WO1997038949A1 - Method for treatment of silicon dioxide containing material - Google Patents

Method for treatment of silicon dioxide containing material Download PDF

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Publication number
WO1997038949A1
WO1997038949A1 PCT/NO1997/000088 NO9700088W WO9738949A1 WO 1997038949 A1 WO1997038949 A1 WO 1997038949A1 NO 9700088 W NO9700088 W NO 9700088W WO 9738949 A1 WO9738949 A1 WO 9738949A1
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WIPO (PCT)
Prior art keywords
microsilica
silicon dioxide
dioxide containing
milling
treatment
Prior art date
Application number
PCT/NO1997/000088
Other languages
French (fr)
Inventor
Eldar DINGSØYR
Original Assignee
Elkem Asa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Elkem Asa filed Critical Elkem Asa
Priority to AU24138/97A priority Critical patent/AU2413897A/en
Publication of WO1997038949A1 publication Critical patent/WO1997038949A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
    • C04B20/02—Treatment
    • C04B20/04—Heat treatment
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Definitions

  • the present invention relates to a method for the treatment of substantially amo ⁇ hous silicon dioxide containing materials having pozzolanic activity, and more particularly to the treatment of microsilica recovered from off gases which evolve during production of silicon and ferrosilicon and fly ash recovered when burning coal in coal fired power plants.
  • Microsilica which is recovered from off gases from smelting furnaces for the production of silicon and ferrosilicon has a strong pozzolanic activity and has for this reason been used as an additive in mortar and concrete.
  • Microsilica has a small particle size of less than 0.5 ⁇ m and a surface area between 10 and 30 m 2 /gram.
  • the colour of microsilica varies between black and light grey, the colour being mainly dependent on the content of carbon in the individual particles. The dark and very often uneven colour makes microsilica unusable for a number of applications where a white colour is required.
  • microsilica From US patent No. 5,290,529 it is known to subject microsilica to a heat treatment at a temperature in the range between 550°C to 750°C in order to combust carbon in the particles whereby a white microsilica is obtained.
  • This known heat treatment of microsilica unfortunately has the drawback that the pozzolanic activity of microsilica is lost.
  • the value of microsilica as an additive for concrete and morter is thereby substantially reduced.
  • fly ash produced during the firing of coal in coal fired power plants shows pozzolanic activity.
  • Fly ash contains a substantial amount of amorphous Si0 2 and has a particle size between 1 and 100 ⁇ m.
  • the colour of fly ash is, however, black or dark grey and fly ash can therefore not be used as an additive in concrete and mortar where a white colour is required.
  • fly ash can be made white by heat treatment. However in the same way as for microsilica it has been found that the pozzolanic activity of fly ash is lost during heat treatment.
  • the present invention relates to a method for the treatment of silicon dioxide containing materials showing a pozzolanic activity, where the silicon dioxide containing materials are subjected to a heat treatment at a temperature of at least 500°C whereafter the silicon dioxide containing materials are subjected to milling for a time period necessary to recover the pozzolanic activity of the materials.
  • the heat treated silicon dioxide containing materials are subject to milling for a time period of at least 30 minutes and preferably for a time period of at least 60 minutes.
  • the milling of the heat treated materials can be carried out both by dry milling or by wet milling. Dry milling can be carried out by the use of known methods such as ball mills and rod mills of different kinds, colloid mills and fluid energy mills. Wet milling can also be carried out in ball mills, rod mills, colloid mills and in fluid energy mills. As microsilica for use as an additive for concrete and mortar often is supplied as aqueous slurries, it is in such cases especially preferred to carry out the milling as wet milling.
  • a further advantage of the method according to the present invention is that the heat treatment can be carried out at higher temperatures than is used in the known processes for heat treatment of microsilica. The reason for this is that sintering of particles which to some extent will take place during heat treatment at high temperatures, will be broken down during the subsequent milling process and thus not give agglomerates in the final product.
  • Microsilica from Elkem ASA was heat treated at different temperatures and for different time intervals.
  • the heat treatment was carried out by placing microsilica in a porcelain crucible which was put into a muffle furnace and heated at the temperatures and time periods as stated in Table 1.
  • a part of the heat treated microsilica was mixed with water to form a slurry and thereafter milled in a laboratory wet mill, Model 12, delivered by Boulton, England.
  • the pozzolanic activity of untreated microsilica, heat treated microsilica and heat treated and wetmilled microsilica was investigated by casting prisms of mortar and measuring the pressure strength of the prisms after curing of the mortar.
  • the composition of the mortars was the same for all the tests.
  • the composition of the mortar was as follows: 20 % by weight of cement, 2.2 % by weight of microsilica, 11.1 % by weight of water and 66.7 % by weight of sand (DIN EN 196-1). For comparison purposes, a mortar was also produced which did not contain microsilica.
  • Table 1 show that the whiteness of microsilica after heat treatment as expected increased substantially, but that the pozzolanic activity was completely lost as the pressure strength of the mortar produced from sample B2 was reduced to about the same as for the mortar containing no microsilica.
  • Table 1 further shows that the pozzolanic activity was at least restored by the wet milling as the pressure strength after milling for 1 hour (sample B3) was higher than for the untreated microsilica (sample B1 ) and the pressure strength after milling for 2 hours (sample B4) was substantially higher than for the mortar produced by addition of untreated microsilica.
  • microsilica from Elkem ASA was heat treated in the same way as described in Example 1.
  • the temperatures and the heat treatment times are stated in Table 2.
  • Samples of the heat treated microsilica were subjected to wet milling for different time periods in the same manner as described in Example 2.
  • the pozzolanic activity for untreated microsilica, heat treated microsilica and for heat treated and wet milled microsilica was investigated by casting prisms of mortar and. testing the pressure strength of the prisms.
  • the composition of the mortars was the same as in Example 1.
  • a mortar was also produced without microsilica.
  • a third sample of microsilica from Elkem ASA was heat treated in the same way as described in Example 1.
  • a sample of the heat treated microsilica was subjected to dry milling in a jet mill to a nominal particle size of 10 ⁇ m.
  • the pozzolanic activity for untreated microsilica, heat treated microsilica and heat treated and dry milled microsilica was investigated by casting prisms of mortars and measuring the pressure strength of the mortars.
  • the composition of the mortars was the same as described in Example 1.
  • Table 3 show that the whiteness of microsilica after heat treatment increased even if the whiteness of the untreated microsilica (sample E1) was high.
  • the pozzolanic activity was strongly reduced by the heat treatment.
  • Table 3 shows that by dry milling of the heat treated microsilica in jet mill (sample E3), a pressure strength of the mortar was obtained which was about the same as the pressure strength for the mortar containing untreated microsilica (sample E1). This shows that the pozzolanic activity was substantially recovered by the method according to the present invention.
  • Table 3 further shows that by dry milling of the heat treated microsilica, a surprising increase in the whiteness of the microsilica was obtained compared to the whiteness of the heat treated microsilica.

Abstract

The present invention relates to a method for treatment of silicon dioxide containing materials showing a pozzolanic activity. The silicon dioxide containing materials are subjected to a heat treatment at a temperature of at least 500 °C whereafter the silicon dioxide containing materials are subjected to milling for a time period necessary to recover the pozzolanic activity of the materials.

Description

Title: Method for treatment of silicon dioxide containing material.
Technical Field
The present invention relates to a method for the treatment of substantially amoφhous silicon dioxide containing materials having pozzolanic activity, and more particularly to the treatment of microsilica recovered from off gases which evolve during production of silicon and ferrosilicon and fly ash recovered when burning coal in coal fired power plants.
Background Art
Microsilica which is recovered from off gases from smelting furnaces for the production of silicon and ferrosilicon has a strong pozzolanic activity and has for this reason been used as an additive in mortar and concrete. Microsilica has a small particle size of less than 0.5 μm and a surface area between 10 and 30 m2/gram. The colour of microsilica varies between black and light grey, the colour being mainly dependent on the content of carbon in the individual particles. The dark and very often uneven colour makes microsilica unusable for a number of applications where a white colour is required.
From US patent No. 5,290,529 it is known to subject microsilica to a heat treatment at a temperature in the range between 550°C to 750°C in order to combust carbon in the particles whereby a white microsilica is obtained. This known heat treatment of microsilica unfortunately has the drawback that the pozzolanic activity of microsilica is lost. The value of microsilica as an additive for concrete and morter is thereby substantially reduced.
Also, fly ash produced during the firing of coal in coal fired power plants shows pozzolanic activity. Fly ash contains a substantial amount of amorphous Si02 and has a particle size between 1 and 100 μm. The colour of fly ash is, however, black or dark grey and fly ash can therefore not be used as an additive in concrete and mortar where a white colour is required. Also, fly ash can be made white by heat treatment. However in the same way as for microsilica it has been found that the pozzolanic activity of fly ash is lost during heat treatment.
Disclosure of Invention
It is an object of the present invention to provide a method for the treatment of silicon dioxide containing material whereby the silicon dioxide containing materials are heat treated and where the pozzolanic effect of the material are restored after 1he heat treatment.
Accordingly the present invention relates to a method for the treatment of silicon dioxide containing materials showing a pozzolanic activity, where the silicon dioxide containing materials are subjected to a heat treatment at a temperature of at least 500°C whereafter the silicon dioxide containing materials are subjected to milling for a time period necessary to recover the pozzolanic activity of the materials.
The heat treated silicon dioxide containing materials are subject to milling for a time period of at least 30 minutes and preferably for a time period of at least 60 minutes.
It was surprisingly found that the pozzolanic activity of these materials could be restored by subjecting the heat treated materials to a milling process. In some cases it was even found that an increased pozzolanic activity was achieved compared to the pozzolanic activity of the untreated material. The milling of the heat treated materials can be carried out both by dry milling or by wet milling. Dry milling can be carried out by the use of known methods such as ball mills and rod mills of different kinds, colloid mills and fluid energy mills. Wet milling can also be carried out in ball mills, rod mills, colloid mills and in fluid energy mills. As microsilica for use as an additive for concrete and mortar often is supplied as aqueous slurries, it is in such cases especially preferred to carry out the milling as wet milling.
A further advantage of the method according to the present invention is that the heat treatment can be carried out at higher temperatures than is used in the known processes for heat treatment of microsilica. The reason for this is that sintering of particles which to some extent will take place during heat treatment at high temperatures, will be broken down during the subsequent milling process and thus not give agglomerates in the final product.
Detailed description of preferred embodiment
The present invention will now be further described by way of examples.
Example 1
Microsilica from Elkem ASA was heat treated at different temperatures and for different time intervals. The heat treatment was carried out by placing microsilica in a porcelain crucible which was put into a muffle furnace and heated at the temperatures and time periods as stated in Table 1.
A part of the heat treated microsilica was mixed with water to form a slurry and thereafter milled in a laboratory wet mill, Model 12, delivered by Boulton, England.
The pozzolanic activity of untreated microsilica, heat treated microsilica and heat treated and wetmilled microsilica was investigated by casting prisms of mortar and measuring the pressure strength of the prisms after curing of the mortar. The composition of the mortars was the same for all the tests. The composition of the mortar was as follows: 20 % by weight of cement, 2.2 % by weight of microsilica, 11.1 % by weight of water and 66.7 % by weight of sand (DIN EN 196-1). For comparison purposes, a mortar was also produced which did not contain microsilica.
The results are shown in Table 1.
TABLE 1
Figure imgf000006_0001
Measured by a method where black felt has a whiteness of zero and where BaS04 has a whiteness of 98.6.
The results in Table 1 show that the whiteness of microsilica after heat treatment as expected increased substantially, but that the pozzolanic activity was completely lost as the pressure strength of the mortar produced from sample B2 was reduced to about the same as for the mortar containing no microsilica. Table 1 further shows that the pozzolanic activity was at least restored by the wet milling as the pressure strength after milling for 1 hour (sample B3) was higher than for the untreated microsilica (sample B1 ) and the pressure strength after milling for 2 hours (sample B4) was substantially higher than for the mortar produced by addition of untreated microsilica.
Example 2
Another sample of microsilica from Elkem ASA was heat treated in the same way as described in Example 1. The temperatures and the heat treatment times are stated in Table 2. Samples of the heat treated microsilica were subjected to wet milling for different time periods in the same manner as described in Example 2.
The pozzolanic activity for untreated microsilica, heat treated microsilica and for heat treated and wet milled microsilica was investigated by casting prisms of mortar and. testing the pressure strength of the prisms. The composition of the mortars was the same as in Example 1. For comparison purposes, a mortar was also produced without microsilica.
The results are shown in Table 2.
TABLE 2
Figure imgf000007_0001
Measured by a method where black felt has a whiteness of zero and where BaS04 has a whiteness of 98.6.
The results in Table 2 show that the whiteness of microsilica after heat treatment as expected was substantially increased, but that the pozzolanic activity was reduced as the pressure strength of the mortar produced with sample C2 was reduced compared to the mortar produced with untreated microsilica (sample C1). Table 2 further shows that the pozzolanic activity of microsilica strongly increased during the wet milling as the pressure strength after milling for 2 hours (sample C3) was better than for the untreated microsilica (sample C1 ). Finally, the results in Table 2 shows that wet milling for more than 2 hours (sample C4) does not show any further increase in the pozzolanic activity for the microsilica.
Example 3
A third sample of microsilica from Elkem ASA was heat treated in the same way as described in Example 1. A sample of the heat treated microsilica was subjected to dry milling in a jet mill to a nominal particle size of 10 μm. The pozzolanic activity for untreated microsilica, heat treated microsilica and heat treated and dry milled microsilica was investigated by casting prisms of mortars and measuring the pressure strength of the mortars. The composition of the mortars was the same as described in Example 1.
The results are shown in Table 3.
TABLE 3
Figure imgf000008_0001
* Measured by a method where black felt has a whiteness of zero and where BaSO, has a whiteness of 98.6.
The results in Table 3 show that the whiteness of microsilica after heat treatment increased even if the whiteness of the untreated microsilica (sample E1) was high. The pozzolanic activity was strongly reduced by the heat treatment. Table 3 shows that by dry milling of the heat treated microsilica in jet mill (sample E3), a pressure strength of the mortar was obtained which was about the same as the pressure strength for the mortar containing untreated microsilica (sample E1). This shows that the pozzolanic activity was substantially recovered by the method according to the present invention. Table 3 further shows that by dry milling of the heat treated microsilica, a surprising increase in the whiteness of the microsilica was obtained compared to the whiteness of the heat treated microsilica.

Claims

1. A method for the treatment of silicon dioxide containing materials showing a pozzolanic activity, which comprises subjecting the silicon dioxide containing materials are to a heat treatment at a temperature of at least 500°C characterized by subjecting the silicon dioxide containing materials, after the heat treatment, to milling.
2. A method according to claim 1 , characterized by subjecting the silicon dioxide containing materials to milling for a time period of at least 30 minutes.
3. A method according to claim 2, characterized by subjecting the silicon dioxide containing materials to milling for a time period of at least
60 minutes.
4. A method according to claim 1 -3, characterized in that the heat treated materials are subjected to wet milling.
5. A method according to claim 1 -3, characterized in that the heat treated materials are subjected to dry milling.
PCT/NO1997/000088 1996-04-17 1997-04-03 Method for treatment of silicon dioxide containing material WO1997038949A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU24138/97A AU2413897A (en) 1996-04-17 1997-04-03 Method for treatment of silicon dioxide containing material

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO961509A NO305896B1 (en) 1996-04-17 1996-04-17 Method of treating silica-containing material
NO961509 1996-04-17

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000063133A1 (en) * 1999-04-15 2000-10-26 'holderbank' Financiere Glarus Ag Method for improving grindability of cement aggregates
WO2004096727A3 (en) * 2003-04-29 2005-04-07 Gary Hunt Cementitious material
WO2006030224A1 (en) * 2004-09-15 2006-03-23 Hanson Building Products Limited Processing of pulverised fuel ash
US7472851B2 (en) 2002-10-17 2009-01-06 Krause Maschinenbau Gmbh Method and device for the disintegration of especially inorganic materials
US7537653B2 (en) 2005-01-31 2009-05-26 Gcc Technology And Processes S.A. Microsilica materials with improved pozzolanic activity

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995027685A1 (en) * 1994-04-08 1995-10-19 N.V. Kema Filler for concrete and similar building material

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995027685A1 (en) * 1994-04-08 1995-10-19 N.V. Kema Filler for concrete and similar building material

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, Vol. 14, No. 290, C-731; & JP,A,02 092 851, (MITSUBISHI HEAVY IND LTD), 3 April 1990. *
PATENT ABSTRACTS OF JAPAN, Vol. 15, No. 345; & JP,A,03 137 041, (MITSUBISHI MATERIALS CORP), 11 June 1991. *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000063133A1 (en) * 1999-04-15 2000-10-26 'holderbank' Financiere Glarus Ag Method for improving grindability of cement aggregates
US7472851B2 (en) 2002-10-17 2009-01-06 Krause Maschinenbau Gmbh Method and device for the disintegration of especially inorganic materials
US7681820B2 (en) 2002-10-17 2010-03-23 Krause Maschinenbau Gmbh Method and device for the disintegration of especially inorganic materials
WO2004096727A3 (en) * 2003-04-29 2005-04-07 Gary Hunt Cementitious material
WO2006030224A1 (en) * 2004-09-15 2006-03-23 Hanson Building Products Limited Processing of pulverised fuel ash
GB2436024A (en) * 2004-09-15 2007-09-12 Hanson Building Products Ltd Processing of pulverised fuel ash
GB2436024B (en) * 2004-09-15 2010-04-28 Hanson Building Products Ltd Processing of pulverised fuel ash
US7537653B2 (en) 2005-01-31 2009-05-26 Gcc Technology And Processes S.A. Microsilica materials with improved pozzolanic activity

Also Published As

Publication number Publication date
NO961509L (en) 1997-10-20
AU2413897A (en) 1997-11-07
NO305896B1 (en) 1999-08-16
NO961509D0 (en) 1996-04-17

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