Process for reacting a zirconia based material

A process for reacting a zirconia-based material comprises reacting, in a reaction step, plasma dissociated zircon with aqueous hydrogen fluoride to produce a soluble fluoro zirconic acid compound.

CROSS-REFERENCES TO RELATED APPLICATIONS 
Not Applicable 
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
Not Applicable 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
THIS INVENTION relates to the treatment of a chemical. It relates in 
particular to a process for treating a zirconia-based material. 
2. Description of the Related Art including information disclosed under 37 
CFR 1.97 and 1.98 
Not applicable 
BRIEF SUMMARY OF THE INVENTION 
According to the invention, there is provided a process for treating a 
zirconia-based material which comprises, broadly, reacting, in a reaction 
step, a zirconia-based material with aqueous hydrogen fluoride (HF), to 
produce a soluble fluorozirconic acid compound. 
In one embodiment of the invention, the zirconia-based material may be 
zirconia. In another embodiment of the invention, it may be dissociated 
zircon (`DZ` or ZrO.sub.2.SiO.sub.2). In yet another embodiment of the 
invention, it may be a zirconia-containing component of dissociated 
zircon. 
When zirconia is used, it may be a naturally occurring zirconium material 
such as baddeleyite. The reaction then proceeds in accordance with 
reaction (1): 
EQU ZrO.sub.2 +6HF.fwdarw.H.sub.2 ZrF.sub.6 +2H.sub.2 O (1) 
Instead, when zirconia is used, it may be that obtained by any suitable 
thermal process. 
The dissociated zircon, when used, can be that obtained by any suitable 
process, particularly a thermal process. Thus, for example, it can be that 
obtained by destroying the crystal matrix of zircon (ZrSiO.sub.4) by 
heating it to a high temperature in a plasma furnace or a plasma 
generator, under oxidizing, inert or reducing conditions. Zircon is a 
mineral which is abundantly available at relatively low cost, but is 
chemically inert. Thus, inert zircon mineral is rendered amenable to 
chemical processing in accordance with the invention, by means of said 
plasma dissociation. During plasma dissociation, zircon is dissociated 
into separate zirconia (ZrO.sub.2) and silica (SiO.sub.2) mineral phases, 
with the product commonly designated as dissociated zircon (`DZ`), plasma 
dissociated zircon (`PDZ`), or ZrO.sub.2.SiO.sub.2. Alternatively, the 
zircon can be processed in a transfer arc plasma furnace under reducing 
conditions effecting essentially the removal of the silica phase with 
essentially ZrO.sub.2, popularly designated fused zirconia, remaining 
behind. 
Zircon normally contains radioactive elements such as uranium (U) and 
thorium (Th) and their decay product elements, as well as other common 
impurities such as Fe, Ca, P, Al, Mg and Ti. These elements are released 
in the process of the invention, but the process provides an effective 
manner of dealing with these elements. In particular, the process results 
in the generation of only relatively small quantities of radioactive 
element containing wastes. Wherever reference is made in this 
specification to U and Th as radioactive elements, this is to be 
interpreted as referring instead or additionally also to their decay 
products. 
In one embodiment of the invention, the PDZ may be non-desilicated, in 
which case the reaction proceeds in accordance with reaction (2): 
EQU ZrO.sub.2.SiO.sub.2 +12HF.fwdarw.H.sub.2 ZrF.sub.6 +H.sub.2 SiF.sub.6 
+4H.sub.2 O (2) 
In another embodiment of the invention, the PDZ may be partially 
desilicated, in which case the reaction to produce the fluorozirconic acid 
is also in accordance with reaction (2). 
In yet a further embodiment of the invention, the PDZ may be wholly 
desilicated, in which case the reaction to produce the fluorozirconic acid 
is in accordance with reaction (1), as given hereinbefore. 
The desilication of the PDZ can be effected by known means, such as caustic 
soda leaching. Wholly or partially desilicated PDZ is also known as 
`DPDZ`. 
It is to be appreciated that whenever, in the reactions of the process of 
the invention, reference is made to hexafluorozirconic acid (H.sub.2 
ZrF.sub.6), this includes the compound ZrF.sub.4.2HF.xH.sub.2 O where x 
can range from 0 to 5. 
The concentration of the HF in the aqueous HF or HF solution may be in the 
range of 5-70% HF by mass. The reaction may be effected at a moderately 
elevated temperature, which may be between 20.degree. C. and 120.degree. 
C. Reactions (1) and (2) are exothermic. Thus, with a 40% HF solution and 
using PDZ as feed material, the reaction mixture reaches a temperature of 
.+-.90.degree. C. within a few minutes, depending on the rate of feeding 
the PDZ into the HF solution. At lower HF concentrations, for example 30%, 
lower final temperatures are reached and in such cases it is preferable to 
heat the reaction mixture from an external source, for example to 
&gt;80.degree. C. for complete reaction to take place. 
The reaction period may be between 10 minutes and 4 hours, depending on the 
HF concentration, the degree of dissociation of the PDZ and the 
temperature of the reaction mixture. 
Instead of, or in addition to hexafluorozirconic acid, ie H.sub.2 
ZrF.sub.6, tetrafluorozirconic acid, ie H.sub.2 ZrOF.sub.4, and/or 
hydrates thereof, can be formed. 
It will be appreciated that, in the reaction step, the zirconia and, when 
present, silica are dissolved in the HF solution, with the reaction 
products such as H.sub.2 ZrF.sub.6 and H.sub.2 SiF.sub.6 also being 
soluble in the aqueous hydrogen fluoride, so that only zircon that was not 
dissociated in the plasma, as well as poorly soluble or insoluble 
impurities or trace element such as U, Th, iron (Fe), titanium (Ti), 
aluminium (Al) and calcium (Ca) remain as more or less undissolved solids. 
The undissolved solids (`white fraction`) can thus be removed as a solids 
fraction by suitable means, such as filtration, decantation or settling, 
optionally preceded, if necessary, by precipitation of the trace 
element(s) in question. The process accordingly provides an effective 
means of purifying PDZ or DPDZ to produce a relatively small quantity of 
residue containing undesirable contaminants such as U and Th, and their 
decay products. 
Any residual zircon which was not dissociated in the plasma can thus be 
separated out, so that the process is not dependent on the availability of 
PDZ with 100% degree of dissociation. The zircon which is removed during 
this step can naturally be recycled back to the plasma stage, after 
separation of non-zircon materials. 
To enhance or optimize efficiency of reaction (2) and to reduce or minimize 
losses of Zr and F to the white fraction, the molar ratio of HF to 
zirconia plus silica, when present, is important, and will be controlled 
to obtain desired dissolution levels. Thus, the molar ratio of HF to 
zircoia plus silica, when present, may be in the range 1.1:0.9 to 0.9:1.1, 
more preferably in the range 1.05:0.95 to 0.95:1.05, and most preferably 
about 1:1. 
If desired, the solids fraction can be subjected to further treatment to 
recover elements such as U and Th. For example, it can be subjected to 
dissolution, eg utilizing suitable acids, eg nitric acid, or bases, 
followed by filtration and ion exchange, with, as stated hereinbefore, 
only small quantities of waste products being produced. Instead, any 
undissociated zircon can be separated from other insoluble compounds by 
means of physical separation, such as flotation, again resulting in 
substantially insignificant volumes of waste products. 
The process may include heating the residual solution containing the 
H.sub.2 ZrF.sub.6, H.sub.2 SiF.sub.6, H.sub.2 O and excess HF to recover 
H.sub.2 ZrF.sub.6. Thus, the solution may, in an evaporation step, be 
heated to a temperature between 20.degree. C. and 120.degree. C. at 
substantially atmospheric pressure, with all H.sub.2 SiF.sub.6, H.sub.2 O 
and excess HF being evaporated. These volatiles can then be condensed in a 
suitable condenser for subsequent recovery of HF and Si species, such as 
SiO.sub.2, in known fashion. The HF thus recovered can be recycled to the 
reaction step. 
Thus, in the evaporation step, reaction (3) takes place: 
EQU H.sub.2 ZrF.sub.6 (aq)+H.sub.2 SiF.sub.6 (aq).fwdarw.H.sub.2 ZrF.sub.6 
(s)+H.sub.2 SiF.sub.6 (g) (3) 
H.sub.2 ZrF.sub.6 (or H.sub.2 ZrOF.sub.4) crystals are obtained from this 
evaporation step, and the process thus enables substantially complete 
separation of all Zr and Si species. 
The H.sub.2 ZrF.sub.6 crystals can then be further purified, in a 
purification step, in accordance with reaction (4): 
EQU H.sub.2 ZrF.sub.6 (impure).fwdarw.H.sub.2 ZrF.sub.6 (pure) (4) 
The purification step may comprise recrystallization or ion exchange. 
Instead, the H.sub.2 ZrF.sub.6 solution can be only partially evaporated to 
produce a saturated solution from which H.sub.2 ZrF.sub.6 crystals can be 
crystallized with or without cooling of the solution. These crystals can 
be separated from the mother liquid by any suitable means, for example 
filtration. These crystals can be of high purity due to the fact that most 
of the impurities remain in solution and are not crystallized with the Zr 
species. After filtration of the H.sub.2 ZrF.sub.6 crystals, the remaining 
solution can be completely evaporated to recover all the remaining Zr as 
H.sub.2 ZrF.sub.6 (or H.sub.2 ZrOF.sub.4). These crystals will of course 
contain any accumulated impurities of the mother liquid. 
As a further alternative, the H.sub.2 ZrF.sub.6 /H.sub.2 SiF.sub.6 solution 
can be fed directly to an ion exchange column to produce a much purer 
H.sub.2 ZrF.sub.6 /H.sub.2 SiF.sub.6 solution, from which pure H.sub.2 
ZrF.sub.6 crystals can be crystallized. 
In one embodiment of the invention, the resultant pure H.sub.2 ZrF.sub.6 
can then be converted to zirconia, for example by means of steam 
pyrolysis, in accordance with reaction (5): 
EQU H.sub.2 ZrF.sub.6 +2H.sub.2 O.fwdarw.ZrO.sub.2 +6HF (5) 
The HF produced in reaction (5) can be recovered and reused in the reaction 
step. 
In other embodiments of the invention, other zirconium chemicals can 
instead be produced from the pure H.sub.2 ZrF.sub.6, such as, for example, 
ZrF.sub.4, ZrOF.sub.2, fluorozirconates such as K.sub.2 ZrF.sub.6, 
zirconium sulphate, or zirconium carbonate. 
The invention will now be described by way of non-limiting example with 
reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1, reference numeral 10 generally indicates a process for treating 
dissociated zircon. 
The process 10 includes a plasma dissociation stage 12, with a zircon feed 
line 14 leading into the stage 12. A PDZ flow line 16 leads from the stage 
12 to a reaction step or stage 18, with a HF solution make-up line 20 
leading into the stage 18. A transfer line 22 leads from the stage 18 to a 
liquid/solid separation step or stage 24. A zircon and white fraction 
withdrawal line 26 leads from the stage 24 to a zircon/white fraction 
separation stage 25, with a zircon return line 27 leading from the stage 
25 back to the stage 12. A transfer line 28 leads from the stage 24 to an 
evaporation step or stage 30, with a volatile product withdrawal line 32 
leading from the stage 30 to a treatment stage 34. A transfer line 36 
leads from the stage 30 to a purification step or stage 38. A transfer 
line 40 leads from the stage 38 to a zirconia production step or stage 42, 
with a HF withdrawal line 44 as well as a ZrO.sub.2 withdrawal line 46 
leading from the stage 42. Instead, or additionally, a zirconium sulphate 
production step or stage 48 can be provided, with a flow line 50 then 
leading from the stage 38 to the stage 48. A H.sub.2 SO.sub.4 feed line 52 
will then also lead into the stage 48 with a HF withdrawal line 54 as well 
as a zirconium sulphate withdrawal line 56 leading from the stage 48. 
Instead, or additionally, a fluorozirconate production step or stage 58 
can be provided, with a flow line 60 then leading from the stage 38 to the 
stage 58. A KOH feed line 62 then leads into the stage 58, with a 
fluorozirconate withdrawal line 64 leading from the stage 58. 
In use, ZrSiO.sub.4 is fed, by means of the flow line 14, into the plasma 
dissociation stage 12, together with recycled zircon entering the stage 12 
along the flow line 26. In the stage 12, the zircon is dissociated, by 
means of plasma dissociation, into PDZ. The PDZ passes along the flow line 
16 to the stage 18. 
In the stage 18, the PDZ is dissolved in a HF solution having a 
concentration of between 5% and 70% HF, and a temperature of between 
20.degree. C. and 120.degree. C., and reacts to form H.sub.2 ZrF.sub.6 and 
H.sub.2 SiF.sub.6 in accordance with reaction (2) 
EQU ZrO.sub.2.SiO.sub.2 +12HF H.sub.2 ZrF.sub.6 +H.sub.2 SiF.sub.6 +4H.sub.2 
O(2) 
The preferred HF concentration is 40% and the preferred temperature is 
80.degree. C., although the dissolution can also be effected at 
concentrations up to 100% HF. 
The solution formed in the stage 18 and containing dissolved H.sub.2 
ZrF.sub.6, H.sub.2 SiF.sub.6, H.sub.2 O and excess HF, as well as any 
undissolved solids, passes to the liquid/solid separation stage 24 where a 
solids fraction comprising undissociated zircon as well as any undissolved 
or precipitated impurities such as U and Th is separated from a liquid 
fraction comprising excess HF solution, H.sub.2 O, dissolved H.sub.2 
ZrF.sub.6 and dissolved H.sub.2 SiF.sub.6. The solids fraction is removed 
along the line 26, subjected to further treatment in the stage 25 to 
separate the white fraction from undissociated zircon, eg by means of 
dissolution in H.sub.2 SO.sub.4, followed by filtration and ion exchange 
to remove therefrom the U and Th, before recycling the zircon to the stage 
12 along the line 27. Thus, only relatively small volumes of U and Th 
containing waste are obtained from the process 10. 
The liquid fraction passes along the line 28 to the stage 30 where a 
volatile fraction comprising H.sub.2 SiF.sub.6, HF and H.sub.2 O is 
withdrawn along the flow line 32, by distilling the solution at a 
temperature between 40.degree. C. and 120.degree. C. and at atmospheric 
pressure. The volatiles enter the stage 34 where they are condensed for 
recovery of HF and high grade Si species, with the HF being recycled (not 
shown) to the stage 18. Separation of the HF from the Si species can be 
effected by means of flame hydrolysis, steam plasma or the like. 
Optionally, instead of the liquid fraction passing directly to the stage 
30, it can first be fed into an ion exchange stage (not shown) for initial 
purification thereof, with the liquid fraction thereafter passing to the 
stage 30. 
In the stage 30, substantially complete separation of Zr species from Si 
species is obtained. Thus, in a laboratory scale simulation of the process 
10, it was found that the H.sub.2 ZrF.sub.6 fraction from the stage 30 
contained 46.1% by mass Zr and less than 0.5% by mass Si, while the 
volatile fraction from the stage 30, after condensation, contained 55.7 
g/l H.sub.2 SiF.sub.6, and less than 1 ppm Zr. 
In the stage 30, when more than 20% of the liquid has evaporated, a highly 
saturated solution of H.sub.2 ZrF.sub.6 is obtained. Depending on the 
amount of liquid that has evaporated, crystallization of the H.sub.2 
ZrF.sub.6 (or H.sub.2 ZrOF.sub.4) takes place without cooling or upon 
cooling thereof to room temperature. This crystallization is in itself a 
further purification step with regard to impurities such as U, Th, Fe, Ti 
and Ca. The crystals can be removed from the residual solution by 
filtration, while the impurities remain largely in solution and can be 
removed subsequently by ion exchange (not shown). 
Instead, in the stage 30, complete evaporation of the H.sub.2 ZrF.sub.6 and 
H.sub.2 SiF.sub.6 solution can be effected, with H.sub.2 ZrF.sub.6 (or 
H.sub.2 ZrOF.sub.4) crystals then being obtained. These crystals can be 
dried in an oven (not shown). If it is desired to minimize fluorine (F) 
losses during this drying step, the temperature should not exceed the 
decomposition temperature of H.sub.2 ZrF.sub.6. Thus, the drying can be 
effected between 40.degree. C. and 90.degree. C., preferably at 
&lt;80.degree. C. The evaporation can be effected by any convenient means 
such as distillation, spray-drying or the like. 
The relatively impure H.sub.2 ZrF.sub.6 from the stage 30 passes to the 
purification stage 38. 
The impure H.sub.2 ZrF.sub.6 crystals which pass from the stage 30 are 
highly soluble in water, and solubilities of up to 1 g/ml of water are 
obtainable. Further purification of these crystals can thus easily be 
effected by dissolution and subsequent recrystallization, or ion exchange, 
in the stage 38, to produce H.sub.2 ZrF.sub.6 having substantially reduced 
radioactivity. 
For recrystallization, the H.sub.2 ZrF.sub.6 crystals are dissolved in the 
minimum volume of warm water, to produce a highly saturated solution. On 
cooling to room temperature, recrystallization takes place. The resultant 
crystals can be recovered by means of filtration, and dried. 
Instead, for ion exchange, the H.sub.2 ZrF.sub.6 crystals can be dissolved 
in water in a concentration range of 0.1M to 2.0M. This solution can then 
be passed through a column containing a suitable ion exchange resin for 
removing impurities such as U and Th. The solution is again evaporated to 
produce H.sub.2 ZrF.sub.6 crystals in which the concentration of 
impurities, especially U and Th, is significantly reduced. The U and Th 
contaminants can subsequently be eluted from the ion exchange resin in 
easily manageable confined volumes. 
EXAMPLE 1 
In a laboratory scale simulation of the various steps of the process 10, 
the following results were obtained: 
TABLE 1 
______________________________________ 
Purifying action effected in the various steps of the 
process of the present invention. 
Zr Si Ca Ti Fe U Th 
SAMPLE (%) (%) (%) (%) (%) (ppm) (ppm) 
______________________________________ 
PDZ entering 
47.9 15.4 0.085 
0.059 
0.048 
350 140 
stage 18 
Filtered out 
44.9 0.8 2.688 
0.018 
0.050 
1169 1891 
undissolved 
impurities 
leaving stage 
24 along the 
flow line 26 
H.sub.2 ZrF.sub.6 /H.sub.2 ZrOF.sub.4 
45.8 &lt;0.2 &lt;0.01 
0.035 
0.04 167 48 
leaving 
stage 30 
along flow 
line 36 
Recrystallized 
45.2 &lt;0.02 &lt;0.01 
&lt;0.01 
&lt;0.01 
42 &lt;20 
H.sub.2 ZrF.sub.6 
(H.sub.2 ZrOF.sub.4) 
leaving stage 
38 along the 
flow lines 
40, 50, 60 
Ion 0.027 
0.03 145 71 
exchange 
Before, ie 
entering 
stage 38 
After, ie &lt;0.01 
&lt;0.01 
83 &lt;20 
leaving stage 
38 
______________________________________ 
The purified H.sub.2 ZrF.sub.6 crystals from the stage 38 can be converted, 
in the stage 42, to zirconia (ZrO.sub.2) by means of steam pyrolysis, at 
temperatures between 450.degree. C. and 850.degree. C., for reaction 
periods ranging from 30 minutes to 3 hours in a suitable oven, such as a 
rotary kiln, in accordance with reactions (6) and (7): 
EQU H.sub.2 ZrF.sub.6 +2H.sub.2 O(steam)ZrO.sub.2 +6HF (6) 
EQU H.sub.2 ZrOF.sub.4 +H.sub.2 O(steam).fwdarw.ZrO.sub.2 +4HF (7) 
Further desilication is effected during the steam pyrolysis. 
An X-ray diffraction pattern of zirconia produced in this manner in the 
laboratory scale simulation of the process 10 is given in FIG. 2. 
Efficient conversion of H.sub.2 ZrF.sub.6 to ZrO.sub.2 in the stage 42 is 
not primarily dependent on feeding the H.sub.2 ZrF.sub.6 as dry crystals. 
Apart from steam pyrolysis conversion, final evaporation can also be 
effected in the rotary kiln. Thus, the crystallization effected in the 
stages 30, 38 can be avoided so that the H.sub.2 ZrF.sub.6 /H.sub.2 
SiF.sub.6 solution from the stage 24 can be fed directly into the stage 
42, or after partial concentration thereof by evaporation. 
The HF that is liberated in the stage 42 can be trapped in a suitable 
condenser or scrubber (not shown) and the thus recovered HF can be 
recycled to the stage 18. 
Instead, or additionally, zirconium sulphate can be produced in the stage 
48 by reacting the H.sub.2 ZrF.sub.6 with H.sub.2 SO.sub.4, with HF also 
being liberated for recycling. 
Yet further, K.sub.2 ZrF.sub.6 can be produced in the stage 58 by reaction 
of H.sub.2 ZrF.sub.6 with any suitable potassium salt, for example KOH. 
Still further, the H.sub.2 ZrF.sub.6 can be converted thermally to 
ZrF.sub.4 in a HF atmosphere (not shown) and the resultant ZrF.sub.4 
purified by means of sublimation/desublimation. 
Further tests to simulate and test the process 10 were also conducted, on a 
larger scale than Example 1. 
Examples 2 to 4 and 8 to 10 were done on laboratory apparatus, while 
Examples 5 to 7 were carried out on a small scale production setup, in 
accordance with FIG. 3. 
In FIG. 3, reference numeral 100 generally indicates the small scale 
production setup. The setup 100 comprises a liquid storage tank 102, with 
a flow line 104 leading from the tank 102 to a stirred reactor 106. An HF 
solution flow line 110, fitted with a pump 112, leads into the reactor 
106, while a solids withdrawal line 114 leads from the bottom of the 
reactor to a solids storage tank 116. The reactor 106 is fitted with 
heating and cooling loops (not shown) and a volatiles withdrawal line 118, 
fitted with a condenser 120, leads from the reactor 106. A liquid recycle 
line 122 leads from the reactor 106 back to the tank 102, and is fitted 
with a pump 124. 
In each of Examples 5 to 7, the first step in the production of H.sub.2 
ZrF.sub.6 was to pump the required amount of 40% HF into the reactor along 
the flow line 110. 
PDZ was then fed into the reactor, under agitation, using a solids feed 
hopper (not shown) situated on the reactor lid. 
The solids in the reaction mixture were separated from the liquid product 
phase using known settling techniques, after which the product (liquid) 
phase was pumped, along line 122, to the liquid storage tank 102. The 
solids were flushed, along line 114, to the solids storage tank 116 and 
the reactor washed. 
The product phase was then fed back into the reactor along line 104, where 
separation between H.sub.2 ZrF.sub.6 and H.sub.2 SiF.sub.6 was done by 
evaporation of the volatile H.sub.2 SiF.sub.6, H.sub.2 O and HF. The 
vapours were condensed and analysed. The residue after evaporation was a 
slurry of H.sub.2 ZrF.sub.6 /H.sub.2 ZrOF.sub.4 crystals. 
EXAMPLE 2 
500 g of plasma dissociated zircon (`PDZ`) (with a total dissociation of 
90%) was added to 1.4 l of a 40% aqueous HF solution in a 5 l PTFE beaker. 
The reaction mixture was continuously stirred throughout the reaction 
period. The temperature of the reaction mixture rose from 24.degree. C. to 
86.degree. C. within 2 minutes. After 4 hours, the reaction mixture was 
allowed to cool, and the undissolved solids were separated from the mother 
liquid by means of filtration and/or decantation/sedimentation. 
The solids consisted of a fine white fraction and undissociated zircon. The 
mass of the zircon portion was 45.0 g (9% of the original starting 
material). This corresponds well with the 90% dissociation of the starting 
material. X-ray diffraction (XRD) analysis confirmed that this portion of 
the solids was mainly zircon--see FIG. 4. The mass of the white fraction 
was 31.8 g (6.4% of the original starting material). XRD analysis of the 
white fraction showed that it consisted of a mixture of ZrO.sub.2, 
ZrOF.sub.2, ZrF.sub.4 and intermediate oxyfluorides. 
The mother liquid was evaporated at a temperature &gt;80.degree. C. After all 
the liquid had evaporated, 348.5 g of H.sub.2 ZrF.sub.6 (or H.sub.2 
ZrOF.sub.4) crystals remained in the beaker. 
The chemical analysis of the unreacted zircon, the white fraction and the 
final product are given in Table 2. 
TABLE 2 
__________________________________________________________________________ 
ppm ppm 
ppm ppm ppm 
ppm 
Sample % Zr 
% Si 
% Hf 
% F.sup.- 
Al Ca Fe Ti U Th 
__________________________________________________________________________ 
Unreacted zircon 
50.3 
15.2 
1.2 
0.1 
586 307 
620 831 351 
149 
White fraction 
58.6 
3.4 
1.4 
13.4 
2698 
7640 
&lt;100 
1659 
539 
680 
Final Product 
58.3 
0.03 
1.5 
37.2 
568 &lt;100 
246 563 238 
69 
__________________________________________________________________________ 
EXAMPLE 3 
100 ml of the mother liquid (obtained from a typical run as described in 
Example 2) was evaporated to 50 ml, and the solution allowed to cool. The 
crystals which formed were filtered off and dried. The filtrate was 
further evaporated until only dried crystals remained. Chemical analysis, 
summarized in Table 3 below, showed the crystals that formed after the 
evaporation of the first 50 ml of the mother liquid (sample A) were much 
purer than the crystals which formed with complete evaporation of the rest 
of the liquid (sample B). 
TABLE 3 
______________________________________ 
Si Ti Al Fe Ca U 
Sample ppm ppm ppm ppm ppm ppm 
______________________________________ 
A &lt;10 &lt;10 837 364 &lt;10 238 
B &lt;10 2047 14506 3781 84 406 
______________________________________ 
It was also established that 24.77 g (82%) crystals formed after 
evaporation of 50% of the mother liquid (sample A) and a further 5.37 g 
(18%) crystals formed after complete evaporation of the filtrate (sample 
B). 
EXAMPLE 4 
Using the procedures and parameters of Example 2, it was demonstrated that 
the amount and the chemical composition of the white fraction can be 
manipulated by the amount of HF available for reaction. For example, 0.43 
kg of plasma dissociated zircon, (with a total dissociation of 71%) was 
added to 910 ml of 40% aqueous HF solution. The reaction mixture was 
stirred throughout the reaction period. After cooling, all the solids were 
separated from the mother liquid by means of filtration and/or 
decantation/sedimentation. The dissociated zircon and the white fraction 
were further separated. The mass of the undissociated zircon was 121.4 g, 
which is 28.2% of the original starting material. This corresponds well 
with the starting material which was 71% dissociated. The mass of the 
white fraction was 154.8 g, which is 36% of the starting material. 
The reaction 
EQU ZrO.sub.2.SiO.sub.2 +xHF.fwdarw.H.sub.2 ZrF.sub.6 +H.sub.2 SiF.sub.6 
+4H.sub.2 O (8) 
was studied further by varying the molar ratio of HF to (ZrO.sub.2 
+SiO.sub.2) in the PDZ. It was found that the molar ratio of HF to 
zirconia and silica determined the composition and amount of the white 
fraction, as can be seen from Table 4. 
TABLE 4 
______________________________________ 
Moles HF(x) Weight % of 
used in reaction 
Weight % of product (H.sub.2 ZrF.sub.6 + 
white fraction 
(8), ie in dissolution 
H.sub.2 SiF.sub.6) formed from PDZ 
formed from 
of ZrO2.SiO.sub.2 
(initial) PDZ (initial) 
______________________________________ 
3 0 100 
4 14.8 85.2 
6 35.5 64.5 
9.6 91.4 8.6 
11.4 90.0 9.1 
20.4 91.4 8.6 
48 100 0 
______________________________________ 
12 moles of HF is needed theoretically to dissolve the ZrO.sub.2.SiO.sub.2 
fully. 
EXAMPLE 5 
40 l of a 40% HF mixture were pumped into the reactor 106. This gave a 
total of 18.56 kg pure HF. 
17 kg of 79% PDZ having a mass of 13.43 kg PDZ, was gradually fed to the 
reactor. A temperature of 88.degree. C. was reached due to the exothermic 
nature of the reaction. The mother liquor was analysed as follows: 
______________________________________ 
H.sub.2 ZrF.sub.6 = 
27.39% (mass base) 
H.sub.2 SiF.sub.6 = 
18.37% 
HF = 0.46% 
H.sub.2 O = 53.78% 
______________________________________ 
The white fraction produced in the reaction amounted to 322 g, which 
represented 2.4% of the actual mass of PDZ fed to the system. The total 
mass of H.sub.2 ZrF.sub.6(s) produced was 13.96 kg (actual) together with 
a mass of 9.71 kg H.sub.2 SiF.sub.6(l) (calculated). 
EXAMPLE 6 
Again 40f of 40% HF were pumped into the reactor 106, giving a total HF 
content of 18.56 kg HF. 
18.4 kg of 73% PDZ, giving a mass of 13.43 kg PDZ, was fed to the reactor 
within 30 minutes. The temperature increased to &gt;90.degree. C. within 5 
minutes, and cooling water was used to stabilize the temperature at 
between 80.degree. C. and 90.degree. C. 
The mother liquor was analyzed as follows: 
______________________________________ 
H.sub.2 ZrF.sub.6 = 
26.98% (mass base) 
H.sub.2 SiF.sub.6 = 
18.07% 
HF = 1.03% 
H.sub.2 O = 53.92% 
______________________________________ 
The white fraction produced in the reaction amounted to 353 g, representing 
a fraction of 2.63% of the pure PDZ fed to the reactor. 13.75 kg H.sub.2 
ZrF.sub.6(s) (actual) was produced in the run together with a mass of 9.56 
kg H.sub.2 SiF.sub.6(f) (calculated) 
EXAMPLE 7 
In this example the setup or system 100 was run at full capacity. 
45 l of 40% HF were pumped into the reactor 106, giving a nett mass of 
20.34 kg HF. 17.85 kg 87% PDZ was fed to the reactor within 30 minutes, 
giving a nett mass of 15.53 kg PDZ. Cooling water was used to stabilize 
the temperature of the reacting mixture at 85.degree. C. 
The mother liquor was analysed as follows: 
______________________________________ 
H.sub.2 ZrF.sub.6 = 
26.74% (mass basis) 
H.sub.2 SiF.sub.6 = 
17.03% 
HF = 2.57% 
H.sub.2 O = 53.66% 
______________________________________ 
A total mass of 407 g white fraction was collected which represented 2.62% 
of the PDZ fed to the reactor. A total mass of 16.85 kg H.sub.2 
ZrF.sub.6(s) (actual) was produced in the run together with a mass of 
11.72 kg H.sub.2 SiF.sub.6 (calculated). 
In all the abovementioned examples, the crystals were formed by evaporating 
between 20% and 40% of the mother liquor. The crystals were extracted and 
the remaining liquor heated in containers to produce the rest of the 
H.sub.2 ZrF.sub.6 crystals. 
During the evaporation of the volatiles, samples were taken for analyses, 
as set out in Table 5. 
Table 5 shows the compositions of the different samples taken as mass 
percentages. The total amount of condensate collected was 37% of the 
liquor (volume) used in the run. As a result of the ever-present HF in the 
system, no blockages due to SiO.sub.2(s) precipitation were found in the 
condenser. No Zr specie could be found in the condensate. 
Typical analytical results of the materials used and produced in the 
reaction, in relation to radioactive components, are summarized in Table 
6. 
TABLE 5 
______________________________________ 
Values obtained in respect of H.sub.2 SiF.sub.6, 
HF and H.sub.2 O in volatile fraations. 
Fraction % H.sub.2 SiF.sub.6 
% HF % H.sub.2 O 
______________________________________ 
1 1.85 2.84 95.31 
2 3.57 4.37 92.06 
3 4.81 4.61 90.58 
4 6.95 4.65 88.40 
5 10.67 4.23 85.10 
6 15.28 4.22 80.50 
7 24.73 2.75 72.52 
8 32.38 1.53 66.09 
9 36.02 2.32 61.66 
______________________________________ 
TABLE 6 
__________________________________________________________________________ 
Alpha 
Beta Uranium 
Thorium 
Radiation 
Radiation 
Radiation 
Radiation 
Radiation 
Concentration 
Concentration 
from from from 
-.alpha. 
-.beta. 
-U! -Th! .sup.226 Ra 
.sup.228 Ra 
.sup.224 Ra 
SAMPLE Bq/g Bq/g .mu.g/g 
.mu.g/g 
Bq/g 
__________________________________________________________________________ 
PDZ raw material 
57 28 400 150 4.2 0.5 0.5 
H.sub.2 ZrF.sub.6 
14 7 166 61 0.4 0.04 0.18 
White fraction 
923 261 444 691 43 6.03 2.05 
__________________________________________________________________________ 
EXAMPLE 8 
2 l of a solution containing H.sub.2 ZrF.sub.6 and H.sub.2 SiF.sub.6, with 
a uranium concentration of 89.5 .mu.g/ml and 4.5% free hydrofluoric acid, 
was run through a 50.0 g Purolite S940 column at a flow rate of 1.32 
cm/min. The column had an inner diameter of 38 mm. Twenty fractions of 100 
ml were collected and analysed for uranium by neutron activation analysis. 
The analysis results showed that the resin was able to remove 81% uranium 
at 200 ml solution with a resulting resin capacity of 0.32 mg U/g resin. 
90% breakthrough was reached at 2000 ml solution with a resulting capacity 
of 1.11 mg U/g resin. 
EXAMPLE 9 
29 l of a solution containing H.sub.2 ZrF.sub.6 and H.sub.2 SiF.sub.6, with 
a uranium concentration of 45.5 .mu.g/ml and 7.7% free hydrofluoric acid, 
was run through a 50. 0 g Purolite S940 column at a flow rate of 1.32 
cm/min. The column had an inner diameter of 38 mm. Twenty fractions of 100 
ml were collected and analysed for uranium by neutron activation analysis. 
The analysis results showed that the resin was able to remove 71% uranium 
at 200 ml solution with a resulting resin capacity of 0.15 mg U/g resin. 
Total breakthrough was reached at 1900 ml solution and the total capacity 
was 0.39 mg U/g resin. 
EXAMPLE 10 
8.75 g H.sub.2 ZrF.sub.6 crystals were reacted with 402 g of superheated 
steam over a period of 2 hours in a static oven, at a temperature of 
650.degree. C. The evolved HF was condensed in a suitable condenser. 5.25 
g of ZrO.sub.2 was formed. XRD-analysis confirmed that the product was 
ZrO.sub.2. The HF that was condensed, had a concentration of more than 
40%. The purity of the ZrO.sub.2 is summarized in Table 6. 
TABLE 6 
______________________________________ 
ppm ppm ppm ppm ppm ppm 
% Zr % Hf % Si % F.sup.- 
Ti Al Fe Ca U Th 
______________________________________ 
73.2 1.0 0.03 0.78 &lt;100 285 772 208 109 21 
______________________________________ 
EXAMPLE 11 
1.5 kg H.sub.2 ZrF.sub.6 crystals were reacted with 1 kg of superheated 
steam in a dynamic "paddle oven" at a temperature of 730.degree. C. The 
feed rate of the solids to the oven was 50 g/min. The feed rate of the 
steam was 500 g/h. The average residence time of the solids in the oven 
was 31/2 hours. XRD analysis confirmed that the product was ZrO.sub.2 
--see FIG. 5. About 600 g of ZrO.sub.2 was withdrawn from the product 
outlet, with the rest of the ZrO.sub.2 still contained in the dead volumes 
in the inside of the oven. The purity of the final product is summarized 
in Table 7. 
TABLE 7 
______________________________________ 
ppm ppm ppm ppm ppm ppm ppm 
% Zr % Hf Si % F.sup.- 
Ti Al Fe Ca U Th 
______________________________________ 
69.1 1.1 &lt;10 0.30 &lt;10 &lt;10 901* &lt;10 425 &lt;10 
______________________________________ 
*The high Fe content is due to corrosion contamination from a stainless 
steel oven component. 
Thus, the process 10 is environmentally friendly in the sense that no 
unmanageable waste products are produced, and essentially all the HF is 
recovered for reuse, which enhances cost-effectiveness. 
Further advantages of the process 10 include the following: 
zirconium products with low U and Th content can be obtained in 
cost-effective manner from baddeleyite and zircon; 
primary dissolution of the zirconia or DZ in the reaction stage 18 and 
secondary purification in the evaporation stage 30 is effected in the same 
medium, ie HF solution, leading to good efficacy and cost-effective 
processing; 
feed contaminants such as Si, Fe, Ti, Al, U and Th are removed 
substantially entirely in a cost-effective manner by selective 
dissolution, selective precipitation, recrystallization, ion exchange and 
combinations hereof, as described hereinbefore; 
any residual HF in any process or product stream can easily be rendered 
harmless by means of lime precipitation.