CONTINUOUS NON-POLLUTING LIQUID PHASE TITANIUM DIOXIDE PROCESS

PROCEDE DE PRODUCTION DE DIOXYDE DE TITANE EN PHASE LIQUIDE, NON POLLUANT ET EN CONTINU

English Abstract

A process and apparatus for producing titanium dioxide from titanium ore or
slag is disclosed. The ore or slag (2) is reacted with sulfuric acid (3) in a
reactor (1) in which hot gas for agitation (4) is used. Makeup acid from line
(6) is fed to line (3). Together with recovered acid from the spray evaporator
(34) reacted product overflows from the reactor to rotary filter (8). The
filter cake is washed in the rotary filter whose water comes in through line
(14). The washed filter cake is delivered to dissolving tank (10).
Concentrated acid together with wash water is returned to the reactor through
line (3). Filtrate is hydrolized in hydrolysis tank (21) to form titanium
dioxide hydrate which is then calcined in a fluid bed calciner (30) to form
titanium dioxide.

French Abstract

L'invention a trait à un procédé, ainsi qu'à l'appareil correspondant, permettant de produire du dioxyde de titane à partir de minerai ou de crasses de titane. On fait réagir le minerai ou les crasses (2) avec de l'acide sulfurique (3) dans un réacteur (1) dans lequel on utilise un gaz chaud pour mise en suspension. De l'acide d'appoint provenant d'un conduit (6) est amené sur un conduit (3). Le produit réagi déborde, en compagnie de l'acide récupéré de l'évaporateur à pulvérisation (34), du réacteur vers un filtre à tambour (8). Le gâteau de filtration est lavé dans le filtre à tambour recevant de l'eau par un conduit (14). Le gâteau de filtration lavé est dirigé sur une cuve de dissolution (10). L'acide concentré et l'eau de lavage sont renvoyés au réacteur par un conduit (3). Le filtrat est hydrolysé dans un réservoir hydrolytique (21) pour former un hydrate de dioxyde de titane qui est ensuite calciné dans un four à calciner à lit fluidisé (30) afin de former du dioxyde de titane.

Claims

8
WHAT IS CLAIMED IS:
1. A non-polluting liquid-phase process for producing titanium dioxide
pigment from titanium ore or slag which comprises the following steps:
a) reacting the ore or slag with sulfuric acid to obtain a solid-form reaction
product,
b) wash-filtering the reaction product with wash water to obtain filter cake
and
filtrate comprising used wash water,
c) recycling the filtrate to step (a),
d) separating out and recovering, in aqueous solution, water-soluble
components
of the filter cake,
e) subjecting the water-soluble components, in solution, to hydrolysis to
convert
titanium values therein to titanium dioxide hydrate, and
f) calcining the titanium dioxide hydrate to obtain titanium dioxide pigment.
2. A process of claim 1 which comprises the following steps:
h) dissolving in water water-soluble components of the filter cake obtained in
step
(b),
i) filtering the product of step (h) to obtain a clear filtrate,
j) hydrolyzing the clear filtrate to obtain titanium dioxide hydrate,
k) filtering the product of step (j) to obtain a further filter cake, and
l) calcining the further filter cake to obtain calcined titanium dioxide.
3. A process of claim 1 for converting titanium ore or slag to anatase
pigment, which process is a continuous process comprising the following steps:
1) reacting the ore or slag with sulfuric acid to obtain, as a reaction
product, titanyl
sulfate, iron sulfate and other sulfates,
2) filtering and washing the reaction product to obtain a washed filter cake,
filtrate
and used wash water,
3) recycling the filtrate and used wash water to step (1),
4) dissolving in water water-soluble components, comprising titanyl sulfate,
iron
sulfate and other water-soluble sulfates, of the washed filter cake,
5) filtering the product of step (4) to obtain a clear filtrate,
6) hydrolyzing the clear filtrate to obtain titanium dioxide hydrate, and

9
7) calcining the titanium dioxide hydrate to obtain titanium dioxide pigment.
4. A process of claim 3 wherein titanium ore is reacted in step (1).
5. A process of claim 4 wherein the titanium ore is ilmenite.
6. A process of claim 3 wherein preoxidized titanium slag is reacted in step
(1).
7. Apparatus for converting titanium ore or slag to anatase pigment, which
apparatus comprises:
a) reactor means to react the titanium ore or slag with sulfuric acid and to
obtain
a reaction product comprising titanyl sulfate, iron sulfate and other
sulfates,
b) means to introduce the ore or slag into the reactor means;
c) means to introduce the sulfuric acid into the reactor means,
d) means to agitate reacting components within the reactor means,
e) first filter means to obtain filter cake and filtrate from the reaction
product,
f) means to conduct the reaction product from the reactor means to the first
filter
means;
g) means to wash the filter cake with wash water and to obtain washed filter
cake
and used wash water,
h) means to recycle filtrate from first filter means (e) and the used wash
water to
reactor means (a),
i) dissolving tank means to place in aqueous solution water-soluble
components,
including titanium values, of the washed filter cake, the aqueous solution
further
comprising, undissolved, insoluble material,
j) means to conduct the washed filter cake to the dissolving tank means,
k) means to conduct water to the dissolving tank means,
l) first separator means to separate the aqueous solution from the insoluble
material obtained from the dissolving tank means,
m) hydrolysis tank means to hydrolyze dissolved titanium values in said last-
noted
aqueous solution to obtain titanium dioxide hydrate,
n) means to conduct the aqueous solution, free from insoluble material, from
the
first separator means to the hydrolysis tank means,
o) second filter means to separate obtained titanium dioxide hydrate from
filtrate,

10
p) means to conduct product from the hydrolysis tank means to the second
filter
means,
q) calciner means to convert the titanium dioxide hydrate to anatase pigment,
and
r) means to conduct titanium dioxide hydrate from the second filter means to
the
calciner means.
8. Apparatus of claim 7 further comprising:
s) spray-drier means,
t) means to conduct gas from the calciner means to the spray-drier means,
u) means to conduct filtrate from the second filter means to the spray-drier
means,
v) second separator means,
w) means to conduct concentrated acid containing ferrous sulfate monohydrate
to
the second separator means,
x) means to withdraw insoluble ferrous sulfate monohydrate from the second
separator means, and
y) means to conduct concentrated acid from the second separator means to
reactor
means (a).
9. Apparatus according to claim 8 wherein means (k) comprises means to
conduct steam together with some acid formed in reactor means (a) and means to
conduct steam and some acid from spray-drier means (s) to the dissolving tank
means.
10. A process of claim 1 for converting titanium ore or slag to anatase
pigment which comprises the following steps:
1) reacting the titanium ore or slag with excess concentrated sulfuric acid,
under
agitation, to obtain a reaction product comprising titanyl sulfate, iron
sulfate and
other sulfates,
2) filtering the reaction product to obtain filter cake and filtrate,
3) washing the filter cake with wash water to obtain washed filter cake and
used
wash water,
4) recycling the filtrate and the used wash water to step (1),
5) dissolving in water water-soluble components, including titanium values of
the
washed filter cake, the resulting aqueous solution further comprising,
undissolved, insoluble material,

11
6) separating the aqueous solution from the insoluble material,
7) hydrolyzing dissolved titanium values in the aqueous solution to obtain
titanium
dioxide hydrate,
8) filtering obtained titanium dioxide hydrate from filtrate, which contains
acid and
ferrous sulfate monohydrate,
9) calcining the titanium dioxide hydrate to convert it to anatase pigment,
10) conducting heat and gas from step (9) to step (11),
11) spray-drying the filtrate, which contains acid and ferrous sulfate
monohydrate,
to obtain concentrated acid, insoluble ferrous sulfate monohydrate and steam,
12) recycling the concentrated acid to step (1),
13) recycling the steam, containing some acid, to step (3), and
14) conducting steam and some acid produced in step (1) to step (3).
11. A non-polluting liquid-phase process for producing titanium dioxide
pigment from titanium ore or slag which comprises the following steps:
a) reacting titanium ore or slag with sufficient hot sulfuric acid to obtain a
liquid
slurry reaction product,
b) filtering the reaction product to separate filter cake of titanyl sulfate
from the
reaction product,
c) combining the filter cake with acid water to form a partially-dissolved
product
as a suspension,
d) filtering the suspension to obtain filtrate thereof,
e) hydrolyzing the filtrate to convert titanium values therein to titanium
dioxide
hydrate, and
f) calcining the titanium dioxide hydrate to obtain hot gases and anatase
pigment.
12. A process of claim 11 which comprises filtering the product of step (e)
to obtain a further filtrate and filter cake, and using the hot gases
(containing sulfuric
acid) from step (f) to evaporate liquid from the further filtrate.
13. A process of claim 12 which comprises washing the further filter cake
to obtain washed filter cake and used wash water, recycling the hot gases from
step (f)
and used wash water to spray dryer means for producing ferrous sulfate
monohydrate
and acid water, and using the acid water in step (c).

12
14. A process of claim 13 which comprises filtering the ferrous sulfate
monohydrate from the acid water to obtain hot concentrated sulfuric acid
filtrate, and
recycling the hot concentrated sulfuric acid filtrate to step (a).
15. Apparatus for producing titanium dioxide pigment from titanium ore or
slag in a non-polluting liquid-phase manner, which apparatus comprises:
a) reactor means to react the ore or slag with sufficient sulfuric acid to
obtain a
liquid slurry reaction product,
b) means to wash-filter the reaction product with wash water to obtain filter
cake
and filtrate comprising used wash water,
c) means to recycle the obtained filtrate to the reactor means (a),
d) means for separating out and recovering, in aqueous solution, water-soluble
components of the filter cake,
e) means for subjecting the water-soluble components, in solution, to
hydrolysis
to convert titanium values therein to titanium dioxide hydrate, and
f) means for calcining obtained titanium dioxide hydrate to obtain titanium
dioxide
pigment.
16. A process of claim 1, wherein sufficient sulfuric acid in step (a) is
sulfuric acid having a concentration of from 65% to 85% and corresponding to
an acid
to ore ratio of from 3/1 to 8/1.

Description

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CONTINUOUS NON-POLLUTING LIQUID PHASE
TITANIUM DIOXIDE PROCESS
Background
There are two types of titanium dioxide pigments; both have a tetragonal
crystal
form. One crystal form is anatase (a soft crystal), and the other is rutile (a
hard crystal).
Anatase, which comprises nearly half of the market, is used in the paper,
textile
fiber and plastic industries where a soft pigment will not wear away the
cutting knives,
extruders and injection equipment. The sulfate process is amenable to the
manufacture
of anatase pigments. The vapor phase chloride process is limited to the
production of
rutile. The prior process employing sulfates produced a large amount of
pollution.
Development of this new process eliminates most of the pollution. For a better
understanding of the invention, this sulfate process is described.
Drying and Grinding
Ilmenite ore or titanium slag (containing 1 to 5% humidity as received in a
plant)
is first dried to 0.3% humidity. It is then ground to from an average of 80 to
98% minus
200 mesh.
Digestion
A typical Ilinealite digestion reacted at 85% reaction acid is described as
follows.
71,000 pounds of 66° Baum~ sulfuric acid are charged into a reactor,
and air agitation
is started. 45,000 pounds of Ilmenite ground ore are slowly added (over 30
minutes),
and then 6700 pounds of acceleration water are added. A reaction starts at
from 95° to
105°C, and the temperature in the reactor rises rapidly from
120° to 200°C with the
evolution of 10,000 to 12,000 pounds of steam (with entrained acids), which is
vented
to the atmosphere, causing so-called acid rain, the reaction is often violent,
emptying to
the atmosphere with explosive force. When the reaction is complete, the
resulting porous
mass is allowed to cool, and water is added to dissolve soluble iron and
titanium sulfates.
Metallic iron is added to reduce any ferric sulfate formed, and the thus-
obtained slurry
(suspension) is pumped to settling tanks. This operation takes from about 12
to 24
hours.

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Sealing arid Washing
Due to the presence of ruble in the ground ore, gangue minerals and colloids
(mostly silica gel formed when digesting ore or slag) the suspension cannot be
filtered
directly, and it is pumped to settling tanks where the clear supernatant
liquor and settled
solids (mud) are obtained. The settled solids are again dispersed and washed
counter
ly in a series of settling tanks to recover a maximum amount of titanium
sulfate.
The number of required tanks and their size take considerable land and entail
significant
cost.
Filtration
The combined clear settled liquors from the first settlers (together with
leach
liquor) are filtered and led to a vacuum evaporator (when using ilmenite ore)
or directly
to a hydrolysis process (when using slag, which contains less iron).
Evaporation under vacuum at temperatures below 60°C is necessary to
prevent
premature hydrolysis. Copperas from a vacuum evaporator crystallizer is
filtered,
washed and dumped to sewage or sold.
A typical analysis of the concentrated filtered solution ready for hydrolysis
is:
Anatyis Typical Yalr~e
Sp~ ~'~ 1.620 at 60°C
% Ti02 15.4
FeS04 10.8
H2S04 27.7
Hydrolysis
The solution is then heated to a temperature of 96° C, and hydrolysis
is started
by pumping part of the liquor into 96°C hot water (about '/4 of the
liquor volume) over
a period of 16 minutes. The mixture is then brought to a boil (102°C to
108°C). Boiling
is continued until about 96% of the titanium is recovered.
The resulting suspension is led to a series of counter-current filter
arrangements
(e.g., Moore filters), in which the titanium hydrate is separated and washed.
The
resulting solution (containing weak sulfuric acid) is discharged to sewage.

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The preceding process causes significant pollution, which is the reason why it
is
being abolished in all industrialized countries.
Summary oJthe Invention
A prime purpose of the present invention is to use a series of novel steps
which
prevent pollution and establish a more economical sulfate process which can
produce
anatase (required in the paper, textile fiber, and plastic industries) and
rutile (for paints,
etc.).
An object of the invention is to eliminate acid rain, overflow of e~uent to
water
ways and injection of e8luents into the ground. Another object is conservation
of water.
A fiuther object is efficient heat balance management. Still fiuther objects
are apparent
from the following description.
The process does not require drying or grinding ore or slag, thus eliminating
costly equipment and labor. Unground wet ilmenite ore as delivered, containing
from 1
to 5% HZO, or titanium slag is continuously fed to a reactor with from 65 to
85% hot
sulfuric acid (121°C to 200°C) in sufficient quantity to keep
the resulting slurry liquid (3
to 8/ 1 sulfuric acid to ore ratio, depending on acid concentration, which can
oscillate
between 65% and 85%). The reaction is very rapid, breaking large particles
into a fine
suspension, and agitation is provided either mechanically or with air
spargers. The
reactor is made of suffcient size so that retention time (which is in the
order of from 2
to 8 hours) of the ore or slag and acid is sufficient to digest 90% of the
Ti02.
The reacted slurry is then continuously fed to a vacuum filter instead of the
first
spray dryer as depicted in antecedent patent application Serial No.
08/645,344.
(Filtration produces about a 4 to 1 acid to Ti02 ratio. As a result a spray
drying
technique was previously developed to evaporate the excess acid back to a 2/1
acid to
Ti02 ratio).
The use of a water wash to r~nove the excess acid was not generally considered
because the titanyl cake is water soluble. However, it has been found that
dissolution of
titanyl sulfate is not rapid and a displacement wash of water (slightly
acidified) does in
fact remove excess acid without removing much titanium dioxide. This has now
become
the preferred process, and one of the advantages is that the displacement wash
yields
strong acid which can be recycled back to the reactor.

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Acid strength can be from 55 to 85%; 65% is preferred because it has a minimum
solubility of salts. When iron is left in the oxidized state, it appears to be
removed to
some extent from the raw cake by the washing procedure.
The ability to recycle acid directly back to the reactor makes it possible to
S decouple the spray drier for the Moore acid recycle from the reactor loop,
and it is only
used to concentrate dilute 25% acid.
The acid from the Moore filter and the above slurry wash contains all the iron
sulfate coming from the system. Since ferrous sulfate is insoluble in
concentrated sulfuric
acid, it is removed by filtration after being concentrated by evaporation in
the sole spray
drier, and the acid is re-circulated to the reactor. The gases from the
reactor and from
the sole spray drier (containing mostly water vapor and some acid) are
condensed and
used to wash the cake. In this manner more than 97% of the acid is recovered
at this
point.
The cake (containing titanyl sulfate, ferrous sulfate, ferric sulfate and
insolubilized
colloids) from the reactor filter is partially dissolved in acid water from
condensers,
taking care not to exceed a temperature of 60°C, preventing premature
hydrolysis.
Reducing agent is added to reduce the iron to the 2 valent state and to put 3
grams per
liter of the titanium to the 3 valent state. The resulting suspension is then
filtered in a
rotary filter with pre-coat and filter aid. The obtained filter cake is washed
and discarded
after proper neutralization.
Obtained filtrate is then conducted to a hydrolysis department, where it is
hydrolyzed, without first removing copperas (ferrous sulfate), to produce
titanium oxide
hydrate. The resulting suspension is fihered to obtain filter cake. The washed
filter cake
(titanium dioxide hydrate) is chemically treated with a precalcination
addition of
chemicals and calcined in a fluidized calciner at a temperature around
925°C to 980°C
to form anatase, which is cooled, ground and packed. Hot gases from the
fluidizer,
containing sulfuric acid and some titanium dioxide, are recycled to the sole
spray dryer,
which absorbs the acid and any S03 formed and evaporates the water. (Note that
the sole
spray dryer is really an evaporator).
There are a number of distinct aspects to the subject invention, each of which
comprises process steps or equipment supporting such steps. Several of the
aspects (in
process terms) are as follows:
..__ _~_.___ ~_.~._ .~.~..__ ._____..

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a) reacting titanium ore or slag with hot sulfuric acid, separating out filter
cake of
titanyl sulfate from the resulting reaction product, combining the cake with
acid
water to form a partially dissolved product as a suspension, filtering the
suspension, hydrolyzing the thus-obtained filtrate to convert titanium dioxide
5 hydrate, and calcining the titanium dioxide hydrate to obtain anatase
pigment;
b} using hot gases from the calcining means to evaporate the solutions
obtained
from the reaction of titanium ore or slag with hot sulfuric acid from
hydrolysis;
c) recycling hot gases (containing sulfuric acid) from the calcine and wash
water
from titanium dioxide hydrate filtering means to spray dryer means for
producing
ferrous sulfate monohydrate and for producing acid water for partially
dissolving
free-flowing solids from the reaction product of titanium ore or slag with hot
sulfuric acid; and
d) recycling filtrate (hot concentrated sulfuric acid) from ferrous sulfate
monohydrate filtering means to the reactor means for reacting titanium ore or
slag with hot sulfuric acid.
Brief Description oJthe Drawing
Figure 1 is a schematic presentation of the process and equipment suitable for
the
invention.
Details
Raw material, e.g., pra-oxidized slag or Ilmenite, is fed through line (2) to
reactor
(1}. Hot gas is fed through line (4) to provide agitation by means of a
Pachuca tube (5).
Acid is fed through line (3) with make up acid from line (6). Together with
recovered
acid from the spray evaporator (34), reacted product (containing titanyl
sulfate, iron
sulfate and other Sulfates) overflows from reactor ( 1 ) through line (7) to
rotary filter (8).
Obtained filter cake is given a displacement wash on rotary filter (8), whose
water comes
in through line (14}. The washed filter cake is delivered through line (9) to
dissolving
tank (10). Concemrated acid from rotary filter (8), together with displacement
wash, is
returned to reactor (1) through line (3), which also receives make-up
concentrated acid
through line (~. Steam, together with some acid formed during reaction in
reactor (1),
is led through line (11) to condenser (12), and from condenser (12) through
line (13) to

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dissolving tank (10). Additional water containing acid from condenser (41) is
led
through line (15) to dissolving tank (10). Reducing material (iron, aluminum)
is added
to dissolving tank (10), together with insoluble materials, through line (16)
to filter (17).
Clear filtrate from filter (17) is led through line (18) to pre-heater (19),
and from pre-
y heater ( 19) through line (20) to hydrolysis tank (21 ). Unreacted ore and
insoluble
material is delivered from filter (17) through line (22) to waste. Hot liquor
from pre-
heater (19) is then introduced through line (20) to hydrolysis tank (21), in
which it reacts
with hot water from line (24), which has been previously introduced to seed
and start
hydrolysis. The resulting mixture is then brought to a boil, using live steam
transnutted
through line (25). After hydrolysis, the obtained titanium dioxide hydrate
flows through
line (26) to Moore filters (27). Filter cake from Moore filters (27) is
delivered through
line (29) to fluid bed calciner (30), where it meets hot gases from line (31).
Calcined
titanium dioxide is delivered through line (39) to coolers, packing, and
grinding, not
shown. Gases flow from cyclone (32) through line (33) to spray drier (34)
through line
(35) to filter (36). Insoluble ferrous sulfate monohydrate from filter (36) is
delivered
through line (37) to washing, drying and packing, not shown. Concentrated acid
is led
through line (42) to line (3) and thus delivered back to reactor (1). Steam
[with some
acid from spray drier (34)] is led through line (40) to condenser (41 ). Water
[with some
acid from condenser (41)] is led to dissolving tank (10) through line (15).
Fxanrple
Beach sand and 65% sulfi~ric acid are added into a reactor with an acid to ore
ratio of from 5:1 to 7:1.
The resulting admixture is heated to 180°C and agitated for 8
hours.
The reacted ore slurry is discharged into a filter, and a vacuum of -28mm Hg
is
pulled to separate excess fluid. The filtrate is 57.3% acid, 7.8% FeZ(S04)3,
0.4% Ti02.
Thus-obtained filter cake is washed with 2% acidified water. The filtrate
contains
40.65% acid, 1.79% Ti02 and 9.1% Fe(SO,)3.
The cake contains 16.2% TiOz, 12.7% Fe2(S04)3 and 33% acid, giving a 2.0 to
1.0 acid to TiOz ratio.

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Acidified water (4% acid) is added to the cake to dissolve it. Aluminum powder
is added to reduce the resulting solution and produce 2 grams per liter of
reduced Ti02.
The solution is heated to 50°C to promote the dissolving.
Insoluble solids are separated from the thus-obtained product by means of a
filter,
washed and dumped.
The filtrate contains 14.3% Ti02, 4.4% FeS04, and 26.5% sulfuric acid, giving
a 1.9 acid to Ti02 ratio.
The solution (filtrate) and a weighed amount of water are preheated. The
resulting hot solution is fed into hot water in the hydrolysis tank. The
mixture is brought
to a boil. After hydrolysis the obtained Ti02 hydrate is filtered and washed.
The obtained filter cake is treated for calcination and calcined at from
925°C to
980°C to obtain the desired pigment quality.
The invention and its advantages are readily understood from the foregoing
description. It is apparent that various changes may be made in the process
and
apparatus without departing from the spirit and scope of the invention or
sacrificing its
material advantages. The process and apparatus hereinbefore described are
merely
illustrative of preferred embodiments of the invention.
r__. _ .... ~ .__..

Representative Drawing