KR970000304B1 - Process for producing magnetic recording iron hydroxide - Google Patents

Abstract

Process for preparing ferric hydroxide from waste water with ferrous chloride is described. Thus, i)waste water with ferrous chloride is added with iron scrap or powder to eliminate Fe+3 and hydrogen chloride from waste water, ii)the obtained solution is added with iron scrap to give a colloidal sludge which contains ferric hydroxide with a concentration of 100mg-1,000mg/L, iii)the colloidal sludge is stirred slowly to give a high dencity ferrous chloride solution, iv)the ferrous chloride solution is reacted with alkali at 40-60 deg.C to givea high dencity ferric hydroxide.

Description

Manufacturing method of high purity ferric chloride using waste acid and manufacturing method of iron hydroxide for magnetic recording medium

The present invention relates to a method of manufacturing ferrous chloride using waste acid and iron hydroxide for magnetic recording medium using the ferric chloride, and more specifically, high-purity FeCl ₂ solution using pickling waste acid generated in a cold mill of a steel mill. The present invention relates to a method for preparing iron hydroxide (α-FeOOH, γ-FeOOH) which is a starting material of γ-Fe ₂ O ₃ based iron oxide used as a magnetic recording medium by wet oxidation.

The FeCl ₂ solution can be used not only for the synthesis of iron hydroxide, which is a starting material for the magnetic recording medium, but also for the production of high purity iron oxide and plating solution.

Iron hydroxide, which is a starting material of γ-Fe ₂ O ₃ based iron oxide used as a magnetic recording medium, has been conventionally manufactured mainly using iron sulfate) (FeSO ₄ ), and α is the most widely used starting material of magnetic recording media. -FeOOH is mostly manufactured using FeSO ₄ as a starting material.

In addition to FeSO ₄ , a process for producing γ-FeOOH iron hydroxide in an acidic region using FeCl ₂ solution is known. In this case, FeCl ₂ is obtained by dissolving iron scrap with hydrochloric acid.

On the other hand, in the cold rolling mill, FeCI ₂ waste acid containing a large amount is discharged, but since Fe ^{+ 3} , HCl and other trace impurities are included in the waste acid, the purification process is required to obtain high purity FeCl ₂ from it. In particular, more stringent purification is required than when the obtained FeCl ₂ is used for the production of iron hydroxide as the starting material of the magnetic recording medium.

Accordingly, the present inventors have disclosed that it is possible to purify waste acid by administering alkali to waste acid and to synthesize α-FeOOH in the alkaline region (Korean Patent Publication 92-5334). It was confirmed that this is possible (Korean Patent Publication 93-4508).

However, in these conventional methods, since the pH is adjusted to a range of 2.5-7 by administering an alkali, such as NaOH, to cold-rolled waste acid, Fe ^{+ 3} ions, HCl, and trace impurities are purified. There was a problem that a large amount of alkali (NaOH, etc.) is consumed to neutralize the acid (free acid).

In addition, there is a problem in that raw material loss occurs because Fe ⁺² ions are sludged into a large amount of Fe (OH) _{2 due} to extreme pH fluctuations when alkali is added. In particular, when NaOH is used as an alkaline agent, Na ions are mixed up to several thousand to tens of thousands of ppm, so the unevenness of the reaction due to excessive Na ⁺¹ ions during the solution reaction and the inconvenience of washing with more water when washing iron hydroxide after completion of the reaction There was this.

It is an object of the present invention to provide a method for producing ferrous chloride of high purity from waste acid with a more improved purification method that solves the conventional problems as described above.

Another object of the present invention is to provide a method for producing iron hydroxide as a starting material of a magnetic recording medium using high purity ferric chloride obtained by purifying waste acid.

According to one aspect of the present invention, iron scrap or iron powder is added to a ferric chloride (FeCl ₂ ) -containing waste acid generated in a cold rolling mill of a steel mill to react with Fe + 3 ions and HCl in the waste acid to react Fe ^{+ 3} ions and HCl. Dissolving and removing; Iron powder was added to this solution or continuously reacted to make the pH of the waste acid above 2.5 and then aged. The Fe-based colloidal sludge such as Fe (OH) ₂ and Fe (OH) _{3 at} a concentration of 100 mg / l-1000 mg / l Generating a; And a high-purity ferric chloride manufacturing process comprising the step of recovering a high purity FeCl by slowly stirring the solution produced the Fe-based sludge by adsorbing, filtering, and removing impurities and organic matter present in a small amount in the waste acid.

According to another aspect of the present invention, there is provided a method for preparing α-FeOOH, which is a starting material of a medium using a high purity ferric chloride, by adding alkali to the purified high purity ferric chloride solution. maintaining a pH of 13 or more and maintaining a temperature of 40-60 ° C .;

According to still another aspect of the present invention, there is provided a method of preparing γ-FeOOH, which is a starting material of a magnetic recording medium using the high purity softener, wherein the method comprises administering alkali to the purified high purity iron softener solution. To maintain the pH at 6-7 and form a γ-FeCl ₂ nucleus by a solution reaction in which the air is blown at a temperature of 20-30 ° C, followed by continuously infusing alkali at 40-60 ° C. Solution reaction.

Hereinafter, the present invention will be described in detail.

The present invention removes Fe ⁺³ ions and HCl using iron scrap or reduced iron oxide instead of alkali in waste acid, and then matures until Fe (OH) ₂ and Fe (OH) ₃ are produced by changing the pH. The present invention relates to a method for producing high purity ferric chloride by adsorbing and removing trace impurities in waste acid, and from this, iron hydroxide, which is a starting material of a magnetic recording medium.

Table 1 shows the components of the cold rolled waste acid, and Fe ^{+ 3} ions in the waste acid become a major cause of reaction unevenness during the iron hydroxide synthesis reaction, causing problems such as particle shape defects and foreign matter mixing. HCl also causes problems such as lowering the pH of the solution and adding more neutralizers. In addition, Si, Al, Cr, etc., among the impurities present in trace amounts, are a slurry-forming element, and thus have a sensitive effect on the reaction rate and cause a problem of lowering the electromagnetic characteristics of the final product, in particular, the saturation magnetization value.

Therefore, it is necessary to suppress the content of such impurities to a minimum.

Fe like this , HCl and other trace impurities are removed as follows.

First, a small amount of iron scrap is added to the waste acid to remove Fe and HCl according to the following formulas (1) and (2).

Fe + 2HCl → FeCl + H... … … … … … … (One)

2Fe Cl + Fe → 3Fe Cl… … … … … … (2)

In Formula (1), since iron (Fe) is easy to react with hydrochloric acid, hydrochloric acid easily reacts with the added iron scrap to produce FeCl.

Fe Fe easily due to electrochemical potential difference with silver iron Reduced to. Reaction (2) proceeds relatively quickly, but reaction (1) changes depending on the residual HCl concentration, the reaction temperature, the size and amount of iron scrap added.

The reaction temperature is 30 ° C or less, the reaction rate is slow, 60 ° C or more, since the generation of fumes (fume) is severe, 30-60 ° C is preferred.

As shown in the reaction formula (1), the iron scrap must be added more than the equivalent ratio in consideration of the concentration of residual hydrogen chloride to sufficiently proceed the reaction.

The dissolution of the added iron scrap by hydrochloric acid is remarkable when the concentration of hydrogen chloride is 10 g / l or more, but the solubility is remarkably reduced when the concentration of hydrogen chloride is reduced to 10 g / l or less according to the reaction formula (1).

If the concentration of hydrochloric acid is 10g / l or less, even if the reaction rate is increased, the amount of hydrogen gas is generated and the fume is not severe. Therefore, in order to increase the reaction rate, the reaction temperature is set to 60 ° C or higher or fine iron powder is added. can do.

The iron powder used in the present invention may be reduced iron prepared by reducing α-FeO produced by roasting in a cold rolling mill under a hydrogen atmosphere of 400 ° C. or higher. The residual free acid is then left to react completely.

The reaction time varies depending on the reaction conditions. When the pH reaches 2.5, almost no residual acid is present. Ie Fe at pH = 2.5 After the residual acid is removed and the pH is continuously maintained until the pH is 2.5 or more, the ferrous metal administered according to the following reaction formulas (3) and (4) at the interface of the iron scrap or iron powder administered as the pH is increased is Due to the oxidative action by the dissolved oxygen, Fe (OH) or Fe (OH) is oxidized to form Fe-based colloidal sludge spontaneously. However, when the pH is lower than 2.5, such sludge is not formed due to the presence of free acid.

Fe + 2HO → Fe (OH) + 2H 2e... … … … … (3)

Fe + 3HO → Fe (OH) + 3H 3e… … … … … (4)

The ferrous hydroxide and ferric hydroxide produced by the above reactions are very strong adsorbents (BET specific surface area = 100-500 m ² / g) and adsorb other impurities in waste acid such as Si, Al, Cr.

After slowly stirring the solution in which the Fe-based sludge is formed, the impurities are sufficiently adsorbed and filtered through a filter to obtain a high-purity ferric chloride solution in which impurities in Fe ⁺³ , hydrochloric acid, and waste acids such as Si, Al, and Cr are removed. This solution contains up to 0.01 mol / l Fe ⁺³ and up to 10 g / l hydrochloric acid. When Fe-based sludge is produced, the concentrations of Fe (OH) ₂ and Fe (OH) _{3 in} the solution are not sufficiently adsorbed at impurities below 100 mg / l, and raw material loss of Fe ⁺³ occurs at 1000 mg / l or higher. And filtration efficiency during filtration decreases, so 100-1000 mg / l is preferred.

On the other hand, cold rolled waste acid contains about 10 ppm of the organic material of the amine-based mainstream as a corrosion inhibitor. The ferrous hydroxide and ferric hydroxide produced by aging above pH 2.5 also adsorb and remove such organic matter as ultrafine adsorbents. Activated carbon is added to the purified waste acid, stirred, and filtered, or the waste acid is passed through a container loaded with activated carbon to remove the organic matter more effectively.

As described above, iron + scrap or reduced iron powder is added to the cold rolled waste acid to remove Fe ^{+ 3} and hydrochloric acid, and the pH is adjusted to form Fe (OH) ₂ and Fe (OH) ₃ to adsorb and remove inorganic and organic materials. Thus, a high purity ferric chloride solution is obtained.

By adding sodium hydroxide to the waste acid containing ferrous chloride purified by the method of the present invention, the pH is adjusted to 13.0 or more, and the solution reaction of blowing air while maintaining the temperature at 40-60 ° C. is excellent in the form of α-FeOOH. Can be obtained.

In addition, by adding sodium hydroxide to the purified acid containing ferric chloride to maintain a pH of 6-7 and performing a solution reaction by blowing air at 20-30 ℃ to form a good γ-FeOOH nucleus Then, the solution reaction of blowing air at 40-60 ° C. while adding alkali can give excellent γ-FeOOH powder without incorporation of impurities.

The powder is dehydrated at 400-600 ° C., reduced in a hydrogen atmosphere of 250-350 ° C., and reoxidized at 200-300 ° C. to obtain γ-Fe ₂ O ₃ having excellent magnetic properties.

As described above, in the case of the method of the present invention, it is economical in terms of cost because it does not require alkali at the time of purification compared to the conventional method, and there is little loss of Fe ⁺² ions, and the FeCl ₂ solution purified according to the present invention. In the case of manufacturing iron hydroxide as a starting material of the magnetic recording medium, the final γ-Fe ₂ O ₃ magnetic material having excellent particle shape and excellent electromagnetic characteristics can be stably manufactured by a uniform reaction. It is. In addition, the loss of Fe ⁺² ions has an economic advantage.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described.

Sourcing 1-3 and Comparative Example 1-5

In order to produce FeOOH suitable for magnetic recording media, a high purity FeCl ₂ solution was prepared by refining the waste acid of a cold rolling mill at a steel mill. The manufacturing process for each sample was as follows.

The Fe concentration in cold rolled waste acid was 198.25 g / l (3.55 mol / l), and the Fe concentration was adjusted to be 1 mol / l by dilution with water because the concentration of the magnetic recording medium was not suitable.

In Comparative Example 1, the diluted waste acid was treated as it is without using iron scrap or iron powder.

Comparative Example 3 is treated by a conventional method for producing NaOH by iron film.

10 kg of Fe scrap was administered to 10 L of diluted waste acid to reduce Fe ⁺³ present in waste acid to Fe ⁺² ions and to remove residual HCl for 10 hours at 30 ° C (Comparative Example 2).

5 L of 10 L of the solution reacted for 10 hours was taken out, and 500 g of reduced iron prepared by reducing iron oxide generated in a cold rolling mill at 500 ^O C under hydrogen atmosphere was administered for 1 hour. (Comparative Example 4)

In addition, the reaction was continued for 10 hours, and 5 L of the remaining waste acid was raised to 70 ° C., and the reaction was continued for 1 hour (Invention Example 3).

In the case of iron powder, the pH increased to 2.5 or more after 1 hour of curing due to rapid reaction. When the pH began to increase to 2.5 or more, Fe hydroxide sludge composed of Fe (OH) ₃ and Fe (OH) ₃ and the like began to be generated in the waste acid (Inventive Examples 1 and 2).

After that, a sample was collected according to the reaction time and filtered to measure the sludge content of Fe-based hydroxide, and the components of the filtered plating solution were analyzed.

In addition, as a result of reacting the remaining 5 l of waste acid for 10 hours at 70 ° C. for 14 hours, sludge composed of Fe (OH) ₂ and Fe (OH) ₃ occurred in the waste acid (Invention Example 3).

The solution was filtered to measure sludge generation and the impurity content in the filtrate was analyzed.

The impurity content of FeCl ₂ solution prepared by various methods, working conditions, sludge generation amount per 1 L of waste acid, and the like are shown in Table 2 below.

On the other hand, in order to compare the impurities removal effect and the sludge generation amount according to the conventional alkali input, the pH was adjusted to 4.0 by adding 4 molar concentration of NaOH to 1 l of waste acid of 1 molar concentration. The solution was then filtered to investigate the sludge production and the filtrate was analyzed and shown in Table 2 (Comparative Example 3).

As can be seen in Table 2, the conventionally used alkali dosing method shows an excellent effect on the removal of trace impurities of Si, Al, Cr and Fe. Relatively effective for removal but NaOH injection There is a problem that a sudden increase in ions occurs. In addition, the pH fluctuates due to the high concentration of alkali. The precipitation of ions occurs badly and Fe The concentration of ions was decreased and the filtration time was long due to excessive sludge generation.

However, in the case of a sample with a sludge content of 100 mg or more in the solution by administering iron powder or by aging the pH of the solution for more than 2.5 hours with iron scrap, Fe , HCl and various impurities are extremely low or not detected. However, when the amount of Fe-based sludge generation is more than 1000mg, it is not necessary to work more than the horn due to the decrease of Fe ion concentration as well as the filtration time.

Example 4

Purification of Inventive Example 1 1 L of 4 L solution of 1 L NaOH waste acid was added thereto to adjust the pH to 13.5, and then, α-FeOOH particles were prepared by a solution reaction of blowing air at 45 ° C.

In addition, 1L NaOH of 1.29 mol was added to 1 L of purified waste acid of Inventive Example 2, γ-FeOOH nuclei were synthesized at 25 ° C., and γ-FeOOH powder was prepared through oxidation at 50 ° C. while alkali was continuously added. Observation of these particles by TEM showed good particle characteristics and no mixing of impurities.

Further, these powders were dehydrated at 550 ° C. for 1 hour, reduced to 250 ° C. for 1 hour in a hydrogen atmosphere, and then oxidized at 250 ° C. in air for 1 hour to prepare γ-FeO particles.

These powders had very good magnetic properties with coercivity of 380, 375Oe saturation magnetization of 74emu / g and 74.5emu / g, respectively.

Claims (2)

Ferrous chloride occurring in the cold rolling mill of a steel mill (FeCl ₂₎ and a spent acid containing addition of iron scrap or iron powder is reacted with Fe ⁺³ ions and HCl in the spent acid phase to dissolve and remove the Fe ⁺³ ions and HCl; Iron powder was added to this solution or continuously reacted to mature the pH of waste acid to 2.5 or more to produce Fe-based colloidal sludge such as Fe (OH) ₂ and Fe (OH) _{3 at} a concentration of 100 mg-1000 mg / l. ; And slowly stirring the solution in which the Fe-based sludge is produced by adsorption filtration to remove impurities and organic substances present in trace amounts in the waste acid to recover FeCl ₂ having high purity. And administering alkali to the high-purity ferric chloride solution to maintain a pH of 13 or more and causing a solution reaction to blow air at a temperature of 40-60 ° C. A method of manufacturing iron hydroxide for a magnetic recording medium. Ferrous chloride occurring in the cold rolling mill of a steel mill (FeCl ₂₎ and a spent acid containing addition of iron scrap or iron powder is reacted with Fe ⁺³ ions and HCl in the spent acid phase to dissolve and remove the Fe ⁺³ ions and HCl; Iron powder was added to this solution or continuously reacted to mature the pH of waste acid to 2.5 or more to produce Fe-based colloidal sludge such as Fe (OH) ₂ and Fe (OH) _{3 at} a concentration of 100 mg-1000 mg / l. And slowly stirring the solution in which the Fe-based sludge is produced, adsorbing and removing impurities and organics present in trace amounts in the waste acid to recover FeCl ₂ of high purity, and administering an alkali to the purified high purity ferric chloride solution to pH. After maintaining at 6-7 and producing a γ-FeOOH nucleus by a solution reaction that blows air at a temperature of 20-30 ℃, followed by a solution reaction of blowing air at a temperature of 40-60 ℃ with continuous alkali administration Iron hydroxide manufacturing method for a magnetic recording medium comprising a.