JP4282626B2 - Magnesium chloride purification equipment - Google Patents

Description

  The present invention relates to a metal salt purification method, a metal salt purification device, and a magnesium chloride purification device that remove impurities that can be decomposed by electrochemical treatment from a solution in which the metal salt is dissolved.

In the chemical industry field, purification of other metals using an aqueous metal salt solution is performed. For example, when titanium metal is obtained, a Kroll method is used in which TiCl ₄ obtained by treating ore (TiO ₂ or FeTiO ₃ ) with chlorine gas and carbon is reduced with magnesium or the like. In this method, magnesium is provided as magnesium chloride and electrolytically reduced magnesium is used. Further, magnesium that is reduced to titanium and returned to ions is reused.

At this time, a high concentration magnesium chloride solution is used. However, in the process of producing high-concentration magnesium chloride, there is a problem that impurities such as ammonia are mixed in the aqueous solution as a nitrogen compound. In the process of refining the metal titanium, impurities contained in the product, particularly impurities including C, O, N, etc., have a great influence on the workability of the metal titanium. Therefore, the magnesium chloride used for the metal titanium is required to have a higher purity, and ammonia in the aqueous solution has been removed by using a nitrogen removing device or the like. As for conventional magnesium electrolytic purification apparatuses, there are known documents as shown in Patent Document 1.
JP-A-5-271976

  The nitrogen removal apparatus used for the purification of magnesium chloride as described above oxidizes ammonia in an aqueous solution to nitrogen gas by hypohalite ions generated in the aqueous solution by immersing the electrode in the aqueous solution and performing electrolysis. Treatment to remove ammonia.

  However, in such a case, the aqueous solution that is the water to be treated has a problem that the pH is lowered and acidified as the electrolytic treatment proceeds. This acidification of the water to be treated often requires special pH adjustment in order to use the purified magnesium chloride solution as a material in the chemical industry, and the pH of the water to be treated is reduced by removing nitrogen compounds. It has been desired to purify an aqueous magnesium chloride solution, and thus a metal salt solution without fluctuation.

  Therefore, the present invention has been made to solve the conventional technical problem, and without changing the pH of the target aqueous solution, nitrogen compounds as impurities can be removed, and target magnesium chloride or the like can be obtained. It is an object of the present invention to provide a processing method and a processing apparatus that can appropriately purify a metal salt.

The apparatus for purifying magnesium chloride of the present invention comprises a pair of electrodes at least partially immersed in water to be treated containing magnesium chloride and an ammonium salt, and a stirring means for stirring the water to be treated. The treated water is treated by the electrochemical method used, and the stirring linear velocity of the stirring means is 2 m / second or less .

The purification apparatus for magnesium chloride according to claim 2 is characterized in that, in the invention according to claim 1, the viscosity of the water to be treated is 1 mPas or more.

According to the present invention, with respect to water to be treated containing magnesium chloride and an ammonium salt, the ammonium salt that is an impurity is effectively removed while maintaining the pH within a predetermined range, or appropriately chlorinated. Magnesium can be purified.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing an outline of a metal salt purification apparatus 1 of the present invention. The apparatus 1 for purifying a metal salt in this embodiment is an apparatus for treating water to be treated containing about 25 wt% of magnesium chloride (MgCl ₂ ) as a metal salt. In addition, ammonium chloride (NH ₄ Cl) is mixed in the treated water at a maximum of 2 wt%, and the pH is 6 before the treatment. The state in which 25 wt% of magnesium chloride is dissolved is substantially saturated, and the equilibrium pH of the solution depending on the concentration is 6.7.

  The purification apparatus 1 in the present embodiment includes at least a part of the treatment tank 2 that constitutes a treatment chamber 4 having an inlet and an outlet of water to be treated (not shown) and water to be treated in the treatment tank 4. A pair of electrodes arranged opposite to each other, that is, an anode 5, a cathode 6, a power source 7 for energizing these electrodes 5, 6, and a control device 12 for controlling the electrodes 7. It is configured. In the figure, 9 is a pH detection means for detecting the pH of the water to be treated in the treatment tank 2, and 10 is a stirrer as a stirring means for stirring the inside of the treatment tank 2.

  In this embodiment, the cathode 6 is made of, for example, brass which is an alloy of copper and zinc. The anode 5 is composed of, for example, a platinum ruthenium shape stable electrode.

  On the other hand, the control device 12 is constituted by a general-purpose microcomputer, and the pH detection means 9 is connected to the input side of the control device 12. Further, on the output side of the control device 12, an alarm lamp 13 for urging replacement of the power source 7, a driving unit (not shown) of the stirring bar 10 and the electrode 6 is connected.

  With the above configuration, water to be treated containing magnesium chloride as a purification target and ammonium chloride as an impurity as described above is stored in the processing chamber 4 in the processing tank 2, and the power supply 7 is turned on by the control device 12. . At this time, magnesium ions, chloride ions, ammonium ions, hydrogen ions, and hydroxide ions exist in the water to be treated.

By applying a potential to the electrodes 5 and 6, on the electrode 5 side constituting the anode, chloride ions in the water to be treated are oxidized to produce chlorine (reaction A), and the produced chlorine is treated. Reacts with water in water to produce hypochlorous acid as hypohalous acid (reaction B). The produced hypochlorous acid reacts with ammonia (ammonium ions) in the water to be treated, undergoes a plurality of chemical changes, and is converted into nitrogen gas (reaction C, reaction D). Hereinafter, Reaction A to Reaction D are shown.
Reaction A 2Cl ⁻ → Cl ₂ + 2e ⁻
Reaction B Cl ₂ + H ₂ O → HClO + H ⁺ + Cl ⁻
Reaction C NH ₃ + HClO → NH ₂ Cl + H ₂ O
NH ₂ Cl + HClO → NHCl ₂ + H ₂ O
NH ₂ Cl + NHCl ₂ → N ₂ ↑ + 3HCl
Reaction D 2NH ₄ ⁺ + 3HClO → N ₂ ↑ + 3HCl + 3H ₂ O + 2H ⁺

On the other hand, in the water to be treated, at the electrode 6 constituting the cathode, water is electrolyzed to generate hydrogen and hydroxide ions (reaction E).
Reaction E 2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻

Here, ammonium ions present in the water to be treated react with hypochlorous acid to generate protons (H ⁺ ) as shown in reaction D. Conventionally, in such a case, in order to improve the treatment efficiency of the nitrogen compound in the water to be treated, the stirring speed by the stirrer 10 is set to a certain linear speed or higher, for example, 3 m / second. For this reason, as the treatment of the nitrogen compound proceeds, protons in the water to be treated increase, and the pH of the water to be treated decreases.

  In the present invention, in order to suppress the increase in protons, the stirring by the stirrer 10 is operated at a linear velocity of 2 m / second or less. Here, it shows in FIG. 2 about the relationship between the said stirring speed and the linear velocity of pH of to-be-processed water.

In the experiment shown in FIG. 2, 80 mL of magnesium chloride containing 25 wt% magnesium chloride, 5800 mg / L ammonium chloride, and a small amount of manganese was used. Then, brass and platinum ruthenium shape stable electrodes, which are alloys of zinc and copper, were used as electrodes, and an electrolytic treatment was performed at 0.8 A (current density 20 mA / cm ² ) for 90 minutes with a distance between the electrodes of 5 mm. During the electrolytic treatment, the rotation speed of the rotor 10 was set to 0, 1.2, and 3.0 m / second, respectively, and the pH was measured for each.

  According to this, when the rotation is not performed at the time of the electrolytic treatment, the pH of the water to be treated is about 6.8 and 1.2 m / sec. The electrolytic treatment was completed while maintaining. On the other hand, the one rotated at 3.0 m / sec finished in the state of pH 0.3 and strong acid.

  Also from the experimental results, by setting the linear velocity of the solution stirring at the time of electrolytic treatment to 2 m / second or less, ammonium ions and the like (nitrogen compound) in the water to be treated and hypochlorous acid and the like generated by electrolysis By reducing the contact cross-sectional area and suppressing the reaction D, the treatment with the nitrogen compound does not affect the decrease in the pH of the water to be treated. Therefore, the pH of the water to be treated is an equilibrium pH according to the concentration of the aqueous solution of the metal salt, that is, the magnesium chloride solution in this embodiment.

  The magnesium chloride solution in this example has a viscosity of about 10 mPas and is a relatively high viscosity substance. Therefore, since the diffusion of ions in the aqueous solution is suppressed, the influence of pH due to the presence or absence of stirring during the electrolytic treatment of the water to be treated increases. However, if the viscosity is not less than water (1 mPas), the effect is exhibited.

  Moreover, in the said Example, the agitation means (stirring bar | burr 10) was provided in the processing tank 2, and it electrolyzed to-be-processed water, stirring with the said agitation means so that it might become 2 m / sec or less. However, in addition to this, when the metal salt to be purified is magnesium chloride and the substance mixed as an impurity contains an ammonium salt such as ammonium chloride, active stirring by the stirring means is not possible. It is assumed that the electrolytic treatment may be performed without the stirring means in the processing tank 2.

Further, the processing efficiency of the nitrogen compound in this case will be described using the experimental results of FIG. In the experiment shown in FIG. 3, 200 mL of magnesium chloride containing 25 wt% magnesium chloride, 5800 mg / L ammonium chloride, and a small amount of manganese was used. Then, brass and platinum ruthenium shape stable electrodes, which are alloys of zinc and copper, were used as electrodes, and the electrolytic treatment was performed at 2.8 A (current density 53 mA / cm ² ) for 3 hours with the distance between the electrodes being 5 mm. As shown in FIG. 3, the rotation speed of the rotor 10 during the electrolytic treatment is rotated at a linear velocity of 3 m / sec from the start of electrolysis until 40 minutes elapses, and from 40 minutes to 140 minutes elapse. Stopped spinning. Further, from the lapse of 140 minutes to the lapse of 160 minutes, the rotation was again performed at a linear velocity of 3 m / second, and the rotation was stopped after the lapse of 160 minutes. During this time, the pH of the water to be treated and the total nitrogen concentration in the water to be treated were measured. In FIG. 3, the pH change is indicated by a dotted line, and the total nitrogen concentration is indicated by a solid line.

  According to this, it can be seen that in any case, when the electrolytic treatment is performed while rotating at a linear velocity of 3 m / sec, the pH which was in the neutral range is lowered to the strongly acidic range. On the other hand, in any case, it was found that when the rotation was stopped and the electrolytic treatment was performed, the pH, which was a strongly acidic region, rose to the neutral region. In this case, since the magnesium chloride concentration in the water to be treated is 25 wt%, the equilibrium pH depending on the magnesium chloride concentration is 6.7. Therefore, it can be seen that the pH of the water to be treated when the electrolytic treatment is performed with the rotation stopped is restored to the equilibrium pH depending on the magnesium chloride concentration.

  On the other hand, it can be seen that the total nitrogen concentration in the water to be treated with respect to the presence or absence of the rotation decreases with time regardless of the presence or absence of the rotation. For this reason, the rotation of the stirrer 10 is stopped, and the contact cross-sectional area between hypohalous acid such as hypochlorous acid generated in the water to be treated by electrolysis and ammonium ion as the nitrogen compound is reduced. Even so, it can be said that the nitrogen compounds in the water to be treated are reduced.

  This is because the nitrogen compound such as ammonium ions in the water to be treated is neutralized with other metal species such as magnesium ions, hydroxide ions, other metal ions and the like in the process of neutralizing the pH of the water to be treated. Since the compound is formed and the metal compound is hardly soluble in water, the nitrogen compound in the water to be treated is treated.

  Therefore, in the water to be treated having a viscosity of 1 mPas or more as in the present invention, by performing the electrolytic treatment while stopping the agitation or performing the linear velocity of 2 m / sec or less, the pH of the water to be treated is reduced by the nitrogen treatment. It becomes possible to treat the nitrogen compound without influencing. Thereby, after removing nitrogen compounds, such as ammonium chloride, it becomes unnecessary to adjust pH of to-be-processed water exceptionally, and simplification of a refinement | purification process can be attained now. Moreover, it becomes possible to use the to-be-processed water after ammonium chloride removal as it is as a solution containing a high concentration magnesium chloride, and to improve the handleability as a material.

  In this example, magnesium chloride is purified as a metal salt, but in addition to this, alkali metal, that is, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium ( Cs), Francium (Fr) or alkaline earth metals, ie, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), transition metals, , Scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn) Yttrium (Y), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Technetium (Tc), Ruthenium (Ru), B Um (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), Lanthanum (La), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Rhenium (Re), Osmium (Os), Metals of iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), actinium (Ac), or a typical metal other than an alkali metal / alkaline earth metal and an anionic species, preferably a halide ion It may be a salt.

  In this example, the impurity for the purification of the metal salt is ammonium chloride, but other than this, those that can be decomposed by electrolysis, such as inorganic substances such as nitric acid, nitrous acid, ammonia, cyanide compounds, organophosphorus compounds ( For example, parathion, methyl parathion, EPN, methyl dimethone), polychlorinated biphenyl (PCB), organic chlorine compounds (for example, trichloroethylene, tetrachloroethylene, carbon tetrachloride, dichloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 1, It may be an organic substance such as 1-dichloroethylene, 1,1,1-trichloroethane), an agrochemical organic compound (for example, 1,3-dichloropropene, thiuram, simazine, thiobencarb).

  Here, in this embodiment, the electrode 6 constituting the cathode is made of brass made of an alloy of copper and zinc as described above, and therefore the surface of the electrode 6 is shown in FIG. As shown in FIG. 3, the surface of the electrode 6 becomes porous as shown in FIG. 3 because the zinc metal is lost from the surface due to the passage of time or the electrolytic reaction. Furthermore, the zinc metal once lost from the electrode 6 adheres to the surface of the electrode 6 again, thereby increasing the roughness of the surface of the electrode 6.

In the electrode 5 constituting the anode, the hypochlorous acid produced in the reaction B is totally dissociated in the alkaline region (pH> 9), and the amount of hydrogen ions and hydroxide ions in the water to be treated becomes equal. This stops the pH change. Simultaneously with this alkalinization, a reaction (reaction F) between magnesium ions and hydroxide ions proceeds. At this time, since the equilibrium pH of magnesium hydroxide and magnesium ions and hydroxide ions is 8 or less, the final pH of the water to be treated is the same as the equilibrium pH of the magnesium ions / magnesium hydroxide, In this example, the pH is 6.7. The equilibrium pH of magnesium ion / magnesium hydroxide varies depending on the magnesium concentration.
Reaction F Mg ²⁺ + 2OH ⁻ → Mg (OH) ₂ (equilibrium)

On the other hand, in the state where the roughness of the surface of the electrode 6 is increased and the unevenness is generated, magnesium ions and hydroxide ions in the water to be treated are formed on the unevenness formed by zinc reattached on the surface of the electrode 6 having a large roughness. It adheres as magnesium oxide (basic salt). Due to the adhesion of the magnesium hydroxide, the unevenness on the surface of the electrode 6 is further increased, so that magnesium hydroxide is deposited on the surface of the electrode 6 (reaction G).
Reaction G Mg ²⁺ + 2OH ⁻ → Mg (OH) ₂

  This deposition of magnesium hydroxide is accompanied by consumption of hydroxide ions in the water to be treated, leading to a decrease in the pH of the water to be treated. Therefore, at the start of the treatment, the pH of the water to be treated, which had a pH of about 6, gradually decreases and tends to be acidic.

  Therefore, in addition to the influence of stirring as described above, the precipitation of the magnesium hydroxide becomes a factor that lowers the pH of the water to be treated. If the electrolytic treatment is continued until the ammonium chloride is decomposed as it is, The pH of is greatly acidic. Therefore, in this embodiment, the control device 12 monitors the pH of the water to be treated by the pH detecting means 9, and when the pH becomes, for example, 4 or less, turns on the alarm lamp 13 to inform the user of the cathode. It is informed that the surface of the electrode 6 constituting the electrode 6 is replaced with a substantially smooth surface, that is, an unused electrode, for example, and the user replaces the electrode 6 accordingly. In this embodiment, the electrode 6 constituting the cathode is exchanged when the pH of the water to be treated becomes 4 or less. The pH changes. That is, it is good also as replacement | exchange, when pH falls to any value of 6.5-4, or when it falls from the pH of the to-be-processed water before a process.

  This also makes it possible to suppress the precipitation of magnesium hydroxide (basic salt) on the surface of the electrode 6 that constitutes the cathode, which causes a decrease in pH. Therefore, ammonium chloride, which is an impurity, can be electrolyzed without maintaining or changing the pH of the water to be treated within a predetermined range from neutral to ammonium chloride during the purification process of magnesium chloride. Therefore, the influence of removal can be minimized. Therefore, it is not necessary to adjust the pH of the water to be treated after removing ammonium chloride, and the purification process can be simplified. Moreover, it becomes possible to use the to-be-processed water after ammonium chloride removal as it is as a solution containing high concentration magnesium chloride, and can improve handling property.

  In this case, the optimum value of the pH value that serves as a reference for electrode replacement in the above-described embodiment differs depending on each metal forming the metal salt. That is, for example, the pH is 6.5 for magnesium, 5.5 for iron, 6.0 for manganese, 4.5 for nickel, 2.9 for copper, and 2.7 for zinc. In the case of cadmium, it is 5.3. The optimum pH value can be determined by the dissociation equilibrium pH at the saturation concentration of the metal salt, and the deposition of the basic salt on the electrode constituting the cathode starts when the dissociation equilibrium pH becomes lower than the dissociation equilibrium pH. Judgment can be made. For this reason, it is preferable to replace the electrode 6 constituting the cathode with an electrode having a substantially smooth surface when the pH is determined to have started to be accumulated.

  In the above embodiment, brass is used as the electrode 6 constituting the cathode. However, as a material that does not reattach to the electrode surface due to dezincification, titanium (Ti), platinum is used as the electrode 6. (Pt) or the like may be used.

  In the treatment of the nitrogen compound of the water to be treated in this case, the electrolytic treatment of the nitrogen compound does not affect the pH of the water to be treated by stopping the stirring speed at 2 m / second or less and then stopping. For this reason, the pH of the water to be treated depends only on the concentration of the metal salt, and this also makes it possible to purify the metal salt without changing the pH. Therefore, it is not necessary to adjust the pH of the water to be treated after removing ammonium chloride, and the purification process can be simplified. Moreover, it becomes possible to use the to-be-processed water after ammonium chloride removal as it is as a solution containing a high concentration magnesium chloride, and to improve the handleability as a material.

  In this case, as compared with the above-described embodiment, it is not necessary to perform an operation for replacing the electrode 6 constituting the cathode, so that it is more suitable for refining the metal salt.

  In this embodiment, magnesium chloride is purified as a metal salt. However, in the same manner as in the above embodiment, an alkali metal, that is, lithium (Li), sodium (Na), potassium ( K), rubidium (Rb), cesium (Cs), francium (Fr) or alkaline earth metals, ie, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) , Radium (Ra), transition metals, ie, scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) , Copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), lanthanum (La), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), actinium (Ac), or a typical metal other than alkali metal / alkaline earth metal and anion species Preferably, it may be a metal salt with halide ions.

  In this example, the impurity for the purification of the metal salt is ammonium chloride, but other than this, those that can be decomposed by electrolysis, such as inorganic substances such as nitric acid, nitrous acid, ammonia, cyanide compounds, organophosphorus compounds ( For example, parathion, methyl parathion, EPN, methyl dimethone), polychlorinated biphenyl (PCB), organic chlorine compounds (for example, trichloroethylene, tetrachloroethylene, carbon tetrachloride, dichloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 1, It may be an organic substance such as 1-dichloroethylene, 1,1,1-trichloroethane), an agrochemical organic compound (for example, 1,3-dichloropropene, thiuram, simazine, thiobencarb).

  According to the present invention, it is possible to industrially advantageously use a high-purity metal salt obtained, for example, magnesium chloride, by appropriately purifying a metal salt mixed with impurities without changing the pH before treatment. It becomes. In particular, with regard to magnesium chloride, it is possible to remove the mixed nitrogen compound without changing the pH. Therefore, when the obtained magnesium chloride is used for processing titanium metal, the handleability is improved.

It is explanatory drawing which shows the outline | summary of the refiner | purifier of a metal salt. It is a figure which shows the change of pH of to-be-processed water with respect to stirring speed. It is a figure which shows the effect of the stirring given to the total nitrogen concentration and pH in the electrolytic treatment of to-be-treated water. It is a schematic explanatory drawing in case the electrode surface which comprises a cathode is a substantially smooth state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Purification apparatus 2 Processing tank 4 Processing chamber 5 Electrode (anode)
6 electrode (cathode)
7 Power supply 9 pH detection means 10 Stirrer (stirring means)
12 Control device 13 Alarm lamp

Claims (2)

A pair of electrodes at least partially immersed in water to be treated containing magnesium chloride and an ammonium salt;
A stirring means for stirring the water to be treated,
An apparatus for purifying magnesium chloride, wherein the water to be treated is treated by an electrochemical method using the electrode, and the stirring linear velocity of the stirring means is 2 m / sec or less . The viscosity of the treated water is 1 mPas or more.
Magnesium chloride purification equipment.

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