Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-06-27
2004-11-16
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S458000, C423S633000, C423S632000
Reexamination Certificate
active
06818052
ABSTRACT:
The present invention relates to the production of synthetic iron based pigments and anticorrosive additives.
Conventional chemical methods for the production of synthetic iron oxide pigments are Known (See. e.g. T. C. Patton: “Pigment Handbook 1988. vol.1. Second Edition. Properties and Economics, pp. 297-302”. U.S. Pat. Nos. 4,911,760, 5,268,640, 3,969,494, 5,185,141, 4,349,385; O. V. Orlova and T. N. Fomitcheva:” Paints and Lacquers Technology, 1990, Moscow, “Chemistry”, pp. 294-302). As a raw materials for such production, there is used ferrous sulfate (FeSO
4
7H
2
O), sodium hydroxide (NaOH) and very high quality iron filings (Fe
0
). In the first step of this method, the ferrous sulfate is reacted with sodium hydroxide in order to produce a ferrous hydroxide (Fe (OH)
2
suspension. The second step is the oxidation of Fe(OH)
2
by air at a temperature of about 85-90° C. in the presence of about 10% of the separately prepared nuclei suspensions of goethite (&agr;-FeOOH).
During the oxidation, Fe(OH)
2
transforms into &agr;-FeOOH yellow iron monohydroxide pigment. At this time of oxidation, the solution's pH changes from about 9.5-10.0 to about 4.0-4.5. In order to prevent the pH decrease and precipitation of ferric sulfate basic salts, it is necessary to continuously add high quality iron filings into the solution. In this manner, elementary iron reacts with the formed sulfuric acid and prevents the decrease in the solution's pH. The complete oxidation of Fe
2+
into Fe
3+
takes place in about 5-18 hours. The third step of this method is to allow for the growth of pigment particles according to predetermined standards. Thereafter, the pigment is separated from the solution (Na
2
SO
4
) by filtration, washed and dried. As a result of this chemical method, there is produced a yellow iron oxide pigment with particle size of about 0.1-0.3×0.5-0.9 microns. The pigment particles have needle or prismatic form. Mineralogically, this is characterized as a goethite (&agr;-FeOOH) form. The by-product of this process is sodium sulfate. In order to produce a red iron oxide, it is necessary to calcine the produced yellow iron oxide at a temperature of about 400-450° C. Red iron oxide is hematite (Fe
2
O
3
).
The disadvantages of the existing chemical technology of the aforementioned yellow iron oxide pigment production are:
The need for high quality initial raw materials since at high alkaline conditions of reaction almost all of the metals accompanying iron production are precipitated and pollute the iron oxide pigment.
The need for a special nucleuses suspension's preparation which is an independent and expensive technological operation, including Fe (OH)
2
complete oxidation and transformation into &agr;-FeOOH at the temperature of about 85-90° C.
Long process duration of Fe(OH)
2
oxidation, utilizing significant quantities of required air and requiring the maintenance of a high solution temperature.
Necessity of the constant use of the extremely pure metal iron: for the pigment quality's stabilization, for the maintenance of pH at a determined level and for the prevention of the basic iron sulfate salts' precipitation together with pigment.
Formation of needle or prismatic forms of particles, worsening the pigment's properties.
Na
2
SO
4
formed as a result of the reaction as a by-product is a practically useless, cheap product and its pollution is harmful for the environment.
The present invention provides a process for the preparation of yellow and other iron-based pigments which does not suffer from the above-mentioned drawbacks. It is much cheaper, ecologically clean and allows to produce very high quality yellow and red iron oxide pigments from low quality initial raw material such as iron waste. At the same time the present process enables the production of other iron-based pigments and anticorrosive additives, such as a black iron oxide pigment (magnetite), Prussian blue and ferric monophosphate (anticorrosive additive) with a minimal added expense.
Thus, according to the present invention, there is now provided a process for the production of iron based pigments and anticorrosive additives from elemental iron comprising:
a. reacting iron Fe° with ferric sulphate Fe
2
(SO
4
)
3
and with sulfuric acid H
2
SO
4
to produce ferrous sulphate FeSO
4
:
b. oxidizing ferrous sulphate FeSO
4
in a bacterial solution containing sulfuric acid and at least 10
7
bacterial cells of thiobacillus ferrooxidans per 1 ml of solution under aerobic conditions to produce ferric sulphate Fe
2
(SO
4
)
3
:
c. reacting said ferric sulphate Fe
2
(SO
4
)
3
with water at a temperature of about 65 to 130° C., to precipitate iron oxide monohydrate Fe
2
O
3
×H
2
O; and
d. re-cycling the solution from step c, to step a, to utilize remaining sulphuric acid and a portion of unhydrolyzed ferric sulphate values therein.
As an initial raw material, there is preferably used iron waste or iron filings, containing from 40 to 100% of elementary iron.
Preferably, the process proceeds at ambient (10-35° C.) temperature in aerobic acidic (pH 1.0-2.9) sulfate environments, at the concentration of iron in working solutions from less 10 up to 40 g/l of iron. The biochemical reaction of ferrous sulfate's oxidation is shown below:
2FeSO
4
+2H
2
SO
4
+O
2
+Th.ferrooxidans=2Fe
2
(SO
4
)
3
+2H
2
O
Produced by bacterias the ferric sulfate solution is used as an oxidizer and further its portion is used for primary iron oxidation and production of the ferrous sulfate:
Fe+Fe
2
(SO
4
)
3
=3FeSO
4
In the proposed biotechnical reaction, the iron's oxidation speed depends on the quantity of bacteria cells in the solution. According to the present invention, it was established, that for the achievement of the economically favorable oxidation's speed (about 1 g of iron in 1 liter of a solution during 3 hours) it is necessary to have no less than 10
7
bacterias cells in 1 ml of the solution. At such concentration of the cells a ratio between incoming ferrous sulfate solution and bacterial suspension of the fermenter is preferably about 1:10. The increase of this ratio for the benefit of the ferrous sulfate solution delays the oxidation's speed. A lack of the ferrous sulfate feed brings to the decrease of the bacterias cells and premature bacterias decease.
During the bacterias vital activitys the resulting solution consists of three main components, i.e. sulfuric acid, ensuring of the solution's pH in the interval 2.1-2.8, colloidal particles of iron hydroxide Fe (OH)
3
, formed as a result of ferric sulfate partial hydrolysis, and unhydrolyzed ferric sulfate. This product is the initial raw material for the production of all above mentioned pigments and anticorrosive additives, e.g. yellow (&agr;-FeOOH), red (Fe
2
O
3
), black (Fe
3
O
4
), Prussian blue (Fe
4
(Fe(CN)
6
)
3
) and ferric dihydrogen phosphate (Fe(H
2
PO
4
)
3
).
Before its further use the solution is separated from bacteria by filtration, and the separated bacteria is recycled into the fermenter. About 30% of iron is in a colloidal form as a phase of Fe (OH)
3
, formed as a result of the partial ferric sulfate hydrolysis which step by step takes place within the fermenter in the presence of a surplus of water, according to the reaction:
Fe
2
(SO
4
)
3
+6H
2
O=2Fe(OH)
3
+3H
2
SO
4
The form of the colloidal particle is spherical. Therefore, if the pigment's production occurs without additional ferric sulfate hydrolysis, formed &agr;-FeOOH has the inherited spherical form of particles. An additional hydrolysis of the remaining ferric sulfate results in the formation of the particles in form of needles. Therefore it is possibility to produce the yellow iron oxide pigment with only spherical particles or as a mixture of spherical and needle particles.
Depending on the requirement, the solution produced by the bacteria treatment can be used as follows:
a) For the manufacture of yellow iron oxide pigment this solution is exposed to trea
Boiko Vladimir
Oryol Boris
Oryol Marlen
Biopigment Ltd.
Koslow C. Melissa
Townsend and Townsend / and Crew LLP
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