Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1999-02-09
2001-05-22
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S724000, C210S726000, C210S915000
Reexamination Certificate
active
06235203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystallization process for removing fluoride from waste water in an economic and efficient manner.
2. Description of the Prior Art
In various industries, including the production of semiconductors, chlorofluorocarbon (CFC) and glass, a large amount of fluoride-containing waste water with a high concentration of fluoride is produced. Therefore, many researchers have attempted to remove fluoride from the fluoride-containing waste water.
Jansen in U.S. Pat. No. 5,106,509 has disclosed a crystallization process for removing fluoride from waste water in a fluidized bed reactor. The process involves adding CaCl
2
into waste water to react calcium ions and fluoride in the waste water to form calcium fluoride crystals. Compared with the coagulation/precipitation process that is utilized in factories to date, the advantages of the Jansen process are that the waste sludge is decreased and can be recycled. Since calcium fluoride has a very low solubility, such a crystallization process can effectively remove a great amount of fluoride. However, another result of the low solubility is that calcium fluoride will easily supersaturate in some locations, thus generating fine particles that can clog the pipes. For this reason, in practical use, waste water discharged from the factory with a high concentration of fluoride should be diluted to a concentration lower than 500 mgF
−
/l. In order to accommodate such a great amount of diluted waste water, the cost for the apparatus and for the land for accommodating the apparatus is increased.
Japanese Patent No. 8-11232 has disclosed a coagulation process for removing fluoride from waste water. The process involves mixing fluoride-containing waste water with aluminum and sodium ions to form cryolite coagulate as a means to remove fluoride. The residual fluoride contained in the treated waste water can be further removed. A water soluble aluminum salt is added into the treated waste water at pH 7 to form flocs aluminum hydroxide [Al(OH)
3
], which can adsorb residual fluoride in the treated waste water to form a coprecipitate. The coprecipitate can be adjusted to be basic or acidic, thus forming an aluminum ion source for the coagulation process for removing fluoride from waste water according to the procedures as mentioned above.
In Japanese Patent No. 8-11232, the cryolite is in a form of coagulation. The coagulated sludge contains about 60~80% water, which is very difficult to dehydrate. In addition, the coagulated sludge is in a very large volume, and has many impurities; thus, it is not easily recycled.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems and to provide a crystallization process for removing fluoride from waste water economically and efficiently.
To achieve the object, the crystallization process for removing fluoride from waste water comprises the following steps of:
(a) introducing fluoride-containing waste water into a fluidized bed crystallizer provided with a carrier;
(b) adding a water soluble sodium reagent and a water soluble aluminum reagent into the fluidized bed crystallizer to form crystallized cryolite (Na
3
AlF
6
) onto the carrier with which the fluoride in the waste water can be removed, wherein the molar ratio of aluminum to fluorine is between 0.8~1:6, and the molar ratio of sodium to fluorine is larger than 0.5; and
(c) discharging the treated waste water from the fluidized bed crystallizer to obtain a primary treated water.
REFERENCES:
patent: 4436629 (1984-03-01), Berglund
patent: 5043072 (1991-08-01), Hitotsuyanagi et al.
patent: 5106509 (1992-04-01), Jansen
patent: 5750033 (1998-05-01), Ikeda et al.
patent: 06190373 (1994-07-01), None
patent: 06320168 (1994-11-01), None
patent: 07171577 (1995-07-01), None
M. Schöller, J.C. Van Dijk, DHV Water BV and O. Wilms, “Fluidized Bed Pellet Reactor to Recover Metals or Anions”—Metal Finishing, p. 49, col. 1, Nov. 1991.
Horng Ren-Yang
Lee Mao-Sung
Liao Chi-Chung
Industrial Technology Research Institute
Lawrence Frank M.
Simmons David A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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