Production of aluminum sulfate from coal ash

Details Production of aluminum sulfate from coal ash Production of aluminum sulfate from coal ash

1996-11-14

2001-04-10

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Treating mixture to obtain metal containing compound

Group iiia metal or beryllium

C423S140000, C423S556000

Reexamination Certificate

active

06214302

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to improvements in the production of aluminum sulfate from the alumina content raw materials.
BACKGROUND OF THE INVENTION
Crystals of alumina sulfate can be obtained by treating minerals containing alumina with sulfuric acid, extracting aluminum salts from the minerals-and crystallizing aluminum sulfate from the extracted solution. Crystalline sulfate can also be obtained together with iron sulfate from waste sulfuric acid or the like which contains considerable amount of iron and aluminum. However, aluminum sulfate crystals cannot be separated easily from crystals of the other metals in these processes.
Herefore, technically pure aluminum sulfate crystals have been generally obtained by crystallizing the impure aluminum salts from previously purified aluminum sulfate solutions. However, these purification procedures have been troublesome and it has been difficult to obtain pure aluminum sulfate crystals inexpensively by such prior art methods. A need, therefore, continues to exist for a simple, low-cost method of obtaining pure, crystalline aluminum sulfate.
SUMMARY OF THE INVENTION
The object of this invention is to provide a new, low-cost method of producing aluminum sulfate purified of iron, which complies with the chemical specifications of the American Water Works Association B403-88 and Federal specification O-A-429D, Type 1, Class 1 and 2, and which may be certified by the National Sanitation Foundation (NSF) for use in the treatment of drinking water at the maximum dosage of 150 mg/l. The required aluminum content is 17% (as aluminum oxide) and maximum of 0.75% of water soluble iron (as iron oxide). The weight ratio of Al
2
O
3
to maximum allowable Fe
2
O
3
content is 22.67.
The objective can be achieved by a process of selective settlement of iron phosphate from the extracted solution of aluminum sulfate with impurities separately from aluminum salts. As a result of this process a pure aluminum sulfate solution with a weight ratio of Al
2
O
3
to Fe
2
O
3
not less than 22.67 can be obtained.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
In the process of the present invention an extracted solution of aluminum sulfate with impurities of iron sulfate is treated with a solution of sodium phosphate (or any other water soluble phosphate salt, or phosphoric acid). The amount of the sodium phosphate should be enough for the completion of the iron precipitation (in our examples 30-100%), and the pH level of the extracted solution is between 2.0-4.0.
It is known that the phosphate salts of aluminum, iron, and other impurities which may be present in the extracted solution are not soluble in water. The solubility constant of the salts are presented in the Table entitled “Solubility Product Constants” of the Handbook of Chemistry and Physics, 67th Edition, p. B-207. According to these data the addition of the sodium phosphate (or any water soluble phosphate salt, or phosphoric acid) should precipitate the above mentioned metals as phosphate salts. In our process of aluminum sulfate production, due to certain pH or extracted solution, we achieved the selective precipitation of iron phosphate. The aluminum sulfate stays in the solution. This unexpected effect of pH and probably other unknown factors will allow us to obtain the technically pure aluminum sulfate.


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patent: 290554 (1991-06-01), None
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