JP2008279552A - Method of recovering rare earth element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive process of efficiently recovering rare earth oxides of high quality from waste grinding slurry containing rare earth elements. <P>SOLUTION: In a method of recovering rare earth elements, rare earth oxides are recovered from waste grinding slurry containing rare earth elements in a first process (I) including steps (1)-(5), and ammonium bicarbonate (precipitant) is reproduced and recycled in a second process (II) including steps (6)-(7). The process (I) comprises steps of: (1) mixing slurry containing rare earth oxides with oxidizing and reducing agents and acid, and heating and solving the slurry; (2) dissociating non-soluble components after adjusting the pH value of rare earth element solution; (3) adding ammonium bicarbonate to the solution to form rare earth carbonate; (4) dissociating the rare earth carbonate from the slurry; and (5) of baking the rare earth carbonate to recover it as rare earth oxides. The process (II) comprises steps of: (6) adding strong alkaline agent to a dissociated solution of rare earth carbonate to generate, condense and recover ammonium; and (7) bringing ammonium into contact with generated carbon dioxide to form ammonium bicarbonate solution and to recycle the welding as a precipitant for forming rare earth carbonates. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for recovering rare earth oxides from a slurry containing rare earth elements, and particularly to an inexpensive process for recovering high-quality rare earth oxides that can be reused as raw materials for high-precision polishing from waste abrasive slurry. .

  Rare earth-based abrasives mainly composed of cerium and lanthanum (hereinafter also simply referred to as “abrasives”) are glass substrates for magnetic recording media such as hard disks, optical lenses, glass substrates for liquid crystal displays, and glass substrates for photomasks. It is widely used as an abrasive for polishing various glass materials.

  When polishing various glass materials with the above-described abrasive, an abrasive slurry in which the finely divided abrasive is dispersed in an aqueous dispersant, and this slurry flows between the glass material to be polished and the polishing pad. By doing so, the polishing work is performed.

  Normally, abrasive slurries are recycled in the polishing process, but the polishing characteristics gradually deteriorate due to the accumulation of the polished glass components, so the polishing efficiency is maintained by intermittent replacement with fresh abrasive slurries. I am trying.

  Normally, waste abrasive slurry extracted from the polishing process is precipitated by adding polyaluminum chloride, ferric chloride, polymer flocculant, etc., and the wet cake after filtration separation is equivalent to industrial waste It is processed by handling. However, in addition to cerium, the waste contains a lot of precious rare earths such as lanthanum, praseodymium, neodymium and the like. Therefore, recovering and reusing these as industrial wastes without simply discarding them is extremely significant from the viewpoint of stable securing of rare earth abrasive raw materials and effective utilization of resources. Thus, development of a low-cost recovery technique that recovers and reuses rare earth components from used waste abrasive slurry is eagerly desired.

  As a method for recycling used abrasives, a re-roasting method at a high temperature has been conventionally known, but it is not practical in terms of cost.

  As a method of improving this, for example, a method of performing an acid treatment as described in Patent Document 1 to Patent Document 3 to recover a rare earth element as an abrasive raw material, or Patent Document 4 to Patent Document 5 As described above, a method of performing an alkali treatment and regenerating as an abrasive has been proposed. However, (i) either method can recover rare earth elements, but it produces a large amount of wastewater and by-product waste containing ammonia, and (ii) iron components dissolved in the recovered rare earth elements. There was a problem in terms of quality such as it was difficult to completely separate aluminum components.

  In particular, when recovering the waste abrasive by dissolving it in an acid, it is preferable to use ammonium bicarbonate as a neutralizing agent, which can be recovered as a rare earth carbonate with good filterability, but this method is expensive. There is a problem in that ammonium bicarbonate is used and waste liquid containing high concentration of ammonia is produced as a by-product, and this detoxification treatment and the like are costly.

Japanese Patent No. 3615943 (Claims (Claims 1 to 5)). Japanese Patent Laying-Open No. 2004-175552 (Claims (Claims 1 to 23)) Japanese Patent Laying-Open No. 2003-211356 ((Claims (Claims 1 to 5)) Japanese Patent No. 3134189 (Claims (Claims 1 and 2)) JP 2003-205460 A (Claims (Claims 1 to 9))

  An object of the present invention is to solve the above problems of the conventional method and to provide an inexpensive process for efficiently recovering high-quality rare earth oxides from waste abrasive slurry containing rare earth elements.

As a result of intensive investigations in view of such points, the present inventors have separated CO ₂ and NH ₃ from carbon dioxide gas and ammonium salt aqueous solution by-produced in the reaction in a method using ammonium bicarbonate as a neutralizing agent. In addition to recycling as ammonium bicarbonate, solid-liquid separation at a specific pH in the presence of hydrogen peroxide in advance in the separation and recovery of rare earth carbonate (hereinafter also referred to as “carbonic acid rare earth”) It has been found that impurities such as iron ions coexisting with dissolution can be selectively removed by precipitation, and a high-purity rare earth carbonate can be easily produced, and the present invention has been completed.

According to the present invention, the following rare earth element recovery method involving recycling of ammonium bicarbonate is provided.
[1]
In the first step [I] comprising the following steps (1) to (5), the rare earth oxide is recovered from the waste abrasive slurry containing the rare earth element oxide, and then the steps (6) to (7). In the second step [II], the ammonium bicarbonate used as the precipitating agent for the rare earth carbonate in the first step [I] is regenerated, and the regenerated ammonium bicarbonate is regenerated in the first step [I]. A method for recovering rare earth elements involving recycling of ammonium bicarbonate, characterized by being reused.
Here, the first step [I]
(1) A slurry containing a rare earth oxide is mixed with an oxidizing / reducing agent and an acid under stirring conditions and dissolved by heating (step (1)).
(2) After adjusting the pH of the obtained rare earth element solution to an appropriate condition, the insoluble components are separated by solid-liquid separation means (step (2)).
(3) Ammonium bicarbonate is added to this solution to precipitate rare earth carbonate, (Step (3))
(4) Separating the rare earth carbonate from the obtained rare earth carbonate-containing slurry (step (4)), and (5) firing the rare earth oxide to recover the generated rare earth element (step (5))
And also
The second step [II]
(6) A strong alkaline agent is added to the aqueous ammonium salt solution from which the carbonated rare earth has been separated to generate ammonia, which is condensed and recovered as an aqueous ammonia solution (step (6)), and (7) and then from the process. From the generated carbon dioxide gas, a solution or slurry of ammonium bicarbonate is formed, and the resulting ammonium bicarbonate solution or slurry is reused as a precipitating agent to form a rare earth carbonate (from step (7)). Become.

[2]
Step (1) is a step of mixing and heating a slurry containing an oxide of a rare earth element, an acid, and an oxidizing / reducing agent to dissolve the rare earth element in the slurry [1] The method described in 1.
[3]
The method according to [1] or [2], wherein the acid in step (1) is hydrochloric acid or sulfuric acid.
[4]
The method according to any one of [1] to [3], wherein the oxidizing / reducing agent in step (1) is hydrogen peroxide.
[5]
The method according to any one of [1] to [4], wherein the heating temperature in step (1) is 50 ° C. or higher.
[6]
The pH condition in step (2) is 5 to 6, and the pH adjuster is a soluble alkali metal salt, [1].
[7]
The method according to [1], wherein the solid-liquid separation means for undissolved components in step (2) is filtration.
[8]
The method according to [1], wherein the ammonium bicarbonate added in step (3) is in the form of a solution or a slurry.
[9]
In the step (4), the produced rare earth carbonate is filtered, washed, separated and purified, [1].
[10]
In the firing in the step (5), the temperature is 300 to 1200 ° C. in an air atmosphere, and the method according to [1].
[11]
The method according to [1], wherein in step (6), the strong alkali agent is sodium hydroxide, potassium hydroxide or calcium hydroxide.
[12]
In the step (6), air is blown into an aqueous ammonium salt solution to strip the generated ammonia, [1].
[13]
The method according to [1], wherein, in the step (6), the concentration of the condensed aqueous ammonia solution is 1 to 5% by mass.
[14]
The method according to [1], wherein the contact temperature in step (7) is 10 to 40 ° C.
[15]
The method according to [1], wherein the concentration of ammonium bicarbonate in the step (7) is 5 to 25% by mass, and the form thereof is a solution or a slurry.
[16]
A polishing agent is used for polishing, a rare earth element is recovered from the generated abrasive slurry by the method according to any one of [1] to [15], and the obtained rare earth element is used again as a raw material for the polishing agent. A method for recovering rare earth elements.

  As will be described in detail below, according to the present invention, a method for recovering rare earth elements from waste abrasive slurry containing a rare earth element such as cerium, which is greatly reduced in polishing rate and is usually discarded, is provided. It is possible to selectively dissolve the oxidized rare earth component using acid and oxidizing / reducing agent to the waste abrasive slurry, and the dissolved oxidized rare earth component is separated as carbonated rare earth. -When recovering, by separating solid and liquid in advance at a specific pH in the presence of hydrogen peroxide, impurities such as iron ions that are dissolved and coexisting are selectively separated as unnecessary solid components. A high-purity rare earth carbonate that can be reused as a raw material can be obtained, and this can be fired to easily collect the rare earth oxide.

  Furthermore, according to the present invention, ammonium bicarbonate is added to and reacted with the acidic aqueous solution in which the oxidized rare earth component is selectively dissolved using an acid to produce and crystallize the rare earth carbonate. Ammonia in the ammonium salt by-produced in the reaction process is recovered and reused as ammonium bicarbonate used as the reaction agent, so that expensive ammonium bicarbonate can be recycled and detoxification of the process waste liquid is easy. .

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a flow chart showing a rare earth element recovery step including a recycling step of ammonium bicarbonate, which is a feature of the present invention. Here, the waste abrasive slurry 10 is a starting slurry to be collected.

  In addition to oxidized rare earth and fluorinated rare earth that are the main components, waste abrasive slurry 10 contains silicon and aluminum compounds that are polished glass components, crushed glass cullet, pad fibers, and other foreign substances. is doing. The components of the waste abrasive slurry vary depending on the process conditions to be used, but are usually discharged from the polishing step 9 in a solid content concentration of about 5 to 50%. As for the composition, the rare earth oxide equivalent amount TREO (= (total rare earth oxide mass / total oxide mass) × 100)) on a dry product basis is about 82 mass% (of which about 25 mass% is dilute fluoride) Soil component), silicon compound is about 5% by mass, aluminum compound and iron compound are about 1% by mass, and other foreign substances such as glass powder and pad fibers are mixed.

The waste abrasive slurry 10 is prepared as a slurry of about 30% by mass in terms of oxidized rare earth component (TREO) by finally concentrating the abrasive slurry repeatedly used in the polishing step 9 while circulating in the gravity sedimentation method. It is a thing.
In addition, when concentrating the slurry by the gravity sedimentation method, the waste abrasive slurry may be performed alone, but the sedimentation and concentration is more effectively performed in combination with a commercially available polymer flocculant. This is the starting material for the waste abrasive slurry to be treated in step (1).

(Process (1))
(Step of obtaining rare earth solution by dissolving rare earth elements in waste abrasive slurry)
First, a waste abrasive slurry 10 is collected in a reaction vessel, and a predetermined amount of acid 20 and an oxidizing / reducing agent 30 such as hydrogen peroxide are added to the reaction vessel, and the mixture is heated and reacted with stirring to dissolve 33 the slurry.

The reaction vessel is not particularly limited, but is preferably a stirring vessel type equipped with at least stirring means, waste abrasive slurry, introduction means such as acid and oxidizing / reducing agent, heating means and the like.
The acid 20 used here may be a mineral acid that can dissolve the rare earth elements contained in the slurry 10 and is selected from hydrochloric acid, sulfuric acid, and nitric acid. From the viewpoint of wastewater treatment, hydrochloric acid or sulfuric acid is preferable, Hydrochloric acid is preferred.

  The concentration of the acid is not particularly limited. For example, when hydrochloric acid is used, 35% by mass of concentrated hydrochloric acid can be used industrially. Moreover, the addition amount of the acid is 40-60 parts with respect to 100 parts of waste abrasive slurry, Preferably about 50 parts are added. If the addition amount is less than 40 parts, the insoluble content of the rare earth element is increased, and if the addition amount exceeds 60 parts, no further effect is obtained, and the amount of chemical (acid) consumed simply is wasted. This is not preferable because only increases.

  As the oxidizing / reducing agent 30, hydrogen peroxide is preferably used. Hydrogen peroxide is known to act as an oxidizing agent or a reducing agent for rare earth elements and impurity components. For example, it acts as a reducing agent for cerium element and suppresses the formation of Ce (IV) having low solubility in mineral acids such as hydrochloric acid and sulfuric acid. On the other hand, it acts as an oxidizing agent for neodymium and iron, and Nd (III) and Fe (III) are formed. That is, neodymium is oxidized to increase the solubility in mineral acids, and iron is oxidized to form an insoluble hydroxide in the subsequent step (2), so that it can be easily separated from rare earth elements. Become.

  Thus, hydrogen peroxide is added for the purpose of improving the solubility of rare earth elements and reducing the solubility of impurities such as iron, but the amount added is 30% by mass with respect to 100 parts of the waste abrasive slurry. It is preferably in the range of 5 to 6 parts in terms of conversion.

  Thus, by adding an acid such as hydrochloric acid and an oxidizing / reducing agent such as hydrogen peroxide to the diluted waste abrasive slurry 10 and heating with stirring, only the rare earth oxide component is selectively dissolved 33. However, at the same time, a highly viscous slurry 35 is formed in which almost all of the iron component and part of the silica and alumina components are dissolved.

  The heating temperature is not particularly limited as long as dissolution of the oxidized rare earth component by the above reaction is sufficiently fast and the viscosity of the formed slurry can be maintained in an easy-to-handle range. A range of (about 100 ° C.) is preferable, and a range of 50 to 70 ° C. is particularly preferably employed.

  The stirring means is not particularly limited as long as the solid particles in the slurry are sufficiently floated so that the solid-liquid reaction can be smoothly performed. Usually, a stirring blade is employed. As the stirring blade, a paddle or an anchor blade is preferable, and the rotation speed is a blade peripheral speed of 0.1 to 1 m / second, preferably 0.3 to 0.6 m / second.

While the reaction time may vary depending on the reaction temperature, it is generally 2 hours to 20 hours, preferably about 3 to 10 hours. When the reaction is carried out at the reflux temperature (about 100 ° C.), the dissolution reaction of the rare earth oxide component is completed by stirring for 4 hours or more, preferably about 5 hours under stirring conditions.

(Process (2))
(Separation process of Si, Al, Fe, undissolved rare earth residue from acidic solution of rare earth elements)
Iron (Fe) dissolved in the slurry (acid slurry) 35 after the step (1) is dissolved by adding a soluble alkali component as a pH adjusting agent 40, adjusting the pH 43, and increasing the pH. Only silica (Si) and aluminum (Al) components can be selectively deposited.

  The pH condition during the pH adjustment is preferably controlled so that the pH is in the range of 5 to 6, more preferably in the range of pH 5.3 to 5.6, and most preferably pH 5.5. If the pH is less than 5, the total amount of Fe, Si, and Al components is not completely precipitated. If the pH is more than 6, the Al and Si components are redissolved and rare earth elements are precipitated.

The soluble alkali component that is the pH adjuster 40 may be an alkali metal salt, an alkaline earth metal salt, or an ammonium salt. From the viewpoint of filterability of the precipitate, an alkali metal carbonate such as sodium bicarbonate ( It is preferable to use sodium bicarbonate) or sodium carbonate (sodium carbonate). For example, NaHCO ₃ , Na ₂ CO ₃ , NH ₄ HCO ₃ , NaOH and the like are preferably used.

  When a sodium carbonate solution is added to the acidic slurry 35 as a pH adjuster, carbon dioxide gas (carbon dioxide gas) is generated and released by the reaction, and the solution is apparently boiled. Therefore, preferably a reflux condenser is installed in the reactor, the released carbon dioxide gas (and entrained water vapor) is cooled, and after condensing only the water vapor, it is introduced and recovered into the carbon dioxide gas absorption device in step (7) described later. Is preferred.

  As described above, after adjusting the pH, the slurry is cooled with stirring, and the dissolved residue containing iron, silica, alumina component, rare earth fluoride as a main component, precipitated under the condition of a temperature of about 40 to 50 ° C. Is separated as solid unnecessary component 53 by solid-liquid separation means 50 such as filtration. Basically, silica and alumina component hydroxides are difficult to filter, but they are precipitated as carbonates, and the dissolution residue of the abrasive acts as a filter aid, and can be efficiently solid-liquid by filtration etc. To be separated. The temperature for filtration and the like is not necessarily limited to the above range, but if the temperature is too high, it is not preferable in the working environment, and it is preferable to operate at around 40 ° C.

In the case of filtration as a solid-liquid separation means, a filter press, a drum filter, a pump pressurization type line filter, or the like is used as a filtration device, but from the viewpoint of safety, the inside of the line filter installed in the piping line is used. It is preferable to process by circulating the pump. In the case of filtration separation, an appropriate filter cloth such as a filter cloth, a ceramic filter or a filter paper can be used according to the amount of processing, the filterability of solids, and the like.
Thus, in step (2), the solid impurity (solid unnecessary component) 53 is removed, and the acidic aqueous solution 60 in which the rare earth element is dissolved is taken out.

(Process (3))
(Step of producing rare earth carbonate from rare earth acid aqueous solution)
The acidic aqueous solution 60 of the rare earth element thus obtained is introduced into a suitable reactor, and ammonium bicarbonate 70 is added to produce and crystallize 80 as a rare earth carbonate, and at the same time, carbon dioxide gas 90 is released. By using ammonium bicarbonate as a crystallization agent, crystals of rare earth carbonate with good filterability can be obtained.

  As the reaction vessel, a stirred tank reactor equipped with introduction means, stirring means, heating means and the like of the acidic aqueous solution 60 and ammonium bicarbonate 70 is preferable. The form and concentration of ammonium bicarbonate 70 to be added are not limited in any way, and may be added in an aqueous solution or in a slurry state, but particularly from the viewpoint of handling, as an aqueous solution of ammonium bicarbonate in a concentration range of 5 to 10%. It is preferable to use it.

  The amount of ammonium bicarbonate 70 added may be an amount necessary and sufficient to neutralize the acidic content of the acidic aqueous solution 60, and the amount is based on the dry product basis per 100 parts of the amount of waste abrasive in step (1). It is preferable to add 10 to 20 parts, and more preferably 12 to 15 parts.

The addition of ammonium bicarbonate 70 to the acidic solution 60 is preferably performed at as high a temperature as possible in order to dissipate the carbon dioxide gas 90 produced by the reaction more smoothly from the system. Usually, for example, warm water of about 80 ° C. is circulated through a jacket of a reactor as a heating means, and ammonium bicarbonate is added in portions over 2 to 3 hours under stirring with heating.

(Process (4))
(Carbonated rare earth separation process)
The carbonated rare earth-containing slurry 83 is cooled to 60 ° C. or lower, preferably 40 to 50 ° C., and then solid-liquid separation 100, for example, filtration, to separate the carbonated rare earth 85 and the aqueous ammonium salt solution 95. . It is preferable that the separated rare earth carbonate 85 is further washed with about 1 to 3 times the amount of water to suppress the re-mixing of impurities in the waste abrasive slurry accompanying the attached mother liquor. In addition, in order to wash | clean more fully, you may repeat the operation | movement which carries out solid-liquid separation operation by disperse | distributing (repulping) the isolate | separated rare earth carbonate cake to water again as a slurry. In this manner, in the step (4), the produced rare earth carbonate is separated and purified by filtration and washing, and the solid-liquid separation 100 here is an operation including filtration and washing. .

(Process (5))
(Recovery of oxidized rare earth)
The rare earth carbonate 85 separated and solid-separated 100 in the step (4) is dried and fired 110 to obtain oxidized rare earth. Drying is performed at about 40 to 200 ° C. As the drying device, any device such as a box dryer, a band dryer, or a vacuum dryer is used. In addition, the baking is performed using rare earth carbonate 85 in an air atmosphere at 300 to 1200 ° C., preferably 400 to 1100 ° C., more preferably 500 to 1000 ° C., for about 1 to 3 hours, preferably about 1.5 to 2 hours. Do. As the baking apparatus, a normal baking furnace such as a box furnace, a rotary furnace, a tunnel furnace or the like is used.

The rare earth oxide (oxidized rare earth) 88 obtained by firing is input as a recovered oxidized rare earth to the atomization treatment step of a normal abrasive production line after pulverization and reused as a raw material for the abrasive.
The above is the first step [I]. That is, in the step [I], the steps (1) to (5) are performed, and the rare earth oxide is recovered from the waste abrasive slurry containing the rare earth element oxide.

Next, the second step [II] will be described. In the step [II], the following steps (6) to (7) are carried out to regenerate the ammonium bicarbonate used as the precipitating agent for the rare earth carbonate in the first step [I], and the regenerated bicarbonate Ammonium is reused in the first step [I].

(Process (6))
(Ammonia recovery)
In the above step (3), by the reaction of the following formula, the charged ammonium bicarbonate 70, an equimolar amount of ammonium chloride or an ammonium salt 95 such as ½ molar amount of ammonium sulfate, and ½ molar amount of carbon dioxide gas 90 is a by-product.
As shown in the flow sheet of FIG. 1, an ammonium salt such as ammonium chloride or ammonium sulfate is dissolved in the mother liquor and remains as an ammonium salt aqueous solution 95 such as an aqueous ammonium chloride solution or an aqueous ammonium sulfate solution. It is discharged out of the system as gas from the top.

Here, when the acidic component is hydrochloric acid and sulfuric acid, the reaction is as follows.

(1) When the acid content is hydrochloric acid (Ln: rare earth element)

2LnCl ₃ + 6NH ₄ HCO ₃ = Ln ₂ (Co ₃ ) ₃ + 6NH ₄ Cl ↓ + 3H ₂ O + 3CO ₂ ↑

(2) When the acid content is sulfuric acid

Ln ₂ (SO ₄ ) ₃ + 6NH ₄ HCO ₃
= Ln ₂ (CO ₃ ) ₃ ↓ + 3 (NH ₄ ) ₂ SO ₄ + 3CO ₂ ↑

(Ammonia recovery method)
Hereinafter, a method for recovering ammonia will be described by taking as an example the case where the acidic component is hydrochloric acid.
A soluble strong alkaline agent 97 is added to an aqueous ammonium chloride solution 95 having a concentration of about 0.6 mol / L to liberate ammonia 98.
Examples of the soluble strong alkali agent referred to here include sodium, potassium, and calcium hydroxides, with sodium hydroxide being particularly preferred.

That is, by adding a strong alkali agent 97 such as sodium hydroxide so that the pH of the aqueous ammonium chloride solution 95 is 10 or more, preferably 12 to 13, ammonia 98 is liberated almost quantitatively according to the following formula. It is.

NaOH + NH ₄ Cl + H ₂ O = NaCl + H ₂ O + NH ₃ ↑

  Next, ammonia is stripped 120 at a high temperature while blowing a small amount of air into the aqueous solution 95, the temperature of the stripping gas 98 containing the volatilized ammonia and water vapor is lowered, and the aqueous ammonia solution 135 is condensed and recovered 130.

  The stripping 120 may be carried out in a batch operation. However, a wet wall tower, a plate or a packed tower system with good gas-liquid contact is adopted, and a preheated ammonium chloride aqueous solution 95 is used as these. Supply from the upper part of a tower such as a wet wall tower, supply hot air and steam as needed from the lower part of the tower, let the liquid flow down from the top, raise the hot air from the bottom, and make countercurrent contact in the tower. Thus, a stripping method is preferable.

  Specifically, the temperature of the stripping 120 is 70 to 100 ° C, preferably 85 to 95 ° C. When the ammonium chloride aqueous solution 95 supplied from the top of the column is introduced at a rate of, for example, 100 kg / hour under the temperature and pH conditions, air is introduced from the bottom of the column at 1 to 15 kg / hour, preferably It is introduced at a rate of 3 to 10 kg / hour, more preferably 4 to 6 kg / hour.

  If the amount of air introduced here (the air flow rate) is too large relative to the amount of aqueous ammonia solution, the amount of water vapor accompanying the stripped ammonia will be very large, and the ammonia will be recovered in the next condensation step. On the other hand, if the amount of introduced air is too small, the ammonia stripping efficiency decreases, so it is preferable to adopt and control the flow rate in the above range.

Next, this stripping gas (ammonia vapor, water vapor) 98 is introduced into an ammonia condensing / recovering step 130 for cooling to 30 ° C. or less, preferably 20 to 35 ° C., and 95% or more of the ammonia gas released from the top of the tower. Is recovered as an aqueous ammonia solution 135. In addition, the said aqueous solution 135 is diluted with process water as needed, and is collect | recovered as 1-5 mass%, Preferably it is 1.5-2 mass% ammonium aqueous solution.
In the ammonium salt aqueous solution 95, the remaining aqueous solution (pot residue) 99 obtained by stripping 120 of the ammonia gas 98 only contains harmless salts (NaCl, Na ₂ SO ₄ etc.). After neutralizing 140 excess alkali with acid (pH adjuster) 142, the neutralized solution can be discharged 145 without any problem.

(Process (7))
(Recovery of carbon dioxide and synthesis of ammonium bicarbonate)
Carbon dioxide gas 90 discharged from the reactor is reacted and absorbed by the aqueous ammonia solution 135 recovered in the above step (6), and recovered as ammonium bicarbonate 70 by the following equation.

NH ₃ + H ₂ O + CO ₂ = NH ₄ HCO ₃

The liquid temperature for reaction absorption is controlled in the range of 10 to 40 ° C, preferably 20 to 30 ° C.
The apparatus that absorbs the carbon dioxide gas 90 to form the ammonium bicarbonate 70 may be a normal absorption tower system, but a locally concentrated ammonium bicarbonate may be deposited, so that a stirred tank type is preferable. That is, as the reaction vessel R for performing the reaction absorption, the stirring type equipped with the carbon dioxide gas introduction means 1, the stirring means 2, the temperature adjusting means 3, the condenser 4, and the countercurrent contact type absorption tower 5 as shown in FIG. Absorbers are preferred. Reference numeral 6 denotes reaction-absorbing ammonia water in which the concentration of the aqueous ammonia solution 135 is adjusted. And it is suitable if the stirring type absorption apparatus concerning a front | former stage is used in combination with countercurrent contact type absorption towers, such as a plate tower, a packed tower, and a wet wall tower, in a back | latter stage. If necessary, fresh carbon dioxide gas 138 and dilution water are supplied to control the concentration of ammonium bicarbonate in the liquid in the range of 5 to 25% by mass, preferably 8 to 10% by mass, which is not higher than the saturation solubility. . If the concentration is too low, the equipment load of the absorber increases, and if the concentration is too high, an ammonium bicarbonate slurry is formed. Therefore, it is preferable to control within this range.

  As a stirring type absorption device, either a batch type with a stirring blade or a continuous type may be adopted, and a tank type absorption device equipped with an anchor, a turbine, a paddle, a full zone blade, etc. may be used. It can select suitably from absorption facilities.

A solution of ammonium bicarbonate 70 produced by reaction absorption with aqueous ammonia solution 135 (ammonia water for reaction absorption 6) is once stocked in an intermediate tank, and then supplied to the rare earth carbonate formation step of step (3). It is suitably reused as a crystallization agent for generating rare earth.

  Hereinafter, the present invention will be described by way of examples. However, these are merely examples of embodiments, and the technical scope of the present invention is not construed as being limited thereto. Unless otherwise specified, “%” means “% by mass”.

[Example 1]
(1) (Rare earth element of waste abrasive slurry is dissolved to produce rare earth solution (slurry), step (1))
The processing operation was performed according to the flow sheet of FIG.
The starting abrasive slurry 10 is prepared as follows. That is,
A waste abrasive slurry generated by polishing a glass disk was collected and subjected to gravity sedimentation to prepare a slurry having a solid content concentration of about 30% by mass on a dry basis.
In addition, the amount of the component element calculated | required by the fluorescent X ray method about the powder which extract | collected some slurry and dried for one day and night on 100 degreeC conditions in the air was the result shown in Table 1.

  First, the waste abrasive slurry 10 was heated and dissolved with the acid 20 and the oxidizing / reducing agent 30. 1 kg of the slurry was collected in a separable flask (installed in a constant temperature water bath) having an inner diameter of 150 mmφ and an internal volume of about 3.5 L equipped with a paddle type stirring blade having a blade diameter of 60 mmφ and a reflux condenser, and a 35 mass% hydrochloric acid aqueous solution. 510 g and 50 g of a 30% by weight aqueous hydrogen peroxide solution were added. Next, the mixture was heated with stirring at a speed of about 150 rpm, and held for 4 hours under the condition of a liquid temperature of 80 to 85 ° C. to dissolve most of the rare earth compound.

(2) (Separation of Si, Al, Fe, undissolved residue from rare earth element acidic solution (slurry), step (2))
Next, a 10% sodium carbonate solution was added to the acidic solution (slurry) 35 as a pH adjuster 40 to adjust the pH 43 to pH 5.5.

  At this time, the carbon dioxide gas generated by the neutralization reaction is dissipated with water vapor, and the solution is apparently boiled. Therefore, after cooling with a reflux condenser and condensing the water vapor, carbon dioxide gas in the step (7) described later It was introduced into an absorber and reacted and absorbed with ammonia, and most of it was recovered as ammonium bicarbonate.

  After pH adjustment, the mixture was cooled to 40 ° C. over about 1 hour under a stirring condition of 120 rpm, and then the stirring was stopped to extract the contents.

  Next, with a Nutsche type suction filter having an inner diameter of 300 mmφ, solid solution separation 50 was performed using an undissolved component as a solid unnecessary component 53 using No5A filter paper (manufactured by Advantech Toyo Co., Ltd.), and an aqueous hydrochloric acid solution 60 in which a rare earth element was dissolved was recovered. .

  The mass of the filtered solid content (solid unnecessary component) on a dry product basis is 30.5 g, and its component is confirmed to be iron, aluminum, silica, and rare earth fluoride by analysis by fluorescent X-ray method. It was.

(3) (Generate and crystallize rare earth carbonate from rare earth solution: Step (3))
The total amount of the acidic aqueous solution 60 in which the rare earth element separated by filtration was dissolved was collected in a 2 L separable flask, and this solution was heated to about 60 ° C. while stirring at a speed of 120 rpm. Next, 1300 g of an ammonium bicarbonate 70 solution having a concentration of about 9% by mass was sequentially added, and the following reaction was sequentially performed to generate / precipitate 80 carbonated rare earth crystals.

2LnCl ₃ + 6NH ₄ HCO ₃ (Ln: rare earth element)
→ Ln ₂ (CO ₃ ) ₃ ↓ + 6NH ₄ Cl + 3CO ₂ ↑

  As shown in the above formula, the added ammonium bicarbonate 70 reacts with rare earth chloride to produce rare earth carbonate and releases carbon dioxide gas. About 20 minutes after the addition of ammonium bicarbonate, generation of carbon dioxide gas ceased and the end of the reaction was confirmed, so the reaction was cooled to 40 ° C. and stirring was stopped. The carbon dioxide produced as a by-product in the reaction was cooled by a reflux condenser at the top of the reactor, and then introduced into the carbon dioxide absorber in step (7) to react with ammonia and recovered as ammonium bicarbonate.

(4) (Separation of rare earth carbonate, step (4))
The carbonated rare earth-containing slurry 83 is filtered 100 using a No. 5A filter paper (manufactured by Advantech Toyo Co., Ltd.) with a Nutsche suction filter having an inner diameter of 200 mmφ, and after filtration, washed with 100 g of pure water three times and recovered. Then, it was dried overnight in the air at a temperature of 100 ° C. to obtain 240 g of a dry cake of rare earth carbonate 85.

Table 2 shows analytical values of the collected rare earth carbonate 85 by ICP emission analysis (manufactured by Shimadzu Corporation). As is apparent from the table, 99% or more of silica, alumina, and iron components, which are trace impurity components (contamination) mixed in the polishing and polishing slurry concentration steps, have been removed, and the purity was industrially obtained. The recovery rate in terms of oxidized rare earth component was about 70%.

(5) (Oxidized rare earth recovery and polishing characteristics)
The carbonated rare earth 85 collected as described above is heat-treated at temperatures of 400 ° C., 500 ° C., and 600 ° C. to form oxidized rare earth 88, and then pulverized under predetermined conditions and simultaneously pulverized. Prepared, mixed, calcined, pulverized, classified, and slurried (about 15% by mass concentration) with the pre-treated rare earth fluoride and reused after processing, and polished with a TAMI Sangyo 6B type polishing machine Characteristics were evaluated.

Table 3 shows the results of evaluating the polishing rate and the surface condition of the oxidized rare earth obtained at the heat treatment temperatures of the recovered carbonated rare earth at 400 ° C., 500 ° C., and 600 ° C., respectively.
As is apparent from Table 3, it was found that the recovered carbonic acid rare earth heat-treated at 500 ° C. and 600 ° C. can obtain the same polishing characteristics as those of an abrasive produced with a normal raw material (fresh raw material).

(6) (Ammonia recovery)
In step (4), about 2900 g of the filtrate (ammonium salt aqueous solution 95) obtained by separating the rare earth carbonate from the rare earth carbonate slurry 83 was charged into a 5 L separable flask with a stirring blade, and the liquid temperature was adjusted by external heating. Control at 95 ° C.

Next, 25% caustic soda (sodium hydroxide), which is a strong alkaline agent 97, was continuously added over about 1 hour while bubbling about 1 L / min of air under stirring conditions to increase the pH of the solution to 13. .
With the addition of caustic soda, ammonia 98, which is a weak alkali, is liberated from the ammonium salt. The generated ammonia gas 98 and water vapor are stripped by blowing air, extracted from the upper part of the stirring tank accompanied by air, cooled to 15 to 20 ° C. with a condenser and condensed 130, and ammonia condensate (ammonia aqueous solution) 135. About 360 g was recovered. The concentration of ammonia in the recovered condensate was about 6.4% by mass, and it was found that about 88% of the ammonium chloride dissolved in the filtrate (in the aqueous ammonia solution) could be recovered as ammonia.

(7) (Recovery of carbon dioxide and synthesis of ammonium bicarbonate, step (7))
Step (7) is a stirrer-type absorber equipped with carbon dioxide gas introducing means (introducing pipe) 1, agitating means 2, temperature adjusting means 3, condenser 4, and countercurrent contact type absorption tower 5 as shown in FIG. (Agitator tank with condenser) R (inner diameter φ120 mm × tank height h150 mm, with paddle type agitator blade (10H × 60 W)) That is, in this stirring tank R with a condenser, the total amount of the 6.4% by mass ammonia aqueous solution 135 recovered, 15% reagent ammonia water 15 g, and 760 g of water for reaction absorption 6 were charged. It is.

While stirring this at a speed of 150 rpm, cold water was passed through the outer jacket 3 to cool the internal temperature to 20 ° C. and the upper condenser 4 to 10 ° C.
Next, carbon dioxide gas 90 (reaction product gas generated when ammonium bicarbonate 70 is added to the acidic rare earth aqueous solution 60 to produce rare earth carbonate) is absorbed from the carbon dioxide gas introduction pipe 1 of this stirring tank into ammonia for absorption. Water 6 was bubbled, carbon dioxide was reacted and absorbed, and ammonium bicarbonate was produced.

  A portion of the recovered ammonium bicarbonate aqueous solution synthesized by reaction absorption was collected and the solid content concentration determined by evaporation to dryness was 9.2% by mass. The amount of ammonium bicarbonate calculated from this was 115 g. .

This means that about 93% of the carbon dioxide gas 90 estimated to have been generated in the rare earth carbonate production process (carbon dioxide rare earth crystallization process) was recovered as ammonium bicarbonate 70. Accordingly, it is shown that fresh ammonium bicarbonate and water can be added and recycled to the rare earth carbonate production and crystallization process 80 and reused as a raw material for the rare earth carbonate synthesis (process (3)). It was.

  According to the present invention, a high-quality rare earth oxide is efficiently recovered from a waste abrasive slurry containing a rare earth element that is greatly discarded and is normally discarded, and this is again polished with a high polishing rate. An inexpensive process is provided that allows it to be used as an agent.

  According to the present invention, the acidic aqueous solution in which the oxidized rare earth component is selectively dissolved using a mineral acid is reacted by adding ammonium bicarbonate to produce and crystallize the rare earth carbonate. Ammonia in the ammonium salt produced as a by-product in the reaction process is recovered and reused as ammonium bicarbonate used as the reaction agent, so that expensive ammonium bicarbonate can be recycled and the process waste liquid can be made harmless easily. is there.

Furthermore, according to the present invention, when separating and recovering a dissolved carbonated rare earth component as a carbonated rare earth, solid-liquid separation is performed in advance in the presence of hydrogen peroxide at a specific pH, so that iron ions coexisting in a dissolved state, etc. The impurities can be selectively removed by precipitation, and high-purity rare earth carbonate can be easily produced and recovered. Therefore, its industrial applicability is extremely large.

It is a flowchart which shows the collection | recovery process of the rare earth elements including the recycling process of the ammonium bicarbonate of this invention. It is explanatory drawing which shows the reaction container which makes carbon dioxide gas react-absorb with ammonia water, and forms ammonium bicarbonate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carbon dioxide gas introduction means 2 such as a nozzle 2 Stirring means 3 Temperature control means such as a cooling jacket 4 Condenser 5 Countercurrent contact type absorption tower 6 Reaction absorption ammonia water 9 Polishing process 10 Waste abrasive slurry 20 Acid 30 Hydrogen peroxide, etc. Oxidizing / reducing agent 33 Heating / dissolving step 35 High viscosity slurry 40 pH adjusting agent 43 pH adjusting step 50 Solid-liquid separation means 53 Solid unnecessary component 60 Acidic aqueous solution in which rare earth elements are dissolved 70 Ammonium bicarbonate 80 Carbonate rare earth formation and crystallization Process 83 Carbonated rare earth-containing slurry 85 Carbonated rare earth 88 Rare earth oxide (oxidized rare earth)
90 Carbon dioxide 95 Ammonium salt aqueous solution 97 Strong alkali agent 98 Ammonia or stripping gas (ammonia vapor, water vapor)
99 Water solution after stripping (residue)
100 Solid-liquid separation means (filtration, washing)
110 Drying and calcination process 120 Stripping 135 Aqueous ammonia solution 138 Fresh carbon dioxide gas 140 Neutralization process 142 Acid (pH adjuster)
145 Neutralization liquid discharge process

Claims (16)

In the first step [I] comprising the following steps (1) to (5), the rare earth oxide is recovered from the waste abrasive slurry containing the rare earth element oxide, and then the steps (6) to (7). In the second step [II], the ammonium bicarbonate used as the precipitating agent for the rare earth carbonate in the first step [I] is regenerated, and the regenerated ammonium bicarbonate is regenerated in the first step [I]. A method for recovering rare earth elements involving recycling of ammonium bicarbonate, characterized by being reused.
Here, the first step [I]
(1) A slurry containing a rare earth oxide is mixed with an oxidizing / reducing agent and an acid under stirring conditions and dissolved by heating (step (1)).
(2) After adjusting the pH of the obtained rare earth element solution to an appropriate condition, the insoluble components are separated by solid-liquid separation means (step (2)).
(3) Ammonium bicarbonate is added to this solution to precipitate rare earth carbonate, (Step (3))
(4) Separating the rare earth carbonate from the obtained rare earth carbonate-containing slurry (step (4)), and (5) firing the rare earth oxide to recover the generated rare earth element (step (5))
And also
The second step [II]
(6) A strong alkaline agent is added to the aqueous ammonium salt solution from which the carbonated rare earth has been separated to generate ammonia, which is condensed and recovered as an aqueous ammonia solution (step (6)), and (7) and then from the process. From the generated carbon dioxide gas, a solution or slurry of ammonium bicarbonate is formed, and the resulting ammonium bicarbonate solution or slurry is reused as a precipitating agent to form a rare earth carbonate (from step (7)). Become.   The step (1) is a step of mixing and heating a slurry containing an oxide of a rare earth element, an acid, and an oxidizing / reducing agent to dissolve the rare earth element in the slurry. The method described in 1.   The method according to claim 1 or 2, wherein the acid in step (1) is hydrochloric acid or sulfuric acid.   The method according to any one of claims 1 to 3, wherein the oxidizing / reducing agent in step (1) is hydrogen peroxide.   The method according to any one of claims 1 to 4, wherein the heating temperature in step (1) is 50 ° C or higher.   The method according to claim 1, wherein the pH condition in the step (2) is 5 to 6, and the pH adjuster is a soluble alkali metal salt.   The method according to claim 1, wherein the solid-liquid separation means for undissolved components in step (2) is filtration.   The method according to claim 1, wherein the ammonium bicarbonate added in step (3) is in the form of a solution or a slurry.   2. The method according to claim 1, wherein in the step (4), the produced rare earth carbonate is filtered, washed, separated and purified. The method according to claim 1, wherein, in the firing in the step (5), the temperature is 300 to 1200 ° C. in an air atmosphere.   The method according to claim 1, wherein in step (6), the strong alkali agent is sodium hydroxide, potassium hydroxide or calcium hydroxide.   The method according to claim 1, wherein in step (6), air is blown into an aqueous ammonium salt solution to strip generated ammonia.   The method according to claim 1, wherein the concentration of the aqueous ammonia solution condensed in the step (6) is 1 to 5% by mass.   The method according to claim 1, wherein the contact temperature in step (7) is 10 to 40 ° C.   The method according to claim 1, wherein the concentration of ammonium bicarbonate in the step (7) is 5 to 25% by mass, and the form thereof is a solution or a slurry.   A rare earth element is recovered from the generated waste abrasive slurry by the method according to any one of claims 1 to 15, and the obtained rare earth element is used again as a raw material for the abrasive. Recovery method for rare earth elements.

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