FIELD OF INVENTION
The present invention relates to a process and method of briquetting of wastes generated in iron and steel industry using ladle furnace slag as binder.
BACKGROUND AND PRIOR ART TO THE INVENTION
In an integrated iron and steel plant, a number of iron bearing by-products are generated which are not suitable for further processing and are termed as "Wastes" and disposed normally in landfill. Moreover these wastes are in fine form varying in granulometry and cannot be directly recycled in their fine form. Therefore, these need to be agglomerated. Agglomeration method of sintering, pelletizing and briquetting are common practices in iron and steel industries for converting iron ore fines, minerals and solid wastes into blocks and lumpy sizes for various metallurgical uses. Depending upon the nature of the metallurgical fines and wastes, its granulometry and rheology, Fe-content, associated minerals and oil contamination, many process developments have been made for the production of briquettes by both hot and cold methods.
The briquetting of the wastes is technically viable, economically attractive and environmental safe way for reuse and recycling of the wastes from the iron and steel industry. The briquettes contain iron - bearing wastes of the iron and steel manufacturing process for the purpose of replacing iron ore hence, reduce the depletion of the earth's limited natural resources which is getting scarce.
Briquetting of waste materials as an aggregate for smelting furnaces of an iron foundry, containing hydraulic binders in the form of MgO filter dust and limestone dust is described by Thomas Bilke, Patent No. EP0861909 Al. Similarly, use of cement and water as a binder in briquetting of iron containing dust from foundry operations is reported by Manfred Dr Rosmann et al., in Patent No. DE19509366 Al.

Briquetting of mill scale, iron-ore fines, iron pellet fines using granulated blast furnace slag cement and bentonite as binder is reported by Eugene A. Boadan et al., Patent No. US5395441 A. Briquetting process having approximately 50% metallic fines, 41% mill scale, 2% bentonite, 3% pitch residue, 2% burnt lime fines, and 2% molasses is described by Robert R. Strange. Patent No. US4369062 A.
Use of hydrated high-alumina cement as the binder for briquetting iron ore fines, sinter fines, BOF and EAF dusts, mill scale is reported by Jay Aota et al., Patent No. US6676725 B2. Addition of small amount of bentonite enhanced the strengths of the pellets at elevated temperature.
Briquetting iron oxide fines at lower temperatures with a binder, such as bituminous coal, pitch, molassess, sulfite liquor or the fines can be briquetted at high temperatures without a binder is described by Brisse Andre H et al., Patent No. US3174846 A.
Mixture of cupola-furnace top-gas filter dust and small particle residue from punching and cutting, which is pressed to form a briquettes and can subsequently charge in cupola furnace for cast iron production and is described in Patent No. DE 44 16 699 Al. Cupola-furnace top-gas filter dust contains approximately 5% to 12% sulphur and sulphur containing compounds which increases the viscosity of the melt and hardness of the casting.
Slag-forming briquettes from filler dust and foundry sand using sulphite lye as a binder is illustrated in Patent No. DE 43 08 294 A. The adverse effect of sulphur compound upon the melt is mentioned above; moreover the concentration of S02 and S03 increases in wastes gas.

Briquetting of iron containing steel-works dust in a rotary hearth furnace at 500oC in an inert atmosphere, without the application of binder is described in Patent No. DE 37 32 351 A1.
Briquetting of filter dust from foundry industry using natural binders such as glucose syrup, maize starch etc. is described in Patent No. DE 42 07 265 Al.
Briquetting of ferrous and non-ferrous ores using ordinary Portland cement as a binder is reported in Patent No. Patent No. JP 80, 100, 940. The briquettes are cured for 3 days at ambient temperature and then steam curing at 100° C followed by drying at 100° to 500° C.
Briquetting of iron ores by using 5 to 15% basic slag as a binder is accounted in Patent No. JP 60 33 319. The briquetting process involves hardening at 200° C and then curing under steam for the development of strength.
Use of ordinary portland cement as a binder for iron ore briquetting is illustrated in Patent No. 8135, 731. The process involves heat treatment for 1 day at 90° C and then drying for 1 hour at 90° C. the briquettes attain strength of 256 Kg.
Cold bonded iron ore pellets by using mixture of chlorides salts and ordinary Portland cement as activator id described in Patent No. USSR 730, 844.
Non-sintered iron ore pellets by using mixture of cement clinkers and limestone as a binder is illustrated in Patent No. JP 7711103.
The setbacks of the aforesaid inventions are the use of various types of expensive natural, organic or inorganic binding materials such as ordinary Portland cement, bentonite, molasses, glucose syrup, maize starch, lime, tar, basic slag, earth materials, chloride salts, sulphite lye, bituminous coal, pitch, blast furnace slag, sulfite liquor, limestone, dolomite by both hot and cold methods which include compacting under pressure and hardening at 90° to 500°

C in the furnace, followed by curing at ambient temperature, under steam at 90° to 500° C and then drying at atmospheric temperature or at 90° to 500° C in furnace to achieve adequate strength. Furthermore, the presence of alkalis, chlorides, sulphates in the binding materials not only adds impurities to the melt but also increases the concentration of S02, S03 and various other hazardous gases in waste gases. Hence, there is a need for a technically viable, economically attractive and environmental safe way of agglomerating iron rich steel plant wastes which overcomes the aforementioned limitations.
OBJECTS OF THE INVENTION
The main objective of the present invention is to develop a briquetting process for cold briquetting of iron and or carbon bearing wastes oxides by using ladle furnace slag as a binder.
Another objective of the invention is to develop briquettes suitable for charging into a furnace which overcome the drawbacks as aforementioned above.
Another object of the present invention is to proffer an briquetting process that produce value added products from steel plant wastes more efficiently to meet the objective of zero waste or green steel concepts.
One more object of the present invention is to proffer a briquetting process that replaces the use of different types of binders that contains various impurities which are deleterious for the metallurgical operations.
Still another object of the present invention is to proffer a briquetting process is to reduce the depletion of earth's limited natural resources produced by discharging untreated waste.

One another object of the present invention is to proffer a briquetting process is to save energy by eliminating energy intensive processes such as hot pressing, heat hardening, steam curing.
Yet another object of the present invention is to proffer a briquetting process that prevents the emission of toxic gases such as SOx and NOx otherwise produces normally during sintering and pelletizing processes.
Furthermore object of the present invention is to proffer a briquetting process that accepts a wide variety of wastes that differ in granulometry to convert into a form which gives improved low temperature mechanical and metallurgical properties.
SUMMARY OF THE INVENTION
Accordingly, this invention relates to development of briquetting composition with ladle furnace slag as a binder. The typical binders used in briquetting operations are ordinary Portland cement, bentonite, molasses, glucose syrup, maize starch, lime, tar, basic slag, earth materials, chloride salts, sulphite lye, bituminous coal, pitch, blast furnace slag, sulfite liquor, limestone and dolomite. A typical ladle furnace slag comprises 25 - 60% by Wt. CaO, about 8 - 30% by Wt. of Al203 + Si02, about 1 - 5% by Wt. of MgO.
This invention provides a process for briquetting of iron bearing metallurgical dust/fines/sludge/mill scale/agglomerate wastes produced in steel plants, mixed together with sufficient amount of Ladle furnace slag as a binder, burnt lime fines and water to form a homogenized moist mix. The moist mix is then compacted under load to form briquettes of any preferred shape, preferably pillow shaped bodies under high pressure in a roll type press. The green briquettes thus formed are cured by moisture treatment under humid atmosphere for 1 to 6 days and water spraying for the next 3 to 10 days and

thereafter drying them under sunlight for next 1 to 4 days. After curing and drying, the briquettes can be used in any either Blast furnace or Rotary Hearth Furnace for iron making or used in LD Converter for Steel making. The amount of binder is optimized to provide briquette with adequate mechanical strength to avoid excessive degradation in handling at ordinary temperatures, and also to withstand temperatures and conditions encountered in iron making and or steel making furnaces. The amount of water is adjusted to provide a uniform shape and complete hydration to ensure complete setting.
DETAILED DESCRIPTION OF THE INVENTION
A process for briquetting of iron and or carbon bearing metallurgical dust/fines/ sludge/mill scale/agglomerate dust using ladle furnace slag as a binder comprises of the following steps:
(a) Mixing of about 40% to about 80% metallurgical dust/fines/sludge/mill scale/agglomerate dust having size less than 6 mm with about 10% to about 50% ladle furnace slag, optionally along with about 2% to about 4% of hydrated burnt lime fines to form a homogenized dry mixture. Burnt lime fines are added to provide green strength to the briquettes.
(b) Adding of about 4% to about 10% water to the dry mixture from step (a) sufficient enough to fully hydrate ladle furnace slag binder and uniformly mixing so as to form a homogenized moist mixture.
(c) Compacting the moist mixture from step (b) in a cylindrical mould under load to form briquettes of any preferred shape, preferably pillow shaped bodies under high pressure in a roll type press.

(d)The green briquettes from step (c) are then subjected to three different stages of curing for 7 to 14 days. The green briquettes were covered with polythene or humidified by spraying water or kept in a humid container/room for the first 1 to 3 days to provide a humidified atmosphere. The humidified briquettes were subsequently water cured for next 3 to 7 days at ambient atmosphere, followed by sun - dry curing for next 2 to 4 days.
Application case study:
This example demonstrates briquetting of LD Sludge, Pellet Dust using Ladle furnace slag as a binder and lime fines as additive. The chemistry and mix-proportion of raw materials used in the experiments are shown in Table 1 and Table 2 respectively.



The briquetting composition as per the current invention comprises LD sludge in the range of 25 to 93 by weight % and Ladle furnace (LF) slag in the range of 5 to 50 weight %. The composition further comprises lime in the range of 2 to 10 weight%. The LD sludge varies preferably in the range of 40 to 85 wt.% and weight percentage is generally varied as per the granulometry/fineness of the waste oxide fines. Similarly Ladle Furnace slag composition varies preferably in the range of 12 to 18 wt.%.
Mix proportion of the aforementioned wastes in Table 2 was thoroughly mixed to form a homogeneous dry mix and the blend was mixed further with 10% water solution containing 2% lime, until a uniform mixture was obtained which takes around 10 minutes. The mixture was then statically compressed in a cylindrical mould with 25 mm in diameter and 30 mm in height. The compression was performed by manual hydraulic press and the compression load was 2 Tons. Specimens were then demoulded, and are subject to three different stages of curing. The specimens were covered with polythene for 3 days to provide a humidified atmosphere. The cover was removed and the specimens were subsequently water cured for next 7 days, followed by sun - dry curing for next 4 days. Green compressive strength of the briquettes were measured by dropping of the briquettes from height of 45 cm and 100 cm on to steel plate. Compressive strengths of the specimens were tested at the ages of 3, 7, 10, 14 days.

Table 3 presents the results of the analysis of the effects of lime fines addition on the green compressive strength of the briquettes from LD sludge and mixture of LD sludge and pellet dust. When Ladle furnace slag is used as a binder, the green compressive strength is increased with the addition of Lime fines. In particular, drop no. is increased to 21 from 45 cm and 11 from 100 cm for Mix 3 as compared to Mix 2 where drop no. is 13 from 45 cm and 6 from 100 cm. The higher early green strength which developed with the addition of the lime fines can be attributed to quick setting of the lime at the early stage. It is evident from the results that combination of LF slag and lime fines yields much better green strength as compare to the use of either lime fines or LF slag independently. The results of compressive strengths of the briquettes from LD sludge and mixture of LD sludge and pellet dust are plotted in Figure 1 and Figure 2 respectively. The compressive strength increased with curing age for both the Mix 3 and Mix 4.


It is to be understood that the invention is not limited by the specific example and embodiment described hereinabove, but includes such changes and modifications as may be apparent to one skilled in the art upon reading the appended claims. The invention of the current invention provides a mechanism to reuse recycle steel wastes in an effective fashion. The process and composition of the briquettes produced as per the current invention reduces the environmental hazard and at the same time makes the whole steel making process further energy efficient.

WE CLAIM:
1. A briquetting composition for steel making and blast furnace operations,
the briquetting composition comprising:
LD sludge in the range of 25 to 93 by weight %; and
Ladle furnace (LF) slag in the range of 5 to 50 weight %
wherein the briquetting composition is cured in humid atmosphere and air dried.
2. The briquetting composition as claimed in claim 1 further comprising lime in the range of 2 to 10 weight%.
3. The briquetting composition as claimed in claim 1, wherein the composition of LD sludge varies preferably in the range of 40 to 85 wt.% as per the granulometry/fineness of the waste oxide fines.
4. The briquetting composition as claimed in claim 1, wherein Ladle Furnace slag composition varies preferably in the range of 12 to 18 wt.%.
5. The briquetting composition as claimed in claim 1, wherein the said Ladle Furnace slag is a fine dry powder with fineness of at least 80% passing by 170 mesh BSS sieve.

6. The briquetting composition as claimed in claim 1, wherein the said LD sludge can be replaced by iron bearing or carbon bearing waste oxides, metallurgical dust/fines/sludge/mill scale produced in steel plants, agglomerate fines.
7. A process for briquetting of iron and or carbon bearing metallurgical dust/fines/ sludge/mill scale/ agglomerate dust and ladle furnace slag, the process comprising:

a) mixing metallurgical dust/fines/sludge/mill scale/agglomerate dust having size less than 6 mm with ladle furnace slag, optionally along with hydrated burnt lime fines to form a homogenized dry mixture;
b) adding 4% to 10% water to the dry mixture from step (a) to fully hydrate ladle furnace slag binder and uniformly mixing so as to form a homogenized moist mixture;
c) compacting the moist mixture from step (b) in a cylindrical mould under load to form briquettes of any preferred shape under high pressure in a roll type press; and
d) subjecting green briquettes from step (c) to three different stages of curing.
8. The process as claimed in claim 7, wherein the said curing process
comprises moisture treatment under humid atmosphere for 1 to 6 days
and water spraying for the next 3 to 10 days and thereafter drying them
under sunlight for 1 to 4 days.

9. The process as claimed in claim 7, wherein burnt lime fines are added in the dry mix by hydrating it with water.
10. The process as claimed in claim 7, wherein LD sludge varies in the range of 25 to 93 by weight %, preferably in the range of 40 to 85 wt.%.
11. The process as claimed in claim 7, wherein Ladle furnace (LF) slag varies in the range of 5 to 50 weight %, preferably in the range of 12 to 18 wt.%.
12. The process as claimed in claim 7, wherein lime varies in the range of 2 to 10 weight%.