Note: Descriptions are shown in the official language in which they were submitted.
~.o7~844
The present invention relates to a method
for economically producing yellow hydrated ferric oxide
from a ferrous salt solution and more specifically it
concerns with a method for rapidly producing yellow
hydrated ferric oxide having a uniform and proper
particle size by partially neutralizing the ferrous
salt with ammonia and then oxidizing it with air.
The yellow hydrated ferric oxide is an ~-
hydrated ferric oxide which is generally expressed
as d-FeooH~ is in the form of acicular particle in
appearance and is widely used as a yellow pigment or
a raw material for magnetic materials.
Various methods have been proposed for
producing ~-hydrated ferric oxide, for example, (1)
a method according to which a seed is dispersed in
an aqueous solution of a ferrous salt and then this
is neutralized with an alkali while being oxidized,
(2) a method according to which an aqueous solution
of a ferric salt is hydrolized while being neutralized
with an alkali, (3) a method according to which a seed
is dispersed in an aqueous solution of a ferrous salt
and this is neutralized with metallic iron while blowing
air thereinto. -
Use of ~-hydrated ferrix oxide as a raw
material for magnetic material and as a yellow pigment
requires that it is in the form of acicular particle
and moreover the particle has proper and uniform size.
Only the known method (3) mentioned above can produce
the ~-hydrated ferric oxide which satisfies said
requirements and according to the known methods (1)
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and (2) it is very difficult to grow the particle to
the desired size and to make the particle size uniform.
Conventionally, ~-hydrated ferric oxide has been mostly
produced by the method (3). According to this method,
however, in order to make the particle size uniform,
fine acicular particle is separately prepared and this
is dispersed in an aqueous solution of a ferrous salt,
which is then gradually oxidized by blowing air there-
into, neutralized with a moderate neutralizing agent
such as metallic iron and the reaction is stopped when
the particle grows to a proper size. Thus, in the
case of such method, there are the following defects;
an excessively large amount of alkali is required for
preparation of the seed; a complicated step of separating
the seed from seed liquid and of washing the seed is
required; since the reaction for growing the particle
must be extremely slowly carried out, a considerably
long time is required and a production plant of a ~arge
capacity is also required.
2~ These defects of the known method as enumerated
above can be overcome by the present method which
comprises allowing an ammonium salt to be present in
a given concentration in a ferrous salt solution,
partially neutralizing it with ammonia, oxidizing it
with air to produce particle which is proper as a seed,
adding an aqueous solution of ferrous salt to said
seed liquid and simultaneously adding ammonia thereto
to maintain a suitable pH value and oxidizing the ferrous
salt with air at said pH whereby it is rapidly grown
to a uniform particle size. That is, the present
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invention is based on the discovery that when an ammonium salt
is allowed to coexist in the reaction liquid before the reaction
takes place, production of seed becomes easy and growth of par-
ticle becomes rapid and can be uniformly adjusted. Thus, the
present invention seeks to provide a method for industrially
easily and economically producing yellow hydrated ferric oxide.
Thus, according to this invention there is pro-
vided a method for producing yellow hydrated ferric oxide which
comprises adding an ammonium salt to a ferrous salt solution so
that ammonium ion concentration in the mixed solution is at least
30 g/l, partially neutralizing it with ammonia and oxidizing it
with air to obtain a seed liquid, continuously adding a ferrous
salt solution to said seed liquid, simultaneously neutralizing
it with ammonia to keep the pH at 4.0 - 6.5 and oxidizing it with
air.
- Figures 1 and 2 are electron micrographs of yellow
hydrated ferric oxide obtained by neutralization and oxidation
of ferrous sulfate solution and ferrous chloride solution under
the coexistence of an ammonium salt in accordance with the pres-
ent invention and Figures 3 and 4 are electron micrographs ofhydrated ferric oxide obtained by neutralization and oxidation
of ferrous sulfate solution and ferrous chloride solution without
addition of ammonium salt before the reaction.
Solutions of ferrous salts such as ferrous sul-
fate, ferrous chloride, pickling waste liquors of iron, etc. in
a high concentration can be widely used in the present invention.
Suitable conditions for working the present in-
vention will be explained below.
An aqueous solution of a ferrous salt is diluted
with an ammonium salt solution to adjust the Fe concentration
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to at least 10 g/l, preferably 20 - 40 g/l, the NH4 concen-
tration to at least 30 g/l, preferably 50 - 70 g/l and ammonium
salt concentration to preferably about 150 - 200 g/l. As the
ammonium
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salt solution to be used for dilution, it is econimical
to repeatedly use a final reaction solution from which
c-hydrated ferric oxide is separated. To thus diluted
solution is added ammonia gas or ammonia water to
partially neutralize the ferrous salt so that about
5 - 20 g~ , preferably about 10 g/~ of Fe is precipitated
as ferrous hydroxide, into which air is blown to complete-
ly oxidize the ferrous hydroxide. This reaction is
carried out at a temperature of 25 - 40 C and good
fine acicular seed of c-hydrated ferric oxide can be
easily obtained. Subsequently, to thus obtained seed
liquid is added a concentrated solution of a ferrous
salt having a concentration of at least 30 g/~ ,
preferably 70 - 80 g/~ at a rate of 3 - 10 kg(Fe)hr/m
(see liquid), preferably 5 - 6 kg/hr/m3. Then, ammonia,
air and a small amount of nitrogen oxide are blown
thereinto to adjust the pH to 4.0 - 6.5 and the tempera-
ture is made to 45 - 60C in order that concentration
of Fe~ remaining at completion of formation of the
seed can be maintained as it is. When iron content
of 3 - 10 times, preferably 3 - 5 times the amount of
the seed has been supplied, addition of the ferrous
salt solution is discontinued and the neutralization and - -
oxidation at the same treating rate are continued until
ne~rly no Fe t+ remains and then the reaction is completed.
Said nitrogen oxide blown into together with air is
an oxidation catalyst for acceleration of oxidation
rate. When the amount of the ammonium salt present
in formation of the seed and in growth of particle is
small, growth in the lengthwise direction difficultly
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proceeds and growth in the width direction proceeds
to result in hydrated ferric oxide of a low acicular
degree. When no ammonium salt is present at the
initiation of the reaction, it is difficult to form
fine acicular seed in the reaction of seed formation.
Moreover, in the growth reaction of particle, too,
when a seed liquid in which no ammonium salt is present
is subjected to reaction, not only growth of the
particle in the acicular direction does not proceed,
as shown in Figs. 3 and 4, but also hydrated ferric
oxides of various shapes are produced and clear yellow
c-hydrated ferric oxide cannot be produced. Furthermore,
according to the method of the present invention,
it is possible to conduct uniform particle growth at
a growth speed of 3 - 10 kg(Fe)/hr/m (see liquid) while
according to the conventional methods, the growth
speed is 0.1 - 0.3 kg(Fe)/hr/m . Thus, capacity of
reaction apparatus can be greatly reduced. When sod~um
hydroxide is used as the neutralizing agent, particle
growth proceeds with difficulty and ~-hydrated ferric
oxide of good quality cannot be obtained.
As explained above, according to the method
of the present invention, ~-hydrated ferri~ oxide of
uniform particle size and of clear yellow can be produced.
Therefore, the present invention can be projected as a
device for treating a pickling waste liquor of iron.
Thus, both of prevention of environmental contamination
and recovery of product can be realized.
The present invention will be further illustrat-
ed in the following Examples.
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Example 1
8.0~ of sulfuric acid pickling waste liquorof irons which contained 80 g~ of Fe~ was introduced
into a 50 ~ -reaction tank with a stirrer, to which 13.5
of ammonium sulfate solution having a concentration of
320 g/ ~ was added to dilute the Fe~concéntration to
30 g/~ . The concentration of ammonium sulfate at this
time was 200 g/ ~ . This mixed solution was kept at
35 C and ammonia gas was added to said solution while
stirring to precipitate ferrous hydroxide until the
Fet~ concentration reached 20 g/ ~ . Subsequently, air
was blown thereinto at a rate of 1200 ~/hr to completely
oxidize ferrous hydroxide in 3.5 hours. The pH value
before the oxidation was 7.2 and the pH value at the
completion of the oxidation was 5.9. At the time of
the completion of oxidation, the precipitate had light
greenish yellow ~olor and was fine acicular c-hydrated
ferric oxide. Temperature of this seed liquid was
elevated to 60C and said ferrous salt solution (Fe~J
concentrat~on 80 g/12 was supplied to said liquid for
10 hours at a rate of 2.0 ~/hr while blowing thereinto
air at a rate of 1200 ~/hr and nitrogen oxide at a
rate of 12 ~/hr, during which ammonia gas was supplied
so that 20 g/~ of Fett always remained in the reaction
liquid and pH of the liquid was 6Ø After discontinuing
the supply of the ferrous salt solution, 20 g/~ of
Fe~ which remained in the reaction liquid was successively
neutralized and oxidized in 3.0 hours to make the
Fe+~ concentrationl~nearly zero.
By said reaction, the seed which was initially
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light greenish yellow was changed to show clear yellow
color. This was dehydrated and dried and observed by
an electron microscope to find that uniform acicular
~-hydrated ferric oxide of about 0.1 ~ in width and
about 0.6 p in length was obtained as shown in Fig. 1.
Example 2
S ~ of hydrochloric acid pickling waste liquor
containing 110 g/~ of Fe~ was introduced into a r~action
tank and 13.3~of ammonium chloride solution having a
concentration of 250 g/~ was added thereto to obtain
a Fe~ concentration of 30 g/~ . Concentration of
ammonium chloride at this time was 180 g/ ~ . A~monia
gas was added to said mixed solution kept at 25C
while stirring to produce ferrous hydroxide until the
Fe~ concentration reached 20 g/~ and then air was
blown thereinto at a rate of 1200 ~/hr to completely
oxidize the ferrous hydroxide in 3 hours. PH value
before the oxidation was 6.7 and that after the oxidation
was 5.3. Precipitate at the time of completion of
the oxidation had light greenish yellow color and was
fine acicular c-hydrated ferric oxide. This seed liquid
was heated to 60C as it was and then said ferrous salt
solution (Fe 110 g/ ~ ) was supplied thereto at a rate
of 0.5 ~ /hr for 10 hours while blowing thereinto air
at 1200 ~/hr and nitrogen oxide at 6 e/hr, during which
ammonia gas was supplied so that 20 g,e of Fe~f always
remained in the reaction solution and the pH value was
kept at 5Ø After supply of the ferrous salt solution
was discontinued, 20 g/~ of Fe re~aining in the
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reaction solution was successively neutralized and
oxidized in 2.5 hours to make the Fe~ concentration
nearly zero. By this reaction, color of the seed
which was in~ially light greenish yellow changed to
clear yellow. The product was dehydrated and dried and
was observed by an electron microscope to find that
uniform needle-like hydrated ferric oxide of about 0.1
in width and about 0.6 ~ in length was produced.
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