KR101972003B1 - Process of red mud using microwave assisted selective extraction and carbonation using leachate and Fe magnetic separation from residue - Google Patents

Abstract

The present invention relates to a method of treating red mud, comprising the step of irradiating a red mud with microwaves and a step of filtering the mixture of red mud and distilled water to separate an extract and a precipitate, Can be recovered as carbonate minerals, and the precipitate can be used for recycling the red mud by magnetically separating and recovering iron.

Description

Technical Field [0001] The present invention relates to a method and apparatus for recovering iron from a fermented mud using a microwave,

The present invention relates to selective metal ion extraction from red mud using microwaves and iron recovery in residues through carbonate mineralization and magnetic separation.

Red mud, also called red mud, refers to the waste left after extracting alumina from bauxite according to the Bayer method. The amount of red mud that occurs according to the Bayer method is about two to three times the amount of alumina extracted from bauxite. More than 120 million tonnes of red mud are emitted globally in the form of sludge and over 40 million tonnes in dry powder form, the amount of which is steadily increasing. In Korea, more than 200,000 tons of sludge is emitted annually.

When alumina is extracted from the bauxite, an aqueous sodium hydroxide solution is used, so that the waste redmud has a strong base having a pH of about 10 to 13. There is no way to fundamentally deal with this red mud, and it has been landfilled or neutralized in artificial reservoirs or abandoned mines and then disposed of in the sea. In addition, crops, groundwater, ecosystem contamination, and human casualties can also occur when red mud is buried or buried in this way. In the past, in 2010, a large amount of red mud sludge buried in artificial reservoirs in Hungary flooded the surrounding villages causing crops and human casualties. Due to these problems, it is urgent to prepare red mud treatment methods.

Conventionally, Red Mud has been limitedly used as building materials such as bricks and concrete. It is difficult to extract metals because red mud contains recyclable metals such as iron, titanium, and aluminum in the form of stable oxides. When such red mud is used as a building material, it is desired to obtain a desired strength due to a large amount of metal components It was difficult. In addition, because of the strong basicity of red mud, there was a limit to use as a product.

In order to solve this problem, a method of extracting metal contained in red mud using strong acid or extracting metal using high pressure and high temperature has been used. However, there has been a problem that only some metal ions are extracted, And commercialization due to high-pressure conditions was also limited. Due to the limitations of this extraction method, limited treatment methods such as treating the surface of red mud with organic matter or sulfonating it as a heavy metal treating agent or an adsorbent have been used but it has not been a method to deal with red mud.

Conventionally, techniques for extracting specific metals such as copper, nickel, zinc, and gold by irradiating microwaves to ores or ores have been studied. However, there has been no research on extracting the recyclable metals contained in red mud using microwaves.

In order to overcome the limitations of the conventional red mud treatment technique as described above, the present invention separates an extract and a precipitate through a step of irradiating a microwave, and the extract solution is subjected to carbonate mineralization to recover metal ions in the extract, And recovering metal ions by magnetic separation to provide a method for recycling metals while solving environmental pollution problems caused by red mud which is an industrial waste.

The object of the present invention is (1) a step of irradiating a red mud with microwaves, (2) a step of dispersing red mud irradiated with microwaves in water, (3) a step of filtering the dispersion obtained in step (2) (4) contacting the extract obtained in the step (3) with carbon dioxide to recover the carbonate of the metal ion, and recovering the iron by magnetic separation of the precipitate obtained in the step (3) And recovering metal ions from the metal ions.

According to the present invention, there is provided a process for producing red mud, comprising the steps of: irradiating a red mud with microwaves; dispersing red mud irradiated with microwaves in water; separating the extract and the precipitate by filtering the dispersion; And recovering the iron by magnetically separating the precipitate obtained in the above step, and recovering the metal ion from the red mud.

When metal ions are recovered from red mud according to the present invention, red mud in a slurry state may be used, or red mud in a dry powder state may be used.

According to the present invention, when microwave is irradiated to the red mud, the cost consumed compared with the conventional method of adding strong acid to red mud or the metal extraction method using high temperature and high pressure conditions is low, Or an alkaline earth metal can be effectively extracted.

According to the present invention, when microwave is irradiated to a mixed powder of a red mud dry powder and an ammonium salt, metal ions can be selectively extracted.

According to the present invention, when metal ions are recovered from red mud, carbon dioxide, which is one of the greenhouse gases, can be removed.

In the case of magnetic separation according to the present invention, the separated iron can be reworked and recycled, and the residues after iron separation can be recycled as building materials such as concrete, cement, building aggregate and the like.

1 is a conceptual diagram showing a method of recovering metal ions from a red mud according to the present invention.
2 is a graph showing the concentration of Na ions extracted when irradiated with a microwave of 500 W at an output of a red mud slurry.
3 is a graph showing the concentration of Na ions extracted when irradiated with a microwave of 5000 W output power to a red mud slurry.
FIG. 4 is a graph showing the concentration of extracted Na ions when irradiated with a microwave of 500 W output power to a mixed powder of red mud dry powder and ammonium salt. FIG.
5 is a graph showing the concentration of extracted Na ions when irradiated with a microwave of 5000 W output power to a mixed powder of red mud dry powder and ammonium salt.
6 is a graph comparing the concentrations of extracted Na ions when irradiated with a microwave of output power of 5000W to each of mixed powders of red mud slurry, red mud dry powder and ammonium salt.
7 is a photograph of a precipitate formed by dispersing a red mud slurry irradiated with a microwave in water, separating the extract, and injecting carbon dioxide.
8 is a scanning electron microscope image of a precipitate obtained by dispersing (50 g / L) red mud slurry irradiated with a microwave of 1100 W for 15 minutes in water.
9 is a scanning electron microscope image of a precipitate obtained by dispersing a red mud slurry irradiated with a microwave of 1100 W for 15 minutes in water (100 g / L).
10 is a graph showing SEM-EDX results of the precipitate of FIG.
11 is a diagram showing SEM-EDX results of the precipitate of FIG.
FIG. 12 is a photograph of a material obtained by dispersing a red mud slurry irradiated with a microwave in water, separating the precipitate, and magnetically separating.
13 is a scanning electron microscope image of a material obtained by dispersing (50 g / L) a red mud slurry irradiated with a microwave of 1100 W for 15 minutes in water and subjecting the separated precipitate to magnetic separation.
14 is a scanning electron microscope image of a material obtained by dispersing (100 g / L) a red mud slurry irradiated with a microwave of 1100 W for 15 minutes in water and subjecting the separated precipitate to magnetic separation.
FIG. 15 is a diagram showing SEM-EDX results of the magnetically separated material of FIG. 13; FIG.
FIG. 16 is a diagram showing SEM-EDX results of the magnetically separated material of FIG. 14; FIG.

Red mud is composed of various kinds of metals and metal oxides as wastes after alumina is extracted from bauxite according to the Bayer method. In the process of extracting alumina according to the Bayer method, bases such as sodium hydroxide are used, so that red mud has a basicity of pH 10 to 13. These red muds have been buried or neutralized in man-made reservoirs or abandoned mines and have been disposed of in the sea. However, there is a risk that environmental pollution and human casualties may occur. Red mud contains recyclable metals such as iron, titanium, and aluminum in the form of stable oxides, making it difficult to recycle the metals contained in red mud, and there is a limit to how to recycle due to strong basicity of red mud. In order to solve such problems, there has been used a method of extracting metal contained in red mud using strong acid or extracting metal using high pressure and high temperature. However, there has been a problem that only some metal ions are extracted, , And commercialization due to high-pressure conditions was also limited.

The microwave refers to an electromagnetic wave having a frequency in the range of about 300 MHz to 300 GHz. When a microwave having a short wavelength is used, the microwave exhibits properties of rectilinear propagation, reflection, and absorption similar to light waves. When a microwave is irradiated onto a substance, the polarized molecule rotates very rapidly in accordance with the vibration of the electromagnetic wave and aligns along the electromagnetic field. At this time, the molecules are pushed, pulled or collided with each other by the rotation of the molecules, and the kinetic energy increases the temperature of the material. At this time, the molecules are vibrated more strongly as the natural frequencies of the molecules and the frequencies of the electromagnetic waves are similar. A technique for extracting specific metals such as copper, nickel, zinc and gold by irradiating microwaves to ores or ore powders has been studied using microwave, but research on extracting the recyclable metals contained in red mud using microwaves .

It has been found that metal ions can be extracted under relatively low temperature and low pressure conditions without using dangerous substances such as strong acids when irradiating microwaves to red mud.

The present invention relates to (1) a step of irradiating a red mud with microwaves, (2) a step of dispersing red mud irradiated with microwaves in water, (3) a step of filtering the dispersion obtained in the step (2) And (4) recovering the carbonate of the metal ion by bringing the extract obtained in the step (3) into contact with carbon dioxide, and recovering the iron particles by magnetic separation of the precipitate obtained in the step (3) And a method for recovering metal ions.

(One) Red Mud  Step of irradiating microwave

The method for recovering metal ions from red mud includes a step of irradiating red mud with microwaves. Here, the microwave may have a frequency in the range of about 300 MHz to 300 GHz, but when the frequency of the microwave is 2.45 GHz, the heating efficiency by the dipole ions is excellent and is suitable for extracting ions. The output of the microwave may be 500 to 5000W. If the output is less than 500W, the preprocessing time may be excessively long. If the output exceeds 5000W, the metals in the red mud may be vaporized. The microwave irradiation time should be adjusted according to the output of the apparatus. The longer the moisture content of the red mud is, the more the reaction time may be about 5 to 30 minutes.

In the present invention, the red mud of step (1) may be in the form of a slurry or powder. The slurry-type Red Mud, which accounts for a significant portion of the annual amount of Red Mud, can be used as is.

If red mud powder is used, it may be added with ammonium salt and irradiated with microwaves. The ammonium salt may be selected from the group consisting of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate and ammonium acetate, and the ammonium salt may be mixed in an amount of 10 to 100 parts by weight per 100 parts by weight of the dried redmud powder Lt; / RTI > The addition of ammonium salts increases the extraction of ions in the red mud by increasing the microwave absorption of the red mud powder and the ammonium salt mixture, but the pH is lowered to inhibit carbonate mineralization.

(2) Red Mud  Step of dispersing in water

The microwave irradiated red mud may be mixed with distilled water and a specific solids ratio. At this time, the liquid-solid ratio may be 1:20 to 1: 2. If the liquid ratio is lower than 1:20, the amount of ions extracted may be lower than the concentration capable of carbonate mineralization. If the liquid ratio is higher than 1: 2, the time required to separate the solid and the liquid becomes long. As the liquid ratio increases, the extraction efficiency decreases. The mixture is stirred for 30 minutes to 24 hours to sufficiently elute the ions in the red mud.

(3) separating the extract and the precipitate by filtering the dispersion

The method of recovering metal ions from red mud includes a step of separating the extract and the precipitate by using a centrifuge.

(4) recovering metal ions

Carbon dioxide is brought into contact with the separated extract to recover the metal ions contained in the extract by carbonate mineralization. At this time, the extract may be a low-temperature carbonate mineralization at 0 ° C to 5 ° C.

The red mud may be in the form of a slurry or a mixed powder of red mud dry powder and ammonium salt. In the case of using red mud powder, the step (3) includes adding a pH adjusting agent to the extracted liquid and then injecting carbon dioxide. Red mud shows a different degree of temperature rise due to microwave irradiation depending on its shape or composition. When a microwave is irradiated by adding an ammonium salt to powdered red mud, the temperature of the red mud may rise to about 1000 ° C., Under these conditions, the ammonium salt is melted and the ammonia evaporates, leaving behind the acid, and the metal ions are extracted. In this case, the extract will exhibit a pH of about 6 to 7, which requires a pH of about 8 to form carbonate minerals by the addition of carbon dioxide. Therefore, in the case of using a mixed powder of red mud dry powder and ammonium salt, the pH is adjusted by adding a pH adjusting agent before injecting carbon dioxide into the extract, thereby making a condition that a carbonate mineral can be formed.

Here, the pH adjusting agent may be selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and ammonia water, and any one that can raise the pH of the extract to 8 or more can be used.

The recovered carbonate may be a carbonate of a metal ion selected from the group consisting of sodium, calcium and magnesium.

The separated precipitate can recover iron from the separated precipitate by magnetic separation. The magnetic separation method may be a dry or wet magnetic separation method. At this time, it is possible to separate by applying magnetic force of 5,000 to 10,000 gauss.

If wet-magnetic separation is used, it may be possible to disperse the separated precipitate in water and to separate the iron using sebum stones. At this time, the separation is a mixture of iron oxide and magnetite, which can be separated through further processing.

When the precipitate is magnetically separated, the main component of the residue may be aluminum or silicon. Such residues can be used as building materials such as concrete and cement.

Example

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the examples.

Example  And Experimental Example

EXAMPLE 1 Red Mud Slurry Pretreatment Using Microwave

Example  1-1. Using 500W microwave Red Mud  Slurry pretreatment

100 g of red mud slurry was pre-treated for 5 minutes, 10 minutes, and 25 minutes with an output of 500 W and a frequency of 2.45 GHz using a microwave.

Example  1-2. Using 1100W microwave Red Mud  Slurry pretreatment

The red mud slurry was pretreated with a microwave having an output of 1100 W under the same conditions as in Example 1-1.

Examples 1-3. Red Mud slurry pretreatment using 5000W microwave

The red mud slurry was pretreated with a microwave having an output of 5000 W under the same conditions as in Example 1-1.

Example 2. Pretreatment of Red Mud Dry Powder Using Microwave

Example 2-1. Red-mud dry powder pretreatment using 500W microwave

13.4 g of ammonium chloride was added to 100 g of dried red mud powder, and the mixture was pre-treated for 5 minutes, 10 minutes, and 15 minutes using a microwave having an output of 500 W and a frequency of 2.45 GHz.

Example 2-2. Red Mud Dry Powder Pretreatment Using 1100W Microwave

Under the same conditions as in Example 2-1, the dried redmud powder was pre-treated with a microwave having an output of 1100 W.

Examples 2-3. Red-mud dry powder pretreatment using 5000W microwave

Red mud dry powder was pretreated with a microwave having an output of 5000 W under the same conditions as in Example 1-1.

Experimental Example 1. Extraction of metal ions contained in red mud

The pretreated red mud slurry or red mud dry powder according to Examples 1 and 2 was mixed with distilled water to have a solid ratio of 20 g / L, 50 g / L and 100 g / L, respectively, and stirred for 24 hours. The stirred mixture was centrifuged to separate the solid phase and the liquid phase. The solutions extracted from Red Mud of Examples 1 and 2 were analyzed by high frequency inductively coupled plasma atomic emission spectrometry (ICP-AES) and shown in Tables 1 and 2, respectively.

 As shown in Table 1, in the case of the red mud slurry, the extraction amount of Na increased as the pretreatment time was increased by the pretreatment under the output of 500 W. However, in the case of the pretreatment of 5000 W, But rather decreased (Figs. 2 and 3).

  In the case of the mixture of red mud and ammonium chloride, Na extraction rate increased with increasing reaction time. Also, the extraction rate increased as the output increased (Figs. 4 and 5).

In the 5000W experiment, it was confirmed that when the pretreatment was carried out for the same time, the extraction ratio of Na was higher in the case of mixing red mud with ammonium chloride than red mud slurry (FIG. 6).

Experimental Example 2: Carbonate mineralization

Experimental Example 2-1. Use of Red Mud slurry according to Example 1

The redmud slurry pretreated according to Example 1 was mixed with distilled water to give a solid ratio of 20 g / L, 50 g / L and 100 g / L, respectively, and stirred for 24 hours. The stirred mixture was centrifuged to separate the precipitate and the extract. The extract solution was injected with carbon dioxide at 0 ° C at 100 cm ³ / min to confirm formation of a pink precipitate.

The precipitates were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). As a result of XRD analysis, it was judged to be an amorphous mineral due to no peak, and NaHCO ₃ , Na ₂ CO ₃ , NaAl (CO ₃ ) (OH) ₂ and the like were analyzed by SEM image and SEM- Of amorphous Na-carbonate, Ca-carbonate, Mg-carbonate. It was also confirmed that the particle size was small and uniform when the content of Na was small.

Experimental Example 2-2. Use of mixed powder of red mud dry powder and ammonium salt according to Example 2

The mixed powder of the red mud dry powder and the ammonium salt that had been pretreated according to Example 2 was mixed with distilled water so as to have a solid ratio of 20 g / L, 50 g / L and 100 g / L, respectively, and stirred for 24 hours. The stirred mixture was centrifuged to separate the precipitate and the extract. After adding 2 mL of 0.1 M sodium hydroxide to the extract and stirring, the extract was injected with carbon dioxide at 0 ° C at 100 cm ³ / min to confirm formation of a pink precipitate.

The precipitates were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis result is not the peak is not determined to be an amorphous mineral, SEM images and component analysis by SEM-EDX mapping _{NaHCO 3, Na 2 CO 3,} NaAl (CO 3) (OH) ₂ amorphous Na- carbonate Carbonate, carbonate, carbonate, carbonate, carbonate, carbonate, carbonate, carbonate, carbonate and carbonate. It was also confirmed that the particle size was small and uniform when the content of Na was small.

Experimental Example 3: Magnetic separation of iron

The precipitate separated according to Experimental Example 2 was dispersed in deionized water and iron was separated using a magnet. The magnetic separation was carried out until the material adhered to the magnet was removed. The separated material and the residual material were respectively dried and pulverized and analyzed by XRD. SEM-EDX analysis was performed by separating only the black particles (FIG. 12) from the separated materials.

As a result of the XRD results, it was difficult to identify the exact components of the separated material and the residual material due to various impurities in the red mud. As a result of SEM-EDX, the content of iron in the magnetically separated material was increased and the content of aluminum and silicon was decreased as compared with that of the non-pretreated red mud (FIGS. 15 and 16).

The present invention has been described by way of examples. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (9)

(1) irradiating a red mud in the form of a mixed powder of red mud dry powder and ammonium salt to a microwave;
(2) dispersing red mud irradiated with microwaves into water;
(3) separating the extract and the precipitate by filtering the dispersion obtained in the step (2); And
(4) adjusting the pH of the extract obtained in the step (3) to 8 or more, bringing the recovered carbonate to contact with carbon dioxide, recovering carbonate of the metal ion, and recovering iron by magnetically separating the precipitate obtained in the step (3);
And recovering the metal ions from the red mud. delete delete The method according to claim 1,
Wherein the ammonium salt is at least one selected from the group consisting of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate and ammonium acetate. The method according to claim 1,
Wherein the ammonium salt is mixed in an amount of 10 to 100 parts by weight based on 100 parts by weight of the red mud dry powder. The method according to claim 1,
Wherein the step (1) is a step of irradiating red mud with a microwave having an output of 500 to 5000W. The method according to claim 1,
Wherein the carbonate recovered in step (4) is recovered from red mud which is a carbonate of a metal ion selected from the group consisting of sodium, calcium and magnesium. The method according to claim 1,
Wherein the extract in step (4) is contacted with carbon dioxide at 0 to < RTI ID = 0.0 > 5 C. < / RTI > The method according to claim 1,
Wherein the magnetic separation in the step (4) is a dry or wet magnetic separation method.

Images