JPH05123682A - Treatment of solution containing iron ion - Google Patents

Abstract

PURPOSE:To efficiently and economically remove iron from a soln. contg. iron ions by a treatment without heating the soln. CONSTITUTION:A soln. contg. at least iron ions as metal ions is acidified to pH< 7 with nitric acid, air is blown into the soln. and the iron ions in the soln. are precipitated and removed by adjusting the soln. to pH >=7 with alkali.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating an iron solution by precipitating and removing iron from a solution containing at least iron ions as metal ions.

[0002]

2. Description of the Related Art A method is well known in which a solution containing a metal ion such as iron is adjusted to pH 7 or more and then heat-treated to precipitate and separate iron as hydroxide. At that time, it is also well known that the presence of various cations and anions in addition to iron ions makes it impossible to efficiently carry out the above-mentioned precipitation separation even if heat treatment is performed.

Examples of a solution in which at least iron ions are present as metal ions that have undergone heat treatment are a concentrator,
There is waste liquid for cleaning the dryer.

In the concentrator, since the heat transfer coefficient decreases when iron scale adheres to the surface, the performance is revived by periodically performing chemical cleaning with acid or physically removing the scale. The same applies to the dryer. At this time, a large amount of acidic waste liquid containing at least iron ions as metal ions that have undergone the heat treatment is generated, and when neutralized and left to stand, it is separated into a precipitate and a supernatant liquid. The supernatant liquid is colored due to insufficient precipitation of iron ions and cannot be discharged as waste water as it is. The following method is used as a method for separating iron and the like from the supernatant. That is, in the prior art, the waste liquid is heated to a temperature near the boiling point using a heating source such as a heater or a heat exchanger, and then alkali-treated to separate the precipitate containing iron and the supernatant.

Further, as an example of the precipitation treatment of a solution containing iron ions, there is a method in which iron ions and an alkali are added to a solution containing uranium to form hydroxides to precipitate and filter uranium. The reason for adding the iron ion and the alkali is to coprecipitate uranium in the hydroxide of iron. Also in this method, heat treatment is performed in order to improve the filterability of the precipitate.

[0006]

In each of the examples, a method of finally heating the solution to be discharged and then performing a precipitation treatment and then cooling is used. As a result, wasteful heat energy is consumed. Will be there.

The problem to be solved by the present invention is to solve the problem of a large amount of solution containing iron ions or iron ions and other ions.
An object of the present invention is to provide a treatment method for efficiently and economically removing iron without heating the solution.

[0008]

In order to solve the problems of the above-mentioned prior art, the inventor has conducted extensive studies and completed the present invention.

According to the present invention, a solution containing at least iron ions as metal ions is acidified with nitric acid having a pH of less than 7, then air is blown into the solution, and then the solution is adjusted to pH 7 or more by using an alkali to form a solution. It is characterized by removing the iron content in the precipitate.

The acid used in the present invention is nitric acid. For example, in the case of sulfuric acid acid or hydrochloric acid acid solution, after neutralizing with caustic soda,
It is good to use nitric acid. The pH at that time may be less than 7, but in order to shorten the air blowing time, that is, in order to oxidize particularly quickly, the lower the pH, the better, and the pH is preferably 4 or less.

Air is blown after acidifying the solution with nitric acid. The blowing time varies depending on the type of the solution, the pH, and the shape of the blower, and is 2 to 60 minutes per 1 m ^{3 of} the solution, and the blowing amount varies depending on the properties of the solution, particularly the iron ion content. The shape of the blower is preferably a shape in which air is uniformly dispersed in order to shorten the blowing time. Even if air is blown in as alkaline, as shown in Comparative Example 2 described later, the treatment capacity is lower than that of nitric acid.

Examples will be shown below, but the present invention is not limited thereto.

The following Table 1 showing the data shows the results of the sedimentation test using a 100 ml measuring cylinder, and the numerical values of the precipitate phase and the supernatant liquid phase in the table represent the scale (height) ml of the measuring cylinder.

[0014]

【Example】

Example 1 As an example of a solution containing at least iron ions as metal ions that have undergone heat treatment, iron 2000 ppm, sodium nitrate 20
g / l, sodium carbonate 5 g / l, sodium iodide 5 g / l,
A pH 7 solution consisting of 5 g / l of sodium nitrite was prepared. The above solution was put into a stainless steel autoclave having a capacity of 1000 cc and 500 cc was concentrated at 130 ° C. to 60% (wt), and the operation of taking out the solution was repeated until scales such as iron were attached to the autoclave.

The autoclave was washed with water to take out contents other than the adhered components separately, and then the autoclave to which scales such as iron adhered was heated to 100 ° C. After the temperature was stopped, the mixture was allowed to cool, and 100 cc of 5% nitric acid solution was divided into 3 times for chemical cleaning. It was further washed with 500 cc of water. A solution sample was prepared by combining 100 cc of a 5% nitric acid solution and 500 cc of washing water. This sample was yellowish brown.

Air was supplied to the above sample 600 cc from an air cylinder at a rate of 300 cc / min for about 25 minutes, and then the pH was adjusted to 7 with a caustic soda aqueous solution.

As a result, a precipitate containing iron rapidly settled and the supernatant liquid was transparent. Example 2 To the sample of Example 1, the entire contents other than the adhered components separately taken out in Example 1 were added, and the same operation was performed.
The results were the same as in Example 1. Comparative Example 1 The cleaning liquid of Example 1 was replaced with 5% sulfuric acid and 5% hydrochloric acid, and the same operation was performed. The result was no precipitation. Comparative Example 2 In Example 1, the pH was adjusted to 7 and air was supplied in the same manner.
As a result, precipitation occurred, but a yellowish brown color remained in the supernatant. Example 3 10, 300, 300, 200 and 20, respectively, as nitrates of uranium, calcium, magnesium, nickel and iron ions in a 400 g / l sodium nitrate aqueous solution.
Air was blown into 100 cc of a pH 3 solution containing 0 ppm under the same conditions as in Example 1. This solution was adjusted to pH 13 with a concentrated aqueous solution of sodium hydroxide and then transferred to a 100 ml graduated cylinder for sedimentation test. Table 1 shows the result of measuring the sedimentation time and the boundary surface of the sediment.

[0018]

[Table 1] Comparative Example 3 A sedimentation test was performed in the same manner as in Example 3 except that the material was boiled for 15 minutes instead of blowing air in Example 3 and cooled to room temperature. The results are shown in Table 1. Comparative Example 4 A sedimentation test was conducted in the same manner as in Example 3 without blowing air. The results are shown in Table 1. Floating precipitates were observed in the supernatant liquid phase.

[0019]

As described above, according to the method for treating a solution containing iron ions of the present invention, iron is efficiently or economically removed or recovered from a solution containing at least iron ions as metal ions. It is also possible to reuse the treatment liquid from which iron ions have been removed or recovered. Further, there is an energy saving effect because no heat treatment is required.

Claims (1)

[Claims] 1. A solution containing at least iron ions as metal ions is acidified with nitric acid at a pH of less than 7, air is blown into the solution, and then the solution is added with an alkali to p
A method for treating a solution containing iron ions, wherein the content of iron in the solution is removed by precipitation by setting it to H7 or more.