“ENHANCING COAL MIDDLING LIBERATION THROUGH PRE-TREATMENT METHODS”

RESEARCH & DEVELOPMENT AND SCIETIFIC SERVICES, TATA STEEL
JAMSHEDPUR
INDIAN SCHOOL OF MINES, DHANBAD
PROJECT REPORT ON
“ENHANCING COAL MIDDLING
LIBERATION THROUGH PRE-TREATMENT
METHODS”
RESEARCH & DEVELOPMENT DIVISION
TATA STEEL, JAMSHEDPUR
DURATION -31ST JUNE – 12 TH JULY 2016
UNDER GUIDANCE OF- SUBMITTED BY-
SONI JAISWAL RAHUL SINGH
(RESEARCHER, R&D, TATA STEEL) REFERENCE NO- VT20162491
FUEL AND MINERAL ENGINEERING
DEPARTMENT
INDIAN SCHOOL OF MINES
DHANBAD

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ACKNOWLEDGEMENT
I take this opportunity to express my heartfelt gratitude to the Head, Raw Material Research Group,
to take up a project on “ENHANCING COAL MIDDLING LIBERATION THROUGH PRE
TREATMENT METHODS”.
I would like to express my sincere gratitude to Mr. Asim Kumar Mukherjee (Head, Raw Material
Research Group).
I am grateful to Mrs. Soni Jaiswal, Researcher (Raw Material Research Group) without her help,
encouragement and continuous guidance all throughout, it would not have been possible to
complete the project.
I would like to express my gratitude to Mr. Abhay Shankar Patra for his numerous effort and for
providing necessary facilities in lab to complete the project.
I acknowledge the wonderful support of Sahu ji, Murmur ji, Baski ji and Mobin ji for their
numerous effort to complete the project.
Their encouragement towards the current topic helped me a lot in this project work which also
created an area of interest for my professional career ahead for this project.
I acknowledge the wonderful support of individuals numerous to mention by name-they allowed
us uninhibited access to their database for the success of this project.
I wish to acknowledge the fuel and Mineral Engineering Department, INDIAN SCHOOL OF
MINES (DHANBAD) for support to conduct this project.

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ABSTRACT
Coal middlings are the by- products of the coal washing/ Beneficiation process obtained in three
stage cleaning process. Steel production requires coal with 18% ash, while coal middling has 35-
45% ash. TATA Steel, a global steel producer, produced 1.8 MT of coal middling in financial year
2015. With the growing popularity of sustainable development and zero waste concepts, the ash
content of the coal middling can be reduced using grinding aids and pre-treatments to the
permissible limit. The rising global coal prices can make the need of this methodology, though
expensive, soon feasible and market demanding. The aim of the project is to enhance liberation of
coal middlings by using grinding aids, microwave treatment and ultrasonic treatment so that 18%
ash clean coal can be obtained with good amount of yield. In the present experimental
investigation enhancement of coal middling liberation is done using grinding aids/chemicals,
microwave heating and ultrasonic. Many set of experiment were done in rod mill at varying
densities from 40-60% using grinding aids/chemical with varying chemical dosages, microwave
heating at different time and ultrasonic. Grinding aids used in the experiments was categorized as
dispersant, water soluble polymeric grinding aids and preswelling liquids.
Grinding aids used in the experiments were found review and after studying review there dosages
were found. Dispersant used were Chemical A, water soluble polymeric grinding aids aged was
Chemical C, Dosages were varied from 0% to 2.0%. Chemical E, Chemical G and Chemical H
were N- based grinding aids and Chemical F was alcohol based preswelling chemicals
Experimental investigation were repeated using microwave heating and ultrasonic with varying
time of treatment from 0 sec to 6 mins for microwave treatment and 15,25,45 mins for ultrasonic
treatment. . Sample was taken out and dried and samples for further analysis like washability, size
analysis and proximate were taken out using proper sampling methods

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CONTENTS
1.0 INTRODUCTION 6
1.1 Introduction: Tata Steel 6
1.2 Coal: Importance & distribution
1.3 Middling Coal and importance of liberation 8
1.4 Grinding :Types of mills and mechanism 15
2.0 EXPERIMENTAL
2.1 Material 22
2.2 Grinding Aids for Coal /chemicals 23
2.3 Microwave heating 30
2.4 Experimental
2.4.1 Experiments with Dispersants 31
2.4.2 Experiments with Water Soluble Polymeric Grinding Aids 31
2.4.3 Experiments with Pre- Swelling liquids 32
2.4.4 Experiments Using Microwave energy 32
2.4.5 Experiments Using Ultrasonic treatment 32
3.0 RESULT & DISSCUSSION
3.1 Experiments with Dispersants 33
3.2 Experiments with Water Soluble Polymeric grinding Aids 34
3.3 Experiments with Pre-Swelling liquids 37
3.4 Experiments Using Microwave Energy 37
3.5 Experiments Using Ultrasonic 39
4.0 CONCLUSION 40
5.0 REFERENCES 41

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LIST OF TABLES
Table 1.0 Company-wise details of coal production 11
Table 2.0 Details of import of coal and products 12
Table 3.0 List of surfactants along with the minerals and the grinding condition 26
Table 4.0 Grinding aids along with the ground material or ore 28
LIST OF FIGURES
Fig. 1.0 Global shares of recoverable coal reserves 9
Fig. 2.0 Utilization of coal in different sector 9
Fig. 3.0 Coal demand in future generation 10
Fig. 4.0 Source: Geological Survey of India 11
Fig. 5.0. Relation between the components of coal 13
Fig. 6.0. Different types of grinding mills 17
Fig. 7.0 Mechanism of grinding in tumbling mills 18
Fig. 8(a) Size vs Cum wt. % passing distribution for chemical A at its different dosage 33
Fig.8 (b) Size vs Ash % distribution for Chemical A at its different dosages 33
Fig. 9(a) Size vs cum wt. % passing distribution for chemical C at its different dosage 34
Fig. 9(a) Size vs cum wt. % passing distribution for chemical C at its different dosage 35
Fig. 10(a) Size vs cum wt. % passing distribution for chemical D at its different dosage 35
Fig.10 (b) Size vs Ash % distribution for Chemical D at its different dosages 36
Fig.11 Washability curve for chemical C at its different dosing 36
Fig 12(a) Size vs cum wt% passing distribution for different microwave heating time 37
Fig 12(b) Size vs Cum wt% passing distribution for different microwave heating time 37
Fig.12 (c) Size vs Ash % distribution for different microwave heating time 38
Fig 13(a) Washability curve for different microwave heating time 39
Fig 13(b) Washability curve for different microwave heating time 39

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1.0 INTRODUCTION
1.1INTRODUCTION: TATA STEEL
Established in 1907 as Asia's first integrated private sector steel company, it was the vision of the
founder; Jamsetji Nusserwanji Tata, that on February 27, 1908, the first stake was driven into the
soil of sakchi. His vision helped Tata steel overcome several periods of adversity and strive to
improve against all odds. Tata Steel Group is among the top-ten global steel companies with an
annual crude steel capacity of over 29 million tonnes per annum. It is now the world's second-most
geographically-diversified steel producer, with operations in 26 countries and a commercial
presence in over 50 countries. The Tata Steel Group, with a turnover of Rs. 1, 48,614 crores in FY
14, has over 80,000 employees across five continents and is a Fortune 500 company.
Tata Steel’s larger production facilities comprise those in India, the UK, the Netherlands,
Thailand, Singapore, China and Australia. Operating companies within the Group include Tata
Steel Limited (India), Tata Steel Europe Limited (formerly Corus), Tata Steel Singapore and Tata
Steel Thailand.
The Tata Steel Group’s vision is to be the world’s steel industry benchmark in “Value Creation”
and “Corporate Citizenship” through the excellence of its people, its innovative approach and
overall conduct. Underpinning this vision is a performance culture committed to aspiration targets,
safety and social responsibility, continuous improvement, openness and transparency.
The Company dedicated the first phase (3 Mntpa) of the 6 Mntpa greenfield steel project at
Kalinganagar to the State of Odisha on November 18, 2015. Tata Steel is also examining further
capacity enhancement through greenfield projects in Jharkhand, Karnataka, etc. The Company also
possesses and operates captive iron ore, coal and chrome ore mines.
Two new Greenfield steel projects are planned in the states of Jharkhand and Chhattisgarh.
Kalinganagar project is underway, it is set to augment production capacity by 3 mntpa in the first
phase.
Mines and collieries in India give the Company a distinct advantage in raw material sourcing. Iron
Ore mines are located at Noamundi (Jharkhand) and Joda (Odisha) both located within a distance
of 150 km from Jamshedpur. The Company’s captive coal mines are located at Jharia and West
Bokaro (Jharkhand).

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R &D
RESEARCH AND DEVELOPMENT
The Research and Development Division of Tata Steel transformed significantly over the years. It
is known today as 'Research, Development and Technology (RD&T)' and operates five research
centers in India, the Netherlands and the United Kingdom.
Research Centers
1. IJmuiden Technology Centre (the Netherlands):
2. Sweden Technology Centre (United Kingdom):
3. Teesside Technology Centre (United Kingdom):
4. Automotive Engineering Group (United Kingdom):
5. Jamshedpur R&D Centre (India):
The Research & Development and Scientific Services division of Tata Steel Limited at
Jamshedpur, set up in 1937 as the 'Research and Control Laboratory', was one of its kinds in India.
Its three departments – Research and Development, Scientific Services and Refractory Technology
Group – support the Tata Steel Group, particularly its operations in India and South East Asia, by
developing new products and processes to create competitive advantage, better environmental
performance and enhanced sustainability.
In 2008-09, R&D became part of the Global Research Development & Technology function of the
Tata Steel Group.
The Jamshedpur R&D Centre in India was established in 1937 and is one of the oldest industrial
R&D centers in the country. Since its inception, this centre has played a pivotal role in the
development of steel products and process routes that have given the Company a competitive
advantage in local and global markets. The innovative processes and superior quality of output is
reflected in 42 filed and 36 granted patents during the past year along with publication of 56 papers
in top international peer-reviewed journals

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1.2 COAL: IMPORTANCE AND DISTRIBUTION
Coal is world’s most abundant and widely distributed fossil fuel. Coal worldwide Reserves are
over 861 billion tons. While India accounts for 286 billion tons of coal Resources, the non-coking
counterpart of which is approximately 85%. Coal is last Around 112 years at the current rates of
production. Coking coal, which is merely 14% of the total deposits, is available mainly in the
Eastern part of India. Jharia coal-fields are the store house of coking coals where prime coking
coals are available. The coking Coals in the Jharia coal-fields may be segregated into two major
sectors, i.e., Eastern and Western. The characteristics of the coals in the Eastern sector are
generally superior in quality than the Western sector. Coking coal is an essential for the
manufacture of Iron & Steel through blast furnace route. Steam coal, as well known as thermal
coal, is used in power stations to get electricity. Coal is used as an energy fuel as well as a Number
of valuable products. Coal gas, ammonia, coal tar and coke are producers from the carbonization
of coal.
Coal represents at present about 70% of the world’s proven fossil fuel resources. Availability of
coal is roughly three times greater than crude oil. According to United States Energy Information
Administration coal is the most abundant fossil fuel in the United States and almost half of all
electricity generated in the United States from cheap, readily mined domestic fuel coal (U.S.
Source of Energy 2009). Coal reserves available almost every country worldwide, with
recoverable reserves is around 70 countries [11]. The Largest reserves are in the USA, Russia,
China and India. The largest reserves are in the USA, Russia, China and India. Coal meets around
30.3% of the global primary energy Needs and generates 40% of the world’s electricity. The global
share of recoverable coal Reserves country wise has been indicated in Figure no. 1.1.1. It has been
evident from the figure below that United States leads the world with over 260 billion short tons
of Recoverable coal reserves which is 28% of total global reserves. On the other hand Russia
possesses the share of 18% of total global reserves the second highest coal Reserves. The other
countries like China, Australia, India and Germany global coal Reserves are 13%, 9%, 7% and 5%
respectively.

9
Figure 1.0 Global shares of recoverable coal reserves
Coal meets around 30.3% of the global primary energy needs and it makes the Mainstay of the
world’s electricity, nearly 40% of world’s electricity generated from coal. India’s power
Figure 2.0 Utilization of coal in different sector
generation is mainly in thermal, which in turn is coal, dominated about 81% of power generation.
As of 31st Jan 2007, Indian power sectors installed capacity grown to 1,28,182.47 Mega Watt
(MW) out of which 69,366.38 MW were through coal (CEA 2007). Eventually, coal will remain
the main source of energy for the country in future also. The ash content of Indian coals has been
increasing over the past three decades due to increased open-cast mining and production from
inherently inferior grades of coal. Indian coal allocated for thermal power generation contains low
grade coal with ash content ranging from 35 to 50 percent and only 20 % of the total coal supplied
to power plants is of superior grade (CPCB, 2000). Combustion of high ash content coal by thermal
power plants gives rise to huge quantity of fly ash with other operational problems finally affecting

10
the power plant efficiency. Fuel wise power generation in India is depicted in Figure 1.1.2.
Currently, India imports about 85 million tons of coal. Out of this about 25 million tons is
metallurgical coking coal for the steel industry. The balance thermal coal used by power plants
(50%), cement industry (17%) and other industries (33%).
IMPORTANCE-:
Steel & Coal – The Projected Growth
Figure 3.0 Coal demand in future generation
COKING COAL AND NON COKING COAL
 COKING COAL-: Coking coal is a fuel with few impurities and a high carbon content,
usually made from coal. It is the solid carbonaceous material derived from destructive
distillation of low-ash, low-sulfur bituminous coal. Cokes made from coal are grey, hard,
and porous
 Coking coal has low avg. ash content (10-15%).
 Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast
furnace. The carbon monoxide produced by its combustion reduces iron
oxide (hematite) in the production of the iron product.
 Metallurgical coal (Coking Coal) is primarily sold to steel mills and used
in the integrated steel mill process. When making steel, two of the key raw
ingredients are iron ore and coke
2006-07 2011-12 2016-17 2021-22 2024-25
COAL DEMAND(MILLON
TES.)
473 630 828 1079 1267
473
630
828
1079
1267
0
200
400
600
800
1000
1200
1400
COALDEMAND
COAL DEMAND (MILLION TES.)

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COAL RESERVE AND COAL PRODUCTION IN INDIA
 COAL RESERVE IN INDIA -: Coal reserves of 306.595 billion tonnes have been
estimated by the Geological Survey of India (01.04.2015). The reserves have been found
mainly in Jharkhand, Odisha, Chhattisgarh, West Bengal, Madhya Pradesh, Telangana and
Maharashtra.
Figure 4.0 Source: Geological Survey of India / The Indian coal sector -Challenges and future
outlook
 COAL PRODUCTION-: The overall production of coal for 2015-16 was projected
at 700 MT. During the period April to December 2015 the actual production was
447.48 Million tonnes compared to 427.278 Million tonnes (MT) during
corresponding period of 2014-15 and showing a growth of 9.1 per cent.
(In Million Tons)
COMPANY 2014-15
Actual
PRODUCTION (2015-16) in MT.
Target Actual Achievement
(%)
Growth
(%)
CIL 494.23 550.00 373.48 69.6 9.08
SCCL 52.54 56.00 43.24 77.2 22.70
CAPTIVE 52.77 75.50 21.55 28.5 -46.86
OTHERS 12.90 18.50 9.21 49.8 1.21
TOTAL 612.44 700.00 447.48 65.2 4.73
Table 1.0 Company-wise details of coal production
12.9
39.8
8.9
5.5
9.3
24.5
11.8
Indian Gondvana Coal Reserve
Chattisgarh
Jharkhand
Madhya Pradesh
Maharashtra
Andhra Pradesh
Orissa
In Billion ton

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IMPORT OF COAL -: Coking Coal is being imported by Steel Authority of India Limited
(SAIL) and other Steel manufacturing units mainly to bridge the gap between the requirement and
indigenous availability and to improve the quality. Coal based power plants, cement plants, captive
power plants, sponge iron plants, industrial consumers and coal traders are importing non-coking
coal. Coke is imported mainly by Pig-Iron manufacturers and Iron & Steel sector consumers using
mini-blast furnace
(In Million Tons)
TABLE 2.0 Details of import of coal and products i.e. coke during the last five
years
1.3 MIDDLING COAL AND IMPORTANCE OF LIBERATION
.
MIDDLING COAL
Coal middlings are the by- products of the coal washing/ Beneficiation process obtained in three
stage cleaning process. It is used for power generation, brick manufacturing units and cement
plants. Coal middlings are particle of the Intermediate specific gravity.
Typical Specification: Fixed Carbon - 45-46%,
Ash: 37-38%
Volatile Matter: 15-16%
LIBERATION OF COAL
Mineral processing has two fundamental operations which are liberation and concentration.
Liberation is the release of valuable mineral from the gangue mineral. Liberation of the valuable
minerals from the gangue is accomplished by comminution, which involves crushing and grinding.
COAL
2011-
12
2012-
13
2013-
14
2014-
15(PROV.)
2015-
16*
Coking Coal 31.80 35.56 36.87 43.71 7.49
Non-Coking Coal 71.05 110.23 129.99 174.07 29.70
Total Coal Import 102.85 145.79 166.86 217.78 37.19
Coke 2.37 3.08 4.17 3.29 0.53

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The degree of liberation is one of the most important and basic indices in particle separation
processes such as mineral processing and waste treatment, and is used to estimate selectively of
grinding and the sharpness of separation. In addition, in coal preparation, the limits of
demineralization and desulfurization depend on the degree of mineral matter liberation. The degree
of liberation has been generally measured by counting the liberated and locked particles using a
microscope. However, because coal has a complicated structure, it is very difficult to discriminate
useful components from ones that are not useful by microscope. Recently, methods of analysing
coal particles using scanning electron microscope-based automated image analysis (SEM-AIA).
For coal liberation, methods of calculating the liberation index by sink–float separation data
(washability data) have been studied. One method reported by Austinet al. (Austin, 1994;
Austin et al., 1994; Austin, 1995) was to quantify the extent of ash liberation by the route the
results would take between the Mayer curves of complete liberation and no liberation. However,
it has been conventionally assumed that each particle in sink–float separation data consists of two
uniform components of ash and combustible matter, and that only the ratio of these components
in each density fraction is important. In order to calculate the degree of mineral matter liberation
from sink–float separation data, it is important to effectively pull out the particle information which
is latent in these data, by taking the density of components into consideration. Although the degree
of liberation can be calculated for mineral matter and coal substance, respectively, the degree of
mineral matter liberation. The components in coal that are not useful are generally shown by the
ash content for convenience, and the sink–float separation data is based on the ash content.
However, needless to say, coal preparation is a process which treat the particles before combustion
(mineral matter (MM) and coal substance (CS)). It is also important to treat the components on a
mineral matter base when estimating the degree of liberation
Fig. 5.0. Relation between the components of coal

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Since some minerals are decomposed to other phases during combustion, and the ash contents of
these are not 100%, mineral matter also includes combustible matter (moisture, sulfur, carbon) in
the calculation. And, ash in coal is not also 0%, because some metal elements such as alkaline
metals included in coal substance remain as ash after combustion. This ash is called inherent ash.
Thus, Coal substance and mineral matter have their own characteristic ash content, and exist as
three kinds of Particles, that is, as liberated coal substance, liberated mineral matter, and locked
particles of both components (Fig. 1(c)). Here, the degree of mineral matter liberation (ML) can
be obtained by the following equation
ML(%) =
Liberated MM
MM
× 100
If the proportion of each mineral among each density Fraction becomes clear, sink–float separation
data based on the ash content (CM and A) could be converted to the data based on the mineral
percentage before being Combusted (CS and MM). Also, it would be possible to
Find out the minimum percentage of locked particles Which can be permitted in each density
fraction Although the Minimum value of ML MLmin) is expected to always be 0%, except for the
case when the mineral rate is 100%.the maximum Value of ML (MLmax), which is expected in
cases where The proportion of locked particles is minimum, depends on the ash content and
elemental data among each Density fraction. It is impossible to know what the true Degree of
liberation from the sink–float separation data is without information on each particle, but it would
be Possible to estimate MLmax by calculating the percentage Of particles that would certainly
become locked from The sink–float separation data, MLmax is Treated as the representative index
for the degree of Mineral matter liberation.
The greatest energy consumer is grinding consuming almost 50% of the total concentrator’s energy
(Wills and Atkinson, 1993). Concentration is to concentrate the valuable mineral to desired market
oriented concentration. It is mostly done after liberation. Crushing is done to reduce the particle
from the run-of-mine (ROM) size to below 1mm, while grinding reduces it to further below 1 mm.
The grinding of coarse-grain material to produce fine powder requires enormous energy
consumption and capital equipment costs to reach the desired size distribution of the fine powder.

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1.4 GRINDING: TYPE OF MILLS AND MECHANISM
The grinding of coarse-grain material to produce fine powder requires enormous energy
consumption and capital equipment costs to reach the desired size distribution of the fine powder.
Grinding is an important industrial operation that is used for the size reduction of materials,
production of large surface area and/or liberation of valuable minerals from their matrices. In
addition to mineral processing, it is widely used in the manufacture of cement, pigments and paints,
ceramics, pharmaceuticals, and cereals. However, the efficiency of this operation is very low. In
mineral beneficiation, grinding is also the most energy-consuming process.
1.4.1 THEORY OF GRINDING
The particle fracture involves crack propagation, which are already present or initiated in it. This
stress can be represented by the Griffitt’s equation.
𝜎 = √
2γ𝐸
𝐿
where, E = Young’s modulus
σ = Stress
L= Crack length
Fracture energy, γ = (brittle material = 103
- 104
erg cm-2
and plastic material = > 104
erg cm-2
)
Upon repeatedly breaking, each new progeny (new fragment particle) tends to be harder. Existing
larger cracks in the parent particle propagate first, creating finer cracks in the progeny. Hence, the
chance / probability of finding a flaw of given minimum fracture stress decreases. As
fragmentation continues, eventually the fracture stress required may increase to the extent that
some plastic deformation is possible. With plastic deformation occurring, the particle cannot be
ground further, consequently, a limit of fineness in grinding exists as1 µm for quartz while 3-5 µm
for limestone.
The amount of elastic energy that must be stored to propagate a crack is limited to the volume of
the particle, and very small particles may not have sufficient stored energy. Fracture stress
increases with low-velocity impact but decreases with increase impact velocity. The initial increase

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is due to large pre-failure plastic deformation when a high compression rate is used. Increased
temperature in the fracture environment can cause an increment in plastic deformation. “As even
under low- temperature conditions, the temperature near a propagating crack-tip can be very high
owing to the release of large quantities of energy in the form of heat which is 10-103
times greater
than the surface energy requirement for the fracture. The temperature under such conditions can
be even greater than the melting point, but after facture propagation, cools down rapidly, freezing
amorphous as other high energy structures at the fracture surface. This newly forming high energy
surfaces can react with the surrounding environment, if the possible environment penetration rate
is equal or greater than the crack propagation speed.
1.4.2 GRINDING MECHANISM:
In grinding process, several particles are continuously subjected to stress application in the
grinding zone at the same time. The crack distribution and their interactions during propagation
essentially determine the particle size distribution. Significance of the particle interaction depends
upon grinding mechanism, relative hardness and particle size, and the extent of size classification
during grinding. The basic grinding consists of
1. Impact/compression
2. Chipping
3. Abrasion
Mechanisms of breakage: (a) impact or compression (b) chipping (c) abrasion (22)
Above these physical interactions, chemical reactions also occur, during prolonged grinding,
Impact type comminution produce a greater normal size distribution, nipping causes a coarser
distribution and the abrasion produces more ultrafines particles. Intense point loading produces
larger fragments while fines are produced at the points of load (intense stressed region).

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1.4.3 DIFFERENT TYPES OF MILLS:
Figure 6.0. Different types of grinding mills
According to the ways by which motion is imparted to the charge, grinding mills are generally
classified into three types: tumbling mills, stirred mills, and vibrating mills.
Tumbling mills: In these mills grinding takes place in a revolving drum where the media
constitutes either of balls, rods or ore itself. The ore gets nipped between the falling media in the
revolving drum. The mill liners help to lift the charge to the shoulder such that the ore and media
fall at the toe of the mill and grinding action takes place. Tumbling mills are of three basic types:
rod, ball and autogenous.
Rod mills: These may be considered as either fine crushers or coarse grinding machines. They are
capable of taking feed as large as 50mm and making a product as fine as 300 µm, reduction ratios
normally being in the range 15-20:1. They are often preferred to fine crushing machines when the
ore is "clayey" or damp, thus tending to choke crushers. The grinding action results from line
contact of the rods on the ore particles; the rods tumble in essentially a parallel alignment, and also
spin, thus acting rather like a series of crushing rolls. The coarse feed tends to spread the rods at
the feed end, so producing a wedge- or cone-shaped array. This increases the tendency for grinding
to take place preferentially on the larger particles, thereby producing a minimum amount of
extremely fine material (Figure). This selective grinding gives a product of relatively narrow size
range, with little oversize or slimes. Rod mills are therefore suitable for preparation of feed to
gravity concentrators, certain flotation processes with slime problems, magnetic cobbing, and ball
mills. They are nearly always run in open circuit because of this controlled size reduction

18
The distinctive feature of a rod mill is that the length of the cylindrical shell is between 1.5 and 2.5
times its diameter. This ratio is important because the rods, which are only a few centimetres
shorter than the length of the shell, must be prevented from turning so that they become wedged
across the diameter of the cylinder. Rod mills are classed according to the nature of the discharge.
Rod mills are normally run at between 50 and 65% of the critical speed, so that the rods cascade
rather than cataract. The feed pulp density is usually between 65 and 85% solids by weight, finer
feeds requiring lower pulp densities.
Ball Mills:
Stirred mills: Here, the grinding mechanism is assisted by mechanical stirrers, which allow the
entire charge to be in uniform suspension. Attrition effect is enhanced, allowing greater ultrafine
generation.
Vibration mills: Vibration assists the grinding operation and ensures greater charge and media
contact with higher impact density.
Figure 7.0 Mechanism of grinding in tumbling mills

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1.4.4 SIZE DISTRIBUTION:
The size distribution has been mathematically stated as:
i. Rosin- Rammler- Benett (Weibull) distribution
ii. Gaudin –Meloy distribution
iii. Gates – Gaudin - Schuhmann distribution
i. Gaudin –Meloy distribution :
𝑦 = (1 −
𝑥
𝑎
)
𝑛
x= size in mm
a = size parameter
n = distribution parameter
y= cumulative weight percent passing size x
ii. Rosin- Rammler- Benett (Weibull) distribution:
𝑅 = 100 ∗ 𝑒
−(
𝑥
𝑥′
)
𝑏
R= cumulative weight percent retained on size x
x’ = size parameter
b = distribution parameter
This double log plot expands at the finer and coarser ends of the size range (<25% and
>75%) and compresses at the mid-range (30-60 %).
iii. Gaudin-Schuhmann Distribution:
𝑦 = 100 ∗ (
𝑥
𝑘
)
𝑎
y= cumulative weight percent passing size x
x= screen aperture size
k= size parameter
a= distribution parameter
This distribution requires limited number of sieves for the size analysis at the required size
range.

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1.4.5 GRINDING KINETICS
Critical Speed: The "Critical Speed" for a grinding mill is defined as the rotational speed where
centrifugal forces equal gravitational forces at the mill shell's inside surface. This is the rotational
speed where balls will not fall away from the mill's shell.
Mills are driven, in practice, at speeds of 50-90% of critical speed, the choice being influenced by
economic considerations. Increase in speed increases capacity, but there is little increase in
efficiency (i.e. kWh/t) above about 40-50% of the critical speed.
Height attained: The maximum height up to which the particles go along the mill shell and then
get thrown off and follow a parabolic path.
Power Consumption: Grinding is the most energy-intensive operation in mineral processing. Size
reduction, as a time function is mainly used for energy consumption calculation. For a constant
energy consumption rate, total energy consumption and time are directly proportional to each
other.
The comminution theory is concerned with the relationship between energy input and the particle
size made from the given feed size (Wills and Atkinson, 1993). There are three theories on
comminution:
a. Rittinger’s law
b. Kick’s law
c. Bond’s law
a. Rittinger’s law (Von Rittinger, 1867): It states that the energy consumed in the size reduction
is proportional to the area of new surface produced. Mathematically,

21
Energy, 𝐸 = 𝐾 ∗ (
1
D2
−
1
D1
)
K is constant, D1 is the initial particle size andD2 is the final product size.
b. Kick’s law (Kick, 1885): It states that the work required is proportional to the reduction in
volume of the particle concerned. Mathematically,
𝐸 = 𝐴 ∗ (
log 𝑅
log 2
)
A is constant and R is reduction ratio. R=f/p, f and p are the diameters of feed and product,
respectively.
c. Bond’s law (Bond, 1952): It states that the work input is proportional to the new crack tip length
produced in the particle breakage, and equals the work represented by the product minus that
represented by the feed. Mathematically,
The basic formula for this is the Bond formula:
Work = 10𝑤𝑖 (
1
√ 𝑃80
−
1
√ 𝐹80
) KWh/t
Wi is the Bond’s work index, which expresses the resistance of material to crushing and grinding.
Numerically, it is the kilowatt hours per short ton required to reduce the material from theoretically
feed size to 80% passing 100 microns.
P and F are the product and feed diameters in microns, at which 80% passes.
where P80 and F80 are the 80% passing sizes of product and feed in microns, and Wi is expressed
as kWh/t.Bond’s work index (Wi) is the comminution parameter which expresses the resistance of
the material to crushing & grinding. Numerically, it is the kWh per short ton required to reduce
the material from theoretically infinite feed size to 80% passing 100 microns (22). The calculated
power requirement is adjusted by utilizing efficiency factors dependent on the size of mill, size
and type of media, type of grinding circuit, etc., to give the operating power requirement. (Rowland
and Kjos, 1978).
Grindability is the ease with which material can be comminuted and it helps to determine the
comminution efficiency. It is determined using HGI (Hard Groove Index) method.
HGI = 13 + 6.93 * W (-200 #) , W (-200#) = weight of materials finer than 200# or 75µm.

22
2.0EXPERIMENTAL
2.1 MATERIALS
2.1.1 SIZE ANALYSIS: (HEAD SAMPLE, HS)
3.0 WASHABILITY DATA:
WASHABILITY FLOA
T
SINK
SPECIFIC
GRAVITY
WEIGHT
OF
FLOAT
WEIGHT
%
ASH
%
CUM
WT%
CUM.
ASH%
CUM.
WT%
ASH% MID
POINT
NGM
+1.3 0.85 0.09 15.55 0.09 15.55 99.91 38.60 0.04 0.00
1.3-1.4 9.55 1.01 14.84 1.10 14.90 98.90 38.97 0.59 13.91
1.4-1.5 122.5 12.90 25.67 14.00 24.83 86.00 44.65 7.55 42.84
1.5-1.6 284.2 29.93 33.01 43.93 30.40 56.07 62.58 28.96 49.37
1.6-1.7 184.5 19.43 41.89 63.36 33.93 36.64 68.80 53.65 28.54
1.7-1.8 86.5 9.11 49.99 72.47 35.95 27.53 62.00 67.92 15.46
1.8-1.9 60.25 6.35 54.91 78.82 37.47 21.18 59.07 75.65 12.32
1.9-2.0 56.7 5.97 59.35 84.79 39.01 15.21 59.35 81.81 0.00
2.0 sink 144.4 15.21 73.98
949.45 100 44.33
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10 11
weightpercentretained
size, mm
cummulative weight % Retained
cummulative
weight %
d20R = 8.00 mm = d80P
d50R = 3.30 mm = d50P
d80R = 1.35 mm = d20P

23
3.1 GRINDING AIDS FOR COAL / CHEMICALS
The terms ‘grinding aid’ or ‘grinding additive refer to a substance which when mixed into the mill
contents causes an increase in the rate of size reduction. The increased rate can be used to grind a
higher feed rate to the desired product size or it can be used to produce a finer product size at a
fixed feed rate whether the use of a grinding aid is justified in any given situation depends on the
cost of the substance versus the improvement of output or product quality obtained with its use.
Obviously, an expensive chemical must be effective in very small concentrations if it is to be
economically justifiable; the cost criteria are calculated on the basis of the cost of the grinding
additive per ton of material ground.
Explanation of grinding aid theory
The adsorption of additive on the surface of a solid lowers the cohesive force which Bonds the
molecules of the solid together. In Particular, adsorption on the surfaces of a Flaw in the surface
of a solid could affect the Bonding forces and surface energy at the Point where fracture initiates
Westwood Have demonstrated the effect of adsorbed Molecules on various surface mechanical
properties And they refer to the phenomena general as ‘chemo mechanical effects’_ they Suggest
that the adsorbed molecules may ‘pin’ Dislocations near the surface, thus preventing Easy
movement of dislocations under stress Gradients_ since plasticity is due to the Movement of the
dislocations, the region near The surface of the solid is thus rendered more Brittle. The surrounding
molecular environment Can certainly affect the critical stress-strain Required to produce fracture
under conditions Where the fracture initiates from a flaw in the Surface Melody and Crabtree [lo]
examined the effect of a Variety of liquids on ball milling and concluded That the action of a liquid
was to coat colliding Surfaces with particles, thus reducing steel-to steel contact which converts
the energy of Tumbling balls to heat without producing breakage It is clear that The results are
about the same for all the Liquids, thus ruling out chemo mechanical Clearly, the rates of breakage
are Unchanged for 50 and 60 wt.% solids, there is some indication that the rate is less at 70%and
clear evidence that the rate is substantially reduced at 80% solids content and that the rate of
breakage is slowing down as fines build up in the system.

24
A number of experimental Observations of grinding without Chemicals formed the basis of this
work: (1)Gradually increasing the percent solids of Slurries ground for a constant time produced
a gradually increasing value of net production of fines less than some specified size; (2) a similar
effect was produced by higher solid Packing efficiencies which could be produced From natural
or synthetic size distributions; (3) these trends occurred as long as the slurry Viscosity was not too
high; and (4) viscosity Lowering using water only was self-defeating With regard to the previous
three observations Because of the inherent volume dilution Effects of water. Therefore, the initial
goal of the research Program was to identify chemical fluidity Modifiers that would allow more
dense slurries To interact with the tumbling media, thus Rending tube trend of observations (1)
and (2) above by eliminating or at least lowering The viscosity limitations_ an efficient and
Economic set of chemicals to accomplish this Would have several benefits, including the Ability
to increase throughput at constant Particle size or grind finer at constant throughput With a given
piece of grinding equipment. A secondary benefit would be the lowering of the amount of water
required, which is Important in many mineral and coal processing Operations
In wet grinding systems, their main influence on grinding is through their effect on slurry rheology.
In some devices, the kinetic energy of the comminuted fragments might result in secondary
breakage. Adding certain chemicals, which are often surface-active, to the mill feed in small
quantities to improve the mill grinding. However in wet grinding, the power drawn by the mill can
be significantly influenced by the presence/absence of the additive, particularly in slurries at high
solid content. Comminution involves several sub process; 1) the transport of particles to the zone
in the mill where they can be stressed, 2) loading or stressing of the particles such that the fracture,
3) prevention of reagglomeration of the fines fragments, and 4) the removal of fine broken particles
from the grinding zone.
Grinding aids potentially can play a role in all four of the subprocesses that occurs during
comminution. The mechanism involved in the grinding aid action may include
a. The reduction of breakage energy,
b. Embrittlement to reduce plastic deformation
c. The flocculation/dispersion of fines
d. The prevention of reagglomeration and

25
e. Control of slurry rheology , useful objective in milling would be to foster breakage along the
grain boundary thereby enhancing liberation
3.1.1 GRINDING AID TYPES:
Grinding aid types
Grinding Aid Types
Water(moisture) Organic liquids Inorganic electrolytes Surface active agents
A. Water(moisture):
Wet grinding is usually more efficient than dry grinding. The credit goes to the reversible reaction
between the unsatisfied surface bonds and water molecules (Lin &Mitzmager). Hydrolytic
corrosive effects of the water vapours as in humid air is ought to be more effective. Wet grinding
reduces cushioning effect since the finest particles remain in suspension with water, which also
affects medium specific gravity and viscosity.
Also reduce fines loss increases the grinding recovery.
B. Organic Liquids:
It is more effective than water. Organic liquid vapours reduce the adhesive forces in the industrial
ball grinding of cement clinker, letting to the de-aggregation of powder and of coating of liners
and balls. This vapour adsorption is significant for prolonged grinding with rapid stress
application.
The organic compounds can also be used as swelling agents for super micronised comminution
process (7).
Some of swelling agents used commonly
1. Pyridine
2. Ethylene Diamine
3. Tetrahydrofuran(THF)

26
4. Acetone Dichloromethane
5. Toulene
6. Cyclohexane
7. Methanol
8. Ethylene gylcol
C. Surface active agents:
Surfactants are effective grinding aids at optimal addition. Reduced surface energy, enhancement
of particle dispersion, de-flocculation or de-aggregation of fines along with impaired ball coating
is beneficial.
Surfactants Mineral Condition
Polysiloxane Ultraporcelain, talc Grinding
Silicones Limestone, quartz Drop-weight crushing
Organo-silicones, organic acetates, carbon
black, wool grease
Cement Grinding
Silicones Quartz Grinding
Acetones in nitromethane benzene, carbon
tetrachloride, hexane
Ground glass, marble
quartz
Vibratory milling
Wool grease Gypsum, limestone,
quartz
Grinding
Table 3.0 List of surfactants along with the minerals and the grinding condition
D. Inorganic electrolytes:
Multivalent electrolytes due to their high valence active ion of the salt have proved their better
efficiencies. But the limitations of other mineral ions into the blast furnace operation restrict their
use due to high ash problem. Examples: AlCl3 and CuSO4 for wet grinding.

27
CONDITIONS FOR GRINDING AID EFFICIENCY:
1. The mill is operated in a region of percentage solids high enough so that a further increase
produces a large slurry viscosity increase in the absence of the grinding aid.
2. The solids in the slurry have sufficient adsorption capacity for the grinding aid so that it can
improve the slurry dispersion characteristics.
3. The grinding aid has consistently good dispersion characteristics over the range of
physiochemical conditions (such as slurry pH, intensity of mixing, impurity type and amount,
shear level, dispersant concentration, etc.) encountered in practical operation of the mill.
3.1.2 EFFECT OF CHEMICAL ADDITIVES ON THE GRINDING DYNAMICS
Though grinding rates are related to mill torque, which can also be used to directly monitor and
analyse grinding mill performance and grinding aid role, but on finer fractions the fines aggregate
to the balls or media and liners. This aggregation, beyond a critical pulp viscosity, can also led to
the sticking or centrifuging of the media or balls to the mill wall, since it cannot detach from the
mill wall during rotation period. This, not only reduces the mill power draft due to the decreased
torque, but also decreases the grinding rate and efficiency. The polymeric additives here help to
reduce the viscosity of the pulp below the critical mark to avoid media centrifuging and full
utilisation of mill power takes place. This effect can also be seen during the unloading of the
products from the mill, as free flowing fines with additives while sticky paste without additives.
Slurry rheology is controlled by 3 factors as:
1. Density of slurry
2. Particle size distribution
3. Chemical environment
At increased solids concentration, the Newtonian rheological characteristics change to non-
Newtonian, which is followed by increased suspension viscosity. Since particle shape, though a

28
major factor cannot be controlled in comminution operation, so at given pulp density (solid
concentration), the particle size distribution changes and the production of fresh surface adsorbs
chemicals present in the system and thus, slurry rheology changes with time (2).
Hence, grinding aids owing to their polar nature and consequent ability to satisfy residual electrical
forces created upon fracture reduces van der Waals adhesive tendencies between ground particles,
thus increasing the grinding efficiency.
Grinding in high surface tension liquids have shown rapid grinding. Coarser particles are faster
ground in more viscous liquid and vice versa, else finer less dense particles will float away from
the grinding zone.
Grinding aid Material or ore Author (Reference)
Humid air Soda lime glass P. Somasundaran,1978(5)
Ethylene glycol, proplylene glycol, butylene
glycol- vapors
Cement/Coal
P. Somasundaran (1978)(5)
Flotigam P, flotation agent (C12-C14 amine) Quartzite and limestone Szantho, 1942(13)
Polysiloxane Ultraporcelain and talc P. Somasundaran,1978(5)
Silicones Limestone and quartz P. Somasundaran,1978(5)
Glycols, amines, organosilicones, organic
acetates, carbon blacks, and wool grease
Cement
P. Somasundaran,1978(5)
Hydrocarbons Aluminum powder (14)
Silicones Quartz (14)
Acetones in nitromethane benzene, carbon
tetrachloride and hexane
Ground glass, marble and quartz
(14)
Wool grease Gypsum, limestone, and quartz (14)
CuSO4 and AICI3 Ceramic industry P. Somasundaran, 1978(5)
Tetrabromoethane Quartz P. Somasundaran, 1978(5)
Vaccum, dry benzene butyl alcohol, propyl
alcohol, water
Silica
P. Somasundaran, 1978(5)
di- or tri-methaloamine
Cement
(14)
Propylene glycol

29
Organo-silicones
Resins, cod oil, Kojic oil, carbon blacks, wool
grease, calcium sulphate, urea, asphaltenes
Cement clinker
(14)
Acidol-naphtenate soap or sodium abietate Cements D.W. Furestanu, 1995(9)
Water Dolomite D.W. Furestanu, 1995(9)
Do-decylammonium chloride, cationic
surfactant Quartz
D.W. Furestanu, 1995(9)
AlCl3
XFS 4272, polycarboxylate by Dow Chemical
company
Taconite
Klimpel and Austin,
1981(2)
Polyacrylic acid (PAA)
Dolomite Velamakanni and
FurestanuHaematite/Coal
Quartz
Sodium polyacrylate(SPA)
Dolomite /Haematite/ Coal
XFS 4272
Dolomite
Haematite/ Quartz
Ethylene glycol Cement clinker D.W. Furestanu, 1995(9)
Water/Na sulphonate
Low volatile bituminous coal
D.W. Furestanu, 1995(9)
Water/ Aerosol OT
Butanol
Water
Methanol
XFS 4272 Dolomite D.W. Furestanu, 1995(9)
Sodium Silicate Coal D.W. Furestanu, 1995(9)
Sodium Hexameta Phosphate(SHMP) Coal D.W. Furestanu, 1995(9)
Table 4.0 Grinding aids along with the ground material or ore

30
3.2 MICROWAVE HEATING
In a mineral processing plant, comminution involves a series of crushing and grinding processes.
The microwave pre-treatment has been done to influence the grindability of high ash Indian coal
which has resulted in better HGI (Hard Groove Index), WI (Work Index) and specific rate of
breakage of coal. Microwave heating is fundamentally different from traditional heating, since
microwaves take the electromagnetic energy wave form and can deep penetrate into the sample,
which initiates heating volumetrically.
Microwave pre-treatment causes differential heating within heterogeneous ores which induce
thermal fracture. This is a function of the different loss factors of each component within the ore,
as in coal and therby influences grindability . The differential heating results from the different
microwave absorbing properties or dielectric permittivity and loss factor of each phase.
Traditional heating process heats the sample outside inward through convection, conduction or
radiation (standard heat transfer mechanisms). Conventional heating process runs from the surface
to the middle of the sample while microwave heating runs from middle or center to surface. Even
microwave drying is 10 times faster than classical drying. Selective heating is also possible in
microwave heating, which is absent in conventional ones.
Ash content is lower in microwave treated coals than untreated ones. Since due to faster heating
of mineral content than coal on microwave treatment, the binding force weakens and it forms fines
more easily upon grinding. Lower moisture content of microwave-treated coal. Higher volatile
matter and fixed carbon of treated coals owing to partial mineral matter removal .XRD analysis
shows greater crystallinity on increasing microwave exposure time. Coal temperature increases
with microwave exposure duration due to 2-3 faster microwave energy adsorptions than that of
carbonaceous matter. Increased HGI of treated coals due to differential thermal expansion of
individual mineral matters/ phases within coal matrix on microwave heating. This expansion
creates stress within the lattice which induces fracture at grain boundaries. Microwave heating can
induce thermal fracture through differential heating of the various phases in a material. This
differential heating results from the different microwave absorbing properties or a different
dielectric permittivity and loss factor of each phase. The microwave treated coal grinds much more

31
rapidly initially than the untreated coal. Using Bond Work Index test, it is found that comminution
energy decreased with increased microwave treatment. .Magnetic methods of mineral removal
from coal depend on the difference in the magnetic moment associated with mineral particles and
that of coal. The microwave heating enhances the magnetic susceptibility of the iron mineral
(pyritic minerals), thus rendering it more amenable to magnetic separation. The main difference
between the thermal and microwave heating was extremely short time for desulphurization in the
case of microwave.
Hence, microwave energy may lead to significant savings in energy consumption, process time
and environmental remediation. Compared with conventional heating techniques, microwave
heating has the following additional advantages: Higher heating rates, no direct contact between
the heating source and the heated material, selective heating may be achieved, and greater control
of the heating or drying process, reduced equipment size and waste
3.3 EXPERIMENTAL
3.3.1 EXPERIMENTS WITH DISPERSANTS
A series of experiment was conducted using rod mill in which 1 kg middling coal sample
were taken with 4 kg rod so to make Coal and media ratio 1:4. The time for grinding was
1 hr .Coal middlings at pulp densities varying from 40-50 % solid by weight were used in
the grinding liberation studies, conducted with different dispersants. Dispersant used in the
experiment were Chemical A and Chemical B. The additive dosages were changed from
0.50%, 1.00%, to 2%. Dispersant used in the experiment was Chemical B and additive
dosages were taken 1% and 2%. . Sample was taken out and dried and samples for further
analysis like washability, size analysis and proximate were taken out using proper sampling
methods
3.3.2 EXPERIMENTS WATER SOLUBLE POLYMERIC GRINDING AIDS
Experiments were repeated with similar condition as done above in dispersants. In the
experiments water soluble polymeric grinding aids and abbreviated as Chemical C and
Chemical D. The additive dosages were changed from 0.25%, 0.50%, 0.75%, 1.00% and
2.00%. The result of size analysis, proximate and washability were observed.

32
3.3.3 EXPERIMENTS WITH PRE- SWELLING CHEMICALS
This set of experiment was repeated similar condition as above with pre swelling
chemicals. Liquid chemical used in the experiment were named as liquid A, liquid B,
liquid C and Liquid D. The Coal sample was soaked in 200ml and soaking time were 6hr,
24hrs.The final mixture was stirred at room temperature and left untouched for 6 hrs. and
24hrs. After 6 hrs. and 24hrs mixture were treated in rod mill for 1 hr. Sample were taken
out and dried and sample for further characteristics was taken out using sampling. In the
presence of swelling solvents, coal molecules dissociate, rearrange and reassociate in
lower free energy
conformations, probably in a different molecular structure. Swelling solvents break
weaker bonds and combine the effect of creating macropores in coal structure, which
decreases diffusional limitations, with the formation of active sites as the result of
breaking some bonds
3.3.4 EXPERIMENTS USING MICROWAVE ENERGY
In this study the middling coal were treated to microwave heating for 2, 4, 3 and 6 mins.
Two type of coal sample were treated in microwave i.e. damped and current mixing.
Damped coal sample was soaked in water for 24hrs and current was soaked for 5 mins.
Microwave treated sample was the treated in rod mill for 1 hr. at varying pulp densities
40-50% solid by weight. Microwave pre-treatment causes differential heating within
heterogeneous ores which induce thermal fracture
3.3.5 EXPERIMENTS USING ULTRASONIC
In this experimental investigation middling coal were treated with ultrasonic for 15, 25 and
45 mins. Coal middling were mixed with water to form slurry of varying pulp densities
from 35-45 %. Ultrasonic probe was dipped in the slurry and slurry was agitated using
agitator. Ultrasonic treated sample were charged in rod mill for 1hrs and sample was dried
for further observation

33
3.0 RESULT AND DISCUSSION
3.1 EXPERIMENTS WITH DISPERSANTS
3.1.1 Size analysis of grinding by various chemicals
 Chemical A
Fig. 8(a) Size vs Cum wt. % passing distribution for chemical A at its different dosage
Figure 8(a). shows that higher size reduction can be achieved at 2% of chemical A which generates
more fine as compared to 1.00% and 0.50%. While D50 for Chemical A at 0.50% & 2.00% dosages is
approx. 3.2mm and for 1.00% dosage D50 is 4.58mm (approx.)
Fig.8 (b) Size vs Ash % distribution for Chemical A at its different dosages
From the figure 8(b) it can be observed that ash % decrease form +6mm to +100# and the increase. It
can be observed that at size +100# mineral matter can be liberated from coal matter efficiently when
0.50% of chemical A is used, as the dosages of chemical A increases from 0.50% to 1.00%, the ash%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
+6mm +3mm +2mm +1mm +30# +60# +100# +150# +200# +300# -300#
Cumwt%passing
Size
0%
0.50%
1.00%
2.00%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
+6mm +3mm +2mm +1mm +30# +60# +100# +150# +200# +300# -300#
Ash%
Size
0%
0.50%
2%
1.00%

34
decreased to 23.12% from 44.15%. So it can be concluded that for chemical A 0.50% gives best
liberation.
Result from washability and proximate analysis were not available at the time of writing of the project
3.2 EXPERIMENTS WITH WATER SOLUBLE POLYMERIC GRINDING AIDS
3.2.1 Size analysis of grinding by water soluble polymeric grinding aids
 Chemical C
Fig. 9(a) Size vs cum wt % passing distribution for chemical C at its different dosage
Figure 9(a) shows that the -300# wt fraction increase 12.18% to 37.15% when dosage of chemical C
increases to 0.75 from 0% and when dosage increase further, it decreases to 3.28% for 1% dosage and
5.037% for 2% dosage of chemical C, Hence it can be concluded that better liberation of coal middling
can be obtained at 0.75% Chemical C.
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
+6mm +3mm +2mm +1mm +30# +60# +100# +150# +200# +300# -300#
Cumwt%passing
Size
0%
0.25%
0.50%
0.75%
1.00%
2.00%

35
Fig. 9(b) Size vs cum wt % passing distribution for chemical C at its different dosage
From figure 9(b), it can observed that minimum ash% obtained when liberated at -150# was 35.41 but
yield of separation is very low when 1% and 2% of chemical C was used, while at 0.75% of chemical
C yield increase to 16.10% from 2.48% at 0% chemical dosing. So it can be said that 0.75% dosing of
Chemical C can be best used to enhance liberation.
 Chemical D
Fig. 10(a) Size vs cum wt % passing distribution for chemical D at its different dosage
Figure.10(a) Shows that the amount of -300# fraction is higher when 0.25% of
chemical D is used and it was observed that D50 for 0%, 0.25%, 0.50%, 75% and 2%
were 2mm, 75#, 72#, 50# and 3.54mm, Hence it can be concluded that 0.25% of
Chemical D give best liberation.
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
+6mm +3mm +2mm +1mm +30# +60# +100# +150# +200# +300# -300#
Ash%
Size
0%
0.25%
0.50%
0.75%
1.00%
2.00%
0
10
20
30
40
50
60
70
80
90
100
+6mm +3mm +2mm +1mm +30# +60# +100# +150# +200# +300# -300#
Cumwt%Passing
Size
0% 0.25% 0.50% 0.75% 2%

36
Fig.10 (b) Size vs Ash % distribution for Chemical D at its different dosages
From the Fig.10(b), it can be observed that when 0.50% chemical D dosing used fraction of -100# was
13.47% with ash 42.14% and when its dosing increases to 0.75%, -100# fraction decrease to 10.62
with ash 38.71% and hence it can be concluded better liberation can be obtained with 0.75% dosing of
chemical D
3.2.2 Washability Analysis of grinding by water soluble polymeric grinding aids
 Chemical C
Fig.11 Washability curve for chemical C at its different dosing
From the figure 11.0 if coal middling were washed at 17% ash, it can be observed that the yield
was 4.95 (approx.) when 2% of chemical C was used. Among all dosing best result was observed
at 2.00% of chemical C but still grinding aids doesn’t make much difference, result with grinding
was not good.
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
+6mm+3mm+2mm+1mm +30# +60# +100# +150# +200# +300# -300#
0%
0.25%
0.50%
0.75%
2.00%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.00 10.00 20.00 30.00 40.00 50.00
Cumwt%
Cum Ash%
0%
0.25%
0.50%
0.75%
1%
2%

37
3.3 EXPERIMENTS WITH PRE SWELLING LIQIUDS
Result from size analysis and washability were not available at the time of writing of
report.
3.3 EXPERIMENTS USING MICROWAVE HEATING
3.5.1 Size Analysis of grinding by using Microwave heating
Fig 12(a) Size vs cum wt% passing distribution for different microwave heating time
Fig 12(b) Size vs Cum wt% passing distribution for different microwave heating time
0
10
20
30
40
50
60
70
80
90
100
+6mm+3mm+2mm+1mm +30# +60# +100#+150#+200#+300# -300#
Cumwt%Passing
Size
0sec
30sec
60sec
90sec
0
10
20
30
40
50
60
70
80
90
100
+6mm +3mm +2mm +1mm +30# +60# +100# +150# +200# +300# -300#
Cumwt%Passing
Size
without
2 min
3 min
4 min
6 min

38
From fig.12(a) & fig.12(b), it was concluded no difference was observed when time for microwave
heating increases from 0 sec to 4 min but when time of microwave heating increased to 6mins -
300# fraction decreases to 1.92% from 12.71% as compared to without microwave treated coal.
D50 for without microwave treated , 30 sec , 60 sec and 90 sec was observed as 2.1mm, 1.82mm,
2.02mm and 2.23 mm and but when the time for microwave heating increased d50 decresed to
1.65 mm which was still not good result.
Fig.12 (c) Size vs Ash % distribution for different microwave heating time
Figure. 12(c) shows that if coal middling were liberated to -300# size, ash % observed was 39.07 with
weight fraction 12.18% when no microwave heat treatment was done whereas within increase of
microwave heating time ash% increases to 50.54 from 39.07 with the same value of weight fraction
but for the 60sec weight fraction gradually decreases to 2.07 %from 12.18%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
+6mm+3mm+2mm+1mm +30# +60# +100# +150# +200# +300# -300#
Ash%
Size
0 sec
30 sec
60 sec
90 sec

39
3.3.2 Washability Analysis of grinding by using Microwave heating
Fig 13(a) Washability curve for different microwave heating time
Fig 13(b) Washability curve for different microwave heating time
From figure.13 (a) and 13(b) it was observed that it was not possible to wash coal at 17% with
better yield, as the time of heating increases to 6 mins from 0 sec, no difference had been observed
as compared with without microwave heat treated coal. It would be possible to wash coal at 22.12
ash% at yield of 10% when time of microwave heating was 2, 3, 4and 6 mins, so it was concluded
that in all cases max.yield cab be obtained was 10% when washed at 22.12%
3.4 EXPERIMENTS USING ULTRASONIC
Result from size analysis and washability were not available at the time of writing of the
report
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.00 10.00 20.00 30.00 40.00 50.00
Cum.Wt%
Cum Ash %
Washability Curve
without
30 sec
60sec
90sec
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.00 10.00 20.00 30.00 40.00 50.00
Cumwt%
Cum Ash%
without
2 min
3 min
4 min
6 min

40
4.0 CONCLUSION
In the present experimental investigation enhancement of coal middling liberation is done using
grinding aids/chemicals, microwave heating and ultrasonic. Many set of experiment were done in
rod mill at varying densities from 40-60% using grinding aids/chemical with varying chemical
dosages and time for grinding varying from 1-2 hrs. Grinding aid’ or ‘grinding additive refer to a
substance which when mixed into the mill contents causes an increase in the rate of size reduction.
The increased rate can be used to grind a higher feed rate to the desired product size or it can be
used to produce a finer product size at a fixed feed rate whether the use of a grinding aid is justified
in any given situation depends on the cost of the substance versus the improvement of output or
product quality obtained with its use. Microwave treated coal sample does not give good result
when time for heating increased to 6 mins from 0 sec, it was concluded that no difference was
observed when time for microwave heating increases from 0 sec to 4 min. D50 for without
microwave treated, 30 sec, 60 sec and 90 sec was observed as 2.1mm, 1.82mm, 2.02mm and 2.23
mm and but when the time for microwave heating increased d50 decresed to 1.65 mm which was
still not good result. It would be possible to wash coal at 22.12 ash% at yield of 10% when time
of microwave heating was 2, 3, 4and 6 mins, so it was concluded that in all cases max.yield cab
be obtained was 10% when washed at 22.12 ash %. When dispersant and water soluble polymeric
grinding aids were used, better results were obtained. When water soluble polymeric grinding aids
was used result were showing different behaviour as compared to dispersant. It was observed -
300# fraction increased to 37.15% from 12.18% when dosing of chemical C was o.75%, where
within increases with dosing of chemical C weight fraction decreases to 3.28%. If coal middling
were washed at 17% ash, it can be observed that the yield was 4.95 (approx.) when 2% of chemical
C was used. Among all dosing best result was observed at 2.00% of chemical C but still grinding
aids doesn’t made much difference, result with grinding was not good, it can be observed that
when 0.50% chemical D dosing used fraction of -100# was 13.47% with ash 42.14% and when its
dosing increases to 0.75%, -100# fraction decrease to 10.62 with ash 38.71% and hence it can be
concluded better liberation can be obtained with 0.75% dosing of chemical D. hence it can be
concluded that better liberation of cola middling were obtained when water soluble polymeric
grinding aids was used with varying dosages from 0.25 to2.0% .

41
6.0 REFERENCES
1. H. EL-SHALL “Mechanisms of Grinding Modification by Chemical Additives: Organic Reagents”
Mineral Processing Engineering. Montana College of mineral Science and Technology. Butte. JfT
59701 &_S.A.) and P. SOMASUNDARAN, Powder Technology. 38 (1983) 267 – 273.
2. H. EL-SHALL “Physico-Chemical Aspects of Grinding: a Review of Use of Additives” Afontana
College of Mineral Science and Technology. Butte. NT 59701 (U.S.A.) and P.SOMASUNDARAN
3. F. Pintoa,, I. Gulyurtlua, L.S. Lobob, I. Cabritaa (INETI, Azinhaga Lameiros, Estrada Pac¸o do Lumiar,
1699 Lisboa Codex, Portugal) “Effect of coal pre-treatment with swelling solvents on coal liquefaction”
4. D.W. Furestanu (1987)” Grinding Aids”, Deapartment of Material Science and Mineral Engineering (
University of Calfornia )
5. R. R. Klimpel and L.G. Austin (1981)-“Chemical additives for wet grinding of minerals”, Powder
Technology. 31 (1982) 239 – 253, Elsevier Science Publishers
6. Philip H. Howard and Rabinder S. Datta -“Chemical comminution: a process for liberating the mineral
matter from coal”, Syracuse Research Corporation, New York
7. A. ANSEMS and R K BLOEBAUM “Chemical Comminution” Powder Technology. 40 (1984) 265 -
268
8. D.W. Furestanu (1984)-“Effect of chemical additives on the dynamics of grinding media in wet ball mill
grinding”,International Journal of Mineral Processing, 15 (1985) 251—267, Elsevier Science Publishers
B.V., Amsterdam
9. S.C. Yen and E.J. Hippo(1990)-“Comminution employing liquid nitrogen pretreatments” U.S.
Department of Energy, Contract Number DE-FC22-89PC89904
10. P. Somasundaran (1978) -“The theories of grinding” Ceramic Processing before Firing, John Wiley &
Sens. Int.
11. B.K. Sahoo, S. De, B.C. Meikap (2010)-“Improvement of grinding characteristics of Indian coal by
microwave pretreatment”, Fuel Processing Technology 92(2011) 1920-1928, Elsevier Science
Publishers B.V
12. Clifford L. Spiro (1985)-“Supermicronized process for coal comminution” United States Patent, Patent
No.: 4,546,925
13. T. Oki , H. Yotsumoto S. Owada “Calculation of degree of mineral matter liberation in coal from
sink–float separation data”( National Institute of Advanced Industrial Science and Technology,
Onogawa, Tsukuba 305-8569, Japan) b Waseda University, Shinjyuku-ku, Tokyo 169-8555, Japan
14. Robert G. Aldrich, Douglas V. Keller, Jr.,Richard G. Sawyer (1974)-“Chemical comminution and
mining of coal”, United States Patent, Patent No.: 3,850,477

42
15. W. Francis (1961) -"Physical Considerations” Chapter XI in Coal, Its Formation and Composition, 2nd
Ed., Edward Arnold, London.
16. I.G.C. Dryden (1952)-"Solvent Power for Coals at Room Temperature" Chem. Indust, (June 2), 502.
17. VanKrevelen, D.W. (1965) - "Chemical Structure and Properties of Coal. XXVIIICoal Constitution and
Solvent Extraction," Fuel 46, 229.
18. S.K. KAWATRA and T.C. EISELE “Rheological Effects in Grinding Circuits” (Metallurgical
Engineering, Michigan Technological University, Houghton, M149931, U.S.A.)
19. A. L. Mular (1965) - "Comminution in Tumbling Mills-A Review:” Can. Metall. Q., 4 (I), 31-73.
B.A.Wills, Int. to Mineral Processing, Elsevier
20. A.A. Griffith (1920-1921) - “The Phenomena of Rupture and flow in solids”, Philos. Trans. Roy. Soc.
London, Ser. A 221:163-198
21. A. Gupta and D.S. Yan -“Particle Size Estimation and Distribution”, Mineral Processing Design and
Operation- An Intro., Elsevier, 2:47-50
22. Tao Wu, Peter Wardle, Jonathan P. Mathews “A Review of Microwave Coal Processing” Journal of
Microwave Power and Electromagnetic Energy, 48 (1), 2014, pp. 35-60.
23. J.A. Menéndez*, A. Arenillas, B. Fidalgo, Y. Fernández, L. Zubizarreta, E.G. Calvo,J.M. Bermúdez
“Microwave heating processes involving carbon materials” Instituto Nacional del Carbón, CSIC,
Apartado 73, 33080 Oviedo, Spain
24.
25. D.A. Jones, S.W. Kingman, D.N. Whittles *, I.S. Lowndes “Understanding microwave assisted
breakage” (School of Chemical Environmental and Mining Engineering, University of Nottingham,
University Park, Nottingham NG7 2RD, United Kingdom.)
26. Ercan Sahinoglu, Tuncay Uslu “Effects of various parameters on ultrasonic comminution of coal in
water media” (Karadeniz Technical University, Department of Mining Engineering, 61080, Trabzon,
Turkey).
27. Source: Geological Survey of India / The Indian coal sector -Challenges and future outlook
28. SOURCE- ANNUAL REPORT 2014-15 MINISTRY OF COAL/ http://coal.nic.in/coal/index.html

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