Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Reexamination Certificate
2000-09-05
2001-09-04
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
C423S658500, C423S626000, C423S628000, C423S328100, C065S019000, C065S031000
Reexamination Certificate
active
06284207
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to selective leaching to obtain a residual material with improved properties and, more particularly, to selective leaching of the different components of blast furnace slag using a controlled process and array of chemicals to obtain a residual silica alumina framework which has considerable surface area and catalytic activity.
2. Description of the Background
The concept of conversion of an inert slag to a catalyst support having surface area and porosity is known in the art. For example, U.S. Pat. No. 4,545,797 to Elattar teaches a process for the manufacture of porous slag from inert slag. Elattar discloses the process for the manufacture of slag having high surface area comprising the following steps (i) calcining the slag (ii) grinding the calcined slag to a size 0.1-0.3 mm (iii) leaching the ground material with aqueous acid having a pK
a
of 1-5 or base having a pK
b
of about 2-6 or a combination thereof. The Elattar process is a one step non-selective leaching operation at an unspecified high temperature. This indiscriminate leaching at an indiscriminate temperature leaches out the desired alumina required for acid catalysis. Moreover, Elattar's leaching agents are NaOH or HF, both of which dissolve silica (see column 3, line 21). As a result, the end product of Elattar's process yields an unspecified framework with surface areas of 13.5 m
2
/g and having “macro-porosity” (therein defined as an average surface area of at least 200 m
2
/g). The resulting slag, representing the synthesis of a high surface area material from an essentially zero porosity and non-existent surface area slag, can be used as a catalyst support, or in building materials, or in the ceramic industry.
There remains a need for a more controlled and selective process for slowly leaching undesired metal oxides in a controlled fashion. It is desirable to produce an end product having micro-porosity with surface areas an order of magnitude greater (between 500 and 200 m
2
/g). In general, the smaller the pores, the greater the surface area, adsorption, and chemical reactivity/selectivity.
U.S. Pat. No. 4,803,188 to Aulich et al. discloses the synthesis of a heterogeneous catalyst based on silicon dioxide and incorporating other metal oxides insoluble in mineral acid. Mined silica is used as a starting material and to it glass-forming additives of aluminum oxide, carbonates of alkali and alkaline earth metals, and desired catalytically active metal oxides (e.g. oxides of iron or zinc) are added and the mixture is heated to form a homogenized melt which is converted to fiber form and the resulting fiber is treated with hot acid to leach out the glass forming additives and other impurities. The resulting porous silicate material has the desired catalytically active metals incorporated into its framework. The fusion of metal oxides having a soluble component and an insoluble component to synthesize a catalyst is also taught by Aulich et al. It is well known that alumina can be leached from amorphous SiO
2
/Al
2
O
3
(e.g., metakaolin clay) with acid yielding a silica with meso-porosity. Therefore, the Aulich method cannot produce a silica/alumina with micro-porosity. Aulich also has the disadvantage in that any occluded alkali metals would be unleachable and destructive to any surface area in high temperature applications.
In summary, neither of the processes of Elattar nor Aulich are capable of producing a silica/alumina micro-porous material, and neither patent teaches or suggests specific products that can be obtained by the selective and controlled removal of the calcium and/or magnesium oxides from blast furnace slag, nor the resulting hierarchy of dissolution from the controlled leaching, nor the improved properties such as greatly increased surface area that can be attained by giving one the choice and flexibility from hierarchical leaching.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved controlled process for controlled selective leaching, and the resulting product is a residual material with improved properties including increased surface area and potential catalytic activity.
It is another object to provide a controlled process for selective leaching out of metal oxides from blast furnace slag using an array of chemicals to obtain a residual silica alumina framework with micro-porosity suitable for use as a catalyst or for catalyst support.
It is a specific object to effect controlled selective leaching in order to capitalize on the resulting hierarchy of dissolution, thereby allowing one the choice and flexibility as no other process can.
According to the present invention, the above-described and other objects are accomplished by providing various embodiments of an improved controlled process for leaching blast furnace slag and other solid solution materials, and the resulting products derived from the process. Blast furnace slag is a solid solution with a chemical composition based on CaO+MgO+SiO
2
+Al
2
O
3
=100%.
CaO
MgO
SiO
2
Al
2
O
3
Mean Wt. %
40.8
10.1
37.8
11.3
Standard Deviation %
4.6
4.4
2.6
2.8
Chemical concentrations less than 1% include oxides of iron, potassium, sodium, titanium, and elemental sulfur. In this invention the different components of the blast furnace slag are selectively leached using an array of chemicals to obtain useful materials. For example, acid leaching of the slag leaves a residual silica alumina framework which has considerable surface area and catalytic activity.
The improved process for leaching blast furnace slag and other solid solution materials generally comprises controlling the leaching by the controlling the following variables:
1. Temperature during leaching (should be ambient).
2. Rate of addition of acid (dropwise and slowly in order to maximize the removal of CaO and MgO and minimize the removal of Al
2
O
3
, preferably while monitoring the pH to ensure that it does not go below 2.0.)
3. Type of the acid (preferably HCl).
4. Concentration of the acid: 37% HCl
5. Concentration of the slag in the slurry: 4% to 10% granulated slag in water.
When these variables are controlled as shown a hierarchy of dissolution occurs. The hierarchy begins with MgO, progresses to CaO, and is followed by Al
2
O
3
, and the rate of acid addition is slow and controlled so that alumina does not dissolve (thereby depriving the remaining silica has no acid sites or catalytic activity). By invoking the hierarchy one gains the choice, flexibility and selectivity that no other process can offer.
REFERENCES:
patent: 3676366 (1972-07-01), Podschus et al.
patent: 4017425 (1977-04-01), Shiao
patent: 4142994 (1979-03-01), Alafandil
patent: 4367215 (1983-01-01), Gjelsvik et al.
patent: 4539187 (1985-09-01), Russ et al.
patent: 4545797 (1985-10-01), Elattar
patent: 4601997 (1986-07-01), Speronello
patent: 4704265 (1987-11-01), Krohn et al.
patent: 4803188 (1989-02-01), Aulich et al.
patent: 4891130 (1990-01-01), Pitts
patent: 5112584 (1992-05-01), Mejdell
Griffin Steven P.
Ildebrando Christina
Law offices of Royal W. Craig
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