FIELD OF INVENTION
The present invention relates to a metliod and an apparatus to produce stable
water-based suspension of iron ore reject slimes for industrial applications.
BACKGROUND OF THE INVENTION
In order to utilize effectively the highly rich mineral components from the
products of beneficiation of iron ore, many improvement and innovative ideas
have been developed and implemented over the years. Indian steel plants
generate large quantity of slime from the beneficiation of iron ore. Slimes are
defined as 25µm particles, and contains an inseparable part during operations of
beneficiation processes and which includes a significant amount of valuable
minerals with high value gangue as compared to RUN of Mine ore.
The disposal of slimes, being a by product of iron ore and posing a great risk of
environmental pollution, the steel producers fixed an economic exploitation of
the slimes which is enriched with high alumina (AI2O3) content and lower iron
content. Hence, the beneficiation of slime assured a top priority for reutilizing the
slime instead of allowing ever-increase of environmental hazards). Accordingly,
attempts have been made to enrich the iron (above 62%) and reduce alumina
content to the desired level (below 1.5% alumina).
Out of many techniques to enrich by treating the slimes, mention can be made of
shear flocculation, selective flocculation, carrier flotation, high gravity separators,
chemical leaching and microbial. Extensive use of dense medium cyclone can be
found in the mineral processing industry to beneficiate various mineral including
coal, diamonds and iron amongst many others. Following the same technology,
hydro cyclones have been used to beneficiate the iron ore reject slime. During
the beneficiation process of the slime, the rejects are obtained as an overflow of
the hydrocyclone. Overflow from the hydro cyclone has been analyzed and it has
been found that it still contains appreciable amount of iron and other oxides.
The further research on reject from slime has given evidence of existence of
smaller size of iron oxides, in the scale below micron size. It may be attempted
to analyze the rejects from slime to find the characteristics of the particles below
the size of micron scale. It is also necessary to disclose an application of the
smaller size particles in the form of water based suspension similar to the
concept of nanofluids.
In recent studies of practical use of nanopartides, excellent heat transfer
performance of nanofluids, produced from water or ethanol based nanopartides
have drawn the attraction of research communities. The reason of superior heat
transfer characteristics of nanofluid may be attributed to the characteristics of
nanopartides for example, (i) increased surface area and heat capacity of the
fluid, (ii) higher number of collisions and interactions amongst the fluid, particles
and the flow passage surface which enhances the heat transfer performance of
nanoflids, and (iii) higher turbulence and mixing fluctuation of the fluid.
Patent in connection with the use of nanofluid can be traced to the early work by
Choi and Eastman in their studies titled as "extended heat transfer using
nanofluids" have devised a method of and apparatus for enhancing heat transfer
in fluids such as deionized water, ethylene glycol by dispersing nanocrystalline
particles of substances such as copper, copper oxide, aluminum oxide or the like
in the field. Use of metallic nanoparticles combined with caboxylates to provide
excellent corrosion protection and improved thermal conductivity properties in
functional fluids such as lubricants and grease is known from the European
patent of Maes et al. titled as "Heat transfer fluid containing nanoparticles and
caboxylates". While most of the prior art are directed towards enhancement of
thermal conductivity of the nanofluids • prepared from commercially available
nanofluid. However, the prior art do not teach or suggest use of the naturally
available nanoparticles obtained after processing the iron ore rejects.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a stable water based
suspension of nanoparticles composite from naturally occurring water-based
minerals rejects, which exhibit longer stability.
Another object of the invention is to propose a method for forming a stable
water based suspension of nanoparticles composite from naturally occurring
water-based minerals rejects, which is enabled to increase heat transfer rate by
convection of nanoparticles suspension.
A further object of the invention is to propose an apparatus to increase in
localized heat transfer rate by convection of nanoparticles suspension by indirect
heat exchange.
SUMMARY OF INVENTION
Accordingly, there is provided a method for forming a stable water-based
suspension of nanopartides composites from naturally occurring water-based
mineral rejects, comprising:
providing a predetermined volume of water/fluid in a heating chamber of
a heat-exchanger unit having a nanofluid chamber and a heating
chamber,
providing a nanofluid suspension of aluminum oxide in the nanofluid
chamber;
Characterized in that
heating of water/fluid in the heating chamber is carried out till the heater
disposed in the heating chamber trips at a preset temperature when the
temperature of the nanofluid starts rising following the heat transfer from the
heating chamber, and wherein the increase in nanofluid temperature is being
continuously recorded by a plurality of resistance temperature detectors (RTDs)
disposed in the heating chamber including the nanofluid chamber.
According to the invention a stable water based suspension of Iron ore reject
slime has been prepared by addition of a stable dispersant. The resultant
suspension has been observed to maintain its stability for a minimum period of a
month. The suspension consists of nanoparticles of hematite, goethlte, alumina
and silica which are potential suspension to use in the field of commercial
application similar to the use of nanofluids described in several technical fields.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS.
Fig. 1 - shows a photographic view of reject slimes (an overflow from the hydro
cyclone) In as received condition.
Fig. 2 - shows a solution of reject slimes in a container after addition of a
dispersant.
Fig. 3 - shows a suspension solution of slime in a container after addition of 0.5
ml/It surfactant, having pH: 7.5 for 7 days.
Fig. 4 - shows a suspension solution of slime in a container after addition of 1
ml/It surfactant having pH: 7.5-8 for 7 days.
Fig. 5 - shows a suspension solution of slime in a container after addition of 1
ml/It surfactant, having pH: 7.5-8 for 30 days.
Fig. 6 - SEM of the particles after addition of surfactant.
Fig. 7 - shows XRD patterns of (A) starting material (B) without surfactant (C)
For 7 days with surfactant, (D) after 15 days with surfactant.
Fig. 8 (a) shows an apparatus for enhancement of heat transfer performance of
nanofluid according to the invention.
Fig. 8 (b) Top and bottom plates of chambers of the apparatus of Figs.8(a).
Fig. 9 : Comparison of performance of Water and nanofluid from the
experiment in RTDs 1 to 6.
Fig. 10: Comparison of performance of Water and nanofluid from the
experiment in RTDs 7 to 12.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The present invention discloses a method of preparation of a stable water based
suspension of goethite -nanocomposites. The present invention further discloses
an apparatus for improvement/enhancement of heat transfer performance by
natural convection of nanofluid. According to the invention, nanofluid contained
in an enclosure of square cross section of an apparatus is heated from one
vertical side and the effectiveness of the nanofluid from nanocomposites of
ghoethite is experimentally observed. Thereafter, a comparison has been made
with the heat transfer capability of water used in the same apparatus. Fig. 1
shows the water based suspension solution of nanocomposites. A measured
quantity of dispersing chemical (composite polyacrylate) is added to the solution.
It has been found that the settled particles inside the containers have started
rising and form a suspension. It has been observed that the particles are
continuing to disperse for more than 15 days as shown in Fig. 2.
As can be seen from Fig.-3, the density and stability of dispersion depends on
the quantity dispersing chemical. Figure-4 shows that the homogenous
suspensions are capable to maintain stability for several days.
In order to characterize the constituents of the particles, the same suspension
was treated with HCI and the sedimentation of composite materials is found at
the base of the containers. The XRD and SEM image of the nanocomposite are
depicted in Fig.5 and Fig.6 respectively. For the operational purpose, the
concentration in different amount has been used.
The apparatus (A) as shown in Fig. 8(a), a heat exchanger unit (H), consisting of
two chambers (1,2), a first chamber (1) containing a heating mechanism (4) and
a second chamber (2) where the instability of flow due to natural convection of
having nanofluid has the potential to cause the enhancement of heat transfer.
The steps involved are:
• Forming a nanofluid
• Sidewall heating of the chamber containing nanofluid by indirect method.
The second chamber (2) adjacent to the heating chamber (1), is separated by a
copper plate (3) for exchanging the heat using a nanofluid. A heater (4) has
been placed at a distance away from the adjoining surfaces of the chamber (1)
such that the heater (4) does not touch the surface of the apparatus. One
Resistance Temperature Detector (RTD) passing through the top cover (la) of
the heating chamber (1) touches the free top surface of the liquid/water.
Another RTD is inserted through the bottom surface 1(b) of the heating chamber
(1).
The square cavity chamber (2) containing nanofluid is provided with eleven
numbers of Resistance Temperature Detectors (RTDs) with the capability of
measuring temperature up to 150 degree Celsius. Nine RTDs (RTDl,
RTD2...RTD9) pass through the top cover (2a) of the nanofluid chamber (2) to
dip near the free surface of the chamber. There are two RTDs (RTD 10 and
RTDU) placed at the bottom surface 2(b) of the nanofluid chamber (2) that
protrude through the bottom surface (2b). A data logger records the
temperature of all RTDs apart from six digital displays with the provision of
display of the temperature of all the RTDs (not shown). A controller with a relay
for the cut off of the heater (4) beyond a set value of 50 degree Celsius is
connected along with the temperature of water in the hot chamber (1) during
the heating with a tolerance limit of +/-0.5°C. The heater trips once the water
temperature reaches 50.5 degree. Following which the water temperature starts
drooping and again it restarts at a temperature of 49.5 degree Celsius. The relay
for the cut-off value operates based on the temperature recorded by the RTD
(RTD6) located at the top cover surface 1(a) of the hot chamber (1). One motor
with a regulator (5) operating a mechanical stirrer (6) along is installed through
the centre (9) of the top covers (la, 2a) of each chamber (1,2) for stirring the
fluid inside the hot chamber (1) for better mixing during heating. As shown in
Fig. 8(b) any fluid can be poured inside through a hole (7) provided with cover
located at the top cover (la, 2a) of each chamber (1,2). A drain with a valve (8)
at the bottom (lb, 2b) of each chambers (1,2) allows the easy draining of any
liquid inside the chamber. Proper insulation around an open outer surface of
each chamber (1,2) ensures the minimization of the heat loss.
The experiment has been performed according to the following sequence. A
volume of 2.5 liter of water/fluid in heating chamber was heated to a
temperature of 50 degree following which the heater trips. A nanofluid
suspension of nanocomposites along with h with the dispersant has been
prepared and added to the cooling chamber (2). The volume of nanofluid added
is the same as that of the water in the heating chamber (1). The temperature of
nanofluid, added at room temperature, starts rising following the heat transfer
from the heating chamber (1). The cyclic operation of heater (4) tripping and the
same due to the relay operation was possible when the temperature of water in
hot chamber (1) is kept in an average temperature of 50 degree Celsius. The
continuous increase of nanofluid temperature is manifested by the recordings of
the RTDs. The corresponding on-line record of RTDs in continuous manner is
first passed to the data logger which is later on fed to a computer. In normal
case, the stable nanofluid in hot chamber (1) is replaced by water for testing, or
standard results of heat exchange for the case of water. The same test
performed by using water in both chambers (1,2).
As can be observed from the comparison of the temperature profiles of different
RTDS used during the experiment with nanofluid suspension and with water,
depicted Fig. 8 and Fig, 9, the higher heat transfer capability for nanofluid
compared to normal water is noted. It is also noted that RTDl, RTD2, .RTD5 are
showing better value for the stable nanofluid compared to the case when water
was used. RTDl to RTDS are at a distance from the intervening copper plate (3)
located in the border of two enclosures (1,2), while RTD 7 to RTD 9 are close to
the copper plate (3). RTD 10 and RTD 11 are at the bottom surface (2b) of
nanofluid chamber (2). RTD 12 is the RTD on the intermediate plate (3). Hence,
for comparison purpose, the value of temperatures recorded by RTDl to RTD 5
is more important.
The suspension of the iron reject slimes was measured for particle size using an
applicable and known instrument. Particles sizes are found to be below 60 nm for
60 % of total population whereas the 70 % of the total particles lie below 75 nm.
The method steps involved are :
• The separation of the suspension from the overflow of iron ore rejects
slime in the cyclone.
• Addition of the dispersant with the suspension.
• Forming a stable nanofluid from the nanocomposites.
• Characterization of the nanocomposites.
• Experimental test to verify the heat transfer capability during the natural
convection. For the operational purpose, the concentration in different amount
has been used.
References:
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«
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We claim:
1. A method for forming a stable water-based suspension of nanopartides
composites from naturally occurring water-based mineral rejects, the method
comprising:
providing a predetermined volume of water/fluid in a heating chamber (1)
of a heat-exchanger unit having a nanofluid chamber (2) and the heating
chamber (1),
providing a nanofluid suspension of aluminum oxide in the nanofluid
chamber (2);
Characterized in that,
heating of water/fluid in the heating chamber (1) is carried out till the heater (6)
disposed in the heating chamber (1) trips at a preset temperature when the
temperature of the nanofluid starts rising following the heat transfer from the
heating chamber (1), and wherein the increase in nanofluid temperature is being
continuously recorded by a plurality of resistance temperature detectors (RTDs)
disposed in the heating chamber (1) including the nanofluid chamber (2).
2. A method as claimed in claim 1, wherein the iron ore reject slime is
collected from the overflow of cyclone in a benefication process, wherein a
solution of the iron ore reject slime is mixed with water to produce a suspension,
and wherein the upper portion of the suspension is used so as to have a clear
suspension containing finer particles.
3. A method as claimed in claim 1 or 2, wherein the remaining portion of the
suspension is added with a dispersant to form a stable suspension.
4. A method as claimed in claims 1 to 3, wherein the suspension of
nanocomposites is enabled to maintain its stability for about three weeks at a
stretch.
5. A method as claimed in claims 1 to 4, wherein the preferred nanofluid can
be stored at room temperature.
6. A method as claimed in claim 1 to 5, wherein the produced nanofluid can
be treated to obtain dry nanocomposites .
7. A method as claimed in claim 1, wherein the nanocomposite is
characterized to obtain its particle size in the range of nanometer to confirm that
the composite constitutes nanoparticles.
8. A method as claimed in claims 1 to 7, wherein the nanocomposite is
characterized to obtain its particle size by XRD to determine the chemical
composition of the particles, and wherein the chemical composition of the
particles exhibits a combination of Geothite, Alumina and silica in the composite.
9. A method as claimed in claims 1 to 8, wherein the nanocomposites is
characterized by SEM to find the size of the nanoparticles.

A method for forming a stable water-based suspension of nanoparticies
composites from naturally occurring water-based mineral rejects, the method
comprising providing a predetermined volume of water/fluid in a heating
chamber (1) of a heat-exchanger unit having a nanofluid chamber (2) and the
heating chamber (1), providing a nanofluid suspension of aluminum oxide in the
nanofluid chamber (2); characterized in that, heating of water/fluid in the
heating chamber (1) is carried out till the heater (6) disposed in the heating
chamber (1) trips at a preset temperature when the temperature of the nanofluid
starts rising following the heat transfer from the heating chamber (1), and
wherein the increase in nanofluid temperature is being continuously recorded by
a plurality of resistance temperature detectors (RTDs) disposed in the heating
chamber (1) including the nanofluid chamber (2).