Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ivb metal
Reexamination Certificate
2000-03-31
2002-03-19
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ivb metal
C423S544000
Reexamination Certificate
active
06358484
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is directed to processes for producing zirconium basic sulfate. More particularly, the present invention is directed to processes for producing zirconium basic sulfate from a zirconium oxychloride solution. The present invention is additionally directed to materials that include zirconium basic sulfate. The invention finds application in, for example, the production of zirconium basic sulfate from zirconium metal, zirconium scrap, zirconium-containing ores, and other materials including zirconium in metallic or other forms.
DESCRIPTION OF THE INVENTION BACKGROUND
Zirconium sulfate, also called zirconium basic sulfate or “ZBS”, is a key intermediate in the manufacture of zirconium chemicals from ores. It is currently a multi-million kilogram per year industry. The ores that are processed into ZBS are chiefly zircon, ZrSiO
4
, and to a much lesser extent, baddeleyite, which is impure ZrO
2
. The two most common means of opening the ores are caustic fusion and carbochlorination. These means are well known and are generally described in, for example, Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 24, Third Edition, 1984, p. 863, the substance of which is hereby incorporated herein by reference. Carbochlorination utilizes zirconium tetrachloride as a source of zirconium ions in producing zirconium sulfate, but that process is disadvantaged, in terms of yield, relative to the caustic fusion process.
In the caustic fusion process, zircon ore is fused with sodium hydroxide, or in variations, with sodium carbonate or lime. The product of the fusion is called a “frit” and is contacted with water to dissolve and remove the silicon moiety as, for example, sodium silicate in the case where the ore is fused using sodium hydroxide. The leached frit is then dissolved in hydrochloric acid to yield a zirconium oxychloride solution. Because the stoichiometric ratio of zirconium oxychloride is two moles of hydrochloric acid for every mole of zirconium, there is little point in adding more hydrochloric acid than is necessary to dissolve the washed frit. Formation of zirconium oxychloride solution in this way is described in, for example, Beyer, et al., Ames Laboratory Report ISC 437 (Dec. 28, 1953), the substance of which is hereby incorporated herein by reference. A method for preparing a commercial ZBS from the zirconium oxychloride solution is described in, for example, U.S. Pat. No. 1,316,107, which also is incorporated herein by reference. A source of sulfate ions, such as sulfuric acid, is added to the zirconium oxychloride solution, and the mixture is then heated with stirring until a precipitate of ZBS forms. The mixture is allowed to digest for a period of time to allow substantially complete precipitation of ZBS as fine particles in the reaction vessel. The warm reaction mixture is filtered and washed to give a moist paste or cake of ZBS which is substantially free of all the metallic impurities that occur in the zirconium-containing ore. The filtrate contains zirconium ions that do not react to form product and, hence, are a yield loss.
In the alternate process for ZBS production, carbochlorination, zirconium values are typically first converted to zirconium tetrachloride by the high-temperature reaction of a mixture of zirconium-containing ore, a carbon source such as coke, and a chlorinating agent such as chlorine. In the case of zircon, this reaction produces substantially equimolar quantities of zirconium tetrachloride and silicon tetrachloride, ZrCl
4
and SiCl
4
, respectively, as well as chlorides of many of the impurities present in the ore. Because silicon tetrachloride is a valuable product useful in, for example, producing fiber optic silica, carbochlorination makes use of the zirconium-containing ore's silicon content, which is merely discarded as a component of a waste sludge in the caustic fusion process. Zirconium tetrachloride is a fuming subliming solid and reacts vigorously and irreversibly with water to form a zirconium oxychloride solution. The zirconium oxychloride solution derived from the zirconium tetrachloride may then be reacted with sulfuric acid, as described above in connection with the caustic fusion process, to produce ZBS.
The amount of hydrochloric acid used to dissolve the leached frit in the caustic fusion process is the minimum amount required to allow the dissolution to occur in a convenient time period. In practice, this amount is that which meets any unneutralized caustic plus the stoichiometric ratio of 2HCl:1Zr, plus a further increment so that the dissolution will be suitably rapid. Ordinarily, this results in a HCl:Zr ratio somewhat larger than 2. Thus, zirconium oxychloride-containing solutions made for ZBS preparation via the caustic fusion process will have an acidity somewhat above 2 moles/liter of hydrogen ion concentration per mole/liter of zirconium. By contrast, zirconium oxychloride-containing solutions prepared from zirconium tetrachloride are found to have a HCl:Zr ratio of about 3.5 to 3.8, with a correspondingly higher acidity. When the higher acidity solutions are converted to ZBS (all other conditions of metal loading, sulfate:Zr ratio, reaction time, and temperature being kept constant), a lower yield of ZBS is obtained. Because zirconium ions lost to the filtrate during precipitation of ZBS are relatively dilute in a large volume of acid, they are not economically recoverable, and end up as a valueless sludge. Thus, the filtrate left upon separating the ZBS precipitate in carbochlorination contains a much higher quantity of unreacted zirconium ions than in the caustic fusion process and, consequently, the yield of ZBS is much lower in the carbochlorination process than in the caustic fusion process.
The carbochlorination process is well known and is disclosed in, for example, U.S. Pat. No. 1,376,161, the entire disclosure of which is hereby incorporated herein by reference. The '161 patent does not refer to the yield deficiency of that method. The caustic fusion process, on the other hand, although providing a higher yield of ZBS, does not provide a means to recover the silicon values from zirconium-containing ore, as in the carbochlorination process.
An alternative to the caustic fusion and carbochlorination processes is to react materials containing metallic zirconium with chlorine at high temperatures to recover zirconium from the materials as zirconium tetrachloride. A carbon source is not necessary in that process. The process, however, requires a starting material composed of or including zirconium metal, which excludes the use of, for example, zircon and baddeleyite ores. In addition, chlorination of metallic zirconium is highly exothermic and difficult to control.
Various means have been attempted to raise the yield of ZBS from zirconium tetrachloride. For example, it is known that it is possible to recoup lost yield from a zirconium tetrachloride solution by neutralizing some excess acidity. This may be accomplished by adding any of the basic reagents sodium hydroxide, sodium carbonate, or ammonia to the sulfate reaction mix. Adding such reagents increases cost and introduces undesirable foreign positive ions, such as sodium or ammonium, into the reaction mix. For most downstream applications of ZBS, the amounts of foreign positive ions retained in the ZBS cake are unacceptable. Furthermore, precipitations conducted under these more basic conditions risk co-precipitating metallic impurity ions, such as iron or aluminum ions.
It is also known in the art to increase yield in the ZBS precipitation step by forcing the precipitation or by lowering the mole ratio of sulfate to zirconium. For example, if ZBS is first made using a ratio of sulfate to zirconium of 3:5, a reaction similar in all other respects except using a ratio of 2:5 will provide a higher ZBS yield. It also is known to incre
ATI Properties Inc.
Bos Steven
Viccaro P. J.
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