Title of Invention

"AN IMPROVED PROCESS FOR THE PRODUCTION OF GEOPOLYMERIC MATERIAL FROM FLY ASH"

Abstract

This invention provides an improved process for the preparation of geopolymeric material from fly ash. The process comprises crushing and grinding of raw fly ash material in a ball mill or vertical roller mill, thereafter proportioning and blending it in a mechanical mixer, followed by mixing with alkaline activator such as silicates or hydroxides of potassium or sodium and shaping it in desired shape and finally curing, at a temperature in the range of 60° - 250°C to obtain the desired product.

Full Text

Field of the invention The present invention relates to an improved process for the production of geopolymeric material from fly ash. The invention particularly relates to an improved process for the production of geopolymeric material from fly ash, which is a waste material from thermal power plants. More particularly, the invention relates to an improved process for the production of geopolymeric material from mechanically activated fly ash The products produced by the process of present invention will use fly ash as the main component, which is abundantly available in India and worldwide. The process does not require large energy consumption and also no CO2 emission. The products produced by the process of present invention may be of very good volume stability, reasonable strength gain in short time, excellent durability and high fire resistance. The geopolymeric material of the present invention shall be useful as main ingredient of fire resistant and insulated panels, decorative stone artefacts, building materials, ceramic tiles, refractory items, aluminium foundry application, geopolymer cement and concrete for building and other applications, and immobilization of toxic wastes. The hitherto known processes to produce geopolymeric material use pure material such as alumina and silica as main raw material and sodium and potassium as alkaline activator. The existing possesses use alumina in the range of 10-50 % by weight and silica in the range of 50-90% by weight. The existing process to produce geopolymeric material consisted of crushing and grinding of raw material in a ball mill or vertical roller mill, proportioning and blending of raw materials in a mechanical mixer, mixing with alkaline activators such as silicates or hydroxides of potassium or sodium , shaping in desired shape and then curing at a temperature in the range of 60° - 250°C. Another known process to produce geopolymeric material use naturally occurring silica bearing minerals such as quartz and quartzite and aluminosilicate bearing minerals such as kaolinite and illite. The existing process to produce geopolymeric material consisted of crushing and grinding quartz or quartzite in a ball mill or vertical roller mill, calcining of kaolinite or illite etc in a gas fired or electrically heated furnace at a temperature in the range of 950° - 1050°C and then cooling to ambient temperature, proportioning and blending of raw materials in a mechanical mixer, mixing with alkaline activators such as silicates or hydroxides of potassium or sodium , shaping in desired shape and then curing at a temperature in the range of 60° - 250°C. Yet another known process to produce geopolymeric material uses fly ash, sand and granite aggregate as raw material. The process consisted of proportioning and blending of raw fly ash, clay and aggregate, mixing with sodium/ potassium based alkaline activators, casting in desired shape and then curing at a temperature in the range of 60° - 200°C. The existing processes (J. Davidovits, Geopolymer 2002 Conference, October 28-29, 2002, Melbourne, Australia ) to produce Geopolymeric material consisted of intermixing of fine powder of silica and alumina for 10 to 60 minutes in a mixer. Geopolymerization reactions are carried out in alkaline environment using sodium or potassium based activator and curing at a temperature in the range of 60° - 200°C. Another known process (D. Hardjito et al, Invited Paper, Concrete World: Engineering &Materials, American Concrete Institute, India Chapter, Mumbai, India, December 9-12, 2004) uses mixing of fly ash, sand and granite aggregate in a mechanical mixer, addition of sodium based alkaline activator, vibration casting in the moulds. Curing the vibration casted material at elevated temperature produced the geopolymer material to be used as concrete. The hitherto known process have the following limitations: a. The production cost of geopolymeric material is relatively high when it uses costly raw materials such as pure silica and alumina. b. The formation of geopolymeric material is an energy intensive process when it uses naturally occurring raw material such as quartz, quartzite, kaolinite and illite. The crushing and grinding of quartz or quartzite, and high temperature calcining of kaolinite and illite consumes high energy. b. The strength development of geopolymer is low when it uses fly ash as one of the raw material. Due to poor reactivity of fly ash, low compressive strength is obtained. Thus only a small proportion of fly ash is used in geopolymers. Traditionally, geopolymeric material has been produced by intermixing the fine powder of silica or silica bearing mineral and alumina or alumina, alumino-silicte bearing minerals with sodium and potassium based alkaline activator and followed by curing at elevated temperature. (J. Davidovits, Geopolymer 2002 Conference, October 28-29, 2002, Melbourne, Australia). The traditional method for making geopolymeric material using sodium, silica and alumina was patented by Davidovits in U.S. (U.S. Patent 4,509,985 , Davidovits et al, Early high-strength mineral polymer) Reference may be made to U.S. Patent 4472199, Davidovits et al, Synthetic mineral polymer compound of the silicoaluminate family and preparation process, wherein cast or moulded geopolymers produced by the existing processes for zeolite application. Reference may be made to D. Hardjito et al "Concrete World: Engineering &Materials, American Concrete Institute, India Chapter, Mumbai, India, December 9-12, 2004" wherein uses of large volume of fly ash in geopolymer concrete have attracted intensive research attention. Fine grinding and mechanical activation of fly ash is suggested to improve its reactivity (A. Z. Juhasz, L. Opoczky, Mechanical activation of Minerals by Grinding: Pulverizing and Morphology of Particles, Ellis Norwood Limited, NY ,1994,). Various types of milling devices have been tried for the fine grinding and mechanical activation of fly ash. Reference may be made to Sanjay Kumar et al, 'Utilization of High Volume of Blast Furnace Slag and Fly Ash in Blended Cements through High Energy Milling', Proceedings of International Conference on Advance Concrete Structure, Chennei, Jan 2005, wherein the reactivity of fly ash was increased by mechanical activation in vibratory mill. According to literature and patent survey and available information, it may be mentioned that at present no process is available to produce geopolymeric material using mechanically activated fly ash. The purpose of this development is to use abundantly available waste materials such as 'fly ash', which is causing environmental pollution, to produce value added product such as geopolymeric material for various application. Objectives of the invention The main object of the present investigation is to provide an improved process for the production of geopolymeric material using mechanically activated fly ash, which obviates the drawbacks as detailed above. . Another object of the present invention is to provide an improved process to .produce geopolymeric material whereby the energy consumption is significantly reduced. Yet another object of the present invention is to provide an improved process to produce geopolymeric material whereby the cost of production is appreciably lowered and the properties of the product is improved. Still yet another object of the present invention is to provide an improved process to produce geopolymeric material whereby the reactivity of fly ash is increased by mechanical activation and the strength development of the product is improved. The fly ash used in the present invention contains silica (SiO2), alumina (Al2O3) and iron oxide (Fe2O3) and is partly crystalline and partly amorphous in nature. In the geopolymeric material produced by existing processes, fly ash does not actively participate in the geopolymerization reaction due to poor reactivity. The outer surface of the fly ash particles, which comes in contact with the alkaline activator, gets reacted but the inner core of the particles remains unreacted. As a result, the resulting geopolymeric materials have the inconsistent and poor strength development. Also only a limited quantity of fly ash is used in geopolymeric material due to its poor reactivity. In the process of the present invention, the fly ash is fine grounded and mechanically activated in high energy mill. The grinding media of high 'energy mill provides larger contact surface between the media and fly ash, higher agitator speed or vibration gives rise to greater kinetic energy of the media. The high energy milling process mechanically activates the fly ash and its reactivity is increased. When an alkaline activator such as sodium or potassium is added, the dissolution of fly ash particles starts. The increased reactivity of fly ash leads to enhanced dissolution activities. The mixture of mechanically activated fly ash and alkaline activator is shaped into desired shapes either by vibration casting or by uniaxial compression. For the geopolymerization reaction, the shaped articles are cured in the temperature range of 50-200°C. Due to enhanced curing temperature the dissolution reactions proceeds simultaneously with the gel formation and poly-condensation reactions, which results into setting of geopolymeric material and strength development. Also due to increased reactivity, higher percentage of fly ash is used in the geopolymeric material. Summary of the invention Accordingly, the present invention provides An improved process for the production of geopolymeric material from fly ash, which comprises a) activating mechanically fly ash by high energy milling, for a period of 10 to 60 minutes in dry condition and reducing the size ranging between 0 to 30 microns, b) mixing 5 to 50 wt% of alkaline activator and 50-95 wt% of water, under stirring, for a period ranging between 10-60 minutes, c) mixing intimately 60 to 90 wt% of vibration milled fly ash obtain in step (i) and 10 to 40 wt% of alkaline activator solution obtain in step (ii), for a period of 15 to 30 minutes, d) shaping the above said mixed powder either by vibration compaction for a period of 2 to 10 minutes or by compressing by using a pressure in the range of 50 to 250 kg/cm2, e) drying the above said shaped articles, at an ambient temperature, for a period of 2 to 24 hours, followed by curing at a temperature in the range of 50 to 200°C for a period of 1 to 24 hours to obtained the desired geopolymeric material. In an embodiment of the present invention the fly ash used has the following composition range: SiO2 - 40 to 70%, AI2O3 - 20 to 40%, Fe2O3 - 0 to 5%, CaO - 0 to 5%, MgO - 0 to 1%, MnO - 0 to 2%. In another embodiment the alkaline activator used is selected from the group consisting of sodium oxide, sodium hydroxide, sodium silicate, sodium nitrate, potassium oxide, potassium hydroxide, potassium silicate and potassium nitrate. In yet another embodiment the high energy milling used is selected from vibratory milling, attrition milling, jet milling and planetary milling. In yet another embodiment the geopolymeric material obtained has a compressive strength in the range of 30 to 160 MPa depending upon the production time period of 4 to 24 hrs. In yet another embodiment the geopolymeric material obtained has an autoclave expansion in the range of 0.01 to 0.02% and hardness of ≥ 5. In yet another embodiment the geopolymeric material obtained has a fire resistance value of about 900°C. Novelty of the present invention lies in the use of inexpensive raw material such as fly ash obtained from industrial waste, which is converted into mechanically activated fly ash for being further used for the preparation of geopolymaric material having excellent compressive strength of 30-150 MPa obtained in a very short time of 4-24 hours, fire resistance value of about 900°C, volume expansion of The following examples are given by way of illustration and should not be construed to limit the scope of invention. EXAMPLE -1 600 grams of fly ash was mechanically activated by attrition milling for 10 minutes. The median particle size(X50) obtained after the attrition milling was 8 µm. 400 gms of alkaline activator was prepared by mixing water and sodium hydroxide into 1:1 ratio for 15 minutes. The mechanically activated fly ash and alkaline activator was intimately mixed for 15 minutes. The mixture of mechanically activated fly ash and alkaline activator was shaped into 50 mm dia cylinder with 50 mm thickness using uniaxial compression of 100 kg/cm2 pressure. The samples were air dried at ambient temperature for 6 hours. The dried samples were cured at 60°C in an electrical oven for 2 hours and then cooled to ambient temperature for various tests. Physical testing such as compressive strength, fire resistance, autoclave expansion and hardness was carried out as per standard test methods. The properties obtained are furnished in table 1. Table -1: Properties of geopolymeric material discussed above (Table Removed) EXAMPLE - 2 700 grams of fly ash was mechanically activated by vibration milling for 30 minutes. The median particle size(X50) obtained after the vibration milling was 12 µm. 300 gms of alkaline activator was prepared by mixing water and potassium hydroxide into 2:1 ratio for 20 minutes. The mechanically activated fly ash and alkaline activator was intimately mixed for 15 minutes. The mixture of mechanically activated fly ash and alkaline activator was shaped into 50 mm dia cylinder with 50 mm thickness using uniaxial compression of 120 kg/cm2 pressure. The samples were air dried at ambient temperature for 8 hours. The dried samples were cured at 80°C in an electrical oven for 2 hours and then cooled to ambient temperature for various tests. Physical testing such as compressive strength, fire resistance, autoclave expansion and hardness was carried out as per standard test methods. The properties obtained are furnished in table 2. Table - 2: Properties of geopolymeric material discussed above (Table Removed) EXAMPLE - 3 .800 grams of fly ash was mechanically activated by jet milling for 30 minutes. The median particle size(X50) obtained after the jet milling was 10.2 µm. 200 grams of alkaline activator was prepared by mixing water and sodium silicate into 8:2 ratio for 30 minutes. The mechanically activated fly ash and alkaline activator was intimately mixed for 20 minutes. The mixture of mechanically activated fly ash and alkaline activator was shaped into 50 mm dia cylinder with 50 mm thickness using uniaxial compression of 150 kg/cm2 pressure. The samples were air dried at ambient temperature for 8 hours. The dried samples were cured at 100°C in an electrical oven for 16 hours and then cooled to ambient temperature for various tests. Physical testing such as compressive strength, fire resistance, autoclave expansion and hardness was carried out as per standard test methods. The properties obtained are furnished in table 3. Table - 3: Properties of geopolymeric material discussed above (Table Removed) EXAMPLE - 4 900 grams of fly ash was mechanically activated by planetary milling for 60 minutes. The median particle size(X50) obtained after the planetar milling was 8.5 µm. 100 grams of alkaline activator was prepared by mixing water and sodium nitrate into 1:1 ratio for 30 minutes. The mechanically activated fly ash and alkaline activator was intimately mixed for 15 minutes. The mixture of mechanically activated fly ash and alkaline activator was shaped into 50 mm dia cylinder with 50 mm thickness using uniaxial compression of 200 kg/cm2 pressure. The samples were air dried at ambient temperature for 12 hours. The dried samples were cured at 60°C in an electrical oven for 24 hours and then cooled to ambient temperature for various tests. Physical testing such as compressive strength, fire resistance, autoclave expansion and hardness was carried out as per standard test methods. The properties obtained are furnished in table 4. Table - 4: Properties of geopolymeric material discussed above (Table Removed) The main advantages of the present invention are: 1 The process utilises higher proportion of abundantly available industrial waste (fly ash) as major raw material to produce geopolymeric material, thereby the cost of production is considerably reduced in comparison to the known process. 2. The process of the present invention is helpful in resource conservation by replacing costly raw materials e.g. alumina, silica, quartz, quartzite, kaolinite, illite etc for its production by an industrial wastes. 3. The process replaces alumina, silica, quartz and quartzite powder, which is produced by an energy intensive grinding process and replaces kaolinite, illite which is calcined at high temperatuture by an industrial waste (fly ash), thereby considerable reduction in energy consumption in comparison to the known process. 4. The process involves low temperature processing (50-200°C), thereby very less to no CO2 emission. 5. The products developed by the process of present invention are superior in terms of strength development in short time then the products produced by the existing process. This is obtained by the mechanical activation of fly ash, which enhances its reactivity and gives improved strength. We claim 1. An improved process for the production of geopolymeric material from fly ash, which comprises a) activating mechanically fly ash by high energy milling, for a period of 10 to 60 minutes in dry condition and reducing the size ranging between 0 to 30 microns, b) mixing 5 to 50 wt% of alkaline activator and 50-95 wt% of water, under stirring, for a period ranging between 10-60 minutes, c) mixing intimately 60 to 90 wt% of vibration milled fly ash obtain in step (i) and 10 to 40 wt% of alkaline activator solution obtain in step (ii), for a period of 15 to 30 minutes, d) shaping the above said mixed powder either by vibration compaction for a period of 2 to 10 minutes or by compressing by using a pressure in the range of 50 to 250 kg/cm , e) drying the above said shaped articles, at an ambient temperature, for a period of 2 to 24 hours, followed by curing, at a temperature in the range of 50 to 200°C, for a period of 1 to 24 hours to obtained the desired geopolymeric material. 2. An improved process as claimed in claim 1 wherein fly ash step (a) used has the following composition range: SiO2 - 40 to 70%, A12O3 - 20 to 40%, Fe2O3 - 0 to 5%, CaO - 0 to 5%, MgO - 0 to 1 %, MnO - 0 to 2%. 3. An improved process as claimed in claims 1&2, wherein the alkaline activator step (b) used is selected from the group consisting of sodium oxide, sodium hydroxide, sodium silicate, sodium nitrate, potassium oxide, potassium hydroxide, potassium silicate and potassium nitrate. 4. An improved process as claimed in claims 1-3, wherein high energy milling - used is selected from vibratory milling, attrition milling, jet milling and planetary milling. 5. An improved process as claimed in claim 1, wherein the geopolymeric material obtained in step (e) has a compressive strength in the range of 30 to 160 MPa depending upon the production time period of 4 to 24 hrs. 6. An improved process as claimed in claim 1, wherein the geopolymeric material obtained in step (e) has an autoclave expansion of ≤ 0.5% and hardness of ≥ 5 in Mohs scale. 7. An improved process as claimed in claim 1, wherein the geopolymeric material obtained has a fire resistance value of about 900°C.

Documents:

2626-del-2005-abstract.pdf

2626-DEL-2005-Claims-(28-02-2012).pdf

2626-del-2005-claims.pdf

2626-DEL-2005-Correspondence Others-(28-02-2012)..pdf

2626-del-2005-correspondence-others.pdf

2626-del-2005-description (complete).pdf

2626-del-2005-form-1.pdf

2626-del-2005-form-18.pdf

2626-del-2005-form-2.pdf

2626-DEL-2005-Form-3-(28-02-2012).pdf

2626-del-2005-form-3.pdf

2626-del-2005-form-5.pdf

2626-DEL-2005-Petition-137-(23-02-2012).pdf