KR20030023153A - Method for preparing magnetite in aqueous solution at room temperature and Method for water-waste-treatment using the said magnetite - Google Patents

Abstract

PURPOSE: A method for preparing magnetite in aqueous solution at room temperature is provided. The resultant magnetite is effectively applied to the disposal of industrial waste water and recycled, resulting in size and cost reduction of disposal equipments. CONSTITUTION: The preparation method of magnetite comprises the steps of: mixing an aqueous ferrous(Fe2+) solution with NaOH(2N) to be a ratio of FeSO4 to NaOH being 1:1 to form intermediates, a mixture of green rust and FeOH+; stirring the intermediates for 30min at room temperature to form precipitates, a mixture of lepidocrocite(gamma-FeOOH) and magnetite(Fe3O4); mixing precipitates with water and stirring to form pure magnetite. The prepared magnetite is used as flocculants or precipitants in waste water generated from plating, dyeing and leather industry.

Description

Method for preparing magnetite in aqueous solution at room temperature and Method for water-waste-treatment using the said magnetite

The present invention relates to a method for producing magnetite at room temperature in an aqueous solution and a method of using the above magnetite for treatment of industrial wastewater.

Magnetite has been studied for the purpose of use as a raw material of magnetic fluid.

Magnetic fluid is a colloidal solution in which fine particles (less than 0.01 μm) of a ferromagnetic material such as iron (magnetite) are mixed in a fluid such as oil and water. Magnetic fluids can be produced by grinding for a long time in an organic acid containing oleic acid in magnetite, agglomeration method by adsorbing oleic acid in wet magnetite, washing with water, dehydrating and dispersing it, and iron divalent ions (Fe ²⁺ ) and iron 3 There is a peptizing method in which the alkali is added to the covalent solution of ions (Fe ³⁺ ) and then heated in the presence of oleic acid and dispersed in kerosene (Kangnamgi, Oh Jae-hyun, Kim Man-man, 1993: magnetic fluid, electron Study, Vol. 2, No. 1, P 31-37). In order to produce a magnetic fluid that is ferromagnetic and remains in a colloidal state, many studies have been conducted on the formation of magnetite by a wet process and the dispersion rate by a solvent (dispersion medium) and a surfactant. Dispersing mediums include water, hydrocarbons, esters, diesters, polyphenylethers, carbon fluorides, and the like, and sodium oleate as a surfactant.

Magnetic fluid is the result of the synthesis of various actions. To understand the basic properties, theoretical studies on forces, surface energy, magnetic force, and thermal action between molecules are necessary. The interaction forces when the ferromagnetic particles approach each other by Brownian motion include van der Waals attraction, magnetic attraction, electrical double layer repulsion, and Steric repulsion. The physicochemical properties of the magnetic fluid can be determined by the dispersion rate, the amount of surfactant deposited, the magnetic (magnetic flux density), and the viscosity according to the magnetic field change.

Magnetite (magnetic iron oxide, Fe ₃ O ₄ ) is black or dark blue and has a spinel crystal structure, and iron divalent ions (Fe ²⁺ ) and iron trivalent ions (Fe ³⁺ ) It is a shared iron oxide. Magnetite is industrially produced by the solid melting of FeO and Fe ₂ O ₃ , and is used as an electrode material, catalyst, glass paint, varnish and anti-corrosion coating (Kirk-Orthmer, 1967: Ferrite. Encyclopedia of Chem. Tech., 8, 881-901).

Magnetite can also be produced from aqueous solutions by oxidation and hydrolysis of iron divalent ions (Feitknecht, W., 1959: Ueber die Oxidation von festen Hydroxyverbindun gen des Eisens in wae rigen L sungen. Z. Elektrochem. 63, 34- 43; Kiyama, M., 1974: Conditions for the formation of Fe 3 O 4 by the air oxidation of Fe (OH) 2 suspensions.Bull. Chem. Soc.Jpn., 47 (7), 1646-1650). Lepidocrocite (γ-FeOOH) and magnetite (Fe ₃ O ₄ ) are slow oxidation reactions in the form of green solution or green rust to form a green solution complex. Is generated by It is known that the pH range at this time is neutral or weak alkali, and when the oxidation reaction is completed, the pH becomes about 3 to 5 weakly acidic (see Fig. 1). If the pH is maintained above 6, it continues to oxidize to produce maghemite (γ-Fe ₂ O ₃ ) at a very slow rate. On the other hand, magnetite formation conditions and mechanisms in aqueous solutions are used to investigate the reaction pathways and formation patterns of various iron compounds in soils and underwater sediments (Schwertmann, U .; Taylor, RM, 1989: Iron oxides.In: Minerals in soil enviroments, Soil Sci. Soc.Amer.Book Series 1, 379-438), or for the treatment of heavy metals in wastewater (Takada, T .; Kiyama, M., 1970: Preparation of ferrites by wet method) In: Ferrite: Proceedings of the International Conference, Japan, 69-71).

Schwertmann (1991) mixed an aqueous ferric salt solution with an alkaline solution at 90 ° C. and cooled it in its natural state to produce magnetite (Schwertmann, U .; Cormell, RM, 1991: Iron oxides in the laboratory. VCH-Verlag, Weinheim, New York, Basel, Cambridge). The magnetite thus produced was Fe _2.08 ³⁺ Fe _0.92 ²⁺ O ₄ (chemical analysis) or Fe _2.03 ³⁺ Fe _0.95 ²⁺ O ₄ (Moessbauer-Spectroscopy), and the surface area was 4 m ² / g or less. The production of magnetite depends on pH, temperature, type of anion, and the like. If the pH is 6-7, gothite (α-FeOOH) and repidocrosite (γ-FeOOH), if the pH is 8 or more magnetite, and if the pH is 14 gothite is produced. In order to obtain pure magnetite, it is better to keep the pH constant by continuously adding alkali. Bernal (1959) and others also found that magnetite and repidocrosite were produced by oxidation of Fe (OH) ₂ -suspension (Kiyama, M., 1974: Conditions for the formation of Fe 3 O 4 by the air). oxidation of Fe (OH) 2 suspensions.Bull.Chem.Soc.Jpn., 47 (7), 1646-1650).

According to Feitknecht (1959), lepidocrocite (γ-FeO (OH)), δ-FeO (OH) and γ-Fe ₃ O ₄ are the surface reactions of green rust, Fe (OH) ₂ and Fe ₃ O ₄ particles. It is reported to generate from. α-FeO (OH) is produced from aqueous iron salt solution. Fe ₃ O ₄ is produced by surface oxidation of green rust particles.

Kiyama (1974) first mixed FeSO ₄ with NaOH to produce Fe (OH) ₂ -suspension (suspension), which was air oxidized at 40 ° C. or higher to produce pure magnetite. The optimum reaction conditions at this time were 2N-NaOH: FeSO ₄ (R) ratio of 1: 1, temperature of 40 ° C. or more, and air supply rate of 200 l / h. 1 shows the reaction conditions in which pure magnetite can be produced.

Generally, FeOH ⁺ is in equilibrium with iron divalent ions (Fe ²⁺ ) in the neutral suspension and HFeO ₂ ^{− in the} alkaline range. When only saturated with Fe (OH) ₂ , most of the iron divalent ions will be Fe (OH) ⁺ , and pure magnetite is produced in the pH range of 9.3 to 9.4. In the formation mechanism, the magnetite particles successively from between Fe (OH) ⁺ and the ferry hydroxy rokso complex co-precipitation (Coprecipitation) with a pH of 9 to 10 from the condition of (Ferrihydroxo complex) generated by oxidizing Fe (OH) ⁺ floor Is generated. Some magnetite particles are slowly oxidized to magnetite (γ-Fe ₂ O ₃ ) at the outside of the layer, and FeO (OH) is produced outside of the perhydroxyl complex layer. The optimum condition for the production of pure magnetite is that the Fe (OH) ⁺ layer is large, which increases with increasing temperature.

Taylor et al. Have published a detailed study of iron oxide production pathways (Taylor, RM; Maher, BA; Self, PG, 1987: Magnetite in soils: Synthesis of superparamagnetic magnetite. CSIRO Div. Soils, South Australia). The thin spherical magnetite particles could be easily produced in nature according to pH and temperature conditions. However, Schoer (1984) did not produce pure magnetite as a result of X-Ray Diffractometry (XRD) of precipitates produced in the laboratory from iron and trivalent ions.

Conventional heavy metal-containing wastewater treatment technologies include high gradient magnetic separation (HGMS) using a ferrite process and magnetite powder.

Ferrite production conditions of the ferrite process are the same as the above-described production conditions of magnetite, and the production methods include the neutralization method and the oxidation method. The neutralization method is a mixture of iron trivalent ions and metals of other divalent ions with an alkali and reacted as shown in Formula 1 below:

2Fe ³⁺ + M ²⁺ (Ma ²⁺ , Zn ²⁺ , Co ²⁺ , Mg ²⁺ , Fe ²⁺ etc.) → MOFe ₂ O ₃

Oxidation is a method of mixing ferrous divalent ions and other divalent ions with an alkali and then air oxidizing at 60 ° C. or higher to produce ferrite (see Formula 2).

Fe ²⁺ + M ²⁺ + OH- + O ₂ → M _1-x Fe _{2 + x} O ₄

In the case of wastewater treatment using a ferrite process, the treatment efficiency is good, but high reaction temperature and air oxidation are required, resulting in a large apparatus and expensive equipment cost. Therefore, sewage treatment method using magnetite adsorption effect and magnetism using magnetite powder is being studied.

High Gradient Magnetic Separation is a method for concentrating and separating sludge in a fast time by using magnetite magnetization. After treating wastewater with a precipitant, it concentrates and separates sludge in a reaction tank installed with an electromagnet by adding magnetite powder and a polymer. It is.

However, this method is not yet widely used due to the specificity of the recovery and reprocessing of magnetite and the magnetic separation reactor. On the other hand, studies on the use of magnetite sludge obtained from wastewater treatment in steel mills instead of magnetite powder and the development of a simple magnetic separation reactor are being conducted.

The present invention is to solve the problems of the prior art as described above, an object of the present invention is to provide a method for producing pure magnetite without air oxidation at room temperature. It is still another object of the present invention to provide an industrial wastewater treatment method in which agglomeration and treatment effect of heavy metals and hardly decomposable substances are improved by adding the magnetite prepared above to industrial wastewater such as plating, dyeing, or leather wastewater.

Figure 1 shows the production range of magnetite according to the temperature, pH and the ratio of sodium hydroxide (NaOH) to iron sulfate (FeSO ₄ ) in order to facilitate the understanding of the present invention.

Figure 2a shows the results of treating and filtering the plating wastewater by adding the magnetite prepared at room temperature in the aqueous solution according to the present invention.

Figure 2b shows the result of treating and non-filtering the plating wastewater by adding the magnetite prepared at room temperature in the aqueous solution according to the present invention.

In order to achieve the above object, the magnetite production method at room temperature in the aqueous solution according to the present invention comprises the steps of: (a) to produce an intermediate product of a mixture of green rust and FeOH ⁺ layer by mixing sodium hydroxide in an aqueous ferrous salt solution; Rapidly stirring the intermediate product of step (a) at room temperature for 10 minutes to 5 hours to obtain a precipitate which is a mixture of repidocrosite and magnetite; And (c) adding pure water to the precipitate of step (b) to generate pure magnetite by secondary stirring.

The industrial wastewater treatment method according to the present invention is characterized in that the magnetite produced by the above method is added to plating, dyeing or leather wastewater to be used as a flocculant, a precipitant or an auxiliary agent.

Hereinafter, the configuration and the effects of the present invention will be described in more detail with reference to Examples and drawings. The following examples illustrate the content of the invention, but the content of the invention is not limited thereto.

The production method of magnetite is as follows. First, the intermediate product (mixture of Green Rust and FeOH ⁺ layer) produced by mixing alkali (NaOH) in an aqueous ferrous salt solution so that the ratio of 2N-NaOH: FeSO ₄ is 1: 1 is rapidly stirred at room temperature for 30 minutes. The precipitate thus produced is a mixture of lepidocrocite (γ-FeOOH) and magnetite (Fe ₃ O ₄ ). If it is continuously stirred, the pH is changed to a weak acid of 3 to 5, and α-FeOOH and Fe ₂ O ₃ are produced. However, pure magnetite (Fe ₃ O ₄ ) is produced when the water is mixed with the first concentrated precipitate (mixture of repidocrosite and magnetite) and subjected to secondary stirring. Precipitation and stirring under a magnetic field results in higher production efficiency of magnetite (Fe ₃ O ₄ ). Magnetite (Fe ₃ O ₄ ) precipitate prepared according to the method was confirmed by X-ray diffractometer (XRD) after drying.

The magnetite production method according to the present invention is understood differently from the existing production mechanism. Existing magnetite production reaction conditions should maintain the pH in an alkaline state of 9 to 10 while air oxidizing at high temperature. The higher the temperature, the lower the concentration of dissolved oxygen. In case of air oxidation, hematite (α-Fe ₂ O ₃ ) or goatite (α-FeOOH) is caused by a sudden surface reaction of particles or complex ions. This is because it is easy to generate. On the contrary, in the present invention, pure magnetite is produced by a weak oxidation reaction by mixing with water in a state where the mixture of high concentrations of lepidocrosite and magnetite is stabilized.

The magnetite prepared at room temperature in aqueous solution according to the present invention was treated by adding to industrial wastewater such as plating, dyeing or leather wastewater. As in the present invention, there is no case of wastewater treatment by adding the magnetite produced in the aqueous solution.

<Example 1>

As a result of precipitation by adding magnetite to an aqueous solution containing 100 mg / l of chromium (Cr), copper (Cu), cadmium (Cd), and lead (Pb), respectively, not only the adsorption of metal ions but also the flux with metal hydroxide ( Floc) formation and cohesion with lead hydroxide in the colloidal state was good. In addition, the amount of precipitate was reduced to 190 ml / l when magnetite was added, whereas the amount of precipitate was 350 ml / l when precipitated with NaOH alone at pH 9.5 and precipitation time was 20 minutes.

<Example 2>

As a result of the precipitation treatment by adding magnetite sludge to the wastewater of the plating plant, the removal efficiency of nickel (Ni) and chromium (Cr) could be increased, and the amount of precipitate was also reduced (see FIG. 2). Also, by installing electromagnet at outlet of sedimentation tank, continuous sedimentation treatment of plating wastewater and concentration separation of sediment were possible within 30 minutes of residence time, and Ni and Cr treatment efficiency was good.

<Example 3>

As a result of dyeing or treating the wastewater by adding magnetite, the chemical oxygen demand (COD _Cr ) for chromium, which had an initial concentration of 20,000 ppm or more, was 2,000 ppm, and the removal efficiency was 80-95%. Chemical Oxygen Demand (COD _Cr ) for chromium, which was below the initial concentration of 5,000 ppm, was 800 ppm, resulting in 60 to 85% removal efficiency. That is, it can be seen that when the magnetite prepared according to the present invention is added to industrial wastewater such as plating, dyeing, or leather wastewater, the coagulation and treatment effect of heavy metal materials are improved.

As described above, in the past, in order to produce pure magnetite, it had to be oxidized with air at 40 ° C. or higher. However, in the present invention, pure magnetite can be prepared without additional air oxidation at room temperature, and thus, magnetite at room temperature in aqueous solution according to the present invention. When manufacturing the reaction apparatus is simplified, the production cost is significantly lowered. In addition, the magnetite produced by the present invention can be utilized not only as a magnetic fluid but also for various uses.

The magnetite produced by the present invention may be added to industrial wastewater such as plating, dyeing, or leather wastewater to treat coagulation and treatment effect of heavy metals and hardly decomposable substances. This is because the magnetite according to the invention is added to industrial wastewater to form flocs. Therefore, according to the present invention, the industrial wastewater treatment method using magnetite is a conventional wastewater treatment technology, a ferrite process requiring conditions such as reaction temperature and air oxidation, sewage treatment using magnetite powder and high gradient of sludge. Compared with High Gradient Magnetic Seperation (HGMS), it is possible not only to reduce the size of the device, to reduce the cost of the facility, to recover and reprocess the magnetite, but also to greatly improve the wastewater treatment effect at a low cost.

Claims (2)

Mixing a sodium hydroxide with an aqueous solution of ferrous salt to produce an intermediate that is a mixture of green rust and FeOH ⁺ layer (a); Rapidly stirring the intermediate product of step (a) at room temperature for 10 minutes to 5 hours to obtain a precipitate mixture of repidocrosite and magnetite; And Method of producing a magnetite at room temperature in an aqueous solution comprising the step (c) of adding water to the precipitate mixture of step (b) and then performing a second stirring to produce pure magnetite. A method for treating industrial wastewater, wherein the magnetite produced by the method of claim 1 is added to plating, dyeing, or leather wastewater to be used as a flocculant, a precipitant or an auxiliary agent.