KR20080100137A - Method for recovering rare earth elements - Google Patents

Abstract

A method of recovering rare earth materials is provided to selectively dissolve the rare earth oxide component by using mine, an oxidation agent and a reducing agent and to separate selectively impurities including a coexisted iron ion by separating in advance solid from liquid at a specific pH. Slurry containing the rare earth oxide is mixed with an oxidation agent and a reducing agent and an acid under the mixing condition and melted. After a pH of the obtained rare earth materials solution is controlled at the proper condition, a non-soluble component is separated by a solid-liquid separating unit, a carbonic acid rare earth(85) is segregated by adding an ammonium bicarbonate in the solution, the carbonic acid rare earth is separated from the obtained carbonic acid rare earth containing slurry and the rare earth oxide is manufactured by plasticizing it. The generated rare earth materials are collected. The strong alkaline agent is added in the ammonium salt aqueous solution separating the carbonic acid rare earth, the ammonia is generated and condensed, the ammonia aqueous solution is collected. A solution of the ammonium bicarbonate(70) or the slurry is formed by contacting carbon dioxide generated from the process. The solution or the slurry of the obtained ammonium bicarbonate is reused as the precipitation agent forming the carbonic acid rare earth.

Description

Recovery method for rare earth elements {METHOD FOR RECOVERING RARE EARTH ELEMENTS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering rare earth oxides from a slurry containing rare earth elements, and more particularly, to a low cost process for recovering high quality rare earth oxides that can be reused as a raw material for high precision polishing from a waste abrasive slurry. will be.

Rare earth abrasives (hereinafter simply referred to as "polishing agents") containing cerium and lanthanum as main components are various glass such as 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 materials.

In the polishing of various glass materials by the above-described abrasives, polishing is performed by flowing the slurry between the glass material serving as an abrasive and the polishing pad, using the abrasive slurry obtained by dispersing the atomized abrasive in an aqueous dispersant. .

Typically, the abrasive slurry is recycled in the polishing process. In the case of recycling, the polishing property gradually decreases due to the accumulation of the polished glass component. Therefore, the polishing efficiency is maintained by intermittently replacing the fresh polishing slurry.

The waste abrasive slurry extracted from the polishing process is precipitated by adding polyaluminum chloride, ferric chloride, a polymer flocculant or the like. The wet cake after the filtration separation is processed by the same handling as industrial waste. However, the waste contains a lot of valuable rare earth elements such as lanthanum, praseodymium, and neodymium in addition to cerium. Therefore, it is very meaningful from the viewpoint of the stable securing of the rare earth abrasive raw material and the effective use of resources, to recover and reuse them without simply discarding them as industrial waste. In this way, the development of a low-cost recovery technique which recovers and reuses the rare earth component from the used waste abrasive slurry is urgently desired.

As a method of recycling the used abrasive, a redistribution processing at a high temperature is known in the past, but it is not practical in terms of cost.

As a method of improving this, for example, Japanese Patent Publication No. 3615943 (Patent Document 1), Japanese Patent Publication (JP-A-2004-175652) (Patent Document 2), Japanese Patent Publication (JP-A) 2003-211356) (Patent Document 3), an acid treatment is carried out to recover a rare earth element that is a raw material for abrasives, and Japanese Patent Publication No. 31418989 (Patent Document 4) and Japanese Patent Laid-Open. As described in Unexamined-Japanese-Patent No. 2003-205460 (patent document 5), the method of performing alkali treatment and regenerating as an abrasive is proposed.

However, any conventional method has a problem. That is, (i) recovery of rare earth elements is possible, but it is difficult to produce a large amount of wastewater or by-product waste containing ammonia, and (ii) difficult to completely separate iron or aluminum components dissolved in the recovered rare earth elements. There was a problem in terms of quality.

In particular, when the waste abrasive is dissolved in acid and recovered, ammonium bicarbonate is preferably used as a neutralizing agent, so that it can be recovered as rare carbonate with good filterability. There is a problem that the waste liquid containing the by-product is by-produced, and the detoxification treatment and the like greatly increase the cost.

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

The present inventors have intensively studied. As a result, in the method using ammonium bicarbonate as a neutralizing agent, to separate the CO ₂ and NH ₃ from the carbon dioxide gas and an ammonium salt aqueous solution by-produced from the reaction, using this recycling as ammonium bicarbonate in order to achieve this object In addition, during the separation and recovery of rare carbonate (hereinafter also referred to as `` rare carbonate ''), the solids are separated in advance in a specific pH in the presence of hydrogen peroxide to selectively precipitate impurities such as iron ions that are dissolved and coexist. It was found that it was possible to remove the carbonic acid, and thus it was possible to easily manufacture a high purity rare carbonate, and completed the present invention.

According to the present invention, there is provided a method for recovering a rare earth element involving the reuse of the following ammonium bicarbonate.

[One]

In 1st process [I] which consists of following process (1)-(5), the said rare earth oxide is collect | recovered from the waste abrasive slurry containing the oxide of a rare earth element, and then consists of process (6)-(7) In 2nd process [II], ammonium bicarbonate used as a precipitant of rare earth carbonate in 1st process [I] is regenerated, and the recycled ammonium bicarbonate is recycled at said 1st process [I]. A method of recovering rare earth elements with reuse of.

Here, the first step [I] is

(1) a slurry containing rare earth oxide is mixed with an oxidizing / reducing agent and an acid under stirring conditions and heated to dissolve it (step (1)),

(2) After adjusting the pH of the obtained rare earth element solution to an appropriate condition, insoluble components are separated by solid-liquid separation means (step (2)),

(3) Add ammonium bicarbonate to this solution to precipitate Rare Earth Carbonate (Step (3)),

(4) separating rare carbonate from the obtained rare carbonate-containing slurry (step (4)), and

(5) firing this to make a rare earth oxide and recovering the generated rare earth element (step (5));

2nd process [II],

(6) A strong alkali is added to the aqueous ammonium salt solution from which rare carbonate is separated to generate ammonia, which is then condensed and recovered as an aqueous ammonia solution (step (6)), and

(7) Next, the carbon dioxide gas generated from the process is brought into contact with each other to form a solution or slurry of ammonium bicarbonate, and the obtained solution or slurry of ammonium bicarbonate is reused as a precipitant for forming rare carbonate (step (7)).

[2]

Process (1) The method as described in [1] which is a process of mixing and heating the slurry containing the oxide of a rare earth element, and an oxidation-reducing agent, and melt | dissolving the said rare earth element in a slurry.

[3]

The method according to [1] or [2], wherein the acid in step (1) is hydrochloric acid or sulfuric acid.

[4]

The oxidation / reducing agent in the step (1) is hydrogen peroxide (Hydrogen Peroxide), the method according to [1] to [3].

[5]

The heating temperature of a process (1) is 50 degreeC or more, The method as described in [1]-[4] characterized by the above-mentioned.

[6]

The pH condition of a process (2) is 5-6, and a pH adjuster is soluble alkali metal salt, The method as described in [1] characterized by the above-mentioned.

[7]

The method according to [1], wherein the solid-liquid separation means for the undissolved component in the step (2) is by filtration.

[8]

The method according to [1], wherein the form of ammonium bicarbonate added in the step (3) is in solution or slurry form.

[9]

The process as described in [1] in the step (4), wherein the produced rare carbonate is filtered, washed, separated and purified.

[10]

The baking of a process (5) WHEREIN: The method as described in [1] characterized by the temperature in 300-1200 degreeC in air atmosphere.

[11]

The method as described in [1] in the process (6), wherein the strong alkali agent is sodium hydroxide, potassium hydroxide or calcium hydroxide.

[12]

The process according to (1), wherein air is blown into the aqueous ammonium salt solution to strip off the generated ammonia.

[13]

The process as described in [1] in the process (6) WHEREIN: The density | concentration of the aqueous solution of condensed ammonia is 1-5 mass%.

[14]

The contact temperature in a process (7) is 10-40 degreeC, The method as described in [1] characterized by the above-mentioned.

[15]

The density | concentration of ammonium bicarbonate in a process (7) is 5-25 mass%, and a form is a solution or slurry, The method as described in [1] characterized by the above-mentioned.

[16]

A rare earth element characterized by using an abrasive for polishing, recovering the rare earth element from the generated waste abrasive slurry by the method according to any one of [1] to [15], and using the obtained rare earth element again as a raw material of the abrasive. Recovery method of the element.

As described above in detail, the present invention provides a method for recovering a rare earth element from a waste polishing slurry containing rare earth elements such as cerium, which is greatly reduced in polishing rate and usually discarded.

In other words, the rare earth oxide component can be selectively dissolved in the slurry of the above-described abrasive polisher using a photoacid and an oxidizing / reducing agent.

In addition, when separating and recovering the dissolved rare earth component selectively dissolved in this manner as rare carbonate, by solid-liquid separation at a specific pH in the presence of hydrogen peroxide, impurities such as iron ions, which are dissolved and coexist, are selectively unnecessary. Separate as a solid component. In this way, a high-purity rare earth carbonate that can be reused as an abrasive raw material can be obtained, and it can be easily baked to recover the rare earth oxide.

Moreover, according to this invention, ammonium bicarbonate is added and made to react with the acidic aqueous solution which selectively dissolves the rare earth oxide component using a mine, and produces | generates and crystallizes rare earth carbonate further, The said reaction process Since the ammonia in the ammonium salt by-produced in the above is recovered and reused as ammonium bicarbonate used as this reaction agent, expensive ammonium bicarbonate can be recycled and the detoxification treatment of the process waste liquid is easy.

EMBODIMENT OF THE INVENTION Hereinafter, the best form for implementing this invention is demonstrated in detail, referring drawings. BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows the collection process of the rare earth element containing the recycling process of ammonium bicarbonate which is the characteristic of this invention.

Slurry Abrasive Slurry

The waste abrasive slurry 10 is the starting slurry to be subjected to the recovery treatment. The waste abrasive slurry 10 includes, in addition to rare earth oxides and rare earth fluorides, the main components of which are polished glass, silicon, aluminum compounds, broken glass cullets, pad fibers, and the like. Foreign object has been mixed. Although the component of this waste abrasive slurry changes also with the process conditions to be used, it is discharged | emitted from the grinding | polishing process 9 in the state of about 5 to 50% of solid content concentration normally. The composition is about 82% by mass of rare earth oxide equivalent TREO (= (total rare earth oxide mass / total oxide mass) x 100) based on a dry product (of which about 25% by mass is rare fluorinated component), and the silicon compound About 5 mass%, an aluminum compound and an iron compound are about 1 mass%, and foreign substances, such as glass powder and a pad fiber, are mixed.

In the polishing step 9, the waste abrasive slurry 10 is circulated in the polishing slurry 9, and finally, the slurry slurry is approximately converted into a rare earth component (TREO (Total Rare Earth Oxide)) by concentration by gravity sedimentation. It is prepared as a 30 mass% slurry.

In addition, in the case of concentration by the gravity sedimentation method of the said slurry, although you may carry out by the said waste abrasive slurry alone, the said sedimentation concentration is performed more effectively by using a commercially available polymer flocculant together. This is the starting material for the waste abrasive slurry to be treated in the step (1).

(1st process [I])

(Step (1))

(Step of dissolving rare earth element in slurry of waste polishing agent to obtain rare earth solution)

First, the waste abrasive slurry 10 is collected in a reaction vessel, and a predetermined amount of acid 20 and an oxidation-reducing agent 30 such as hydrogen peroxide are added thereto, followed by heating and reacting with stirring to dissolve the slurry (33) do.

Although it does not specifically limit as a reaction container, It is preferable that it is a stirring tank type provided with the stirring means, the slurry of waste polishing agent, the acid, the introduction means, such as an oxidation-reducing agent, a heating means, etc. at least.

The acid 20 used here may be a mineral acid capable of dissolving the rare earth element contained in the slurry 10 and is selected from hydrochloric acid, sulfuric acid, and nitric acid. Hydrochloric acid or sulfuric acid is preferable from the viewpoint of drainage treatment, and particularly preferably hydrochloric acid.

The concentration of the acid is not particularly limited. For example, when hydrochloric acid is used, 35 mass% of concentrated hydrochloric acid can be used industrially. Moreover, the addition amount of this acid adds 40-60 parts, Preferably about 50 parts with respect to 100 parts (Part) of a waste abrasive slurry. If the added amount is less than 40 parts, the insoluble content of the rare earth element increases, and if the added amount exceeds 60 parts, it is not preferable because the effect is not increased, but simply the amount of drugs (acids) consumed unnecessarily increases. .

Moreover, it is preferable to use hydrogen peroxide as the oxidation-reducing agent 30. Hydrogen peroxide is known to act as an oxidizing agent or reducing agent on rare earth elements and impurity components. For example, the cerium element acts as a reducing agent to suppress the formation of Ce (IV) having low solubility in photoacids such as hydrochloric acid and sulfuric acid. On the other hand, it acts as an oxidizing agent to neodymium or iron and forms Nd (III) and Fe (III). In other words, neodymium is oxidized to add solubility to photoacids, and iron is oxidized to form insoluble hydroxide (Hydroxide) in the subsequent step (2), which facilitates separation from rare earth elements.

Thus, hydrogen peroxide is added for the purpose of improving the solubility of a rare earth element and reducing the solubility of impurities, such as iron. It is preferable that the addition amount is a range of 5-6 parts in terms of 30 mass% concentration with respect to 100 parts of waste polishing slurry.

In this way, only the rare-earth oxide component of the rare earth component is selectively dissolved (33) by adding to the diluted waste abrasive slurry 10 and heating while adding an oxidation-reducing agent such as hydrogen peroxide and hydrogen peroxide and stirring. Simultaneously with this dissolution, a highly viscous slurry 35 is formed in which almost the entire amount of the iron component and some of the silica and alumina components are also dissolved.

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

The stirring means is not particularly limited as long as the solid particles in the slurry can be sufficiently suspended to enable solid-liquid reaction to be performed smoothly, and stirring blades are usually employed. As a stirring blade, a paddle and an anchor blade are preferable, As a rotation speed, the blade circumferential speed is 0.1-1 m / sec, Preferably the conditions of 0.3-0.6 m / sec are employ | adopted.

Although reaction time can change according to reaction temperature, it is 2 hours-20 hours normally, Preferably it is about 3 to 10 hours. In addition, when reacting at reflux temperature (about 100 degreeC), the dissolution reaction of the said rare-earth oxide component is completed by stirring by stirring for 4 hours or more, preferably about 5 hours, under stirring conditions.

(Step (2))

(Separation step of Si, Al, Fe, undissolved rare earth residues from acidic solution of rare earth elements)

To the slurry (acid slurry) 35 completed in the step (1), as a pH adjuster 40, a soluble alkali component is added, the pH is adjusted (43), and the pH is dissolved. Only iron (Fe), silica (Si), and aluminum (Al) components can be selectively precipitated.

As pH conditions at the time of this pH adjustment, Preferably it is pH 5-6, More preferably, it is controlled so that it may become the range of pH 5.3-5.6, Most preferably pH 5.5. If the pH is less than 5, the total amount of the Fe, Si, and Al components is not completely precipitated. If the pH is more than 6, re-dissolution of the Al and Si components and precipitation of rare earth elements occur, which is not preferable.

As a soluble alkali component which is a pH adjuster 40, it should just be an alkali metal salt, alkaline-earth metal salt, or ammonium salt. In view of the filterability of the precipitate, it is preferable to use an alkali metal carbonate such as sodium bicarbonate (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.

In addition, when adding the sodium carbonate solution as a pH adjuster to the acidic slurry 35, carbon dioxide gas (carbonic acid gas) is produced | generated and discharge | released by reaction, and a solution becomes a boiling state in appearance. Therefore, it is preferable to install a reflux condenser in the reactor, to cool the discharged carbon dioxide gas (and the accompanying steam), to condense only the water vapor, and to introduce and recover the carbon dioxide gas absorbing device in the step (7) described later. desirable.

After the pH adjustment as described above, the slurry is cooled while stirring, and a solid unnecessary component containing iron, silica, an alumina component, a dissolved residue mainly containing rare fluoride, and the like precipitated under a temperature condition of about 40 to 50 ° C. It separates by solid-liquid separation means 50, such as filtration. Basically, the hydroxides of silica and alumina components are poorly filtration, but are efficiently separated into solids by filtration or the like by precipitating as carbonates and by dissolving the abrasive as a filter aid. Although temperature, such as filtration, is not necessarily limited to the said range, When temperature is too high, since it is unpreferable in a working environment, it is preferable to operate around 40 degreeC.

In the case of filtration as the solid-liquid separation means, the filtration apparatus is not particularly limited. For example, a filter press, a drum filter, or a pump pressurized line filter is used. From the viewpoint of safety, it is preferable to pump-circulate and process the inside of the line filter provided in the piping line. In addition, in the case of filtration separation, a suitable filtration cloth such as a filtration cloth, a ceramic filter, a filter paper, or the like can be used depending on the throughput, the solid filterability, and the like.

In this way, in the step (2), the solid impurities (solid unnecessary component) 53 are removed and the acidic aqueous solution 60 in which the rare earth element is dissolved is taken out.

(Step (3))

(Step of generating rare 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 crystallize as the rare earth carbonate 80 to simultaneously dissipate the carbon dioxide gas 90. By using ammonium bicarbonate as a crystallization agent, the crystal | crystallization of rare carbonate with good filterability can be obtained.

As a reaction container, the stirring tank reactor provided with the introduction means, the stirring means, the heating means, etc. of the acidic aqueous solution 60 and the ammonium bicarbonate 70 is preferable. The form and concentration of the ammonium bicarbonate 70 to be added are not limited at all. Although ammonium bicarbonate 70 may be added in aqueous solution or a slurry state, it is preferable to use it as aqueous solution of ammonium bicarbonate in the range of 5 to 10% of concentration especially from a handling viewpoint.

The addition amount of ammonium bicarbonate 70 should just be an amount sufficient in order to neutralize the acid component of the acidic aqueous solution 60, and the quantity adds 10-20 parts per 100 parts of waste abrasives of a process (1) on a dry goods basis. It is preferable to carry out, More preferably, it is 12-15 parts.

The addition of the ammonium bicarbonate 70 to the acidic solution 60 is preferably carried out at a high temperature as much as possible in order to more smoothly disperse the carbon dioxide gas 90 generated in the reaction from the system. Usually, ammonium bicarbonate is dividedly added over a period of 2 to 3 hours under stirring conditions while circulating hot water at around 80 ° C. in a jacket of a reactor which is a heating means, and circulating 80 ° C. and heating.

(Step (4))

(Separation process of rare carbonate)

After the said rare carbonate containing slurry 83 is cooled to 60 degrees C or less, Preferably it is 40-50 degreeC, solid-liquid separation (100) is performed by filtration etc., for example. Filtration separates the rare earth carbonate 85 and the aqueous ammonium salt solution 95. It is preferable that the separated rare carbonate 85 is further washed with water in a quantity of about 1 to 3 times by mass to suppress reincorporation of impurities in the waste abrasive slurry accompanying as the adherent mother liquor. In addition, in order to wash | clean more fully, the operation | movement which carries out solid-liquid separation operation may be repeated by disperse | distributing (repulping) the separated rare carbonate cake to water, and making it as a slurry.

In this way, in the step (4), the produced rare carbonate is separated and purified by filtration and washing. In addition, solid-liquid separation 100 here is operation | movement containing filtration and washing | cleaning.

(Step (5))

(Recovery of rare oxide)

The rare earth carbonate 85 obtained by solid-liquid separation (100) in the step (4) is dried and calcined (110) to obtain a rare earth oxide. Drying is performed at about 40-200 degreeC. As a drying apparatus, arbitrary things, such as a box type dryer, a band dryer, and a vacuum dryer, are used. In addition, the firing is performed at 300 to 1200 ° C, preferably 400 to 1100 ° C, more preferably 500 to 1000 ° C, for about 1 to 3 hours, preferably 1.5 to 2 hours, in the atmosphere. Do it. As the firing apparatus, conventional firing furnaces such as box furnaces, rotary furnaces and tunnel furnaces are used.

The rare earth oxide (rare earth oxide) 88 obtained by firing is put into the atomization treatment process of a conventional abrasive production line after disintegration as recovered rare earth oxide, and reused as a raw material of an abrasive.

The above is the 1st process [I]. That is, in process [I], process (1)-(5) is performed and the said rare earth oxide is collect | recovered from the waste abrasive slurry containing the oxide of a rare earth element.

(2nd process [II])

Next, 2nd process [II] is described. In step [II], the following steps (6) to (7) are carried out, and in the first step [I], ammonium bicarbonate used as the precipitant of rare earth carbonate is regenerated, and the regenerated ammonium bicarbonate is the first step. Reused in [I].

(Step (6))

(Recovery of ammonia)

In the step (3) described above, ammonium salts (95) such as ammonium bicarbonate (70) and equimolar ammonium chloride (Ammonium Chloride) or 1/2 molar amount of ammonium sulfate (95) And 1/2 mol of carbonic acid gas 90 are by-produced.

As shown in the flow sheet of FIG. 1, ammonium salts, such as ammonium chloride and ammonium sulfate, are melt | dissolved in a mother liquid, are stored as ammonium chloride aqueous solution 95, such as an ammonium chloride aqueous solution or an ammonium sulfate aqueous solution, and the produced | generated carbon dioxide gas 90 is It is discharged out of the system as gas from the upper part of the reactor.

Here, when the acid component is hydrochloric acid and sulfuric acid, the reactions are as follows.

(1) When the acid component 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 component is sulfuric acid

Ln ₂ (SO ₄ ) ₃ + 6 NH ₄ HCO ₃

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

(Ammonia recovery method)

The recovery method of ammonia is demonstrated below, taking the case where an acid component is hydrochloric acid as an example.

To the aqueous ammonium chloride solution 95 at a concentration of about 0.6 mol / L, a soluble strong alkali agent 97 is added to liberate ammonia 98.

Examples of the soluble strong alkaline agent include sodium, potassium, and calcium hydroxides (sodium hydroxide, potassium hydroxide, calcium hydroxide), and sodium hydroxide is particularly preferable.

Namely, 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 pH 12-13, the ammonia 98 is almost quantitatively To be liberated.

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

Subsequently, ammonia is stripped 120 at a high temperature while blowing a small amount of air into the aqueous solution 95, thereby lowering the temperature of the stripped gas 98 containing the volatilized ammonia and water vapor. The aqueous ammonia solution 135 is condensed and recovered.

The stripping 120 may be carried out in a batch operation (batch operation), but a wet-wall tower, a plate tower, or a packed tower system having good gas-liquid contact. Is employed. That is, the pre-warmed ammonium chloride aqueous solution 95 is supplied from tower tops, such as these wet wall towers, and air and steam are supplied from the bottom of a tower as needed. In this way, a method of flowing the liquid from the upper side, raising the hot air from the lower side, making the countercurrent contact in the column, and stripping is preferable.

Specifically, as for the temperature of the said stripping 120, 70-100 degreeC, Preferably 85-95 degreeC is employ | adopted. Under this temperature and pH conditions, when the ammonium chloride aqueous solution 95 supplied from the column top is introduced at a rate of, for example, 100 kg / hour, on the other hand, air is introduced from the column bottoms at 1 to 15 kg / hour, preferably 3 to It is introduced at a rate of 10 kg / hour, more preferably 4-6 kg / hour.

If the amount of air introduced (air flow rate) is too large relative to the amount of aqueous ammonia solution, the amount of water vapor accompanying the ammonia to be stripped becomes very large, and the recovery rate of ammonia in the next condensation step is lowered, which is not preferable. On the other hand, if the amount of introduced air is too small, the stripping efficiency of ammonia is lowered, and therefore, it is preferable to employ and control the flow rate in the above range.

Subsequently, this stripping gas (ammonia vapor, water vapor) 98 is introduced into the ammonia condensation and recovery step 130, cooled to 30 ° C or lower, preferably 20 to 35 ° C, and released from the column top. 95% or more of the was recovered as the aqueous ammonia solution 135. In addition, the said aqueous solution 135 is diluted with process water as needed, and is recovered as 1-5 mass%, Preferably it is 1.5-2 mass% aqueous solution.

Further, in the aqueous ammonium salt solution 95, the remaining aqueous solution (tank residue) 99 obtained by stripping 120 of the ammonia gas 98 only contains harmless salts (NaCl, Na ₂ SO _4, etc.). Therefore, after neutralizing 140 the excess alkali with the acid (pH regulator) 142, the neutralizing liquid can be discharged 145 without a problem.

(Step (7))

(Recovery of carbon dioxide gas and synthesis of ammonium bicarbonate)

The carbon dioxide gas 90 discharged from the reactor is subjected to reaction absorption (Gas Absorption Accompanied by Chemical Reaction) by the aqueous ammonia solution 135 recovered in the 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 of reaction absorption is 10-40 degreeC, Preferably it controls in 20-30 degreeC.

The apparatus for absorbing the carbon dioxide gas 90 to form the ammonium bicarbonate 70 may be a conventional absorption tower method, but a locally stirred ammonium bicarbonate may be precipitated, and therefore, a stirred tank type is preferable.

That is, as reaction container R which performs reaction absorption, the carbon dioxide gas introduction means 1, the stirring means 2, the temperature control means 3, the condenser 4, and countercurrent contact type as shown in FIG. (Counter Current) A stirring absorption device provided with the absorption tower 5 is preferable. 6 is ammonia water for reaction absorption which adjusted the ammonia aqueous solution 135 to density | concentration. In addition, it is preferable to use such a stirring absorption device at the front end in combination with a countercurrent contact absorption tower such as a banding tower, a packed column, and a wet wall column at the rear end. Moreover, fresh carbon dioxide 138 or dilution water is supplied as needed, and the density | concentration of ammonium bicarbonate in a liquid is controlled in 5-25 mass% which is below saturated solubility, Preferably it is 8-10 mass%. If the concentration is too low, the equipment load of the absorber is high, and if the concentration is too high, an ammonium bicarbonate slurry is formed, so it is preferable to control within this range.

As a stirring absorption device, any of stirring blade batch type and a continuous type may be employ | adopted, and the shaping | molding absorption device equipped with an anchor, a turbine, a paddle, a full zone wing | blade, etc. may be sufficient, but a commercially available stirring type gas absorption installation is possible. Can be selected appropriately.

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

Example

Hereinafter, an Example demonstrates this invention. However, these are examples of simple embodiments, and the technical scope of the present invention (the scope of rights covered by the present invention) is not to be construed as being limited or limited in any way by these examples. In addition,% is mass% unless there is particular notice.

EXAMPLE 1

(1) (The rare earth element of the waste abrasive slurry is dissolved, and a rare earth solution (slurry) is produced. Step (1).)

The processing operation was performed in accordance with the flow sheet of FIG. 1.

The waste abrasive slurry 10 of the starting material is adjusted as follows. In other words,

The waste abrasive slurry produced by polishing of the glass disk was collected and subjected to gravity settling to prepare a slurry having a solid content concentration of about 30% by mass on a dry basis.

In addition, the quantity of the component element calculated | required by the fluorescence X-ray method (X-ray Fluorescence Analysis) with respect to the powder which extract | collected a part of this slurry and dried all day under the conditions of 100 degreeC in 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 and reducing agent 30. 1 kg of the slurry was collected into 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 having 35 mass% hydrochloric acid. 510 g of aqueous solution and 50 g of 30 mass% hydrogen peroxide aqueous solution were added. Subsequently, the mixture was warmed with stirring at a rate of about 150 rpm, and held for 4 hours under conditions of a liquid temperature of 80 to 85 ° C to dissolve most of the rare earth compounds.

(2) (Separation of Si, Al, Fe, Undissolved Residues from Acid Solution (Slurry) of Rare Earth Element, Step (2))

Subsequently, a 10% concentration of sodium carbonate solution was added to the acidic solution (slurry) 35 as the pH adjusting agent 40 to adjust the pH to pH 5.5.

At this time, the carbon dioxide gas generated in the neutralization reaction is dissipated with water vapor, and the solution is in a boiling state in appearance. The carbon dioxide gas was cooled with a reflux condenser, condensed with accompanying steam, introduced into a carbon dioxide gas absorbing device in the step (7) described later, and the reaction was absorbed with an aqueous ammonia solution to recover most of it as ammonium bicarbonate.

After pH adjustment, after cooling to 40 degreeC over about 1 hour under stirring conditions of 120 rpm, stirring was stopped and the contents were taken out.

Subsequently, in a Nutsche type suction filter having an inner diameter of 300 mmφ, the undissolved component was solid-liquid separated (50) as a solid unnecessary component (53) using No. 5A filter paper (manufactured by Advantech Toyo Co., Ltd.), and a rare earth element. The dissolved hydrochloric acid aqueous solution 60 was recovered.

The mass of the dried product reference | standard of the solid content (solid unnecessary component) isolate | separated from filtration was 30.5 g, and it confirmed that the component was iron, aluminum, silica, and rare fluoride earth from the analysis by the fluorescent X-ray method.

(3) (Generation and crystallization of rare 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 the solution was heated to about 60 ° C. while stirring at a speed of 120 rpm. Subsequently, 1300 g of a solution of ammonium bicarbonate (70) at a concentration of about 9% by mass was added sequentially, and the following reaction was performed in order to precipitate crystals 80 of rare carbonate.

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 chloride to produce rare carbonate and release carbon dioxide gas. Since carbon dioxide gas disappeared for about 20 minutes after the addition of ammonium bicarbonate, and the end of reaction could be confirmed, it was cooled to 40 degreeC and stirring was stopped. In addition, the carbon dioxide gas by-produced in the reaction was cooled by a reflux condenser at the top of the reactor, then introduced into the carbon dioxide gas absorbing device in the step (7), reacted with an aqueous ammonia solution and recovered as ammonium bicarbonate.

(4) (Separation of rare carbonate, process (4))

The rare earth carbonate-containing slurry 83 was filtered (100) using a No. 5A filter paper (manufactured by Advantech Toyo Co., Ltd.) in a liquid-type suction filter having an inner diameter of 200 mmφ, and washed three times with 100 g of pure water after filtration separation. It collect | recovered and dried in air throughout the day at 100 degreeC temperature conditions, and obtained the dry cake of 240 g of rare carbonate (85).

Table 2 shows the analysis values of the recovered rare carbonate 85 by ICP emission spectrometry (manufactured by Shimadzu Corporation, Shimadzu Corporation). As can be seen from the table, at least 99% of the trace impurities (trace contaminant), silica, alumina, and iron components mixed in the polishing and polishing slurry concentration processes are removed, and industrially, As it was obtained, there was no comparable. The recovery rate (Yield) in terms of the rare oxide component was about 70%.

(5) (Recovery and polishing characteristics of rare oxides)

The rare carbonate 85 recovered as described above was subjected to heat treatment at temperatures of 400 ° C., 500 ° C. and 600 ° C. to obtain rare earth oxide 88. This was pulverized under predetermined conditions, and mixed, mixed, calcined, pulverized, classified, and slurried (about 15 mass% concentration) was treated at the same time with the pulverized fluoride soil adjusted to pulverization treatment, and reused. Polishing characteristics were evaluated using a mold polishing machine.

Table 3 shows the results of evaluating the polishing rate and the surface state of the rare earth oxide obtained at the heat treatment temperatures of the recovered rare carbonate at 400 ° C, 500 ° C and 600 ° C, respectively.

As can be seen from Table 3, it was found that the heat treatment of the recovered rare carbonate at 500 ° C. and 600 ° C. yielded polishing properties equivalent to those of the abrasive prepared from a conventional raw material (fresh raw material).

(6) (recovery of ammonia)

In the step (4), about 2900 g of the filtrate (an ammonium salt aqueous solution 95) which can separate the rare earth carbonate from the rare earth carbonate slurry 83 is injected into a 5 L separable flask equipped with a stirring blade, and subjected to external heating. By controlling the liquid temperature to 95 ℃.

Next, while stirring about 1 L / min of air under stirring conditions, 25% caustic soda which is a strong alkali (97) was continuously added over about 1 hour, and pH of the solution was raised to 13.

With 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 with blown air, extracted from the upper side of the stirring vessel with air, and then cooled to 15 to 20 ° C. with a condenser and condensed (130) to form an ammonia condensate (ammonia aqueous solution). About 135 g of (135) was recovered. The concentration of ammonia in the recovered condensate was about 6.4 mass%, and it was found that about 88% of the ammonium chloride dissolved in the filtrate (in the ammonia aqueous solution) could be recovered as ammonia.

(7) (Recovery of carbon dioxide gas and synthesis of ammonium bicarbonate, process (7))

In the step (7), the carbon dioxide gas introduction means (introduction pipe) 1, the stirring means 2, the temperature regulating means 3, the condenser 4, the countercurrent contact absorption tower 5 as shown in FIG. Was performed by a stirring absorption device (agitator tank with a capacitor) (R) (with an inner diameter of φ 120 mm × bath height h 150 mm and a paddle type stirring blade (10H × 60W)). That is, the ammonia water for reaction absorption (6) which added the total amount of the 6.4 mass% aqueous ammonia solution 135 collect | recovered to this condenser with a condenser, 15 g of 25% of reagent ammonia waters, and 760 g of water was added. Was injected.

While stirring this at the speed of 150 rpm, cold water was sent to the outer jacket 3, and the internal temperature was cooled to 20 degreeC, and the upper condenser 4 was cooled to 10 degreeC.

Next, carbon dioxide gas 90 (reaction product gas generated when ammonium bicarbonate 70 is added to the acid rare earth solution 60 to generate rare carbonate) from the carbon dioxide gas introduction pipe 1 of this stirring tank, It was bubbled in ammonia water for absorption (6), reaction carbon dioxide was absorbed and produced ammonium bicarbonate.

A part of the recovered ammonium bicarbonate aqueous solution synthesized by reaction absorption was collected and determined by evaporative drying method, and the solid content concentration was 9.2 mass%, and the amount of ammonium bicarbonate calculated therefrom was 115 g.

This means that about 93% of the carbon dioxide gas 90 estimated to be generated in the rare earth carbonate generation process (rare carbonate crystallization process) was recovered as ammonium bicarbonate 70. Fresh ammonium bicarbonate and water were added to this aqueous solution as needed, and it was recycled to the rare earth carbonate generation and crystallization process 80 as it was, and it showed that it can be reused as a raw material of a rare earth carbonate synthesis (process (3)).

According to the present invention, it is possible to efficiently recover high-quality rare earth oxides from a waste polishing slurry containing rare earth elements which are greatly reduced in polishing rate and usually discarded, and can be used again as an abrasive having a high polishing rate. An inexpensive process is provided.

According to the present invention, ammonium bicarbonate is added to the acidic aqueous solution in which the rare earth oxide component is selectively dissolved using a mineral acid, and reacted to produce rare crystal carbonate. Here, since the ammonia in the ammonium salt by-produced in the said reaction process is recovered and recycled as ammonium bicarbonate used as this reaction agent, expensive ammonium bicarbonate can be recycled and the detoxification process of a process waste liquid is easy.

According to the present invention, when separating and recovering the dissolved rare carbonate component as rare carbonate, by solid-liquid separation at a specific pH in the presence of hydrogen peroxide, impurities such as iron ions dissolved and coexist can be selectively precipitated. Since the high purity rare carbonate can be easily produced and recovered, its industrial applicability is very large.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow-sheet showing a recovery process of rare earth elements including a recycling step of ammonium bicarbonate of the present invention, and Fig. 2 is a reaction vessel for reacting and absorbing carbon dioxide gas with ammonia water to form ammonium bicarbonate. It is explanatory drawing which shows.

In these figures, 1 is carbon dioxide gas introduction means, such as a nozzle, 2 is stirring means, 3 is temperature control means, such as a cooling jacket, 4 is a condenser, 5 is a countercurrent contact absorption tower, 6 is ammonia water for reaction absorption, 9 Silver polishing process, 10 silver abrasive polishing slurry, 20 silver acid, 30 silver oxidation / reduction agent such as hydrogen peroxide, 33 silver heating and melting process, 35 high viscosity slurry, 40 silver pH adjusting agent, 43 silver pH adjusting process, 50 silver solid solution Separation means, 53 is a solid unnecessary component, 60 is an acidic aqueous solution in which rare earth elements are dissolved, 70 is ammonium bicarbonate, 80 is rare carbonate generation and crystallization process, 83 is rare carbonate-containing slurry, 85 is rare carbonate, 88 is rare earth oxide ( Rare earth oxide), 90 is carbonic acid gas, 95 is ammonium salt aqueous solution, 97 is strong alkaline agent, 98 is ammonia or stripping gas (ammonia vapor, water vapor), 99 is aqueous solution after stripping (tank residue), 100 is solid-liquid separation means (Filtration, three ), 110, 120 stripping, drying and firing process, 135 is an aqueous ammonia solution, 138 is the fresh carbon dioxide, and 140 is the neutralizing step, 142 is acid (pH adjusting agent), and 145 denotes a neutralizing liquid discharge processes, respectively.

Claims (16)

In the 1st process [I] which consists of following process (1)-(5), the said rare earth oxide is collect | recovered from the waste abrasive slurry containing the oxide of a rare earth element, and then goes to process (6)-(7). In the second step [II], the ammonium bicarbonate used as the precipitant of rare earth carbonate in the first step [I] is regenerated, and the regenerated ammonium bicarbonate is reused in the first step [I]. A method of recovering a rare earth element involving the reuse of ammonium. Here, the first step [I] is (1) a slurry containing rare earth oxide is mixed with an oxidizing / reducing agent and an acid under stirring conditions and heated to dissolve (step (1)), (2) After adjusting the pH of the obtained rare earth element solution to an appropriate condition, insoluble components are separated by solid-liquid separation means (step (2)), (3) add ammonium bicarbonate to this solution to precipitate rare carbonate (step (3)), (4) separating rare carbonate from the obtained rare carbonate-containing slurry (step (4)), and (5) firing this to make a rare earth oxide and recovering the generated rare earth element (step (5)); 2nd process [II], (6) a strong alkali is added to the aqueous ammonium salt solution from which rare carbonate is separated to generate ammonia, which is then condensed and recovered as an aqueous ammonia solution (step (6)), and (7) Next, the carbon dioxide gas generated from the process is brought into contact with each other to form a solution or slurry of ammonium bicarbonate, and the obtained solution or slurry of ammonium bicarbonate is reused as a precipitant for forming rare carbonate (step (7)). The method of claim 1, Process (1) A process characterized by mixing and heating a slurry containing an oxide of a rare earth element, and an oxidation / reducing agent to dissolve the rare earth element in the slurry. The method according to claim 1 or 2, The acid in step (1) is hydrochloric acid or sulfuric acid. The method according to claim 1 or 2, The oxidation / reducing agent in the step (1) is hydrogen peroxide. The method according to claim 1 or 2, The heating temperature of process (1) is 50 degreeC or more, The method characterized by the above-mentioned. The method of claim 1, The pH condition of process (2) is 5-6, and a pH adjuster is soluble alkali metal salt, The method characterized by the above-mentioned. The method of claim 1, The method for solid-liquid separation of the undissolved component in step (2) is by filtration. The method of claim 1, The method characterized in that the form of ammonium bicarbonate added in step (3) is in solution or slurry form. The method of claim 1, In the step (4), the produced rare carbonate is filtered, washed, separated and purified. The method of claim 1, The baking of a process (5) WHEREIN: The temperature is 300-1200 degreeC in air atmosphere, The method characterized by the above-mentioned. The method of claim 1, The method according to step (6), wherein the strong alkali agent is sodium hydroxide, potassium hydroxide or calcium hydroxide. The method of claim 1, The process according to (6), wherein air is blown into the aqueous ammonium salt solution to strip off the generated ammonia. The method of claim 1, The process of (6) WHEREIN: The density | concentration of the aqueous solution of condensed ammonia is 1-5 mass%, The method characterized by the above-mentioned. The method of claim 1, The contact temperature in a process (7) is 10-40 degreeC, The method characterized by the above-mentioned. The method of claim 1, The concentration of ammonium bicarbonate in the step (7) is 5 to 25% by mass and the form is a solution or slurry. A rare earth element is recovered by using the abrasive for polishing, recovering the rare earth element from the generated waste abrasive slurry by the method according to claim 1 or 2, and using the obtained rare earth element again as a raw material for the abrasive. Way.

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