Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Reexamination Certificate
2000-08-24
2002-09-10
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
C423S132000, C423S082000, C423S083000, C423S150100
Reexamination Certificate
active
06447738
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to aluminum and alumina mineral-extraction processes, and more specifically to processes which include a basic aluminum alkali sulfate as an intermediate-stage product instead of aluminum hydroxide.
2. Description of the Prior Art
Conventional methods for producing aluminum are not environmentally friendly. The aluminum industry is estimated to produce at least forty million metric tons of greenhouse-gas emissions worldwide each year. The use of so-called “inert anodes” in the production of aluminum has long been recognized as a solution to these emissions, but the high electrolysis temperatures needed, e.g., 950° C., have proven too challenging for commercial production.
The “Bayer process” is the most common, and uses a caustic as an extractant on alumina feedstock. Both U.S. Pat. Nos. 5,124,008, and 5,997,828, issued to the present inventor, John Rendall, describe methods for producing alumina from bauxite and clay ore bodies by using sulfuric acid. Both are incorporated herein by reference.
Prior art systems allow both iron and aluminum values to be in solution together within the leach liquor. The caustic in the Bayer process solubilizes some silica, and loses both the alumina and caustic in the form of aluminum silicate.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a process for the efficient extraction of alumina, iron oxide and titanium dioxide from bauxite ore and clays.
It is another object of the present invention to provide an environmentally safer system for the extraction of alumina, iron oxide and titanium dioxide from bauxite ore and clays.
Briefly, a process embodiment of the present invention is a method for the extraction of alumina, iron oxide and titanium dioxide from bauxite ore and clays, and other ore bodies and feedstocks. The process starts with a sulfuric acid leaching of the feedstocks in pressure autoclaves at 180-250° C. and appropriate pressure. A leach liquor of sulfate salts of aluminum, iron and titanium is obtained. Any iron values are converted to a ferrous state. A recycled potassium sulfate helps produce double aluminum alkali sulfate crystals in the reduced leach liquor. The crystals are removed at 20° C. to 60° C. with the help of SO
2
gases that reduce the ferric ions to ferrous. Such double salt is hydrolyzed into a basic aluminum alkali precipitated sulfate salt. This is then dried and calcined at about 950° C. Any alkali sulfate is washed out and recycled. The remainder is alumina. The ferrous sulfate is crystallized out at 10° C. It is dried and calcined at about 450° C. to produce an iron oxide.
Such calcination of both alumina and iron sulfates produces gases (SO
2
+SO
3
) which are recycled to an acid plant. A bleed stream from a recycled raffinate is used to remove a titanium salt by precipitation at 90° C., e.g., using seeding and steam sparging. The bleed stream from the recycled raffinate is removed when the ratio of ferrous sulfate to TiO
2
is about 0.8:1. A TiO
2
precipitate is removed, washed, and converted for use in commercial products. Another TiO
2
removal system raffinate bleed stream helps purge impurities that would otherwise build up. Another way to remove impurities is by evaporation drying and calcining of the metal values.
An advantage of the present invention is that a process is provided that can be used at temperatures significantly lower in electrolysis for production of aluminum and therefore reduces the challenge of inert anode use at this reduced temperature.
Another advantage of the present invention is that a process is provided that significantly improves over conventional processes by converting crystallized double salt aluminum alkali sulfate into a precipitated basic double salt. It recycles about sixty to seventy percent of the water, sulfuric acid and alkali sulfate.
A still further advantage of the present invention is that a process is provided that produces iron oxide and titanium values available as hydroxides.
Another advantage of the present invention is that a process is provided that effectively overcomes conventional problems by using potassium or other alkali sulfate carriers in double salt crystallization and recycling such carriers. The benefits are the coproduction of ferrous sulfate or iron oxide for making steel. The alumina yield also increases, because silica does not affect the reaction.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment as illustrated in the drawing figure.
REFERENCES:
patent: 4244928 (1981-01-01), Ziegenbalg et al.
patent: 5124008 (1992-06-01), Rendall et al.
patent: 5997828 (1999-12-01), Rendall
F. A. Peters, P. W. Johnson, and R. C. Kirby, “Methods For Producing Alumina From Clay”, 1963, Bureau of Mines Report of Investigations 6290, US Dept. of the Interior., No month.
Ahghar Massoud
Aiken Fred A.
Fox Jerry V.
Rendall John S.
Bos Steven
Law Offices of Thomas E. Schatzel A Prof. Corp.
Schatzel Thomas E.
Solv-Ex Corporation
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