JP2014109064A - Metal recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal recovery method which can recover metals efficiently by an inexpensive and simple method.SOLUTION: The metal recovery method uses a carboxylic acid ester of polysaccharide as a metal capture agent, which captures metals which dissolve in a solution. The present metal recovery method preferably selectively captures gold which dissolves in an acidic solution. As the carboxylic acid ester of polysaccharide, preferably used is an ester of a carboxylic acid and cellulose.

Description

  The present invention relates to a metal recovery method for capturing and recovering a metal dissolved in a solution.

  Precious metals such as gold, platinum, and palladium are extremely important substances in cutting-edge fields such as electronic parts, semiconductors, automobile exhaust gas purification catalysts, liquid crystal glass, and LEDs. Was a problem. On the other hand, electrical and electronic equipment waste (e-waste) contains a large amount of precious metals, sometimes containing more than 10 times the amount contained in ores. For this reason, it is required to separate and recover precious metals from wastes of electric and electronic equipment by an inexpensive and simple method and reuse them.

  Patent Documents 1 to 3 disclose a cellulose acetate reverse osmosis membrane that selectively permeates only a noble metal such as gold, silver, palladium, rhodium, etc., for a method of separating and recovering only a noble metal from a solute of a processing solution in a noble metal plating treatment process. How to use is described. However, the permeate obtained by permeation through the cellulose acetate reverse osmosis membrane needs to be concentrated by electrodialysis, and the work process is complicated. Moreover, it has not been possible to selectively recover only specific noble metals from among noble metals such as gold, silver, palladium and rhodium.

  Patent Document 4 describes a method for recovering noble metals (gold, platinum, and palladium) in a solution using a tyramine polymer as a metal adsorbent. However, even this method cannot selectively recover only a specific noble metal from gold, platinum, and palladium.

JP-A-2-44892 JP-A-2-44893 JP-A-2-58328 JP 2011-178853 A

Accordingly, an object of the present invention is to provide a metal recovery method capable of recovering metal efficiently by an inexpensive and simple method.
Another object of the present invention is to provide a metal recovery method capable of recovering gold efficiently and selectively by an inexpensive and simple method.
Furthermore, another object of the present invention is to provide a metal capturing material capable of recovering gold efficiently and selectively at low cost.

  As a result of intensive studies to solve the above problems, the present inventors have found that by using an inexpensive polysaccharide carboxylic acid ester as a metal-trapping material, it is possible to adsorb and recover metals easily and efficiently. . The present invention has been completed based on these findings.

  That is, the present invention provides a metal recovery method for capturing a metal dissolved in a solution using a polysaccharide carboxylic acid ester as a metal capturing material.

  The metal recovery method is preferably a method for selectively capturing gold dissolved in an acidic solution.

  As the carboxylic acid ester of the polysaccharide, a carboxylic acid ester of cellulose is preferable, and cellulose acetate is particularly preferable.

  The acyl group total substitution degree of the carboxylic acid ester of the polysaccharide is preferably 2.2 to 2.7.

  The polysaccharide carboxylic acid ester is preferably in the form of a fiber, particularly preferably in the form of a fiber having a single fineness of 0.5 to 5.0 denier.

  The present invention also provides a metal-capturing material containing fibrous cellulose acetate having a single fineness of 0.5 to 5.0 denier.

  The cellulose acetate is preferably cellulose acetate having a total acetyl group substitution degree of 2.2 to 2.7.

  Since the metal recovery method of the present invention uses an inexpensive polysaccharide carboxylic acid ester as a metal scavenger, the cost of metal recovery can be reduced, and a metal that dissolves in a solution efficiently can be recovered by a simple method. Can do. In particular, when a solution in which a metal is dissolved is adjusted to be acidic, gold can be selectively and efficiently recovered among metals. According to the metal recovery method of the present invention, the metal contained in the electrical and electronic equipment waste (e-waste) can be efficiently recovered and reused effectively, and the cost reduction and the cutting-edge field are extremely effective. A stable supply of important metals can be realized.

[Metal recovery method]
The metal recovery method of the present invention is characterized by capturing a metal dissolved in a solution using a polysaccharide carboxylic acid ester as a metal capturing material. For example, the polysaccharide is contained in a solution in which a metal is dissolved (= metal solution). The carboxylic acid ester can be added and stirred to capture and recover the metal.

In the metal recovery method of the present invention, preparing the metal solution in an acidic manner selectively selects only gold from a metal solution that dissolves two or more kinds of metals including gold (for example, gold, palladium, and platinum). It is preferable in that it can be captured. Other metals (eg, palladium, platinum, etc.) exist stably as cations in the acidic metal solution, but gold is not as a cation but an anion (eg, AuCl ₄ ⁻ , acidic metal sulfate in hydrochloric acid metal solution). In the solution, it is stably present as Au (SO ₄ ) ₂ ⁻ ). And since the surface of the polysaccharide carboxylate ester has the characteristic that electron acceptability is large specifically, gold | metal | money can be selectively adsorb | sucked by interacting with the anion (= gold | metal anion) containing gold | metal | money.

  Examples of the acid used for adjusting the metal solution to be acidic include hydrochloric acid, sulfuric acid, nitric acid, and mixed acids thereof. In the present invention, among them, hydrochloric acid or sulfuric acid has a smaller radius, can form a gold anion that is more easily adsorbed by the surface of the polysaccharide carboxylic acid ester, and can improve the adsorptivity of gold. Is preferably used.

The metal solution is preferably adjusted to a pH of, for example, 4 to 1 (preferably 3 to 1 and particularly preferably 2 to 1) in terms of improving metal (especially gold) scavenging properties. When the pH is below the above range, the decomposition of the polysaccharide carboxylic acid ester used as the metal-trapping material tends to proceed. On the other hand, when pH exceeds the said range, there exists a tendency for the capture amount of a metal (especially gold) to fall. For example, in an acidic metal solution of hydrochloric acid, as represented by the following formula, the gold anion stably present varies depending on the pH, and in particular, the gold anion represented by [AuCl ₄ ⁻ ] is present on the surface of the polysaccharide carboxylate ester. This is because it is easily adsorbed.

  The time required for capturing the metal (that is, the time for immersing the metal capturing material in the metal solution) is, for example, 10 minutes or more, preferably about 50 to 300 minutes. If the immersion time is too short, the metal tends not to be captured sufficiently.

  In the metal recovery method of the present invention, a polysaccharide carboxylic acid ester is used as a metal-capturing material, so that the metal can be captured in a mild temperature environment. The temperature of the metal solution during immersion is, for example, about 5 to 60 ° C., preferably 5 to 30 ° C.

  The metal adsorbed and captured on the polysaccharide carboxylic acid ester by the metal recovery method of the present invention can be separated and recovered by subjecting the polysaccharide carboxylic acid ester capturing the metal to incineration or calcination, for example. it can.

[Metal capture material]
The metal-trapping material of the present invention contains a polysaccharide carboxylic acid ester.

  A polysaccharide is a compound obtained by a glucoside bond between monosaccharides, and examples thereof include cellulose and starch. In the present invention, it is preferable to use a polysaccharide obtained by β-glucoside bond of monosaccharide (= polysaccharide having β-glucoside bond), especially cellulose (especially cellulose derived from cotton linter pulp). Use is preferable in that the captured metal can be easily recovered.

  A polysaccharide carboxylic acid ester is a compound in which an acyl group (RC (═O) — group) is introduced into the hydroxyl group of the polysaccharide. R in the RC (═O) — group is a hydrocarbon group, and in particular, R is methyl, ethyl, propyl, in terms of excellent electron acceptability on the cellulose surface (particularly [1, -1,0] plane). Alkyl groups having about 1 to 10 carbon atoms (preferably 1 to 2) such as butyl, pentyl and hexyl groups are preferred.

  As the carboxylic acid ester of the polysaccharide in the present invention, a carboxylic acid ester of cellulose in which an acyl group (RC (= O) -group) is introduced into the hydroxyl group of cellulose represented by the following formula (1) is used. Is preferred. In formula (1), X is the same or different and represents an acyl group (RC (═O) —group: R is the same as described above) or a hydrogen atom (except when all X are hydrogen atoms). n shows the number of repetition of the structural unit shown in a parenthesis, for example, is 100-250.

  Examples of the carboxylic acid ester of cellulose represented by the above formula (1) include cellulose acetate (cellulose acetate), cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate. it can. In the present invention, among them, cellulose acetate is preferable because of its excellent electron accepting property on the cellulose surface (particularly [1, -1, 0] plane).

The surface free energy of cellulose acetate depends on the acyl group total substitution degree (average substitution degree), and cellulose acetate having an acyl group total substitution degree (average substitution degree) of 2.2 to 2.7 is hydrophobic ( = [1, -1,0] plane) and the electron donating property of metal ions (especially gold anions such as AuCl ₄ ⁻ ) are balanced and stabilized. It is preferable at the point which exhibits adsorptivity. Meanwhile, cellulose acetate acyl total substitution degree is outside the above range hydrophobic face (= [1, -1,0] surface) and an electron-accepting in the metal ions (especially, AuCl ₄ ^- or the like gold anion) Electronic Since the balance of donating property is lost, the metal ion adsorption power tends to decrease.

In the present invention, the total degree of acetyl group substitution on the glucose ring of cellulose acetate is a value measured by NMR according to the method of Tezuka, Carbondr. Res. 273, 83 (1995) below.
1. The free hydroxyl group of the cellulose acetate sample is propionylated with propionic anhydride in pyridine.
2. The obtained sample is dissolved in deuterated chloroform, and a ¹³ C-NMR spectrum is measured.
3. The carbon signal of the acetyl group appears in the order of 2, 3, 6 from the high magnetic field in the region of 169 ppm to 171 ppm, and the signal of the carbonyl carbon of the propionyl group appears in the same order in the region of 172 ppm to 174 ppm. From the abundance ratios of acetyl groups and propionyl groups at the corresponding positions, the degree of acetyl substitution at the 2, 3, 6 positions of the glucose ring in the original cellulose acetate can be determined.

  Furthermore, the C—H bond of the glucose ring, which is a structural unit of cellulose acetate, is an axial bond perpendicular to the glucose ring, and a group into which an OH group and an acyl group have been introduced (= OX in the above formula (1)) Is a equatorial bond parallel to the glucose ring. From this, cellulose acetate has a hydrophilic surface ([1,1,0] surface) rich in a group having an OH group and an acyl group introduced in the molecule and a hydrophobic surface ([1,1,0] surface rich in C—H bond). -1,0) plane) is localized. And since the said hydrophobic surface has the outstanding electron accepting property, the adsorptivity of a metal ion can be improved further by exposing more hydrophobic surfaces to the surface.

  Polysaccharide carboxylic acid esters have a particularly large electron accepting property on the surface (especially [1, -1,0] plane), and thus are excellent in adsorbing metal ions (especially gold ions). (For example, the average particle size is about 0.5 to 1 μm) or a carboxylic acid ester of a fibrous polysaccharide, in particular, a single fineness obtained by a dry spinning method such as an electrospinning method is, for example, 0.05 to 10 denier (preferably Is a carboxylic acid ester of a fibrous polysaccharide having a total fineness of 600 to 60000 denier (particularly preferably 3000 to 30000 denier), for example, 0.5 to 5.0 denier, particularly preferably 0.5 to 1.0 denier. Is preferable because it exposes many hydrophobic surfaces on the surface and has particularly excellent metal ion adsorption. Moreover, about the fibrous polysaccharide carboxylic acid ester, when the fineness exceeds the said range, there exists a tendency for the adsorptivity of a metal ion to fall. On the other hand, if the fineness is less than the above range, it tends to be easily cut and complicated to handle.

  The weight average molecular weight (Mw) of the carboxylic acid ester of the polysaccharide is, for example, 100,000 to 1,000,000, preferably 100,000 to 500,000, particularly preferably 100,000 to 300,000. When the weight average molecular weight (Mw) is below the above range, the viscosity tends to be too low, and the processability tends to decrease. On the other hand, when the weight average molecular weight (Mw) is lower than the above range, the viscosity tends to be too high, and the workability tends to decrease.

  The dispersity of the carboxylic acid ester of the polysaccharide (molecular weight distribution obtained by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn): Mw / Mn) is, for example, 2 to 10, preferably 3 to 8, particularly preferably 4 to 6. If the degree of dispersion (Mw / Mn) is below the above range, the fiber tends to become brittle. On the other hand, when the dispersity (Mw / Mn) exceeds the above range, the fiber tends to become brittle due to elution of the oligomer component.

  The number average molecular weight (Mn), weight average molecular weight (Mw), and dispersity (Mw / Mn) of a carboxylic acid ester of a polysaccharide can be determined by a known method using gel permeation chromatography (Gel Permeation Chromatography). . The average molecular weight (Mn), weight average molecular weight (Mw), and dispersity (Mw / Mn) are within a desired range by appropriately selecting and mixing polysaccharide carboxylic acid esters having different average molecular weights and dispersities. Can be adjusted.

  Adsorption of metal ions can be confirmed using atomic absorption spectrometry.

  The metal-trapping material of the present invention is excellent in metal ion adsorption, and its adsorption capacity (Q: metal ion adsorption amount in 1 kg of polysaccharide carboxylate ester) is, for example, 0.5 g / kg or more, preferably 0.5 to 150 g / kg.

[Production method of polysaccharide carboxylate ester]
Polysaccharide carboxylic acid esters can be produced by known methods. Commercial products can also be used. Hereinafter, a method for producing cellulose acetate will be described as a typical example of a carboxylic acid ester of a polysaccharide. Polysaccharide carboxylic acid esters other than cellulose acetate can be produced by known and commonly used methods.

  Cellulose acetate consists of (A) activation step (pretreatment step), (B) acetylation step, (C) acetylation reaction termination step, (D) ripening step (hydrolysis step), and (E) ripening reaction. It can be manufactured through a stop process, (F) a fractionation process, and (G) a molding process.

[(A) Activation step]
In the activation step (or pretreatment step), the raw material cellulose is treated with an acetylated solvent to activate the cellulose. As the acetylated solvent, acetic acid, methylene chloride, and the like can be used alone or in combination. Usually, since raw material cellulose is often supplied in the form of a sheet, the cellulose is pulverized in a dry manner and then subjected to an activation treatment (or pretreatment).

  As the raw material cellulose, various cellulose sources such as wood pulp (conifer pulp, hardwood pulp) and linter pulp (cotton linter pulp, etc.) can be used. These pulps usually contain foreign components such as hemicellulose. Accordingly, in the present specification, the term “cellulose” is used in the sense that it also contains different components such as hemicellulose. As a wood pulp, the 1 type (s) or 2 or more types selected from a hardwood pulp and a conifer pulp can be used. Wood pulp and linter pulp may be used in combination. In the present invention, it is preferable to use at least linter pulp (particularly cotton linter pulp) in terms of containing cellulose having a high degree of polymerization. The raw material cellulose may contain some carboxyl groups in a state of being bonded to cellulose molecules and / or hemicellulose molecules.

  The processing time of the activation process is, for example, 10 hours or more.

  The usage-amount of the acetylation solvent in an activation process is about 10-100 weight part per 100 weight part of raw material cellulose, for example. The temperature in the activation step is, for example, in the range of 10 to 40 ° C.

[(B) Acetylation step]
Cellulose acetate can be produced by reacting cellulose activated by the activation treatment with an acetylating agent in the presence of an acetylation catalyst in an acetylation solvent.

  As the acetylation catalyst, it is preferable to use a strong acid (particularly sulfuric acid). The usage-amount of an acetylation catalyst is about 1-20 weight part with respect to 100 weight part of raw material cellulose, for example.

  As the acetylating agent, for example, carboxylic acid halides such as acetic acid chloride and propionic acid chloride, and carboxylic acid anhydrides such as acetic anhydride and propionic anhydride can be used. The usage-amount of an acetylating agent is about 1.1-4 equivalent with respect to the hydroxyl group of a cellulose, for example. Moreover, the usage-amount of an acetylating agent is 200-400 weight part with respect to 100 weight part of raw material cellulose, for example.

  As the acetylated solvent, acetic acid, methylene chloride and the like can be used alone or in combination. The amount of the acetylated solvent used is, for example, about 50 to 700 parts by weight with respect to 100 parts by weight of cellulose.

  The acetylation reaction can be performed at a temperature of about 0 to 55 ° C., for example. The acetylation reaction time (total acetylation reaction time) varies depending on the reaction temperature and the like, but is, for example, in the range of 20 minutes to 36 hours.

[(C) Stopping step of acetylation reaction]
After the acetylation reaction is completed, a reaction terminator is added to the reaction system in order to deactivate the acetylating agent remaining in the reaction system.

  Examples of the reaction terminator include water alone or at least one mixture selected from water and the above acetylated solvent, alcohol and neutralizing agent.

  It is preferable to use a basic substance as the neutralizing agent. Examples of the basic substance include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal hydrogen carbonates such as sodium hydrogen carbonate; sodium acetate and acetic acid Alkali metal carboxylates such as potassium; alkali metal alkoxides such as sodium methoxide and sodium ethoxide; alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide; alkaline earths such as magnesium carbonate and calcium carbonate Examples thereof include metal carbonates; alkaline earth metal carboxylates such as magnesium acetate and calcium acetate; alkaline earth metal alkoxides such as magnesium ethoxide. These can be used alone or in combination of two or more. In the present invention, it is particularly preferable to use an alkaline earth metal carboxylate (particularly magnesium acetate).

  The stop time of the acetylation reaction is preferably less than 10 minutes.

[(D) Aging step (hydrolysis step)]
After stopping the acetylation reaction, the generated cellulose acetate is aged [hydrolyzed (deacetylated)] in acetic acid to adjust the total substitution degree of acetyl groups and the substitution degree distribution. (B) The acetylation catalyst (especially sulfuric acid) used in the acetylation step may be used as an aging catalyst with a part thereof neutralized or neutralized with a neutralizing agent. In the aging step, a solvent or the like (acetic acid, methylene chloride, water, alcohol, etc.) may be newly added as necessary. As the neutralizing agent, those exemplified in the acetylation reaction termination step (C) can be used.

  The aging temperature (hydrolysis temperature) is, for example, 40 to 90 ° C.

[(E) Aging reaction stopping step]
After ripening the cellulose acetate, the neutralizing agent exemplified (preferably using an alkaline earth metal hydroxide such as calcium hydroxide) is added if necessary in the acetylation termination step (C). To stop the ripening reaction.

[(F) Sorting step]
The cellulose acetate obtained through the above steps is preferably fractionated and purified thereafter. For the separation method, the method described in JP-A-09-77801 can be used.

  Specifically, cellulose acetate is subjected to precipitation fractionation or dissolution fractionation in a solvent system in which each of the high acetylation degree component and the low acetylation degree component is selective. Examples of the solvent having high selective solubility for the high acetylation component include methylene chloride such as dichloromethane and chloroform. Examples of the solvent having high selective solubility for the low acetylation component include methanol, acetone / methanol (20/80, weight ratio) and the like.

[(G) Molding process]
The cellulose acetate that has been separated and purified can be formed into a desired shape by a well-known and commonly used method. For example, fibrous cellulose acetate is prepared by dissolving the cellulose acetate obtained through the above steps in a suitable solvent, extruding it from a nozzle, and drying the solvent with warm air (especially, the polymer solution is syringed). Electrospinning is performed by injecting a polymer solution while applying a high voltage between the syringe needle and the collector, generating a charged jet, extending the jet in the electric field to form a fiber, and collecting it on the collector Method). The powdered cellulose acetate is prepared by sequentially adding a poor solvent for cellulose acetate to the solution containing cellulose acetate obtained through the above steps, or the cellulose acetate solution obtained through the above steps and the cellulose acetate. It can manufacture by the method of cooling the mixed solution with the poor solvent, and depositing a granular cellulose acetate.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited by these Examples.

Example 1
At room temperature, 10 mg of cellulose acetate (powder, substitution degree: 2.5, weight average molecular weight (Mw) as a metal-trapping material in 5 mL of hydrochloric acid acidic solution (hydrochloric acid concentration: 0.1 M) containing 10 ppm of gold ions (Au conversion) ): 200000, molecular weight distribution (Mw / Mn): 5.0, trade name “L-50” (manufactured by Daicel Corporation) was added and stirred for 300 minutes. Then, the ICP emission spectrum of the solution was measured using an inductively coupled plasma emission spectrometer (trade name “Perkin-Elmer Optima 3100 RL”, manufactured by Glass Expansion) to determine the concentration of gold ions in the solution. The amount of gold ions adsorbed on the trapping material (Au conversion) was calculated. The results are shown in the table below.

Examples 2 to 12, Comparative Example 1
Example 1 except that the material and shape of the metal-trapping material, the hydrochloric acid concentration in the hydrochloric acid acidic solution, the type and initial concentration of the metal ions in the hydrochloric acid acidic solution, and the treatment time (= stirring time) were changed to those shown in the table. And so on. The results are shown in the table below.
In Example 2, cellulose acetate (powder, substitution degree: 2.9, weight average molecular weight (Mw): 200000, trade name “LT-35”, manufactured by Daicel Corporation) was used.
In Examples 3 to 11, cellulose acetate (single fineness 3.0 denier, long fiber bundle shape with total fineness 25000 denier, substitution degree: 2.5, trade name “Cigatow (registered trademark)”, manufactured by Daicel Corporation) It was used.
In Example 12, cellulose acetate in the form of a long fiber bundle having a single fineness of 0.9 denier and a total fineness of 20000 obtained by spinning the above-mentioned trade name “L-50” (substitution degree: 2.5) by a dry spinning method. It was used.
In Comparative Example 1, cellulose (derived from cotton linter pulp, cotton-like, substitution degree: 0, trade name “fluff pulp”, manufactured by Nippon Paper Industries Co., Ltd.) was used.

Claims (9)

  A metal recovery method using a carboxylic acid ester of a polysaccharide as a metal capturing material and capturing a metal dissolved in a solution.   The metal recovery method according to claim 1, wherein gold dissolved in the acidic solution is selectively captured.   The metal recovery method according to claim 1 or 2, wherein the polysaccharide carboxylate is a cellulose carboxylate.   The metal recovery method according to claim 1 or 2, wherein the polysaccharide carboxylic acid ester is cellulose acetate.   The metal recovery method according to any one of claims 1 to 4, wherein the total degree of acyl group substitution of the carboxylate ester of the polysaccharide is 2.2 to 2.7.   The metal recovery method according to any one of claims 1 to 5, wherein the polysaccharide carboxylic acid ester is fibrous.   The metal recovery method according to any one of claims 1 to 5, wherein the polysaccharide carboxylic acid ester is in a fibrous form having a single fineness of 0.5 to 5.0 denier.   A metal capturing material comprising fibrous cellulose acetate having a single fineness of 0.5 to 5.0 denier.   The metal-trapping material according to claim 8, wherein the cellulose acetate is cellulose acetate having an acetyl group total substitution degree of 2.2 to 2.7.