Paper: Technologies for Decreasing Mining Losses
txt: Environmental and Climate Technologies
_________________________________________________________________________________________________2013 / 11
41
doi: 10.2478/rtuect-2013-0006
Technologies for Decreasing Mining Losses
Ingo Valgma
, Vivika Väizene1
, Margit Kolats1
Tallinn University of Technology
Abstract - In case of stratified deposits like oil shale deposit in
Estonia, mining losses depend on mining technologies. Current
research focuses on extraction and separation possibilities of
mineral resources. Selective mining, selective crushing and
separation tests have been performed, showing possibilities of
decreasing mining losses. Rock crushing and screening process
simulations were used for optimizing rock fractions. In addition
mine backfilling, fine separation, and optimized drilling and
blasting have been analyzed. All tested methods show potential
and depend on mineral usage. Usage in addition depends on the
utilization technology. The questions like stability of the material
flow and influences of the quality fluctuations to the final yield
are raised.
Keywords – oil shale, losses, mining, extraction.
I. INTRODUCTION
In case of stratified deposits like oil shale deposit in
Estonia, mining losses depend on mining technologies.
Stratified deposits are being developed from lower bedding
depth to deeper and more complicated conditions [23].
Continuously the environmental or social restrictions require
increasing coefficients that increase mineral losses [20]. This
could be limited with the help of technological development
[34,13, 36]. During the period starting from 1916 many
technologies have been used and tested [31]. Currently the
market economy is the main driving force for choosing
technologies. This causes short term choices and works
against sustainability.
Current research focuses on extraction and separation
possibilities of oil shale. Selective mining, selective crushing
and separation tests have been performed, showing
possibilities of decreasing mining losses. Rock crushing and
screening process simulations were used for optimizing
fractions. In addition mine backfilling, fine separation of oil
shale, and optimized drilling and blasting have been analyzed.
All tested methods show potential and depend on mineral
usage [37]. Usage also depends on the utilization technology.
Questions like stability of the material flow and influences of
the quality fluctuations to the final yield are raised. Tonnage,
calorific value and size distribution of the product form the
quality indicators [43]. Avoiding losses in any of these
processes decreases mining losses and has a positive effect on
resource usage and sustainability. In addition, decreasing
losses increases the amount of resource and sustainability of
energy supply for the country [30, 32]. If optimized
technology allows maintaining required productivity, it could
be applied, even if fitting into the existing technological
structure is taking longer than technically available [33, 35, 8].
The aim of the current study is to clarify what technical
solutions could be applied for decreasing oil shale mining
related losses.
II.ANALYSES AND TESTS
A. Selective mining
Selective extraction of oil shale seam was analyzed to
understand following methods:
1. Cutting with bulldozer and excavator rippers
2. Cutting with surface miners
3. Cutting with longwall miners
4. Cutting with shortwall miners.
a) Cutting with rippers
Selective extraction of the oil shale seam can be done by a
bulldozer ripper or hydraulic excavator ripper. Ripping is a
low-selective technology [42]. In deeper surface mining areas,
100 tonnes class bulldozers were used and in more weathered
areas or partial ripping zones, the 60 tonne class was used.
One disadvantage of bulldozer ripping is excessive crushing of
oil shale by heavy bulldozers with crawlers [18].
b) Cutting with surface miners
Tests with surface miners Vermeer T1255 and Wirtgen
2500 SM were carried out. The tests were followed after
longer period tests with smaller class surface miners during
the last 25 years. Tests have been performed with different oil
shale and limestone layers. Surface miners are considered as
BAT (Best Available Technology) for surface oil shale mining
extraction [12, 42, 18, 15, 5].
c) Cutting with longwall miners
The planning and testing has been done for longwall mining
possibilities. Shearers were used and tested for 30 years in five
oil shale mines in Estonia [1]. Longwall technology has also
been chosen as one of the alternatives for phosphate rock
mining [41]. Technologically, this technological solution has
improved compared with initial possibilities. Since the
hydraulic support system was limiting the height of the
longwall face (1,5 m) and the power of the shearers was
relatively low (210 kW) the losses have been 50% in longwall
section. Today’s sharers utilize power in the range of 2200
kW, which is 10 times higher than in the tested units. Since
the productivity (equal to income) could be increased,
longwall technology is one of the possibilities for lowering
losses. In case of removing protective side pillars between
longwall section, rough estimation shows, that losses could be
lowered down to 5% taking into account the geological
dislocations and disfollowing the exact horizontal plane of the
oil shale seam. The main obstacle of longwall shearing
Brought to you by | Tallinn Technical
Authenticated | 193.40.249.178
Download Date | 10/17/13 10:07 AM
Environmental and Climate Technologies
2013 / 11_________________________________________________________________________________________________
42
technology is solving environmental and social questions,
regarding subsiding the ground and accepting certain areas
where such subsiding could be allowed. In comparison to the
surface mining stripping in the open cast mining areas,
longwall mining could be considered as a technology which
causes less impact to the landscape. The ground would be
lowered by up to 70% of the created space. That makes 2
meters. In open casts, even the fluctuations in the leveled
overburden spoil could be 5 meters. In trench or ditches areas,
the level fluctuations are up to 40 meters. This makes longwall
mining the most sustainable mining method for oil shale.
d) Cutting with shortwall miners
Evaluations of breakability have been made with
roadheaders F2 and 4PP-3. As a recommendation, a doubledrum
road header was proposed. Currently the power of the
machines has increased and pick properties allow cutting
harder rock. It is proposed, that both longitudinal or transverse
head continuous miners (roadheaders) could be used for
cutting oil shale [12]. The selectivity option is directly related
to the waste material handling and should be tested in the mine
[11].
Shortwall miner utilization could be the solution for making
development entrances, drifts and rooms for mining. In case of
satisfactory cutting performance, it could be used for
extracting oil shale in production sections as well. The tests
have shown, that shortwall mining is a promising technology
and requires, as with longwall mining, surface miner mining
and axle bucket crushing changes in some operations and
processes in mining technology. Shortwall mining requires
fast roof supporting technology. The supporting could be in
addition in some extent easer because of lower possible
fragmentation of rock caused by absence of blasting in the
mine.
B. Selective crushing
For selective crushing, the following methods were tested:
1. crushing in a drum (Bradford drum) with help of rock
falling impact and hammer crusher inside the drum;
2. impact crusher in underground sections as first stage
crusher or impact crusher for aggregate production
from oil shale waste rock;
3. axle crusher buckets with cutting and skimming
process.
An impact crusher has been used in underground sections as
a first stage crusher and for aggregate production from oil
shale waste rock that is limestone [27].
The purpose of underground crushing is to reduce ROM
(run of mine) size to the required size of up to 300 mm for
transporting it on belt conveyors to the surface.
C. Separation
Separation tests have been performed by jigging and
cycloning. The purpose was to find out the percentage of the
fine material that could be separated. Jigging tests have shown
relatively good results allowing separating initially mixed
material into five different fractions. The calorific value of
best fraction is highest and the limestone fraction in opposition
should be considered as the ready selected material for
limestone aggregate. Up to now the main focus has been
mechanical experimenting with jig. The main obstacle of the
technology could be achieving required productivity. It is
similar to the filter press technology where the productivity of
the single unit could be low. On the other hand, if the
production line could be completed with different stages, the
required productivity could also be to some extent lower. To
decrease required machine productivity for the same output,
drum crushing or axle crushing could be used prior to the
jigging.
Cycloning has shown that the calorific value of cycloned
and non- cycloned fine material has no remarkable difference.
Since cycloning could be done on many variations, the initial
test could be considered as failed because of short time and no
variations. These tests should be continued, preferably with
apilot unit or laboratory units at first.
D. Rock crushing
For crushing, the following options have been analysed:
1. Crushing with sizers
2. Crushing with impact crushers
3. Crushing with double drum crushers
4. Crushing with drum crusher
5. Crushing with jaw crusher.
Crushing process simulations were used to evaluate the
distribution curves of the final product. The necessary data for
this purpose is bulk density of material and the maximum size
of the particles going for crushing. In order to get optimal
results on certain cases, crushing units, crushers and mobile
crushers can be added to the scheme. This gives extra value in
lowering engineering costs, on experimenting with different
devices and on further changes [19, 45].
As an example, material data for thesimulation program has
been:
Input material < 1000 mm
Solid density 1,84 t/m3
Crushability 85% - which is the maximum
Productivity 1000 t/h
Gravel 31% - does not influence the results (Fig. 1.).
The value of abrasiveness has been between 0,1…1500 g/t,
calculations show that this does not affect the simulation
results. Neither does moisture. The crusher output cavity is set
on 180mm which means that the maximum size of the
outcoming particle is 200mm.
The workload of the impactor crusher is 97% of the
maximum capacity. After crushing, the feed moves to the
roller screen, where the feed flows into three classes:
0…25 mm 22,8%
12…107 mm 55,2% - which include 11% 12…25
mm (Fig.2.)
107…200 mm 22% .
It can be detected that the fines part is 28,9%.
Brought to you by | Tallinn Technical
Authenticated | 193.40.249.178
Download Date | 10/17/13 10:07 AM
Environmental and Climate Technologies
_________________________________________________________________________________________________2013 / 11
43
Fig. 1. Material data insertion window
Fig. 2. Flow data
Fines are added on the secondary crushing/particle size is
107...200 mm. Calculations have shown that in this way 5% of
fines are added. At the present moment the best crushing
option in making the minimum fines is crushing with the sizer.
Experiments show that the minimum in generating fines is
achieved when the rotating speed of sizer was 175 rpm. In
slow rotation the generation was 11,8% and fast rotation gave
6,5% of fines (Fig.3).
As experiments show, it is possible to decrease the fines
generation which mostly is considered to be waste.
Each simulation manufacturer focuses on separation
methods or some part in the separation process. When it
comes to crushers, then simulations are also manufacturer
based and reflect types and models, what the company offers
[7, 4]. Newer products are introduced in the simulation
programmes later. In case of the roll crusher for example, the
characteristics and behaviours are still added to the
programme. Sizers are even more complex, because they have
been used only a few years and therefore are relatively new
products among crushers. In Estonia there are a lot of
questions concerning the fines in the crushing process.
Fig. 1. Experiments resulted in fines generation of 2,2% [10]
E. screening
Two basic screening solutions have been analysed in
addition to the traditional vibration screening:
1. Screening in drum screen
2. Screening on rotary screen
3. Screening on roller screen.
F. Mine backfilling
The tests contained testing of mixes properties of the
backfill material, testing of backfilling technology and
analyzing backfilling material flows. The main hypotheses are
that backfilling reduces mining losses and the amount of waste
on the ground surface [27]. In addition it increases land
stability [12]. Stability issues have been developed in sense of
information availability. Mapping, special information
systems and seismological methods allow one to detect any
collapses which have occured [21, 25].
G. Fine separation
Fine separation tests were carried out with CDE equipment
and with jigging equipment. The aim of the fine separation test
is to separate fines from pulp before they reach sedimentation
pond and to take it into use as a product.
III. RESULTS AND DISCUSSION
A. Selective mining
a) Cutting with rippers
In Ubja oil shale open cast, the productivity of oil shale
hydraulic ripping was nearly 600 m3/h. At the Ubja open cast,
overall oil shale losses are 0% based on the Environmental
Register. Bulldozer ripping is considered as semi-selective
ripping where seam losses make 12% in comparison to 5%
with surface miners [42]. The first problem of ripping
technology has been power of ripping machines. Before 100
tonnes class bulldozers were applied, the low ripping power
was one of the main concerns. Excavator ripping is in similar
stage like bulldozer ripping has been in its beginning stage.
The power of the excavator ripper is not satisfactory to reach
required productivity. Excavator ripping does not solve the
losses question because of the principle of vertical movement.
Brought to you by | Tallinn Technical
Authenticated | 193.40.249.178
Download Date | 10/17/13 10:07 AM
Environmental and Climate Technologies
2013 / 11_________________________________________________________________________________________________
44
Excavator ripping could be considered in low bedding areas,
where drilling and blasting is prohibited, the oil shale seam is
weathered meaning weaker bonds between layers. A bulldozer
ripper, therefore could be used as low selective miner, but it is
limited by availability of keeping losses down. The main
problem is limestone and oil shale pieces and lumps that
contain both material and could not be separated by the ripper.
If needed, one of the solutions could be skimming with axle
crushers.
b) Cutting with surface miners
It was found that extracting with a high selective surface
miner is the main possibility of decreasing losses in case of
surface mining. The main obstacle for using such technology
is the partly unsolved overburden stripping technology. In the
future, combined methods should be considered like high
selective cutting plus selective axle crushing for aggregate
separation.
Mining with surface miner Wirtgen 2500 SM helps to
reduce losses and improve calorific value of oil shale. It is
possible to mine limestone and oil shale seams separately with
higher accuracy than rippers (2-7 cm) with deviations about
one centimetre [42]. Losses can be decreased from 12 percent
to 5 percent compared to ripping [18]. Based on practical data,
the surface miner enables to increase the output of oil shale up
to 1 tonne per square meter. The oil yield increases 30%,
reaching up to 1 barrel per tonne of oil shale during the oil
shale retorting, because of better quality, meaning higher
calorific value of the material that is sent to the retorts [42].
c) Cutting with longwall miners
It was found that distribution of required large particles of
oil shale is possible with longwall shearers.
The practice with longwall shearers shows that the subject
for cutting is oil shale and the larger size is distributed to the
limestone fraction [1]. This is due to the hardness difference of
the rocks. Longwall mining could decrease horizontal losses
by 20 to 40%.
d) Cutting with shortwall miners
One of the main advantages that a shortwall miner could
present are the possibility of avoiding weakening pillars in the
mine by blasting [20].
This in addition could give the possibility to decrease pillar
size and to decrease losses left to the pillars. Pillar losses that
are caused by pillars with cross section area of 16 to 49 square
meters could be decreased therefore by 16 to 28% with
avoidance of the 0,3 zone by sides of the pillars.
The pillas strength and stability of the ground are directly
related but have the opposite influence on sustainability. In
case of backfilling this dilemma could be solved [22]. In some
areas also smooth and directed subsidence could be solution.
B. Selective crushing
The underground crushing process where ROM (run of
mine) size is reduced to the required size up to 300 mm has no
direct influence on the percentage of losses. Nevertheless,
ROM size distribution is influenced by impact crushing and
fines are produced. In case of oil production with vertical
generators, fines and small classes of oil shale are considered
as waste, if no other uses are found, like cement, electricity or
oil production with SHC technology.
Selective crushing is important both for cleaning and sizing
oil shale and cleaning and sizing limestone. Therefore
selective crushing or selective mining methods are
recommended [27].
C. Rock crushing
a) Crushing with sizers
One of the options could be using slow rotating or
optimized rotating sizer for oil shale ROM crushing.
According to the recommendations of crusher producers, all
crusher types are suitable for crushing oil shale [25]. In
relation to the moisture content, jaw crusher and gyratory
crushers are unsuitable, requiring relatively dry material
(
