Claims:We Claim:

1. A method of manufacture of belite based cementitious material from steel slag comprising:
steps of remelting, reduction and metal separation from iron containing steel slag to render it suitable for cementitious material involving
providing steel slag;
melting the steel slag in a furnace at a temperature between 1600 °C- 1650OC;
adding reducing agents to molten steel slag for reduction;
separating the iron from the reduced steel slag; and
fast air cooling of the iron separated steel slag to obtain the belite based cementitious material.

2. The method as claimed in anyone of claims 1 or 2, wherein the slag is selected from basic oxygen furnace(BOF) slag.

3. The method as claimed in anyone of the claims 1 to 2, wherein the reducing agent is selected from source of carbon or aluminium without any impurities.

4. The method as claimed in anyone of the claims 1 to 3, wherein the mass percentage of the reducing agent used is 5% to 8.4%.

5. The method as claimed in anyone of the claims 1 to 4, wherein the said step of air cooling is carried out to maintain the belite content of the belite based cementitious material in the range of 50% to 55%.

6. The method as claimed in anyone of the claims 1 to 5, wherein the belite based cementitious material is obtained free from lime.

7. The method as claimed in anyone of the claims 1 to 6, wherein periclase percentage decreased from 10% in steel slag to 5% in the belite based cementitious material.

8. The method as claimed in anyone of claims 1 to 7 comprising adding to said belite based cementitious material Portland clinker in a mass ratio of not more than 3:2 to produce cement.

9. A belite based cementitious material produced by the method as claimed in anyone of claims 1 to 8 contains belite in the range of 50% to 55%.

10. The cementitious material as claimed in claim 9 is mixed with Portland clinker in the ratio of not more than 3:2 respectively, to form cement.

11. The cement as claimed in claim 10, have compressive strength greater than 39 MPa and the heat of hydration in the range of 260 J/g to 263 J/g.

Dated this the 24th day of February, 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 METHOD OF MANUFACTURE OF BELITE BASED CEMENTITIOUS MATERIAL FROM STEEL SLAG.



2 APPLICANT (S)

Name : JSW CEMENT 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 generally to the field of cementing material technology. More specifically, the present invention relates to providing a cementitious material composition obtained of iron separated steel slag and contains belite based cementitious material in the range of 50% to 55% having belite(Ca2SiO4) to achieve cementitious properties and method of its making through selective steps by bulk utilization of steel slag.

BACKGROUND OF THE INVENTION

Globally, the total steel production is about 1691 million tons which produced almost 423 million tons slag (World Steel Association, 2019) while in India total steel production is about 107 million tons per year (Ministry of Steel, 2019), which produced approximately 32 million tons slag. In addition, it has been estimated that in 2020 the world steel production will expected to reach about 1781 million tons, which will cause a huge amount of slag generation that needs to be managed (‘Steel Statistical Yearbook 2018 ; Bureau and Mines, 2018). Basic Oxygen Furnace (BOF) slag is a byproduct of the steelmaking process generated during the manufacture of steel.
Efforts have been made to utilize these steel slags as cementitious material. Wang, Q., Yan, P., and S. Han. 2011. “The influence of steel slag on the hydration of cement during the hydration process of complex binder”. Science China Technological Sciences, 54 (2), 388–394, utilized the steel slag in a cementitious binder. This study concluded that steel slag application with cement provides later strength after hydration. However, early hydration of slag cement was decreased and dormant phase of cement hydration increased with the adding percentage of steel slag. Also, the expansion effect of free lime and magnesia on application of cement was not studied. Xue Y., Wu S., Hou H., and Zha J. 2006. “Experimental investigation of basic oxygen furnace slag used as aggregate in asphalt mixture”. Journal of Hazardous Material, 138, 261–268, wherein the BOF slag was utilized as aggregate. However, only small part could be utilized due to the presence of free lime and magnesia. The free lime and magnesia absorbs moisture and carbon dioxide from the air and forms hydroxides and carbonates respectively which is the reason for volume expansion/swelling resulting in the formation of cracks. This leads to the need to explore other ways of steel slag utilization Agrawal, S.K., Vanguri, S., Chaturvedi, S.K., Kumar, A., and Reddy, A.S. 2017. “Performance evaluation of granulated bf slag -steel slag based Portland slag cement.” 15th NCB International Seminar on Cement, Concrete and Building Materials, New Delhi, India, 413, 1-11, wherein BOF slag was applied for partial replacement of granulated blast furnace slag (GBS) in Portland slag cement (PSC). However, only 7.5% of BOF slag can be recycled as a fractional substitution to GBS in PSC due to expansion of steel slag on application with higher percentage.

To overcome the expansion on the direct application, researchers also tried to utilize steel slag in clinkerization process. Singh R, Gorai AK, Segaran RG, 2013. Characterization of LD slag of Bokaro steel plant and its feasibility study of manufacturing commercial ‘fly ash–LD slag’ bricks. International Journal of Environmental Technology Managment 16:129–145, wherein BOF slag was used to replace iron ore in raw feed during clinker manufacture. However, only 2% of BOF slag can be used as a raw mix component for the correction of iron content in the raw mix.

In addition to mentioned studies, several referenced have also been made for the development of cementitious products from steel slags. European patent EP1741683A2 discloses a major component of cement is cement clinker made from a mixture of raw materials calcium oxide, silica, aluminum, and iron oxide by mixing, milling, and firing. According to the invention, the raw material mixture comprises a lime component and converter slag and/or electro-steelworks slag. As a result, both natural resources can be spared and the carbon dioxide emissions are reduced when burning the cement clinker. The basic oxygen furnace (BOF) slag was utilized in the proportion of 5-8% with 25-35% of blast furnace slag in the preparation of the cement clinker.

European patent EP3315471A1 discloses the BOF slag was activated to utilize it as a composite material for cement industry. The BOF slag was modified at a high temperature to achieve the activation of the belitic phase in the BOF slag. However, this activated steel slag was crystalline in nature and had limited applications.

Chinese patent (CN101466650A) wherein, the invention provides a process for conversion of basic oxygen furnace slag into construction materials like a hydraulic binder and other applications. The fluorspar was added to the molten slag to increase its fluidity and then the slag was allowed to cool. However, the reduction process for separation of metallic and nonmetallic iron was not performed in this method. Also, modified BOF slag with fluorspar could not achieve the desired cementitious properties due to lack of silica and slow cooling.

Korean patent application no. 10-2010-0111768, wherein method of an ultra-rapid-hardening hydraulic binder preparation from reduced steel slag powder is provided. The method comprises the process of scattering electric arc furnace to high pressure in a steel mill; quick freezing at room temperature; pulverizing the reduction slag into a fixed fineness, and mixing gypsum with the pulverized reduction slag was prepared through and a manufacturing method thereof are provided to enhance rapid hardening property and replace normal Portland cement. However, the slag was cooled at room temperature which leads to crystallization of the slag, which is the major drawback of this invention.

Chinese patent (CN101466650A) wherein, the invention provides a process for conversion of basic oxygen furnace slag into construction materials like hydraulic binder in masonry blocks, flat sheets, bricks and tiles and also as a blend in cement manufacture or as in mortar for various applications. A required quantity of fluorspar is added to the molten slag for increasing its fluidity and the mixture is allowed to cool. The slag is then crushed to -3 mm size and any metallic fraction is separated using a magnetic separator. The -3 mm size non-metallic slag is ground to about 3000-4000 blain depending upon the application for which it is required. A desired quantity of gypsum can be mixed with the non-metallic fraction of the -3 mm slag before grinding.

Despite progress made by previous studies as shown in the above prior arts, further efforts are required for bulk utilization of steel slags. In prior mentioned arts the methods for steel slag reduction and modification and then fast air cooling to get belite based cementitious material are not available. Also, the bulk utilization of BOF slag is not available as most of the studies and inventions are focused on the co-utilization of these slags in very less proportion. BOF slag reduction, modification and fast air cooling for enhanced cementitious properties are not available. In present invention, BOF slag was re-melted, reduced, and fast cooled to obtain belite based cementitious material.

OBJECTS OF THE INVENTION

The main object of the present invention is directed to provide a method for the reduction of baic oxygen furnace (BOF) slag to produce belite rich cementitious material.

Yet another object of the present invention is to provide a method for bulk use of BOF slag to reduce the content of use of Portland cement clinker.

It is a further object of the present invention to provide a method to reduce and remove iron from the BOF steel slag.

It is another object of the present invention to use belite based cementitious material to make cement for increasing the compressive strength of the concrete.

It is another object of the present invention to beneficially use waste industrial material like steel slag in the production of cement/mortar/concrete.

It is an object of the present invention to reduce the cost of cement products.

It is a further object of the present invention to lower the heat of hydration of the cement.

It is a further object of the present invention to conserve the natural resources through replace them by BOF slag in cement manufacturing.

It is a further object of the present invention to reduce the carbon footprint through the reduction of Portland clinker composition in cement manufacturing.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to method of manufacturing belite based cementitious material from basic oxygen furnace slag involving remelting, reduction and metal separation from iron containing steel slag to render it suitable for cementitious material involving the following steps: Firstly, providing steel slag; then melting steel slag in a furnace at a temperature between 1600°C- 1650 °C; then, adding the reducing agents to the molten steel slag for reduction; next,separating the iron from the reduced steel slag; and lastly, the fast air cooling of reduced and iron seperated steel slag to obtain the belite based cementitious material.

There is further provided that the steel slag is selected from basic oxygen furnace slag.

There is further provided said method wherein the reducing agent is selected from source of carbon or aluminium without any impurities.

In accordance with the method of present invention,the mass percentage of the reducing agent used is 5% to 8.4%.

In accordance with the present invention,the said step of fast air cooling is carried out to maintain the belite content in the belite based cementitious material in the range of from 50% to 55%.

In accordance with the method of present invention, the belite based cementitious material is obtained free from lime.

According to a further aspect of the present invention directed to said method wherein, the belite based cementitious material is obtained with periclase percentage decreased from 10% in steel slag to 5% in the belite based cementitious material.

A still further aspect of the present invention is directed to said method comprising adding to said belite based cementitious material Portland clinker in a mass ratio of not more than 3:2 to produce cement.

Yet another aspect of the present invention is directed to provide cementitious material which is sourced from iron separated steel slag and contains belite based cementitious material in the range of 50% to 55%.

A further aspect of the present invention is directed to provide a cement comprising of belite based cementitious material and Portland clinker having compressive strength greater than 39 MPa and the heat of hydration in the range of 260 J/g to 263 J/g.

The above and other objects and advantages of the present invention are described hereunder in greater detail with reference to the following accompanying non-limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 illustrates the flow chart of a method of manufacture of belite based cementitious material from steel slag;

FIG. 2 illustartes the XRD analysis of raw BOF slag;

FIG. 3: illustartes the XRD analysis of belite based cementitious material;

Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity to help to improve understanding of embodiments of the invention.

DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS

The accompanying figure together with the detailed description below forms part of the specification and serves to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

The present invention is now discussed in more detail referring to the drawings that accompany the present application. In the accompanying drawings, like and/or corresponding elements are referred to by like reference numbers.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts.

Before describing in detail embodiments that are in accordance with the invention, it should be observed that the embodiments reside primarily to the full metallurgical reduction of the steelslag and conversion to belitic form, having belite phase of Portland clinker. More specifically, the present invention relates to the utilization of steel slag as a starting material. The slag was re-melted, reduced and fast cooled which resulted in a belite based cementitious material.

The present invention discloses a steel slag reduction method to form belite based cementitious material. Method 100 as illustrated in FIG.1 comprises the following steps. In step 102, BOF slag is provided. The slag is selected from basic oxygen furnace slag., the steelslag is melted in a furnace at a temperature between 1600°C - 1650 °C. The slag was melted in the Tammann furnace.

In step 104, the reducing agents are added to the steel slag.The melting and reduction of are done to recover the hot metals. The reducing agent is selected from the group consisting of source of carbon or aluminium without any impurities. The mass percentage of the reducing agent is 5% to 8.4%.

In step 106, the iron is separated from the reduced BOF slag.The hot metal that is iron was separated.

Lastly in step 108, fast air cooling is performed for the reduced and iron separated BOF slag to obtain a belite based cementitious material.The fast air cooling after re-melting was also done in order to prevent free lime and periclase formation during the cooling of the melted BOF slag.The belite content of the belite based cementitious material is in the range of 50% to 55%. The belite based cementitious material is free from lime

The cementitious material is mixed with Portland clinker in a mass ratio of 3:2 to form cement. The belite based cementitious material is mixed with Portland clinker in a mass ratio of not more than 3:2 to form cement. The cement prepared has a compressive strength greater than 39 MPa and heat of hydration in the range of 260 J/g to 263J/g.

Hence the steel slags could be effectively utilized in the manufacturing of cement. This will not only save natural resources but also help in reducing landfilling issues and encouraging cleaner production. The sustainable use of slags will also contribute towards environment friendly, economical, and energy-efficient construction.It works as an efficient metal recovery process.It provides the cement industry with alternative cementitious material.It also provides protection for natural resources and reserves. The products are cost-effective as well as eco-friendly as waste materials from the steel industry were valorised.

In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or composition that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article or composition. An element proceeded by "comprises...a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or composition that comprises the element.

In the present specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless specifically stated otherwise.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. Commonly used dictionary-defined terms are additionally interpreted as having meanings consistent with related technical documents and currently disclosed content and are not interpreted as ideal or very formal meanings unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

In addition, unless otherwise specified, % means weight%.

The advantages and features of the present invention and methods for achieving them will be clarified with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms, and only the embodiments allow the disclosure of the present invention to be complete, and are conventional in the art to which the present invention pertains. It is provided to fully inform the knowledgeable person of the scope of the invention, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same components throughout the specification.

Thus, in some embodiments, well-known techniques are not specifically described to avoid obscuring the present invention. Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used as meanings commonly understood by those skilled in the art to which the present invention pertains.

The present invention is described further hereinafter by reference to a series of accompanying examples.

Experiments that were actually performed are now described by way of the following examples.

Examples
Example 1: Chemical evaluation of BOF slag
The analyses of BOF slag was done by XRF, gravimetric (SO3), titration (S2-, Cl-, free lime), photometry (Cr-VI, F-), and infrared spectroscopy (CO2 and H2O). Table 1 illustrates the chemical analysis of BOF slags. Table 2 illustrates the XRD analysis of BOF slag.

Table 1: Chemical composition of the BOF slag (in wt.-%)
Elements BOF Slag
CaO 42.2
CaOfree, titra. 6.1
MgO 8.2
SiO2 12.1
Al2O3 4.1
TiO2 0.67
Na2O ?d.l.
K2O 0.03
Fetotal 16.7
Femet* 1.85
FeO * 11.9
Fe2O3 * 8.74
P2 O5 1.79
Stotal 0.12
SO3, gravi. 0.11
S2-titra 0.02
Cr 0.075
Cr-VI, photo[mg/kg] ?0.0
Cl-titra. ?0.001
Mn 1.433
V 0.053
CO2 , IR 1.2
H2O, IR 2.7
C/S 3.49
* Separate analyses of Fetotal, Femet., FeO and Fe2O3 calculation

Table 2: Semi-quantitative evaluation of the XRD diagram (FIG.2) of BOF slag(in wt.-%)
Phase BOF Slag
Quartz <5
Larnite (Ca2SiO4)- ß C2S <50
Srebrodolskite Ca2(Fe, Al)2O5 15
Lime 10
Portlandite 5
Calcite <5
Periclase Mg 0,7 Fe0,1 O 10
Wustite FeOx 10

According to XRD analysis of raw BOF slag in FIG. 2, the BOF slag showed major peaks of larnite. Quantatitive analysis of XRD pattern revealed that raw BOF slagcontained about 50% ß-belite. However, it reacts very slowly. The presence of free lime and periclase was also a concern for the BOF slag. The composition of Fetotal in BOF slag was found high which is the sole reason for remelting, reduction, and metal separation from the slag.

Example 2: Method of manufacture of belite based cementitious material from BOF slag
A BOF slag reduction method to form belite based cementitious material comprising of following steps. Firstly, batching the BOF slag; secondly, melting BOF slag in a furnace at a temperature between 1600°C- 1650 °C; thirdly, adding the reducing agents to the molten steel slag for reduction; fourthly,separating the iron from the reduced steel slag; and lastly, fast air cooling for the iron separated steel slag to obtain the belite based cementitious material.

The treatment conditions for BOF slag are given in Table 3.

Table3: Treatment conditions for BOF slag
Temp. Reduction agent Cooling
? Type Addition
- Wt.-%
BOF 1650 C, Al 3.2, 1.3 Fast air Cooling

Example 3: Chemical analysis of reduced BOF slag

Table 4 represents the chemical analysis of the reduced BOF slag. The analysis reflected the recovery of 98.3% of Fe from the original slag. Table 4 reveals the mineralogical analysis of reduced BOF slag which clearly shows the decrease of Fe from 16.7 to 0.28 in reduced slag.

Table 4:Chemical composition of the modified BOF (in wt.-%)
BOF Slag
Insoluable residue 0.24
CaO 44.5
MgO 10.2
SiO2 31.5
Al2O3 9.37
TiO2 0.78
Na2O 0.00
K2O 0.01
Fetotal 0.28
Femet* ? 0.1
FeO * ? 1.0
Fe2O3 * 0.40
Stotal 0.14
SO3, gravi. 0.15
S2-titra 0.10
Cr [mg/kg] 91
Cl-titra. 0.009
Mn 1.32
V[mg/kg] 211
CO2 , IR 0.15
H2O, IR 0.11
C/S 1.41
* Separate analyses of Fe total, Fe met., FeO and Fe2O3 calculation

Example 4: Effect of fast air cooling on the belite content of belite based cementitious material

FIG. 3 represents the image of XRD analysis of belite based cementitious material. The patternrepresents the minerology of the cementitious material formed by using BOF slag.

Table 5 represents the compositionsal analysis of the cementitious material. Dicalciumsilicate (ß- belite) is found as major compound of the cementitious material.

Table 5: Semi-quantitative evaluation of the XRD diagrams (in wt.-%)
Phase BOF Slag
C3S (Ca3SiO5) 15-20
Larnite (Ca2SiO4)- ß C2S 50-55
Brownmillerite Ca2FeAlO5 10
Periclase Mg 0,7 Fe0,1 O <5
Wustite FeOx 5

Example 4: Comparision of cement made from belite based cementitious material formed by reduced BOF slagwith Portland Slag Cement (PSC)

Cement was made from modified, iron separated BOF slagand belite based cementitious material separately and was tested and compared for properties. The modified, iron separated BOF slag and belite based cementitious materialwere blended with Portland clinker in the ratio of 3:2then tested for compressive strength and heat of hydration test.

The strength properties and heat of hydration of the cement prepared with cementitious material of the present invention were compared with the strength properties and heat of hydration of Portland slag cement inTable 6.

Table 6:Comparision of propertiesof different cements containing belite based cementitious binder and PSC
Belite based cementitious material Cement Portland Slag Cement
Steel Slag 60 0 Wt.-%
GBS - 60 Wt.-%
OPC Clinker 40 40 Wt.-%
w/c (Water to cement ratio) 0.505 0.485 -
Spread 208 206 mm
1 day Compressive Strength 3.4 5.8 MPa
3 daysCompressive Strength 12.9 19.6 MPa
7 days Compressive Strength 24.5 33.2 MPa
28 days Compressive Strength (IS 383) 39.3 49.3 MPa
Heat of Hydration
7 days (w/c = 0.50) 263 260 J/g

The strong impact of the belite based cementitious materialwas recognizable in the heat of hydration analysis. The cement developed by belite based cementitious material generates more heat of hydration than Portland Slag cement. The water demand increament was also found negotiable with water to cement (w/c) ratio of 0.505. The cement comprising the belite based cementitious material has compressive strength greater than 39 MPa and the heat of hydration in the range of 260 J/g to 263 J/g of the heat of hydration.