Description:CROSS REFERENCE TO RELATED APPLICATION
This application is a patent of addition of application number 201711025433 titled “improved process and method of extraction of Zinc from Air Pollution Control Device Dust (APCD Dust)” filed on 18 July 2017. The Patent to the said Applicant has been granted under No. 427561 dated 29 March 2023

FIELD OF THE INVENTION
This invention relates to improved process and method of extraction of Zinc from Air Pollution Control Device Dust (APCD Dust), more particularly, to an on-site method of efficient treatment of APCD Dust and manufacturing of Zinc Sheet The invention disclosed · the improved process of collecting hazardous elements of air pollutants emanated in the form of dust and fumes during the process of melting the steel scrap while producing steel outputs; and to convert the gathered APCD Dust into Zinc Sheets as byproduct using improved and inventive process.

BACKGROUND AND RELATED PRIOR ART
The demand for reducing the Air Pollution and treatment of Industrial waste continues to grow globally, in order to keep our environment clean and healthy. The major sources of air pollution are Dust and Dirt, Rust, Oil and Grease, Paint, Galvanized Iron, PVC coated steel. The industrial development is basic cause of Air Pollution. Like every industry, the Steel Industry sector is also growing rapidly, so at every stage of steel making, better efficiency and pollution control is inevitable.

In the Steel Producing Industry ("Steel Industry"), during the process of melting the Steel Scrap and producing the steel outputs, a huge amount of hazardous elements of air pollutants emanated in the form of dust, gases and fumes. These elements are very dangerous for the environment and also contain many hazardous elements which cannot be disposed or diffused in environment and need proper treatment. Due to increasing environmental concerns associated with industrial waste, the entities have taken various steps to incorporate waste management and prevention strategies into their industrial processes.
The collection of APCD Dust in the form of Gases and Dust particles is common to Industries; however, on-site treatment of APCD Dust is rare, more particularly in Steel Industry. In Steel Industry most of the manufacturers, either, do not collect APCD Dust properly or simply hand over, so collected APCD Dust to governmental authorities to dump into the underground tanks specifically install for such APCD Dust. Though the purpose of dumping of APCD Dust by Government Authorities in the said dust tanks is to avoid assimilation of such hazardous gases and dust particles into the environment, however, there exist chances of leakage and/or outflow of such tanks containing harmful gases and dust particles. Therefore, on-site treatment of such harmful gases and dust is highly required.

In particular, APCD Dust collected from Steel manufacturing site prominently contains Zinc and this invention discloses the improved method to collect APCD Dust and treat the said APCD Dust appropriately as to extract Zinc in the form of Zinc Sheets out of APCD Dust The process disclosed in the present invention, on the one hand significantly reduces the emission of hazardous gases into the environment and other hand extracts the valuable byproduct i.e. Zinc manufactured on-site.
Previously, many methods have been disclosed to treat the APCD Dust, however, no specific method has been disclosed, more particularly a method which claimed to be on-site extraction of Zinc from APCD Dust

Therefore, the principle object of the present invention is to disclose an improved method to collect the APCD Dust from the furnace during melting or steel scrap and to extract the APCD Dust into the Zinc as byproduct by using process disclosed herein.

The method disclosed herein to collect APCD Dust is very sophisticated, simple, cost effective and useful for environment, which is, at one hand, capable of preventing and reducing the toxic contents to merge into the environment to an agreeable level by properly treating the flue gases and remove the dust particles/gases before being discharged into the atmosphere and other hand, providing additional produce to the industry i.e. extracts pure Zinc from APCD Dust.

DESCRIPTION
Steel manufacturers generate large volumes of hot and dirty gases wherein iron scrap is melted in Induction Furnace and is solidified into 'Billets' through the process of continuous casting. As described above, this invention disclosed improved process to collects APCD Dust and to extract Zinc out of the APCD Dust using process disclosed herein after. Therefore, the invention runs into two parts. In one part, we collect APCD Dust and in second part, we treat the APCD Dust through on-site installed process in order to extract Zinc out of APCD Dust.

PROCESS OF DUST COLLECTING
An Air pollution controlling device (APCD) is installed on the work station which is a dry bag air filtration system. The first part of method to collect APCD Dust includes the melting of various types of steel scrap from which liquid iron is produced which transformed into 1MT bars being basic product. Resulting to melting of steel scrap "Flue Gases" are generated during melting of scrap as an "Industrial Waste" (FIG 1)

The characteristic and volume of these gases mainly depends upon type of scrap used in the furnace, i.e. with the degree of contamination in the Scrap. The steel scrap which comes from various sources and generally have contamination/coating on it. Therefore, when this steel scrap is heated contamination/coating disintegrates from steel and comes out either as slag or becomes air borne, thus causing air pollution.

In order to void air pollution and appropriate use, the said Flue Gases are collected available in the form of smoke and dust through a "vacuum suction" which is attached on a canopy hood (movable roof) and the said Canopy Hood is placed above the furnace (see FIG 2 ) so it may effectively collect as much dust as possible.

The Canopy Hoods having "vacuum suction" to collect Flue Gases are available in the form of smoke and dust are specifically designed based on crucible diameter and optimum clearance of hood from furnace (see FIG 3).

Once the Flue Gases and Dust i.e. APCD Dust is properly collected through vacuum suction, the same are conveyed to spark arrestor through ducts and bends. The spark arrestor prevents the emission of said APCD Dust from combustion sources into the environment. The Spark arrestor also used for arresting live particles and large hot particles which can damage & burn bags. The size of Spark Arrestor would depend upon gas volume and unit layout which primarily consists Pulse Jet Cleaning system, Clean Air out system, Dust Laden Gas In, Venturi Mounting Plate, Filter Bags, Rotary Air Lock I Discharge Valve. It facilitates in settling of large dust particles and works as a pre-cleaner as illustrated in FIG 4.

Once entire fumes have been conveyed through Spark Arrestor, it transferred to bag filtration unit which is used for fine filtration of Flue gases to remove dust particulate matter. The dust is retained on one side of Bag and clean gases are received on other side. The combined treated APCD Dust from all the bags are collected at top of bag house and are passed through to ID Fan. The dust collected on other side of bags is de-dusted through pulse air jet mechanism with high pressure air. The dust is collected at bottom of hopper and is discharged through Rotary Air Lock Valve. Pulse jet mechanism is carried out through high pressure air with the help of sequencer and solenoid valve. Further in last steps ID fan is used which provides necessary driving force to convey flue gases from suction hood to top of the chimney. The volume sucked overcomes the total resistance offered by apparatus and duct with the help of fluid horse power provided by ID Fan driven by suitable motor and finally the generated gases are passed through chimney of suitable height and diameter. The chimneys are provided and based on volume of flue gases temperature, dispersion desired, composition of gases and legal provisions for height. From this process hazardous waste dust is collected. (see FIG 5)

In order to find out the quantity of Zinc available in APCD Dust so collected, due testing dust is required in the laboratories. After laboratories test of APCD Dust, following results received:-

The summary of above said results of APCD Dust Laboratories test reveals as under:-
i. APCD Dust contained a high amount (around 60.82 % ) of Zinc(Zn) in form of Zinc Oxide(ZnO);

ii. Small quantity of Silica, Calcium, Magnesium, Aluminum, Potassium, Sodium, Cadmium, Manganese and Iron was also present in the Dust Sample.

iii. Zinc Oxide in this waste dust was present due to burning and capturing of zinc elements which were found to be in paint coated and galvanized scrap which was melted.

PROCESS TO RETRIEVE THE ZINC OUT OF DUST COLLECTED
In the second part of this invention, a process is disclosed to extract the Zinc out of the APCD Dust. The process according to the present invention comprises the steps of smoulding, leaching, purification, filteration using Hydrogen peroxide (H202). and Zinc Powder to recover refined liquid removing insoluble particles from APCD Dust.

In addition, apart from Hydrogen peroxide, other Chemicals namely Potassium Permanganate and Potassium perchlorate may also be used as substitute to Hydrogen peroxide (H2O2), however, Potassium Perchlorate is less useful in the process as compare to Potassium Permanganate and Hydrogen Peroxide. Therefore, the preference should either may be given to Hydrogen Peroxide and Potassium Permanganate

During this process many insoluble particles recover like Silica, Calcium, Magnesium, Aluminum, Potassium, Sodium, Cadmium, Manganese and Iron from the leach solution.

In addition, aforesaid particles of Silica, Calcium, Magnesium, Aluminum, Potassium, Sodium, Cadmium, Manganese and Iron have relatively high Flouride/ Chloride, making it difficult to do acid process, unless where Chloride goes with the iron precipitates by goethite iron precipitation method during the acid process. If the Chloride is accumulated in the acid solution, it will be detrimental to the acid electrowinning. In contrary to acid process, ammonia process is favoured to have certain Chloride from raw material, making it an ideal process to treat high Flouride/ Chloride crude zinc oxide dust.

The present invention further relates to processes for recovering / extracting Zinc through electro-winning process using aluminum sheets as cathode and graphite sheets as anode.

In addition, as an alternative to Aluminum (Al), the electro-winning process can be conducted by using Titanium (Ti).

SMOULDERING
The first steps in this process to ignite the APCD Dust, which have been collected and filtered during the first part of the invention. The APCD Dust is ignited in a dark and closed smouldering room having a Air Pollution Control Device within the said dark room.

In addition, the ignited APCD Dust smoulders on its own for about 24 hours. In addition, the ignited APCD Dust smoulders may take variation in time to smoulder between 18 to 48 hours based upon the quality, climate and condition.

During the smouldering APCD Dust removes I discharges Carbon dioxide and sulphar dioxide below harmful level and appropriately treated through the Air Pollution Controlled Devices installed therein mounted with a specific Chimany.

During the smouldering process, APCD Dust changes its colour form black/dark grey to yellow. Smouldering of dust helps to bum volatile materials like sulphur, carbon and removes them from the APCD dust It also oxidises ZnS present in the APCD dust into ZnO. During smouldering about 20% of the dust gets converted into smoke and leaves the system. During smoulding of APCD Dust, there is emission of the reaction involved is:

2ZnS + O2 HEAT 2ZnO + S

LEACHING
After the completion of smouldering process, the dust is transferred into the leaching tank and Hydrogen peroxide i.e. H2O2 (6.5%-8.5% of Zn present in APCD dust) is added into the mixture of APCD dust. Hydrogen peroxide is a chemical compound with the formula H 20 2 in its pure form, it is a colourless liquid, slightly more viscous than water. Hydrogen peroxide is the simplest peroxide. It is used as an oxidizer, bleaching agent and disinfectant. Its role is to oxidize FeO into Fe2O3. FeO is referred to "Iron(II) oxide" or “ferrous oxide" which is the inorganic compound . Its mineral form is known as wustite. One of several iron oxides, it is a black-colored powder which consists of hydrated ferrous oxide. In addition, apart from Hydrogen peroxide, other Chemicals namely Potassium Permanganate and Potassium perchlorate may also be used as substitute to Hydrogen peroxide (H2O2), however, Potassium Perchlorate is less useful in the process as compare to Potassium Permanganate and Hydrogen Peroxide. Therefore, the preference should either may be given to Hydrogen Peroxide and Potassium Permanganate

In addition, leaching tank for leaching process takes place in the presence of ammonia solution mixed with water. The source of Ammonia can be Ammonia Solution (22-25%), Ammonium Bicarbonate and/ or Ammonium Chloride (NH4CL)

In the leaching process, Zn and the other heavy metals contained are dissolved together with ammonia chlorides and part of alkaline earth salts according to the following reactions:

ZnO +iNH3 +H2O = [ Zn(NH3)i] 2+ +2OH-

PbCl2 + n XCl ? (X)nPbCl(2+n) (X = Na+, K+, NH +)

Normally all the zinc contained materials are leached. Only the zinc ferrite and iron oxide remains in solid. In the leaching slurry, Fe usually accounts for 50% and can be sold out to cement production plant or iron-making plant. In case the zinc remained in the leaching slurry and accounts for more than 10%, the zinc-bearing leaching slurry can be treated by waelz kiln to enrich zinc by volatile. After zinc evaporation, there remains iron slag which can be send to steel converter for iron refining.

The plant needs to equip with zinc dust storage area, dust volume-constant feeding system, dust leaching, liquid-solid separation from leaching solution. The pulping of zinc dust and leaching are performed in the tank. Liquid-solid separation is done by membrane-type filter press.

Due to the oxidation of FeO into Fe203, Fe becomes insoluble in the liquid and gets filtered in next step. Total duration of leaching is about 75 minutes, additionally, the time may vary from 60 to 90 minutes. The reaction involved is:
2FeO+H202 Fe203+H20

FILTRATION
Thereafter, the entire liquid present in leaching tank is passed from a filter press. In filter press, all the insoluble particles like Iron (Fe), silica (Sio), magnesium, (MgO) etc get filtered out of Fe203 within 75 minutes and filter liquid is recovered out of the said process which is more particularly described in FIG 6. In addition, in filter press, all the insoluble particles like Iron (Fe), silica (Sio), magnesium, (MgO) etc also get filtered out of Fe203 within 75 minutes.

PURIFICATION
After filtration, the liquid is purified by adding Zn powder (of about 94% purity). It is of about 4%-6% of Zn present in APCD Dust. Its role is the reduction of PbO (lead) present in the system into Pb, which precipitates at the bottom of the tank and becomes insoluble. This process takes about 20 minutes, which may vary 15-30 Mins. The reaction involved is:

PbO+Zn ZnO + Pb(precipitate)

In addition, the purification process is replacement reaction where zinc powder is added and impurities are replaced by zinc. The reaction is expressed as:

Me(NH3)2+j +Zn +(i -j)NH3 =Me?+[ Zn(NH3)i]2

(Me = Pb2+, Cd2+, Cu2+, Ag+, ...)

From different raw material, the impurities dissolved into the solution will be different, therefore, batch sampling would be necessary to decide the zinc powder used for purification and purification stages to make sure stable high quality zinc cathode. The purification is taken place in the tank. Liquid-solid separation is done by filter press.

Dust particles which contains high quantity of Lead which is transmitted to lead manufacturers for further process in order to recovery of Lead out of the said left outs.

Thereafter, the purified liquid is transferred through anther filtered device for final time. The filter press used in this process and the remaining insoluble particles get filtered out within 1 hour of continuous filtration process.

ELECTRO WINNING PROCESS

The final liquid which is obtained after second filtration is transferred to Cell house, where it undergoes "electro winning process". In this electro-winning process, aluminium sheets as cathode and graphite sheets as anode are used

In addition, use of Titanium in Electro-winning process is considerable and another suitable component, however, due to high cost of Titanium, it will increase the production cost effectively as oppose to the use of Aluminum (Al). Therefore, inventors prefer to use the Aluminum in Electro-winning process to be conducted to perform the present invention.

These sheets are subjected with high current with current density of about 400 ampereslmetre2. In addition, due to high electric current passing through the cathode and anode, the Zinc ions (Zn+ ions) present in the liquid gets deposited on Aluminium plates (Cathode) which are negatively charged. Peg is also added in cellhouse to increase the hardness of zinc sheets and for the easy removal of zinc sheet from Aluminium plate) Bone glue can also be added to substitute the PEG

After 24 hours, which may vary between 18-48 hours, of electro winning process, strips of zinc are formed on cathode (aluminium sheets) which are removed from the sheets and are considered as the final product of process disclosed herein. (see FIG 7).

In Addition, the electrolytic zinc sheet needs to be melt and then casted into ingot, saleable on the market. Zinc melting furnace can be corded induction furnace or coreless induction furnace. After melting of the cathode sheet, the zinc will be casted into ingot by linear ingot casting machine.
, Claims:We claim,

1. a process for recovering Zinc from Air Pollution Controlling Device Dust that initially includes Zinc, Silica, Calcium, Magnesium, Aluminum, Potassium, Sodium, Cadmium, Manganese and Iron, comprising the steps of;
a. ignite the Air Pollution Controlling Device Dust in a dark and closed smouldering room having an Air Pollution Control Device within the said dark room which takes 18 to 48 hours to smoulder on its own based upon quality, climate and condition; and
b. recover the refined solution after smouldering process; and then

c. leaching the solution recovered through igniting process using Hydrogen peroxide (H202); or Potassium Permanganate; or Potassium perchlorate as substitute to each other; thereafter

d. then entire solution present in leaching tank is passed from a filter press; and

e. a process of purification of solution is conducted; thereafter

f. the purified solution is passed through another filtered device for final time; then

g. the final solution which is obtained after second filtration is transferred to Cell house, where it undergoes "electro winning process"; and thereafter

h. strips of zinc are formed on cathode (aluminium sheets) which are removed from the cathode and are considered as the final product of process disclosed herein.

2. The process of claim 1, wherein the ignited Air Pollution Controlling Device Dust smoulders on its own for normally about 24 hours wherein time to smoulder may be varied 18 to 48 hours based upon the quality, climate and condition; and
during the smouldering Air Pollution Controlling Device Dust removes / discharges Cerein carbon dioxide and sulphur dioxide below harmful level and appropriately treated through the Air Pollution Controlled Devices installed; and
dust changes its colour form black/dark grey to yellow which helps to bum volatile materials like sulphur, carbon and removes them from the Air Pollution Controlled Device dust It also oxidises ZnS present in the APCD dust into ZnO. During smouldering about 20% of the dust gets converted into smoke and leaves the system. During smoulding of APCD Dust, there is emission of the reaction involved is:

2ZnS + O2 HEAT 2ZnO + S

3. the process of claim 1, wherein the leaching of the material recovered through igniting process with Hydrogen peroxide (H202) which produces a leach solution in a leaching tank in the presence of ammonia solution mixed with water;
the source of Ammonia can be Ammonia Solution (22-25%), Ammonium Bicarbonate and/ or Ammonium Chloride (NH4CL);
in the leaching process, Zn and the other heavy metals contained are dissolved together with ammonia chlorides and part of alkaline earth salts according to the following reactions:
ZnO +iNH3 +H2O = [ Zn(NH3)i] 2+ +2OH-
PbCl2 + n XCl ? (X)nPbCl(2+n) (X = Na+, K+, NH +)

in the process of leaching only the zinc ferrite and iron oxide remains in solid; and due to the oxidation of FeO into Fe203, Iron (Fe) becomes insoluble in the liquid and in case, in the leaching slurry, Iron (Fe) usually accounts for 50% and can be sold out to cement production plant or iron-making plant;
in case the zinc remained in the leaching slurry and accounts for more than 10%, the zinc-bearing leaching slurry can be treated by waelz kiln to enrich zinc by volatile; and
after zinc evaporation, there remains iron slag which can be send to steel converter for iron refining;

4. the process of claim 3, wherein the leaching of the material recovered through igniting process, apart from Hydrogen peroxide, other Chemicals namely Potassium Permanganate and Potassium perchlorate may also be used as substitute to Hydrogen peroxide (H2O2), however, Potassium Perchlorate is less useful in the process as compare to Potassium Permanganate and Hydrogen Peroxide. Therefore, the preference should either may be given to Hydrogen Peroxide and Potassium Permanganate; and

5. a process of claim 1, wherein for producing zinc, a process of filtration leaching material is conducted through a filter press wherein the insoluble particles like Iron (Fe), silica (Sio), magnesium, (MgO) etc get filtered out of Fe203 within 75 minutes and filter liquid is recovered out of the said process which is more particularly described in FIG 6.

6. the process of claim 1, further comprising the step of purification of solution wherein the solution is purified by adding Zn powder (of about 94% purity) and it is of about 4%-6% of Zn present in Air Pollution Controlling Device Dust in which its role is the reduction of PbO (lead) present in the system into Pb, which precipitates at the bottom of the tank and becomes insoluble which normally takes 20 minutes, time may vary 15-30 minutes which involves the following reaction

PbO+Zn ZnO + Pb(precipitate)

the purification process is replacement reaction where zinc powder is added and impurities are replaced by zinc. The reaction is expressed as:

Me(NH3)2+j +Zn +(i -j)NH3 =Me?+[ Zn(NH3)i]2

(Me = Pb2+, Cd2+, Cu2+, Ag+, ...)

7. the process of claim 1, comprising further filtration process of solution recovered as stated in Claim 5 and during the final filtration through a filter press remaining insoluble particles get filtered out;
8. the process of claim 1, final solution which is obtained after second filtration is transferred to Cell house, where it undergoes "electro-winning process" and in this electro-winning process, aluminium sheets as cathode and graphite sheets as anode are used and these sheets are subjected with high current with current density of about 400 amperes/metre2;
use of Titanium in Electro-winning process is also a good option being another suitable component, however, due to high cost of Titanium, it will increase the production cost effectively as oppose to the use of Aluminum (Al);
due to high electric current passing through the cathode and anode, the Zinc ions (Zn+ ions) present in the liquid gets deposited on Aluminium plates (Cathode) which are negatively charged. Peg is also added in cellhouse to increase the hardness of zinc sheets and for the easy removal of zinc sheet from Aluminium plate) Bone glue can also be added to substitute the PEG

9. The process of claim 1, comprising final steps to remove Zinc strips after 24 hours, which may vary between 18-48 hours, of electro winning process, strips of zinc are formed on cathode (aluminium sheets) which are removed from the sheets and are considered as the final product of process disclosed herein.