JPS63295442A - Method for removing impurity contained in waste acid - Google Patents

Abstract

PURPOSE:To efficiently obtain waste acid available for production of high-purity iron (hydro)oxide at low cost by adding base to waste acid contg. large amounts of iron to neutralize it and regulating pH to form hydroxide, naturally precipitating and filtering or centrifugal separating it. CONSTITUTION:Waste acid (HCl or H2SO4) produced in pickling of iron and steel is stored in a receiving tank 1. Then this waste acid is sent to a dissolving tank 3 via a heater 4 with a waste acid pump 2 and iron content such as iron scale is added and dissolved to decrease free iron. Then this soln. is sent to a pH regulation tank 6 with a transfer pump 5 and base such as NaOH is added to regulate pH to 3-7 and hydroxide of the impurities is formed. Then it is sent to a centrifugal separator 8 with a transfer pump 7 and subjected to centrifugal separation and a purified iron salt aq. soln. free from the impurities is collected by settling hydroxide and recovering only supernatant liquid. If necessary, the filtrate obtained by separating the above-mentioned hydroxide with an Oliver filter is treated with a wet treating method and thereby high- purity oxide or the like is collected.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is applicable to the production of iron oxide and iron hydroxide, which require high purity, such as ferrite raw materials, from waste acid pickling for steel plates, etc. This invention relates to a method for removing impurities from waste acid so that salt aqueous solutions can be efficiently purified at low cost.

(Prior art and its problems) As is well known, waste acid from pickling steel plates, etc., is roasted as it is or as iron salt crystals, and the resulting iron oxide is effectively used as a ferrite raw material or pigment. .Also, on the other hand,
Wet processing is also performed, and the resulting iron oxides and hydroxides are also effectively used as magnetic materials and pigments.

However, the pickling waste acid may vary depending on the type of pickling steel plate,
Or, due to invasion from the outside, nonmetals such as Sin, and nonferrous metals Al, Mn, and Ca.

Contains impurities such as Ni, Cr, Cu, and Ti,
Most of these impurities are mixed into the iron oxide and iron hydroxide. Therefore, these impurities have a great effect on the magnetic properties of ferrite raw materials and magnetic materials, and on the color tone of pigments, making it difficult to use them in high-grade applications. Furthermore, when heavy metals such as Ni, Cr, and Cu are contained, they are required to be reduced as much as possible not only from the viewpoint of properties but also from environmental considerations, and industrial applications are also limited. Moreover, as pickled steel sheets themselves tend to be made of special steel, it is thought that impurities of heavy metals will become more of a problem.

Among these impurities, various methods have been proposed for removing 5ift. For example, according to the method disclosed in Japanese Patent Application Laid-Open No. 61-222925 proposed by the present applicant, up to several pp- It is possible to reduce the However, other methods for removing impurities include solvent extraction,
Only crystallization methods have been proposed, and these methods are large-scale purification methods and have to be expensive. Furthermore, these methods require a mechanism to discharge impurities from the system. Therefore, impurities must be filtered and the remaining liquid must be treated separately.Additionally, a washing method with water has also been proposed, but it is only applicable to some alkalis and cannot reduce impurities as described above. Can not.

In general, iron oxide and iron hydroxide produced by conventional waste acid treatment methods are contaminated with impurities and have limited uses.

Therefore, the present invention aims to provide a relatively inexpensive and simple means for obtaining a purified iron salt solution by removing problematic impurities prior to treatment of waste acid. In addition, in conventional purification methods, -a condensation of impurities is a problem, but we propose a relatively simple method for discharging impurities out of the system in this respect as well.

[Means for solving problems]

The purpose of the present invention is to produce iron salts (iron chloride) using waste acids (hydrochloric acid, sulfuric acid) as raw materials to produce high-quality iron oxides and iron hydroxides with few impurities.

The purpose of this method is to purify an aqueous solution (iron sulfate), and its feature is to add a base to the waste acid for pickling steel plates, etc. to neutralize it and adjust it to pi 3 to 7. After that, the generated hydroxide is naturally settled, filtered,
Alternatively, a purified iron salt solution is obtained by separation by centrifugal sedimentation or the like. By using this as a raw material and subjecting it to the well-known roasting method or wet processing method, it is possible to obtain high-quality iron oxide or iron hydroxide with few impurities.

[Effect]

As a result of repeated research on impurities in waste acids, the present inventors were able to experimentally confirm the following three points.

■ By adjusting the pH of waste acid containing a large amount of iron to 3 to 7, Fe'' and Cu'' are removed before Fe''.

Precipitates of hydroxides of Ni", Cr", Al", and Ti" are formed.

(2) The generated hydroxide precipitate can be separated relatively easily by applying conventional general separation techniques such as natural sedimentation, filtration, and centrifugal sedimentation.

(2) Regarding pH adjustment, in the above pH range, the type of base to be neutralized has little effect on the formation of impurities, and a large amount of base is often required to neutralize free acid.

The pH range where these hydroxides are generated is Ti.

Since Ai is about 4, Cr and Cu are about 5, and Fe'' is about 6, which is high, it is thought that hydroxides of these impurities are preferentially generated when waste acid is neutralized. , Ni, etc. alone are not much different from Fe'', but can be reduced. These impurities can be reduced in a lower pH range when a large amount of Fe coexists than when Fe is used alone. That is, as shown in Examples below, it became possible to reduce the amount of these impurities to the initial content of 1710 or less.

First, regarding the base used for neutralization to adjust the pH, it needs to be strongly basic in order to adjust the pH to 3 to 7. This includes caustic soda, carbonated soda,
Lime etc. can be used, but if you also dislike Na and Ca as impurities, use NH.

By using , contamination with impurities can be avoided. In this pH range of 9M, the formation of complex salts due to NH does not pose a problem, and in some cases, it can also be used to neutralize other compounds such as Zn compounds.

Next, as mentioned in ①, in the case of ordinary pickling waste acid, there is a lot of free acid, and the pH is close to 0, and a very large amount of base is required to neutralize it.For example, hydrochloric acid In the case of waste acid from washing, the amount of free hydrochloric acid may be several percent, and in the case of waste acid from sulfuric acid pickling, the amount of free sulfuric acid may reach 10% or more. If these free acids are close to 0, the pH will also be 1 or higher, making it possible to achieve the objective with a small amount of base added for adjustment. Bringing the free acid level close to 0 can be achieved relatively easily by employing the following two methods.

(a) Dissolve iron such as scrap iron and iron scale in waste acid.

(b) Iron salts are crystallized and recovered from waste acid and dissolved in water to form an aqueous solution of iron salts.

Regarding (a), it is possible to dissolve scrap iron, iron scale, etc. in waste acid by heating it, or by using a catalyst (platinum, etc.) even at room temperature, and it is easy to dissolve free acid. It can be reduced to 0.2% or less.

In the case of (b), it is possible to crystallize the iron salt by heating, concentrating, cooling, etc. The free acid contained in this crystal is very small, and when it is made into an aqueous solution, the free acid is easily extracted. It can be reduced to 0.2% or less. If this crystal separation is carried out carefully, it is possible to reduce the amount of free acid to almost 0. As is well known, this crystallization method is widely used as a purification method, and if appropriate conditions are selected. Although it is possible to reduce these impurities by crystallization alone, C
Although r and the like are often mixed into crystals, and it is difficult to set conditions to avoid this, impurities can be sufficiently removed by employing the method of the present invention. Furthermore, when performing crystallization based on the present invention, there is less need to prioritize the removal of impurities and priority can be given to crystal collection efficiency, increasing the degree of freedom in crystallization operations and significantly reducing crystallization costs. This makes it possible to achieve significant reductions. Furthermore, since the present invention discharges impurities out of the system, it is possible to deal with the concentration of impurities. In addition, in the crystallization method, it is easier to precipitate crystals when there is a large amount of free acid because the solubility of the iron salt is low, but in the case of the present invention, crystallization conditions using strong ms, which can include many impurities, can also be adopted. It is also possible to melt scrap iron and iron scale prior to crystallization.

In addition to the above-mentioned method, a method of reducing free acid using an ion exchange membrane, which is often used in waste acid treatment, can also be considered.

Furthermore, trivalent iron precipitates as an impurity hydroxide during neutralization, resulting in a loss of iron, but in small amounts it also acts to co-precipitate other impurities.
Since it is also effective for precipitation separation, it is advantageous to have some amount of it. In the case of waste acid for pickling steel plates, etc., most of the acid is divalent iron,
Since the amount of trivalent iron is small, it is not much of a problem. However, if it is in a large amount, iron will be lost, a large amount of base will be required, and a large amount of hydroxide will be produced, making it extremely difficult to separate the hydroxide. This becomes a problem. In such a case, trivalent iron can be easily reduced to divalent iron by performing fJ analysis on a metal such as scrap iron.

Finally, regarding the adjustment range for p), in the pH range below 3, most of the precipitated hydroxide is trivalent iron, and the hydroxide of impurities contained in ordinary waste acid When the pH is around 3, Al can be removed without precipitation, but all of these impurities can be efficiently removed at a pH of 5 or higher. In addition, if the pH is 7 or more, the precipitation of divalent iron hydroxide is significantly formed, making the product unusable.
Therefore, the pH adjustment range is 3 to 7, preferably pH
It is best to set it to 5-6.

〔Example〕

The drawing is a flow sheet illustrating one embodiment of the method of the invention.

Waste acid (hydrochloric acid or sulfuric acid) generated from steel wire pickling, etc. is temporarily stored in a receiving tank 1.

Next, the waste acid is sent to the dissolution tank 3 by the waste acid pump 2, and iron is dissolved and added to this waste acid in order to reduce the amount of free acid. It is economical to use scrap iron, iron scale, etc. as the iron content to be melted. If the waste acid in the recipient tank 1 is heated via the heater 4 and then sent to the dissolution tank 3, the dissolution will be accelerated. For this heating, if a roasting furnace or the like is nearby, its exhaust gas can be used.

Next, the pH is increased by the transfer pump 5! 11 Send to tank 6,
Add a base such as NaOH, NH, or water to adjust the pH to 3.
~7 to generate impurity hydroxide.

Next, the hydroxide is sent to a centrifugal separator 8 by a transfer pump 7 and centrifuged. Since the hydroxide is precipitated, a purified iron salt aqueous solution containing few impurities can be obtained by collecting only the supernatant liquid. Hydroxide may be separated by a filtration method (for example, an Oliver filter). Furthermore, high-purity oxides and hydroxides can be separated by using a well-known roasting method or wet processing method. Obtainable. Furthermore, since the purified iron salt aqueous solution obtained here has a low content of heavy metals, it can be used as is as a flocculant for water treatment, etc.

When an alkali was added to waste hydrochloric acid, centrifuged and sedimented, and the supernatant was analyzed, the results were as shown in Table 1.

After dissolving iron in waste hydrochloric acid, an alkali was added thereto, centrifugal sedimentation was performed, and the supernatant was analyzed, and the results were as shown in Table 2.

After heating and concentrating the Illyoshi waste hydrochloric acid, it was crystallized and separated, an alkali was added to the aqueous solution, centrifugal sedimentation was performed, and the supernatant was analyzed, and the results were as shown in Table 3.

When an alkali was added to the waste sulfuric acid, centrifugal sedimentation was performed, and the supernatant liquid was analyzed, the results were as shown in Table 4.

After water was added to the waste sulfuric acid to dissolve iron, an alkali was added thereto, centrifugal sedimentation was performed, and the supernatant liquid was analyzed, and the results were as shown in Table 5.

Table 1 After heating and concentrating the waste sulfuric acid, it was separated by crystallization, an alkali was added to the aqueous solution, centrifugal sedimentation was performed, and the supernatant liquid was analyzed, and the results were as shown in Table 6.

〔Effect of the invention〕

According to the present invention, it is possible to reduce impurities contained in waste acid (hydrochloric acid or sulfuric acid) by a simple method, and it is possible to reduce impurities contained in waste acid (hydrochloric acid or sulfuric acid) by a simple method. Since it becomes possible to carry out production, it is extremely useful industrially.

[Brief explanation of the drawing]

The drawing is a flow sheet illustrating one embodiment of the method of the invention.

Claims (1)

[Claims] 1. Neutralize waste acid containing a large amount of iron by adding a base to pH 3.
A method for removing impurities in waste acid, which comprises adjusting the concentration to 7 to 7 and separating and removing the generated hydroxide by natural sedimentation, filtration, centrifugal sedimentation, etc. 2. The method for removing impurities in waste acid according to claim 1, which comprises dissolving iron in waste acid to reduce free acid and then adding a base to neutralize it. 3. Impurities in the waste acid according to claim 1, characterized in that the iron salt is crystallized and recovered from the waste acid, and the resulting aqueous solution of the iron salt is neutralized by adding a base. How to remove. 4. The method for removing impurities from waste acid according to claim 3, characterized in that iron is dissolved in the waste acid and then crystallized.