AU2007200076A1 - An Improved Process for the Production of Geopolymeric Material from Fly Ash - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Address for Service: Invention Title: Council of Scientific Industrial Research CULLEN CO.

Level 26 239 George Street Brisbane QId 4000 An Improved Process for the Production of Geopolymeric Material from Fly Ash The following statement is a full description of the invention, including the best method of performing it, known to us: 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 00 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 Iimproved 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 Sthe main component, which is abundantly available in India and worldwide. The process does not require large energy consumption and also no CO 2 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 600 250 0

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 9500 10500C 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 Ssodium shaping in desired shape and then curing at a temperature in the range of 00 600 2500C.

NYet 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 Sin the range of 600 2000C.

The existing processes 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 600 2000C.

Another known process 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.

c. 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 Sobtained. Thus only a small proportion of fly ash is used in geopolymers.

CO

00 Traditionally, geopolymeric material has been produced by intermixing the fine powder of silica or silica bearing mineral and alumina or alumina, alumino-silicte I bearing minerals with sodium and potassium based alkaline activator and followed Sby curing at elevated temperature. Davidovits, Geopolymer 2002 Conference, SOctober 28-29, 2002, Melbourne, Australia). The traditional method for making geopolymeric material using sodium, silica and alumina was patented by Davidovits in 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 Z. Juhasz, L. Opoczky, Mechanical activation of Minerals by Grinding: Pulverizing and Morphology of Particles, Ellis Horwood 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, Chennai, 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 Sprocess for the production of geopolymeric material using mechanically activated fly 00 ash, which obviates the drawbacks as detailed above.

INDAnother object of the present invention is to provide an improved process to Sproduce geopolymeric material whereby the energy consumption is significantly reduced.

S SYet 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 (SiO 2 alumina (A1 2 0 3 and iron oxide (Fe20 3 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 Senhanced 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 00oO cured in the temperature range of 50-2000C. Due to enhanced curing temperature the dissolution reactions proceeds simultaneously with the gel formation and poly- NOcondensation reactions, which results into setting of geopolymeric material and Sstrength development. Also due to increased reactivity, higher percentage of fly ash Sis used in the geopolymeric material.

(io SSummary 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 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 and 10 to 40 wt% of alkaline activator solution obtain in step 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 2 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: SiO 2 40 to 70%, A1 2 0 3 20 to 40%, Fe 2 0 3 0 to CaO 0 to MgO 0 to MnO 0 to 2%.

In another embodiment the alkaline activator used is selected from the group Sconsisting of sodium oxide, sodium hydroxide, sodium silicate, sodium nitrate, potassium oxide, potassium hydroxide, potassium silicate and potassium nitrate.

00 In yet another embodiment the high energy milling used is selected from vibratory milling, attrition milling, jet milling and planetary milling.

IND

SIn yet another embodiment the geopolymeric material obtained has a Scompressive 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 In yet another embodiment the geopolymeric material obtained has a fire resistance value of about 9000C.

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 9000C, volume expansion of and hardness of >5 on Mohs scale.

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 minutes. The median particle size(X50) obtained after the attrition milling was 8 pm.

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/cm 2 pressure. The samples were air dried at ambient temperature for 6 hours. The dried samples were cured at 600C in an electrical oven for 2 hours and then cooled to ambient temperature for various Stests. Physical testing such as compressive strength, fire resistance, autoclave 00 expansion and hardness was carried out as per standard test methods. The properties obtained are furnished in table 1.

IND

STable 1: Properties of geopolymeric material discussed above Properties Values Compressive strength (MPa) 4 hours 100 24 hours 130 Autoclave expansion 0.02 Fire resistance withstand 900 0

C

Hardness (Mohs scale) EXAMPLE -2 700 grams of fly ash was mechanically activated by vibration milling for minutes. The median particle size(X 50 so) obtained after the vibration milling was 12 gm. 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 mm thickness using uniaxial compression of 120 kg/cm 2 pressure. The samples were air dried at ambient temperature for 8 hours. The dried samples were cured at 800C 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 Properties Values Compressive strength (MPa) 4 hours 24 hours Autoclave expansion 0.02 Fire resistance withstand 900°C Hardness (Mohs scale) EXAMPLE 3 800 grams of fly ash was mechanically activated by jet milling for 30 minutes.

The median particle size(X5o) obtained after the jet milling was 10.2 tim. 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 unlaxial compression of 150 kg/cm 2 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 Properties Values Compressive strength (MPa) 4 hours 24 hours Autoclave expansion Fire resistance Hardness (Mohs scale) 0.01 withstand 900°C EXAMPLE -4 900 grams of fly ash was mechanically activated by planetary milling for Sminutes. The median particle size(X 5 0 obtained after the planetar milling was 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 00 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 IDthickness using uniaxial compression of 200 kg/cm 2 pressure. The samples were air Sdried at ambient temperature for 12 hours. The dried samples were cured at 600C in an electrical oven for 24 hours and then cooled to ambient temperature for various S 10 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 Properties Values Compressive strength (MPa) 4 hours 24 hours Autoclave expansion 0.01 Fire resistance withstand 9000C Hardness (Mohs scale) The main advantages of the present invention are: F11. The process utilises higher proportion of abundantly available industrial waste (fly cnash) as major raw material to produce geopolymeric material, thereby the cost of 00 5 production is considerably reduced in comparison to the known process.

2. The process of the present invention is helpful in resource conservation by O replacing costly raw materials e.g. alumina, silica, quartz, quartzite, kaolinite, illite Setc for its production by an industrial wastes.

3. The process replaces alumina, silica, quartz and quartzite powder, which is S 10 produced by an energy intensive grinding process and replaces kaolinite, illite Swhich 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 0 thereby very less to no CO 2 emission.

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.

Definitions The term "comprise" and variants of the term such as "comprises" or "comprising" are used herein to denote the inclusion of a stated integer or stated integers but not to exclude any other integer or any other integers, unless in the context or usage an exclusive interpretation of the term is required.

Any reference to publications cited in this specification is not an admission that the disclosures constitute common general knowledge in Australia.

Claims (7)

1. An improved process for the production of geopolymeric material from fly ash, which comprises 5 a) activating mechanically fly ash by high energy milling, for a period of 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 and 10 to 40 wt% of alkaline activator solution obtain in step 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 2 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 2001C, for a period of 1 to 24 hours to obtained the desired geopolymeric material.

2. An improved process according to claim 1, wherein fly ash used has the following composition range: SiO 2 40 to 70%, A1 2 0 3 20 to 40%, Fe20 3 0 to CaO 0 to MgO 0 to MnO 0 to 2%.

3. An improved process according to claim 1, wherein 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.

4. An improved process according to claim 1, wherein high energy milling used is selected from vibratory milling, attrition milling, jet milling and planetary milling.

An improved process according to claim 1, wherein 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.

6. An improved process according to claim 1, wherein the geopolymeric material obtained has an autoclave expansion of 0.5% and hardness of 5 in Mohs scale. 00 oO

7. An improved process according to claim 1, wherein the geopolymeric material obtained has a fire resistance value of about 9000C.