hydrous metasomatism and partial melting. This process
was documented on Tromøy in the Bamble Belt (e.g. Cooper and Field,
1977, Smalley et al, 1983) where the K and Rb concentrations of
acid and intermediate gneisses are amongst the lowest ever reported
for granulite facies terrain's (Touret, 1987). Therefore, leaching
of LIL-elements may improve the conditions for crystallisation of
HPQ although the formation of quartz from partial melts, which also
form during granulite facies conditions, may enforce the formation
of quartz with high impurity concentrations. To avoid quartz that
formed from partial melts but still to benefit from the positive
effects of granulite facies metamorphism, quartz from quartzites
may be the most promising target. Quartzites, being near
mono-mineralic lithologies, will not melt at granulite facies
conditions because the melting point even under water saturated
conditions, will be higher than granulite facies T and P. The low
concentration of other minerals in quartzites also reduces the
possibility of incorporation of structural impurities during
repetitive recrystallisation of the quartz. Being a sedimentary
lithology that probably contains compositionally contrasting quartz
from multiple sources, repetitive re-crystallisation also has the
positive effect of homogenising the quartz compositions throughout
the quartz-bearing lithology. Finally, foreign minerals in
granulite facies quartzites, being relative coarse-grained compared
to lower-grade quartzites, are more easy to handle by conventional
dressing techniques. Research strategy Fieldwork Detailed field
studies and the main body of sampling are committed in the high
grade metamorphic belt of the Bamble shear zone (SE-Norway) and the
Rogaland metamorphic envelope (SW-Norway) because the general
geologies of these areas are well documented throughout earlier
studies. The Bamble shear zone may be divided into four metamorphic
zones that from NW to SE (i.e. from A to D) comprise progressively
higher metamorphic grades. Zones 'A' and 'B' reaches upper
amphibolite facies whereas zones 'C' and 'D' are well within the
granulite facies regime (e.g. Touret 1987). Particularly zone 'D'
is void of hydrous minerals and is characterised by strong LIL
element depletion. Quartzite lithologies and orthogneises are
present in all metamorphic zones, but from the considerations
outlined in the previous section, quartzites in zones 'C' and 'D'
are most interesting. The metamorphic envelope embracing the
Rogaland Intrusive Complex comprises a rich diversity of magmatic
and sedimentary successions that experienced granulite facies
metamorphism. Quartzites are particularly common in the Faurefjell
meta-sedimentary successions that intersect different intensities
of granulite facies metamorphism throughout the metamorphic
envelope.
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Analytical techniques in addition to methods outlined under
other sub-projects LA-HR-ICP-MS: the Geological Survey of Norway
(NGU) recently purchased a Laser Ablation High Resolution
Inductively Coupled Mass Spectrometer (LA-HR-ICP-MS). In short, the
advantage with this instrument is its ability to analyse virtually
any isotope in the periodic table by in situ ablation of small
volumes of material directly from the sample surface. Simultaneous
analysis of the ablated material by a high-resolution mass
spectrometer ensures detection limits down to the sub ppm level.
Finally, the laser pit may have a diameter of only 20 µm, which
make it possible to obtain an exceptionally high spatial
resolution. NGU has developed an analytical procedure that utilises
this instrument in quantifying the trace element concentration in
quartz and is considerably more rapid than conventional methods for
quartz analysis. Hallimond tube micro-flotation: in order to
evaluate the results from LA-HR-ICP-MS analysis it is necessary to
conduct control analysis by more conventional methods. These
include micro-flotation of small sample quantities by the Halimond
tube technique that has proved very successful in the separation of
quartz from feldspar and micas. Hallimond tube micro-flotation is
mastered by NTNU (Prof. Knut Sandvik) and will be followed by
conventional solution HR-ICP-MS at NGU. Fluid inclusion analysis:
analysis of fluid inclusions is an essential part of the present
study, because they provide important information about the P-T-X
conditions that prevailed during the genesis of HPQ. The
composition of the fluid inclusions will be determined with a state
of the art Linkam freezing-heating stages at the Department of
Geology and Mineral Resources engineering (NTNU) and will be
supplemented with non-destructive raman micro-probe analysis at
Free University, Amsterdam. The later method is imperative in
identifying solid and fluid species (particularly C-O-H-N
compounds) in the fluid inclusions. EPMA: Electron Probe Micro
Analysis will be applied to selected phases co-existing with quartz
in order to obtain independent P-T estimates and to calculate the
principal distribution co-efficients for trace-impurities in
quartz. Autoclave experiments: exchange of elements between quartz
and the surrounding environment under different P-T-X conditions
will be approached by autoclave experiments at University of Tromsø
and University of Copenhagen where the proper instrumentation is
available. Collaboration partners
• Dr. Nikos Arvanitides is an expert in both the formation and
industrial applications of HPQ. NA is director at the Institute of
Geology and Mineral Exploration (IGME) in Greece.
• Dr. Jens Konnerup Madsen at the Department of Geology
(University of Copenhagen) is an expert in thermodynamic modelling
of volatile fluids.
• Expert in metamorphic petrology and metamorphic
mineral-melt-volatile reactions (individual not yet decided).
• Doctoral students
• Doctoral student in metamorphosis and mineral-fluid-melt
interaction processes in quartzites • Doctoral student in
mineral-chemistry and element exchange reactions of quartz based
on
laboratory experiments (autoclave-experiments)
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Research area: Quartz beneficiation Supervisors: Professor Knut
L Sandvik Dept. of Geology and Mineral Resources Engineering.
Professor Otto Lohne Dept. of Materials Technology and
Electrochemistry. Objective Norway has had, and still has a strong
mining sector, which over the last years have changed from metal to
industrial minerals as products. The products are generally
exported. An even stronger electro-metallurgical industry makes
export products mainly from imported raw materials. However, very
little refining of Norwegian raw materials takes place. In this
project we aim to: • Establish a process chain producing
sophisticated products from Norwegian raw materials. • Concentrate
on silicon raw materials, because we assume there will be an
especially strong
development in the silicone solar cell sector. Results from this
project may therefore rapidly lead to practical applications in the
industry.
• Develop further Norway’s unique situation to hold a key
position in solar cell production. We have a raw material base and
key industrial producers already working in related segments of the
industry all the way from refined quartz to silicone wafers.
Background Quartz is found in the nature in varying purity and
is traded in varying quality at strongly differentiated prices. Raw
material for glass is probably the largest market, which is
dominated by Belgian quartz sand. Belgian quartz sand sets the
price and quality standard for such products. The same material is
also used for chemical feedstock and fetches prises around 150
NOK/t. Lump quartz of reasonable purity and high thermal strength
for the smelter industry may be priced at 300 NOK/t while the
prices of quartz for optical purposes are not disclosed. The
material chain from quartz can be drawn to metallurgical grade
silicon metal from 2000 NOK/t, which also is refined by Elkem to
Silgrain, trichlorosilane, silicon tetrachloride at 4900 NOK/t and
semiconductor quality silicon at 600 000 NOK/t. Special products of
silicon derived from quartz are often made via the expensive routes
of trichlorosiane, silicon tetrachloride or sodium silicate. Volume
markets are rheology control and filler in addition to the well
paying semiconductor sector. The demands of purity in the last
sector are in the order of 1 ppb. The chemical refinement in
several steps ensures that the demands on the raw material
paradoxically are not extreme, but it makes the final product
expensive. A more promising and expanding market for quartz is
solar cells. Here are the demands of purity much lower than for
semiconductors, in the order of 1 ppm, but not yet well defined. Up
till now the supply of raw material for solar cells has been based
upon scrap from the semiconductor production. The price of this
scrap is in the order of 150-200 NOK/kg. The demand for solar cells
is outgrowing that of semiconductors and the price of silicone
wafers has to be reduced in order to give a competitive solar cell
energy price. This means that the cost of silicone
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also has to be cut substantially and sufficient long term
supplies of this material has to be developed. In the near future
lack of sufficient amounts of cheap silicone for an expanding
market may threaten the position of silicone as solar cell material
no 1. A cheaper production may be achieved by using purer quartz
and thereby omitting some of the expensive chemical refining steps.
Norwegian Crystallite at Drag in Nordland is already producing a
few thousand tonnes of refined quarts from a local deposit.
(combined amount of impurities is in the range of 1 ppm). The
nucleus for a industry of considerable size do therefore exist
provided large reserves of quartz and reasonable methods for
beneficiation are found. Project In this project we will work with
Norwegian sources of quartz. A close co-operation with the ongoing
NFR project “From sand to solar cells” have to be established as
alternative process paths based upon purer raw materials have to be
developed as an extension of existing Norwegian technology. This is
the reason why professor Otto Lohne from the Department of
Materials Technology and Electrochemistry is chosen as one of the
supervisors for this part of the project. One possibility, which
can be based upon existing processes, is to upgrade the Elkem
Silgrain production, for such a purpose. In this process carbon
reduced silica is purified to a certain degree. Use of improved
quality raw materials may bring the product from this process to a
stage where further removal of impurities may take place in a
process combined with wafer production. Our project on pure quartz
production should be aimed at making the kind of sand, which would
give a cost efficient chain of value development from the raw
material in the ground to the finished product. Quartz, one of the
most common minerals, is found all over Norway, some as deposits of
relatively pure quartz, but mostly associated with other rock
forming minerals. Generally quartz has been mined from the mono
mineral deposits, although some quartz has been a secondary product
when making feldspar from pegmatite and granites. Existing
Norwegian processing technology for quartz sand beneficiation is
mainly based upon the Lillesand operation of North Cape Minerals,
where first iron bearing minerals are removed by flotation, then
feldspar is concentrated by another step of flotation. Finally the
remaining iron bearing minerals are removed from feldspar is by
strong field magnetic separation. The process was originally based
upon knowledge from the Spruce Pine area in North Carolina. The
major product from such operations is feldspar, however, but at
Spruce Pine the quartz is pure enough to warrant upgrading to
excellent qualities. When the process for the Drag quartz deposit,
now operated by Norwegian Crystallites, was developed, our
knowledge about this technology was further refined for production
of pure quartz products from a high grade deposit. Regarding other
quartz mineral deposits the technology has to be developed to
remove other impurities. Critical elements for the use of quartz in
solar cells are first of all boron and phosphorus as they are
difficult to remove by metallurgical refining. Maximum values are
below 1 ppm. for each. Calcium, aluminium and metal oxides are also
unwanted. To obtain a physical removal of the last traces of
unwanted elements, the elements have to be present in separate
minerals of sufficient size to
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be liberated. The characterisation and analysis of the unwanted
elements and how they are distributed in the minerals will be
important. Our department has access to new advanced analysis
instruments, which makes such characterisation possible.
Alternatives to traditional purification to purer sand do exist.
Mechanical activaton, that is disturbance of the crystal lattice of
the mineral by crushing may give a more reactive quartz, which may
be cleaned by weak acids such as CO2. Other alternatives to
increase the reactivity of quartz at relatively low temperatures
and pressures may also exist. The traditional smelting/reducing
technologies for silicon, which is a path for silicon production,
depends today on lumpy quartz, which is heat resistant without
cracking. Little is known about the mechanism, which gives
competent lumps, or how to determine without full-scale tests,
which deposits are suited for this purpose. This itself is an
interesting point for investigation. Furthermore the most likely
product from a beneficiation process will be in the form of quartz
sand. Fine grained feed will blind a smelter furnace and has
therefore to be agglomerated to give the required lumpy material
provided the Silgrain process should be chosen. Development of
competent and cheap agglomerates including binders not adding
unwanted impurities will also be an important task if this path is
to be followed. The fact is that surprisingly little research has
been done to assess the different quartz types of Norway or quartz
generally. The way to a process for solar cell raw material
therefore possesses many challenges of a basic nature.
Collaboration with expertise from the geological side to the
metallurgical side is required. Because the project “From sand to
solar cells” already is established, formation of such contacts is
already established for this project. Because mineral processing is
a wide subject, some tasks that are of importance to other parts of
the value chain may also be included.. Industrial contacts We have
discussed this application with Norwegian Crystallites, which at
present is the only producer of highly refined quartz in Norway.
The company is very interested in co-operating with us in the
project. Norwegian Crystallites is backed by Hustadkalk A/S, which
should have the capacity to commercialise viable research results.
Other interested parties may be Elkem, which has quartz quarries
and is a major user of quartz for ferrosilicone and silicone metal
production and North Cape Minerals, which has the plant in
Lillesand. Elkem is well connected to the “Sand to solar cells”
programme. Doctoral students Under the programme Erik Larsen is
engaged as a doctoral student and Rolf Arne Kleiv as a post
doctoral student for the last part of the project.
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Research area: Mineral Characterisation “Development of
quantitative methods to describe raw materials and mineral
products”. Supervisors Professor Terje Malvik, Department of
Geological and Mineral Resource Engineering Professor Jarle Hjelen,
Departement of Materials Technology Dr.candidate Kari Moen
Objective The project aims at developing automatic SEM - based
quantitative techniques in order to:
• quantify the mineral content, both major and trace minerals in
rocks/ores and in milled products,
• quantify the mineral texture • quantify the occurrence of
minerals in different types of particles in milled materials
and
mineral products (PTA: Particle Texture Analysis) Background All
mineral processes are treating particles, and not chemical
elements. The particles are containing one or more minerals. To
achieve high quality products meeting the different requirements
from the customers, and with a minimum waste, a thorough and
detailed knowledge concerning the occurrence of the minerals in the
raw materials and in the mill products is needed. In investigations
of ore minerals, particularly the base metal sulphides, there has
for a long time been used automatic SEM-based image analysers to
quantify the occurrence of the minerals. Special emphasis has been
laid on determining the liberation properties of the economic
minerals to avoid under- or over grinding of the minerals. It is
recognized that the behaviour of particles in separation processes
is a function of different properties of the particles of which the
most important are: Mineralogical parameters; types of minerals
making up the particles, mineral chemistry,..; Textural properties;
size, shape, grain boundaries, type of intergrowths (particle
texture)…; Specific properties of the minerals including specific
gravity, surface property, magnetic property…; In Norway, there has
been a strong and positive development within industrial minerals.
Due to this the project aims at developing methods which can be
used on industrial minerals. In additions the methods also can be
used on all kinds of other materials.
Principals of PTA - Particle Texture Analysis Purpose Describe
mineral liberation, mineral associations and how the minerals are
grown together by means of backscatter electron images and X-ray
data in the scanning electron microscope (SEM).
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Performance • Polished sections of narrow grain size fractions
are analysed by Oxford Inca Feature • The backscatter electron
images are thresholded by grey levels and analysed by means of
X-
rays aiming to obtain analyses of every single mineral grain. •
The images and the classified mineral analyses are stored. • Inputs
for the PTA software are the Inca database and the uncompressed
images from each
field. • Composite particles are found by means of image
analysis. • Results from the image analysis is stored in a database
• Queries are then performed to get desired information • The
results can be presented as distributions of
o relative amount of minerals in particles o mineral
associations in particles o free grinding distributions o
statistics
Figure 1 Examples of classified minerals, identified grains,
free grinding decisions and mineral associations
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Principals of EBSD - Electron BackScatter Diffraction lattice
and grain texture
Electron backscatter diffraction The EBSD technique is based on
the weak diffraction pattern that forms when a focused, stationary,
primary electron beam strikes a polished sample, backscatters and
diffracts. The diffraction pattern is formed on a fluorescent
screen and transferred by a camera to the computer (Hjelen 1990).
Rapid developments in both hardware and software in the past 10
years have made EBSD easy to use and ideal for the rapid analysis
of microstructures of crystalline materials. The diffraction
pattern is therefore characteristic for the crystal structure and
space orientation of the crystal.
Figure 2 Origin of Kikuchi lines from EBSD (Schwartz et.al.
2000)
Figure 3 EBSD patterns from 2 orientations of calcite
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The EBSD software automatically locates the positions of
individual diffraction bands, compares these to theoretical data
about the relevant phase and rapidly calculates the 3-D
crystallographic orientation. The whole process from start to
finish can take from 0.025 sec. to more than one second dependent
on the phases analysed. For each pixel the phase and orientation
are stored and can be visualised by maps or plots. Different kinds
of plots can show misorientation, grain size, poles etc. The
spatial resolution of this technique is superior to x-rays, since
elastic backscattered and diffracted electrons have a smaller
interaction volume than x-rays. The interaction volume is dependent
on acceleration voltage and atomic number of the analysed minerals,
but is usually in the sub micron range. (Moen et. al. 2003) (Moen
et. al. 2004)
Grain orientation distribution (14)
Orientation
0 20 40 60 80 100 120 140 160 180 200
Share
0
2
4
6
8
1 0
1 2
1 4
V0V1V2
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Figure 4 EBSD orientation map, (0001) and (11-20) pole figures
and grain shape orientationdistribution for 3 orthogonal directions
of a marble block (Moen et. al. 2004).
Cooperation with the industry The importance of being able to
quantify the mineralogical parameters is fully recognized by the
industry. Several industry partners (TITANIA, Hustadmarmor,
Norwegian Crystallite) support the project in order to benefit from
the developments being made. In the future, an on line measurement
system using the web, and where the industry partner can take an
active part in the measurements, is aimed. Combined with flexible
solutions and measurement settings this will lead to techniques
being able to describe most mineralogical and textural phenomena
occurring in rocks/ores and in mineral products. By use of new and
advanced laboratory equipment determine physical and chemical
properties of industrial minerals and beneficiated products of
industrial mineral with special emphasis on thermal, mechanical and
surface properties. The results may be used to define areas for new
applications of minerals, establish correlations between material
properties and geological processes leading to the different
mineral raw materials, and modelling of micro processes occurring
during heating and mechanical impact of minerals. Electron
Microscopy Laboratory facilities The Scanning Electron Microscopy
laboratory is the largest SEM-lab. in Scandinavia, with a suite of
7 conventional, low-vacuum and field emission SEMs. In addition a
Transmission Electron Microscope (TEM) and an Electron Probe
Micro-Analyser (EPMA) belong to the EM-lab.
(http://www.material.ntnu.no/lab/material/index.html) These
analytical electron microscopes are designed for material
characterization using a range of imaging and analytical methods.
(Pdf). The instruments are equipped with Energy Dispersive
Spectrometers (EDS), Wavelength Dispersive Spectrometers (WDS),
Electron BackScatter Diffraction (EBSD) detectors, CL etc.Automatic
EBSD analysis is combined with deformation- and heat treatment
experiments in a special in-situ substage to study dynamic
processes.
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Project: “Quartz raw-material for metallurgical production of
FeSi and Si-metal”
Image 1: Furnace no. 1 at Elkem Thamshavn (Photo: Elkem ASA,
Silicon Division)
Project overview
Doctoral candidate: Siv. ing. Kurt Aasly (Department of Geology
and Mineral Resources Engineering, NTNU) Supervisor Professor Terje
Malvik (NTNU) Co-supervisor is Dr. ing. Edin Myrhaug (Elkem Silicon
Division ASA) The Project period is scheduled to June 1st, 2003 to
May 31st, 2007 and financing is through a University scholarship at
NTNU with Elkem ASA, Silicon Division as a partial sponsor for the
project, through project expenses. The project is integrated in the
SUP financed by the Norwegian Research Council (NFR) “The value
chain from deposit to beneficiated product with emphasis on
quartz”.
Project – outline
The main focus is on the development of knowledge concerning
quartz used as a raw material for the metallurgical production of
ferrosilicon and silicon metal. The main objective for this PhD
project is: - by using systematic investigations and modern
analytical equipment
- to obtain a basic knowledge about the properties of quartz raw
material that are important for the production of silicon
- and further, develop methods to test these properties
The work will mainly be carried out on typical quartz used for
FeSi and Si-production.
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Quartz properties
The raw materials for Si for the metallurgical production of
ferrosilicon and silicon metal, are Quartz and Quartzites. These
are in operational terms separated into two types: Rock quartz and
Gravel quartz, which are blasted rock and non-blasted, sedimentary
deposited materials respectively. The high purity of the products
and the nature of the production process necessitate the need of
some requirements to the specifications for the raw materials. The
most important property requirements for quartz/quartzite, are: -
purity (pollution and inclusion)
- mechanical strength
- thermal strength
- softening properties
Because of Elkems involvement in the project, the focus will
mainly be related to problems and challenges described by Elkem: -
What causes too much fines to be generated from the
raw-material?
- Which properties make the quartz decrepitate when shock heated
in the furnace?
- Which properties are important for the melting- (softening)
properties of the quartz resulting in a certain melting
progress?
Earlier work
Little published research has been carried out on the properties
of quartz related to the metallurgical production of ferrosilicon
and silicon metal prior to this project. However, it appears that
company-internal research has been more frequent, unfortunately
results from such work is difficult, if not impossible, to reach.
Operational experience and none scientific tests seem to have been
the working method in most (Fe)Si plants.
Analytical techniques in the project
Several analytical techniques will be evaluated in this project.
Examples of techniques which are more or less known and understood,
for application on quartz for (Fe)Si production is listed below:
Optical microscopy investigations
• Polarization microscopy
– Mineralogy
– Texture (e.g. grain size)
• Fluorescence microscopy
– Porosity
– Grain boundaries
• Linkam TS1500 High Temperature System
– Microscopic technique
– In situ heating effects (up to 1500 ºC)
– Causes of these effects
Scanning Electron Microscope (SEM) techniques:
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• Cathodoluminescence (CL)
– classify different generations
– internal zoning in minerals
– distribution of trace minerals
– Micro cracks
• Electron Backscatter Diffraction (EBSD)
– Crystal structure
– Orientation map
• Energy-dispersive x-ray Spectrometry (EDS)
– Semi quantitative in situ element analysis
Microprobe – quantitative in situ element analysis
XRD – Mineralogy (crystal structure)
DTA – Mineralogy
– Phase transitions
Dilatometry and Segercone – Softening properties (melting
properties)
And other techniques relevant for testing mechanical and thermal
properties of quartz.