Field of the Invention
This invention relates to a process for selective fragmentation and liberation to recover
iron values from low grade iron ores with complex liberation characteristics. More
particularly, the invention relates to a process of selective fragmentation of low grade iron
ores exhibiting an interlock relationship of iron minerals with gangue minerals to liberate
at a particle size less than 45microns.
Background of the Invention
The high depletion of superior grade (>55 Fe%) iron ore reserves rendered imperative
search for alternate resources such as sub grade or low grade or inferior grade iron ores
(<55 Fe%). These low grade iron ores have not been optimally exploited because of
challenges in beneficiation due to poor liberation and complex relationship of minerals.
Therefore, these consolidated iron ores are associated with the requirement of fine
grinding to achieve necessary liberation of valuable minerals. But, the traditional
mechanical size reduction of ores is an energy-intensive and highly inefficient process due
to indiscriminate nature of breakage. Most of the energy is absorbed due to impact and
dissipated as heat or noise in the prior art process of mechanical size reduction, excepting a
small a part of energy is utilized to generate new surfaces. Based on the energy
requirement to create new surfaces, conventional grinding efficiency is found to be less
than 1%. Additionally, the ultra-fine slime generation is inevitable and thereby increases
the loss of valuable minerals due to the inefficiencies of prior art towards mineral recovery
at finer sizes. Unfortunately, conventional grinding technologies are driven to reduce size
by producing transgranular fractures (random) in ore particles.

Inadequate mineral liberation leads to improper beneficiation and low recovery of mineral
with high operating costs. Hence, selective fragmentation is highly desirable which interalia
allows recovery of mineral particles, thus making the separation process more efficient.
The accumulated fractures in fact lowers the strength of mineral and increase the grinding
efficiency. The promoted improvement in comminution is significant only to reduce its high
operating costs. The important role of comminution is not merely to reduce the particle
size but to liberate minerals from each other, which interalia improves the efficiency of size
reduction processes. Therefore, the selective fragmentation and liberation by pre-
treatment processes can significantly enhance the grinding and beneficiation to recover
iron values.
The available sub grade or low grade or inferior grade iron ores (<55 Fe%) are in the form
of goethite rich hematite iron ore along with alumina or quartz or aluminosilicates. These
ores are generally rejected at mine site due to presence of high gangue composition with
iron ore. Traditional beneficiation of goethite rich hematite iron ore is inefficient and not
amenable for concentration. Hence it is significant to develop a new process of conversion
of goethite to hematite for goethite rich hematite iron ores to generate crack formation and
selective fragmentation to liberate iron minerals from gangue minerals by pre-treatment
processes.

According to the known non-patent publications, the low grade iron ores are goethite rich
hematite iron ore of different composition are subjected to pre-treatment processes such
as high pressure compression, electric and ultrasonic treatment, thermal treatment or
microwave treatment to improve the liberation, to reduce to grinding energy and to
enhance the separation through downstream processes. During high pressure
compression, the material nipped between the counter rotating rolls under pressure and
generate micro cracks. The ores are broken down along the boundaries of minerals
because the molecular structures in the boundary are much weaker. But, high pressure
compression method has disadvantages over thermal or microwave treatment because of
simultaneous formation of fractures and closing of existed fractures. Electroacoustic
comminution to generate hydraulic Shockwave of explosive intensity is unsafe and not
feasible at plant. Unfortunately, these processes require high energy for breakage and
selective only for coarser sizes.
During thermal heating, the energy is transferred through convection, conduction and
radiation of heat from the surface to the center of the ore particles due to thermal
gradients. This method relies on cyclic heating and cooling of an ore, and promotes internal
fracture by exploitation of different responses (resistance, liberation and size distribution)
of ore constituents. Thermal shock fragmentation and its severity to nucleate fracture in
ore particles were estimated. The relationship of critical stress time with the fracture
length as per critical stress theory is known to have been developed (Lehnhoff T. F., 1975;
GellerL.B., 1972).

In contrast to thermal heating, the microwave heating rapidly penetrate, deposit energy
directly to the center of ore particles through molecular interaction with the
electromagnetic field and does not rely on diffusion of heat from the surfaces. The
commercial microwave has nonionizing electromagnetic spectrum of2.45GHz frequency.
Microwave heating is unique and have number of advantages over conventional heating.
These effects are compositionally dependent and had significant effect on heating rate.
Different minerals attributed to the differences in conductivities or dielectric loss factors
and bonding properties. In respect of bonding, minerals with metallic bonds can more
effectively absorb microwaves than those with purely ionic or covalent bonds.
During thermal or microwave treatment of goethite ores, water or hydroxyl group of
goethite is converted to vapor during transformation and cause internal stresses within the
ore matrix. The stresses due to phase transformation and water content during goethite to
hematite dehydroxylation reaction formed cracks to improve the liberation and
beneficiation. This phenomenon was studied for nickeliferous laterite ore to separate
serpentine, chlorite; high phosphorous iron ores to separate phosphorous (Rizov, 2012;
Michael John et al, 2012). U.S. 3730445 described the process of improving grindability of
alumina-silica ores by thermally heating to remove iron impurities at high temperatures
using calcinations process. Production of iron pigments by transformation of goethite to
hematite was studied (Rodrigo et al, 2011).

The pretreatment of coals showed significant crack formation, reduced Bond work index
and increase in specific rate of breakage due to expansion of responsive inherent moisture
and changing its phase under differential expansion of gangue phases(Lester E., 2004;
Marland S., 1998, 2000, 2001; Sahoo B. K., 2011; Ed Lester, 2005). The preferential heating
of pyrite and ash fraction of coal enhanced the magnetic susceptibility and improved the
desulphurization of coal (Fanslow G. E., 1980; Rowson, 1990).The phenomenon of a phase
silica to (3 phase silica transformation in coal slurries improved the rheological flow
characteristics and hence the separation (Meikap B. C. et al, 2005). The microwave
treatment of metallurgical coke attenuated the grinding energy up to 40% (Ruisanchez E. et
al, 2012).
The pre-treatment along with quenching of different copper ores at high electric field
strength with short exposure time showed significant reduction in ore strength and Bond
work index, increase in specific rate of breakage with improved liberation due to
differences in thermal expansion coefficient of minerals (Vorster W., 2001; Kingman S. W.,
2004; Sahyoun, 2004; Scott G., 2008; Vladimir, 2011).The influence of pre-treatment on
flotation of copper ore indicated the improvement in recovery and cumulative grade with
increasing treatment time and power (Sahyoun C., 2005). The pretreatment on Zinc and
Cu-Cobalt, Lead-zinc ores was elucidated (Antoine F. M., 2005, Kingman, S. W., 2004). This
process was used to augment the grinding of gold ore and beneficiation by gravity
concentration (Amankwah R. K., 2005, 2011). US 2003/0029944 Aldescribed the process
of facilitating recovery of copper from its ore by microwave treatment to form a plasma
and oxidation of sulfur to enhance comminution and recovery by downstream processes
such as leaching, smelting.

During thermal or microwave treatment of magnetite-quartz/jasper magnetic taconite
ores, cracks were formed due to difference in thermal expansion enhanced the magnetic
separation (Tevfik A., 2011). Pre-treatment of hematite-quartz/jasper nonmagnetic
taconite ores at high temperatures at reducing atmosphere converted the hematite to
magnetite (reduction roasting) and enhanced magnetic separation (John W. W., 1995). It
was found that first order grinding kinetics with faster specific rater of breakage was
followed for the treated ore (Javad, 2012). U.S. 3202502 described the process of
conversion of hematite to magnetite of hematite-quartz ore at high temperatures in the
presence of reducing gases (chemically active atmosphere) to improve the concentrate
yield by magnetic separation. U.S. 7476829 B2 described the process of microwave
pretreatment of multi-phase materials to weaken the bond between the phases of ores due
to differential expansion rates. The influence of pre-treatment on ilmenite ore showed that
the factors such as microwave exposure time, power density and sample mass had effect on
heating and the recovery and grade during magnetic separation was improved (Kingman
S.W., 1999, Guo Sheng-hui, 2011). The oolitic type iron ore with high phosphorus was
subjected to microwave treatment to induce internal cracks and reduced the energy of
grinding (Shaoxian Song, 2013). US 20100263483 Aldescribed the process of recovering
iron ore composed of hematite, magnetite and silica by microwave treatment and spiral
classification.
Because the constituents of ores typically have very different thermal and dielectric
properties with difference in thermal expansion coefficients so that stresses of sufficient
magnitude to create fractures can be developed differently for different composition ores.
The phase transformation of goethite phase to hematite phase will enable the beneficiation

process. From the prior art, goethite is not amenable for flotation or beneficiation due to
constraints with surface properties.
This method of heat treatment for phase transformation promoted micro crack formation
and made ore amenable for beneficiation particularly flotation. This invention focused on
low grade iron ores of goethite rich hematite ores where the beneficiation process is not
mentioned in literature. The novelty of this invention lies in the phase transformation and
beneficiation of low grade goethite rich hematite iron ores.
Objects of the Invention
It is therefore an object of the invention to propose a process of selective fragmentation of
low grade iron ores exhibiting an interlock relationship of iron minerals with gangue
minerals to liberate at a particle size less than 45microns, which can form internal
fractures and micro cracks inside the mineral-gangue phases of iron ore.
Another object of the invention is to propose a process of selective fragmentation of low
grade iron ores exhibiting an interlock relationship of iron minerals with gangue minerals
to liberate at a particle size less than 45microns, which enhances the existing cracks of iron
ores by pre-treatment process.
A still another object of the invention is to propose a process of selective fragmentation of
low grade iron ores exhibiting an interlock relationship of iron minerals with gangue
minerals to liberate at a particle size less than 45microns, which improves liberation of
iron minerals from iron ores.

A further object of the invention is to propose a process of selective fragmentation of low
grade iron ores exhibiting an interlock relationship of iron minerals with gangue minerals
to liberate at a particle size less than 45microns, which constitutes a process of thermal or
microwave pretreatment of iron ores for crack formation due to phase transformation and,
differential heating.
A. still further object of the invention is to propose a process of selective fragmentation of
low grade iron ores exhibiting an interlock relationship of iron minerals with gangue
minerals to liberate at a particle size less than 45microns, which enhances both the grade
and recovery of treated iron ore by downstream process such as flotation.
Yet further object of the invention is to propose a process of selective fragmentation of low
grade iron ores exhibiting an interlock relationship of iron minerals with gangue minerals
to liberate at a particle size less than 45microns , which is enabled to recover iron values
from low grade high alumina, high silica goethitic or hematitic iron ores.
Summary of the Invention
Accordingly, there is provided a method of selective fragmentation to improve liberation
and beneficiation of different types of low grade iron ores such as goethite rich hematite
iron ores of different compositions where goethite can be phase transformed to hematite
during pre-treatment processes such as microwave heating or thermal heating followed by
quenching. This method enhances the liberation characteristics and amenable to
beneficiation through internal fractures by pre-treatment processes.

Detailed Description of the Invention
The low grade iron ores such as goethite rich hematite iron ores with different
compositions along with alumina or silica oraluminasilicateswas used in the present
invention. These iron ores were subjected to thermal or microwave pre-treatment to
recover and liberate iron oxide minerals from gangue minerals such as aluminosilicates,
quartz, gibbsite, alumina etc.
Natural goethitic phase of iron ore associated with impurity elements such as silica or
alumina or aluminasilicates is not amenable to beneficiation processes. The goethite is
always associated with the aluminosilicates of the ore. These impurities can be separated
using gravity based beneficiation processes that separate goethite and leads to loss of iron
values. Conventional flotation of these ores is adversely affected with the presence of
goethite. In the present invention, the method of disrupting the structure of goethite and
transformation to hematite in the ore by pre-treatment has altered the physicochemical
properties and showed to be effective to remove impurities such as alumina, silica or ■
aluminasilicates by flotation.
The low grade iron ores such as goethite-hematitic iron ore, limonite ore with impurities of
kaolinite, silica, gibbsite comprises goethite minerals that are usually have water content in
the form of chemically bonded hydroxyl groups in the crystal structure. The changes in
properties of goethite are due to phase transformation to hematite because of
dehydroxylation/dehydration reaction in thermal or microwave treatment (Webb W. E. et
al, 1986). As dehydration

proceeds, the hydroxyl groups (OH) replace the oxygen ions (O2) in the hematite structure
and the hydroxyl radicals form associations with vacancies in the cation sub-lattice from
300 to 400°C (Pickles C. A., 2011).

Heterogeneous iron ore have different conductivities or dielectric properties lead to
selective heating and depend on the size of the material. In these iron ores, gangue
minerals (gibbsite, alumina silicates, quartz/jasper) are heated due to the presence of iron
oxides hematite, goethite. The pre-treatment process initially heats the iron oxides, which
subsequently heats the gangue minerals associated with them due to transfer of thermal
conduction into surrounding phases. It is revealed that chemically bonded water or
hydroxyl group of goethite is converted to vapor during transformation and cause internal
stresses within the ore matrix leads to formation of micro cracks to improve liberation and
beneficiation during thermal or microwave pre-treatment. Differential heating of different
minerals present in the ore further enhanced the breakage process and quenching of
treated iron ore with water or acid or alkali or salt solution released the internal stored
energy and append the process of cracking further. Hence, the present process of invention
enhanced the liberation and converted goethite to hematite with improved recovery in
flotation.
In the present invention, goethite rich iron ore is collected as representative sample. The
collected sample is chemically analyzed as shown in the Table 1. It is shown that the loss of
ignition (LOI) is high which represents the presence of goethite in the iron ore. This
contributed for the production of micro cracks in the ore during thermal or microwave

treatment of ore. The major minerals are iron oxides with alumina oxides and minor
minerals are silica, phosphorous. Negligible quantity of magnetite is observed with this
iron ore. The XRD analysis showed the presence of hematite, goethite as major iron bearing
minerals with gibbsite, alumina silicates as major gangue bearing minerals in the feed
sample of iron ore. XRD analysis of treated sample confirmed the conversion of goethite to
hematite and gibbsite to alumina and Fe-alumina oxides. It also revealed the association of
goethite with aluminasilicates as described in Figure 1.

Thermo gravimetric analysis of goethite rich iron ore is shown in the Figure 2. It showed
that at initial temperatures, inherent moisture of iron ore is vaporized followed by
conversion of goethite to hematite and gibbsite to alumina at temperatures below 400°C. At
high temperatures kaolinite is converted to corresponding alumina silicates during TGA
analysis. The sample is screened at different size fractions as thermal treatment is
dependent on palrticle size. Three particle size samples: +40mm, -40+10mm and -10mm
size fractions of are subjected to thermal treatment in a muffle furnace of Kanthal make.
The two factors controlled during thermal treatment are heating rate and temperature. The
sample is inserted inside the furnace and heated to200-400°C temperature for 10 - 30 min
at heating rate of 10°C/ min. Rapid quenching with water and other coolants in which ore is

dropped into this immediately after taking out from the furnace to give the constant
cooling rates. No measurable rise in temperature of the water is noticed. Excess water is
decanted and samples are dried. Quenching of treated iron ore with water or acid or alkali
or salt solution can release the internal stored energy and append the process of cracking.
The rapid quenching of high temperature treated iron ore particles produce internal
stresses with intense micro cracking result in ease of comminution and reduction of
grinding energy. This process further weakens the ore due to enhanced stresses and
reduces the boundary cohesion.
The weight of samples before and after the thermal treatment are measured and analyzed.
The weight reduction is high for higher size fractions as shown in Figure 3 and it has
advantage over conventional grinding and beneficiation.
The treated iron ore was concentrated by the process of flotation at 30% pulp density with
particular suite of chemical reagents. It was found that the grade of the sample was
enhanced from 53% to 58.5% and iron recovery was enhanced at least by 3 units due to
the conversion of goethite to hematite and improved liberation. The results of the flotation
tests for untreated and treated sample along with goethite-hematite feed sample is shown
in the Table 2.

Table 2: Flotation results of feed, untreated and treated samples of goethitie-hematite low
grade iron ore

Microwave treatment
The microwave heating set up is multimode household LG make microwave oven with
dimensions of 530 mm X 295 mm X 550 mm with an input rating of 230V and 900W
(Output power). The microwave heating system is made up of four basic components:
power supply, magnetron, applicator i.e., oven for the heating of the target material and
waveguide for transporting microwaves from the generator to the applicator. The
microwave source and wave guide is present at the right-hand side wall of the oven
cabinet. Proper insulation was provided to the stainless steel cabinet with the help of
alumina-silicate refractory bricks based on glass wool protection. The oven consists of a
radiation proof, transparent door, and an electronic programmable panel with options for
controlling the microwave power and heating duration as shown in the simplistic Figure 4
of the laboratory microwave heating system. The ore was kept inside the microwave to a
temperature of 200-400°C for 30-60sec at 0.9kW. The iron recovery was enhanced by 3
units as in thermal treatment.

We Claim is:
1. A method of selectively fragmenting and liberating iron values from low grade iron
ores, the method comprising:
Heat treating the iron ore to a temperature where goethite is phase transformed to
hematite; and quenching the heat treated low grade iron ores.
2. The method as per claim 1, wherein the heat treatment involves thermal heat
treatment.
3. The method as per claim 1, wherein the heat treatment involves microwave heat
treatment.
4. The method of claim 1, wherein the quenching is done using water or brine solution.
5. The method as claimed in claim 1, wherein the low grade iron ores comprises
goethite rich hematite low grade iron ore along with alumina or silica or
aluminasilicates as gangue bearing minerals.
6. The process as claimed in claim 1, wherein the heat treatment results in goethite
hydrous phase to release chemically bonded water molecules to water vapors.
7. The process as claimed in claim 6, wherein the release of chemically bonded water
molecules happens at a minimum temperature at which goethite phase transforms
to hematite phase.
8. The method as claimed in claim 1, wherein goethite rich hematite low grade iron ore
undergo phase transformation at a temperature in the range of 200-400°C
9. The method as claimed in claim 2, wherein the thermal treatment is conducted at a
heating rate of 5 to 10°C/min for at least 10 minutes.

10. The method as claimed in claim 3, wherein the microwave treatment is conducted at
a output power of 0.9kW for at least 30sec.
11. The method as claimed in claim 1 further comprising the step of beneficiation,
cationic reverse flotation at pH 8-10 with ether monoamine collector.
12. The process as claimed in claim 1, wherein the process results in increase of iron
recovery by at least3%.

ABSTRACT

A method of selective fragmentation to improve liberation and beneficiation of low
grade iron ores such as goethite rich hematite iron ores of different compositions
where goethite can be phase transformed to hematite during pre-treatment
processes such as microwave heating or thermal heating followed by quenching.
This method enhances the liberation characteristics and amenable to beneficiation
through internal fractures by pre-treatment processes.