Method for preparing iron oxides

a technology of iron oxides and iron oxide particles, applied in the field of iron oxide preparation, can solve the problems of difficult filtering and washing, difficult to filter and wash, and too fine oxide particles that form, and achieve the effect of reducing or eliminating drawbacks and high productivities

Inactive Publication Date: 2009-12-31
SUD EHEMIE MT SRL
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0015]It has now been found unexpectedly that it is possible to reduce or eliminate the drawbacks of the processes of the prior art and obtain, with high productivities that are distinctly higher than those of hitherto known processes, and with substantially complete conversion of the iron to oxides that are practically free from alkaline, alkaline-earth and ammonium ions and in which after washing there are relatively small qualities of impurities relate to anions of carboxylic acids, which however can be eliminated by heating in the step for converting the oxides to Fe2O3 oxides.

Problems solved by technology

The disadvantage of the method is the difficulty in eliminating, even after thorough washing, the impurities of sulfate and chloride anions that are present in the oxides, which have a negative effect on the quality of pigments.
At temperatures below 50° C., the oxide particles that form are too fine and difficult to filter and wash in order to achieve values of impurities due to acid radicals of less than 0.1% by weight.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0057]200 cc of deionized water and 37 g of formic acid are placed in the 1-liter reactor, which is brought to 60° C. by means of the heating jacket; agitation is performed, and 40 g of microspheroidal iron are poured into the reactor. The iron is checked to ensure that it is properly kept in suspension and then a micropump is used to introduce in the reactor 100 cc of 35% hydrogen peroxide.

[0058]The addition operation lasts approximately 4.2 hours, and the temperature is kept at 60° C. throughout the test.

[0059]At the end, the entire mass is poured into a vessel, from which the unreacted iron is removed by means of a magnet. The product of the reaction is then recovered by filtration and placed in an oven at 140° C. for one night. The mother liquor is analyzed to determine the iron content. Substantially pure goethite is obtained: iron conversion is 90% and part of the metal is dissolved in the mother liquor. The specific surface area is 111 m2 / g.

example 2

[0060]200 cc of deionized water and 33 g of formic acid are placed in the 1-liter reactor, which is brought to 60° C. by means of the heating jacket; agitation is performed, and 40 g of microspheroidal iron are poured into the reactor. The iron is checked to ensure that it is properly kept in suspension and then a micropump is used to introduce in the reactor 100 cc or 35% hydrogen peroxide as follows: pumping is performed at the rate of 13 cc / h for 4.1 hours and then at the rate of 3 cc / h for 16 hours. In total, the operation for adding the hydrogen peroxide lasts 20.5 hours and the temperature is kept at 60° C.

[0061]The resulting product is filtered and the precipitate is dried as in example 1.

[0062]The mother liquor is analyzed to determine the iron content. A mixture of goethite and maghemite is obtained; iron conversion is 100%; iron in the mother liquor is 5.8% of the fed iron.

example 3

[0063]200 cc of deionized water and 16.5 g of formic acid are placed in the 1-liter reactor, which is brought to 50° C. by means of the heating jacket; agitation is performed, and 40 g of microspheroidal iron are poured into the reactor. The iron is checked to ensure that it is properly kept in suspension and then a micropump is used to introduce in the reactor 100 cc of 35% hydrogen peroxide.

[0064]The addition operation lasts approximately 16.7 hours and throughout the test the reactor is kept under a slight flow of nitrogen an the temperature is at 50° C.

[0065]At the end, the entire mass is filtered and the resulting solid fraction is placed in an oven at 140° C. for one night.

[0066]The mother liquid is analyzed to determine the iron content. One obtains pure maghemite with 100% iron conversion. Iron in the mother liquor is negligible; the specific surface area is 7.6 m2 / g.

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Abstract

Highly pure iron oxides are prepared by reaction of metallic iron, in the form of microspheroidal particles or of scraps or cuttings, with an agitated aqueous solution of a mono- or polycarboxylic acid with a pKa of 0.5 to 6 relative to the first carboxyl and capable of decomposing, by heating in air at 200 to 350° C., to carbon dioxide and water, using 0.03 to 1.5 moles of acid per g-atoms of iron, a water / iron weight ration of 1 to 20, and by oxidation of the ferrous carboxilate to ferric salt, with an agent selected from oxygen, mixtures containing oxygen, hydrogen peroxide, organic peroxides and hydroperoxides.

Description

CROSS REFERENCE[0001]The following application is a divisional application of U.S. patent application Ser. No. 10 / 836,304 filed Apr. 30, 2004 which was a continuation of U.S. patent application Ser. No. 10 / 386,798 filed Mar. 12, 2003.FIELD OF THE INVENTION[0002]The present invention relates to an improved method for producing highly pure iron oxides, usable in particular as pigments and as precursors of catalysts or of materials for electronic devices.BACKGROUND OF THE INVENTION[0003]The method most commonly used to produce iron oxides used as pigments employs, as its source material, pickling liquids that contain ferrous sulfate or chloride originating from the iron industry of from the process of producing titanium dioxide.[0004]The acid aqueous solution of ferrous salts is first neutralized by dissolving iron scrap and is then treated in conditions of oxidation with sodium hydroxide to precipitate FeOOH nuclei which are then pumped into a reactor that contains iron scrap and is m...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C01G49/02B01J23/745B01J35/10B01J37/08B01J37/12B41F1/08B41F1/50C01G49/06C09C1/24
CPCB01J23/745B01J35/10B01J35/1014B01J35/1019B01J37/086B01J37/12C09C1/24B41F1/50C01G49/02C01G49/06C01P2006/12C01P2006/13B41F1/08
Inventor CONCA, ESTERINORUBINI, CARLOPETRINI, GUIDO
Owner SUD EHEMIE MT SRL
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