DEVICE FOR ELECTROWINNING EUROPIUM WITH CHANNELED CELL AND METHOD THEREOF

Abstract

Disclosed are a device for electrowinning europium and a method thereof. The device for electrowinning europium using a channeled cell including a cathode cell includes a channel having an inlet and an outlet; an anode cell including a channel having an inlet and an outlet; and an ion-exchange membrane tightly interposed between the cathode and anode cells, wherein reduced europium is exhausted from the outlet of the cathode cell.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2013-0060319 filed on May 28, 2013 in the Korean Intellectual Property Office, the entirety of which disclosure is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a device for electrowinning europium and a method thereof. More particularly, the present invention relates to a device for rapidly electrowinning europium using a channeled cell and a method thereof.

2) Background of Related Art

First, europium (Eu) subject to electrowinning in the present invention will be described. Since the Eu is one of rare metals, a general scheme of electrowinning the Eu will be additionally described.

The rare metals refer to metallic elements which have features of scarcity due to a tiny amount of deposits and localization because the rare metals are exclusively concentrated on specific regions, so the rare metals are subject to the danger of early exhaustion and are unstable even in supply. In Korea, the rare metal becomes a generic term to refer to 35 kinds of elements such as Li, a rare earth element and In.

The rare earth element, which is a generic term to refer to total 17 elements of scandium (Sc), yttrium (Y) and fifteen lanthanides, has been used as a core material in phosphor (TV, fluorescent lamp), an abrasive (semiconductor, display) or a permanent magnet (electric vehicle, wind turbine).

As describe above, since the rare metal has the feature of scarcity and localization, China is a powerful nation in terms of reservation and production of the rare elements.

Specifically, since the physical and chemical properties of the rare earth elements are similar with each other, the rare earth elements could not be refined into the pure elements until the 1990's, so that they are rarely utilized. However, recently, as the technique of separating the rare earth elements has been developed, the utilization of the rare earth elements is abruptly increased from 1950.

Conventionally, schemes of separating and extracting a rare earth element include fractional crystallization, fractional precipitation, selective oxidation-reduction, ion exchange, solvent extraction, and extraction chromatography.

Hereinafter, an electrowinning scheme, which is an ion exchange scheme to separate europium (₆₃Eu) from among various rare earth elements, will be described.

The europium is an element used for CRTs and three-wavelength fluorescent lamps as an activator of red phosphor in the form of high-purity oxide so that the demand of the europium has been increased.

However, in spite of the increasing of the demand, the content of the europium contained in a rare earth element mineral is less than 0.5% based on all rare earth elements. Thus, a process having several stages is required for high-purifying the europium.

Until the 1940's to 1950's, the intermediate concentrate containing 8˜13% of europium has been obtained through a precipitation or ion exchange resin scheme. After the 1960's, the concentrate containing 75% of europium has been produced through solvent extraction. To obtain high-purified europium from the intermediate concentrate, the europium property, in which Eu³⁺ can be easily reduced into Eu²⁺, is utilized.

In detail, the Eu²⁺ loses a property of trivalent rare earth element ion and represents a property of alkaline earth metal ion. Based on the above property difference, the europium may be easily separated from the rare earth elements.

The metallic reduction and electrowinning have been used to reduce Eu³⁺. As describe above, in the present invention, the description of the metallic reduction will be omitted and the electrowinning of europium will be described.

First, as electrowinning, Hg-cathode electrowinning will be described with reference to FIG. 12 in which an Hg-cathode electrowinning device is depicted.

The Hg-cathode electrowinning, which is used first to refine europium through the electrowinning, uses Hg as a cathode and Pt as an anode in two electrolytic baths connected to each other through a salt bridge.

In detail, according to the electrowinning, the europium concentrate containing SO₄²⁻ ions is put in a cathode bath and sulfuric acid solution having the concentration of 1 mol/L is put in an anode bath. Then, if electrolyzed, EuSO₄ precipitate is formed by the europium in the cathode bath.

However, the Hg-cathode electrowinning can process only a small quantity and cause bad purity of europium, and in addition, may cause mercury contamination when europium oxide is produced, so the Hg-cathode electrowinning is not industrially used in recent years.

Next, as an electrowinning scheme, an ion-exchange membrane electrowinning scheme will be described with reference to FIG. 13 which schematically shows an ion-exchange membrane electrowinning device.

The ion-exchange membrane electrowinning scheme, which had been developed in 1980's, uses porous carbon electrodes installed in an electrolytic bath divided by an ion-exchange membrane.

According to the ion-exchange membrane electrowinning, europium is electrowinning while FeCl₂ solution is being input to the cathode bath at a predetermined speed in the state that concentrated europium (RECl₂, specifically, Eu³⁺) solution is put in the cathode bath.

In this case, the primarily reduced solution is secondarily reduced in an electrolytic bath having the same structure as that of the primary reduction, so that the europium reduction rate is increased to 99% or more. Then, the Eu²⁺ solution is transferred into a precipitation device.

In the precipitation device, the Eu²⁺ solution transferred from the electrolytic bath reacts with the mixing solution of ammonium sulfate of 2 mol/L and sulfuric acid of 1 mol/L to obtain EuSO₄ precipitate. Then, the europium is separated from the EuSO₄ precipitate. In this case, to restrain europium oxidation due to air contact, the EuSO₄ precipitate is preferably purged with nitrogen gas.

Next, porous carbon electrode electrolytic reduction will be described with reference to FIG. 14 which schematically shows a porous carbon electrode electrolytic reduction device.

In FIG. 14, reference numerals 1 and 3 denote outlets, reference numeral 2 denotes a gas exhaustion hole, reference number 4 denotes an inlet, reference number 5 denotes a glass reaction container, reference numeral 6 denotes a cathode, reference numeral 7 denotes an anode, and reference numeral 8 denotes porous graphite.

Similar to the ion-exchange membrane electric reduction, although the porous carbon electrode electrolytic reduction using the porous carbon electrode electrolytic reduction device depicted in FIG. 14 uses a porous carbon electrode, the porous carbon electrode has holes smaller than those of the ion-exchange membrane electrolytic electrode. In this case, the porosity is about 43%.

The porous carbon electrode electrolytic reduction utilizes the principle that, when the solution containing europium-concentrated rare earth chloride and Br is input to the material inlet under a pressure, the europium reduction reaction occurs while the solution passes through the air gaps of the cathode and the oxidation reaction of Br occurs at the anode.

However, the porous carbon electrode electrolytic reduction also has a low reduction rate so that the recovery rate is deteriorated. In addition, the product is contaminated by Br.

As described above, according to the conventional electrowinning schemes, there is adopted a scheme of increasing a reaction area, in which a stirrer such as a propeller is used or the reduction bath itself is rotated in order to increase the quantity of reaction and the reaction speed, or a scheme of increasing a reaction time, in which, as the ion-exchange membrane electrolytic reduction described with reference to FIG. 13, the electrowinning solution obtained through a primary electrolytic reduction is secondarily electrolytically reduced, has been used.

There is a related art which is Korea Unexamined Patent Publication No. 10-1997-0006187 (published on Feb. 19, 1997) entitled “a method of treating waste fluid using electrolytic oxidation and apparatus thereof”.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to provide a device which is capable of greatly increasing a reaction quantity of europium by increasing the contact area of an electrowinning solution containing europium ions, and at the same time, reducing a reaction time of the europium by increasing a reaction speed of the europium, without using a stirring unit and a porous electrode, without rotating an electrolytic bath and without performing a process of electrowinning several times, and a method thereof.

Another object of the present invention is to solve a problem of contaminating a target metal, that is, europium (Eu) which occurs in the related art.

The present invention suggests several objects without limitation to the above objects, and other objects, which are not described, can be clearly comprehended from the following description by those skilled in the art.

To achieve the above-described objects, according to an embodiment of the present invention, there is provided a device for electrowinning europium using a channeled cell including a cathode cell including a channel having an inlet and an outlet; an anode cell including a channel having an inlet and an outlet; and an ion-exchange membrane tightly interposed between the cathode and anode cells, wherein reduced europium is exhausted from the outlet of the cathode cell.

Preferably, the cathode and anode cells include graphite.

Preferably, at least one bead for generating a turbulent flow is formed on each inner surface of the channels of the cathode and anode cells.

In addition, a sectional shape of the channel may be one of a rectangular shape, a U-shape, and a V-shape.

Preferably, an electrowinning solution input to the inlet flows at Reynolds number of 2000 or more.

Preferably, a quantity of electric charge applied to the cathode and anode cells is 110% or more when the quantity of electric charge is substituted into a value obtained by dividing a quantity of applied electric charge by a theoretical quantity of electric charge.

According to an embodiment of the present invention, a solution containing Eu³⁺ is input to the inlet of the cathode cell, and a solution containing Fe²⁺, which is able to pair-react with the solution containing Eu³⁺ input to the cathode cell, is input to the inlet of the anode cell.

Further, at least one bead for generating the turbulent flow is installed per a unit length of the channel.

To achieve the above-described objects, according to another embodiment of the present invention, there is provided, a method of electrowinning europium using a channeled cell including preparing a substrate for a cathode cell and a substrate for an anode cell; forming channels in the substrates; fixing the substrates having the channels to both sides of an ion-exchange membrane by closely attaching the substrates to both sides of the ion-exchange membrane; and electrowinning europium after inputting a solution containing an europium ion through an inlet formed in the substrate.

Preferably, the substrate includes graphite.

In addition, at least one bead for generating turbulent flow is formed on an inner surface of the channel of the substrate.

Further, an electrowinning solution input to the inlet flows at Reynolds number of 2000 or more.

In addition, a quantity of electric charge applied to the cathode and anode cells is 110% or more when the quantity of electric charge is substituted into a value obtained by dividing a quantity of applied electric charge by a theoretical quantity of electric charge.

The details of other embodiments are described in the detailed description and shown in the accompanying drawings.

The advantages, the features, and schemes of achieving the advantages and features of the present invention will be apparently comprehended by those skilled in the art based on the embodiments, which are detailed later in detail, together with accompanying drawings. The present invention is not limited to the following embodiments but includes various applications and modifications. The embodiments will make the disclosure of the present invention complete, and allow those skilled in the art to completely comprehend the scope of the present invention. The present invention is only defined within the scope of accompanying claims.

The same reference numerals denote the same elements throughout the specification, and sizes, positions, and coupling relationships of the elements may be exaggerated for clarity.

According to the present invention, a reaction quantity of europium may be increased and, at the same time, an electrowinning speed of the europium may be increased without using a stirring unit and a porous electrode, without rotating an electrolytic bath and without performing a process of electrowinning several times.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view showing a channeled cell constituting a device for electrowinning europium according to an embodiment of the present invention.

FIG. 2 is a schematic plan view showing a channeled cell constituting a device for electrowinning europium according to an embodiment of the present invention.

FIG. 3 is a schematic sectional view showing a channeled cell constituting a device for electrowinning europium according to an embodiment of the present invention.

FIG. 4 is a schematic sectional view showing a device for electrowinning europium according to an embodiment of the present invention.

FIGS. 5a and 5b are a view showing a simulation of a fluid flow difference according to Reynolds number in a channel of a device for electrowinning europium according to an embodiment of the present invention, where FIG. 5a is a view showing a case that the Reynolds number is 69.44 and FIG. 5b is a view showing a case that the Reynolds number is 6944.

FIG. 6 is a graph showing variations of Reynolds number and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

FIG. 7 is a graph showing a quantity of electric charge (which is a value substituted into applied quantity of electric charge/theoretical quantity of electric charge) and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

FIG. 8 is a graph showing variations of a channel length and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

FIG. 9 is a graph showing variations of a channel sectional area and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

FIG. 10 is a graph showing variations of pH of a solution containing europium electrolytic Eu³⁺ and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

FIG. 11 is a flowchart schematically illustrating a method of electrowinning a rare metal according to an embodiment of the present invention.

FIG. 12 is a schematic view showing an Hg-cathode electrowinning device according to the related art.

FIG. 13 is schematic view showing an ion-exchange membrane electrolytic reduction device according to the related art.

FIG. 14 is a schematic view showing a porous carbon electrode electrolytic reduction device according to the related art.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter embodiments of the present invention will be described in detail with reference to accompanying drawings.

FIG. 1 is a schematic perspective view showing a channeled cell constituting a device for electrowinning europium according to an embodiment of the present invention.

Referring to FIG. 1, a channeled cell 100 constituting a device for electrowinning europium according to an embodiment of the present invention may include a substrate 120, a channel 160 including an inlet 130 through which an electrowinning solution is input and an outlet 140 through which an electrowinning completed solution is discharged, and a turbulent flow generating bead 180 formed at a part of the channel 160.

As shown in FIG. 1, although only one channeled cell 100 constituting a cathode or anode of the device for electrowinning europium is depicted in FIG. 1, it should be understood that two channeled cells 100 are required for the cathode and anode. This will be described below with reference to FIG. 4.

As shown in FIG. 1, although the channel 160 of the channeled cell 100 may have an arc shape, if required, the channel 160 may have a shape formed by alternating a U-shape and an inverted-U shape. That is, the channel 160 may include a bent portion having a curved shape.

Only, since the channel 160 depicted in FIG. 1 has the by-effect that the fluidity of the electrowinning solution, that is, the Reynolds number is increased at the portion bent at a right angle, it is preferable to allow the channel 160 to have the arc shape.

Preferably, the channeled cell 100 or the substrate 120 is formed of graphite.

The reason of forming the channeled cell 100 or the substrate 120 of graphite is because the graphite is not corroded by acid, does not react with the europium obtained through the electrowinning, has excellent workability, and is a low price material.

As described above, it is preferable in the device for electrowinning europium to form the channeled cell 100 and the substrate 120 in the same shape.

As will be described below with reference to FIG. 4, the channeled cell 100 and the substrate 120 are preferably arranged to be matched with each other.

Further, as shown in FIG. 1, at least one turbulent flow generating bead 180 is preferably formed in the channel 160 provided on the substrate 120 every a unit length.

The unit length will be described below with reference to FIG. 2. Further, the preferable turbulent flow generating bead 180 will be described with reference to FIG. 3.

FIG. 2 is a plan view showing a channeled cell constituting a device for electrowinning europium according to an embodiment of the present invention.

It may be understood that the channeled cell 200 constituting the device for electrowinning europium depicted in FIG. 2 substantially has the same configuration as that depicted in FIG. 1. Thus, in the description of FIG. 2, the same elements will be assigned with the same reference numerals, and the repetition in the description of the same elements having the same reference numerals will be omitted in order to avoid redundancy.

As shown in FIG. 2, it may be known that the turbulent flow generating bead 180 is formed at a central portion of the channeled cell 200 with respect to a horizontal width.

In this case, it should be understood that the unit length represents the length from left to right of each channel 160 shown in FIG. 2.

As shown in FIG. 2, although the channel 160 may be formed from left to right in a single unit 160, the channel 160 may be formed in two columns separated from each other in the channel cell 200 like a double-arc shape.

If the unit length of the channel 160 having the arc shape is equal to ‘1’, the unit length of the channel 160 having the arc shape may be equal to ‘½’.

In this case, it is preferable to understand the unit length as a substituted unit length.

Thus, when at least one turbulent flow generating bead 180 is formed every the unit length in a case of the arc shape, at least one turbulent flow generating bead 180 may be formed every the unit length in a case of the double-arc shape. When the number of turbulent flow generating beads 180 having the double arc shape is compared with that of turbulent flow generating beads 180 having the arc shape, the number of turbulent flow generating beads 180 having the double-arc shape may be two times more than the number of turbulent flow generating beads 180 having the arc shape.

FIG. 3 is a schematic sectional view showing a channeled cell constituting a device for electrowinning europium according to an embodiment of the present invention.

In the channeled cell 300 constituting the device for electrowinning europium according to an embodiment of the present invention, a sectional shape of the turbulent flow generating bead 180 formed on the inner surface of the channel 160 may be known from FIG. 3.

As shown in FIG. 3, the turbulent flow generating bead 180 substantially has a cross-sectional surface of a trapezoid shape, but the sectional shape of the turbulent flow generating bead 180 is not limited thereto.

For example, the turbulent flow generating bead 180 may have a cross-section surface of a hexagonal pillar, a water drop shape or a semicircular shape.

In short, preferably, the turbulent flow generating bead 180 protrudes from the inner surface of the channel 160 at a suitable height.

To the contrary, the turbulent flow generating bead 180 may be formed by allowing the inner surface of the channel 160 to be concaved.

That is, according to an embodiment of the present invention, the bead 180 may be formed on the inner surface of the channel 160 in a concave-convex shape.

The bead 180 may be alternately formed on the inner surface of the channel 160.

It should be known that the bead 180 may have any shapes if the bead 180 can cause turbulent flow on the inner surface of the channel 160.

As described above, the turbulent flow generating bead 180 may protrude from the inner surface of the channel 160. In this case, a height of the turbulent flow generating bead 180 may have preferably a half of the height of the channel 160, or more preferably, two thirds of the height of the channel 160.

Even when the bead 180 is formed by allowing the inner surface of the channel 160 to be concaved, the height of the bead 180 is preferably determined in accordance with the above description.

A width or length of the turbulent flow generating bead 180 may be equal to that of the channel 160. However, the width of the turbulent flow generating bead 180, that is, the width, which is widened to the left and right in a direction of the unit length based on the width, is not limited to the width of the channel 160, but even when the width of the turbulent flow generating bead 180 is not smaller than that of the channel 160, if the by-effect of turbulent flow generation, that is, stirring is obtained, the turbulent flow generating bead 180 may have any widths.

The inlet 130 is depicted at a low end of FIG. 3. The reason is because it is assumed that the electrowinning solution is input from the rear surface of the substrate 120 when an ion-exchange membrane 420 (see FIG. 4) is finally interposed in the substrate 120.

Thus, it should be known that the shape of the inlet 130 may be changed into another suitable shape.

Three turbulent flow generating beads 180 are depicted in FIG. 3. As described above, this means that three turbulent flow generating beads 180 are formed per the unit length of the channel having.

That is, the turbulent flow generating bead 180 formed at one place in the channel 160 having the unit length has the arc shape as shown in FIG. 2. However, in FIG. 3, the turbulent flow generating beads 180 are formed at three places per the unit length of the channel having.

FIG. 4 is a schematic sectional view showing a device for electrowinning europium according to an embodiment of the present invention.

It may be known from FIG. 4 that right and left substrates 120-1 and 120-2 are tightly coupled to each other in the device 400 for electrowinning europium according to an embodiment of the present invention in the state that the ion exchange membrane 420 is interposed between the right and left substrates 120-1 and 120-2.

It is preferably understood that the right and left substrates 120-1 and 120-2 serve as a cathode cell and an anode cell. In the following description, the cathode cell may be referred to as a cathode or a substrate and the anode cell may be referred to as an anode or a substrate. However, it should be noted that they represent the same objects.

It is the most preferable that the right and left substrates 120-1 and 120-2, which serves as the anode and cathode cells, are formed of graphite.

The reason that the right and left substrates 120-1 and 120-2, all are formed of graphite has been described above.

It may be known from FIG. 4 that the cross-sectional shape of the channel 160 is rectangular. However, as described above, the sectional shape of the channel 160 may not be limited to the rectangular shape.

Meanwhile, it is preferable that the right and left substrates 120-1 and 120-2 have the same shape as described above.

All of the channels 160 formed in the right and left substrates 120-1 and 120-2 are arranged to match with each other.

In this case, the matched arrangement of both channels 160 means that the openings of both channels 160, which are formed in the right and left substrates 120-1 and 120-2 and face each other about the ion-exchange membrane 420, match with each other.

That is, when three channels 160 are formed in the right substrate 120-1, three channels 160 are formed in the left substrate 120-2. In addition, the right and left substrates 120-1 and 120-2 are arranged such that the openings of the channels 160 of one side are matched with the openings of the channels 160 of the opposite side.

Next, the chemical reaction of Eu ion (Eu³⁺) caused in FIG. 4 will be described.

The arrow {circle around (a)} of FIG. 4, which is depicted to describe one example of the rare metal electrowinning according to the present invention, represents that a solution containing Eu³⁺ is input into the cathode cell as an electrowinning solution. For example, the input of the electrowinning solution is preferably performed through the inlet 130 of FIG. 1.

The solution containing Eu³⁺ refer to a solution that contains Eu³⁺ among solutions which are obtained by removing light rare earth elements from solutions, in which the rear earth element is leached, through a solvent extraction.

The Eu³⁺ contained in the solution containing Eu³⁺ is reduced to europium through the sequential reactions of following chemical reaction formulas 1 and 2

Eu³⁺+e⁻→Eu²⁺  [Chemical Reaction Formula 1]

Eu²⁺+SO₄²⁻→EuSO₄(s)↓  [Chemical Reaction Formula 2]

Since the reduction of europium occurs on the electrode surface during the reduction reaction through the electrowinning expressed as the chemical reaction formula 1, in the related art, a scheme of increasing a reaction surface area using a porous electrode (see FIGS. 13 and 14) is utilized to improve the reaction efficiency.

To the contrary, it should be noted that the electrowinning is performed by using the configuration of the substrates 120-1 and 120-2, the channels 160 formed in the substrates 120-1 and 120-2, and the turbulent flow generating bead 180 formed in at least one part of the channels 160 in the present invention as shown in FIGS. 1 to 4.

Preferably, as soon as the Eu³⁺-containing solution is input in the direction of arrow {circle around (a)}, for example, a Fe²⁺-containing solution, which can cause a pair reaction, is input in the direction of arrow {circle around (c)}.

In this case, the pair reaction represents a reaction that can cause the most suitable reaction of reducing Eu³⁺ contained in the Eu³⁺-containing solution to Eu²⁺. In the present invention, the Fe²⁺-containing solution is used for the pair reaction.

While the Fe²⁺-containing solution is flowing from the allow {circle around (c)} to the arrow {circle around (d)}, the Fe²⁺-containing solution makes the pair reaction with the Eu³⁺-containing solution.

As the result, the Fe^2÷-containing solution is oxidized by the Eu³⁺-containing solution. In this case, while the Fe²⁺ is oxidized into Fe³⁺, an electron (e⁻) generated from the left substrate 120-2 flows into the right substrate 120-1 electrically connected thereto through a current flow (not shown), so that the Eu³⁺ in the Eu³⁺-containing solution input in the direction of arrow {circle around (a)} is reduced to Eu²⁺ by the electron (e⁻).

It should be understood that the reduction of Eu³⁺ in the Eu³⁺-containing solution to Eu²⁺ occurs not only on a part of the surface of the right substrate 120-1, but also actually on the remaining three surfaces of the channel 160 except for a part making contact with the ion-exchange membrane 420 at the same time.

The detailed mechanism of simultaneously causing the reduction of Eu³⁺ in the Eu³⁺-containing solution to Eu²⁺ on the three surfaces of the channel 160 will be described with reference to FIGS. 5a and 5b.

Only, it is preferable to understand that the reason of simultaneously causing the reduction of Eu³⁺ in the Eu³⁺-containing solution to Eu²⁺ on the three surfaces of the channel 160 is because the Eu³⁺-containing solution flows at Reynolds number of 2000 or more so that a turbulent flow is generated.

For reference, it should be noted that the Eu³⁺-containing solution as the electrowinning solution flows in the direction perpendicular to the ground, that is, in the y-axis direction perpendicular to the ground when it is assumed that the ground is an x-axis.

The remaining Eu³⁺-containing solution after being reduced to Eu²⁺ may be discharged through the outlet 140 denoted as arrow {circle around (b)} in FIG. 4.

In FIG. 4, while the Eu³⁺-containing solution flows from the arrow {circle around (a)} to the arrow {circle around (b)}, most Eu³⁺ is reduced to Eu²⁺. This is because current flows into the ion-exchange membrane 420 formed between the right and left substrates 120-1 and 120-2 so that the current helps most Eu³⁺ to be reduced to Eu²⁺ while the Eu³⁺-containing solution flows.

In this case, it is preferable that Cl⁻ ions exist in the ion-exchange membrane 420, so that the reduction of Eu³⁺ to Eu²⁺ is accelerated by Cl⁻ ions.

It has been already described above that the oxidation of Fe²⁺ to Fe³⁺ as the pair reaction corresponding to the reduction of Eu³⁺ to Eu²⁺ occurs on the left substrate 120-2 while the reduction of Eu³⁺ to Eu²⁺ occurs on the right substrate 120-1.

The solution containing Eu²⁺ reduced from Eu³⁺, that is, the Eu²⁺-containing solution is discharged in the direction of arrow {circle around (b)} and then, may be collected in the europium reaction container 440 containing a H₂SO₄ solution previously prepared.

The reaction of Eu²⁺ and SO₄²⁻ ions in the europium reaction container 440 may be expressed as the chemical reaction formula 2 of Eu²⁺+SO₄²⁻→EuSO₄(s)↓.

Finally, it should be noted that although the europium is selectively precipitated as EuSO₄ precipitation, other rare earth element ions (Sm³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Y³⁺, etc.) react with sulfuric acid (H₂SO₄) so that other rare earth elements are not precipitated but continuously exist in an ion state.

FIGS. 5a and 5b are a view showing a simulation of a fluid flow difference according to Reynolds number in a channel of a device for electrowinning europium according to an embodiment of the present invention, where FIG. 5a is a view showing a case that the Reynolds number is 69.44 and FIG. 5b is a view showing a case that the Reynolds number is 6944.

In more detail, FIG. 5a is a view showing the case that the Reynolds number of 69.44 and the flow rate of 10 cc/hr, and FIG. 5b is a view showing the case of the Reynolds number of 6944 and the flow rate of 1000 cc/hr.

Specifically, FIGS. 5a and 5b are views showing the mass-transfer phenomenon according to each of the Reynolds (Re) numbers as velocity vectors colored according to velocity magnitudes when the electrowinning solution is provided into the channel 160.

It may be known from FIG. 5a that, when the Re number is low, most of the mass migrations occur at the central portion of the channel 160, that is, only a portion colored with yellow. Specifically, the mass migration occurs only in the y-axis direction and rarely occurs in the x-z axis direction.

To the contrary, It may be known from FIG. 5b that, when the Re number is high, the mass migration actively occur in the x-z axis directions. The above phenomenon may occur because the electrowinning solution input through the inlet 130 forms swirl and the swirl continuously flows in the y-axis direction.

It is known in the art that the swirl actually occurs in a turbulent flow state and the swirl phenomenon due to the turbulent flow is effectively generated at the Re number 2000.

Hereinafter, ‘Re number’ will be described in brief.

The Reynolds number is a term of the hydrodynamic field that is defined as the ratio of “an inertia force” to “a viscous force”. In detail, the Re number is defined as the simple formula of (liquid density*flow velocity*vertical height)/liquid viscosity.

The Re number is utilized as one of the most important non-dimensional numbers in hydrodynamics and specifically, hydrokinetics. It has been know that, when the Re numbers are similar with each other, two types of fluid flows represent flows that are similar to each other in hydrodynamics.

When the Re number is low, a laminar flow dominated by a viscous force, which is calm and has a constant fluid flow, is generated. To the contrary, When the Re number is high, a turbulent flow dominated by an inertial force, which includes a vortex and has extreme perturbations, is generated.

Meanwhile, the Re number is named after Osborne Reynolds(1842-1912).

As described above, it should be understood that the case of the Re number of 2000 or more is noted in the present invention.

When the Re number is 2000 or more, it may be expected that since a flowing material, for example, an electrowinning solution makes contact with the electrode surface, and in more detail, makes contact with x and y axes, the probability that the flowing material makes contact with the electrode surface is increased, so that the reaction efficiency is proportionally increased.

To the contrary, when the Re number is less than 2000, it may be expected that although the flowing material, for example, an electrowinning solution makes contact with the electrode surface, the probability that the flowing material makes contact with the electrode surface is decreased, so that the reaction efficiency is proportionally decreased.

Hereinafter, various examples of the device for electrowinning europium according to the embodiment of the present invention will be described.

First, as described above, the solution containing Eu³⁺ refers to a solution that contains Eu³⁺ among solutions which are obtained by removing light rare earth elements from solutions, in which the rear earth element is leached, through a solvent extraction. In this case, although the pH value of the Eu³⁺-containing solution is about 0.5, it should be noted that the Eu³⁺-containing solution may have a pH value in the range −1 to 4 under various situations. However, it should be noted that the solution having 0.5 pH has been used in the present invention.

The composition of the Eu³⁺-containing solution used in the specific embodiment of the present invention is as following Table 1.

TABLE 1
Element Concentration (ppm)
Sm      9094
Eu      2000
Gd      15372
Tb      913
Dy      732
Y       1368

It may be understood based on Table 1 that the concentration of Eu contained in the Eu³⁺-containing solution is 2000 ppm.

Meanwhile, a rectangular shape has been applied as the cross sectional shape of the channel.

The cross sectional areas of the channel have been set into 0.2, 0.5 and 1.0 cm².

The lengths of the channel have been formed at 10, 50, 100, and 200 cm, respectively. In these cases, the cross sectional areas have been fixed to 0.2 cm² for convenience.

The theoretical quantity of electric charge required for reducing Eu³⁺ ions to 100% may be calculated according to Faraday law. It has been set in the present invention to apply 90%, 100%, 150% and 200% of the theoretical quantity of electric charge.

As described above, it is preferable to prepare the H₂SO₄ solution for precipitating EuSO₄ in the europium reaction container 440 (see FIG. 4). In this case, it is preferable to satisfy the interaction formula [SO₄²⁻]/[Eu³⁺]=1˜5. In the present invention, the quantity of SO₄²⁻ ions is maintained to be two times the quantity of europium.

Further, in the present invention, the recovery rate is obtained by measuring the quantity of Eu residual in the solution using the ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometer) after solid-liquid separating the EuSO₄ precipitates.

Meanwhile, based on various kinds of basic conditions described above, the experiments have been performed under following various different conditions: {circle around (1)} Re number (see FIG. 6), {circle around (2)} Quantity of electric charge, {circle around (3)} channel length (see FIG. 8), {circle around (4)} Cross-sectional area of channel (see FIG. 9), {circle around (5)} pH of Eu³⁺-containing solution (see FIG. 10). Hereinafter, the recovery rates (%) under the above various kinds of electrolytic condition will be described.

First, the recovery rate according to the Re number will be described.

FIG. 6 is a graph showing variations of Reynolds number and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

In FIG. 6, various kinds of variable control conditions are the same as those in following Table 2.

TABLE 2
	Cross-sectional	Channel		Quantity of
	area of channel	length	[SO42−]/	applied electric
pH	(cm2)	(cm)	[Eu3+]	charge (%)
0.5	0.2	100	2	150

According to the experimental result of the europium reduction performed based on the variable conditions in Table 2, the recovery rate (%) exceeds about 60% at the Re number less than 2,000, that is, about the Re number of 1,500. However, it is known that the recovery rate (%) reaches at 95% at the Re number of 2,000 or more so that the recovery rate actually approaches to 100%.

Meanwhile, even though the Re number reaches at 3,000, there is no difference in the recovery rate. Thus, it is understood that the Re number of at least 2,000 according to an embodiment of the present invention is preferable.

Next, the recovery rate according to the quantity of electric charge will be described.

FIG. 7 is a graph showing a quantity of electric charge (which is a value substituted into applied quantity of electric charge/theoretical quantity of electric charge) and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

In FIG. 7, various kinds of variable control conditions are the same as those in following Table 3.

TABLE 3
	Cross-sectional	Channel
	area of channel	length	[SO42−]/	Re
pH	(cm2)	(cm)	[Eu3+]	number
0.5	0.2	100	2	2082

According to the experimental result of the europium reduction performed based on the variable conditions in Table 3, as shown in FIG. 7, when the ratio of the substituted value of the quantity of applied electric charge into the theoretical quantity of electric charge, that is, the quantity of electric charge is 90%, the recovery rate (%) is less than 70%. However, when the quantity of electric charge is 110% or more, the recovery rate (%) are about 90% in all cases. Thus, when the quantity of supplied electric charge is over 110%, the quantity of electric charge has no correlation with the recovery rate (%).

Next, the recovery rate according to the channel length will be described.

FIG. 8 is a graph showing variations of a channel length and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

In FIG. 8, various kinds of variable control conditions are the same as those of following Table 4.

TABLE 4
	Cross sectional	Quantity of
	area of channel	applied electric	[SO42−]/	Re
pH	(cm2)	charge (%)	[Eu3+]	number
0.5	0.2	150	2	2082

Since the contact time and contact area are increased as the channel length is increased, it is expected that the reaction efficiency of europium electrowinning may be remarkably improved. Based on the above fact, the recovery rate will be described with reference to Table 4 and FIG. 8.

According to the experimental result of the europium reduction performed based on the variable conditions in Table 4, as shown in FIG. 8, in the relationship between the channel length and the recovery rate (%), the recovery rate (%) is not increased proportionally to the channel length.

In more detail, when the channel length is about 50 cm, the recovery rate (%) is about 88%. However, when the channel length is 100 cm, the recovery rate (%) is increased to 93%. When the channel length is lengthened to 200 cm, against expectations, the recovery rate (%) is not more increased.

Next, the recovery rate according to the cross-sectional area of the channel will be described.

FIG. 9 is a graph showing variations of a channel sectional area and a recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

In FIG. 9, various kinds of variable control conditions are the same as those in following Table 5.

TABLE 5
	Channel	Quantity of
	length	applied electric	[SO42−]/	Re
pH	(cm)	charge (%)	[Eu3+]	number
0.5	100	150	2	2082

It will be first mentioned that the quantity of flowing fluid must be more increased to maintain a constant Re number when the cross-sectional area of channel is increased.

As the result of the europium reduction according to the variable conditions in Table 5, as shown in FIG. 9, when the cross-sectional area of channel is 0.2 cm², 0.5 cm² or even 1.0 cm², the recovery rate is not almost changed.

This means that the cross sectional area of channel does not exert influence on the recovery rate when the Re number is 2,000 or more.

Next, the recovery rate and pH of the Eu³⁺-containing solution will be described.

FIG. 10 is a graph showing variations of the pH of the Eu³⁺-containing solution and the recovery rate in a device for electrowinning europium according to an embodiment of the present invention.

In FIG. 10, various kinds of variable control conditions are the same as those in following Table 6.

TABLE 6
	Channel	Quantity of
Cross-sectional	length	applied electric	[SO42−]/	Re
area of channel	(cm)	charge (%)	[Eu3+]	number
0.2	100	110	2	2082

First, it has been expected that since an H₂ discharging voltage is lowered when the pH is increased, the efficiency of the Eu³⁺ reducing reaction is increased.

As the result of the europium reduction according to the variable conditions in Table 6, as shown in FIG. 10, the recovery rate (%) is somewhat increased as the pH is increased. However, since it is obvious that high recovery rates (%) are actually obtained in most of pH values, this means that the variation of a pH value is not very important when reducing europium.

Hereinafter, a method of electrowinning europium according to an embodiment of the present invention will be described.

FIG. 11 is a flowchart schematically illustrating a method of electrowinning a rare metal according to an embodiment of the present invention.

Referring to FIG. 11, a method of electrowinning europium according to an embodiment of the present includes a step S10 of preparing substrates, a step S20 of forming channels in the substrates, a step S30 of attaching the substrates to both side surfaces of an ion-exchange membrane, a step S40 of electrowinning europium after inputting an Eu³⁺-containing solution, and a step S50 of reacting electrolyzed Eu³⁺-containing solution with H₂SO₄ solution to obtain EuSO₄ precipitation.

Step of Preparing Substrate

As described with reference to FIG. 1, in the step S10 of preparing substrates, the substrates 120 including graphite are prepared.

In this case, as described above, two substrates 120-1 and 120-2 for a cathode and an anode are prepared.

Step of Forming Channel in Substrate

As described with reference to FIGS. 1 to 3, in the step S20 of forming channels in the substrates, the channels 160 having a particular shape are formed in the substrates 120-1 and 120-2.

In this case, although the description of the various kinds of conditions about the channel 160 will be omitted since the various kinds of conditions about the channel 160 has been described above, it should be noted that at least one turbulent flow generating bead 180 must be formed in the channels every a unit length.

Step of Attaching Substrates to Both Side Surfaces of Ion-Exchange Membrane

In the step S30 of attaching the substrates to both side surfaces of the ion-exchange membrane, the substrate 120-1 and 120-2 for a cathode and an anode are attached to both side surfaces of the ion exchange membrane 420 (see FIG. 4).

In the present invention, a negative ion exchange membrane has been used as the ion exchange membrane 420 because an Eu³⁺-containing solution has been used as the electrowinning solution.

Step of Electrowinning Europium after Inputting Eu³⁺-Containing Solution

In the step S40 of electrowinning europium after inputting an Eu³⁺-containing solution, as described above, the Eu³⁺-containing solution is input through the inlet 130 and then the electrowinning is performed.

In this case, as shown in FIGS. 5a and 5b, the Eu³⁺-containing solution flows at the Re number of 2,000 by the turbulent flow generating bead 180 formed in the substrate 120-1, so that the Eu³⁺-containing solution is electrolyzed on the three surfaces of the channel 160 to reduce Eu³⁺ to Eu²⁺.

Although the Re number of 2,000 or more is achieved by inputting the Eu³⁺-containing solution into the inlet 130 at a high rate, it should be noted that the Re number of 2,000 or more may be achieved through the turbulent flow generating bead 180.

Step of Reacting Electrolyzed Eu³⁺-Containing Solution with H₂SO₄ Solution to Obtain EuSO₄ Precipitation

Finally, in the step S50 of reacting the electrolyzed Eu^3÷-containing solution with H₂SO₄ solution to obtain EuSO₄ precipitation, the Eu²⁺-containing solution reduced in the step S40 is collected in the europium reaction container 440 and then, the Eu²⁺-containing solution reacts with the sulfuric acid (H₂SO₄) contained in the europium reaction container 440, so that the EuSO₄ is finally obtained.

The detailed chemical reaction formula has been described with reference to the Chemical reaction formula 2, and the reaction process has been described with reference to FIG. 4.

Although the present invention has been described by making reference to the embodiments and accompanying drawings, it should be understood that the present invention is not limited to the embodiments but includes all modifications, equivalents and alternatives. Accordingly, those skilled in the art should understand the spirit and scope of the present invention as defined in the following claims. In addition, those skilled in the art should understand that the equivalents and the modifications belong to the scope of the spirit of the present invention.

Claims

1. A device for electrowinning europium using a channeled cell, the device comprising:

a cathode cell including a channel having an inlet and an outlet;

an anode cell including a channel having an inlet and an outlet; and

an ion-exchange membrane tightly interposed between the cathode and anode cells,

wherein reduced europium is exhausted from the outlet of the cathode cell.

2. The device of claim 1, wherein at least one bead for generating a turbulent flow is formed on each inner surface of the channels of the cathode and anode cells.

3. The device of claim 1, wherein a quantity of electric charge applied to the cathode and anode cells is 110% or more when the quantity of electric charge is substituted into a value obtained by dividing a quantity of applied electric charge by a theoretical quantity of electric charge.

4. The device of claim 1, wherein the cathode and anode cells include graphite.

5. The device of claim 1, wherein a sectional shape of the channel is one of a rectangular shape, a U-shape, and a V-shape.

6. The device of claim 1, wherein an electrowinning solution input to the inlet flows at Reynolds number of 2000 or more.

7. The device of claim 1, wherein a solution containing Eu3+ is input to the inlet of the cathode cell, and

a solution containing Fe2+, which is able to p-react with the solution containing Eu3+ input to the cathode cell, is input to the inlet of the anode cell.

8. The device of claim 2, wherein at least one bead for generating the turbulent flow is installed per a unit length of the channel.

9. A method of electrowinning europium using a channeled cell, the method comprising:

preparing a substrate for a cathode cell and a substrate for an anode cell;

forming channels in the substrates;

fixing the substrates having the channels to both sides of an ion-exchange membrane by closely attaching the substrates to both sides of the ion-exchange membrane; and

electrowinning europium after inputting a solution containing an europium ion through an inlet formed in the substrate.

10. The method of claim 9, wherein the substrate includes graphite.

11. The method of claim 9, wherein at least one bead for generating turbulent flow is formed on an inner surface of the channel of the substrate.

12. The method of claim 9, wherein an electrowinning solution input to the inlet flows at Reynolds number of 2000 or more.