KR20190124133A - Recovering method for alumina from black dross - Google Patents

Abstract

The present invention relates to a method for enabling high recovery of alumina from black dross. The method according to the present invention comprises: a mechanical activation step of activating black dross by applying mechanical energy to black dross; and a leaching step of selectively dissolving an alumina component contained in the activated black dross by using a leaching solution comprising sodium hydroxide (NaOH).

Description

Recovery method of alumina from black dross {RECOVERING METHOD FOR ALUMINA FROM BLACK DROSS}

The present invention relates to a method for allowing high purity recovery of alumina from black dross.

Aluminum has properties such as light weight, high specific strength and good corrosion resistance. Aluminum metal is produced from ore, such as bauxite, or from secondary resources. However, compared to producing aluminum metal from ore, recycling secondary resources can save more than 95% energy.

Aluminum dross is produced through the processing of secondary resources containing aluminum metal, which contains a mixture of aluminum metal and nonmetallic materials such as aluminum oxides, nitrides, carbides, salts, metal oxides and other materials. Is done. This aluminum dross is partially recovered as a metal in the aluminum contained therein, the rest is a black dross.

Black dross is considered a hazardous waste because some toxic gases are produced during the treatment of black dross. However, black dross still contains aluminum metal and some metal oxides. Therefore, the recovery of valuable components contained in the black dross is important in terms of environmental problems and energy saving.

In order to recover aluminum, silica, and other components from such black dross, dry smelting and wet smelting processes have been developed as in the following patent document. Both processes have their advantages and disadvantages.

First, in the case of wet smelting, an acidic or alkaline solution is used to selectively elute some components from the black dross.

For example, at least 80% of alumina is dissolved in HCl solution, wherein the leaching rate of silica is 40%. However, HCl leaching is not preferable for the recovery of pure alumina because some oxides contained in the black dross are dissolved together in addition to alumina and silica.

On the other hand, the leaching rate of alumina by NaOH solution is relatively higher than that of HCl, but alkaline leaching solution has a little selectivity for alumina, and Ca, Fe and Mg oxides are hardly dissolved during NaOH leaching, but together with silica There is a problem that elutes.

Republic of Korea Patent Application Publication No. 10-2005-0080923 Republic of Korea Patent Publication 10-2005-0100985 Republic of Korea Patent Publication 10-2015-0070726

An object of the present invention is to solve the problem of selectively dissolving only an alumina component from black dross and providing an advantageous method for pure alumina recovery.

In order to solve the above problems, the present invention, the mechanical activation step of activating by applying mechanical energy to the black dross, and the alumina component contained in the mechanically activated black dross using a leaching solution containing sodium hydroxide (NaOH) It provides a method for recovering alumina from the black dross comprising a leaching step of selectively dissolving.

According to the present invention, only the alumina component can be selectively recovered in the leaching process of the black dross, so that the recovery of high purity alumina becomes easy.

FIG. 1 shows the XRD pattern of the black dross which was not mechanically activated and mechanically activated by milling the ball mill for 1 hour, 3 hours, 5 hours, 7 hours and 10 hours.
FIG. 2a shows a black dross without ball milling, FIG. 2b shows a black dross with ball milling for 1 hour, FIG. 2c shows a black dross with ball milling for 3 hours, and FIG. 2d shows a ball for 7 hours. Scanning electron microscopy image of black dross that performed milling.
FIG. 3 shows the effect of milling time on leaching of mechanically activated black dross at 5 ° C. NaOH solution at 50 ° C. (stirring rate 200 rpm, pulp density 20 g / L).
FIG. 4 shows the effect of milling speed on leaching of mechanically activated black dross at 5 ° C. NaOH solution at 50 ° C. (2 hours reaction time, 20 g / L pulp density).
5a shows a black dross without ball milling, FIG. 5b shows a black dross with ball milling at 400 rpm, and FIG. 5c shows a scanning electron microscope image of the black dross with ball milling at 700 rpm.
Figure 6 shows the effect of the concentration of NaOH on the leaching of the mechanically activated black dross at 50 ℃ (2 hours reaction time, 200rpm stirring, 20g / L pulp density).
FIG. 7 shows the effect of reaction temperature on leaching of mechanically activated black dross in 5M NaOH solution (2 hours reaction time, 200 rpm stirring speed, 20 g / L pulp density).
FIG. 8 shows the effect of pulp density on leaching of mechanically activated black dross at 50 ° C. (2 hours reaction time, stirring speed 200 rpm) in a 5M NaOH solution.
FIG. 9 shows the effect of reaction time on leaching of mechanically activated black dross in 50 ° C. (stirring rate 200 rpm, pulp density 20 g / L) in a 5 M NaOH solution.

Hereinafter, the configuration and operation of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

A method for recovering alumina from the black dross according to the present invention includes a mechanical activation step of activating the black dross by applying mechanical energy to the black dross and using the leached solution containing sodium hydroxide (NaOH) in the activated black dross. And a leaching step of selectively dissolving the prepared alumina component.

Further, in the method according to the present invention, the mechanical activation step may be preferably performed through ball milling, but is not necessarily limited to ball milling as long as it is a method capable of applying mechanical energy to the black dross.

In addition, in the method according to the present invention, the ball milling speed is preferably 250 to 550 rpm, in order to maintain leaching efficiency and to prevent elution of oxides such as Ca, Mg, Fe, and more preferably. Is 300 ~ 500rpm.

In the method according to the present invention, the concentration of sodium hydroxide (NaOH) in the leaching step is preferably maintained at 3 to 6M in terms of leaching efficiency, more preferably the concentration of sodium hydroxide (NaOH) is 4.5 ~ 5.5M

In the method according to the present invention, the pulp density in the leaching step is preferably maintained at 70 to 120 g / L in order to prevent dissolution of the silica while maintaining the leaching efficiency, and more preferably the pulp density is 90 to 110 g / L.

In addition, in the method according to the present invention, in the leaching step, the temperature of the leaching liquid is preferably maintained at 40 to 100 ° C. to increase the leaching efficiency, and more preferably, the temperature of the leaching liquid is 50 to 100 ° C.

Further, in the method according to the invention, the leaching time in the leaching step is preferably maintained at 2 hours or more.

EXAMPLE

First, black dross having an average particle size of 150 μm or less was prepared, and salts present in the black dross were removed by washing with water at 90 ° C., and the black dross was dried using an oven and used in the test. .

The chemical composition of the black dross thus prepared was analyzed using X-ray fluorescence spectroscopy (XRF), and the results are shown in Table 1 below.

ingredient Al Ca Fe Mg Si Ti content
(weight%) 40.52 3.55 8.34 2.86 15.13 12.01

As shown in Table 1, the black dross used in the examples of the present invention contained about 40% by weight of an aluminum component, and the metal components in the order of silicon, titanium, iron, calcium, and magnesium.

In order to mechanically activate the black dross thus prepared, ball milling was performed.

The ball mill used a vertical planetary ball mill (Fritsch Pulverisette 7 Bead Mill) with a maximum rotational speed of 800 rpm. Specifically, ball milling loads black dross (8 g) into a container with 40 g of agate balls (6 mm diameter ball) so that the weight ratio of the ball to the black dross is 5: 1, and then at various rotational speeds. The milling was carried out for 1 hour, 3 hours, 5 hours, 7 hours and 10 hours, respectively.

The crystal structure and shape of the black dross subjected to ball milling as described above were analyzed using X-ray diffraction and scanning electron microscopy under CuKα (40 kV / 40 mA, λ = 0.15406) radiation conditions.

The black dross mechanically activated via ball milling was carried out using NaOH solution. The leachate was prepared by dissolving NaOH (Duksan, 93%) in double distilled water. Specifically, the leaching process was performed using a 250 ml three necked flask equipped with a magnetic stir bar in the heating mantle. In order to avoid evaporation losses in this process, Teflon tape was used to seal the outer joint of the glass article. The leaching rate was examined while changing process conditions such as leaching temperature, pulp density, leaching time in leaching process. In addition, after the leaching of the slurry sample was filtered using a vacuum filtration method, the metal concentration of the leachate was analyzed by ICP-OES.

Crystal structure, crystal size and shape

Figure 1 shows the XRD pattern of the mechanically activated black dross without ball milling and with milling for 1, 3, 5, 7 and 10 hours.

As confirmed in FIG. 1, no difference in crystallinity is observed between the sample that is not mechanically activated and the sample that is mechanically activated. That is, no new crystal phases were observed in the mechanically activated sample.

However, the diffraction peak of Al ₂ O ₃ tends to widen and increase in intensity with increasing mechanical activation time. In addition, the ball milling process results in a significant change in the shape of the black dross due to severe plastic deformation of the particles during the milling process. Ball milling treatment reduced the crystal size of the black dross. The average crystal size (d) of the treated ball mill was estimated using [Equation 1] below.

[Equation 1]

(Where λ is the radiation wavelength, β is the maximum half value in radians, and θ is the Bragg angle in radians).

The full width at half maximum of the different patterns at 2θ = 65.189 is 0.2651 to 0.3240 when ball milled for 1 to 10 hours, and the determined values are shown in Table 2 below.

Milling time (hours) Average grain size (nm) One 52.6 3 50.6 5 45.0 7 44.0 10 43.0

As shown in Table 2 above, the ball milling time has a slight effect on the reactivity of the black dross, making the average grain size slightly finer. That is, the average grain size decreased from 52 nm to 43 nm as the ball milling time increased from 1 hour to 10 hours.

FIG. 2a shows a black dross without ball milling, FIG. 2b shows a black dross with ball milling for 1 hour, FIG. 2c shows a black dross with ball milling for 3 hours, and FIG. 2d shows a ball for 7 hours. Scanning electron microscopy image of black dross that performed milling.

As shown in FIGS. 2B-2D, the black dross initially contained particles of different sizes, and after mechanical activation was completed, were broken into smaller particles, and due to the agglomeration of small nanoparticles, large micrometers of large size Clusters were observed.

Effect of Milling Time

The structure of the mechanically activated black dross affects the leaching behavior of the oxide in the dross. In the ball milling process, milling time and milling speed are two important factors, which cause a change in the structure of the mechanically activated material. Therefore, the milling time effect was investigated.

First, ball milling applied a rotational speed of 400 rpm and the milling time was changed from 1 hour to 10 hours. The mechanically activated black dross was leached under the conditions of 50 ° C., 2 hours, pulp density 20 g / L, and stirring speed of 200 rpm using 5 M NaOH solution.

FIG. 3 shows the effect of milling time on leaching of mechanically activated black dross at 5 ° C. NaOH solution at 50 ° C. (stirring rate 200 rpm, pulp density 20 g / L). As shown in FIG. 3, when black dross was leached into NaOH solution, only alumina and silica were eluted, and no other metal oxide was eluted, regardless of the mechanical activation time. The leaching rates of alumina and silica were about 50% and 30%, respectively, and showed no regularity with respect to ball milling time.

As shown in Table 2, when the milling time increased up to 5 hours, the average crystal size rapidly decreased from 52.6 nm to 45.0 nm, but in the additional milling, there was no decrease in the average crystal size. The change in shape of the mechanically activated dross with the change in crystal size with milling time is in good agreement with the leaching results shown in FIG. 3.

Effect of Milling Speed

In order to investigate the effect of milling speed on the leaching behavior of the black dross, mechanical activation was performed while varying the milling speed for the dross from 250 rpm to 700 rpm. The mechanically activated dross was leached under the conditions of 50 ° C., 2 hours, pulp density 20 g / L, and stirring speed 200 rpm using 5 M NaOH solution.

FIG. 4 shows the effect of ball milling speed on leaching of mechanically activated black dross at 5 ° C NaOH solution at 50 ° C. (2 hours reaction time, 20 g / L pulp density). As shown in FIG. 4, the leaching rates of alumina and silica were about 45% and 25%, respectively, at a ball milling speed range of 250 rpm to 500 rpm, with little other oxides being eluted.

However, when the ball milling speed was increased from 550 rpm to 700 rpm, a significant change in the leaching behavior of oxides except alumina was observed, and the leaching rate of silica rapidly decreased from about 25% to about 5%. At this time, Ca, Fe, Mg and Ti oxide slightly increased.

High ball milling speeds lead to defect generation and reduction of diffusion distance in the microstructure of mechanically activated samples, which is when the leaching rates of Ca, Fe, Mg and Ti oxides change from 550rpm to 700rpm It seems to be the cause of the increase. The constant leaching rate of alumina in relation to the ball milling speed seems to be associated with the production of large clusters, which prevent the NaOH solution from moving into smaller nanoparticles containing alumina.

FIG. 5A is a black dross without ball milling, FIG. 5B is a black dross with ball milling at 400 rpm, and FIG. 5C is a scanning electron microscope image of black dross with ball milling at 700 rpm.

In FIG. 5C the black dross mechanically activated at high ball milling speed appears to be agglomerated. That is, fine particles with extremely high surface energy tend to aggregate to reduce their surface energy. This causes the leaching rate of the silica to decrease when the ball milling speed increases from 500 rpm to 700 rpm. The optimum ball milling speed required for the selective leaching of alumina from mechanically activated black dross is approximately 250-550 rpm, at which the impurities such as Ca, Fe, Mg and Ti oxides are negligibly dissolved, This is because the degree of filtration is a problem. More preferable ball milling speed in terms of leaching rate is 300 to 500 rpm.

Effect of NaOH Concentration

The effect of NaOH concentration on the leaching behavior of mechanically activated black dross was investigated at various NaOH concentrations at 1-7M and 50 ° C for 2 hours. For this test, a mechanically activated black dross was used at 400 rpm for 1 hour.

6 shows the effect of the concentration of NaOH on leaching of mechanically activated black dross at 50 ° C. (2 hours reaction time, 200 rpm stirring, pulp density 20 g / L).

As shown in Figure 6, as the NaOH concentration increased to 5M, the leaching rates of alumina and silica increased from 36% and 8% to 46% and 27%, respectively, after which the leaching rate was further increased when NaOH concentration increased. Rather, it tended to decrease slightly.

Ca, Fe, Mg and Ti oxides did not dissolve in all NaOH concentration ranges investigated. Low NaOH concentrations were not sufficient to maximize the leaching reaction, whereas high NaOH concentrations resulted in alkaline degradation of dissolved alumina and silica. In addition, some of the dissolved alumina reacted with silica to form sodium alumina silicate precipitates. The formation of sodium alumina silicate is described by the reaction scheme as shown in [Formula 2].

[Equation 2]

Therefore, when the NaOH concentration is in the range of 5-7 M, the leaching rate of alumina and silica is slightly reduced. Therefore, considering the leaching rate of alumina, the concentration of NaOH is preferably 3 to 6 M, and more preferably 4.5 to 5.5 M.

Effect of Leaching Temperature

In order to investigate the effect of the leachate temperature on the elution of the oxides in the black dross, leaching was carried out while changing the mechanically activated black dross at 400 rpm for 1 hour from 30 ° C. to 100 ° C. At this time, the concentration of the leachate was maintained at 5M, pulp density 20g / L.

FIG. 7 shows the effect of reaction temperature on leaching of mechanically activated black dross in 5M NaOH solution (2 hours reaction time, 200 rpm stirring speed, 20 g / L pulp density).

As shown in FIG. 7, as the leaching temperature increased from 30 ° C. to 100 ° C., the leaching rates of alumina and silica increased from 40% and 19% to 47% and 37%, respectively, while leaching of other oxides was negligible. It was enough.

As such, as the leaching temperature increases, the leaching rate of alumina and silica is due to an increase in available energy that contributes to atomic and molecular collisions that promote the interaction between hydroxyl ions, alumina and silica. see.

In view of such a point, 40-100 degreeC is preferable and, as for the temperature of a leach liquid, 50-100 degreeC is more preferable.

Effect of Pulp Density

In order to confirm the effect of pulp density on leaching, the effect of pulp density on leaching behavior of mechanically activated black dross at 400 rpm for 1 hour was measured by changing the pulp density from 20 g / L to 120 g / L. Was performed. At this time, the leaching process was carried out to react the 5M NaOH solution at 50 ℃ for 2 hours.

FIG. 8 shows the effect of pulp density on leaching of mechanically activated black dross at 50 ° C. in a 5M NaOH solution (2 hours reaction time, 200 rpm stirring speed).

As seen in FIG. 8, as the pulp density increased from 20 g / L to 120 g / L, the leaching rate of alumina decreased slightly. The leaching rate of silica decreased rapidly as the pulp density increased, and the silica did not dissolve at all when the pulp density was 100 g / L or more. In addition, Ca, Mg, Fe and Ti oxides also did not dissolve at all pulp densities, resulting in a pure alumina solution under these conditions.

As the pulp density increases, the amount of NaOH available in the leaching reaction decreases and the viscosity of the solution increases, which increases the mass transfer resistance at the solid-liquid interface. Accordingly, an increase in the pulp density is expected to lead to a decrease in the leaching rate of alumina and silica, while leaching behavior of alumina meets this tendency, but in the case of silica, the leaching rate rapidly decreases. The reason why the leaching rate of silica decreases rapidly seems to be due to the precipitation of silica by reaction of NaOH with dissolved alumina.

From these results, it can be seen that by controlling the pulp density, only alumina can be selectively eluted from the mechanically activated black dross. In this case, the pulp density is preferably 70 g / L or more from the viewpoint of the selectivity of the alumina, 120 g / L or less is preferable from the viewpoint of the leaching efficiency, and more preferably 90 to 110 g / L.

Effect of leaching time

The effect of leaching time was investigated using 5 M NaOH at a pulp density of 100 g / L and a temperature of 50 ° C. Specifically, the leaching process was performed while changing the leaching time of the mechanically activated black dross at 400 rpm for 2 hours to 10 hours.

FIG. 9 shows the effect of reaction time on leaching of mechanically activated black dross in 50 ° C. (stirring rate 200 rpm, pulp density 20 g / L) in a 5 M NaOH solution.

As shown in Figure 9, the leaching time performed in this test did not appear to substantially affect the leaching behavior of the mechanically activated black dross. That is, the leaching time is sufficient as long as the leaching is made constant, preferably 2 hours or more is sufficient, the leaching time may be limited to within 6 hours in terms of process efficiency.

The leaching rate of alumina through this test was about 35%. At this time, the leaching rate of other metal oxides including silica was substantially close to zero, and the purity of alumina obtained from the leaching solution at leaching time for 2 hours was 98.8%.

That is, according to the method according to the present invention, only alumina can be selectively eluted with little restriction on the elution of the metal oxide containing silica, thereby facilitating recovery of pure alumina.

Claims (7)

A mechanical activation step of activating by applying mechanical energy to the black dross,
A leaching step of selectively dissolving an alumina component contained in the activated black dross using a leaching solution containing sodium hydroxide (NaOH),
A method for recovering alumina from black dross. The method of claim 1,
The mechanical activation step is made through ball milling,
A method for recovering alumina from black dross. The method of claim 2,
The rotation speed of the ball mill is 250 ~ 550rpm,
A method for recovering alumina from black dross. The method of claim 3,
In the leaching step, the concentration of sodium hydroxide (NaOH) is 3 ~ 6M,
A method for recovering alumina from black dross. The method according to any one of claims 1 to 4,
In the leaching step, the pulp density is 70 ~ 120g / L,
A method for recovering alumina from black dross. The method of claim 5,
In the leaching step the temperature is 40 ~ 100 ℃,
A method for recovering alumina from black dross. The method of claim 5,
In the leaching step, leaching time is more than 2 hours,
A method for recovering alumina from black dross.

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