Method of hydrolyzing metal halides

A process relating to the hydrolysis of metal halides and their production of corresponding metal oxides by the hydrolysis of their chlorides and the calcining of the hydrolysis product is disclosed. Novel aspect including obviating the neutralizing step for the hydrochloric acid by using ammonia and disposing of the resulting ammonium chloride and the two step addition initially of metal halides to water until there is no observable positive heat of reaction and then adding the metal halide in amounts up to the stoichiometric quantity for the hydrolysis product obtained.

BACKGROUND OF THE INVENTION 
The present invention relates to the hydrolysis of metal halides and more 
particularly to the production of the corresponding metal oxides by the 
hydrolysis of the chloride and calcining the hydrolysis product. 
Current practice for the production of Nb.sub.2 O.sub.5 and TaCl.sub.5 
utilizes for example, NbCl.sub.5 from a ferroniobium (FeNb) chlorinator as 
the feed for Nb.sub.2 O.sub.5 production. The NbCl.sub.5 is mixed with 
H.sub.2 O forming a hydrolysed NbOCl.sub.3.xH.sub.2 O in a highly 
acidified (HCl) solution. This solution is pH adjusted with ammonia to 
further convert the NbOCl.sub.3.xH.sub.2 O to hydrolysed Nb.sub.2 O.sub.5. 
The solution is then filtered and calcined at high temperature to produce 
dry Nb.sub.2 O.sub.5. The addition of ammonia is expensive and produces a 
waste disposal problem. Further, the addition or loading of NbCl.sub.5 to 
water is limited in the present practice to about 2 lbs of NbCl.sub.5 per 
gallon of water. The filtration of the ammoniated NbCl.sub.5 water mixture 
is required to eliminate excess water and decrease the mass of material 
going to the kiln which typically would then contain only 15% to 20% 
solids. Finally the prior use of ammonia produced ammonium chloride in the 
off gases from the kiln which required a large flue gas scrubbing 
capacity. 
It is therefore an object of the present invention to eliminate the use of 
ammonia in the production of Nb.sub.2 O.sub.5 by the hydrolysis of 
NbCl.sub.5. 
It is a further object of the present invention to increase the production 
of Nb.sub.2 O.sub.5 while decreasing the volume of water required. 
It is also an object of the present invention to provide a more energy 
efficient process for the production of Nb.sub.2 O.sub.5. 
SUMMARY OF THE INVENTION 
It has been discovered that the hydrolysis of NbCl.sub.5 if done at a 
loading greater than about 3 pounds per gallon of water produces a fluid 
mixture which can be directly charged into a calcining kiln to produce 
Nb.sub.2 O.sub.5.

DETAILED DESCRIPTION OF THE INVENTION 
Conventionally the hydrolysis of the chlorides of niobium, tantalum 
vanadium and titanium have all employed a neutralizing step, e.g. ammonia 
to produce a solid suitable after filtering for charging into a kiln. As 
previously described, the process steps thought to be necessary limited 
the loading of the chloride in the water and produced further process 
complications and inefficiencies. 
The process steps shown in Table 1 compare the prior process to the process 
of the present invention when hydrolyzing NbCl.sub.5. 
TABLE 1 
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Old Process Process of This Invention 
______________________________________ 
1.8# NbCl.sub.5 15# to 20# NbCl.sub.5 
+ + 
1 gal H.sub.2 O 1 gal H.sub.2 O 
+ 
NH.sub.4 OH Kiln (750.degree. C.) 
Filtration 400 to 600#/hr 
waste HCl 
liquor to 
Kiln (1000.degree. C.) 
Nb.sub.2 O.sub.5 
scrubber 
200 to 400# for 
Nb.sub.2 O.sub.5 /hr recovery and 
sale or use 
waste 
NH.sub.4 Cl to 
scrubber 
Nb.sub.2 O.sub.5 
______________________________________ 
It will be clearly seen that the steps of adding ammonia and filtering have 
been eliminated. Likewise, since the niobium loading or concentration is 
so much higher in the process of the present invention, the evaporative 
loading of the kiln is lower and therefore the overall process efficiency 
increases since the kiln can process more oxide with less fuel, at lower 
temperatures. 
It is surmised that the prior process was designed with the highly acidic 
nature of the chlorides in mind and the perceived need to protect 
downstream process equipment. These concerns then dictated the use of a 
large volume of water and the step of neutralizing the solution. Further, 
loading NbCl.sub.5 into water at the level of one to two pounds per gallon 
produced a significant heat of reaction and heat of solution which raised 
concerns about the containment of the materials when the mixture became 
hot enough to boil out liquid HCl above its dew point and perhaps even 
NbCl.sub.5. 
Surprisingly, it has been discovered that continued additions of the 
chloride does not continue to heat the solution. Initial additions, i.e. 
up to two to three pounds per gallon will raise the temperature of the 
water to 70.degree. C. to 90.degree. C. At this point the temperature 
stopped rising as further additions were made and there were indications 
that the heats of reaction and/or solution had indeed ceased being 
positive and even turned from positive to negative, permitting substantial 
additions up to a point where one half of the stoichiometric amount of 
NbCl.sub.5 to available water was reached. In addition to this phenomenon 
the solution which was becoming more viscous at the two to three pounds 
per gallon level began to become more fluid and would accept up to about 
25 pounds of NbCl.sub.5 per gallon of water before the viscosity again 
rose sufficiently to pose a problem for continued stirring and pumping. 
The liquid after mixing was capable of being fed directly into the kiln 
even though it was highly acidic i.e. a pH less than 1, with respect to 
HCl. Large volumes of HCl are given off in the mixing of NbCl.sub.5 with 
water as well as in the direct firing in the kiln by a variety of 
reactions which would include, but not be limited to: 
EQU NbCl.sub.5 +H.sub.2 O.fwdarw.NbOCl.sub.3 +2HCl 
EQU 2NbOCl.sub.3 +3H.sub.2 O+HEAT.fwdarw.Nb.sub.2 O.sub.5 +6HCl 
HCl gas with water is very corrosive at temperatures below the dew point or 
approximately 100.degree. C. Care should then be taken in the selection of 
materials for the mixing tank and any scrubber over the tank using 
materials that are not attacked by warm HCl. Likewise the scrubber on the 
kiln has to be designed so that hot kiln off gas will reach the scrubber 
before cooling to the dew point, but will operate at a cool enough 
temperature so that the materials selected are not harmed by heat from the 
kiln. It was found that the HCl gas or acid is more easily scrubbed with 
water or HCl acid than the prior scrubbing required to remove the NH.sub.4 
Cl of the ammonia neutralization process system. 
The following experiments were designed and conducted to evaluate the 
prospect of increasing the NbCl.sub.5 loading in the conventional process. 
EXPERIMENT 1 
The first experiment was to see how much NbCl.sub.5 could be added to 
water, since an obvious disadvantage of the prior process was the large 
amounts of water involved. 
The experimental design was simply to add 222 g NbCl.sub.5 to 500 ml of 
water, or double the normal loading, in 10 g increments. At the same time, 
any temperature variations would be noted along with general observation 
of the changing nature of the mixture. 
The procedure was as follows for two times the usual concentration of 1.85 
pounds/gal: 
A 2000 ml beaker with 500 ml of H.sub.2 O was packed in an ice bath with a 
stirrer to assist mixing and/or dissolution of the NbCl.sub.5. 
After adding about half the 222 g of NbCl.sub.5, the mixture became so 
thick, like mud, that it stopped the stirrer motor and the temperature had 
risen to 57.degree. C. Adding more NbCl.sub.5 up to 222 g the temperature 
reached 69.degree. C. but the mixture became thin and watery and stayed 
that way down to 10.degree. C. After standing overnight without stirring, 
it looked like a thick lemon milk shake. 
EXPERIMENT 2 
A second experiment gave the following results: 
Objective: To add three times normal, or 333 g, NbCl.sub.5 to 500 mls 
water. As the experiment proceeded, it was decided to add more NbCl.sub.5. 
TABLE 2 
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Total Temperature 
NbCl.sub.5 
of 
NbCl.sub.5 Addition 
Added Mixture .degree.C. 
Observations 
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0 0 10.degree. C. 
In ice bath 
135 g 135 g 60 Thick like mud 
+178 g 313 g 60 Thin, watery 
+43 g 356 g 75 More watery 
+97 g 453 g 26 Still watery 
+350 g 803 g 
+92 g 895 g 31 NbCl.sub.5 would sit on top 
for a while before 
mixing in. Ice 
completely melted. 
+105 g 1000 g 26 very liquid 
Net weight of the mixture 
1250 g 
volume 625 cc 
density 2 g/cc 
______________________________________ 
The mixture was then poured into a quartz tray heated on a hot plate for 
preliminary drying. When there was no apparent moisture in the mix, it was 
then calcined at 1000.degree. C. for 11/2 hours in a muffle furnace. 
EXPERIMENT # 3 
This experiment was a repeat of Experiment 2 but without the ice bath and 
more rapid addition of the NbCl.sub.5 up to 1.5 times as much, or 1550 g, 
for 500 ml of water. 
TABLE 3 
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Total Temperature 
NbCl.sub.5 
of 
NbCl.sub.5 additions 
Added Mixture .degree.C. 
Observations 
______________________________________ 
0 0 23 
375 g 375 g 85 No thickening like 
occurred in the ice 
bath experiments. 
375 g 750 g 45 NbCl.sub.5 floating on top 
and dissolving slowly. 
250 g 1000 g 37 Long dissolving time, 
minutes. 
500 g 1500 g 18 Mixture is thickening 
but still very fluid. 
As soon as stirring 
stops, a skin forms on 
the top. 
Considerable fuming is evident during mixing, which is largely 
HCl. 
Net weight 
1450 g 
Volume 575 cc 
Density 2.5 g/cc 
______________________________________ 
The mixture was then dried in a quartz tray on a hot plate and calcined at 
1000.degree. C. in a muffle furnace for 11/2 hours 
In an experiment to check recoveries of Nb.sub.2 O.sub.5 from NbCl.sub.5, 
the mixing, drying and calcining were done in one vessel with a resulting 
recovery of 97.5%. 
Further laboratory experiments show that the high loading of TaCl.sub.5 
into water exhibits much the same behavior as NbCl.sub.5. At the first 
additions of TaCl.sub.5, there is a rapid rise of both temperature and 
viscosity as the loading of TaCl.sub.5 continued. The following are two 
experiments conducted in the laboratory. 
______________________________________ 
Experiment #1 
TaCl.sub.5 
Temperature 
Time Added Before-After 
Min. grams .degree.C. 
______________________________________ 
0 5 20.5-32 Bright yellow solution 
2 5 ---41 
4 5 38-48 
6 5 41-50 
8 5 46-45 Solution became thick, and as 
it cooled, even thicker 
Stir Motor Failed and Was Changed 
23 5 26-31 Consistency of cream cheese-- 
bright yellow 
27 5 25-38 
-- 5 37 
-- 5 33-39 
34 5 35-37 Darker yellow color like 
mustard--same consistency 
36 5 34-37 
38 5 35-36 Looking watery 
40 5 35-35 Thinner and more watery 
42 5 35-33 Thinner still 
44 5 33-32 Dark yellow, consistency of 
mustard 
47 5 26-27 
49 5 26-27 Turned greenish 
-- 10 26-28 Starting to thicken again 
54 10 21-26 Skin forming on top of solution 
56 10 24-24 
-- 10 21-21 
-- 10 19.5-17 Getting very thick, turning 
green gray 
-- 10 17-15 Stalled stir motor, looks like 
glue 
64 10 15.5-16 Semi solid lump 
10 16-13.5 Thick blob 
69 10 15-15 TaCl.sub.5 did not mix in at this 
point 
Total 175 
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About 3.3 g of TaCl.sub.5 per ml of water was the maximum loading reached. 
In terms of having a pumpable slurry, mix or solution, the optimum loading 
appears to be 1.5 to 1.9 g of TaCl.sub.5 per ml of water. This is a lower 
loading than was obtained with NbCl.sub.5 in water, but still exhibits a 
similar and useful cooling effect with a more watery consistency. Recovery 
is approximately 94%. 
EXPERIMENT #2 
In this experiment, the additions of TaCl.sub.5 were larger and more rapid 
to a total of 150 g in 50 mls of water. 
______________________________________ 
TaCl.sub.5 
Temperature 
Time Added Before-After 
Min. grams .degree.C. 
______________________________________ 
0 25 21-71 Thick yellow paste 
-- 25 57-65 
6 25 55-53 Looks Watery--greenish in color 
8 25 46-42 Stir motor stalled, chunky 
yellow-green 
13 25 42-34 Dry looking mud, stirred by 
hand 
-- 25 32-24 Almost solid 
Total 150 
______________________________________ 
The rapid heating and thickening are at first evident at 0.5 g per ml of 
water, then at 1.5 g TaCl.sub.5 /ml water it is obviously watery and 
cooling. The temperature drops rapidly at 2.0 g TaCl.sub.5 ml water and 
the mix thickens. 
It is apparent from the foregoing that the same advantages exist in 
producing Ta.sub.2 O.sub.5 from TaCl.sub.5 as described for NbCl.sub.5 to 
Nb.sub.2 O.sub.5 conversion even though the loading figures are somewhat 
lower. 
The foregoing descriptions of the present invention demonstrates several 
important differences and advantages over the prior conventional practice. 
First, only water and a kiln are required to form Nb.sub.2 O.sub.5 from 
NbCl.sub.5. This elimination of the neutralization step produces several 
important advantages, including cost savings in material, labor and 
equipment in both the running of the process and the handling of 
by-product waste from the process. 
Finally, the calcined oxide produced by the practice of the present 
invention exhibits a higher bulk density without further processing than 
the product of the prior process. This property makes the product more 
suitable for subsequent processing into the pure metal or use in niobium 
containing ceramics. 
The invention has been described in terms of its preferred embodiments, 
however, it will be appreciated that the process is applicable to the 
hydrolysis of any metal chloride with or without subsequent conversion to 
the oxide. It is therefore contemplated that the invention is not limited 
to the embodiments described and should only be limited in scope to the 
scope of the appended claims interpreted in view of the pertinent prior 
art.