Claims:WE CLAIM:
1. White aluminum dross based briquetted synthetic slag comprising (by weight percent):

CaO: 4 to 6; preferably about 4.81 wt.%.
Al2O3: 70 to 75; preferably about 73.91 wt.%
MgO: 6 to 8; preferably about 7.90 wt.%
SiO2: 1 to 4; preferably about 3.64 wt.%
Fe2O3: 0 to 1; preferably about 0.67 wt.%
Na2O: 2 to 3; preferably about 2.15 wt.%; and
K2O: 0.5 to 2; preferably about 0.95 wt.%; and
elemental content of Al 0.5 to 2 preferably about 0.75 wt.% and AlN 15 to 20 preferably about 17.15 wt.%

2. White aluminum dross based briquetted synthetic slag as claimed in claim 1 comprising sodium silicate binder as the briequetting material having melting point of 1088°C.
3. White aluminum dross based briquetted synthetic slag as claimed in anyone of claims 1 or 2 wherein said aluminium dross is sourced from raw white aluminum dross powder contains 10% greater than 600 micron size particles, 5% greater than 250 micron size particles, 12% greater than 160 micron size particles, 17% greater than 75 micron size particles and 56% less than 75 micron size particles.

4. White aluminum dross based briquetted synthetic slag as claimed in anyone of claims 1 to 3 wherein the white dross content is sourced from waste product of aluminium smelting processes.

5. White aluminum dross based briquetted synthetic slag as claimed in anyone of claims 1 to 4 comprising alkali oxides Na2O and K2O.

6. White aluminum dross based briquetted synthetic slag as claimed in anyone of claims 1 to 4 which is capable of achieving avg. desulphurization rate = 4.78 ppm/min., avg. nitrogen pick up = 16 ppm during secondary steel making process.

7. A process for the manufacture of white aluminum dross based briquetted synthetic slag as claimed in anyone of claims 1 to 6 comprising the steps of briquetting white aluminum dross with sodium silicate binder such as to obtain white aluminum dross based briquetted synthetic slag comprising (by weight percent):

CaO: 4 to 6; preferably about 4.81 wt.%.
Al2O3: 70 to 75; preferably about 73.91 wt.%
MgO: 6 to 8; preferably about 7.90 wt.%
SiO2: 1 to 4; preferably about 3.64 wt.%
Fe2O3: 0 to 1; preferably about 0.67 wt.%
Na2O: 2 to 3; preferably about 2.15 wt.%; and
K2O: 0.5 to 2; preferably about 0.95 wt.%; and
elemental content of Al 0.5 to 2 preferably about 0.75 wt.% and AlN 15 to 20 preferably about 17.15 wt.%
8. A process as claimed in claim 7, wherein the steps of manufacturing white aluminum dross based briquetted synthetic slag comprising
(i) providing the raw white aluminium dross powder comprising the composition by weight percent: % CaO 0.75-1.25, % Al2O3 76-78, % MgO 1-2, % SiO2 3-4, % Fe2O3 0-1, % Na2O 1-2 and % K2O 1-2, as well as % elemental Al 1-2 and % AlN 15-20;
(ii) screening said raw white aluminium dross powder to get rid of different foreign elements like metallic particles having greater than 5mm particle size;
(iii) mixing caustic calcined magnesia with said dross powder in the ratio of 1 to 6, to increase the MgO content in the product powder mixture;
(iv) mixing sodium silicate with water separately in binder preparation tank, followed by adding around 3 wt % (of the final product powder mixture) binder-water mixture to the previously made mixture of raw white aluminium dross powder and caustic calcined magnesia in step (iii);
(v) Next, this whole mixture of step (iv) is mixed with hydrated dolomite to get the final desired amount of MgO 6 to 8 wt% and CaO 4 to 6 wt% in final product powder mixture.
(vi) Subsequently, the final mixture is charged into a briquetting equipment where briquettes are formed by applying roll force in the range of 18 to 22 Ton.
(vii) Finally, briquettes are dried by blowing hot air having temperature in range of 140 deg C to 180 deg C.
9. A process for steel making involving synthetic slag during secondary steel making process including step of tapping of low carbon aluminium killed steel grades without any fume generation involving white aluminum dross based briquetted synthetic slag comprising:

CaO: 4 to 6; preferably about 4.81 wt.%.
Al2O3: 70 to 75; preferably about 73.91 wt.%
MgO: 6 to 8; preferably about 7.90 wt.%
SiO2: 1 to 4; preferably about 3.64 wt.%
Fe2O3: 0 to 1; preferably about 0.67 wt.%
Na2O: 2 to 3; preferably about 2.15 wt.%; and
K2O: 0.5 to 2; preferably about 0.95 wt.%; and
elemental content of Al 0.5 to 2 preferably about 0.75 wt.% and AlN 15 to 20 preferably about 17.15 wt.%
10. A process for steel making as claimed in claim 9 wherein the level of sodium oxide (Na2O) and potassium oxide (K2O) used in said white aluminum dross based briquetted synthetic slag during tapping of low carbon aluminum killed steel grades favour increasing fluidity of slag layer, and thereby improve kinetics of refining reaction between liquid steel and slag layer.
11. A process for steel making as claimed in claim 9 or 10 wherein 190 to 200 Kg of white aluminum dross based briquetted synthetic slag (briquetted by Sodium Silicate inorganic binder) is added to 180 to 190 tonne of liquid steel during tapping along with primary aluminum and lime in the ratio of around 4: 7: 18 (i.e. briquetted dross: primary aluminium: lime per ton of liquid steel tapped.)

12. A process for steel making as claimed in anyone of claims 9 or 10 wherein said white aluminum dross based briquetted synthetic slag enables avg. desulphurization rate = 4.78 ppm/min., avg. nitrogen pick up = 16 ppm.

13. A process for steel making as claimed in anyone of claims 9 to 11 wherein free aluminum in the form of elemental aluminum and aluminum nitride in said white aluminum dross based briquetted synthetic slag is used as a deoxidizer thereby favouring reducing consumption of primary aluminium per tonne of liquid steel produced.

14. A process for steel making as claimed in anyone of claims 9 to 12 wherein said white aluminum dross based briquetted synthetic slag used comprising sodium silicate binder having melting point of 1088°C as the briequetting material, so that the constituent compounds of the used synthetic slag dissolve fast due to the lower melting point and the binder succeeds to hold the constituent compounds before they dissolve into liquid steel, thereby arresting fume generation.

15. A process for steel making as claimed in anyone of claims 9 to 13 wherein in said White aluminum dross based briquetted synthetic slag said aluminium dross is sourced from raw white aluminum dross powder contains 10% greater than 600 micron size particles, 5% greater than 250 micron size particles, 12% greater than 160 micron size particles, 17% greater than 75 micron size particles and 56% less than 75 micron size particles.

16. A process for steel making as claimed in anyone of claims 9 to 14 wherein in said white aluminum dross based briquetted synthetic slag the white dross content is sourced from waste product of aluminium smelting processes.

Dated this the 19th day of March, 2019
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION:
Present invention relates to low cost white aluminium dross based briquetted synthetic slag and a process of steel making using the same during tapping of low carbon aluminum killed (LCAK) steel grades. This is a replacement of pre-melted synthetic slag which is costlier than white aluminum dross based briquetted synthetic slag. This invention is directed to the utilization of white aluminum dross based briquetted synthetic slag of selective composition wherein said white aluminum dross briquetted using sodium silicate binder, instead of costlier pre-melted synthetic slag, without hampering desulphurization rate and nitrogen pick up during secondary refining of steel. Available aluminum present in this slag in the form of elemental aluminum and aluminum nitride (AlN) can act as a deoxidizer. Aluminum nitride dissociates at steel making temperature and produce aluminum. Therefore, present invention can reduce primary aluminum (aluminum bar/ aluminum wire/ aluminumcube) consumption per heat during secondary steel making. This invention can effectively recycle waste product (white aluminum dross) of aluminum manufacturing companies around the world, reduce accumulation of white aluminum dross, thereby can diminish their harmful effect on soil and ground water. This invention ensures utilization of white aluminum dross based briquetted synthetic slag during tapping of low carbon aluminum killed steel grades without any fume generation, thereby assuring hazard free operation in the shop floor.
BACKGROUND OF THE INVENTION:
In recent years, consumption of natural resources has been increased significantly due to the extensive growth in world population. This situation has already aggravated the worrisome problem of waste management, more importantly to deal with toxic wastes. Generation of huge amount of waste everyday has already started to show it’s harmful impacts on environment. Proper disposal of aluminum dross produced during aluminum production process is a worldwide concern now. Aluminum manufacturing companies produce approximately four million tonnes of white dross and more than a million tonnes of black dross each year all over the world. These drosses are basically waste product of aluminum smelting process. Aluminum dross is classified based on the available aluminum metal content. Black dross contains low amount of metal and high amount of salts. On the other hand, white dross has high metal content and low amount of oxides and salts. Earlier, aluminum manufacturing companieswere interested to recover aluminum from aluminum dross. They used to process aluminum dross in rotary kilns using high amount of salt fluxes. This process consumes high amount of energy. After recovering aluminum, they used to send final waste (it is known as salt cake) for land filling. These salt cakes are potential source of toxic metal ions. It has harmful effect on soil and ground water. Therefore, search for alternate practices becomes an essential challenge for aluminum industry to process this huge amount of dross effectively for sustainable development. It was acknowledged that recycling is the best solution to this frightening condition.

The necessity to achieve high productivity and stringent quality simultaneously, steel makers divided the steel making process into two stages: (a) Primary steel making and (b) Secondary steel making. Primary steel making is basically practiced to convert carbon rich iron to steel. Any post primary steel making process prior to casting comes under secondary steel making process. The purpose of secondary steel making process is to produce properly deoxidized and homogenized steel having required chemistry, low level of inclusion (as low as possible) and appropriate temperature. Primary and secondary steel making at Applicant’s Steel Plant are done at Converter Cum Electric Arc Furnace (CONARC) and Ladle Furnace (LF) respectively. Deoxidation and synthetic slag practice are the two important secondary steel making process. It is necessary to remove dissolved oxygen from liquid steel after primary steel making process to avoid formation of blow holes and undesirable non-metallic oxide inclusions. Deoxidation of liquid steel is generally carried out during tapping or at ladle furnace. The most popular elements used for deoxidation of steel are manganese (Mn), silicon (Si), aluminum (Al) and calcium (Ca). In case of low carbon aluminum killed (LCAK) steel grades, aluminum is the deoxidizer element added during tapping of liquid steel from primary steel making furnace to ladle. However, depending on the process requirements, aluminum is added during ladle furnace operation also. After tapping, within less than around 5-6 mins, the ladle goes to the ladle furnace station where secondary refining is carried out.

Conventionally, aluminum is added into liquid steel in the form of aluminum ingot, aluminum wire or aluminum cube. These are called primary aluminum. Synthetic slag practice is the another crucial secondary steel making process. Synthetic slag is essentially a mixture of various oxides whose chemical composition can be varied depending on the requirements. The objective of using synthetic slag during secondary steel making process is to change the characteristic of ladle slag to a fluid and adequately basic slag which offers faster desulphurisation rate and efficiently removes inclusions to produce clean steel. Synthetic slag also provide cover to the molten steel bath to reduce heat loss and re-oxidation of steel from atmospheric oxygen. Like the addition of deoxidizers, synthetic slag is also generally added during tapping of liquid steel from primary steel making furnace to ladle. However, depending on the process requirements, synthetic slag is added during ladle furnace operation also. However, in case of addition of deoxidizers and synthetic slag during tapping, the advantage of vigorous mixing of liquid steel, slag and deoxidizers can be achieved. Therefore, it will improve the kinetic conditions of different required reactions. Synthetic slags can be produced using natural resources or by using secondary processed materials collected from different industries. These oxides are processed to produce various forms of synthetic slag (pre-melted, sintered, palletized etc.).

Earlier, steel plants around the world used to add pre-melted synthetic slag during secondary steel making process. The required raw materials for producing this synthetic slag are bauxite, limestone and small amount of other oxides. In order to achieve good basicity in the final product mixture, bauxite should have very low silica content. This definite requirement convinces industries to use high quality bauxite sources. However, nowadays, there are very few no. of bauxite mines can be found in the world having very high quality bauxite raw material. This situation increases production cost of synthetic slag. Therefore, steel plants were looking for an alternate low cost material which can offer functional advantages of using pre-melted synthetic slag during secondary steel making. White aluminum dross based briquetted synthetic slag can be a potential solution to this problem. Here, instead of black aluminum dross, only white aluminum dross is considered because of it’s low salt content and high metal content. However, considering the essential results (desulphurization rate and nitrogen pick up during ladle furnace operation) which is found during the use of pre-melted synthetic slag during tapping, this white aluminum dross based briquetted synthetic slag should also deliver similar kind of results.

Table 1: Typical chemical composition of pre-melted synthetic slag
Chemical composition (wt%)
(By X-Ray Fluorescence analysis) Chemical composition (wt%)
(By X-Ray Diffraction analysis)
CaO Al2O3 MgO SiO2 Fe2O3 Al AlN
34 - 38 41 - 44 7 - 8 4 - 5 2 – 3 0 0

Table 2: Required values of desulphurisation rate and nitrogen pick up with synthetic slag addition during tapping

Case type No. of heats considered Avg. initial sulphur at LF (LFinitial),
wt% Avg. primary aluminum consumption,
Kg/TLS Avg. desulphurisation rate considering first and last stage of LF operation,
(ppm/min), Avg. nitrogen pick up during LF operation,
ppm
With pre-melted synthetic slag addition during tapping 38
0.029
3.12
4.78
16

Several steel plants have already tried to utilize aluminum dross by several ways. Most of the time, at first the aluminum was recovered from aluminum dross. After that, the remaining aluminum residue (also known as non-metallic product (NMP)) was mixed with several type of materials (calcium carbide, different fluxes, final ladle refining slag, final primary steel making slag, different salts etc.) to produce different products. Some of the products produced had the properties of synthetic slag. However, steel plants were struggling to use those slags during secondary steel making process due to the high amount of fume generation when it is added to liquid steel. Even, at Applicant’s Steel plant, earlier attempts was made with white aluminum dross based briquetted synthetic slag having the following composition in percentage by weight (according to the X-Ray Fluorescence analysis) : % CaO: 1.23, % Al2O3: 77.61, % MgO: 7.52, % SiO2:3.24, % Fe2O3:0.38, % Na2O:2.01 and % K2O:1.79. This slag was briquetted using Novolac organic binder (Novolac softens and flows between 650C to 1050C and it’s boiling point is 1820C). It was added during tapping and as well as during ladle furnace operation. Slag produced after the addition of synthetic slag was visually witnessed and good fluidity was observed. It may be due to the presence of alkali oxides in the material. However, during both the cases high fume generation was observed. It was supposed that this fume generation was may be due to the use of different organic binders which have very low melting point and boiling point. These binders might have been converted into vapour phase as soon as it came in contact with the high temperature liquid steel, thereby failing to hold the constituent compounds present in the briquetted synthetic slag. Therefore, the constituent compounds of synthetic slag material have been disintegrated into fine particles and formed massive amount of fumes. The another reason is may be the very high melting point of synthetic slag than the melting point of organic binders. Hence, the binder might have started to melt first and the synthetic slag might have taken longer time to dissolve in the liquid steel due to it’s high melting point. Therefore, the binder failed to hold the constituent compounds present in the synthetic slag before this slag dissolved properly in the liquid steel. Thus, the constituent compounds of the synthetic slag material have been disintegrated, thereby generating high amount of fume. Hence, this attempt was failed. At ladle furnace station, the problem related to the fume generation is not a worrisome problem. The suction hood present at the ladle furnace station sucks this fume. However, during tapping of liquid steel from primary steel making furnace to ladle, there is no such arrangement available to suck the fume. It is very important for a tapping operator to see the liquid steel stream falling from the primary steel making furnace to the ladle for executing appropriate and risk free tapping. However, during such enormous amount of fume generation it is very difficult for a tapping operator to see the liquid steel stream. Further, such high amount of fume is not permitted at shop floor as it can hamper the health of the workers also.
Accompanying, Fig. 1(a) is a photo image showing location of primary steel making furnace and ladle at tapping station just before tapping; (b) is the photo image showing Fume generation during tapping addition of white aluminum dross based synthetic slag briquetted using Novolac organic binder and here, the liquid steel stream falling from the primary steel making furnace to ladle is not visible.

Some relevant patent documents in the same filed revealing the state of the prior arts are summarized below:
Patent no. US5279639A, titled “Compositions for synthesizing ladle slags” discloses a composition for synthesizing and treating ladle slags comprised of from about 5 to about 50 percent of calcium carbide, from about 10 to about 20 weight percent of magnesium carbonate, from about 40 to about 55 percent of calcium carbonate, from about 5 to about 20 weight percent of alumina, and from about 2 to about 5 weight percent of coke. This invention involves the manufacture of an in situ secondary ladle slag, treating of ladle slag, and the protection of refractory linings by the addition of materials including calcium carbide, foaming agents such as one or more carbonates of calcium, magnesium, and sodium, and other components used to adjust slag composition.
In this patent, aluminum dross was not used to prepare the composition. The prepared composition does not contain elemental aluminum and aluminum nitride. Therefore, this composition can not act as a deoxidizer. The composition was prepared to add during ladle furnace operation i.e. after tapping. It was not made to add during tapping of liquid steel from primary steel making furnace to ladle. This composition contains high amount of calcium carbide which is hazardous in nature. This composition does not contain alkali oxides (Na2O and K2O).
Patent no. US5284504A, titled “Powdered desulfurizing reagent and process of use” discloses a reagent for the desulfurization of molten iron which is based on calcium carbide and/or lime and which contains, as a gas generating component, an asphaltite. The reagent may contain, in addition, magnesium which is either uniformly distributed within the reagent mixture, or stored separately and added to the mixture during fluidized transport of the reagent just prior to injection to vary the addition of magnesium for any given injection.
This invention (reagent) is meant to be used for desulfurization of molten iron, outside a blast furnace, in the open ladle or in the torpedo. Hence, this reagent was not prepared to refine liquid steel. It was not made to add during tapping of liquid steel from primary steel making furnace to ladle. This reagent contains high amount of calcium carbide which is hazardous in nature. This reagent contains fine asphaltite power to generate gas which can be a reason for safety hazard. This reagent does not contain elemental aluminum and aluminum nitride. Therefore, this reagent cannot act as a deoxidizer. This composition does not contain alkali oxides (Na2O and K2O).
Patent no. US5385601A, titled “Process for converting aluminum dross to ladle flux for steel processing” discloses a plasma arc process for processing aluminum dross. This invention relates to the high-temperature pro cessing of aluminum dross and dross by-products. More particularly, this invention relates to a process for treating aluminum dross and dross by-products at high ten peratures in the presence of a flux by use of an indirect plasma-arc furnace. This invention is basically related to the processing of black dross. The dross is first crushed to -6 mesh to liberate as much of the metallic aluminum as possible. The metallic aluminumis removed and sold to a secondary aluminum smelter or it is remelted internally. The crushed dross is then mixed with the silicate based flux. This combination of materials is then fed into the dross processor and melted. The resultant slag composition contains about 13%-18% SiO2, by weight, about 30%-46% CaO, by weight, about 25%-43% Al2O3, by weight, and about 4%-7% MgO, by weight.

This invention is not related to the white aluminum dross, but it is related to the black dross containing high amount of salts (NaCl and KCl). This invention is only related to the making of slag from black aluminum dross by proper processing. This patent does not include the description of utilization of the final product slag during tapping of liquid steel from primary steel making furnace to ladle. The final product slag mentioned in this patent does not contain elemental aluminum and aluminum nitride. The final product slag mentioned in this patent does not contain alkali oxides (Na2O and K2O).

Patent no. US6267798B1, titled “Composition for treating steel making slags” discloses a slag composition containing steelmaking slag and from about 0.5 to about 10 weight percent of reducing agent (additive) of the total weight of Steelmaking Slag and reducing agent. The steelmaking slag contains from about 25 to about 55 weight percent of calcium oxide, from about 10 to about 50 weight percent of ferrous oxide, from about 5 to about 20 weight percent of magnesium oxide, from about 5 to about 20 weight percent of silicon oxide, and from about 0.5 to about 8 weight percent of manganese oxide. The reducing agent contains both calcium carbide and elemental aluminum. From about 5 to about 80 weight percent of the reducing agent is comprised of calcium carbide, and from about 10 to about 50 weight percent of such reducing agent is comprised of elemental aluminum. Also, optionally, the additive contains at least one fluxing agent. The aluminum used to form the additive of this invention may be pure elemental aluminum. Alternatively, or additionally, it may be elemental aluminum in combination with other materials. Aluminum dross, which contains elemental aluminum, often is used as one reagent for making the additive of this invention. The additive of this invention is preferably made by dry blending the calcium carbide, the aluminum-containing material, and, optionally, one or more of the fluxes in the desired Stoichiometry.

In this invention, the disclosed slag composition contains steel making slag, a reducing agent which includes calcium carbide and elemental aluminum and optionally at least one fluxing agent. Therefore, this invention is a mixture of different type materials. It does not contain only aluminum dross. This invention contains high amount of calcium carbide which is hazardous in nature. This invention does not contain aluminum nitride. Presence of Na2O and K2O is not mentioned in this invention. This invention is basically providing a mixture to kill iron oxide (FeO) and Manganese oxide (MnO) present in the final primary steel making slag (carryover slag from converter to ladle furnace) at ladle furnace. Therefore, calcium carbide and elemental aluminum present in this invented composition, do not kill dissolved oxygen content of liquid steel. Instead of that, they deoxidize iron oxide (FeO) and Manganese oxide (MnO) of carryover slag at ladle furnace. This invented mixture was not made to add during tapping of liquid steel from primary steel making furnace to ladle.

Patent no. US5716426A, titled “Methods of processing aluminum dross and aluminum dross residue into calcium aluminate” discloses a method of processing of aluminum dross containing Al and Al2O3originating from aluminum production. This method comprises the steps of separating aluminum from the dross to produce a dross residue (also known as non-metallic product (NMP)) and reacting the dross residue at a temperature above 1360°C with a calcium-oxygen compound to form calcium aluminate as an at least partially melted material. To obtain a product especially suitable for use in steel-making the calcium aluminate is rapidly cooled to form a glassy Solid product. The two steps may be performed in the same vessel, which has a suitable refractory lining. The material added to the aluminum dross residue to form the melt preferably contains no silica. The calcium aluminate melt is preferably rapidly cooled by pouring it onto a cooled surface, e.g. a cooled steel sheet. It may be cooled in a cooled granulation drum, which allows large-scale processing.

This invention is basically a process of converting aluminum dross to aluminum dross residue and then converting aluminum dross residue to calcium aluminate slag. Therefore, here, the final calcium aluminate product slag does not contain any elemental aluminum and aluminum nitride. Hence, the final product slag can only be used for desulphurisation of steel only. Therefore, this composition cannot act as a deoxidizer. Presence of Na2O and K2O in the final product slag is not mentioned in this invention. The final product slag was prepared to add during ladle furnace operation i.e. after tapping. It was not made to add during tapping of liquid steel from primary steel making furnace to ladle. The ratio of Al2O3 and CaO in the final product is 1:1. In this invention, the final product slag (calcium aluminate) is glassy solid type. It is not a non-glassy briquetted type product.

There has been thus a need to utilize low cost white aluminium dross in suitably briquetted form, instead of costly pre-melted synthetic slag, to substantially replace/substitute primary aluminium addition in steel refining, and more specifically low carbon aluminium killed(LCAK) steel during tapping from primary steel making furnace to ladle, which would meet on one hand, the required metallurgical parameters including the desulphurization rate and nitrogen pick up in secondary refining of steel while also ensure minimum fume generation so that the stream of liquid metal being tapped is visible to the operator to ensure operational safety avoiding health hazards.

OBJECTS OF INVENTION
The basic object of the present invention is directed to provide white aluminum dross based briquetted synthetic slag to be utilized during tapping of low carbon aluminum killed steel grades, instead of pre-melted synthetic slag, without any fume generation.

Another object of the present invention is directed to provide aluminum dross based synthetic slag which is briquetted by Sodium Silicate inorganic binder for utilization during tapping of low carbon aluminum killed steel grades as a synthetic slag, which can act as a deoxidizer also.

Another object of the present invention is to provide said white aluminum dross based briquetted synthetic slag for use in steel making by addition during tapping of low carbon aluminum killed steel grades which is having much low cost compared to conventional pre-melted synthetic slag presently used.

Another object of the present invention is to provide white aluminum dross based briquetted synthetic slag having the following compounds in percentage by weight (according to the X-Ray Fluorescence analysis): % CaO 4.81, % Al2O3 73.91, % MgO 7.90, % SiO2 3.64, % Fe2O3 0.67, % Na2O 2.15 and % K2O 0.95 and also having percentage by weight (according to the X-Ray Diffraction analysis): % elemental Al 0.75 and % AlN 17.15.

Yet another object of the present invention is to provide white aluminum dross based briquetted synthetic slag in which the raw white aluminum dross powder (before briquetting) contains 10% greater than 600 micron size particles, 5% greater than 250 micron size particles, 12% greater than 160 micron size particles, 17% greater than 75 micron size particles and 56% less than 75 micron size particles.

A further object of the present invention is directed to provide white aluminum dross based briquetted synthetic slag having elemental aluminum and aluminum nitride for utilization during tapping of low carbon aluminum killed steel grades, wherein said elemental aluminum and aluminum nitride can act as deoxidizer, thereby ensure reduced consumption of costly primary aluminum per tonne of liquid steel produced.

A still further object of the present invention is directed to provide said white aluminum dross based briquetted synthetic slag having sodium oxide (Na2O) and potassium oxide (K2O) for addition during tapping of low carbon aluminum killed steel grades wherein these oxides increase fluidity of slag layer, thereby improve kinetics of refining reaction between liquid steel and slag layer.
A further object of the present invention is to provide good or similar average desulphurisation rate and low or similar average nitrogen pick up (as compared to addition of pre-melted synthetic slag) during ladle furnace operation, if said white aluminum dross based briquetted synthetic slag is added during tapping of low carbon aluminum killed steel grades.
A still further object of the present invention is to ensure low or similar average primary aluminum consumption (considering the avg. primary aluminum consumption achieved with the addition of pre-melted synthetic slag during tapping of low carbon aluminum killed steel grades) if white aluminum dross based briquetted synthetic slag is added during tapping of low carbon aluminum killed steel grades.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide white aluminum dross based briquetted synthetic slag comprising (by weight percent):

CaO: 4 to 6; preferably about 4.81 wt.%.
Al2O3: 70 to 75; preferably about 73.91 wt.%
MgO: 6 to 8; preferably about 7.90 wt.%
SiO2: 1 to 4; preferably about 3.64 wt.%
Fe2O3: 0 to 1; preferably about 0.67 wt.%
Na2O: 2 to 3; preferably about 2.15 wt.%;
K2O : 0.5 to 2; preferably about 0.95 wt.%; and
elemental content of Al 0.5 to 2 preferably about 0.75 wt.% and AlN 15 to 20 preferably about 17.15 wt.%
A further aspect of the present invention is directed to White aluminum dross based briquetted synthetic slag comprising sodium silicate binder as the briequetting material.
A still further aspect of the present invention is directed to White aluminum dross based briquetted synthetic slag wherein said aluminium dross is sourced from raw white aluminum dross powder contains 10% greater than 600 micron size particles, 5% greater than 250 micron size particles, 12% greater than 160 micron size particles, 17% greater than 75 micron size particles and 56% less than 75 micron size particles.

A still further aspect of the present invention is directed to White aluminum dross based briquetted synthetic slag wherein the white dross content is sourced from waste product of aluminium smelting processes.

Another aspect of the present invention is directed to White aluminum dross based briquetted synthetic slag comprising alkali oxides Na2O and K2O to favour increasing fluidity of slag layer, and thereby improve kinetics of refining reaction between liquid steel and slag layer.
Yet another aspect of the present invention is directed to White aluminum dross based briquetted synthetic slag which is capable of achieving avg. desulphurization rate = 4.78 ppm/min., avg. nitrogen pick up = 16 ppm during secondary steel making process.

A further aspect of the present invention is directed to a process for the manufacture of white aluminum dross based briquetted synthetic slag as described above comprising the steps of briquetting white aluminum dross with sodium silicate binder such as to obtain white aluminum dross based briquetted synthetic slag comprising (by weight percent):

CaO: 4 to 6; preferably about 4.81 wt.%.
Al2O3: 70 to 75; preferably about 73.91 wt.%
MgO: 6 to 8; preferably about 7.90 wt.%
SiO2: 1 to 4; preferably about 3.64 wt.%
Fe2O3: 0 to 1; preferably about 0.67 wt.%
Na2O: 2 to 3; preferably about 2.15 wt.%;
K2O : 0.5 to 2; preferably about 0.95 wt.%; and
elemental content of Al 0.5 to 2 preferably about 0.75 wt.% and AlN 15 to 20 preferably about 17.15 wt.%

A still further aspect of the present invention is directed to said process, wherein the steps of manufacturing white aluminum dross based briquetted synthetic slag comprising
(i) providing the raw white aluminium dross powder comprising the composition by weight percent: % CaO 0.75-1.25, % Al2O3 76-78, % MgO 1-2, % SiO2 3-4, % Fe2O3 0-1, % Na2O 1-2 and % K2O 1-2, as well as % elemental Al 1-2 and % AlN 15-20;
(ii) screening said raw white aluminium dross powder to get rid of different foreign elements like metallic particles having greater than 5mm particle size;
(iii) mixing caustic calcined magnesia with said dross powder in the ratio of 1 to 6 ,to increase the MgO content in the product powder mixture;
(iv) mixing sodium silicate with water separately in binder preparation tank, followed by adding around 3 wt % (of the final product powder mixture) binder-water mixture to the previously made mixture of raw white aluminium dross powder and caustic calcined magnesia in step (iii);
(v) Next, this whole mixture of step (iv) is mixed with hydrated dolomite to get the final desired amount of MgO 6 to 8 wt% and CaO 4 to 6 wt% in final product powder mixture;
(vi) Subsequently, the final mixture is charged into a briquetting equipment where briquettes are formed by applying roll force in the range of 18 to 22 Ton;
(vii) Finally, briquettes are dried by blowing hot air having temperature in range of 140 deg C to 180 deg C.

A further aspect of the present invention is directed to a process for steel making involving synthetic slag during secondary steel making process including step of tapping of low carbon aluminium killed steel grades without any fume generation involving white aluminum dross based briquetted synthetic slag comprising (by weight percent):

CaO: 4 to 6; preferably about 4.81 wt.%.
Al2O3: 70 to 75; preferably about 73.91 wt.%
MgO: 6 to 8; preferably about 7.90 wt.%
SiO2: 1 to 4; preferably about 3.64 wt.%
Fe2O3: 0 to 1; preferably about 0.67 wt.%
Na2O: 2 to 3; preferably about 2.15 wt.%;
K2O : 0.5 to 2; preferably about 0.95 wt.%; and
elemental content of Al 0.5 to 2 preferably about 0.75 wt.% and AlN 15 to 20 preferably about 17.15 wt.%

A still further aspect of the present invention is directed to a process for steel making wherein the level of sodium oxide (Na2O) and potassium oxide (K2O) used in said white aluminum dross based briquetted synthetic slag during tapping of low carbon aluminum killed steel grades favour increasing fluidity of slag layer, and thereby improve kinetics of refining reaction between liquid steel and slag layer.
A still further aspect of the present invention is directed to said process for steel making, wherein 190 to 200 Kg of white aluminum dross based briquetted synthetic slag (briquetted by Sodium Silicate inorganic binder) is added to 180 to 190 tonne of liquid steel during tapping along with primary aluminum and lime in the ratio of around 4: 7: 18 (i.e. briquetted dross: primary aluminium: lime per ton of liquid steel tapped.)

A still further aspect of the present invention is directed to a process for steel making wherein said white aluminum dross based briquetted synthetic slag enables avg. desulphurization rate = 4.78 ppm/min., avg. nitrogen pick up = 16 ppm.

A still further aspect of the present invention is directed to a process for steel making wherein free aluminum in the form of elemental aluminum and aluminum nitride in said white aluminum dross based briquetted synthetic slag is used as a deoxidizer thereby favouring reducing consumption of primary aluminium per tonne of liquid steel produced.

Another aspect of the present invention is directed to said process for steel making wherein said white aluminum dross based briquetted synthetic slag used sodium silicate binder having melting point of 1088°C as the briequetting material, so that the constituent compounds of the used synthetic slag dissolve fast due to the lower melting point and the binder succeeds to hold the constituent compounds before they dissolve into liquid steel, thereby arresting fume generation.

Yet another aspect of the present invention is directed to said process for steel making wherein in said White aluminum dross based briquetted synthetic slag said aluminium dross is sourced from raw white aluminum dross powder contains 10% greater than 600 micron size particles, 5% greater than 250 micron size particles, 12% greater than 160 micron size particles, 17% greater than 75 micron size particles and 56% less than 75 micron size particles.

A still further aspect of the present invention is directed to said process for steel making wherein in said white aluminum dross based briquetted synthetic slag the white dross content is sourced from waste product of aluminium smelting processes.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to following accompanying non-limiting illustrative drawings.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

Fig. 1: (a) photo image showing the location of primary steel making furnace and ladle at tapping station just before tapping; (b) Fume generation during tapping addition of white aluminum dross based synthetic slag briquetted using Novolac organic binder and here, the liquid steel stream falling from the primary steel making furnace to ladle is not visible.

Fig. 2: photo image showing White aluminum dross based briquetted synthetic slag (briquetted by Sodium Silicate inorganic binder).
Fig. 3: (a) photo image showing location of primary steel making furnace and ladle at tapping station just before tapping; (b) No fume generation during tapping addition of white aluminium dross based synthetic slag briquetted by Sodium Silicate binder

DETAILED DESCRIPTION OF THE INVENTION

The present invention is thus directed to provide white aluminum dross based briquetted synthetic slag for utilization during tapping of low carbon aluminum killed steel grades instead of pre-melted synthetic slag and without any fume generation. This white aluminum dross based briquetted synthetic slag is briquetted using Sodium Silicate binder (melting point is 10880C).

According to the X-Ray Fluorescence (XRF) analysis, this white aluminum dross based briquetted synthetic slag comprises the following compounds in percentage by weight: % CaO 4.81, % Al2O3 73.91, % MgO 7.90, % SiO2 3.64, % Fe2O3 0.67, % Na2O 2.15 and % K2O 0.95. According to the X-Ray Diffraction (XRD) analysis, this white aluminum dross based briquetted synthetic slag comprises the following compounds in percentage by weight: % elemental Al 0.75 and % AlN 17.15.

The raw white aluminum dross powder (before briquetting) contains 10% greater than 600 micron size particles, 5% greater than 250 micron size particles, 12% greater than 160 micron size particles, 17% greater than 75 micron size particles and 56% less than 75 micron size particles.

The input raw material for briquetting i.e. white aluminum dross powder having the composition comprising (by weight percent): % CaO 0.75-1.25, % Al2O3 76-78, % MgO 1-2 %, SiO2 3-4, % Fe2O3 0-1, % Na2O 1-2 and % K2O 1-2, as well as % elemental Al 1-2 and % AlN 15-20.

White aluminum dross based briquetted synthetic slag can only be considered as replacement of pre-melted synthetic slag if it has potential to fulfil the above stated requirements (avg. desulphurization rate = 4.78 ppm/min., avg. nitrogen pick up = 16 ppm). Additionally, white aluminum dross based synthetic slag contains high amount of free aluminum in the form of elemental aluminum and aluminum nitride. Therefore, besides it’s use as a synthetic slag, this type of slag can act as a deoxidizer also. Hence avg. primary aluminum consumption per tonne of liquid steel (TLS) should be less than equal to 3.12 kg if white aluminum dross based briquetted synthetic slag is used instead of pre-melted synthetic slag. This can provide huge amount of saving to the steel makers as the cost of primary aluminum is very much high compared to the cost of white aluminum dross based briquetted synthetic slag. Further, this white aluminum dross based briquetted synthetic slag contains alkali oxides (Na2O and K2O). After the addition of primary aluminum, lime and white aluminum dross based synthetic slag, these oxides help to increase fluidity of slag layer, thereby improve kinetics of refining reaction between liquid steel and slag layer.

EXAMPLE:

A. At first white aluminium dross based briquetted synthetic slag was produced by the following steps:
(i) Picking the raw white aluminium dross powder comprising the composition by weight percent: % CaO 0.75-1.25, % Al2O3 76-78, % MgO 1-2, % SiO2 3-4, % Fe2O3 0-1, % Na2O 1-2 and % K2O 1-2, as well as % elemental Al 1-2 and % AlN 15-20.
(ii) After that, this raw white aluminium dross powder was screened to get rid of different foreign elements like metallic particles having greater than 5mm particle size.
(iii) Then, it was mixed with caustic calcined magnesia to increase the MgO content in the product powder mixture.
(iv) Separately, sodium silicate was mixed with water in binder preparation tank. After that, around 3 wt % (of the final product powder mixture) binder-water mixture was added to the previously made mixture of raw white aluminium dross powder and caustic calcined magnesia.
(v) Next, this whole mixture was mixed with hydrated dolomite to get the final desired amount of MgO and CaO in final product powder mixture.
(vi) Subsequently, the final mixture was charged into a briquetting equipment where briquettes were formed by applying high pressure.
(vii) Finally, briquettes were dried by blowing hot air.
Accompanying Fig. 2 shows the photo image of white aluminum dross based briquetted synthetic slag (briquetted by Sodium Silicate inorganic binder) obtained by the process for utilization in steel making.

B. In the next step, Carbon rich liquid hot metal produced from Blast Furnace was converted to liquid steel during primary steel making process with help of CONARC furnace. After that, around 190 to 200 Kg of white aluminum dross based briquetted synthetic slag (briquetted by Sodium Silicate inorganic binder) was added to 180 to 190 tonne of liquid steel during tapping along with primary aluminum and lime in the ratio of around 4: 7: 18 (i.e. briquetted dross: primary aluminium: lime per ton of liquid steel tapped.)
C. Then, secondary steel making was done at ladle furnace station to produce different low carbon aluminum killed (LCAK) steel grades. In this way, total thirteen no. of trial heats were made. Subsequently, avg. desulphurization rate and avg. nitrogen pick up during ladle furnace operation were calculated. Avg. primary aluminum consumption per tonne of liquid steel was also calculated.

Table 3: Chemical composition of the white aluminum dross based briquetted synthetic slag (briquetted by Sodium Silicate inorganic binder)

Chemical composition (wt%)
(By X-Ray Fluorescence analysis) Chemical composition (wt%)
(By X-Ray Diffraction analysis)
CaO Al2O3 MgO SiO2 Fe2O3 Na2O K2O Al AlN
4.81 73.91 7.90 3.64 0.67 2.15 0.95 0.75 17.15

Table 4: Size analysis of raw white aluminium dross powder

Sl. No.
Size (micron) Percentage,%
1 600(+) 10
2 250(+) 5
3 160(+) 12
4 75(+) 17
5 75(-) 56

Table 5: Results of the trials

Case type No. of heats considered Avg. initial sulphur at LF (LFinitial),
wt% Avg. primary aluminium consumption,
Kg/TLS Avg. desulphurisation rate considering first and last stage of LF operation,
(ppm/min), Avg. nitrogen pick up during LF operation,
ppm
withwhite aluminium dross based briquetted synthetic slag(briquetted by Sodium Silicate inorganic binder) addition during tapping 13
0.029
2.97
6.12
14

Accompanying Fig. 3(a) shows the location of primary steel making furnace and ladle at tapping station just before tapping; and wherein in (b) no fume is generated/can be seen during tapping with addition of white aluminium dross based synthetic slag briquetted by Sodium Silicate binder, so that the falling liquid metal stream in ladle is clearly visible to the operator.

Slag produced after the addition of white aluminium dross based briquetted synthetic slag was visually witnessed and good fluidity was observed. Almost no fume generation was observed.

In this case, tapping operator was able to see the liquid steel stream clearly. In case of these trials, the used briquetted synthetic slag contains lower amount of alumina and higher amount lime compared to the previously used white aluminium dross based synthetic slag briquetted by Novolac binder. This type of composition reduces the melting point of the used synthetic slag in these trials. In the present trial, the constituent compounds of the used synthetic slag were dissolved fast due to the lower melting point and the binder succeeded to hold the constituent compounds before they dissolved into liquid steel. Therefore, no fume generation was observed.

It is thus possible by way of the present invention to provide low cost white aluminium dross based briquetted synthetic slag which is briquetted with sodium silicate inorganic binder for addition with LCAK steel during tapping from primary steel making furnace into ladle for secondary refining, instead of pre-melted synthetic slag, to substantially substitute the requirement of primary aluminum addition that would ensure avg. desulphurization rate = 4.78 ppm/min., avg. nitrogen pick up = 16 ppm, avg. primary aluminum consumption per tonne of liquid steel (TLS) should be less than equal to 3.12 kg, without any fume generation.