JPH0513095B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention is a method for producing an iron-based flocculant by using iron oxide as a raw material, leaching and dissolving it with sulfuric acid to obtain an iron sulfate solution, and oxidizing ferrous sulfate in the resulting solution. It is related to. Conventional technology It has been thought that iron oxide, especially triiron tetroxide with a Fe/Fe molar ratio of 1/2, is soluble in hydrochloric acid but poorly soluble in sulfuric acid, making it impossible to obtain a highly concentrated iron salt solution. was. For this reason, most of the iron oxide is discarded, with only a portion being used as a raw material for ferric chloride. Problems to be solved by the invention Iron oxides include ferrous sulfate, ferrous chloride, and ferrous nitrate.
Those produced by the neutralization of iron, etc., those produced from wastewater treatment using iron-based coagulants, and recently the ferrite industry has become popular and sophisticated, but non-standard products are generated in large quantities during the manufacturing process. Iron oxides are produced in large quantities as by-products during the production of ferrous sulfate and ferrous sulfate, and the effective use of these iron oxides is strongly desired. The present inventor has developed the previously proposed polyferric sulfate solution (Tokuko Showa).
We conducted various studies to produce an iron-based flocculant equivalent to No. 51-17516), and found that the dissolution of iron oxide in sulfuric acid at a temperature of 30°C is as follows:
Although it cannot be said that sufficient dissolution depends on the molar ratio of Fe, on the other hand, as shown in Figure 1, if the dissolution temperature is appropriately raised, the dissolution/leaching rate can be improved, the concentration of sulfuric acid at the time of dissolution, and SO ₄ /Fe. A highly concentrated iron sulfate solution can be obtained by adjusting the molar ratio of

【table】

[Table] It was found that a ferric sulfate solution was obtained. It was also discovered that this product exhibits remarkable efficacy as a flocculant for sewage treatment. Means for Solving the Problems and Their Effects This invention is based on the above-mentioned knowledge, and contains divalent iron and trivalent iron, with a molar ratio of 1/5.
The above iron oxide and sulfuric acid at a concentration of 35 to 50% are mixed in a molar ratio of sulfate ions to the sum of divalent and trivalent iron ions.
Consisting of a first step of preparing and mixing at a ratio of 1.2 to 3.0 and melting at a temperature of 75°C or higher, and a second step of oxidizing divalent iron in the iron sulfate obtained in the first step. A method for producing a ferric sulfate-containing flocculant characterized by the following. The iron oxide used in this invention can have various molar ratios as shown in Table 1, but those discharged from the various processes described above are mainly used. In this invention, the molar ratio of sulfate ion to the sum of divalent and trivalent iron ions is set to 1.2 to 3.0 because
As is clear from Table 2, if it is less than 1.2, especially less than 1.0, the iron dissolution and leaching rate will be less than 50%, which will result in poor stability especially after oxidation and a large amount of precipitate, making it impractical. Also, if it is 3.0 or higher, there are many free acids,
This is not preferable because the solubility of iron decreases and the pH of the treated water becomes too low when used as a flocculant. If the molar ratio of sulfate ions to the sum of divalent and trivalent iron ions is set to 1.2 to 1.5, the iron sulfate solution of iron oxide becomes a ferric sulfate solution with appropriate basicity. This solution is equivalent to the polyferric sulfate solution previously proposed by the present inventor.

【table】

[Table]
Next, determine the concentration of sulfuric acid used for dissolving and leaching iron oxide.
The reason for setting it at 35-50% is that if the concentration is below 35%, especially below 20%, the leaching rate will be below 60% and the iron concentration will be 50%.
g/1 or less, the iron sulfate solution after oxidation tends to be hydrolyzed and becomes unstable. Further, at a concentration of 50% or more, especially 65% or more, the water in iron oxide becomes partially dehydrated, and the surface reacts rapidly and solidifies, resulting in poor dissolution rate. In this invention, the temperature at which iron oxide is dissolved in sulfuric acid is preferably 75°C or higher. The reason for this is that, as is clear from Table 1 and Figure 1, the dissolution of iron oxide by sulfuric acid increases as the molar ratio of Fe/Fe increases.
Although the dissolution/leaching rate is good, if the temperature is set to 75°C or higher, a dissolution/leaching rate of 60% or more can be obtained even with a molar ratio of 1/5. Next, the oxidation in the second step of this invention includes direct oxidation with oxygen, air, etc., oxidation with oxidizing agents such as hydrogen peroxide, manganese dioxide, sodium chlorate, etc., and oxidation with oxygen, air, etc. using Tituso oxide as a catalyst. Methods such as oxidation are used. Example 1 1000g of iron oxide, whose main components are 58% total iron and 11% divalent iron, was treated with sulfuric acid at a concentration of 420g/.
Prepared so that the SC ₄ /Fe molar ratio was 1.3, and
When the solution was allowed to react at ℃ for 30 minutes, 98% of the iron content was leached out. This was oxidized with oxygen using Tituso oxide as a catalyst, and the total iron content was 160g/, and the Fe content was 0.1g/
, SC ₄ ^--65 g/flocculant 3.55 was obtained. When an aggregation test was conducted using this, the same effect as polyferric sulfate solution was obtained. 2. 1000 g of iron oxide, which is produced as a by-product in the process of manufacturing ferrous sulfate from ferrous sulfate, whose main components are 62% total iron and 20% divalent iron, was reduced to SO ₄ /Fe mol with sulfuric acid at a concentration of 420 g/Fe. Adjust the ratio to be 1.4,
When reacted at 90°C for 2 hours, 99% of the iron content was leached out. When this was oxidized with hydrogen peroxide, the total iron content was
A solution of 155g/, Fe0.1g/, SO ⁼ _4380g /3.92 was obtained. Using this, an aggregation test was conducted and the same effect as in Example 1 was obtained. Effects of the Invention As described above, according to the present invention, an iron-based flocculant can be produced using iron oxide, which has not been used in the past, as a raw material, and therefore has great industrial value.

[Brief explanation of the drawing]

Figure 1 shows iron oxide (Fe/Fe molar ratio 1/1).
5) is a diagram showing the relationship between the dissolution temperature and the dissolution/leaching rate of Fe. The concentration of sulfuric acid used was 40%.
The SO ₄ /Fe molar ratio is 1.2.

Claims (1)

[Claims] 1 Contains divalent iron and trivalent iron, the molar ratio of which is 1/5
The above iron oxide and sulfuric acid at a concentration of 35 to 50% are mixed in a molar ratio of sulfate ions to the sum of divalent and trivalent iron ions.
Consisting of a first step of preparing and mixing at a ratio of 1.2 to 3.0 and melting at a temperature of 75°C or higher, and a second step of oxidizing divalent iron in the iron sulfate obtained in the first step. A method for producing a flocculant containing ferric sulfate, characterized by: