Title of Invention

"A PROCESS FOR PREPARATION OF MONODISPERSED IRON (III) OXIDE OF HIGH COERCIVITY"

Abstract A process for preparation of monodispersed iron oxide of high coercivity which comprises : (i)preparing aqueous solution of iron chloride of concentration in the range of 50 to 150 g/L by dissolving electrolytic iron powder or scrap iron in hydrochloric acid, (ii) purifying the iron solution prepared from scrap iron by solvent extraction using methyl isobutyl ketone or tri-n-butyl phosphate with organic: aqueous (O/A) ratio in the range 2:1 to 4:1, (iii) adding ammonium hydroxide solution to iron chloride for precipitating iron as iron hydroxide while stirring with the help of suitable stirrer and maintaining the pH of the hydroxide slurry in the range 2.5 to 3.5, (iv) autoclaving the iron hydroxide slurry in the temperature range of 140 to 220 °C for 2 hours to precipitate hematite and cooling thereafter to 70 °C, wherein the concentration of iron in the hydroxide slurry during hydrothermal precipitation is in the range of 10 - 50 g/L (v) filtering the slurry and washing the precipitate for complete removal of chloride and drying in the temperature range of 50 to 80 °C for 48 hours..
Full Text This invention relates to a process for preparation of monodispersed iron oxide ofhighcoercivity
This invention particularly relates to a process for preparation of high coercive iron oxide hydrothermally with varying size, magnetic and microstructural properties which are useful for preparing high quality ferrites.
Iron oxide is a major constituent of ferrite material and the demand of which is drastically increased because of enormous development in electronic industry. The quality of iron oxide controls the grain size, shape, hardness, permeability, magnetic losses etc. of the ferrite products. Therefore, high grade iron oxide is needed in order to produce high quality ferrites.
Conventional methods for preparation of iron involves high temperature reaction which produce several defects, voids etc. and non reproducible products in terms of their magnetic properties are obtained. Hydrothermal precipitation technique have several advantages over conventional methods of preparation such as (1) effective control of size and shape of the particles (2) incorporation of less impurities in the hydrolysed products (3) regeneration of lixiviant and (4) relatively low reaction temperature.
Efforts are continuing to produce monodispersed iron(III) oxide particles, uniform in shape, size and composition as an ideal constituent for variety of advanced material. The various processing techniques developed for production of such particles are spray roasting (Klading W. F. and Zengen M. F., J. Eur. Ceram. Soc. 1992, Vol. 9, p. 341; Ruthner M. J. in Proc. lst Int. Conf. in ferrites, 1970, Kyoto, Japan) gel-sol (Sugimoto T., Muramastu A. Sakata K. and Shindo, D., J. Colloid Interface Sci, 1993, Vol. 158, p. 420; Bailey J. K., Brinker C. J. and Mecartney M. L., J. Colloid Interface Sci., 1994, Vol. 168, p. 178; Ozaki M., Kratohvil S. and Matijavic E., J. Colloid Interface Sci., 1984, Vol. 102, p. 146; Hamanda S., Matijevic E. J. Chem. Soc. Faraday Trans., 1982, Vol. 178, p. 2147; Sugimoto T., Khan M. M. and Muramastu A., Colloids Surface 1993 Vol. 70, p. 167) and hydrothermal method (Shang Y. and Weert G. V., Hydrometallurgy, 1993 Vol. 33, p. 273; Konishi Y., Kawamura, T. and asai, S., Matall. Trans B, 1994, Vol. 25, p. 165).
Gel-sol method of preparation of iron oxide comprise of preparation of a thick gel by concentrated iron salt and sodium hydroxide solution and heating the mass at 100 °C for about 8 days. The hydrothermal decomposition of iron nitrate or carboxylate solution to produce iron oxide is reported by Shang et al. and Konishi et. al. respectively. Though several attempts have been made to prepare monodispersed pseudocubic hematite particles by gel-sol method from iron chloride solution, there is rarely any attempt made to prepare pseudocubic hematite particle hydrothermally. Iron(III) oxide of uniform size pseudocubic particles of very high coercivity prepared from scrap iron have not been reported so far.
The main object of the present invention is to provide a process for preparation of monodispersed iron oxide of high coercivity
Another object of the present invention is to prepare very uniform in size and shape of polycrystalline monodispersed pseudocubic particles by hydrothermal precipitation method from iron chloride solution.
Yet another object of the present invention is to prepared iron oxide of different microstructure and magnetic properties.
Still another object of the present invention is to prepare hematite from iron chloride solution with the aim to utilise naturally abundant and waste material like blue dust and iron scrap, which would favour a hydrochloric acid leaching route. In chloride media direct hydrothermal decomposition of iron chloride to iron oxide is difficult due to re-dissolution of precipitated iron oxide.
Still another object of the present invention is to prepared iron oxide by neutralising iron chloride solution by aqueous ammonia solution in order to avoid alkali metal ion incorporation in to the matrix.
Accordingly, the present invention provides a process for preparation of monodispersed iron oxide of high coercivity which comprises :
i) preparing aqueous solution of iron chloride of concentration in the range of 50 to 150 g/L by dissolving electrolytic iron powder or scrap iron in hydrochloric acid, ii) purifying the iron solution prepared from scrap iron by solvent extraction using methyl isobutyl ketone or tri-n-butyl phosphate with organic : aqueous (O/A) ratio in the range 2:1 to 4:1,

iii) adding ammonium hydroxide solution to iron chloride for precipitating iron as iron hydroxide while stirring with the help of suitable stirrer and maintaining the pH of the hydroxide slurry in the range 2.5 to 3.5,
iv) autoclaving the iron hydroxide slurry in the temperature range of 160 to 200 °C for 2 hours to precipitate hematite and cooling thereafter to 70 °C, wherein the concentration of iron in the hydroxide slurry during hydrothermal precipitation is in the range of 10 - 50 g/L
v) filtering the slurry and washing the precipitate for complete removal of chloride and drying in the temperature range of 50 to 80 °C for 48 hours,
In an embodiment of the present invention the concentration of iron in the hydroxide slurry during hydrothermal precipitation is in the range of 10 - 50 g/L.
In another embodiment of the present invention the concentration of ammonia solution used for precipitation may have concentration in the range of 5 - 20% (w/v).
In yet another embodiment of the present invention the hydrochloric acid and nitric acid used may be of commercial grade and may have concentration in the range of 20 - 36% (w/v) and 50 - 70% (w/v) respectively.
In still another embodiment of the present invention the iron solution prepared from scarp iron is purified by solvent extraction using tri-n-butyl phosphate with organic : aqueous (O/A) ratio in the range 2:1 to 4:1.
In still another embodiment of the present invention the pH of the hydroxide slurry may be adjusted in the range 2.5-3.5.
In still another embodiment of the present invention the heating of the hydroxide slurry in the autoclave may be carried out in the temperature range of 140 - 220 °C.
In still another embodiment of the present invention the size of the monodispersed pseudocubic particles prepared hydrothermally is in the range of 300 to 1200 nm.
In still another embodiment of the present invention the coercivity of the prepared monodispersed pseudocubic particles obtained in the range as high as 2500 to 6000 Oe.
In still another embodiment of the present invention the monodispersed pseudocubic particles of high coercivity is prepared hydrothermally from scrap iron.
A titanium lined stainless-steel autoclave of 2 L capacity (model 4542, PARR) was used for the hydrothermal preparation of hematite. The reactor has provision for gas inlet, out let, agitation and temperature control and has arrangement for sampling. Stirring rate was fixed at 300 rpm. Magnetic measurements of the samples were done using vibrating sample magnetometer (VSM, Model - 4500, PARR) and a. c. magnetic susceptibility set up.
Novelty of the present invention is the adjustment of initial pH in the hydroxide precipitation stage so as to maintain a condition to obtain polycrystalline monodispersed pseudocubic hematite particles of very high coercivity.
The following examples are given to illustrate how the process of the present invention is carried out in actual practice.
EXAMPLE -1
200 mL of ferric chloride solution containing 100 g/L iron is taken in a 2 L polythene beaker and diluted to double the volume by distil water. Ferric chloride is used as a starting material as it can be obtained from the dissolution of iron scrap or blue dust or as pickle liquor from steel industry. To the dilute solution of ferric chloride, 10% ammonia solution is added to precipitate iron chloride as hydroxide. The pH of the slurry is adjusted to 3.0 and the volume of the content is made 1 L by adding balance distil water. The slurry so obtained is transferred to an autoclave and heated to 160 °C while stirring at a speed of 300 rpm for a period of 2 hours. The content are cooled to 70 °C, discharged, filtered and washed to free of chloride. Prepared oxide is dried for 48 h at 70 °C.
Analysis of X- ray diffraction patterns suggests that formation of pure a-Fe2O3 phase and high degree of crystallinity is indicated in the pattern. The transmission electron micrographs of the prepared particles indicate the formation of very uniform in size of 350 nm monodispersed pseudocubic shape particles. The details of size along with various magnetic parameters were incorporated in Table - 1.
Table-1 : Various parameters obtained for hematite particle prepared hydrothermally at 160°C,[Fe]-20g/L.
(Table Removed)
EXAMPLE - 2
In a 2 litre polythene beaker, 200 mL of ferric chloride solution containing 100 g/L iron is taken and diluted to double the volume by distil water. To the dilute ferric chloride solution, 10% ammonia is added to precipitate iron as hydroxide. The pH of the slurry is adjusted to 3.0 and the volume of the content is made 1 L. The hydroxide slurry so obtained is transferred to a 2 L autoclave and heated to 200 °C for a period of 2 hours. The content are cooled to 70 °C, discharged, filtered and washed to free of chloride and dried at 70 °C for a period of 48 h.
a-Fe2Os phase and high degree of crystallinity are confirmed by X- ray diffraction patterns. The transmission electron micrographs of the prepared particles indicate the formation of very uniform in size pseudocubic particle of size 820 nm. The details of magnetic measurement data are incorporated in Table - 2.
Table-2 : Various parameters obtained for hematite particle prepared hydrothermally at 200 °C, [Fe] - 20 g/L.
(Table Removed)
EXAMPLE-3
400 niL of ferric chloride solution containing 100 g/L iron in a 2 litre polythene beaker is diluted to double the volume by distil water. Iron in the solution is precipitated as iron hydroxide by 10% (w/v) ammonia solution. The pH of the slurry is maintained at 3.0 and the volume of the content is made 1 L by adding distil water. The slurry so obtained transferred to a 2 L autoclave and is maintained at 200 °C for a period of 2 hours while stirring. The content are cooled to 70 °C, discharged, filtered and washed to free of chloride and dried at 70 °C for a period of 48 h.
X- ray diffraction patterns confirm formation of pure α-Fe2O3 phase with high degree of crystallinity. The transmission electron micrographs of the prepared particles indicate the formation of very uniform in size of 1100 nm monodispersed pseudocubic shape particles. The magnetic measurement data of the prepared sample are incorporated in Table - 3.
Table-3 : Various parameters obtained for hematite particle prepared hydrothermally at 200 °C, [Fe] - 40 g/L.
(Table Removed)
EXAMPLE-4
250 mL of iron(III) chloride solution prepared from scrap iron containing 100 g/L of iron and 40 g/L of hydrochloric acid is added to 500 mL of tri-n-butyl phosphate (TBP) in a 1L separating funnel and shaken vigorously for 5 minutes. Iron is loaded to TBP in a 3 stage counter current extraction step. The iron loaded TBP is stripped with distil water with 3 stage counter current step. In this manner 38.4 g/L of purified iron chloride solution is generated.
650 mL of above purified ferric chloride solution is taken in a 2 L polythene beaker. Iron in the solution is precipitated as iron hydroxide by 20% (w/v) ammonia solution. The pH of the slurry is maintained at 3.0 and the volume of the content is made 1 L by adding distil water. The slurry so obtained transferred to a 2 L autoclave and is maintained at 200 °C for a period of 2 hours while stirring. The content are cooled to 70 °C, discharged, filtered and washed to free of chloride and dried at 70 °C for a period of 48 h.
X- ray diffraction patterns confirms formation of pure α-Fe2O3 phase with high
degree of crystallinity. The transmission electron micrographs of the prepared particles
, indicate the formation of very uniform in size of ~700 nm monodispersed pseudocubic
shape particles. The magnetic measurement data of the prepared sample are
incorporated in Table - 4.
Table-4 : Various parameters obtained for hematite particle prepared hydrothermally at 200 °C, [Fe] - 40 g/L.
(Table Removed)
The major advantages of the process are :
1. All process steps are easy comprising of precipitation and washing.
2. Use of ammonia solution for precipitation avoids contamination of sodium/
potassium in to the host matrix. Ammonium ion if at all will present that will
decompose at about 320 °C during ferrite making at high temperature.
3. Less time involvement in the preparation.
4. Very easy to control size and shape of the hematite particle and specific nature of
particle can be engineered by controlling suitable parameters.
5. Produce very uniform in size monodispersed speudocubic particles of different
magnetic properties.
6. Produce very high green density and high coercive iron oxide suitable for preparing
hard ferrites.
7. The preparation techniques can be applied to utilise various waste material like blue
dust/plain scrap as a raw material for iron oxide.






We claim
1. A process for preparation of monodispersed iron oxide of high coercivity which
comprises :
i) preparing aqueous solution of iron chloride of concentration in the range of 50 to 150 g/L by dissolving electrolytic iron powder or scrap iron in hydrochloric acid,
ii) purifying the iron solution prepared from scrap iron by solvent extraction using methyl isobutyl ketone or tri-n-butyl phosphate with organic: aqueous (O/A) ratio in the range 2:1 to 4:1,
iii) adding ammonium hydroxide solution to iron chloride for precipitating iron as iron hydroxide while stirring with the help of suitable stirrer and maintaining the pH of the hydroxide slurry in the range 2.5 to 3.5,
iv) autoclaving the iron hydroxide slurry in the temperature range of 140 to 220 °C for 2 hours to precipitate hematite and cooling thereafter to 70 °C, wherein the concentration of iron in the hydroxide slurry during hydrothermal precipitation is in the range of 10 - 50 g/L
v) filtering the slurry and washing the precipitate for complete removal of chloride and drying in the temperature range of 50 to 80 °C for 48 hours.
2. A process as claimed in claim 1 wherein the iron hydroxide is precipitated from
iron chloride solution using ammonia solution of concentration in the range of 5-
20% (w/v).
3 A process as claimed in claims 1 - 2 wherein the hydrochloric acid and nitric acid
used may be of commercial grade and may have concentration in the range of 20 -
36% (w/v) and 50 - 70% (w/v) respectively.
4 A process as claimed in claims 1-3 wherein the heating of the hydroxide slurry in
the autoclave is carried out in the temperature range of 160 - 200 °C.
5 A process as claimed in claims 1 - 4 wherein the size of the monodispersed
pseudocubic particles prepared hydrothermally is in the range of 300 to 1200 nm.
6 A process as claimed in claim 1-5 wherein the coercivity of the prepared monodispersed pseudocubic particles obtained in the range as high as 2500 to 6000 Oe.

Documents:

2422-DEL-2004-Abstract-(11-02-2011).pdf

2422-DEL-2004-Abstract-(24-03-2011).pdf

2422-del-2004-abstract.pdf

2422-DEL-2004-Claims-(11-02-2011).pdf

2422-DEL-2004-Claims-(24-03-2011).pdf

2422-del-2004-claims.pdf

2422-DEL-2004-Correspondence Others-(24-03-2011).pdf

2422-DEL-2004-Correspondence-Others-(09-03-2011).pdf

2422-DEL-2004-Correspondence-Others-(11-02-2011).pdf

2422-del-2004-correspondence-others.pdf

2422-del-2004-description (complete).pdf

2422-DEL-2004-Description Complete-(24-03-2011).pdf

2422-DEL-2004-Form-1-(11-02-2011).pdf

2422-del-2004-form-1.pdf

2422-del-2004-form-18.pdf

2422-del-2004-form-2.pdf

2422-DEL-2004-Form-3-(11-02-2011).pdf

2422-del-2004-form-3.pdf

2422-del-2004-form-5.pdf


Patent Number 247568
Indian Patent Application Number 2422/DEL/2004
PG Journal Number 17/2011
Publication Date 29-Apr-2011
Grant Date 21-Apr-2011
Date of Filing 02-Dec-2004
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 KAMALA KANTA SAHU NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, JHARKHAND, INDIA.
PCT International Classification Number C01G49/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA