Claims
- 1. A process for precipitating an acid aluminum sulfate of the formula Al.sub.2 (SO.sub.4).sub.3.0.5H.sub.2 SO.sub.4.11 to 12H.sub.2 O from an initial solution resulting from the treatment of an aluminous material with a sulfuric acid solution and containing aluminum sulfate hydrate as a result of the treatment, comprising the steps of sequentially treating the initial solution in a series of crystallizers in cascade relation by:
- (a) heating the initial solution in a first crystallizer vessel to establish a state of supersaturation of aluminum acid sulfate and wherein the composition of the solution within a triangle defined graphically by an abscissae denoting the percentage of free H.sub.2 SO.sub.4 and an ordinate denoting a percentage of sulfates of aluminum expressed as Al.sub.2 O.sub.3, wherein the triangle ABC whose vertex A represents precipitated aluminum sulfate has an abscissae of about 17% by weight and an ordinate of about 8% by weight and vertices B and C have abscissae of about 39% and about 56% respectively and ordinates of about 1% and about 0.5% by weight respectively;
- (b) maintaining the first crystallizer at a temperature at most equal to about 80.degree. C. for a solution residence time sufficient to provide a suspension that has generally reached a state of static equilibrium of precipitation of said acid aluminum sulfate;
- (c) cascading the suspension to at least a second crystallizer maintained at a temperature lower than that of a preceding crystallizer and repeating step (b); and
- (d) recovering precipitated acid aluminum sulfate of the formula Al.sub.2 (SO.sub.4).sub.3.0.5H.sub.2 SO.sub.4.11 to 12H.sub.2 O as product.
- 2. The process of claim 1 wherein the temperature of the last crystallizer in a series is between about 30.degree. C. and about 40.degree. C.
- 3. The process of claim 1 wherein the temperature of the last crystallizer is as low as about 15.degree. C.
- 4. The process of claim 1 wherein a series of successive crystallizers have about the same volumetric capacity wherein the reduction in temperature between any one crystallizer and a succeeding crystallizer is similar.
- 5. The process of claim 4 wherein a reduction of 10.degree. C. is effected between successive crystallizers.
- 6. The process of claim 1 including adding acid aluminum sulfate seed crystal recycle from a succeeding crystallizer to a preceding crystallizer.
- 7. The process of claim 1 wherein residence time in each crystallizer is in the order of about three hours.
Parent Case Info
This application is a continuation-in-part of application Ser. No. 917,067, filed June 19, 1978, now abandoned, which is a continuation of application Ser. No. 733,855, filed Oct. 19, 1976, now abandoned.
US Referenced Citations (8)
Foreign Referenced Citations (1)
Number |
Date |
Country |
584728 |
Jan 1947 |
GBX |
Non-Patent Literature Citations (1)
Entry |
Hemy et al., "Journal of American Chem. Soc.", vol. 72, 1950, pp. 1282-1286. |
Continuations (1)
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Number |
Date |
Country |
Parent |
733855 |
Oct 1976 |
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Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
917067 |
Jun 1978 |
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