Description:FORM 2

THE PATENTSACT, 1970

COMPLETE SPECIFICATION

(See section10 and rule13)

Title

Shot Blast Dust treatment method

APPLICANTS

Mabric Technologies, Small manufacturing industries,
village –Limtara, Dhamdha , District- Durg, Chattisgarh

The following specification particularly describes the invention and
how it is to be performed
Field of the invention:

The present invention relates to a simple process to stop hazardous waste from polluting the environment and recycle the hazardous waste which is presently being dumped in land fill. More specifically, Shot Blast Dust (SBD) is generated as an industrial waste which was chemically fed in optimized condition to minimize carbon reduction and to stop the leaching of the hazardous material to the environment and use the same for future work. The process is optimized in respect to the temperature and time to minimum level to reduce cost as well as to avoid any side reactions with fluxes already present in raw material.

Background:

Aluminum is normally produced by dissolving alumina at high temperature (about 900° C.) in molten cryolite (Na3 AlF6) in electrolytic cells, or pots, provided with electrically conductive carbon linings, and electrolyzing the molten solution by passing an electric current between carbon anodes dipped into the melt and the carbon linings acting as cathodes. Anode also acts as consumable reducing material. Therefore, after a certain time it becomes too small and therefore removed. This removed piece is called Anode Butt. The anode butt is cleaned by shot blasting and recycled. The dust generated is called Shot Blast Dust (SBD). It chiefly consists of 50-60% carbon and 40-50% bath material, having fluoride as hazardous material. Till date SBD is dumped in land fill.

To solve this problem in Aluminum industries a new inventive process for treating SBD waste has been invented to make the waste environmentally non-hazardous and recyclable.
Following are a few related art in this area

JP2003113432ARecovering Method for Collected Shot-Blast Zinc Dust discloses a method for recovering collected shot-blast zinc dust which is conventionally discarded for landfill. The method for recovering the collected shot-blast zinc dust comprises a separation step of separating the collected shot-blast zinc dust into a raw material for a zinc oxide powder, and an oxidation step of heating and vaporizing the separated raw material, and subsequently oxidizing the vaporized zinc oxide by air or an oxygen-containing gas, or the like, to obtain a high-purity zinc oxide powder or a fine spherical zinc powder. The cited document is completely different w
CA2835800A1-Process and device for limiting the emission of gaseous pollutants from anode butts discloses a method and device for treating anode butts (5) from aluminum production tanks by igneous electrolysis by covering the anode butts (5) with alumina (8) having a fluorine-capturing power, the method consisting in that, upon removal of the butt (5) from the electrolysis tank, it is immersed in alumina (8) previously fluidized to facilitate immersion and in that the fluidization of the alumina is stopped at the end of the immersion so that the butt is covered by static alumina until the end of its transfer from the electrolysis tank to a station equipped with fume suction and treatment devices, in particular a hot crushing station or a cooling station, so as to confine the part and limit its emission of gaseous pollutants, in particular fluorinated pollutants.
IN202321072957A discloses an improved process for recovery of graphite from discarded carbonaceous electrode waste relates to an improved process for the recovery of valuables in the form of graphitic carbon fractions, cryolite, sodium fluoride, sodium carbonate/sulphate, and mixed hydroxides from spent anode dust and first-cut spent pot lining materials obtained from electrolytic reduction cells which are used to produce aluminium metal. The recovered graphite has various applications in electrostatic charge dissipative coating, Li-Battery and so on.
The present invention is completely different from the cited patents. The present invention discloses a process where SBD is treated with (calcined/hydrated) lime in an optimized process to generate hazard free waste material and the carbon content is not reduced much. The process optimizes the temperature and time to minimum level to reduce cost and the process is energy efficient.
With this, the metal extraction and processing industries, for example, iron and steel industry, considerable metal is lost with discarded slag wherein the process slag is crusty. Crusty slag do not allow all intended metallurgical reactions to reach completion which in turn hamper removal of impurities from molten metal. Similarly, along with fluidity, if slag is not in reduced state, atmospheric oxygen enters molten metal. The present invention addresses both purpose of supplying carbon and flux to the slag phase thereby making slag fluid and reducing it very efficiently and cheaply.

Therefore, to the best of our knowledge, none of the prior art attempts, individually or collectively, the proposed method indicated and disclosed by the present invention

The object of the invention:

The objective of the present invention is to formulate a simple process to convert leachable hazardous waste to non-leachable form and recycle a hazardous waste which is presently being dumped in land fill

Another objective of the present invention is to recover carbon value as well as fluxes value without generating any waste.

Summary of the Invention:

The present invention discloses a simple process to stop hazardous waste from polluting the environment and recycle the hazardous waste which is presently being dumped in land fill. In an aspect of the invention, Shot Blast Dust (SBD) is generated as an industrial waste which was chemically fed in optimized condition to minimize carbon reduction and to stop the leaching of the hazardous material to the environment and use the same for future work. The process is optimized in respect to the temperature and time to minimum level to reduce cost as well as to avoid any side reactions with fluxes already present in raw material.

Brief Description of the Drawing:

A complete understanding of the system and method of the present invention may be obtained by reference to the following

Figure 1: Flow diagram of Shot Blast Dust treatment method

Detailed description of the embodiment

The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to communicate the disclosure. The amount of detail offered has the intention to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and together with the description, serve to explain the principles of the invention.
As used in the description herein and throughout the claims that follow, the meaning of “a,”“an,” and “the” includes plural reference unless the context dictates otherwise.

In the preferred embodiment, SBD (as received) and hydrated lime are stored in separate feed hopper. They are fed via spiral type feeder at 0.5-5 kg/hr. to a continuous paddle type mixer. The feeder capacity is such that, hydrated lime quantity is varied from 2 to 10 % of SBD. First part of the mixer will mix dry and then 5-15 % (w/w) of water from feeder tank is added to the mixer to make mix of semidry consistency. Mixing time is 10-15 minutes (of which 30% of time utilized for dry mixing and 70% of time in wet mixing) .

Mixture is directly fed to rotary kiln wherein D/L ratio was 1/12, RPM varies from 0.5 to 10 and temperature varies from 100 to 600℃. All leachable fluoride is converted to non-leachable CaF2.The process makes the product non-hazardous retaining all carbon and fluxes in the product.

It can easily be used in industry.
Leachable Fluoride in SBD react with hydrated lime as follows

F- + Ca+  CaF2

SBD contains 1000-2000 mg/lit leachable fluoride when tested as STLC method as per CPCB requirement (Allowable limit is 180 mg/lit). 2-5% Lime hydrate is used in the process. Following experiments were conducted and leachable fluoride was tested as per CPCB guideline, STLC test as per Wet procedure in Appendix 2 of California Code Regulation.

Ca(OH)2, % Temperature, oC Time, min Leachable F, mg/lit
Variation in lime %
2.0 400 30 150.5
3.5 400 30 35.3
5.0 400 30 12.7
6.5 400 30 30.1
Variation in Temp.
5.0 200 30 100.3
5.0 350 30 20.9
5.0 500 30 32.2
5.0 400 30 12.7
Variation in time
5.0 400 15 25.4
5.0 400 20 15.3
5.0 400 25 15.4
5.0 400 30 12.7

In another aspect of the invention batch or continuous mixers and kiln/furnaces can be used in the process to get similar product. In another embodiment, calcined lime or similar material can be used in place of hydrated lime. That should not be considered outside purview of this patent.

The results above are well within CPCB limit of 180mg/lit but best result is achieved with 5% hydrated lime at 400 deg. C and residence time of 30 min. Thus, SBD can be successfully detoxified with 5% Ca(OH)2 at 350-400 deg. C and residence time in rotary kiln of 15-30 min.
Advantage of the present invention:

The advantage of the present invention is to convert leachable hazardous waste to non-leachable form and recycle a hazardous waste which is presently being dumped in land fill

Another advantage of the present invention is to recover carbon value as well as fluxes value without generating any waste. The present invention also addresses both purpose of supplying carbon and flux to the slag phase thereby making slag fluid and reducing it very efficiently and cheaply.

It will be understood that the invention may be carried out into practice by skilled
Persons with many modifications, variations and adaptations without departing from its spirit or exceeding the scope of the claims in describing the invention for the purpose of illustration.

It is also to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-
, Claims:We claim:
1. An energy-efficient Shot Blast Dust (SBD) treatment method characterizing

-feeding SBD and hydrated lime stored in separate feed hopper through spiral type feeder at 0.5-5 kg/hr. to a continuous paddle type mixer for uniform mixing
- mixing in two parts wherein first part of the mixer will mix dry and then 5-15 % (w/w) of water from feeder tank is added to the mixer to make mix of semidry consistency
-Rotation in a rotary kiln wherein D/L (Diameter /Length) ratio maintained 1/12 and RPM varies from 0.5 to 10 and temperature varies from 100 to 600℃ wherein leachable fluoride in Shot Blast Dust (SBD) is converted to non-leachable CaF2

2. The Shot Blast Dust (SBD) treatment method as claimed in claim 1 wherein feeder is used to hold volume percentage of hydrated lime which varies from 2-10% of SBD.
3. The Shot Blast Dust (SBD) treatment method as claimed in claim 1 wherein hydrated and calcined lime both is used as per requirement
4. The Shot Blast Dust (SBD) treatment method as claimed in claim 1 wherein the process is characterised in batch and continuous mixers whereas kiln and furnaces are used as per requirement of the system.
5. The Shot Blast Dust (SBD) treatment method as claimed in claim 1 wherein mixing time varies 10-15 minutes of which 30% of time utilized for dry mixing and 70% of time in weight mixing to get
6. The Shot Blast Dust (SBD) treatment method as claimed in claim 1 wherein 2-5% Lime hydrate was used to treat 1000-2000mg/litre leachable fluoride present in SBD.
7. The Shot Blast Dust (SBD) treatment method as claimed in claim 1 wherein residence time in rotary kiln varies 15-30 min for resulting leachable fluoride in finish products in the range of 12.7-150.5 mg/litre.

Signature :
Name :MAHUYA HOM CHOUDHURY
IN/PA502