Note: Descriptions are shown in the official language in which they were submitted.
20~7~
Process for the removal of chloride ions from a
fine-particle titanium dioxide, -uch fine-particle
titanium dioxide freed from chlor$de ions and its use
Description
5 The invention relates to a process for the remoYal of chloride
ions from a fine-particle titanium d~oxide that was produced using
hydrochloric acid, titanium tetrachloride and/or the products of
its reaction with water and which contain~ seeding crystals
consisting o~ titanium dioxide of the rutile crystal modification,
to such fine-particle titanium dioxide freed from chloride ions
and obtainable by said process and to its use in various fields of
application
In this patent application, ~fine-particle titanium dioxide~ is
unaerstood to be titanium dioxide of a particle ~ize below that
lS which i~ normAl and optically eff-ctive in titanium dioxide
plgmentJ~ ~aid titanium dioxide may contain hydroxyl groups and/or
water bonded like in a usual product denoted as titanium dioxide
hydr~te
A ~nown process for producing titanium dioxide consists of
~u~ecting ~ titanyl sulphate solution to a thermal hydrolysis,
which result~ in a titanium dioxide hydrate from which titanium
__ __ : __r.~l--
dlo~ide i~ produced by calc.nation This process is often termed
-_ r__~sulphate process~ Titanium ~ioxide of the anata~e crystal form
is deve:oped from ~uch titanium dioxide hydrate by ca'cining it at
temperatures where there i~ -ot yet an excese'~e par~'cle croh~h
and at which the pigmentary properties are maintained To produce
titanium dioxide of the rutile crystal form ~hereinafter referred
to 08 ~rut$1e titanium dioxide~), one adds, prior to calcination,
20697~5
small amounts of a seed which promotes the transformation of the
first formed anatase into the rutile modification ~hereinafter
this seed being referred to as ~rutilisation seed~). The
rutilisation ~eed is mostly used in the form of a t$tanium dioxide
sol containing seeding crystals of rutile titanium dioxide.
Since such seeding erystals consisting of rutile titanium dioxide
are preferably formed in solutions which contain only univalent
acid radicals, e.g. chloride ions, the proce~ses used to produce
the titanium dioxide sol containing seeding cry~tals of rutile
titanium dioxide are preferably those in which hydrochloric acid,
titanium tetrachloride and/or the products of lts reaction with
water are used as the compounds furnishing chloride lons.
According to J. Barksdale, ~Titanium~, 2nd edition, The Ronald
Press Company, 1966, Pages 341-345, for instance, such a titanium
dioxide ~ol is produced by ~reating with hydrochloric acid an
alkali titanate washed free of sulphate. This ac~d treatment
decomposes the alkali titanate, whereby seeding crystal~ of rutile
t~tanlum diox~de are formed. Subseguently, these seeding crystals
are pcptl~ed by the addltlon of furth-r quantitiei of hydrochloric
acid, a titanlum dloxlde 801 thu~ being form~d.
ln another proc-~, described on Page~ 302-304 o~ the above-cited
publication, an aqueous titanium tetrachlorlde solution i8 U8ed a8
th- ource mat-rial ~n which the deJired seeding cry~tal~ of
rutile titanium dioxide are formed by heating and/or partlal
neutrallzation. The titanium dioxide 801 thus obtalnea can be used
dlr-ctly as the rutilisation seed in the production of the rutile
tltanlum d~oxlde. Thls titanium diox~de sol, bow-v-r, contains
5~~guantltleJ of procesJ-integrated chloriae ion~. These
chloride ion~ may cau~- corro~ion, more ~peci~ically, pitting
~ r--
corro~ion of equipment parts used in the titanium dioxide
manufacture. Moreover, the corros~on product~ have an adverce
effect on the titan'um dioxide, eQpec'ally on the pigment
properties of a rutile titanium dloxide pigment produced using the
titanium dioxide ~ol.
2~$~7~
-- 3 --
There is a particularly great risk of corrosion as a result of the
chloride ions introduced by the titanium dioxide sol into the
TiO2 manufacturing process, when the washing liquids obtained in
the TiO2 manufacturing process cannot be simply removed for
environmental reasons but are returned to the process.
~or the above-stated reasons it is necessary to reduce as far as
possible the chloride ion content of the titanium dioxide sol.
Attempts were made, therefore, to wash the titanium dioxide sol
free of chloride prior to using it (DE-Cl 39 38 693). But owing to
the extremely flne particle size of the seeding crystals, this
method is very expensive technically and i8 not customary. In
other procedures, as are described in DE-Al- 38 17 909, US-A-2 494
492 und US-A-2 479 637, the fine-particle titanium dioxide
contained in the titanium dioxide sol is flocculated by addition
of an alkaline reagent and the flocculated fine-particle titanium
dioxide is separated from the liquid phase and washed with water.
In this process, the titanium dioxide sol usually contains
relatively little TiO2 before being flocculated. Long flltration
times are required, and the washing of the flocculated and
separatcd fine-particle titanium dioxide is intricate ~nd
tlm--consuming. During these washing procedureJ, the flocculated
fine-particle titanium dioxide i8 repeotedly slurried with water
and filtered again. Crack~ may readlly form ln the fllter cake and
permlt TiO2 to penetrate through the filter. It may happen that,
during the washlnq procedure, the ~cparated fine-part~cle titanium
aioxlde i8 rodi~pcrsed though thls is unaesirable, the flocs being
brok-n down.
A new process has therefore been searched for which overcomes the
dr~b~rck~ of the known methods while permitting to separate and
wash the flocculated flne-particle tltanium dioxide readily and
r--
rapidly. Surprisingly, this ob~ective ~as found to be achievable
by a combir.atlon of certain process steps, thls combination
unexpectedly showing additional advantages over the known
procedures in other respects.
2~7~5
Accordingly, a new process has been found for the removal of
chlor$de ions from a fine-particle titanium dioxide that was
produced using hydrochloric acid, titanium tetrachloride and/or
the products of its reaction with water and which contains seeding
5 crystals consisting of titanium dioxide of the rutlle crystal
form This process comprises
a) using a titanium dioxide sol as the source material which has a
titanium dioxide content of at least 100 g/litre, calculated as
TiO2;
b) mixing said titanium dioxide sol with an aqueoug solution of an
alkaline reagent, the fine-particle titanium dioxide being
flocculated, under such condition~ that
(i) the solution of the alkaline reagent containE this
reaqent in a concentration of from 10 per cent by weight
to the point of ~aturations
(ii) the alkaline reagent is added to the titanium dioxide 801
in such a quantity that the mixture has a pH of between
4 0 and 11 0;
(iii) the titanium dioxlde sol, during the addition of the
alkaline reagent, iQ kept at a temperature between 40C
and the boiling point and iJ stirrea ln a vessel, without
g-n-rating hlgh ~hear forc-, Juch as to produco in the
veJJ-l Js-ntlally only ~ tang-ntial to radlal flow of
the ligulds
c) ~-paratlng the ~locculat-d fine-particle titanium dioxide by
flltr~tion at a temp-rature between 20C and lOO-C7 and
hing th- ~-parat-a fln--particle titanium dloxide at a
t-~p-ratur- be~w-en 20-C and lOO-C with an aqu-ous solution of
~n l-ctrolyte who~e concentratlon ln the wasb liquid i9
between 0 1 per cent by weight and the point of ~aturation,
-_ ~J~oK~o~ive ~ubstances, particularly chloride ion~, being
excluded aJ an electrolyte
The preferable source material i8 a titanlum dioxide 801 which has
a titanium dloxide content of between '00 ana 200 g/litre,
preferably between 150 and 170 g/litre, calculnted as TiO2 The
preferable alkaline reagent for the i'locculatlon i~ hydroxides
and/or carbonates of sodium and/or of pota~sium, and/or ammonia,
and~or ~mmonium hvdroxide, and~Gr carbonate~ of the a~o~iu~ on
20~7~
The solution of the alkaline reagent is added to the titanium
dioxide sol preferably at a temperature between 60~C and 90C.
The solution of the alkaline reagent is added to the titanium
dioxide sol preferably in a quantity to attain a p~ of between 7
and 9 in the mixture.
The flocculated fine-particle titanium dioxide is separated by
filtration preferably at a temperature between 60C and 90C.
~he separated fine-particle titanium dioxide is washed also
preferably at a temperature between 60C and 90C.
The interaction of all the process parameters claimed i~ essential
for achievin~ the ob~ective, which is to obtain a readily
filterable and washable fine-particle titanium dioxide with a
sufficiently reduced chloride ion content and containing seeding
crystal~ of rutile titanium dioxide.
The solution of the alkaline reagent may contain said reagent in a
wide variety of concentrations. But in order to prevent the
titanlum dioxide from being too much diluted through the addition
o~ aaid solution, this solution ~hould contain the alkaline
reagent generally ln not too low a concentration. This solution
may be even a saturated solution.
Tho temperature, at which the alkaline reagent should be added to
the ~itanlum dioxide 801, at which the fine-particle titanium
dloxide contained in the titanium dioxide 801 should be
flocculated through ~aid addltion, and/or ~t which the flocculated
- 2~--1~e-p~rticle tit~nium in the solutions should be filtered, may be
ad~u~ted by an external heating and/or by utilization of the heat
~ that i8 generated in the reaction of the added alkaline reagent
with the acid in the titanium dioxide sol.
7 ~ ~
In this $nvention, particular attention is paid to stirring while
adding the alkaline reagent to the titanium dioxide ~ol The
solutions need tO be thoroughly and rap~dly m~xed while avoiding,
however, that high she~r i8 applied to the mixture If the ~ixing
i~ done too slowly, there i8 a risk of having an excessively high
pH in parts of the mixture and/or of having in the mixture zones
with considerably different pH values; in both cases there will be
_ an unde~irable increa~e in viscosity If excessive shear forces
are appl~ed, the flocs formed will be di~integrated again A
satisfactory effect of stirring esQentially depends on the type of
stirrer ~n order to homogenizc the mixture, i e homogenizing the
concentration witbin the mixture while adding the alkaline
reagent, stlrrer~ are su~table which effect in the mixture an
essentially tangential to radial flow of the liquid An axial flow
of the liquid, however, should be avoided -as far as ever possible
Suitablc stlrrers ~re crossed-beam paddle mixers, gate paddle
mixers or flat-blade paddle mixers, the two latter types being
particularly appropriate Further det~ a~out su~table stirrers
are given in ~Ullmanns Enzyklop~die der techniRchen Chemie~, 4th
edition, volume 2, 1972, pages 261-262
A particularly favourable embodlment of this invontlon comprises
~tirring th- tit-nlum dioxlde rol during the additlon of the
alk~line r--gent wlth a gate paddl~ mixer or a flot-bl~de paddle
mix~r.
ln ddlng th- alkaline reagent to the titanlum dloxide 801~ after
p~ o~ ~ ha~ been attained, one experiences a marked decline ln
the relativ- vl~co~ity of the mixture ~ratio of the vi~cosity of
the mlxture at the pH v~lues attainea to the viaco~ity of the
titan~um aioxide 801 before the addition of the a~kaline reagent);
3e'~ien the p~ i~ further increased, the rclative vi~coslty
es~entially remains at the low lovel reached
2~S97~S
This behaviour is extremely surprising and differs essential'y
from the behaviour the titanium dioxide sol shows when not all of
the claimed steps are adhered to. In such a case, the relative
viscosity markedly increases when pH 4 is exceeded to decrease but
insignificantly with further rising pH and the initial value of
tbe relati~e viscosity is not reached again.
In the process of this invention, the mixture i9 filtered after
~ the desired p~ has been reached. If the flocculated fine-particle
titanium dioxide in the mixture settles prior to the filtration,
this titanium dioxide will form a fluffy ~ediment which can be
~tirred up again without problem by one of the stirrers mentioned.
The filtered product is washed to remove the chloride ions
adhering to it. The wash liquid u~ed therefor is an eleetrolyte
solution: the use of pure water is to be avoided.
1~ As a rule, the electrolyte consists of ~alts of inorganic and/or
organic acids or of a buffer mixture. Accordingly, a particularly
favourable embodiment of this invention comprises washing the
separated f$ne-particle titanium dioxide with an aqueous solution
of an electrolyte which consists of one or several ~alt(s) of
inorganic and/or organic acids or of a buffer mixture. The
electrolyte solution contains, for instance, saltJ of monovalent
and~or multivalent ions, specifically salts of alkali metals or of
alkalirearth met~ls or of ammonium, more specifically saltJ of
sodium or potasniu~ or mixtures thereof. The electrolyte solution
must not contain ~ubstances which, on further processing and use
of the washcd fine-particle titanium dioxidc, are corroslve
toward~ the equ$pment employed.
It i~ particularly advantageous to use chloride-free wash liquids
-_o~ cntially neutral reaction and derived from the titan$um
dloxide manufacturing process: particularly adv~ntageous f~ltrates
are tho~e derived from the post-treatment of titanium dioxidc in
the titan~um dioxide manufacture or neutralized filtrates o~tained
~n washing an alkal$ titanate free from sulphate, which ti~anate
206~7~
is meant for the titanium dioxide sol productions the latter
filtrates comprise especially sodium sulphate solutions In this
way, it is possible profitably to utilize liquids obtained as
waste material in the manufacture of titanium dioxide
S As a rule, the washing of the flocculated and filtered
fine-particle titanium dioxide is to be carried on until the
residual chloride ion content in said fine-particle titanium
dioxide is not more than 0 1 to 0 5 per cent by weight Cl ,
related to ~iO2 To this end, a preferable embodiment of this
invention continues washing the fine-particle titanium dioxide
separated by filtration until the chloride ion content in the wash
filtrate has dropped to 0 1 g/litre at most
In general~ the mixture obtained from the t$tanium dioxide sol and
containing the flocculated fine-particle titanium dioxide has so
low a viscosity that it can readily be filtered immediately after
the desired p~ range has been ad~usted In a particular embodiment
of thi~ invention it may be advisable, however, to dilute the
mixture containing the flocculated fine-partlcle t$tanium dioxide
prior to filterlng it Dilution, for example, may be with water
Sometim-s it i8 advi~able, according to anoth-r embodiment of this
invention, to add an organic flocculant, g polyacrylamide, to
th- mixture containlng the flocculat-d fin--partlcle titanium
dioxid-
It wa~ found that flocculating the titanium dioxld- ~ol ln
co~pliance wlth thi~ inv-ntion, and filtrating and wa~hing the
flocculated flne-particle titanium dioxide do not alter the
propertieJ of the J-eding cry~talJ of rutile titanium dioxide
n~a~rned in ~aid titanlum dloxide It i~, in particular, the
,rutilizing e~-ct of the Jeed~ng cry~tals o~ rutile titanium
dioxide which i8 pre~erved unrestr$ctealy
~he washed product can readily be redi~persed in ~ulphuric
acid-containing wnter
20~97~
~he flocculated and neutralized mixture obtained from the titanium
dioxide sol, with a titanium dioxide content of 120 to 250 9/
litre, calculated as TiO2, has a viscosity of from 6.B x 10 2
Pa.s to 16.~ x 10-2 Pa.s at 25~C.
The size of the flocs ranges from 10 to 40 microns: the seeding
crystals contained in the flocs have a particle size of 0.01 to
0.1 microns (measured on the longest axiQ) and, as a rule, are
needle-shaped and have rutile crystal form.
The flocs readily settle and are very easily filtered and washed.
It is not necessary to slurry the fine-particle titanium dioxide
prior to washing or between the various washing steps.
The titanium dioxide 801 wbich is the source material in the
process of the present invention can be produced by various ways.
One embodiment of the present invention, for example, comprises
lS producing the titanium dioxide 801 by reacting a titanium dioxide
hydrate suspended in water and produced by hydrolysis of A titanyl
sulphate solutlon with an alkali hydroxide solution thus forming
alkali titanat-, waJhing free of sulphate the mixture obtained in
th- r-action, decomposing with hydrochloric acld the alkali
tltanate obtain-d thus forming titanium dlo~lde hydrate, ~nd
peptizing this titanium dioxide hydrate by adding a further
quantity of hydrochloric acid.
A p~rticularly dvantageous embodiment of this production method
con-~ts Or thc following rteps:
25 a) A titanium dloxide hydrate of anatase cry~tal form produced by
the hydrolysiJ of a titanyl sulphate Jolution is ~lurried with
~ r ~uch a~ to obtain ~n the ~lurry a concentration of 20 to
.-_ r'_~_ 26 per cent by weight TiO2J
b) the titanium dioxide hydrate slurry obtained ls heated to
between 60C and 70C.
.
2~6~
- 10 -
c) the heated titanium dioxide hydrate slurry is added, while
stirring, to an aqueous sodium hydroxide solution heated to
between 90C and 100C in sufficient amount to achieve, after
addition, a weight ratio of NaOH to TiO2 of between 1.25 and
1.65 in the mixture:
d) the mixture is heated to the boil and maintained at the boiling
point for 120 to 140 minutes:
e) the mixture is then cooled down to between 50C and 60C and is
filtered;
f) the filter cake obtained is washed until the So2 content $n
the wash filtrate i9 less than 0.05 g/litre;
g) the washed filter cake is slurried in water to obtain a TiO2
content of between 10 and 25 per cent by we~ght: the mixture
thus obtained i8 mixed with hydrochloric acid containing 20 to
25 per cent by weight HCl to attain a pH value of 2.8 to 3.1
h) the mixture is heated to between 55C and 65C and kept at this
temperature for 30 to 45 minutes, the pH range of between 2.8
and 3.1 being maintained:
il the mixture is peptised at 55 to 65C with hydrochloric acid of
20 to 25 per cent by weight HCl in suff$cient amount to ad~ust
a weight ratio of hydrochloric acid, expressed as HCl, added in
this stage, to TiO2 of between 0.15:1 and 0,25:1~ and
k) the suspenslon obtained i8 heated to the boil within 30 to 40
minute~ and kept at the boiling point for 60 to 90 minutes.
In another advantageous embodiment of the present invention, the
titanium dioxide 801 is produced by hydrolysis of a solution of
titanium tetrachloride in water and/or by an agueou~ solution of
one or several compoundg formed by the reaction of titanium
tetrachloride with water.
~~- 34h~n produc~ng the titanium dioxide sol, substances may be added
which have defined effects on the particle size and/or the
particle sha?e of the seeding crystals of rutile tita~ium dioxide.
20~7~
Among such substances, fine-particle tin dioxide is particularly
suitable. An addition of such tin dioxide in the production of the
titanium dioxide sol is described in the German patent application
P 41 05 345.1.
Accordingly, a particularly advantageous embodiment of the
invention consists in using a titanium dioxide 901 in the
production of which a fine-particle tin dioxide is used the
particle size of wh~ch is between 1 and 10 nm, preferably between
1 and 4 n~, the tin dioxide being added in an amount of between
0.5 and 10 per cent by weight, related to the amount of titaniu~
dioxide contained in the titanium dioxide sol.
According to an advantaqeous method of operation, one may proceed
as follows, for example:
a) A titanium dioxide hydrate of anatase crystal form produced by
the hydrolysis of a titanyl sulphate solution is slurried with
water such as to obtain in the slurry a concentration of 20 to
26 per cent by weight TiO2:
b) the titanlum dioxide hydrate slurry obtained is heated to
between 60 and 70cl
. 20 c~ the heated titanium dioxide hydrate slurry i~ added, while
stlrring, to an aqueous sodlum hydroxide solutlon heated to
between 90C and 100C in sufficlent amount to achieve, after
~ddition, a weight ratio of NaOH to ~iO2 of between 1.25 and
1.65 in the mixture~
d) the mixture is he~ted to the boil ~nd maintained at the boiling
polnt for 120 to 140 minutes;
e) the mixture i8 then cooled down to between 50C and 60C and is
i'lltered;
filter cake obtained is washed until the So2 content in
3gL~ - the wash filtrate is less than 0.05 g/litre:
g) the washed filter cake is slurried in water to obtain a TiO~
content of between 10 and 25 per cent ~y weight; the mixture
thus obtained is mixed with hydrochloric acid containing 20 to
25 per cent by welght NCl to attain a pH value of 2.8 to 3.1;
,
20~7~
- 12 -
hl the mixture is heated to between 55C and 65C ~nd kept at this
temperature for 30 to 45 minutes, the pH range of between 2.8
and 3.1 being maintained;
i) a colloidal tin dioxide solution is added to the mixtyre, in
which tin dioxide solution the tin dioxide has a particle size
of between 1 and 10 nm, preferably between 1 and 4 nm;
j) the mixture to which the colloidal tin dioxide solution was
added ls peptized at 55C to 65~C with hydrochlor$c acid of 20
to 25 per cent by weight HCl in sufficient amount to adjust a
weight ratio of hydrochloric acid, expressed as HCl, added in
this stage, to TiO2 of between 0.15:1 and 0.25:1; and
k~ the suspension obtained is heated to the boil within 30 to 40
minute~ and kept at the boiling point for 60 to 90 minutes.
The invention also relates to a fine-particle titanium dioxide
freed of chloride ions that was produced using hydrochloric acid,
tltanium tetrachloride and/or the products of its reaction with
water and which contains seeding crystals consistlng of titanium
dioxide of the rutile crystal modification and which can be
obtalned by a proceQ~ according to this invention. This
20 i'ine-partlcle tltanium dioxlde, according to a proferred
embodiment of thi8 invention, i8 tO have a chloride ion content
not in exce8~ of 0.5 per cent by welght Cl , related to TiO2,
in ~pecial ca~eJ not in excess of 0.1 per cent by weight Cl ,
related to TiO2.
25 Sald fine-partlcle tltanlum dioxide can be employed in numerous
fi-lds of application.
A particularly preferred mode of application consist~ of using the
- -_ ~c~pnrt$cle tltanlum dloxlde as the rutll~zatlon ~eed for the
manufactur- of rutile titanium dioxide from titanium dioxide
r--
30 hydrate that wa~ obtained through hydroly~i~ of a titanyl sulphate
solution.
2~7~
- 13 -
Further preferable modes of application are its use as a uY
absorber in plastics or paints, as a uV absorber in sunscreen
compositions or in other cosmetic articles or as an agent for the
generation of special optical effects in paints, such as the
so-called ~down flop~ (cf. EP-Al-0 270 472).
The fine-particle titanium dioxide freed from chloride ions
according to this invention can be dried before being used, a
substance be~ng added optionally, prior to drying, which prevents
the formation of hard agglomerates. The titanium dioxide
agglomerates formed in drying may be milled and/or tempered. Prior
to and/or after drying and/or tempering, the fine-particle
titanium dioxide may be post-treated with one or several inorganic
and/or organic substances.
The invention ls illustrated in more detail in the following
Examples.
ExamPle
A tltanium dioxlde 801 was produced in a known way in which,
essentlally according to DE-Al-38 17 909, a titanlum dioxide
hydrate having anatase crystal structure and having been obtained
by the hydrolysis of a titanyl sulphate solution was reacted, at
elevated temperature, slurried in water, with a sodium hydroxide
solutlon and the product obtalned was ~iltered and washed until
the wash filtrate contained less than 0.05 g/l sulphate ions
(S0~ d-tectlon by the BaC12 test). The washed product was then
25 slurried with water and mixed with hydrochloric acid up to a pH of
2.8 to 3.1 and heated to 60 at this pH. The resulting product was
then pepti~ed by addition of a further amount of hydrochloric acid
r~oncentration 25 per cent by wsight) up to a weight ratio of
Cl to TiO2 of 0.15:1 and by heating to the boiling point.
~0~7~
- 14 -
In producing the titanium dioxide sol, operation was such that the
titanium dioxide sol obtained had a titanium dioxide content of
220 9/1, calculated as ~iO2. 455 ml quantities of this titanium
dioxide sol, corresponding to 100 g TiO2, were cbarged into
s beakers of 9 cm inner diameter and mixed with various quantities
of sodium hydroxide solution of an NaO~ content of 30 per cent by
weight in order to attain different p~ values in the range from
4.1 to 8.5. During the addition of the sodium hydroxide solution,
which took about 2 minutes, the temperature of the mixture was
adjusted to 80C by means of a thermostat and the mixture was
stirred by way of a flat-blade paddle mixer, initially at a speed
of 350 rpm. The flat-blade paddle mixer was 6.4 cm high and 3.6 cm
wide. After a pH of 3-4 was attained, the titanium dioxide sol
began to flocculate. When the flocculated state was reached, the
viscosity of the mixture dramatically dropped and the stirrer
speed had to be reduced to 200 rpm. After the desired p~ was
reached, the mixture was stirred for 5 minutes: the stirrer then
was stopped and product adhering to the wall was stirred into the
suspension by means of a glass rod. Then, without lowering the
temperature, the mixture was stirred for another 10 minutes by
mean~ of the flat-blade paddle mixer.
SubJequently the mixtures were cooled down to 23C and each
mlxture wa8 divlded i~to ten equal portisn8, ach portion thus
containlng 10 g TlO2. Each portlon was filtered through a
laboratory ~uctlon ilter 17.5 cm diameter) (0.3 bar pressure).
The i'iltet medium was a binder-fre0 glass fibre filter paper of a
baJi~ w-lght of 90 q/m in the form of a round filter. The time
required from the beginning of flltration up to slight surface
. _a,~ UL ltime of filtration) was measured. The mean values were
determined from 10 trlals each. (~Slight surface drying~ refers ~o
'~ the state at whlch the liquid level has dropped to the level of
the 'ilter cake surface).
-
20~7~
- 15 -
After the slight surface drying was attained, a wash solution,
which was a solution of sodium sulphate in water of a
concentration of 2.5 g/l Na2S04 and a temperature of 22C, was
passed onto the filter cake and the time was measured that was
required for 250 ml and 350 ml of this solution to pass through
the filter cake, again until a slight surface drying (wash time)
was achieved. The efficiency of the washing was assessed by
- determining the chloride lon content in the filtrate at the end of
the washing by means of a silver nitrate solution in nitric acid
lO medium. The chloride ion content in the filter cake, after 350 ml
wash solution having been passed through it, wa6 0.08 per cent by
weight Cl , related to TiO2. The particle size of the flocs
was between 10 and 40 microns. Particle size was measured on a
SALD-llO0 particle size instrument by Shimadzu.
The filtered and washed fine-particle titanium dioxide could be
redispersed in sulphuric acid-containing water.
The results shown in Table 1. In this Table, chloride contents
smaller than or equal to 0.1 g/l are denoted as ~chloride-free~;
chlorlde contents of more than 0.1 g/l are denoted ~not
20 chlorlde-free~.
Example 2 ~comparatlve example)
The tltanlum dloxide 801 was the same sourc- material a8 in
Ex~mple 1. In oraer to attain dlfferent pH values, varying ~mounts
oi' the sodium hydroxide solutlon usea in Example 1 were added at a
25 ~peea of about 1 ml per mlnute. Addltlon, however, was at amblent
temperature while stlrring at 800 rpm by means of a propeller
stirrer. The filtration and washing time~ were measured as in
Example 1. The results are al80 shown in Table 1.
r--
~0~7~5
- - 16 -
The comparison of the two examples shows that though it was
possible to achieve an absence of chloride ions also in the
comparative example, the filtration and washing times were
considerably longer than with the process of the $nvention and the
filter cake showed cracking while this was not the case with the
process of the invention
Example 3
The procedure was the same as in Example 1 But the washing
solution was a sodium sulphate solution of a concentration of
5 9/1 Na2S04 instead of 2 5 g/l Na2S04 Compared with the
use of a solution of 2 5 g/l Na2S04, a further marked
shortening of the washing times was achieved, especially with
lower pH values
~he results of Example 3 are shown in ~able 2
Example 4
Tho procedure wa~ th- same as ~n Example 1 with the difference
that the flocculation of the titanium d~oxide 801 was achieved, in
one ln~tance, by addltion of 55 0 ml of an ammonium hydroxide
~olutlon of a concentration of 25 per cent by weight NH3 and, in
another in-tance, by addition of 100 ml of a ~odium carbonate
~olution of a concentration of 25 per cent by weight Na2C03
ln both in~tancc~, flocculation took place up to p~ 7 In this
Exampl-, too, xcellcnt ~lltration ana washing times were achieved
Th- rc~ult~ of Example ~ are shown in ~able 3
. ~ ,,.~,_r--
- 17- 2~6~7~
7~ble 1
E~pl~ ~emper-ture Sodium hydroxide pH ~djust~d Filtr tion l~shlng time ~sh solution
Of th solution dded time Na2so4
flocculation
C ~1 s~e ~in 9/1
250 ~1 350 ~1
8047 5 4.1 7 13~ 20~ 2 5
110 50.0 5.2 5 ~ 14~ 2.5
110 52 0 7.0 3 2.5~ ~ 2.5
8054.5 8 5 2 2~ ~ 2 5
2 2348 5 5 0 250 60~ 94~ 2 5
2351 0 6 D 250 49~ 73~ 2 5
2352.0 7.0 200 71~101~ 2 5
2354.0 9.0 120 51~ 76~ 2 5
5 ~) e~ O ~So.l 9~1)
~) not el~-f,.- (~0.19~1)
~~1ng of the filt r ca'~e ~i~h eont1nu1ng ~uhing
':
2~7~
- lB -
T-ble 2
Ex~mple IEmper~-ure Sodium hydroxide pH ~djusted filtr~tion ~shing tire ~ash solution
of the solution ~dded time ~254
floecul~tion
_ _
C ~1 see min 9/1
250 ~1 350 ml
3 ~0 48 5 S 0 5 5 5~ 8~ S
Sl 0 6 0 ~ 3 5~ 6~ S
52 0 7 0 ~ 2~ 3~ 5
1 0 80 53 0 8 0 3 2~ 3~ 5
~) tl -~r~ 0 1 9~1)
~) not Cl-- r~o (>0 1 9/1)
T~ble 3
E~pl~ Tomper~ture ~lk~lln ph ~dJusted F11tr~tion ~ shlng t h e ~ sh solutlon
1 5 O- tho solut1On ~dd d t1me ~b2S04
flocc41~t~o~
C ml see 1n 9~1
2S0 ~1 3S0 ~1
4 ~0 55 0 ~H3- ol 7 0 4 3.5~ S 5~ 2 5
2 0 ~0 100 ~2C03 7 0 ~ 3~ 5 2 5
tl -fr~ 0 1 9~1)
2~7~
Example S
A titanium dioxide sol was produced as in Example 1 but with a
TiO2 content of 160 9/l
This titanium dioxide 801 was adjusted to different pH values by
addition of a 30 per cent by weight NaOH solution and flocculated
in the same way as in Example 1 In the flocculated mixtures, the
viscosity was determined as the relative viscosity, i e the ratio
of the viscosity of the mixture, at the p~ ad~usted, to the
viscosity of the original titanium dioxide 801 which had a pH of
about 0 Moreover, the filtrat$on and washing times were
determlned as in Example 1
The results are shown in Table 4
~xample 6 (comparat$ve example)
~he titanium dioxide sol of Example S was used as the source
material and the procedure was that of Example 5 with the
dli'ference of the Jodlum hydroxide Jolution being 810wly added at
ambient temperature ~about 1 ml/mln) a~ in Example 2, whlle
Jtirrlng by means of a propell-r mlxer at a rate of BOO rpm The
r-sults ar- also shown ln Table 4
Table 4 ~hows that there was no differ-nce between the two
example~ in th-lr vlscoaity behaviour up to p~ 4, but then with
rl~lng pH thelr behaviour markedly dlffered While, in the
proccdure of the comparative example, the relative vl~coffity
markedly ~ncrea~ed and remained at a high l-vel up to p~ 11 0, the
relative vlJcoJity~ in the proccsJ of the inventlon, warkedly
dkopped on reaching the flocculated Jtate and remained at this low
level up to pH 11 Accordingly, the process of the invention
yielded much shorter times of filtration and waQhing and better
washing efficiency than the procedure of the comparative example
The proce~s of the invention did not involve any def~ciency in the
filter cake as was encountered wlth the procedure of the
comparative example
206~7~S
- 20 -
Table 4
Example pH ad- Relative Filtration Washing time
~usted viscosity time (sec) 250 ml 350 ml
.
S 3 0 l l 720 redispersion after 50 ml
s 4 0 1 4 410 redlspersion after 60 ml
~ 5 0 0 2 220 62~ 9S~
6 0 - 30 35* 49
7 0 0 1 30 16~ 21
8 0 - 40 l9~ 30
9 0 0 1 25 16~ 23
11 0 0 1 40 41~ 68
6 3 0 1 1 960 redispersion after 20 ml~
4 0 1 4 810 redispersion after 80 ml~
S 0 2 8 440 92~ 133~/*~
7 0 3 9 370 S9~ 78
9 0 3 7 300 61~* redispersion~
11 0 2 9 275 65~ 86
~) Cl~-fre- ~ 0 1 g/l Cl-)
~ ) not Cl~-fr-e ~ ~ 0 1 9/l Cl-)
zo ~) Cracklng of th- filter cnke with continuing wn~hlng
~x~mDl- 7
~ an~um d$oxide ~ol~ with different TiO2 loadings were produced
- like in ~xample l A~ in Example l, these titanium dioxide sols were
floccul~ted at 80 C by ~d~usting a pH v~lue of 7 0 by means of a
sodium hydrox$ae solution of 30 per cent by weight NaOH:
2~6~7~
- 21 -
subsequently, the fine-particle titanium dioxide was filtered like
in Example l and washed with 250 ml of a sodium sulphate solution of
a concentration of 2.5 g/l Na2SO4. The filtration and washing
times determined like Example l are shown in Table 5.
Table 5
;
TiO2 concentration Piltration time Washing time
;
9/1 sec min
lO0 120-360 46-60
120 60-120 30-32
140 30-60 15_25
160 15-30 10-17
200 5 3-5
220 3 2-3
The results of Table 5 show that the filtration and washing times of
the product produced according to this invention are rather short
alr-ady at a TiO2 content of as little as 100 g/l in the original
titanlum dioxide 801, but are becoming markedly shorter still with
rising TlO2 content in the original titan~um diox~de 801.
Th- u~e of high TiO2 concentrations in the original titanium
dloxide 801 has the advantage of smaller vessels being required and
~maller volumes of waste water being obt~ined.
_ Exluu~Le 8
$ne procedure was like in Example 7 with the difference that, after
addition of the sodium hydroxide solution and the resulting
flocculation of the titanium dioxide 801, the m~xture was diluted
with water to a uniform TiO2 content of 100 g/l prior to
filtration. The filtration and washing times determined are shown in
~able 6.
-
. :.
2~7~5
- 22 -
Table 6
TiO2 concentration TiO2 concentration Filtration Washing
after flocculation prior to filtrat1on time time
g/l g/l sec min
- 5 100 100 250 59
120 100 147 37
140 100 lOS 21
160 100 82 16
200 100 22 5
220 100 17 4
The results of Table 6 indicate that the improved filtr~tion times
are less due to the quantity of liguid passed through the iilter
during filtration than to the TiO2 content of the slurry during
flocculation and that this TiO2 content ha3 al80 a beneficial
ffect on th- wa~hing behaviour
A great advantage of the process of thi~ invention is the
posslbil~ty o~ using, as the sourc- material, tltanium dioxide 8018
as are typical produo-d which need not be dlluted for the
~locculation and or the Jubsequent ~tep~ The proce~s is very
~l-xibl- and can be largely adapted to the requir-ments of each
Jitu-tion.
The invention relates to a process for th- removal of chloride ions
_ from a fin--part~cle titanium dioxide A titanium dioxide 801
containing at l-ast 100 gJl TiO2 i8 mixed, at a temp-rature
between 40C and th- boiling point, with an aqueous alkaline
solution up to a pH of between 4 0 ana 11 0 whil- ~tirring without
generating high shear, resulting essentially in a tangential to
2~6~7~5
- 23 -
radial flow of the liquid; the fine-particle titanium dioxide is
flocculated in this procedure, subsequently it i8 filtered and
washed with an aqueous electrolyte solution. The flocculated mixture
ha3 a low viscosity, which results in short filtration and washing
times and in an improved removal of chloride. The titanium dioxide
sol can be produced by reacting titanium dioxide hydrate with
alkali, decomposing the titanate formed and peptising, with
hydrochloric acid, the mixture washed free of sulphate or by heating
and/or partially neutralizing an aqueous ~iC14 solution.
The invention also relates to the fine-particle titanium dioxide
freed of chloride ions that is obtainable in the process of this
invention and to its use as a rutilisation seed in the production of
rutile from titanyl sulphate solutions, as a ~ absorber and for the
generation of special optical effects in paints.
,, ,- ~
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