Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2002-02-12
2003-12-23
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C203S034000, C159S047300, C210S718000, C210S724000, C210S737000, C210S750000, C423S321100, C423S490000
Reexamination Certificate
active
06666973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to a method of fixing and eliminating fluorine and phosphorus in waste water including a fluorophosphate compound.
2. Description of the Related Art.
In recent years, a fluorophosphate compound has been taken into confidence in every direction, and has been increased in quantity consumed. Among others, lithium hexafluorophosphate has been rapidly increased in quantity demanded as an electrolyte for a secondary lithium ion battery. Waste water which arises when a hexafluorophosphate is produced, or when a battery is manufactured, or a waste battery is withdrawn, is necessarily contaminated with fluorophosphoric acid. Since fluorophosphate compounds including PF
6
−
are stable, it is difficult to eliminate fluorine therefrom by merely adding a calcium salt thereto for treatment. In particular, when it is desired to decrease fluorine to an amount of 50 ppm or less in remaining concentration, it is difficult to decrease to such a concentration.
As a method of fixing fluorine from waste water including fluorine so as to eliminate the same, a method which comprises adding a calcium salt thereto so as to produce calcium fluoride to eliminate the same has been commonly used. However, in the case of waste water including a fluorophosphate compound, it is difficult to fix fluorine and/or phosphorus according to this conventional method wherein a calcium salt is added thereto for treatment.
On the other hand, as a method of fixing fluorine in waste water including a fluorophosphate compound, a technique as described in Japanese Patent Kokai (Laid-Open) No. 170380/94 is known.
This technique is the one of fixing fluorine as calcium fluoride, wherein sulfuric acid is added to waste water including fluorophosphate ions so that the concentration of sulfuric acid can be in the range of about 25% to about 35% by weight, and it is heated at a temperature of 200° to 80° C. for a period of 0.5 to 2 hours, and thereafter, a calcium compound is added thereto.
However, according to this technique, because of using a large amount of sulfuric acid, a large amount of calcium hydroxide is required for neutralizing iron content therein. Furthermore, as result of neutralization, a large amount of calcium sulfate is produced as a by-product, and thus it is necessary to treat the same as industrial wastes.
Besides, the amount thereof to be treated as industrial wastes is immense. For example, when waste water including about 70000 ppm of F is treated in an amount of 1000 kg, a cake thereof is caused as industrial wastes in an amount of 1000 to 1100 kg.
It is an object of the present invention to provide a method of fixing and eliminating fluorine and phosphorus in waste water including a fluorophosphate compound, which makes it possible to reduce the concentrations of fluorine and phosphorus in the waste water including the fluorophosphate compound to a very low level, which has been difficult according to a conventional calcium salt addition method.
It is an object of the present invention to provide a method of fixing and eliminating fluorine and phosphorus in waste water including a fluorophosphate compound, according to which a small amount of an acid is sufficient for use, and the occurrence of industrial waste can be remarkably suppressed.
SUMMARY OF THE INVENTION
According to the present invention, a method of fixing and eliminating fluorine and phosphorus in waste water including a fluorophosphate compound is characterized in that al hydrochloric acid is added to the waste water including the fluorophosphate compound so that the concentration of hydrochloric acid in the waste water can be in the range of 2% to 10% by weight: and then the waste water to which hydrochloric acid has been added is heated to a temperature of 80° C. to the boiling point of the waste water so as to decompose the fluorophosphate compound into hydrogen fluoride and phosphoric acid, while hydrogen chloride gas in a treating vessel in which the waste water is contained is introduced into a condenser which is provided out of the treating vessel so as to condense and reflux a volatile vapor; and thereafter, a calcium salt is added to the waste water after decomposition so as to fix and eliminate fluorine and phosphorus.
Effect
(Hydrochloric Acid)
According to the present invention, first of all, hydrochloric acid is added to waste water including a fluorophosphate compound so that the concentration of hydrochloric acid in the waste water can be in the range of 2% to 10% by weight, so as to acidify the waste water. Incidentally, when hydrochloric acid is added thereto so as to heat and hydrolyze the waste water, it is preferred to agitate the same by using a stirring apparatus.
Fluorophosphate ions are stably in an aqueous solution, and it is said that they are not decomposed even in a boiled state in an aqueous alkaline solution, while are slowly hydrolyzed in an aqueous acid solution.
The present inventor has been devoted to studying the decomposition of fluorophosphate ions. Consequently, it has been found that hydrochloric acid is added thereto, and the mixture is subjected to heat treatment, and thereby fluorophosphoric acid is decomposed into hydrogen fluoride and orthophosphoric acid in a relatively short period of time. With respect to using hydrochloric acid, Japanese Patent Kokai (Laid-Open) No.170380/94 discloses that in order to hydrolyze fluorophosphate ions, even hydrochloric acid can be used; however, when hydrochloric acid is used, the step of heat treatment generates hydrogen chloride gas, and furthermore, the following step of treatment with a calcium compound, particularly the step of treatment with calcium hydroxide, can not fix chlorine, so that hydrochloric acid is drained as waste water, and therefore, it is not practical; thus this official gazette contradicts the practical use of hydrochloric acid.
However, the present inventors have fundamentally reviewed the practical use of hydrochloric acid. Consequently, it has been found that if particular conditions are established, hydrochloric acid can be used, and furthermore it is more practical than sulfuric acid, and besides it is equivalent or superior to sulfuric acid in the ability to decompose fluorophosphoric acid, and thereby the efficiency of fixing and eliminating fluorine and phosphorus can be enhanced.
According to the present invention, hydrochloric acid loadings shall be taken as 2 to 10% by weight; namely, there is a feature in its loadings, wherein this concentration is the one in waste water. Thus acid loadings in the present invention shall be smaller than the ones in the above official gazette. Even such a smaller amount thereof can provide specified effects.
A concentration of less than 2%t by weight is insufficient therefor, wherein it takes too long to carry out hydrolysis. For example, even when waste water is treated therewith at a temperature of 95° C. for a period of eight hours, a remaining fluorine concentration is limited to 50 to 100 ppm.
A concentration of about 10% by weight provides a maximum effect thereof. Therefore, even if hydrochloric acid is added thereto so that the concentration thereof can be more than 10% by weight, not only the cost of hydrochloric acid is increased, but also an excessive amount of calcium hydroxide is required to neutralize an excess of hydrochloric acid, which causes an increase in cost. Furthermore, when the concentration thereof is more than 10% by weight, an amount of hydrogen chloride gas which is evaporated during heating is dramatically increased, and thus such a concentration is not preferred.
Incidentally, a concentration of 3 to 6% by weight within the range of 2 to 10% by weight is more preferable.
(Heating Temperature)
According to tho present invention, after adding hydrochloric acid thereto, waste water is heated. A heating temperature is in the range of 80° C. to the boiling point of waste water, more preferably 90° C. to the boiling point thereof. Incidentally, the boiling point of an aqueous s
Fukudome Toshirou
Kikuyama Hirohisa
Miyashita Masayuki
Hruskoci Peter A.
Knuth Randall J.
Stella Chemifa Kabushiki Kaisha
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