Note: Descriptions are shown in the official language in which they were submitted.
1~34'~17~3
The present invention relates to a process for manu-
facturing basic zirconium carbonate from zirconium salts,
especially such salts as produced on the decomposition of
naturally occurring zirconium ores.
Basic zirconium carbonate is known to be prepared by
different techniques relying upon the reaction of a solution of
an ammonium or alkali metal carbonate with acid solutions of
zirconyl chloride or solid basic zirconium sulfate. A known
method for preparing basic zirconium carbonate consists of
reacting an acid solution of zirconyl chloride with an aqueous
solution of ammonium carbonate whereby a gelatinous precipitate
of the basic carbonate is formed. This process, however, suffers
from several disadvantages due to the nature of the precipitate
and the final product. The precipitate is very difficult to
filter and consequently difficult to free from soluble impurities.
Although useful for other purposes, these forms of zirconium
carbonate are not suitable for use as intermediates for the pro-
duction of zirconium chemicals as they have low zirconia contents.
Further, an essential property of basic zirconium carbonate for
commercial usage is that it should be completely soluble on
treatment with an organic acid. The products of the process,
as described above, do not retain this property for long periods.
The production of basic zirconium carbonates from
basic zirconium sulfate iq usually by processes which entail at
least two stages, namely 1) precipitating the basic zirconium
~ulfate by reacting an aqueous soluble sulfate at an elevated
temperature with a solution of a zirconium salt and 2) reacting
the solid basic sulfate with an ammonlum carbonate solution to
form the required basic carbonate. m e carbonates of this pro-
CeSs are usually more stable and reactive than those of the for-
mer process and have high zirconia contents.
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When, for example, sodium carbonate solution is mixed
with a solution of acid zirconium sulfate, a gelatinous pre-
cipitate of zirconium carbonate is produced. This material is
not suitable for commercial use as it is difficult to free from
entrained impurities and its reactivity to an organic acid
declines rapidly on storage and is lost on drying.
Accordingly, an object of the present invention is to
provide a single stage process for the manufacture of basic
zirconium carbonate from water-soluble zirconium salts to pro-
duce an easily filterable, stable, reactive product having azirconia content high enough for the product to be employed as
a useful intermediate in the manufacture of other zirconium
chemicals.
The present process comprises reacting a water-soluble
zirconium salt in acid solution in the presence of the sulfate
. . .
ion with an aqueous solution of an alkali metal or ammonium
carbonate or bicarbonate.
According to one embodiment of the present invention,
an acidified zirconyl chloride solution, produced, for example, ~ -
from the decomposition of zircon sand or baddeleyite, is mixed
with an aqueous soluble sulfate solution. The solution mixture
is then passed into a reactor at a measured rate of flow while
a solution of an aqueous soluble carbonate or bicarbonate is
introduced from another source. The flows are stirred counter-
currently for a set period while basic zirconium carbonate pre-
cipitates. The precipitate i9 then filtered or centrifuged and
washed by conventional methods to give as the final product a
paste of basic zirconium carbonate.
In another embodiment of the present invention, the
starting material is acid zirconium sulfate, an intermediate
formed in the upgrading of zirconium ores. An aqueous solution
.. . . . .
1~4;~17~
of this material is fed into a reacting vessel while an aqueous
solution of a soluble carbonate or bicarbonate is introduced
from another source. This mixture is stirred countercurrently
while basic zirconium carbonate precipitates. The precipitate
is then filtered and washed to produce the final product.
In a further embodiment of the present invention, the
flow rates of the incoming solutions are controlled in order
that basic zirconium carbonate may be manufactured on a continu-
ous basis by incorporating an overflow system into the reactor
whereby the zirconium carbonate product is collected.
It has been proposed that basic zirconium carbonate
is, in fact, a carbonated trioxodizirconium hydroxide. This is
based on a covalent Zr203 unit in which an oxygen atom links two
zirconyl groups, while a six-membered ring is formed by the two
zirconium atoms being coordinately linked to a common carbon
dioxide molecule as follows:
HO-ozr-o-zro-oH
o = C = o
The material is not composed of carbonate ions and zirconyl ions
possessing electrovalent stability, but it is thought that it
i8 stable only when a carbon dioxide molecule is linked at
both ends to a Zr203 unit.
The structures of the basic sulfate and other zir-
conium salts in solution differ in a fundamental way, that allows
the former to be converted quantitatively to the stable carbonate
by stirring with a carbonate solution while the latter are con-
verted to a mixture of stable carbonate and weakly carbonated
basic structures. This is because the basic sulfate already
possesses the OZr-O-ZrO units found in the carbonate. ;~
It has now been found that a transient intermediate,
probably similar in structure to the basic zirconium sulfate
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1¢~4'~179
(possessing OZr-O-zro units), can be prepared in situ in a
reactor which can then react with carbonate ions in solution to
form the stable forms of basic zirconium carbonate. The forma-
tion of the polymeric species is induced by monitoring the
rates of entry of the carbonate and zirconium solutions into
the reactor and the technique of mixing the solutions in the
reactor.
On slowly raising the pH of an acidified sulfate sol-
ution of zirconium, the polymeric species of zirconium sulfate
are formed as a precipitate. These transient intermediates will -
react with carbonate ions in solution to precipitate basic
zirconium carbonate.
The invention will now be described with reference to
the accompanying drawings, in which:-
FIGURE 1 is a schematic illustration of a reactionvessel, and
FIGURE 2 is another schematic illustration of a
continuous reactor.
In the process of the present invention, an~alkali
metal or ammonium carbonate or bicarbonate is used both to raise
the pH of the solution and to provide the carbonate ions for
subsequent formation of basic zirconium carbonate. However,
it is essential that the inflowing zirconium solution is not
diluted by a solution rich in carbonate ions or the gelatinous
form of zirconium carbonate will precipitate. As shown in
Fig. 1, the positions of inlets for zirconium and carbonate sol-
utions are arranged in order that the pH of the zirconium sol-
ution is raised slowly for the transient intermediate to form.
The stirring action in the reactor i8 therefore necessarily
countercurrent.
To ensure sufficient dilution of the zirconium solution
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1C~4~17~3
be~ore carbonate formation, it is advantageous to incorporate
a suitable screen into the reactor to separate the two solutions.
However, if the rates of the incoming solutions are carefully
controlled, this design feature will not always be necessary.
Variables to be considered in the production of sub-
stantially pure, reactive basic zirconium carbonate according -
to the process of the present invention include:
1. Reagent ratio
2. Solution strength
3. Residence time in reactor
4. Reaction temperature
5. Alkaline reagent employed
The reagent ratio is defined as the quantity of alkaline
reagent used, expressed as a percentage of the theoretical
required to react with the sulfate groups of the inflowing
zirconium sulfate solution. When acid zirconium sulfate is the
starting solution, this will be according to the following
equation. -
2[H2ZrO(S04)2 3H20] + 4M2C03
2 3 (OH)2 CO2 7H20 + 4M2So4 + 3C2
The symbol M representing an alkali metal or ammonium ion.
Levels between 85% and ll~/o of the theoretical value
have been found to be satisfactory for producing substantially
pure basic zirconium carbonate. ~he preferred levels are between
95% and 105%. At levels between 60~o and 75% of the theoretical
carbonate requirement, the intermediate polymeric sulfate
material precipitates with minimal further reaction to produce
the basic carbonate.
This polymeric material is easy to filter and wash
free from impurities and on calcining forms high purity zirconia.
The Zr:SO4 ratio of the polymeric intermediate decreases from
2:1 to 5:3 on decreasing the ratio of percentage carbonate input.
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The flow rates of the respective solutions into the
reactor are usually equal, the adjustments of the reagent ratio
being made externally.
The strengths of the feed solutions are dependent as
an upper limit on the solubility of the salts in solution after
carbonate formation to avoid possible coprecipitation. However,
in practice, more dilute solutions are used to ensure complete
conversion of the incoming zirconium solution to the polymeric
intermediate before reaction with the carbonate ions.
The residence time is defined as the average time
spent by the reactants in the reaction vessel for the production
of basic zirconium carbonate. The reaction of the inflowing
zirconium salt to form the transient sulfate intermediate and
subsequently the carbonating reaction both proceed rapidly and
it has been found that residence times as low as ten minutes
can be employed. The preferred residence times of the reactants
using the process of the invention are between about 30 minutes
and 2 hours.
Using the present process, basic zirconium carbonate
can be manufactured at temperatures up to approaching the
boiling points of the solutions. However, it is preferred to
manufacture the materials at ambient temperature.
As stated in the foregoing, any aqueous soluble car-
bonate or bicarbonate is suitable as an alkaline reagent. Sodium
carbonate is usually selected on economic grounds the exception
being when sodium contamination of the product is undesirable.
Other suitable reagents include potassium carbonate, ammonium
carbonate and the corresponding bicarbonates.
The invention can be further illustrated by the
following examples.
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1'1~4'~179
EXAMPLE I
A 300 ml. reaction vessel as shown in Fig. 1 was
charged with 100 ml. of water. A solution of acid zirconium
sulfate was prepared containing 15 per cent ZrO2 W/V. Sodium
carbonate solution containing a reagent ratio equivalent to 101
per cent of the theoretical value was prepared in a separate
vessel. The two solutions were pumped into the reaction vessel
at ambient temperature at a rate of 150 ml. per hour using a
positive displacement metering pump. The solutions were stirred
at a rate of approximately 500 rpm until the reaction vessel
was full. The resultant product was vacuum filtered and washed
with water.
The paste product contained 34.5% ZrO2, 0.5% SO4, -
0.2% Na and 5.3% CO2.
EXAMPLES 2-6
The procedures employed were similar to that of
Example 1 with the variations indicated in the following table.
Prod uct A~ ~alvsis
Example zrO2 inPUt Residence Reagent ZrO SO Na CO2
_ solution time (hr) Ratio % 2 %4 % %
2 5 1 105 34.2 0.3 0.5 6.5
3 15 - 1/2 100 36.1 0.7 0.1 6.4 `
4 10 2 96 34.0 1.0 ~0.1 6.0
6 10 2 70 Z6.0 12.2 <0.1 5.8
~. .
All of the products in Examples 1 - 6 were obtained
in a paste form. The products may be further dried by air dry-
ing or washing with a solvent mixture and air drying without
loss of reactivity to organic acids.
EXAMPLE 7
A 300 ml. continuous reactor as shown in Fig. 2 was
charged with 100 ml. of water. A solution of acid zirconium
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lU4'~179
sulfate was prepared containing 5 per cent ZrO2. Sodium car-
bonate solution containing a reagent ratio equivalent to 104
per cent of the theoretical value was prepared in a separate
vessel. The two solutions were pumped continuously into the
reaction vessel at a rate of 150 ml. per hour. The solutions
were stirred at a rate of approximately 500 rpm continuously.
The basic zirconium carbonate, in the form of a slurry,
continuously overflowed from the product overflow outlet from
which it is pumped or gravity fed to filters or a centrifuge to
obtain the final paste product.
After filtration, the product showed an average
analysis of 34.8% ZrO2; 0.5% S04; 0.2% Na and 5.8% C02.
EXAMPLE 8
Sodium sulfate solution was added to an acid solution
of zirconyl chloride to give a ZrO2:S04 ratio of 4:3. The pro-
cedure as described in Example 7, was employed to produce a
product of basic zirconium carbonate.
The undesirable impurities, iron and heavy metals,
usually found in zirconyl chloride solutions after the decompo-
sition of zirconium ores, can be complexed before the productionof zirconium carbonate so that they will pass into the effluent.
Various changes and modifications of the invention can
be made, and, to the extent that such variations incorporate the
spirit of this invention, they are intended to be included
within the scope of the appended claims.
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