Claims:We Claim:
1. A method to recover iron from dust material including dust in iron and steel plant comprising the following specific steps:
subjecting said dust material comprising dust in iron and steel plant including 20.8 to 100% of iron having particle size <45 µm and 5.20 to 97.8% of iron having particle size <10µm,
to an initial gravity separation, and
subjecting the thus obtained concentrate of gravity separation tocontrolled magnetic separation by applying stage wise selective magnetic field intensity to effectively recover ironfrom the feed material.

2. The method to recover iron from dust in iron and steel plant as claimed in claim 1 wherein said dust from iron and steel plant comprises of average iron in the dust is in the range of 35.8 to 56.4% and on which the following specific steps are carried out sequentially:
initially subjecting the dust in iron and steel plant to gravity separation, and
thereafter ,subjecting the concentrate of gravity separation to said controlled magnetic separation twice by applying the magnetic field intensity in the range of 1500 to 1200 Gauss for first magnetic separation and the magnetic field intensity in the range of 800 to 1000 Gauss to recover 39.71 to 40.70 weight % of iron.

3. The method to recover iron from dust in iron and steel plant as claimed in anyone of the claims 1 to 2, wherein the dust includes 5.56 – 5.82% of Al2O3, 8.82 – 9.0% of SiO2, 7.08 to 7.20% of FeO, 8.72 – 8.87% of C, 5.64 – 5.81% of CaO, 0.77 – 0.98% and 0.198 – 0.211% of MgO.

4. The method to recover iron from dust in iron and steel plant as claimed in anyone of the claims 1 to 3, wherein the dust in iron and steel plant is subjected to gravity separation in spiral concentrator.

5. The method to recover iron from dust in iron and steel plant as claimed in anyone of the claims 1 to 4, wherein the Spiral concentrator tailing is subjected to magnetic separation twice in Wet High Intensity Magnetic Separator (WHIMS) and Low Intensity Magnetic Separator (LIMS).

6. The method to recover iron from dust in iron and steel plant as claimed in claim 5, wherein the dust in iron and steel plant is subjected to gravity separation in spiral concentrator by maintaining the feed rate 1.8 to 2.4m3/hr and feed % of solids 25 to 30%.

7. The method to recover iron from dust in iron and steel plant as claimed in anyone of the claims 1 to 6, wherein slurry solid percentage of the first magnetic separation is maintained in the range of 15 to 20%.and slurry solid percentage of the second magnetic separation is maintained in the range of 18 to 22%.

8. The method to recover iron from dust in iron and steel plant as claimed in anyone of the claims 1 to 7 wherein said dust in iron and steel plant is selected from BF dust, FAP dust, SIP dust and SMS dust.

9. The method to recover iron from dust in iron and steel plant as claimed in anyone of the claims 1 to 8 comprising:

(i) passing feed material of said dust material through wet screen followed by settling;
(ii) collecting the thus settled dust material and maintaining the dust material slurry density of 25 to 30% solids;
(iii) feeding the said dust material slurry to spiral concentrator at the rate of 1.8 to 2.4 m3/hr. to thereby obtain spiral concentrator tailing and collecting spiral concentrate as final product;
(iv) processing said spiral concentrator tailings through WLIMS by applying 1500 to 1800 Gauss magnetic field intensity under pulsation rate is 200 to 250rpm and % of solids by weight is 15 to 20%.to thereby obtain WLIMS tailing as final product and WLIMS concentrate for further processing ;
(v) processing the thus obtained said WLIMS concentrate in LIMS involving magnetic field intensity of LIMS 800 to 1000 preferably about 800 Gauss (fix) and wherein the feed rate was varied from 12 to 17 kg/min with % of solids by weight is 18 to 22%. following which the LIMS concentrate was considered as final concentrate and LIMS tailing was considered as final tailing.

Dated this the 25th day of October, 2021
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
A METHOD TO RECOVER IRON FROM DUST IN IRON AND STEEL PLANT.


2 APPLICANT (S)

Name : JSW STEEL LIMITED.

Nationality : An Indian Company incorporated under the Companies Act, 1956.

Address : JSW CENTRE,
BANDRA KURLA COMPLEX,
BANDRA(EAST),
MUMBAI-400051,
MAHARASHTRA,INDIA.




3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION

The present invention relates to the technical field of comprehensive utilization of steel plant waste materials to conserve metallurgical resources and particularly to a method to recover iron value from waste dust materials in an iron and steel plant.

BACKGROUND OF THE INVENTION

The steel plant waste material recycling rates have reached to 95 - 97 %. ~2 Mt of plant waste material (BF dust, FAP dust, SIP dust and SMS dust), is dumped at tailing pond. The Fe content in dust material is varying from 36 to 56%. Utilization of dumped material through suitable beneficiation process is the crucial issue and economic asset. Reduction in generation of waste and gainful utilization and recycling of these wastes not only improve the economics of operation but also prevent degradation of the ambient environment. Additionally, the depletion of high–grade iron ores imposes broad research work to utilize the waste materials. The dumped material can be utilized in pelletization/briquetting process after suitable beneficiation process. The aim of a steel industry is to recover iron value from waste materials where a number of manufacturing processes are employed involving use of various raw materials and during process, many seemingly significant substances are generated which are known as waste materials. The steel plant waste solid materials are raw material fines, slag, mill scale, flue dust and sludge. One of the major concerns of world steel plants are the disposal of wastes generated at various stages of processing. Over the years, due to technological improvement in steelmaking and strict environmental regulations, emphasis on raw material quality and new markets coupled with innovative ideas on waste reduction and rescue have resulted in drastic reduction in the quantity of waste generated in this project is to develop the suitable process flow sheet to recover iron bearing minerals and utilization of beneficiated product in pelletization process.

The technical paper titled Recovery and utilization of iron and carbon values from blast furnace flue dust, A. Yehia, and F.H. El-Rehiem, The European Journal of Mineral Processing and Environmental Protection, Vol.5, No.2, 1303-0868, 2005, pp. 184-189, stated that a typical flue dust sample obtained from Egyptian iron and steel company was characterized and the amenability of recovering iron and carbon values from it, was investigated. Flotation was used to recover carbon values while magnetic separation was employed for iron values recovery. It was possible to recover about 99% of carbon values with 87.18%. Besides, high intensity magnetic separation was adopted to recover clean magnetic fraction with 79% recovery and assayed 52.40% Fe.

The technical paper titled Test research on comprehensive recovery of carbon and iron from blast furnace flue dust, Yi Miao Nie and Qi Hui Dai, Applied Mechanics and Materials, Volumes. 543-547, pp. 2014, 3826-3829, revealed that the flue dust could be enriched by flotation-gravity-magnetic separation technology to produce carbon concentrate and iron concentration. The results showed that 56.67% iron concentrate and 65.29% carbon concentrate could be got.

The technical paper titled Effective Utilization of Blast Furnace Flue Dust of Integrated Steel Plants , B. Das*, S. Prakash, P. S. R. Reddy, S. K. Biswal, B. K. Mohapatra, V. N. Misra, The European Journal of Mineral Processing and Environmental Protection Vol. 2, No. 2, 1303-0868, 2002, pp. 61-68, revealed that the blast furnace flue dust generated at steel plants have indicated that most of the carbon values can be recovered by cell or column flotation. Magnetic portion of the sample can be separated by low intensity magnetic separator techniques. Flotation technique was employed to recover the carbon values present in the sample. It was possible to obtain a product containing around 80% carbon with more than 90% recovery from both the flue dust samples using diesel oil and MIBC as the collector and frother respectively. Magnetic separation of flotation tailings gave an iron concentrate of 61-64% Fe with 50-56% over all recovery.

OBJECTS OF THE INVENTION

The main object of the present invention is directed to development of suitable process flow sheet for processing of steel plant wastes.

Yet another object of the present invention is directed to a process to recover the iron bearing minerals from steel plant dusts and the Fe content in produced product is ~57 to 59%, for effective utilization in iron and steel making.

A further object of the present invention is directed to conserve consumption of scarce and valuable mineral resources.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide a method to recover iron from dust material including dust in iron and steel plant comprising the following specific steps: subjecting said dust material comprising dust in iron and steel plant including 20.8 to 100% of iron having particle size <45 µm and 5.20 to 97.8% of iron having particle size <10µmto an initial gravity separation, and subjecting the thus obtained concentrate of gravity separation to controlled magnetic separation by applying stage wise selective magnetic field intensity to effectively recover iron from feed material.

A further aspect of the present invention is directed to said method to recover iron from dust in iron and steel plant wherein said dust from iron and steel plant comprises of average iron in the dust is in the range of 35.8 to 56.4% and on which following specific steps are carried out sequentially :initially subjecting the dust in iron and steel plant to gravity separation, and thereafter subjecting the concentrate of gravity separation to said controlled magnetic separation twice by applying the magnetic field intensity in the range of 1500 to 1200 Gauss for first magnetic separation, and then to magnetic field intensity in the range of 800 to 1000 Gauss to recover 39.71 to 40.70 weight % of iron.

A still further aspect of the present invention is directed tosaid method to recover iron from the dust which includes 5.56 – 5.82% of Al2O3, 8.82 – 9.0% of SiO2, 7.08 to 7.20% of FeO, 8.72 – 8.87% of C, 5.64 – 5.81% of CaO, 0.77 – 0.98% and 0.198 – 0.211% of MgO.

A still further aspect of the present invention is directed to said method to recover iron from the dust in iron and steel plant which is subjected to gravity separation in spiral concentrator.

Yet another aspect of the present invention is directed to said method to recover iron from the dust in iron and steel plant wherein the spiral concentrator tailing is subjected to magnetic separation twice in Wet High Intensity Magnetic Separator (WHIMS) and Low Intensity Magnetic Separator (LIMS).

A further aspect of the present invention is directed to said method to recover iron from the dust in iron and steel plant wherein the dust in iron and steel plant is subjected to gravity separation in spiral concentrator by maintaining the feed rate 1.8 to 2.4m3/hr and feed % of solids 25 to 30%.

A still further aspect of the present invention is directed to said method to recover iron from the dust in iron and steel plant wherein the slurry solid percentage of the first magnetic separation is maintained in the range of 15 to 20%.and slurry solid percentage of the second magnetic separation is maintained in the range of 18 to 22%.

A still further aspect of the present invention is directed to said method to recover iron from dust in iron and steel plant wherein said dust in iron and steel plant is selected from BF dust, FAP dust, SIP dust and SMS dust.

A still further aspect of the present invention is directed to said method to recover iron from dust in iron and steel plant comprising:
(i) passing feed material of said dust material through wet screen followed by settling;
(ii) collecting the thus settled dust material and maintaining the dust material slurry density of 25 to 30% solids;
(iii) feeding the said dust material slurry to spiral concentrator at the rate of 1.8 to 2.4 m3/hr. to thereby obtain spiral concentrator tailing and collecting spiral concentrate as final product;
(iv) processing said spiral concentrator tailings through WLIMS by applying 1500 to 1800 Gauss magnetic field intensity under pulsation rate is 200 to 250rpm and % of solids by weight is 15 to 20%.to thereby obtain WLIMS tailing as final product and WLIMS concentrate for further processing ;
(v) processing the thus obtained said WLIMS concentrate in LIMS involving magnetic field intensity of LIMS 800 to 1000 gauss preferably about 800 Gauss (fix) and wherein the feed rate was varied from 12 to 17 kg/min with % of solids by weight is 18 to 22%. following which the LIMS concentrate was considered as final concentrate and LIMS tailing was considered as final tailing.

The above and other objects and advantages of the present invention are described hereunder in greater detail with reference to the following accompanying non-limiting illustrative drawings and examples.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: Show the Micrographs of dust samples with phase analysis.
Figure 2: Show the developed flow sheet for processing of steel plant dusts according to present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING FIGURES AND EXAMPLES

The accompanying figure together with the detailed description below forms part of the specification and serves to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

The present invention is now discussed in more detail referring to the drawings that accompany the present application. In the accompanying drawings, like and/or corresponding elements are referred to by like reference numbers.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts.

The present invention relates to the development of a suitable beneficiation process to recover the iron bearing minerals from steel plant process dusts like BF dust, FAP dust, SIP dust and SMS dust to further utilise in pelletization process. More particularly, the present invention is directed to recovery of iron bearing minerals from various steel plant dusts comprising of Fe grade varying from 36 to 56% and less than 10µm particle size varying from 5.4 to 97.4% (5.4% in Blast furnace dust, 97.4% in SMS dust, 36.6% FAP dust and 40.8% in SIP dust) solid fraction. The present invention related to the recovery of iron bearing minerals based on the association of wanted and unwanted minerals present in the steel plant wastes using X-ray diffraction (XRD) and for chemical analysis of phases used Electro probe micro analyser (EPMA). More particularly, the present invention is directed to the production of high Fe rich material from steel plant process waste using spiral concentrator as gravity separation followed by two stage magnetic separation using wet high intensity magnetic separator (WHIMS) & low intensity magnetic separator (LIMS) at optimum operating conditions to utilize the produced product in pelletization process to achieve the Fe content in final product 57 to 59%. Present invention relates to the recovery of iron bearing minerals from steel plant process waste. In steel Industry, the production of steel is associated with the generation of solid waste materials like slag, dust, sludge, etc. Significant quantities of wastes are generated from steelmaking process, which is a focus point for its utilization as well as to reduce the environmental impact. This work highlights the processing of waste materials like blast furnace dust (BF dust), Ferro alloy plant dust (FAP dust), sponge iron plant dust (SIP dust) and Steel making shop dust (SMS dust) to recover iron bearing minerals for their optimum utilization by agglomeration. For recovering iron bearing minerals from dusts a simple beneficiation process was adopted using gravity separation followed by magnetic separation units. The Fe content and -10µm size in collected various dust material is varying from 35.8 to 56.4% (mixed material average Fe: 45.5 to 47.7%) and 5.2 to 97.8% respectively. Dusts samples consists of hematite, magnetite, calcium aluminium silicate and quartz minerals. In SMS dust wustite and iron particles were observed. Widely varying the quality of waste makes the one of the major concerns of waste management, this makes it very difficult to tailor it for any downstream usage. From the developed flow sheet, it is possible to remove the alumina, silica and zinc from steel plant waste material to further utilize in pellet making. The developed process is the efficient and cost effective process.

The dumped materials like BF dust, FAP dust, SIP dust and SMS dust were collected from JSW steel tailing pond. The chemical analysis of the collected waste material is shown in Table 1. Size analysis of the waste material is shown in Table2. From size analysis it was found that BF dust consists of ~29.6 to 30.6% +150 µm size particles, SMS dust consists of 97.0 to 97.8% and 66.0 to 66.5 -10µm and –2µm size particles respectively. FAP and SIP dusts consist of -10µm particles 36.42 – 36.85 and 40.55 – 41.02% respectively.

In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or composition that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article or composition. An element proceeded by "comprises...a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or composition that comprises the element.

In the present specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless specifically stated otherwise.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. Commonly used dictionary-defined terms are additionally interpreted as having meanings consistent with related technical documents and currently disclosed content and are not interpreted as ideal or very formal meanings unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

In addition, unless otherwise specified, % means weight%.

The advantages and features of the present invention and methods for achieving them will be clarified with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms, and only the embodiments allow the disclosure of the present invention to be complete, and are conventional in the art to which the present invention pertains. It is provided to fully inform the knowledgeable person of the scope of the invention, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same components throughout the specification.

Thus, in some embodiments, well-known techniques are not specifically described to avoid obscuring the present invention. Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used as meanings commonly understood by those skilled in the art to which the present invention pertains.
The present invention is described further hereinafter by reference to a series of accompanying examples.

Experiments that were actually performed are now described by way of the following examples.

Examples
Example 1: Under this example various types of steel plant waste dust materials samples were analysed for their chemical composition and the results are summarised in following Table 1.
Table 1 Chemical analysis of dust samples

Example 2:Under this example size analysis of various waste dust samples were carried out and the results are summarised in following Table 2.
Table 2 Size analysis of the dusts
Description -2µm -10 µm -45 µm -75 µm -150 µm +150 µm
BF dust 2.1 2.5 5.2 - 5.6 20.8 - 22.3 39- 39.8 69.4-70.4 29.6-30.6
FAP dust 9.0-9.6 36.6-39.3 83.4-83.6 91.8-92.5 99.2-99.9 0.1 - 0.8
SIP dust 7.8-8.2 40.6-41.0 92-92.4 97.3-98.5 100.0 0.0
SMS dust 66.0-66.5 97.0-97.8 100.0 100.0 100.0 0.0

Example 3:
The collected waste dumped material was subjected to X-ray diffraction (XRD) analysis to know the different mineralogical phases present in the sample. Table 3shows the XRD phase analysis of dust samples. Phase analysis of phases was carried out by using Electro probe micro analyser. The micrographs of dust samples along with chemical analysis of phases are shown in Figure 1.
Table 3 XRD analysis
Phase,% BF dust FAP dust SIP dust SMS dust
Iron 1.3 - 2.3
Wustite 9.5 - 11.5
Magnetite 35 – 37.4 11 - 13 10.5 -12.5 10 - 12
Hematite 33.7 - 35.7 37 - 39 45.5 - 47.5 55 - 57
DicalciumAluminiunAluminosilicate 15.3 -17.3
Calcium dialuminodisilicate 31 - 33 27 - 29
Dicalcium silicate 22.3 - 24.3
Quartz low 11.7 - 13.7 17 - 19 13 - 15

Applicant’s aim herein is to develop simple cost effective flow sheet to process the steel plant wastes. FeO content in the collected waste samples is varying from 3 to 12.5%. The process consists of gravity separation followed by 2 stage magnetic separation at low magnetic field intensity was tried to recover the iron bearing minerals. Based on the preliminary magnetic separation studies it was found that at higher gauss =3000 Gauss magnetic field intensity the whole feed material was reported in magnetic concentrate because the whole material was attracted to matrix. So for development of flow sheet and laboratory studies the magnetic field intensity was maintained less that 3000 Gauss.

The waste dusts material was passed through wet screen and sample was kept for settling. The settled material was collected and maintained the feed slurry density of 25 to 30% solids. The slurry was fed to spiral concentrator at the rate of 1.8 to 2.4 m3/hr. The spiral concentrator tailing and concentrate was collected. The spiral concentrator concentrate was treated as final product. The spiral concentrator tailing was further processed through WLIMS by applying 1500 to 1800 Gauss magnetic field intensity. The pulsation rate is 200 to 250rpm and % of solids by weight is 15 to 20%. The WLIMS tailing was considered as final tailing and WLIMS concentrate was further processed in LIMS. The magnetic field intensity of LIMS is 800 Gauss (fix). The feed rate was varied from 12 to 17 kg/min with % of solids by weight is 18 to 22%. The LIMS concentrate was considered as final concentrate and LIMS tailing was considered as final tailing.

The developed flow sheet for processing of various dusts is shown in Figure 2. The test results of developed flow sheet of each unit process is shown in Table 4. The summary of test results are shown in Table 5.

Table 4 Test results of each unit process

Table 5 Test results Summary

At higher magnetic intensity (more than optimum magnetic intensity) the SLon and LIMS magnetic separator magnetic concentrate weight recovery was increased and grade was decreased (Table 6 and Table 7).This will reduce the overall concentrate grade. At higher gauss the unliberated iron bearing minerals will reporting into the magnetic concentrate and increases the weight recovery and reduces the concentrate grade.

Table 6: Magnetic separation results on spiral tailing with various magnetic field intensity

Table 7: Magnetic separation results on SLon mag with various magnetic field intensity