Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Alkaline earth metal
Patent
1989-02-27
1990-07-31
Stoll, Robert L.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Alkaline earth metal
423155, 423164, 423497, 423639, C01F 506, C01F 510
Patent
active
049449281
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the preparation of pure magnesium oxide, especially suitable for the preparation of refractory products, from magnesium silicate and magnesium hydrosilicate materials such as olivine, serpentine, garnierite, or the like, the starting material being decomposed with hydrochloric acid, the residue being separated from the decomposition slurry and the sesquioxides to be regarded as contaminants, and other contaminants, being precipitated from the crude brine thus obtained by the addition of a pH-increasing substance, the precipitates being separated and the magnesium chloride solution thus obtained being subjected to thermal decomposition, particularly by spray-calcining, whereby magnesium oxide is obtained and hydrogen chloride is recovered.
The following are suitable as starting materials for this process: so-called ultra-mafitic rocks of the peridotite, dunite, harzburgite group and the like, the transformation products thereof, usually known as serpentine or serpentinite, weathered products of said rocks, halfproducts and byproducts arising during the processing thereof, and industrial byproducts and waste products of similar composition, as long as they have an MgO content of at least 15% by weight. These materials are called hereinafter with the term "serpentine" or "crude serpentine".
In known processes of this kind the pH-increasing substance used to precipitate sesquioxides is generally magnesium oxide, mostly in the form of caustic calcined magnesia. However, the use of such a precipitant has disadvantages. The serpentines, and similar starting materials, usually have a high content of iron and other sesquioxide contaminants and large additions of precipitant are needed. Since all kinds of caustic magnesia are costly, for the reason that they can be prepared only with a considerable expenditure especially of thermal energy, the use of caustic magnesia as a precipitating agent imposes a heavy economic burden. If pure magnesium oxide obtained as the end product of the process is used as precipitating agent, depending upon the amount of iron and other sesquioxide contaminants contained in the crude serpentine or the like starting material, up to about 30% by weight of the obtained magnesium oxide must be circulated internally, and this is economically unacceptable.
It is known from U.S. Pat. 2,398,493 to add calcined serpentine to a magnesium chloride slurry produced by decomposition of serpentine with hydrochloric acid as precipitating agent for contaminants. However, this method has the disadvantage that the silicic acid portion of the serpentine is converted, by the calcination, into a form which is more easily dissolved or suspended in the magnesium chloride slurry. The result thereof is that during the subsequent separation of the residues or precipitates a larger proportion of silicic acid remains in the magnesium chloride brine and the SiO.sub.2 content in the end product is therefore higher. In addition this increased amount of amorphous or dissolved silicic acid in the magnesium chloride slurry means that the Fe(OH).sub.3 and other hydroxide precipitates obtained during subsequent precipitation are slimy and therefore difficult to filter. Finally, a considerable amount of energy is also required to calcine serpentine.
It is the object of the invention to provide a process of the type mentioned at the beginning hereof in which the disadvantages mentioned are eliminated, which process permits economical operation, and which makes it possible to obtain easily filtered hydroxy precipitates.
The process according to the invention is characterized in that finely ground crude serpentine having a grain size of between 0 and 1mm, preferably between 0 and 0, 1mm, is used as the pH-increasing substance for precipitating oxides of iron and of aluminum.
Said precipitating agent ensures complete precipitation of aluminum and extensive precipitation of trivalent iron in the pH range below 5.
If bivalent iron is present in the starting material and if it also is to be rem
REFERENCES:
patent: 2398493 (1946-04-01), Butt et al.
patent: 2549798 (1951-04-01), Gee et al.
patent: 3980753 (1976-09-01), Grill et al.
patent: 4100254 (1978-07-01), Grohmann et al.
patent: 4200618 (1980-04-01), Pitts
patent: 4255399 (1981-03-01), Grill et al.
Chemical Abstracts, vol. 82, No. 142242x, p. 133, Jun. 2, 1975.
Hackh's Chemical Dictionary, Fourth Edition, (1969), McGraw-Hill, Inc., p. 605.
Graf Gerhard
Grill Michael
Langel Wayne A.
Stoll Robert L.
Veitscher Magnestiwerke-Actien-Gesellschaft
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