Claims:1. A method for recycling slag produced during steelmaking process, the method comprising acts of:
introducing, a pre-determined quantity of boron oxide (B2O3) into the slag to form a mixture;
treating, the mixture with at least one carbonaceous reductant at a first pre-determined temperature, to obtain a treated slag, wherein, the boron oxide (B2O3) maintains the slag in a fluid state during the treating;
cooling, the treated slag to a second pre-determined temperature, wherein the treated slag solidifies during cooling; and
ageing, the solidified slag for a pre-defined period of time;
wherein, the solidified slag disintegrates into a mineral fraction and a metallic fraction during ageing.

2. The method as claimed in claim 1, wherein boron oxide (B2O3) is introduced into the slag during treating of the slag with the carbonaceous reductant.

3. A method for processing slag during steelmaking process, the method comprising acts of:
adding, a pre-determined quantity of boron oxide (B2O3) to molten iron;
separating, a mixture of slag and boron oxide (B2O3) from a crude steel;
recycling, the mixture, wherein the recycling comprising acts of:
treating, the mixture with at least one carbonaceous reductant at a first pre-determined temperature, to obtain a treated slag, wherein, the boron oxide (B2O3) maintains the slag in a fluid state during the treating;
cooling, the treated slag to a second pre-determined temperature, wherein the treated slag solidifies during cooling; and
ageing, the solidified slag for a pre-defined period of time;
wherein, the solidified slag disintegrates into a mineral fraction and a metallic fraction during ageing.

4. A method for processing iron ore, the method comprising acts of:
adding, a pre-determined quantity of boron oxide (B2O3) to the iron ore;
reducing, a mixture of iron ore and boron oxide (B2O3) in a blast furnace to obtain an aggregate of molten iron and boron oxide (B2O3);
subjecting, the aggregate of molten iron and boron oxide (B2O3) to a steelmaking process;
separating, a mixture of slag and boron oxide (B2O3) from a crude steel after the steelmaking process;
recycling, the mixture of slag and boron oxide (B2O3), wherein the recycling comprising acts of:
treating, the mixture of slag and boron oxide (B2O3) with at least one carbonaceous reductant at a first pre-determined temperature, to obtain a treated slag, wherein, the boron oxide (B2O3) maintains the slag in a fluid state during the treating;
cooling, the treated slag to a second pre-determined temperature, wherein the treated slag solidifies during cooling; and
ageing, the solidified slag for a pre-defined period of time;
wherein, the solidified slag disintegrates into a mineral fraction and a metallic fraction during ageing.

5. The methods as claimed in claims 1 or 3 or 4 comprises an act of pouring the treated slag on a surface before cooling.

6. The methods as claimed in claims 1 or 3 or 4, wherein the steelmaking process is primary steelmaking process.

7. The method as claimed in claim 6, wherein the primary steelmaking process is carried out by at least one of basic oxygen steelmaking (BOF) process and electric arc furnace (EAF) process.

8. The methods as claimed in claims 1 or 3 or 4, wherein the carbonaceous reductant is at least one of coal dust, pearl coke, nut coke, coke breeze and coke return fines.

9. The methods as claimed in claims 1 or 3 or 4, wherein the slag is treated with carbonaceous reductant in a vessel with carbon lining on its inner surface.

10. The method as claimed in claim 9, wherein the slag is introduced into the vessel in at least one of solid state and liquid state.
11. The methods as claimed in claims 3 or 4 comprises an act of pouring the slag into container after separating the mixture of slag and boron oxide from the crude steel.

12. The method as claimed in claim 11 comprises an act of optionally cooling the mixture of slag and boron oxide (B2O3) by water quenching after separating the slag.

13. The methods as claimed in claims 1 or 3 or 4, wherein ageing of the treated slag is carried out under normal atmospheric conditions.

14. The methods as claimed in claims 1 or 3 or 4, wherein the pre-defined period of time ranges from about 1 day to 10 days.

15. The methods as claimed in claims 1 or 3 or 4, wherein the first predetermined temperature ranges from about 1400 ºC to 1700ºC.

16. The methods as claimed in claims 1 or 3 or 4, wherein the second pre-determined temperature is room temperature.

17. The methods as claimed in claims 1 or 3 or 4, wherein the pre-determined quantity of boron oxide (B2O3) is introduced into the slag, such that the treated slag contains boron oxide (B2O3) ranging from about 1 wt% to about 2 wt %.

18. The methods as claimed in claims 1 or 3 or 4, wherein the pre-determined quantity of boron oxide (B2O3) is introduced into the slag, such that free lime content of the treated slag is below 3 wt %.

19. A slag recycled by methods as claimed in claims 1 or 3 or 4, comprising:
Calcium oxide (CaO) at about 35 wt% to about 55 wt %;
Silicon dioxide (SiO2) at about 7 wt% to about 30 wt %;
Phosphorous pentoxide (P2O5) at about 1 wt% to about 5 wt %;
Iron oxide (FeO) at about 10 wt% to about 50 wt %;
Iron (Fe) at about 5 wt% to about 40 wt %;
Magnesium oxide (MgO) at about 2.5 wt% to about 8 wt %;
Manganese oxide (MnO) at about 0.3 wt% to about 6.5 wt %;
Aluminium oxide (Al2O3) at about 0.3 wt% to about 5 wt %
Free lime at about 5 wt% to about 20 wt %.
, Description:TECHNICAL FIELD

The present disclosure generally relates to a field of material science and metallurgy. Particularly, but not exclusively, the present disclosure relates to treatment of slag produced during the steelmaking process. Further embodiments of the present disclosure disclose a method for recycling of slag produced during primary steelmaking process.

BACKGROUND OF THE DISCLOSURE

Steel is an alloy of iron and carbon and is by far the most widely used material for building the world’s infrastructure and industries. Steels are used in fabricating almost everything, from sewing needles to oil tankers. In addition, the tools required to build and manufacture are made of steel as well. Conventionally, for producing steel, raw iron ores which is removed from the earth is fed into the blast furnace plant in the form of pellets or sinters and is subjected to treatment to obtain hot metal iron in liquid state. The hot metal is then subjected to further treatment to obtain steel i.e. the hot metal undergoes primary steelmaking process and secondary steelmaking process to obtain steel.

The primary steelmaking process is typically carried out by basic oxygen steel making process, generally using a Linz - Donawitz (LD) converter which uses pure oxygen to obtain crude steel. The crude steel obtained during the primary steelmaking process is known to contain large amount of slag. For instance, the primary steelmaking process generates about 120 kg to about 200 kg of slag per ton of steel production. Since the quantity of slag produced is large, recycling of this slag for further applications is vital. The primary steelmaking slag typically comprises of metal oxides such as calcium oxide (CaO), silicon dioxide (SiO2), phosphorous pentoxide (P2O5), iron oxide (FeO) etc. The slag when recycled could be used in applications such as but not limiting to metallurgical flux for processed raw materials like sinters and pellets for ironmaking in a blast furnace. The slag produced during primary steelmaking process is known to become very viscous with the lowering of its iron oxide content, primarily due to rise in the slag liquidus temperature with the lowering of its iron oxide content. Another important attribute of the primary steelmaking slag is its high slag basicity (CaO/SiO2 ratio) which affects the outcome of slag after recycling for further applications. Considering the limitations of melt viscosity and free lime content of slag, a number of methods for recycling of slag have been previously proposed.

In one such conventional method, slag is heated and subjected to reduction process in a graphite crucible. The reduction reaction produces a slag fraction with leaner FeO and P2O5 contents and a metallic fraction which is essentially a Fe-C-P alloy. However, due to introduction of SiO2 during slag reduction process, the weight ratio of CaO/SiO2 is altered and hence the reduced slag fraction would agglomerate with the metallic fraction on solidification. Thereafter, physical separation of these two fractions would demand additional efforts for separation and thus making the process complex.

In another such conventional methods, a mixture of slag is subjected to treatment with reducing agent containing carbon, silicon, aluminium etc. The slag is reduced to recover iron and phosphorous from iron oxide and phosphorous oxide. The treatment is carried out in an electric furnace, in which blast furnace hot metal is added to facilitate separation of high phosphorous iron from the slag. However, it has been observed that there is a significant quantity of free lime present in the treated mineral fraction of the slag and the presence of free lime in the mineral fraction hinders its usage for the intended applications. In yet another method of recycling of slag, steelmaking slag is reduced using reductants like carbon, aluminium or silicon. Further, additives like bauxite ore are deliberately added to increase the alumina content in the slag and the slag metal physical separation is carried out in the molten state itself. However, there is substantial amount of alumina in the final mineral fraction which limits its usage for further processing of iron and steel.

Furthermore, in one of the conventionally known techniques, a metallo-thermic reduction of molten steelmaking slag for reducing the FeO and P2O5 contents is described. However, due to the addition of metallo-thermic reducing agents, the basicity of the slag was brought down and this compromise on reduction of slag basicity makes the treated slag not suitable as a fluxing agent in blast furnace.

In the above described conventional methods and other conventional methods which are not particularly described herein for reusing the steelmaking slag pose a number of problems. These problems include increase in viscosity of molten primary steelmaking slag with decrease in iron oxide content, which leads to high free lime content, which is undesirable. Also, in most of the conventional methods, the slag is treated with SiO2 which results in variation in slag basicity. If the slag basicity is not maintained as high as initial, the treated mineral fraction of the slag is known to contain significant quantity of free lime which limits its application. Also, as described in some of the conventional methods above, separation of treated slag and recovered metal after solidification is difficult as the two fractions amalgamate in solid state. This makes the process complex. Yet another limitation of the conventional methods is that when metallothermic reduction of primary steelmaking slag by FeSi or Al, or treatment involving additions of alumina bearing materials to the slag is carried out, composition of the slag is disturbed and thus making it unfit for recycling as a flux in the ironmaking and steelmaking operations.

In light of the foregoing discussion, there is a need to develop an improved method for recycling of slag produced during primary steelmaking process to overcome limitations stated above.

SUMMARY OF THE DISCLOSURE

One or more shortcomings of the prior art are overcome by method as disclosed and additional advantages are provided through the method as described in the present disclosure.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

In one non-limiting embodiment of the disclosure, there is provided a method for recycling slag produced during steelmaking process. The method comprises acts of introducing a pre-determined quantity of boron oxide (B2O3) into the slag to form a mixture. Then, the mixture is treated with at least one carbonaceous reductant at a first pre-determined temperature to obtain a treated slag. The boron oxide (B2O3) maintains the slag in a fluid state during the treating. The method further comprises acts of cooling the treated slag to a second pre-determined temperature, the treated slag solidifies during cooling and ageing the solidified slag for a pre-defined period of time. The solidified slag upon ageing disintegrates into a mineral fraction and a metallic fraction during ageing.

In an embodiment of the disclosure, boron oxide (B2O3) is introduced into the slag during treating of the slag with the carbonaceous reductant.

In another non-limiting embodiment of the disclosure, there is provided a method for processing slag during steelmaking process. The method comprises acts of adding a pre-determined quantity of boron oxide (B2O3) to molten iron and separating a mixture of slag and boron oxide (B2O3) from a crude steel. Then, the mixture is recycled, which comprises acts of treating the mixture with at least one carbonaceous reductant at a first pre-determined temperature to obtain a treated slag, the boron oxide (B2O3) maintains the slag in a fluid state during the treating, cooling the treated slag to a second pre-determined temperature, the treated slag solidifies during cooling. The recycling further comprises act of ageing the solidified slag for a pre-defined period of time, the solidified slag disintegrates into a mineral fraction and a metallic fraction during ageing.

In another non-limiting embodiment of the disclosure, there is provided a method for processing iron ore. The method comprises acts of adding a pre-determined quantity of boron oxide (B2O3) to the iron ore, reducing a mixture of iron ore and boron oxide (B2O3) in a blast furnace to obtain an aggregate of molten iron and boron oxide (B2O3), and subjecting the aggregate of molten iron and boron oxide (B2O3) to a steelmaking process. The method further comprises acts of separating a mixture of slag and boron oxide (B2O3) from a crude steel after the steelmaking process and recycling the mixture of slag and boron oxide (B2O3). The recycling of slag comprises acts of treating the mixture with at least one carbonaceous reductant at a first pre-determined temperature to obtain a treated slag, the boron oxide (B2O3) maintains the slag in a fluid state during the treating, cooling the treated slag to a second pre-determined temperature, the treated slag solidifies during cooling. The recycling further comprises act of ageing the solidified slag for a pre-defined period of time, the solidified slag disintegrates into a mineral fraction and a metallic fraction during ageing.

In an embodiment of the disclosure, the methods comprise an act of pouring the treated slag on a surface before cooling.

In an embodiment of the disclosure, the steelmaking process is primary steelmaking process.

In an embodiment of the disclosure, the primary steelmaking process is carried out by at least one of basic oxygen steelmaking (BOF) process and electric arc furnace (EAF) process.
In an embodiment of the disclosure, the carbonaceous reductant is at least one of coal dust, pearl coke, nut coke, coke breeze and coke return fines.

In an embodiment of the disclosure, the slag is treated with carbonaceous reductant in a vessel with carbon lining on its inner surface.

In an embodiment of the disclosure, the slag is introduced into the vessel in at least one of solid state and liquid state.

In an embodiment of the disclosure, the methods comprise an act of pouring the slag into container after separating the mixture of slag and boron oxide from the crude steel.

In an embodiment of the disclosure, ageing of the treated slag is carried out under normal atmospheric conditions.

In an embodiment of the disclosure, the pre-defined period of time ranges from about 1 day to 10 days.

In an embodiment of the disclosure, the first predetermined temperature ranges from about 1400ºC to 1700ºC.

In an embodiment of the disclosure, the second pre-determined temperature is room temperature.

In an embodiment of the disclosure, the pre-determined quantity of boron oxide (B2O3) is introduced into the slag, such that the treated slag contains boron oxide (B2O3) ranging from about 1 wt% to about 2 wt %.

In an embodiment of the disclosure, the pre-determined quantity of boron oxide (B2O3) is introduced into the slag, such that free lime content of the treated slag is below 3 wt %.

In yet another non-limiting embodiment of the disclosure, the slag recycled by a method as disclosed above, comprises Calcium oxide (CaO) at about 35 wt% to about 55 wt%, Silicon dioxide (SiO2) at about 7 wt% to about 30 wt%, Phosphorous pentoxide (P2O5) at about 1 wt% to about 5 wt%, Iron oxide (FeO) at about 10 wt% to about 50 wt%, Iron (Fe) at about 5 wt% to about 40 wt%, Magnesium oxide (MgO) at about 2.5 wt% to about 8 wt%, Manganese oxide (MnO) at about 0.3 wt% to about 6.5 wt%, Aluminium oxide (Al2O3) at about 0.3 wt% to about 5 wt%, Free lime at about 5 wt% to about 20 wt%.

It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

The novel features and characteristics of the disclosure are set forth in the appended description. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

FIG.1 illustrates a flowchart depicting a method for recycling slag produced during steelmaking process according to an embodiment of the present disclosure.

FIG.2A illustrates a schematic representation of introduction of Boron oxide (B2O3) into solid slag during recycling of the solid slag with carbonaceous reductant using method of FIG.1, according to some embodiment of the present disclosure.

FIG.2B illustrates a schematic representation of introduction of Boron oxide (B2O3) into liquid slag during recycling of the liquid slag with carbonaceous reductant using method of FIG.1, according to some embodiment of the present disclosure.

FIG.3A illustrates a schematic representation of addition of Boron oxide (B2O3) during steelmaking process and introducing a mixture of solid slag and B2O3 into a reaction chamber for recycling the solid slag using method of FIG.1, according to some embodiment of the present disclosure.

FIG.3B illustrates a schematic representation of addition of Boron oxide (B2O3) during steelmaking process and introducing a mixture of liquid slag and B2O3 into a reaction chamber for recycling the liquid slag using method of FIG.1, according to some embodiment of the present disclosure.

FIG.4A illustrates a schematic representation of addition of Boron oxide (B2O3) during ironmaking process and introducing a mixture of solid slag (produced during steelmaking process) and B2O3 into a reaction chamber for recycling the solid slag using method of FIG.1, according to some embodiment of the present disclosure.

FIG.4B illustrates a schematic representation of addition of Boron oxide (B2O3) during ironmaking process and introducing a mixture of liquid slag (produced during steelmaking process) and B2O3 into a reaction chamber for recycling the liquid slag using method of FIG.1, according to some embodiment of the present disclosure.

FIG.5 illustrates a photographic view of tapping or pouring of treated slag on a surface, according to some embodiment of the present disclosure.

FIG.6 illustrates graphical representation of the results of X-Ray Diffraction (XRD) analyses before the slag is subjected to treatment in comparison with the slag after treatment using method of FIG.1, according to some embodiment of the present disclosure.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent methods do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such method. In other words, one or more acts in a method proceeded by “comprises… a” does not, without more constraints, preclude the existence of other acts or additional acts in the method.

To overcome one or more limitations stated in the background, the present disclosure discloses a method for recycling slag produced during steelmaking process. The present disclosure particularly discloses method for recycling slag produced in the primary steelmaking process. In the present disclosure, the slag produced during primary steelmaking process is treated with carbonaceous reductant and during the treatment even though the content of FeO and P2O5 reduces, the slag is maintained in fluid state at high temperature in the range of about 1600°C. Accordingly, by adopting the method of present disclosure, the slag generates mineral and metallic fractions. The treated mineral fraction of the slag is found to be rich in tri-calcium silicate with very low free lime content. This treated slag therefore can be used in applications such as to partially substitute Ordinary Portland Cement (OPC) cement or clinker in cement manufacturing. Further, the mineral fraction of the slag recycled has significant inherent hydraulic binding attribute. Therefore, it can be used as an industrial binder for agglomeration of fines and for production of self-setting lime rich pellets which can be charged as flux in ironmaking and steelmaking processes. In addition, the treated metallic fraction of the slag consists of high phosphorous content and this composition of the recovered metallic fraction is suitable for wide range of applications. Also, in the method as disclosed in present disclosure, the separation of metallic fraction and mineral fraction is simple, as the mineral fraction naturally disintegrates from the treated slag. Thus, unlike the conventional methods where further operations like grinding and magnetic separation of slag – metal mixture maybe required, the present disclosure doesn’t necessitate further operations for separation.

In the method of present disclosure, the slag produced during primary steelmaking process is subjected to recycling. In an embodiment of the disclosure, the primary steelmaking process is carried out by at least one of basic oxygen steelmaking (BOF) process or electric arc furnace (EAF) process. The slag is treated in a carbon-lined vessel using carbonaceous reductants at a first pre-determined temperature. In one embodiment, the first pre-determined temperature is about 1600°C and is generally in the range of 1400°C to 1700°C. The system where reduction mechanism is carried out is referred to as reaction system. In an embodiment of the disclosure, the carbonaceous reductants includes but is not limited to coal dust, pearl coke, nut coke, coke breeze and coke return fines. Further, as highlighted in previous paragraphs, with the reduction of FeO content, the fluidity of the slag reduces and this is not desirable. Hence, to maintain the fluidity of primary steelmaking slag at temperature of about 1600°C, boron oxide (B2O3) bearing or forming material is introduced into the reaction system. In an embodiment of the disclosure, boron oxide (B2O3) may be introduced to the slag during reduction process. In an alternative embodiment, the boron oxide (B2O3) can be added to iron ore during ironmaking or hot metal iron during steelmaking, so that the slag separated from the crude steel during primary steel making will have boron oxide (B2O3) in it. The boron oxide (B2O3) material is alternatively referred to as modifier in the present disclosure. The boron oxide (B2O3) bearing or forming material assists in maintaining fluidity of the slag during the reduction mechanism at a temperature range of 1600°C in spite of reduction in iron oxide (FeO) content. The amount of boron oxide (B2O3) introduced into the slag is such that final content of the treated slag contains about 1 wt% to 2 wt% of boron oxide (B2O3). Once the slag is treated with carbonaceous reductant in the reaction system, the treated slag is tapped or poured into a non-wettable container or over an open surface and is allowed to solidify subjected to cooling for solidification of the slag. In an embodiment of the disclosure, the slag is cooled to room temperature. The slag after solidification is subjected to ageing for few days. Ageing of slag results in two fractions – metallic fraction and mineral fraction, each fraction further used in various applications. In an embodiment of the disclosure, with the ageing of solidified slag under normal atmospheric conditions, the mineral fraction naturally disintegrates into a fine powder, while the metallic fraction is in the form of lumps. Since, the mineral fraction is of very fine size, separation of mineral and metallic fractions can be done by simple screening methods unlike the prior arts where separation process is complex.

Henceforth, the present disclosure is explained with the help of figures for recycling slag produced during steelmaking process, particularly primary steelmaking process. However, such exemplary embodiments should not be construed as limitations of the present disclosure. A person skilled in the art can envisage various such embodiments without deviating from scope of the present disclosure.

FIG.1 is an exemplary embodiment of the present disclosure which illustrates a flowchart depicting a method for recycling slag produced during steelmaking process. In the present disclosure, the method intends to recycle and utilize the significant amount of slag produced during primary steelmaking process. Accordingly, by subjecting the slag for treatment, it could be used as a flux in ironmaking and steelmaking processes, also treated mineral fraction of the slag is found to be rich in tri-calcium silicate with very low free lime content. This treated slag can therefore be used to partially substitute OPC cement or clinker in cement manufacturing and various other applications. The method of the present disclosure to recycle the primary steelmaking slag is now described with reference to the flowchart blocks and is as below –

At block 101, the method comprises an act of introducing pre-determined quantity of boron oxide (B2O3) into the slag. The slag, to which B2O3 is introduced, is obtained during primary steelmaking process. In an embodiment of the disclosure, B2O3 is introduced into the slag in the form of boron oxide (B2O3) bearing material or boron oxide (B2O3) forming material. The boron oxide (B2O3) bearing or forming material is introduced into the slag to maintain fluidity of the slag at first predetermined temperature. In an embodiment of the disclosure, the first predetermined temperature is in the range of about 1400°C to 1700°C, in an exemplary embodiment it is about 1600°C. The fluidity of the slag which is dependent on the iron oxide (FeO) content is maintained at this temperature even though there is continuous fall of iron oxide (FeO) content in the slag. By introducing B2O3 into the slag, melting point of the slag reduces and hence fluidity of the slag is maintained. Further, the addition of boron oxide (B2O3) also reduces the free lime content of the slag and hence could be used for its intended applications. The slag and boron oxide (B2O3) forms a mixture and B2O3 could be introduced into the slag at various stages.

At block 102, the method comprises act of treating the mixture with carbonaceous reductant at a first pre-determined temperature. In an embodiment of the disclosure, the first pre-determined temperature is about 1600°C and is generally in the range of 1400°C to 1700°C. The slag is treated in a carbon-lined vessel through a reduction mechanism with carbonaceous reductants such as but not limited to coal dust, pearl coke, nut coke, coke breeze and coke return fines. In an embodiment of the disclosure, the slag in the vessel is fed as solid or liquid and the system for carrying out reduction mechanism is referred to as reaction system. As highlighted in the previous paragraphs, introduction of B2O3 assists in maintaining the slag at fluid state at a temperature of about 1600°C by reducing the melting point of slag and B2O3 bearing or forming material could be introduced into the slag at various stages. In an embodiment of the disclosure, the boron oxide (B2O3) bearing material or forming material is added to the slag during treating of the slag in the vessel or the reaction system. The B2O3could also be introduced into the reaction system to form a mixture with the slag before treating of the slag with the carbonaceous reductants. In an embodiment of the disclosure, B2O3 could be added to Linz Donawitz (LD) converter or Electric Arc Furnace (EAF) during steelmaking operation. In yet another embodiment of the disclosure, B2O3could be introduced into the slag by adding it to the iron ore in the blast furnace during ironmaking or hot metal formation process. In all the methods of addition of B2O3, the amount of B2O3 added is such that the final fraction of the slag is to contain about 1 wt% B2O3 to 2 wt% B2O3. The slag obtained after treating it in the vessel with carbonaceous reductants is referred to as treated slag. The treatment of slag with the carbonaceous reductant reduces oxides into metals by reacting with carbon to form a treated slag.

At block 103, the method comprises an act of cooling the treated slag to a second pre-determined temperature. The slag after treatment is tapped or poured into a non-wettable container or over an open surface, wherein the slag begins to cool. The cooling of the slag allows solidification of the treated slag. In an embodiment of the disclosure, the second pre-determined temperature is room temperature. In an exemplary embodiment of the disclosure, the room temperature ranges from about 15°C to 40°C.

After solidification of the treated slag, the solidified slag is subjected for ageing [as shown in block 104 under normal atmospheric conditions i.e. the solidified slag is maintained under normal atmospheric conditions for a pre-defined period of timer. In an embodiment of the disclosure, the pre-defined period of time ranges from about 1 day to 10 days. In an embodiment of the disclosure, the term normal atmospheric conditions refers to atmospheric condition at which the temperature at about 20°C and pressure of about 101.325 kPa.

With the ageing of solidified slag, the final fraction of the slag results into two fractions – mineral fraction and metallic fraction. The solidified slag when subjected to ageing for about 1 day to 10 days, the mineral fraction of the slag progressively crumbles into a fine powder while the metallic fraction are in the form of lumps. In an embodiment of the disclosure, the mineral fraction has a Blaine no. > 800 cm2/g. Since the mineral fraction is finer compared with the metallic fraction, separation of these two fractions is simple and can be carried out by simple methods such as but not limited to screening method. Hence, the final metallic and mineral fractions of the slag exhibiting desirable characteristics such as free lime content less than 3 wt%, good hydraulic binding property, cold compressive strength in the range of 55-75 kgf/piece etc could be used in wide range of applications.

Referring to FIG.2A - FIG.4B which are exemplary embodiments of the present disclosure illustrates various stages of introduction of boron oxide (B2O3) into the reaction system (204) for recycling slag produced during the steelmaking process. Boron oxide (B2O3) bearing or forming material is used as modifier, and is introduced into the slag for maintaining fluidity of the slag in the reaction system (204) with lowering of iron oxide (FeO) content. The B2O3 addition also helps in reducing the free lime content of the final fraction of the recycled slag and thus enabling optimum usage of the slag for further applications.

As illustrated in FIG.2A – FIG.4B, the boron oxide (B2O3) bearing or forming material interchangeably refereed as B2O3 or modifier may be added at various stages of the process. The process, in general involves several steps of recycling of the primary steelmaking slag in the reaction system (204). In an embodiment of the disclosure, boron oxide (B2O3) may be introduced to the slag during reduction process. In an alternative embodiment, the boron oxide (B2O3) can be added to iron ore during ironmaking or hot metal iron during steelmaking, so that the slag separated from the crude steel during primary steelmaking will have boron oxide (B2O3) in it.

The slag produced during steelmaking process may be recycled using the method as described in the present disclosure. Before, steel making process iron oxides extracted from the earth are treated in a blast furnace (205) [as shown in FIG.4A and FIG.4B] to obtain molten iron or hot metal iron in liquid state. This treatment of iron oxides or iron ore may be referred to as ironmaking process. In an embodiment of the disclosure, the resulting hot metal iron form the blast furnace (205) is charged into a Linz-Donawitz converter (201). Subsequently, the hot metal is subjected to basic oxygen process or main blow to obtain crude steel, this process is alternatively referred to as steelmaking process. Further, the liquid crude steel is tapped into a container and the slag resulting from the main blow is tapped into another container (202) for recycling in a reaction system (204). In an embodiment of the disclosure, the slag is primary steelmaking slag. Furthermore, the primary steelmaking slag could be introduced into the reaction system (204) in liquid state or solid state. In an embodiment of the disclosure, when primary steelmaking slag is to be introduced into the reaction system (204) in solid state, the primary steelmaking slag is additionally subjected to water quenching in a slag pit (203) and is crushed, magnetically separated, classified based on its size before undergoing carbo-thermic reduction process in the reaction system. Broadly, as shown in FIG.2A – FIG.4B, boron oxide (B2O3) bearing or forming material could be introduced at three stages – during treating of the slag in reaction system (204), during steelmaking in LD converter (201) and during ironmaking in blast furnace (205). These different stages of boron oxide (B2O3) addition are explained in subsequent paragraphs.

FIG.2A and FIG.2B are exemplary embodiments of the present disclosure which illustrates introduction of Boron oxide (B2O3) into slag during recycling of the slag with carbonaceous reductants. In these exemplary embodiments, boron oxide (B2O3) is added to the reaction system (204) during treating of the slag with carbonaceous reductants such as but not limited to coal dust, pearl coke, nut coke, coke breeze and coke return fines. Further the slag produced during primary steelmaking process can be fed into the reaction system in solid state [as shown in FIG.2A] or in the liquid state [as shown in FIG.2B]. As shown in FIG.2A and 2B, the hot metal iron is initially charged into LD converter (201) and is subjected to basic oxygen steelmaking process to obtain crude steel. After obtaining crude steel, the slag is separated from the liquid steel and is tapped into a container (202) for further recycling. Finally the slag along with carbonaceous reductants and B2O3 bearing material is charged into the reaction system (204) for recycling of the slag. If the slag obtained in primary steelmaking process is in solid state [as shown in FIG.2A], it is additionally subjected to water quenching in a slag pit (203). Further the slag is then crushed, magnetically separated and classified based on its size before charging it into the reaction system (204) for recycling.

FIG.3A and FIG.3B are exemplary embodiments of the present disclosure which illustrates introduction of Boron oxide (B2O3) into molten iron or hot metal iron during steelmaking process. As shown in FIG.3A and FIG.3B, the hot metal iron obtained from the blast furnace (205) is subjected to primary steelmaking process and then slag is separated from the crude steel. The primary steelmaking process may be carried out in any conventionally known methods including but limited to basic oxygen treatment in LD convertor (201). As the slag produced during primary steelmaking process may be used for various applications, the slag is recycled using the method as described in previous paragraphs. B2O3 which is used as modifier in the method may be introduced during the steelmaking process as shown in FIG.3A and FIG.3B. Here, the B2O3 is added to the molten iron into the LD convertor (201). As highlighted in the previous paragraph, the slag could be charged into the reaction system (204) in solid state [as shown in FIG.3A] or in the liquid state [as shown in FIG.3B]. The steps followed are similar to the steps described for FIG.2A and FIG.2B except that boron oxide (B2O3) bearing or forming material is added at a different stage.

In an embodiment of the disclosure, better results in terms of both high yield of B2O3 in the final treated mineral fraction of the slag and lower energy requirement for treatment of the slag is obtained when B2O3 is added during the steelmaking process to the LD converter as shown in FIG.3B. However, one should note that B2O3 added in other stages as described above and below would also help in achieving desired results and hence addition of B2O3 as shown in FIG.3B should not be considered as a limitation.

Referring to FIG.4A and FIG.4B which are exemplary embodiments of the present disclosure which illustrates schematic representation of introducing Boron oxide (B2O3) into iron oxides or iron ores in a blast furnace (205) during ironmaking process. In these exemplary embodiments of the present disclosure, the boron oxide (B2O3) bearing or forming material added to the blast furnace (205) results in hot metal iron consisting boron. This hot metal consisting boron in dissolved state is then fed into LD converter (201), wherein almost all of boron in oxidized form is transferred to primary steelmaking slag for further processing as described in pervious paragraphs. Further, similar to other methods of addition of B2O3, in this method too slag could be charged into the reaction system (204) in solid state [as shown in FIG.4A] or in the liquid state [as shown in FIG.4B].

In an embodiment of the present disclosure, a slag recycled by the methods of present disclosure comprises Calcium oxide (CaO) at about 35 wt% to about 55 wt %, Silicon dioxide (SiO2) at about 7 wt% to about 30 wt %, Phosphorous pentoxide (P2O5) at about 1 wt% to about 5 wt %, Iron oxide (FeO) at about 10 wt% to about 50 wt %, Iron (Fe) at about 5 wt% to about 40 wt %, Magnesium oxide (MgO) at about 2.5 wt% to about 8 wt %, Manganese oxide (MnO) at about 0.3 wt% to about 6.5 wt %, Aluminium oxide (Al2O3) at about 0.3 wt% to about 5 wt %, Free lime at about 5 wt% to about 20 wt %.

The slag as disclosed above when recycled with carbonaceous reductants by introducing boron oxide (B2O3) would have: mineral fraction with free lime content 3 wt%, mineral fraction Blaine no. > 800 cm2/g, mineral fraction with 1-2 wt % B2O3, good hydraulic binding property, rich in tri-calcium silicate with FeO < 2%, P2O5 < 1.5%, unaltered slag basicity (CaO/SiO2) in the range of about 2.8, cold - compressive strength in the range of about 55 – 75 kgf/piece.

Examples:

Further embodiments of the present disclosure will be described with examples of composition of carbonaceous reductant used for reduction mechanism. In an embodiment, the carbonaceous reductant used is coke breeze. Coke breeze of particular composition is used for treatment of primary steelmaking slag in a reaction system. The composition of coke breeze for which experiments were carried out is as shown in below table.

Carbon (C) [wt%] Ash [wt%] Volatiles [wt%] Sulphur (S) [wt%]
80 - 90 15 – 17 1 - 5 0.5 – 1.5

Table – 1
In one exemplary experimental test on the slag, 150 kg of solid primary steelmaking slag of size 2-10 mm was used for treatment with coke breeze for composition as mentioned in Table – 1. In this experimental, treatment of the primary steelmaking slag was carried out in a 150 kVA 3 phase AC Electric Arc Furnace comprising 3 electrodes. As solid slag is not electrically conductive, 2 kg of metallurgical coke was used to initiate electrical arcing. After about 2 hours of preheating of lining, 15 kg slag along with 1.5 kg pure B2O3 (99.55% purity) was charged at slow rate from hopper to the furnace through vibrator. It was possible to generate enough power due to resistance offered by three electrodes. A batch of 15 kg primary steelmaking slag was charged at 30 minutes interval. After melting 75 kg of this slag, it was possible to melt about 60 kg primary steelmaking slag without B2O3 within 30 minutes. Melting was smooth and the temperature of slag was estimated as 16000C using a properly calibrated optical pyrometer. A mixture of remaining 15 kg primary steelmaking slag with 15 kg coke breeze was charged in 2 batches at 7 minutes interval. Tapping of slag was carried after 15 min of addition of coke breeze into the melt. Tapping was done by oxygen lancing at a taphole provision in the experimental setup. The diameter of the taphole obtained after lancing was ~10mm. FIG.5 is an exemplary embodiment of the present disclosure which illustrates the flow of treated slag stream out of the furnace through this 10 mm diameter taphole. Hence, it is evident that the treated slag is sufficiently fluid at around 1600oC, so that it is able to drain out of a 10 mm taphole over a sand surface in open atmospheric conditions. On solidification and cooling till room temperature, the solidified treated lumps are kept in open atmosphere for few for example 1 day to 10 days of ageing. Due to progressive crumbling of the treated mineral fraction, the metallic and mineral fractions could be physically separated by screening the mixture through a fine mesh. The composition of the original slag and the separated metallic and mineral fractions are as shown in below table.

Slag Constituents Fe(T) FeO CaO SiO2 MgO Al2O3 P2O5
Free Lime
Original Slag (wt %) 15.65 10.78 53.67 14.40 1.58 0.97 2.00
10
Treated Slag (wt %) 1.2 0.90 66.46 22.55 0.68 4.21 0.81
2.3
Metal Constituents Fe(T) Mn P Si Ca
Recovered Metal (wt %) 82.72 2.23 3.91 2.67 5.2

Table – 2

Wherein, Fe (T) represents Iron (total), FeO represents Iron oxide, CaO represents Calcium oxide, SiO2 represents Silicon dioxide, MgO represents Magnesium oxide, Al2O3 represents Aluminium oxide, P2O5 represents Phosphorous pentoxide, Mn represents Manganese, P represents Phosphorous, Si represents Silicon and Ca represents Calcium.

It was observed that the final mineral fraction of the recycled slag was found to be below 3% and fineness of the treated mineral fraction is found to be of Blaine number 870 cm2/g. Further X-Ray Diffraction analyses were carried out on the original slag produced during primary steelmaking process, and mineral fraction of the treated slag.

Referring to FIG.6 which is an exemplary embodiment of the present disclosure which illustrates graphical representation of the results of XRD analyses carried out on the original primary steelmaking slag as against the results of XRD analyses carried out on the treated mineral fraction of the primary steelmaking slag by the method of present disclosure. As can be seen form the graph, pre-dominant phase of the treated mineral fraction of the slag is tri-calcium silicate and thus makes it suitable for a wide range of applications. Furthermore, the self-setting pellets prepared using the treated slag is found to have an average cold - compressive strength (CCS) of 60-70 kgf/piece and can be used as flux in ironmaking and steelmaking operations as a partial replacement of lime/limestone.

In another experimental process, test was carried out for treating 100 kg of primary steelmaking slag with the method of present disclosure. In this test 1 kg pure B2O3 (99.55% purity) was mixed with 100 kg of slag produced during steelmaking process. Further, 10 kg of Coke breeze was introduced as the reductant in this test. By treating 100 kg of solid primary steelmaking slag, 21.5 kg of metallic fraction and 62 kg of mineral fraction were achieved. The natural disintegration of treated mineral fraction led to easy slag-metal separation after few days of ageing of the treated and solidified melt. Compositions of the initial slag and final product fractions are as shown in the below table.

Slag Constituents Fe(T) FeO CaO SiO2 MgO Al2O3 P2O5 Free Lime
Original Slag (wt %) 15.65 10.78 53.67 14.40 1.58 0.97 2.00 10
Treated Slag (wt %) 0.70 67.32 21.76 0.97 4.09 1.1 2.85
Metal Constituents Fe(T) Mn P Si C
Recovered Metal (wt %) 94.75 0.037 1.8 3.26

Table – 3

Wherein, Fe (T) represents Iron (total), FeO represents Iron oxide, CaO represents Calcium oxide, SiO2 represents Silicon dioxide, MgO represents Magnesium oxide, Al2O3 represents Aluminium oxide, P2O5 represents Phosphorous pentoxide, Mn represents Manganese, P represents Phosphorous, Si represents Silicon and Ca represents Calcium.

It was observed that the free lime content in the treated mineral fraction was found to be below 3%. Fineness of the treated mineral fraction is found to be of Blaine number 830 cm2/g.

In yet another experimental process, test was carried out for treating 207 kg of primary steelmaking slag with the method as disclosed in the present disclosure. In this test 2 kg pure B2O3 (99.55% purity) was mixed with 200 kg of the slag produced during primary steelmaking process. Further, 20 kg of Coke breeze was introduced as the reductant in this test. By treating 207 kg of solid slag, 28 kg of metallic fraction and 131 kg of mineral fraction were achieved. The natural disintegration of treated mineral fraction led to easy slag-metal separation after few days of ageing of the treated and solidified melt. Compositions of the initial slag and final product fractions are as shown in below table.

Slag Constituents Fe(T) FeO CaO SiO2 MgO Al2O3 P2O5 Free Lime
Original Slag (wt %) 15.65 10.78 53.67 14.40 1.58 0.97 2.00 10
Treated Slag (wt %) 1.55 66.52 22.55 1.66 3.18 1.14 1.89

Table – 4

It should be understood that the experiments are carried out for a particular type and composition of carbonaceous reductant as shown in Table – 1 and the carbonaceous reductant used is coke breeze. However, this composition and type of carbonaceous reductant should not be construed as a limitation to the present disclosure as it could be extended to other compositions and other types of carbonaceous reductants.

Advantages

The present disclosure discloses a method for recycling the slag produced during primary steelmaking process. By adopting the method of present disclosure, the final treated mineral fraction of the slag will have low free lime content and is rich in tri-calcium silicate while the slag basicity is unaltered. The slag thus can be used to partially substitute OPC (Ordinary Portland Cement) or clinker in cement manufacturing and the slag can also be charged as flux in ironmaking and steelmaking processes.

The present disclosure discloses a method for recycling the slag, wherein the mineral fraction naturally disintegrates into fine powder from the solidified slag and hence simple screening operation would be sufficient to separate metallic and mineral fraction of the treated slag.

Equivalents

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc. It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Referral Numerals

Referral Numerals Description
101-104 Flowchart blocks
101 Act of introduction of B2O3
102 Treatment stage
103 Cooling stage
104 Ageing stage
201 Linz – Donawitz (LD) converter
202 Container for collecting primary steelmaking slag
203 Slag pit
204 Reaction system
205 Blast furnace