Claims:We Claim:

1. A method for beneficiation of fly ash by reducingits unburned carbon content comprising of:

subjecting the fly ash to a first stage beneficiation of fly ash involving hydroclyclone for initial separation of the fly ash content between an overflow content containing majority of fine particles based thus beneficiated fly ash carrying low level of acceptable carbon of upto5.12% and an underflow content containing majority of coarser particle of the fly ash carrying higher level of carbon of beyond 19.85%; and
thereafter subjecting the hydroclone underflow content still carrying fly ash with higher level of carbon beyond 19.85% to a second stage beneficiation of said hydrocylone underflow fly ash involving froth floatationbased separation process to thereby further spate as float further beneficiated fly ash with reduced acceptable carbon content of upto 2.26% and a sink having fly ash with higher carbon content of beyond 45.38%.

2. The method as claimed in claim 1 comprising :

separation of fine and coarse fraction in hydrocyclone with having 19.85% in coarse fraction and 5.12% carbon in fine fraction achieved from feed 11.87% carbon.

separation of carbon rich (45.38% of carbon) and carbon reduced (2.26% of carbon) products were obtained by the flotation process from feed 19.85% of carbon.

3.. The method as claimed in anyone of claims 1 or 2 , wherein said first stage of beneficiation of fly ash in hydroclyclone include step of the separation of fine and coarse fraction at process parameters including 5-inch cyclone diameter, 2 bar feed pressure (in the range of 1.8 to 2 bar), 45 mm spigot diameter (in the range of 40 to 45 mm) and 25mm vertex finder diameter ( in the range of 20 to 25mm).

4. The method as claimed in any of the claims 1 to 3, whereinsecond stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process for desired separation of carbon rich and carbon reduced products by froth flotation involving process parameters including 750 gm/ton of collector (in the range of 740 to 760 gm/ton), 200gm/ton of frother (in the range of 190 to 210 gm/ton), 3 min of conditioning time, 2 min of frothing time ( in the range of 2 to 2.5 min) and 5 min of froth collection time ( in the range of 4 to 6 min).

5. The method as claimed in any of the claims 1 to 4, whereinsaid second stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process is carried out including diesel as collector.

6. The method as claimed in any of the claims 1 to 4, whereinsaid second stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process is carried out such as for generating carbon reducing product with 81.31% by weight with having 4.17% of carbon and 18.69% of weight with having 45.38% of carbon from 11.87% of carbon fly ash with using hydrocyclone.

7. The method as claimed in any of the claims 1 to 6, for enabling beneficiation of fly ash by carrying out controlled reducing of fly ash carbon content whereby the reduced carbon is around 64.86%.

8. The method as claimed in anyone of claims 1 to 7 wherein said

first stage beneficiation of fly ash involving hydroclyclone for initial separation of the fly ash content as the overflow content containing majority of fine particles based thus beneficiated fly ash carrying low level of acceptable carbon of upto5.12% and said second stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation processgenerating said floatation float further beneficiated fly ash with reduced acceptable carbon content of upto 2.26% together provide for beneficiated reduced carbon containing fly ash.

9. The method as claimed in anyone of claims 1 to 7 wherein particle size distribution of feed fly ash ranges from 90 to 95% of 150 micron passing and wherein the operating specifications of the said first stage of hydrocyclone include :

Hydrocyclone size is 5 inch;
Vortex finder diameter in the range of 25 to 30 mm;
Spigot diameter in the range of 40 to 45 mm;
Feed pressure in the range of 1.8 to 2 bar; and
Slurry feed density in the range of 1.2 to 1.25 gm/cc;

and
the operating specifications in the said second stage of froth floatation include:

Collector dosage rate (Diesel) : 740 to 760 gm/ton;
Frother dosage rate : 190 to 210 gm/ton;
Conditioning time 3 min;
Percentage of solids : 15 to 18%
Frothing time : 2 to 2.5 minutes;
Froth collection time : 4 to 6 minutes;
Stirrer speed: 900 to 1000 rpm.

Dated this the 30th day of July, 2021
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199

, Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
A PROCESS FOR BENEFICIATION OF FLY ASH BY REDUCING ITS UNBURNED CARBON CONTENT.


2 APPLICANT (S)

Name : JSW STEEL LIMITED.

Nationality : An Indian Company incorporated under the Companies Act, 1956.

Address : JSW CENTRE,
BANDRA KURLA COMPLEX,
BANDRA(EAST),
MUMBAI-400051,
MAHARASHTRA,INDIA.



3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:

The present invention relates tothe beneficiation of fly ash for reducing the carbon content which are present in the flyash as unburnt form. The fly ash contains 11.87% of carbon.More specifically, the invention is related to beneficiation of fly ash using two stage beneficiation processto produce carbon reduced product and also produce enriched carbon concentrate with reduced alumina and silica. In order to reduce the maximumcarbon bearing mineral, a two stage beneficiation process i.e., classification and froth flotation process has been developed. The carbon reduced product can be used in cement making as a raw material.

BACKGROUND OF THE INVENTION:

Thermal power plants are the main source of power generation.The coal fired power plants produces fly ash in very large volumes as waste product. Fly ash is a coal combustion residue (CCR) is a complex heterogeneous material. Because of the poor combustion efficiency of the combustors lack of proper quality control in maintaining the particle size of the coal feed. The fly ash has a wide distribution of char, semi-coke or coked carbon. It is irregularly in shape, containing lacy, vesicular, alumino-siliceous matter of complex composition and fine solid or hollow alumino-siliceous spheres.
At high temperatures and pressures in power stations the combustion of pulverized coal produces different types of ash based on the different methods of fly ash transfer. The fly ash (fine fraction) is carried upwards with the flue gases and captured before reaching the atmosphere by electro-static precipitators. This material is called as ‘FLY ASH’ or ‘Pulverized Fuel Ash’ (PFA). It is mainly composed of glassy spheres and extreme fine in size. Fly ash particles are spherical in shape allowing them to flow and blend freely in mixtures. This is one of the properties making fly ash a desirable admixture for concrete. Industrial utilization of fly ash from coal combustion is an important environmental and economic issue. Disposal of fly ash, e.g. in a landfill enhances the risk of contaminating the ground water by leaching of heavy metals contained in the fly ash. Today, the primary market for fly ash utilization is as pozzolanic additive in the production of concrete. The fly ash utilization in concrete affects the required dosage of AEAs (Air Entraining Admixtures) to entrain the required amount of air in the concrete mixture. The AEAs are strongly absorbed by the carbon content present in fly ash. Due to this reason the high unburned carbon particles present in fly ash makes it unsuitable for use as a cement admixture. As part of a concrete mix when fly ash is used the maximum concentration of unburned carbon in the concrete mix should be less than 6%.
Fly ash particles are very fine, density (1.94-2.90 g/cc) (lightweight), specific surface area (3500-10000 cm²/g), diameter (1-150µ), spherical in shape and have pozzolanic ability. Fly ash is dependent upon the type of the coal and also type of the combustion process. It has (dielectric constant -104) dielectric property which can be used in an electronic application.

Thermal power plant uses non coking / steam coal as raw material for power generation.The fly ash generated as a waste from the power plant has higher amount of carbon which is unburnt carbon resulting in rejection by cement manufacturers where fly ash is an ingredient. The fly ash is used in cement making as raw material. However, the presence of carbon in the fly ash adversely effect in the process of cement making and the quality. The removal of carbon from the flyash using suitable beneficiation process and results better utilization of fly ash in cement making. In characterization studies it was found that, the fly ash contains Carbon, calcium, silica and iron in the form of unburnt carbon, calcium oxide, quartzite and wustite respectively. Obtained carbon rich product from the beneficiation process may be used as a raw material for thermal power plant and carbon reduced product can be used as raw material for cement making. The particle size distribution of flyash sample is shown in Table 1 and chemical analysis given in Table 2. The fly ash sample contains higher percentage of ultra-fine particles, i.e., more than 40% of -10 micron size particles wherein 100% particles are less than 200 micron in size (Table 1).

Table 1:Particle size distribution of feed sample
Particle size, microns -10 -25 -45 -63 -75 -150 -200
Weight,% 41.78 53.34 65.34 78.67 83.02 95.79 100

Table 2:Chemical analysis feed sample, wt%
VM CARBON SULFUR SiO2 Al2O3 Fe CaO MgO
2.21 11.87 0.075 45.09 26.45 7.8 2.85 1.36

Beneficiation of fly ash has been investigated by several researchers and the gist of this findings are given below.

US patent No. 4121945,dated16thApril,1976 by HURST VERNON Jet.al,this patent is all about the beneficiation process of fly ash.In this patent he developed a beneficiation process for producing a carbon concentrate, cenospheres, an iron concentrate, an enhanced pozzolan and an inert mineral filler. The raw fly ash contains 0.5 – 10% carbon, 35 – 55% SiO2, 3 – 25% Fe2O3 and 15 – 35 Al2O3 having size less than 350 microns. The wet beneficiation process comprisesof water mixing, froth flotation, magnetic separation and grindding, resulting concentrate with having less than 1% Carbon. And the process mainly focused on increasing the pozzolan properties fo fly ash by usinng beneficiation techniques and adding lime etc.
US patent No. 3,533,819 issued Oct. 13, 1970 by Pennachetti et al, certain processes were applied to fly ash in an attempt to provide useful fractions therefrom. The fly ash was handled in its dry state and was air classified to separate the finer fraction from the coarser fraction, and the finer fraction was then used as a pozzolan to replace Portland cement. Magnetic separation was applied to remove a magnetic fraction and to form an iron concentrate product and the coarse fraction was screened to obtain a coarse carbon product. However, in the Pennachetti et al patent, a major portion, if not all, of the original carbon content by percentage was allowed to remain in the pozzolan material, and nothing further was done to the pozzolan material to improve or enhance it.
US patent No. 2,987,408 issued June 6, 1961by Minnick et al,this patent invention claims an Magnetic separation of whole fly ash to provide a non-magnetic fly ash fraction for use as a pozzolan.

EP patent No. 310539 issued April 13th 1989 by KAUTZ, et al, describes the method of processing fly ash from incineration plants is characterised in that the ashes are successively subjected to multiple stages of the following separation procedures in some slelected sequence depending on their origin and composition. The proecsses are flotation, separation in a hydrocyclone, wet and/or drymagnetic separation, air classification, wet and/or dry sieving, sink/float separation. after which, ifdesired, a dehydration, a thickening and a drying takes place. The device for carrying out the method comprises a combination of different separating devices connectable one behind the other in any sequence.

US patent No. 4652433A, dated 24March’1987 by ASHWORTH ROBERT Aet.al. invented a novel comprehensive process for maximizing recovery of valubles such as cenospheres (hollow microspheres), carbon, magnetite (Fe3O4), alumina (Al2O3), iron oxide (Fe2O3) and iron chloride (FeCl3) may be produced. The developed benficiation process used many number of process equipmnets with different cicrcuits. It includes multiple stages of beneficiation process such as screening, froth flotation, wet magnetic separation, dry magnetic separation and acid leaching. The sequence of process is different and the process does not having the hydrocyclone.

Europinpatent No.0EP0355386A2, dated 28thFebruary,1990;this patent invention claims an fly ash beneficiation method for separate cenospheres with the use of froth flotation process. According to the invention, the cenospheric components are first separated before the fly ash is further processed by flotation for the purpose of separating the carbon-containing components. It is mentioned possiblities to use the flotation processes for the separation of the cenospheres,especially pneumatic flotation, in which no agitators are used, but rather floating with the help of small airbubbles that are generated in so-called gassing reactors.
US patent No. US5047145A dated 10thSeptember,1991;Awet process has been developed for the beneficiation of a fly ash has involved gravity separation, froth flotation process and magnetic separation process. The claims are forming a slurry mixture, separating magnetic fraction from the slurry by subjecting the slurry to a magnetic field of about 300 gauss toabout 10 kilogauss. The froth flotation process claims using fuel oil at a dosage of 1.32 g as a collector and Dowfroth 250 (0.31 g) as frother to performing a froth flotation to recovery carbon from fly ash.

US patent No. 10968137B1, dated 06th April 2021 by GUYNN JOHN M et.al;The invention discloses a beneficiation method for converting a non-conforming fly ash into conforming fly ash, which comprises the following steps that are one or two stage air classifeir for produce at least two seaprate flys as streams including fine fly ash and coarse fly ash, adding sulfate sources for compensate for sulfate deficiency, addion of lime in to the fine fly ash and blending the fine fly ash with an aluminosilicate source to increases the SAF etc.

OBJECTS OF INVENTION:

The basic object of the present invention is directed to provide a novel benefication process for reducing carbon content from fly ash generated from the thermal plant.

Another main objective is to increase the waste utilization of fly ash for production of cement.

A further object of the invention is directed to obtain a product having less than 4.5% of carbon and another product with having more than 40% carbon.

SUMMARY OF THE INVENTION:

The basic aspect of the present invention is directed to a method for beneficiation of fly ash by reducing its unburned carbon content comprising of:

subjecting the fly ash to a first stage beneficiation of fly ash involving hydroclyclone for initial separation of the fly ash content between an overflow content containing majority of fine particles based thus beneficiated fly ash carrying low level of acceptable carbon of upto 5.12% and an underflow content containing majority of coarser particle of the fly ash carrying higher level of carbon of beyond 19.85%; and
thereafter subjecting the hydroclone underflow content still carrying fly ash with higher level of carbon beyond 19.85% to a second stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process to thereby further separate as float further beneficiated fly ash with reduced acceptable carbon content of upto 2.26% and a sink having fly ash with higher carbon content of beyond 45.38%.

A further aspect of the present invention is directed to said method comprising:

separation of fine and coarse fraction in hydrocyclone with having 19.85% in coarse fraction and 5.12% carbon in fine fraction achieved from feed 11.87% carbon.

separation of carbon rich (45.38% of carbon) and carbon reduced (2.26% of carbon) products were obtained by the flotation process from feed 19.85% of carbon.

A still further aspect of the present invention is directed to said method, wherein said first stage of beneficiation of fly ask in hydroclyclone include step of the separation of fine and coarse fraction at process parameters including 5-inch cyclone diameter, 2 bar feed pressure (in the range of 1.8 to 2 bar), 45 mm spigot diameter (in the range of 40 to 45 mm) and 25mm vertex finder diameter ( in the range of 20 to 25mm).

A still further aspect of the present invention is directed to said method, whereinsecond stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process for desired separation of carbon rich and carbon reduced products by froth flotation involving process parameters including 750 gm/ton of collector (range can be 740 gm/ton to 760 gm/ton), 200gm/ton of frother (range can be maintained 190 gm/ton to 210 gm/ton), 3 min of conditioning time, 2 min of frothing time and 5 min of froth collection time.

A still further aspect of the present invention is directed to said method, whereinsaid second stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process is carried out including diesel as collector.

Another aspect of the present invention is directed to said method, whereinsaid second stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process is carried out such as for generating carbon reducing product with 81.31% by weight with having 4.17% of carbon and 18.69% of weight with having 45.38% of carbon from 11.87% of carbon fly ash with using hydrocyclone.

Yet another aspect of the present invention is directed to said method, for enabling beneficiation of fly ash by carrying out controlled reducing of fly ash carbon content whereby the reduced carbon is around 64.86%.

A still further aspect of the present invention is directed to said method wherein said

first stage beneficiation of fly ask involving hydroclyclone for initial separation of the fly ash content as the overflow content containing majority of fine particles based thus beneficiated fly ash carrying low level of acceptable carbon of upto 5.12% and said second stage beneficiation of said hydrocylone underflow fly ash involving froth floatation based separation process generating said floatation float further beneficiated fly ash with reduced acceptable carbon content of upto2.26% together provide for beneficiated reduced carbon containing fly ash.

A still further aspect of the present invention is directed to said method wherein particle size distribution of feed fly ash ranges from 90 to 95% of 150micron passing and wherein the operating specifications of the said first stage of hydrocyclone include :

Hydrocyclone size is 5 inch,
Vortex finder diameter in the range of 20 to 25 mm;
Spigot diameter in the range of 40 to 45 mm;
Feed pressure in the range of 1.8 to 2 bar; and
Slurry feed density in the range of 1.2 to 1.25.

And
the operating specifications in the said second stage of froth floation include:

Collector dosage rate (Diesel) : 740 to 760 gm/ton;
Frother dosage rate : 190 to 210 gm/ton;
Conditioning time 3 min;
Percentage of solids : 15 to 18%
Frothing time : 2 to 2.5 minutes;

Froth collection time : 4 to 6 minutes;
Stirrer speed: .900 to 1000 rpm.

The above and other objects and advantages of the present invention is described hereunder in details with reference to the following accompanying non limiting illustrative drawing.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING:
Figure 1:shows the flow chart for two stage beneficiation process for separation of carbon from fly ash according to present invention.

DETAILED DESCRIPTION OF THE INVENTION:
The purpose of the present invention is separation of unburned carbon from fly ash to obtain high quality fly ash for applications of concrete. An another incentive for a well-established separation technology is that to efficiently utilize fly ash. By separation of individually functional components, fly ash is converted from a completely waste material into various high value-added products.

Fly ash beneficiation is the process of separation of carbon particles from the fly ash. Most of the fly ash uses in cement making as raw material. Higher carbon levels lead to poor air entrainment, discoloration and segregation of mix components. Beneficiation is required to enhance the ability to extract carbon from the ash for the production of cement and other value added products. Beneficiation technique is based on the differences in density, size, electrostatic andphysical properties. Recycling back of unburned organic fractions to the burner as a fuel or can be used as a catalyst, activated carbon. The inorganic fraction which is reduced carbon can be utilized as a cement additive.
The fly ash generated from thermal power plant contains 11.87% of carbon with ultra-fines of -10micron size.Fly ash contains iron as wustaite, silica as a quartzite and calcium as calcium oxide phases. The density of the carbon is around 08 to 1.1 gm/cc. The densities of all other phases (iron, alumina, silica and calcium) are in the range of 2.2 to 4.8 gm/cc. The carbon separation from the fly ash is possible through classification and froth floatation process based on the density and particle size difference between carbon and other minerals. To reduce the maximumcarbon content from the fly ash, a two stage beneficiation process have been developed by using classification andfroth flotation based on the characterization of the samples. Hydro cyclone was used as a classification for 1st stage to remove fineswhich is having low high carbon bearing material and less inother minerals (Iron, calcium, silica & alumina) content. Flotation cell was used as a froth flotation process at 2nd stage to increase the reduction of carbon from the hydrocyclone underflow product.
A two-stage beneficiation process studies have been carried out using Hydro cyclone and froth flotation cell. Size analysis and chemical analysis of the fly ash sample which are used for the experiments are shown in table 1 and Table 2 respectively. The developed process flow diagram for the fly ash beneficiation is shown in Figure 1.The fly ash sample treated in first stage with using hydrocyclone(5 inch) by maintaining optimized parameters which are shown in Table 3. Obtained over flow (O/F) material from the first stage hydrocyclone was declared as carbon reduced product because it contains less carbon (5.12%).The hydrocyclone under flow (U/F) was fed to froth flotation cell (2nd stage) by maintain parameters which is shown in Table 4. Obtained sink product from the froth floatation was considered as carbon rich product due to having more carbon (45.38%) percentage. Obtained froth product from the froth flotation process is mixed with the first stage (hydrocyclone) overflow and considered both together as carbon reduced product due to low carbon (4.17%) content.

The present invention relates to a method of separating carbon minerals from fly ash using physical separation techniques. For decades various researchers have investigated means for extraction of minerals and elements from fly ash. Some techniques have been promulgated to initiate new business opportunities while others are due solely to environmental concerns associated with landfill disposal of certain coal ashes. Most of the state-of-the-art processes have concentrated on the recovery of one or perhaps two minerals or elements from fly ash either using physical separation techniques or chemical separation techniques, but rarely combining the two. It would thus be extremely advantageous to provide a method for the economic recovery of mineral values from coal ash. The present invention incorporates both physical and chemical separation techniques, maximizing saleable products and minimizing energy consumption and waste streams to yield an economically and environmentally attractive minerals recovery process.
According to the characterization study on fly ash sample, it has been found that the major mineral components in fly ash are iron oxides, silicates, low-density silicates and unburned carbon. These particulate mineral materials after various treatments can be used as raw material in cement making process and carbon rich product can be used as recycle to thermal power plant along with coal.
The carbon separation from the fly ash is possible through classification and froth floation process based on the density difference between carbon and other minerals. To reduce the maximum carbon content from the fly ash, a two stage beneficiation process have been developed by using classification and froth flotation based on the characterization of the samples. Hydro cyclone was used as a classification for 1st stage to remove slimes which is having high carbon bearing material and less in other minerals (Iron, calcium, silica & alumina) content. Flotation cell was used as a froth flotation process at 2nd stage to increase the reduction of carbon from the hydrocyclone underflow product.
A two-stage beneficiation process studies have been carried out under the present invention using Hydro cyclone and froth flotation cell. The fly ash sample treated in first stage with using hydrocyclone (5 inch) by maintaining parameters which are shown in Table 3. Obtained over flow (O/F) material from the first stage hydrocyclone was declared as carbon reduced product because it contains less carbon (5.12%) bearing minerals and rich in other minerals. The hydrocyclone under flow (U/F) was fed to 2nd stage froth flotation cell by maintaining parameters which is shown in following Table 3.
Table 3: Opimized process parameters of two stages (Hydrocyclone and froth flotation)

Hydrocyclone Froth flotation
Parameters Specification Parameters Specification
Hydrocyclone size 5 inch Collector dosage rate (Diesel) 750 gram/ton
Vortex Finder diameter 25 mm Frother dosage rate 200 gram/ton
Spigot diameter 45 mm Conditioning time 3 minutes
Feed pressure 2 bar Percentage of solids 15%
Slurry feed density 1.2 gm/cc Frothing time 2 minutes
Froth collection time 5 minutes
Stirrer speed 1000 rpm

In many engineering disciplines, hydrocyclones are effectively used as a dynamic particle separation unit based on their size differences only. This is a continuously operating device, which utilizes centrifugal force to enhance the relative settling velocity differentials between the particles. The primary objective of this research was to study the effectiveness of a classifying hydrocyclone to produce graded fly ash particles. To do this the principal challenge was on the optimization of the process and the design variables to generate graded fly ash particles of various size ranges.
The test was conducted on fly ash samples using a laboratory scale 5 inch diameter Tegahydrocyclone made of polyurethane fitted in a closed circuit test rig. To transport the slurry (mixture of water and fly ash particles) continuously from bottom of the tank to feed inlet of the cyclone a centrifugal pump was used. Slurry feed rate to the separator and the pressure at the inlet was adjusted by using the by-pass valve (gate valve). A representative sample were collected at underflow and overflow for each experiment. The collected samples were then mixed thoroughly and representative samples of each were sampled out using the conventional coning and quartering method and analyzed its chemical analysis by following standard methods. The respective weights of slurry collected through each outlet i.e. overflow and underflow were recorded for further analyses. The same procedure was followed in all the experiments. The optimum results were given in Table 4 and optimum process parameters are mentioned in table 3.
Table 4:Weight and chemical details of hydrocyclone products
wt% Carbon
Feed 100 11.87
Under flow (coarse) 45.83 19.85
Over flow (Fines) 54.17 5.12

The obtained underflow contains most of the coarse particles and overflow contains majority of fine particles, the size distribution of both products are shown in table 5.

Table 5:Particle size distribution of hydrocyclone products
Particle size, microns U/F (Coarse) O/F (Fines)
-350+210 3.24 0
-210+150 12.97 0
-150+75 17.76 0
-75+63 7.02 0.06
-63+45 14.55 1.32
-45+32 11.20 4.67
-32+25 8.90 5.45
-25+10 11.61 37.87
-10+2 9.45 40.6
-2 3.29 10.03

The optimum results, under flow having 45.83% weight with 19.85% carbon achieved and the overflow 54.17% weight with 5.12% carbon was achieved at optimum process parameters such as 2 bar feed pressure, 45 mm spigot diameter and 25mm vertex finder diameter.

The obtained underflow material from the first stage of hydrocyclone subjected to froth flotation process as a second stage for further reduction of carbon. Froth flotation process is a widely used separation technique in beneficiation. In the slurry of solid and water, physico-chemical processes take place at the interface of solid, liquid and gas phases during the process of froth flotation. A collector (chemical reagent) selectively coats the surfaces of certain mineral particles causing the surface of one or more of the components in the slurry to become hydrophobic and responsive to the attachment of air bubbles introduced into the slurry. Separation is accomplished as the mineral- air bubbles rise to the surface in a froth which flows over a weir, leaving in the slurry particles that are not coated with the collector. These pass out the bottom of the cell. Under proper conditions, almost all materials can be made to float. Success depends on the capability to control the surface chemistry to yield selective adsorption of collectors. A second reagent, known as a frother is used to stabilize the air bubbles upon which the floatable minerals become attached.
However, oxidized coal is notoriously difficult to float, and because of the probable similarity of the oxidized carbon surfaces in coal and fly ash, flotation of fly ash carbon is probably no easier. In either case the flotation of a partially oxidized carbon or coal particle requires making the surface of the particle more hydrophobic through adsorption of a flotation reagent or collector.Flotation tests were conducted with a Denver laboratory flotation cell having a total volume of 1250 cm3. To prepare for a test, the cell was filled with approximately 1000 cm3 of water and while the agitator was operated at 1000 rpm, a measured quantity of fly ash was introduced. The pulp was subsequently conditioned for 3 min. while using the same agitator speed and with the air valve closed. During this time the collector (diesel) was added around 750g/ton was then added to the flotation cell, and the pulp was conditioned for 3 min. using the same agitator speed and with the air valve closed. At this point 200gm/ton of the MIBC was introduced directly into the pulp and conditioning was continued for an additional 2 min. The air valve was then opened, which generated froth, and flotation was continued for 5 min. During this time the froth that collected on the surface of the pulp was scraped at frequent intervals into a collection pan. Also, the walls of the cell above the pulp level were sprayed with water as needed to prevent a buildup of carbon particles and to maintain the pulp level more or less constant. At the end of the flotation, the air valve was closed to interrupt flotation. Then, the pulp remaining in the cell was removed and considered as sink product. The floated and sink product from each test was dried, weighed and prepared samples for analysis.

Obtained 40.79% weight with 45.38% of carbon as sink product and obtained 59.21% weight with 2.6% carbon as a froth product at optimised conditions such as 750 gm/ton of collector(diesel), 200gm/ton of frother, 3 min of conditioning time, 2 min of frothing time and 5 min of froth collection time. The results obtained from optimised conditions are given in table 6.

Table 6:Weight and chemical details of froth flotation products

Wt.% C %
Feed (hydrocyclone under flow) 100 19.85
Sink 40.79 45.38
Float 59.21 2.26

A good separation of unburned carbon from fly ash was achieved with two stage beneficiation process using with hydrocyclone and flotation process. In first stage (hydrocyclone) separation was obtained as coarse and fine fraction contains 19.85% and 5.12% carbon respectively. The coarse fraction obtained from hydrocyclone subjected to flotation as second stage. Two products were obtained as float and sink having 2.6 and 45.38% carbon respectively. The froth product obtained from froth flotation cell was considered as carbon rich productdue to having high carbon (45.38%).The sink obtained from the froth flotation cell was considered as carbon reduced product due to having very less carbon content (2.26%) which can be suitable for cement making together with hydrocyclone overflow. Overflow product obtained from hydrocyclone and float product obtained from the flotation process both were mixed together and considered as a carbon reduced product which is having 81.33% of weight with 4.17% of carbon which can be used in cement making as a raw material. Obtained sink product from the flotation process wasconsidered as final carbon rich product which is having 18.69% eight with 45.38% carbon. The details optimised process results are given in Table 7 and complete optimised developed process flow sheet is shown in accompanying Figure 1.

Table 7:Weight and chemical details of overall developed process

Specification Product description Weight, % Carbon%
Feed 100 11.87
Hydrocyclone Over flow (fine product) 54.17 5.12
Froth flotation Froth (float product) 27.16 2.26
Sink 18.69 45.38

Final carbon rich product ( obtained sink product from flotation) 18.69 45.38
Final carbon reduced product (mixing of hydrocyclone overflow product and flotation sink product) 81.33 4.16

It is thus possible to provide the two stage beneficiation process to separate/reduce carbon from fly ash according of the present invention for effective utilization in cement manufacturing having following salient features:
i. Two stage beneficiation process is designed to process fly ash which is having around 11.87 % of carbon to reduce carbon percentage upto 4.16.
ii. The developed beneficiation process deals with the fine particles of 70 to 80% of -10 µm size using combination of classification and froth flotation process.
iii. The hydrocycloneis used as classification as first stage to separate two different streams coarse and fine fraction from the fly ash.
iv. To enrich maximize the reduction of carbon from fly ash, obtained from the underflow of hydrocyclone was subjected to froth flotation process.
v. Through newly developed two stage beneficiation flow sheet, achieves two products one is carbon rich and another one is carbon reduced product.Both products can be used for different applications.
vi. The majority of reduction was achieved in froth flotation process that is from 20.14% of carbon to 2.6% carbon with 40.71% of weight.