WO2007105029A1

WO2007105029A1 - A process for the production of reactive blast furnace slag

Info

Publication number: WO2007105029A1
Application number: PCT/IB2006/002077
Authority: WO
Inventors: Rakesh Kumar; Sanjay Kumar; Thomas Callottutheckathil Alex; Surya Pratap Mehrotra
Original assignee: Council Of Scientific And Industrial Research
Priority date: 2006-03-10
Filing date: 2006-07-31
Publication date: 2007-09-20
Also published as: CN101405237A; CA2645348A1; EP1993968A1; KR20080102294A; AU2006340282A1

Abstract

The invention particularly relates to a process for increasing the reactivity of ground granulated blast furnace slag using surface activation through short mechanical activation time (10-60 min) and it starts to hydrate in short time (48 h or less) when mixed with water without any chemical additive and completely hydrates in maximum 28 days forming cementitious product. The products produced by the process of present invention may be of different particle sizes and shapes, different specific surface areas, different surface charge (Zeta potential) and different reactivity. The reactive blast furnace slag shall be useful in Portland Slag Cement (PSC), Geopolymer, immobilisation and stabilisation of toxic wastes and newer nano-composite materials.

Description

'A PROCESS FOR THE PRODUCTION OF REACTIVE BLAST FURNACE SLAG'

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:

The present invention relates to a process for the production of reactive granulated blast furnace slag. The invention particularly relates to a process for increasing the reactivity of ground granulated blast furnace slag using surface activation through mechanical activation in high energy mills that exploit large contact area between milling media and the material.

The products produced by the process of present invention may be of different particle sizes and shapes, different specific surface areas, different surface charge (Zeta potential) and different reactivity. The reactive blast furnace slag shall be useful in Portland Slag Cement (PSC)₅ Geopolymer, immobilisation and stabilisation of toxic wastes and newer nano-composite materials.

The blast furnace slag has latent hydraulic activity, i.e. develops cementitious properties when exposed to water. The reactivity of blast furnace slag is defined in terms of rate at which it hydrates and forms the hydration product in water. Water is present in the slag hydration product in evaporable and non-evaporable forms. Higher amount of non- evaporable water signifies greater hydration. If the two slag samples are hydrated under identical condition, then the one that shows higher amount of non-evaporable water will have greater reactivity. The blast furnace slag reacts with water but the process of hydration is very slow due to the formation of an impervious aluminosilicate film on the surface [ACI Committee 226, Ground Granulated Blast Furnace Slag as a Cementitious Constituent in Concrete, ACI Manual of Concrete Practice, 226.1R, 1989, pp 1-16; and H.F.W. Taylor, Cement Chemistry, 2^nd ed., Thomas Telford Publication, London, 1998, 270-271]. No significant hydration product can be found even after several months due to poor reactivity of blast furnace slag. Many attempts have been made to improve the reactivity of blast furnace slag. Reference may be made to International Patent, PCT, No. WO2004/041746 Al, 2004, Process for producing blended cement with reduced carbon dioxide emissions, by Vladimir Ronin, wherein the reactivity of the blast furnace slag was improved by dry grinding to a specific surface area of 1000 cm²/g in the first step and 3000 cm²/g in the final step. Reference may be made to US Patent 6,776,839, 2004, Slag Cement by Ko Suz Chung, wherein grinding of slag to a specific surface area greater than 4500 cm²/g is carried out to minimise the impact of low reactivity of slag on the strength of cement. The hitherto known process to increase the reactivity of the blast furnace slag without any chemical addition is based on prolonged grinding in a conventional mill device such as ball mill, rod mill etc. Even with prolonged grinding in wet condition for several weeks, only limited improvement in hydration of blast furnace slag is possible and complete hydration is not achieved without a chemical additive [S. Song, H.M. Jennings, Pore solution chemistry of alkali-activated ground granulated blast-furnace slag, Cement and Concrete Research, 29 (1999) 159-170]. Poor reactivity of slag restricts its utilisation in Portland slag cement and any other application where the reactivity of the slag is of importance. The hitherto known process have the following limitations: a. The formation of reactive blast furnace slag is an energy intensive process due to prolonged grinding in a conventional mill. b. The rate of hydration is very slow. The hydration of blast furnace slag takes few months to years. c. The slag does not form any crystalline product during hydration reactions. d. The production cost of slag is relatively high as it uses prolonged grinding and consumes energy. e. Due to slow hydration rate, the use of slag, e.g. in Portland slag cement, is restricted.

Traditionally, the reactivity of blast furnace slag is enhanced by prolonged grinding in a ball mill. Reference may be made to ACI Committee 233, Ground Granulated blastfurnace slag as a cementitious constituent in concrete, ACI Mater J 1995;92(3): 321-2, wherein the Portland slag cement produced by existing processes using blast furnace slag have lower early strength and longer setting time than the ordinary Portland cement and this restricts the use of large proportion of slag in blended cement. Reference may be made to A. Z. Juhasz and L. Opoczky, Mechanical activation of Minerals by Grinding: Pulverizing and Morphology of Particles, Ellis Horwood Limited, NY ,1994, who have reported limitation imposed by slag reactivity on its usage in blended slag cements due to lowering of early strength. Reference may be made to M. Oner, K. Erdogdu and A. Gunlu, 'Effect of components fineness on strength of blast furnace slag cement', Cement and Concrete Research, VoI 33, 2003, 463-9, wherein slag has to be ground for very long time to avoid drop in the strength. According to literature and patent survey and available information, it may be mentioned that at present no process is available to produce reactive blast furnace slag by mechanical activation that refers to reduction in particle size together with any other bulk or surface change(s) induced in the solid phase by any milling process. Complete hydration of the blast furnace slag without any chemical addition is not possible with any of the hitherto known processes. The purpose of this development is to produce a reactive blast furnace slag with faster hydration rate, and use abundantly available waste materials, that is blast furnace slag, to produce value added product such as Portland slag cement, matrix for immobilisation and stabilisation of toxic wastes, geopolymers and nano-composites.

The main object of the present investigation is to provide a process for the production of reactive blast furnace slag, which obviates the drawbacks as detailed above.

Another object of the present invention is to provide an improved process to produce reactive blast furnace slag whereby the energy consumption is significantly reduced.

Yet another object of the present invention is to provide an improved process to produce reactive blast furnace slag whereby the reactivity of the slag significantly enhanced.

Still yet another object of the present invention is to provide an improved process to produce reactive blast furnace slag 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 reactive blast furnace slag whereby the crystallinity of its hydration product is significantly improved.

The present invention particularly provides a process for increasing the reactivity of ground granulated blast furnace slag using surface activation through short mechanical activation time (10-60 min) and it starts to hydrate in short time (48 h or less) when mixed with water without any chemical additive and completely hydrates in maximum 28 days forming cementitious product. The products produced by the process of present invention may be of different particle sizes and shapes, different specific surface areas, different surface charge (Zeta potential) and different reactivity. The reactive blast furnace slag shall be useful in Portland Slag Cement (PSC), Geopolymer, immobilisation and stabilisation of toxic wastes and newer nano-composite materials.

The granulated blast furnace slag used in the present invention contains calcium oxide (CaO), silica (SiO₂), alumina (Al₂O₃) and magnesium oxide (MgO) and it is mostly glassy in nature.

In the existing processes, the blast furnace slag does not actively participate in the hydration reaction; as a result it hydrates very slowly and incompletely. In the process of the present invention, the blast furnace slag is wet milled in water using a high-energy mill to mechanically activate the slag. The mill is characterised by small media size (< 10 mm) and an agitator that rotates the media at high rpm (> 250 rpm) resulting in high kinetic energy and large contact between the material and the grinding media. The mill is referred to as an attrition mill or agitator bead mill or stirred media mill (the term attrition mill is used in all subsequent description). The milling process mechanically activates the granulated blast furnace slag and its reactivity is increased. The process of mechanical activation results due to breakage of slag to very fine size and other physicochemical changes, in particular surface changes or surface activation. The increased reactivity of blast furnace slag results from the destabilisation of impervious aluminosilicate surface film that is responsible for retardation/inhibition of slag hydration in the case of conventionally milled slag. The increased reactivity leads to enhanced hydraulic activity of slag. As soon as water is added, slag particles undergo hydration. The reactive blast furnace slag can begin to hydrates in 24-48 hours even if no chemical activator is present. Complete hydration can be achieved in less than 28 days. The nature of hydration product and its crystallinity is changed through the variation of parameters during mechanical activation process.

Accordingly, the present invention provides a process for the production of reactive blast furnace slag, which comprises:

(i) reducing size of granulated blast furnace slag by any known process to obtain the

size in the range between 210 to 100 μm,

(ii) preparing the slag slurry maintaining slag to water ratio in the range of 0.2 to 2 for use as feed material for mechanical activation in the attrition mill,

(iii) feeding the slag slurry to the attrition mill using slag to ball ratio in the range of 5 to 50, (iv) preparing the reactive blast furnace slag through mechanical activation in an attrition mill using milling media size in the range of Ito3 mm, agitator speed in the range of 500 to 4000 revolution per minute, and milling time in the range of 10 to 60 minutes, (v) separating reactive slag slurry from media by any known process,

(vi) using reactive slag slurry directly in the application or removing the water completely by any known process.

In an embodiment of the invention, the granulated blast furnace slag used has the following composition range: SiO₂ - 20 to 40%, Al₂O₃ - 20 to 40%, Fe₂O₃ - 0 to 2%, CaO - 20 to 40%, MgO - 5 to 17%, MnO - 0 to 5%, SO₃ - 0 to 2% and glass content >85%.

According to a feature of the invention, the blast furnace slag may be selected from the following composition range: Constituent Granulated blast furnace slag

(wt. %)

SiO₂ 20-40

Al₂O₃ 20-40

Fe₂O₃ 0-2

CaO 20-40

MgO 5-17

MnO 0-5

SO₃ 0-2

Glass content(%) >85 The reactive : blast furnace slag obtained in the present invention may have the following range of properties:

(a) Median Particle size : 2 to 50 μm

(b) Morphology : Angular

(C) Stable suspension volume : 100-25O mIAOO g slag

(d) Zeta potential : - 25 to -35 mV

(e) Hydration start time : 24 - 100 h

CD Reactivity (measured as

Thermogravimetric water loss in the hydration product

105-950 ⁰C) : 12-30 g/g of slag paste

15-36 g/g of slag

(g) Hydration after 28 days : Near Complete/Complete

(h) Microstructure of hydrated

Product : Compact with closely packed hydrated slag particle or fully hydrated fribllar slag particle with porosity

(i) Phases after hydration time : Amorphous to mostly crystalline phases depending upon properties (a)-

(f) Novelty of the present invention is that the reactivity of the slag is significantly improved in short mechanical activation time (10-60 min) and it start to hydrate in short time (48 h or less) when mixed with water without any chemical additive and completely hydrates in maximum 28 days forming cementitious product. Also, the hydration phases formed are crystalline in nature. Due to enhanced reactivity the higher proportion of slag is used in products such as Portland slag cement, matrix for immobilisation and stabilisation of toxic wastes, geopolymers and nano-composites.

The following examples are given by way of illustration and should not be construed to limit the scope of the present invention invention.

EXAMPLE - 1

1 kg of the blast furnace slag was dry milled in a ball mill for a period of 45 min. The particle size obtained after the ball milling was -100 micron. 150 grams of ball milled blast furnace slag was used as a feed material and wet milled in an attrition mill for 10 minutes using water as medium. The material to water ratio was kept as 1 :1.5 and material to ball ratio was kept 1 :10. The size of the ball was 2 mm and agitator speed was 1000 rpm. The attrition milled slag was evaluated in terms of median particle size, morphology, Zeta potential, stable suspension volume (volume occupied by 100 g slag when excess water is present), hydration start time. Standard isothermal conduction calorimetric procedure was employed to find hydration start time. Slag slurry from the mill, equivalent to 100 g of slag, was allowed to hydrate for 28 days at room temperature. Reactivity of the slag was measured using a 28 day hydrated neat slag sample and expressed in terms of thermogravimetric weight loss in the temperature range 105-950 ⁰C per gram of hydrated slag or slag taken for hydration. The hydration product was also evaluated in terms of its microstructural characteristic and phases present and their crystallinity. The properties of the reactive blast furnace slag obtained are furnished in table 1.

Table 1 - Properties of reactive blast furnace slag cement discussed above

EXAMPLE - 2

1 kg of the blast furnace slag was dry milled in a ball mill for a period of 45 min. The particle size obtained after the ball milling was -100 micron. 150 grams of ball milled blast furnace slag was used as a feed material and wet milled in an attrition mill for 15 minutes using water as medium. The material to water ratio was kept as 1:1.5 and material to ball ratio was kept 1:10. The size of the ball was 2 mm and agitator speed was 1000 rpm. The attrition milled slag was evaluated in terms of median particle size, morphology, Zeta potential, stable suspension volume (volume occupied by 100 g slag when excess water is present), hydration start time. Standard isothermal conduction calorimetric procedure was employed to find hydration start time. The water present in attrition milled slurry was separated by filtering and then the material was dried at 40⁰C in an electric oven for 6 hours and then cooled to room temperature. 100 g of the dried slag was mixed with excess water such that it was completely immersed in water, and allowed to hydrate for 28 days at room temperature. Reactivity of the slag was measured using a 28 day hydrated neat slag sample and expressed in terms of thermogravirnetric weight loss in the temperature range 105-950⁰C per gram of hydrated slag or slag taken for hydration. The hydration product was also evaluated in terms of its microstructural characteristic and phases present and their crystallinity. The properties of the reactive blast furnace slag obtained are furnished in table 2.

Table 2 - Properties of reactive blast furnace slag cement discussed above

EXAMPLE - 3

1 kg of the blast furnace slag was dry milled in a ball mill for a period of 45 min. The particle size obtained after the ball milling was -100 micron. 150 grams of ball milled blast furnace slag was used as a feed material and wet milled in an attrition mill for 30 minutes using water as medium. The material to water ratio was kept as 1:1.5 and material to ball ratio was kept 1:10. The size of the ball was 2 mm and agitator speed was 1000 rpm. The attrition milled slag was evaluated in terms of median particle size, morphology, Zeta potential, stable suspension volume (volume occupied by 100 g slag when excess water is present), hydration start time. Standard isothermal conduction calorimetric procedure was employed to find hydration start time. Slag slurry from the mill, equivalent to 100 g of slag, was allowed to hydrate for 28 days at room temperature. Reactivity of the slag was measured using a 28 day hydrated neat slag sample and expressed in terms of thermogravimetric weight loss in the temperature range 105-950 ⁰C per gram of hydrated slag or slag taken for hydration. The hydration product was also evaluated in terms of its microstructural characteristic and phases present and their crystallinity. The properties of the reactive blast furnace slag obtained are furnished in table 3.

Table 3 - Properties of reactive blast furnace slag cement discussed above

EXAMPLE - 4

1 kg of the blast furnace slag was dry milled in a ball mill for a period of 45 min. The particle size obtained after the ball milling was -100 micron. 150 grams of ball milled blast furnace slag was used as a feed material and wet milled in an attrition mill for 60 minutes using water as medium. The material to water ratio was kept as 1 :1.5 and material to ball ratio was kept 1:10. The size of the ball was 2 mm and agitator speed was 1000 rpm. The attrition milled slag was evaluated in terms of median particle size, morphology, Zeta potential, stable suspension volume (volume occupied by 100 g slag when excess water is present), hydration start time. Standard isothermal conduction calorimetric procedure was employed to find hydration start time. Slag slurry from the mill, equivalent to 100 g of slag, was allowed to hydrate for 28 days at room temperature. Reactivity of the slag was measured using a 28 day hydrated neat slag sample and expressed in terms of thermogravimetric weight loss in the temperature range 105-950 ⁰C per gram of hydrated slag or slag taken for hydration. The hydration product was also evaluated in terms of its microstructural characteristic and phases present and their crystallinity. The properties of the reactive blast furnace slag obtained are furnished in table 4.

Table 4 - Properties of reactive blast furnace slag cement discussed above

The main advantages of the' present invention are:

1. The process adds value to the abundantly available industrial waste (granulated blast furnace slag) for the development of value added product thus helpful in resource conservation

2. The process is fast and energy efficient due to increased contact between the milling media and the slag, high kinetic energy in the mill, and wet operation..

3. The reactivity of the slag can be controlled through the control of milling parameters and not dependent on any extraneous chemical addition. 4. The products developed by the process of present invention are superior in terms of reactivity, early start of hydration and complete and faster hydration properties then the products produced by any of the existing processes.

5. The products developed by the process of present invention are superior in terms of crystallinity after hydration reactions then the products produced by the existing processes.

Claims

WE CLAIM:

1. A process for the production of reactive blast furnace slag, comprising the steps of: (i) reducing size of granulated blast furnace slag by a known process to obtain the size in the range between 100 to 210 μm,

(ii) preparing the slag slurry maintaining slag to water ratio in the range of 0.2 to 1.5 : 1 to 2 for use as feed material for mechanical activation in the attrition mill,

(iii) feeding the slag slurry to the attrition mill using slag to ball ratio in the range of lto 5 : 10 to 50,

(iv) preparing the reactive blast furnace slag through mechanical activation in an attrition mill using milling media size in the range of Ito3 mm, agitator speed in the range of 500 to 4000 revolution per minute, and milling time in the range of 10 to 60 minutes, (v) separating reactive slag slurry from media by a known process,

(vi) using reactive slag slurry directly in the application or removing the water completely by a known process.

2. A process as claimed in claim 1 where in granulated blast furnace slag used has the following composition range: SiO₂ - 20 to 40%, Al₂O₃ - 20 to 40%, Fe₂O₃ - 0 to

2%, CaO - 20 to 40%, MgO - 5 to 17%, MnO - 0 to 5%, SO₃ - 0 to 2% and glass content >85%.

3. A process as claimed in claim 1, wherein the preferred size of blast furnace slag obtained in step (i ) is 100 μm. 4. A process as claimed in claim 1, step (ii), wherein the preferred slag to water ratio is 1 to 1.5. A process as claimed in claim 1, step (iii) wherein the preferred slag to ball ratio is

1 to 10.

A process as claimed in claim 1, step (iv) wherein the preferred milling media size is 2mm.

7. A process as claimed in claim 1, step (iv) wherein the preferred agitator speed is

1000 rpm.

The properties of the reactive blast furnace slag obtained from the process of claims 1 is

(a) Median Particle size : 2 to 50 μm

(b) Morphology : Angular

(c) Stable suspension volume : 100-25O mIAOO g slag

(d) Zeta potential : - 25 to -35 mV

Q) Hydration start time : 24 - 10O h

(k) Reactivity (measured as

Thermogravimetric water loss in the hydration product 105-950 ⁰C) : 12-30 g/g of slag paste 15-36 g/g of slag