JP2009247981A - Adsorbent and method for recovering noble metals - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adsorbent with high recovering efficiency of noble metals even if the substrate is composed by a plant material as a raw material, and to provide a method for recovering noble metals. <P>SOLUTION: The adsorbent that adsorbs the noble metal is prepared by binding iminodiacetic acid or dialkylamine as a functional group to cellulose included in the substrate to adsorb the noble metals, wherein the crystallinity of cellulose is approximately 70% or less and the substrate contains appropriate amount of hemicellulose and/or lignin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an adsorbent that adsorbs noble metals such as gold, palladium and platinum, and a method for recovering noble metals using the adsorbent.

  Since the demand for noble metals such as gold, palladium and platinum is increasing as a material for electric / electronic parts or as a catalyst material, development of a technique for efficiently recovering the noble metal from waste or waste liquid is required.

  In order to efficiently recover precious metals from waste or liquid waste, a metal solution in which the metal in the waste is dissolved with a strong acid solution is prepared for waste, and various metals including precious metals are included in the waste liquid. Therefore, there is known a method in which a noble metal in a metal solution is adsorbed to the adsorbent by adjusting the pH as it is or by bringing the adsorbent into contact with the metal solution.

  As an adsorbent for adsorbing a noble metal, for example, a commercially available ion exchange resin such as Diaion (registered trademark) WA30 (Mitsubishi Chemical Corporation) can be used. Therefore, there is a problem that the recovery rate of the noble metal is low in the process of desorbing the noble metal adsorbed thereto.

  Therefore, a method of recovering the noble metal by burning the ion exchange resin on which the noble metal is adsorbed can be considered. However, since the expensive ion exchange resin must be used batchwise, the recovery cost of the noble metal increases. Further, for example, in the above-mentioned commercially available resin, since a granular polymer having a three-dimensional structure in which polystyrene is crosslinked with divinylbenzene is a base, it cannot be easily burned, and a new problem such as an exhaust problem. Invite a problem.

  Therefore, Patent Document 1 described later discloses an adsorbent in which a chelate-forming group such as an iminodiacetic acid group, an amine group, an amidoxime group, or a phosphoric acid group is introduced into a polymer substrate such as cellulose, polyethylene, or polypropylene by graft polymerization. It is disclosed.

In such an adsorbent, the noble metal can be easily desorbed from the adsorbent by bringing an inorganic acid, an organic acid, or an organic solvent into contact with the adsorbent that has adsorbed the noble metal.
JP 2006-26588 A

However, such conventional adsorbents have the following problems.
That is, when synthetic resins such as polyethylene and polypropylene are used as the polymer substrate, new problems such as exhaust problems are caused as before in disposing of the adsorbent that has become unusable.
In order to avoid this, it is conceivable to use cellulose as the polymer substrate. In this case, however, there is a limit to the amount of chelate-forming groups that can be introduced into the polymer substrate. There is a problem that the recovery efficiency of precious metals is low.

  The present invention has been made in view of such circumstances, and even when a substrate is constituted by using plant material as a raw material, an adsorbent having high recovery efficiency of noble metal, and noble metal using the adsorbent. Provide a way to recover.

  In the adsorbent comprising a substrate made of plant material, the amount of the functional group that can be bound to the substrate is limited because the functional group enters the crystallized region of cellulose contained in the substrate. It was thought that it was not possible.

  Therefore, when the present inventors diligently studied, when a base containing cellulose having a crystallinity of a standard value or less was used and an operation for binding a functional group to the cellulose was performed, the binding reaction of the functional group to cellulose was performed. As an opportunity, the present invention was completed by obtaining the knowledge that the crystallized region of cellulose became avalanche amorphous, thereby allowing functional groups to be introduced into the avalanche.

  That is, (1) the adsorbent according to the present invention comprises iminodiacetic acid or dialkylamine bonded to cellulose contained in a substrate as a functional group that adsorbs a noble metal, and the crystallinity of the cellulose is approximately 70% or less. And the substrate contains an appropriate amount of hemicellulose and / or lignin.

  The reference value of the crystallinity described above is about 70%. Therefore, when the degree of crystallinity exceeds approximately 70%, almost no functional group that binds to the noble metal can be introduced inside the cellulose crystal, and the amount of functional group binding to cellulose is extremely low. Recovery efficiency is low.

  On the other hand, when a substrate containing cellulose having a crystallinity of approximately 70% or less is used, the cellulose crystallized region is avalancheally amorphous due to the functional group binding reaction to cellulose as described above. Therefore, a functional group is introduced into the inside thereof, and the amount of the functional group bonded to cellulose is dramatically increased. As a result, the amount of adsorption of the noble metal per unit mass of the adsorbent increases, so that the collection efficiency of the noble metal is dramatically improved.

By the way, since the bond strength between cellulose fibers also falls as the crystallinity degree of a cellulose becomes low, a cellulose fiber becomes easy to flow out and it becomes difficult to maintain the form as an adsorbent.
However, the substrate of the adsorbent according to the present invention contains hemicellulose and / or lignin as a shape maintaining component, and even when the crystallinity of the cellulose is lowered, a plurality of the shape maintaining components are used. Since the cellulose fibers are in a crosslinked state, the three-dimensional form of the adsorbent is maintained. Therefore, it is possible to easily handle the adsorbent, and to prevent a part of the adsorbent from flowing out and reducing the recovery rate of the noble metal.
In addition, the alkyl group of the dialkylamine mentioned above is 1 type selected from the group containing a methyl group, an ethyl group, and a propyl group, and a methyl group is suitable.

(2) In addition, when the adsorbent according to the present invention binds iminodiacetic acid as the functional group as necessary, the amount of the functional group bonded per dry mass of the substrate is from 1.0 mol / l to 4 0.0 mol / l.
When the amount of bound iminodiacetic acid is less than 1.0 mol / kg per dry mass of the substrate, the amount of precious metal adsorbed is not sufficient, and when it exceeds 4.0 mol / kg, chemical modification to cellulose is difficult. .

(3) Further, in the adsorbent according to the present invention, when dialkylamine is bonded as the functional group as necessary, the amount of the functional group bonded per dry mass of the substrate is from 1.0 mol / l to 5 0.0 mol / l.
When the amount of bound dialkylamine is less than 1.0 mol / kg, the amount of precious metal adsorbed is insufficient, and when it exceeds 5.0 mol / kg, chemical modification to cellulose is difficult.

  (4) On the other hand, in the method for recovering a noble metal according to the present invention, the solution is brought into contact with an adsorbent obtained by bonding a functional group that adsorbs a noble metal to cellulose contained in a substrate, and the noble metal contained in the solution is brought into contact with the adsorbent. In the method of recovering the noble metal by adsorbing to the cellulose, iminodiacetic acid or dialkylamine is bonded to the cellulose as the functional group, the crystallinity of the cellulose is about 70% or less, and the substrate is suitably used. An adsorbent containing an amount of hemicellulose and / or lignin is used.

In such an adsorbent, the amount of precious metal adsorbed per unit mass of the adsorbent is large as described above, so that the precious metal recovery efficiency is high.
On the other hand, since this adsorbent contains hemicellulose and / or lignin as a form maintaining component, the three-dimensional form is maintained and its handling is easy. Moreover, it is prevented that a part of the adsorbent flows out and the recovery rate of the noble metal decreases.
The contact between the adsorbent and the solution may be performed by a batch method in which the adsorbent is added to the solution and stirred, or by a column method in which the solution is passed through a column filled with the adsorbent.

  (5) The precious metal recovery method according to the present invention allows a precious metal to be adsorbed to the adsorbent, if necessary, and then contacted with a mixed solution of thiourea and hydrochloric acid to remove the precious metal from the adsorbent. It is characterized by being separated.

  By bringing the mixed solution of thiourea and hydrochloric acid into contact with the adsorbent that has adsorbed the noble metal, the noble metal can be desorbed from the adsorbent with high efficiency. Further, since the adsorbent is regenerated along with the desorption of the noble metal, the recovery operation can be carried out again without performing the adsorbent regeneration operation, so that the efficiency of the recovery operation can be achieved.

(Embodiment of the present invention)
Embodiments according to the present invention will be described below.
(Adsorbent base material)
As a raw material for the substrate of the adsorbent according to the present invention, paper containing cellulose as an adsorbing component and hemicellulose and / or lignin as a shape maintaining component was used. As such paper, newspaper can be used, but other paper such as kraft paper and office paper can be used.

  The cellulose contained in the substrate preferably has a crystallinity of about 70% or less. When the degree of crystallinity exceeds about 70%, almost no functional group that binds to the noble metal can be introduced into the cellulose crystal and the introduction rate of the functional group into the cellulose is remarkably low. Is low.

  On the other hand, when a substrate containing cellulose having a crystallinity of about 70% or less is used, the crystalline portion becomes avalanche amorphous during the operation of introducing a functional group into cellulose, which will be described later. A functional group is introduced, and the rate of introduction of the functional group into cellulose increases dramatically. As a result, the amount of adsorption of the noble metal per unit mass of the adsorbent increases, so that the collection efficiency of the noble metal is dramatically improved.

  In order to reduce the crystallinity of cellulose, a method of treating with sodium hydroxide solution, a method of treating with an enzyme such as cellulase and / or hemicellulase, a method of irradiating with ultraviolet rays, etc., may be applied alone or in combination. Can do.

Therefore, even if the paper contains cellulose having a crystallinity of more than about 70% as a main component, by applying the above-described method, the crystallinity of the cellulose is reduced to about 70% or less. The adsorbent substrate can be used as a raw material.
On the other hand, in the case of used paper and recycled paper obtained by recycling the used paper, since the crystallinity of cellulose is about 70% or less from the beginning, such low crystallization operation can be omitted.

  The crystallinity of cellulose is described in L. Segal, et al., “An Empirical Method for Estimating the Degree of Crystallinity of Cellulose Using the X-Ray Diffractometer” TEXTILE RESEARCH JOURNAL 786-794 (1959). Measurement was performed using an X-ray measurement method.

By the way, since the bond strength between cellulose fibers also falls as the crystallinity degree of a cellulose becomes low, a cellulose fiber becomes easy to flow out and it becomes difficult to maintain the form as an adsorbent.
However, the raw material of the adsorbent substrate according to the present invention contains hemicellulose and / or lignin as a form-maintaining component, and even if the crystallinity of cellulose is low, Since the plurality of cellulose fibers are in a crosslinked state, the three-dimensional form of the adsorbent is maintained. Therefore, it is possible to easily handle the adsorbent, and to prevent a part of the adsorbent from flowing out and reducing the recovery rate of the noble metal.

  Here, it is preferable that hemicellulose and / or lignin as a form maintaining component is contained in an amount of about 10% or more per unit mass of the dry substrate. When hemicellulose and / or lignin is less than about 10% per unit mass of the dry substrate, there is a risk that the effect of maintaining the shape of the adsorbent may be insufficient, and handling of the adsorbent becomes difficult, and part or all of the adsorbent In some cases, the recovery rate of the noble metal decreases due to the outflow.

The upper limit of the amount of hemicellulose and / or lignin contained in the substrate is not particularly limited because it depends on the upper limit of the amount of hemicellulose and / or lignin contained in the raw material of the substrate, but the content of hemicellulose and / or lignin is large. In this case, since the cellulose content is relatively reduced and the amount of functional groups per unit mass of the adsorbent is also reduced, it is preferable that the content is at least smaller than the cellulose content.
More preferably, the upper limit of the content of hemicellulose and / or lignin is approximately 40% per unit dry substrate mass. As a result, a wide range of paper such as kraft paper or cardboard can be used as a raw material.

  More preferably, the upper limit of the content of hemicellulose and / or lignin is approximately 20% per unit dry substrate mass. Thereby, even when the crystallinity of cellulose contained in the substrate is further reduced, the three-dimensional structure of the adsorbent can be reliably maintained, while the crystallinity of cellulose is further reduced. , The amount of functional group binding can be increased, and the recovery efficiency of the noble metal can be further increased.

(Pretreatment of adsorbent substrate)
Next, a method for pretreating the substrate to introduce functional groups into the substrate will be described.
The pretreatment includes a process of physically and mechanically processing paper to form a fiber. Specifically, the base paper is pulverized by a pulverizer until it becomes fibrous.

When used paper is used, the pulverized product is treated with a sodium hydrogen carbonate solution to wash and wash the ink components contained in the used paper, and then washed with water. If necessary, the pulverization process is performed again.
In addition, when used printed paper such as newspaper is used, the ink component may be removed by performing the operation of treating the pulverized material with a cleaning liquid for cleaning and removing the ink a required number of times.

(Preparation of adsorbent)
An adsorbent is prepared as follows using the pulverized material obtained by the pretreatment.
That is, the cellulose contained in the pulverized product is bonded to a functional group that selectively adsorbs a noble metal such as iminodiacetic acid or alkyldiamine to obtain an adsorbent. A 6-position hydroxyl group of certain glucose is substituted with a hydrochloric acid group to produce a cellulose derivative.

  Such a chlorination treatment can be carried out by the following reaction scheme in which the hydroxyl group at the 6-position of glucose is replaced with the hydrochloric acid group of thionyl chloride.

  The cellulose derivative thus produced is directly reacted with a dialkylamine to replace the 6-position hydrochloric acid group of the glucose with a dialkylamine, and the dialkylamine is bound and fixed to the cellulose.

On the other hand, since iminodiacetic acid is difficult to fix directly in this way, diethyliminoacetic acid is reacted with a cellulose derivative to replace the 6-position hydrochloric acid group of glucose with diethyliminoacetic acid. After fixing diethyliminoacetic acid to cellulose, diethyliminoacetic acid is hydrolyzed to iminodiacetic acid.
These reaction schemes can be summarized as follows.

In this reaction scheme, R1 is one selected from the group containing a methyl group, an ethyl group, and a propyl group, and R2 is one selected from the group containing a methyl group, an ethyl group, and a propyl group. However, both R1 and R2 are preferably methyl groups.
In this way, an adsorbent is obtained.

  Here, the amount of iminodiacetic acid fixed to the cellulose in the adsorbent is 1.0 mol / kg to 4.0 mol / kg, preferably 2.0 mol / kg to 3 in terms of the dry mass of the substrate. 0.0 mol / kg. When the amount is less than 1.0 mol / kg, the amount of precious metal adsorbed is insufficient, and when it exceeds 4.0 mol / kg, chemical modification to cellulose is difficult.

  Further, the amount of dialkylamine fixed to cellulose in the adsorbent is 1.0 mol / kg to 5.0 mol / kg, preferably 2.0 mol / kg to 4. mol when converted to the dry mass of the substrate. 0 mol / kg. When the amount is less than 1.0 mol / kg, the amount of adsorption of the noble metal is not sufficient, and when it exceeds 5.0 mol / kg, chemical modification to cellulose is difficult.

(Precious metal recovery method)
The adsorbent thus obtained is brought into contact with a metal solution containing a noble metal to adsorb the noble metal on the adsorbent. Such an adsorption operation may be performed by a so-called batch method in which the adsorbent and the metal solution are stirred and mixed and then separated from each other, but also by a continuous method in which the metal solution is passed through a column packed with the adsorbent. good.

Here, as the metal solution containing the noble metal, a solution obtained by dissolving a waste containing the noble metal with an acid such as hydrochloric acid can be used. Alternatively, a waste solution can be chlorinated to obtain a chloride (solid), which is dissolved in a solvent such as water or acid. On the other hand, when recovering the precious metal contained in the waste solution such as the exhaust plating solution, it is preferable to adjust the concentration of chloride ions in the waste solution to an appropriate value by adding, for example, a hydrochloric acid solution to the waste solution.
Then, the noble metal is desorbed from the adsorbent that has adsorbed the noble metal.

  In order to desorb the noble metal from the adsorbent, the noble metal is eluted from the adsorbent by bringing a mixed liquid of thiourea and hydrochloric acid into contact with the adsorbent. As a result, the adsorbent can be regenerated simultaneously with the elution of the noble metal. Further, most of the noble metal adsorbed on the adsorbent can be eluted from the adsorbent.

In the mixed solution of thiourea and hydrochloric acid, the blending amount of thiourea is 0.5 mol / l to 5 mol / l, and the blending amount of hydrochloric acid is 1.0 mol / l to 10 mol / l. When the blending amount of thiourea is less than 0.5 mol / l, the elution of noble metal is insufficient, and when the blending amount of thiourea exceeds 5 mol / l, sulfur may precipitate. In addition, when the amount of hydrochloric acid is less than 1% by mass, the elution efficiency is lowered, and when the amount of hydrochloric acid exceeds 10 mol / l, the substrate of the adsorbent is significantly deteriorated, while the handling of the solution Is dangerous.
In addition, as a method of desorbing the noble metal from the adsorbent, a method of leaving the noble metal adsorbed on the adsorbent by burning the adsorbent can be applied.

  In this case, since the adsorbent substrate is paper, the adsorbent can be incinerated quickly and easily. In addition, no toxic gas is generated when the adsorbent is incinerated, and the incineration operation can be performed with relatively simple equipment, so the cost required for the incineration operation is low.

A. Preparation of adsorbent (a. Pretreatment and chlorination)
The newspaper was pulverized until it became cotton-like using a pulverizer (Dalton P-35 type power mill), and the operation of stirring and filtering the pulverized product in an aqueous detergent solution was repeated several times. The obtained washed product was stirred in a 20% by mass aqueous sodium hydrogen carbonate solution for 5 hours, and then the water washing operation was repeated until neutrality, followed by filtration to obtain a treated product. The treated product was pulverized again and dried at 50 ° C. for 24 hours using a convection dryer.

  25 ml of pyridine was added to 0.5 g of the substrate thus obtained, and 5 ml of thionyl chloride was added dropwise with stirring in an ice bath. Next, the temperature of the stirring liquid was increased to 70 ° C., and stirring was performed for 6 hours in a nitrogen atmosphere, thereby generating the cellulose derivative described above. The resulting product was washed with water and dried at 70 ° C. using a convection dryer.

(B. Immobilization of functional group of diethyliminodiacetic acid)
Ethanol 400 ml saturated with hydrochloric acid and 20 g of iminodiacetic acid were mixed and stirred at 80 ° C. for 24 hours, then neutralized with an aqueous sodium hydrogen carbonate solution and further washed with chloroform to obtain diethyliminodiacetic acid.

  Next, 0.5 g of the product dried as described above and 1.14 g of diethyliminodiacetic acid were stirred with 50 ml of acetonitrile and 1.4 g of potassium carbonate at 50 ° C. for 72 hours and then filtered. Of ethanol and 10 ml of a 0.1 mol / l aqueous sodium hydrogen carbonate solution were stirred and dissolved at 60 ° C. for 1 day. When the pH of this solution is kept at 2-3, a precipitate is formed. The precipitate was filtered, washed with 0.1 mol / l hydrochloric acid and then with water, and dried at 60 ° C. using a final convection dryer to immobilize 0.35 g of the adsorbent immobilizing the functional group of iminodiacetic acid. Got.

  Elemental analysis was performed on this adsorbent, and the content of nitrogen was measured to determine the amount of the functional group of iminodiacetic acid, which was 2.17 mol / kg based on the dry weight of the adsorbent. This is equivalent to immobilization of functional groups on 60% of the hydroxyl group at the 6-position of glucose constituting cellulose contained in the substrate.

(C. Immobilization of functional group of dimethylamine)
Add 0.5 ml of dimethylamine and 1 ml of 35% formalin to 0.5 g of the dried product, stir at 90 ° C. for 3 hours, and wash with 0.1 mol / l hydrochloric acid and 0.1 mol / l sodium chloride aqueous solution. Then, after washing with water, the adsorbent was obtained by drying at 60 ° C. for 12 hours using a convection dryer.

  This adsorbent was also subjected to elemental analysis and the nitrogen content was measured to determine the amount of the functional group of diethylamine. The amount was 3.60 mol / kg based on the dry weight of the adsorbent. This corresponds to the immobilization of the functional group on 69% of the hydroxyl group at the 6-position of glucose constituting the cellulose contained in the newspaper.

B. Examination of adsorption characteristics of adsorbent (a. Examination of selectivity of adsorbent immobilizing functional group of iminodiacetic acid)
Chlorogold (III) acid, chloroplatinum (IV) acid and palladium (II) chloride as noble metals, and copper (II), iron (III), nickel (II) and zinc (II) hydrochlorides as base metals Using.

20 mg of the adsorbent according to the present invention in which the functional group of iminodiacetic acid is immobilized is dispensed in a dry mass and charged into a flask with a stopper, and 0.5 to 4 mol containing 0.2 mol / l of each of the above metal ions. An adsorption treatment was performed by injecting 15 ml of a hydrochloric acid solution having a concentration of / dm ³ and shaking for 24 hours in a constant temperature water bath maintained at 30 ° C.

The concentration of each metal ion in the hydrochloric acid solution before and after the adsorption treatment was measured with an ICP analyzer (ICP88100 type ICP emission spectrometer manufactured by Shimadzu Corporation), and the adsorption percentage of each metal ion adsorbed on the adsorbent was determined by the following equation. .
Percentage of adsorption = (metal concentration in hydrochloric acid solution before adsorption treatment—metal concentration in hydrochloric acid solution after adsorption treatment) / metal concentration in hydrochloric acid solution before adsorption treatment × 100

  FIG. 1 is a graph showing the relationship between the percentage of adsorption of metal ions and the concentration of hydrochloric acid using an adsorbent in which the functional group of iminodiacetic acid is immobilized. The vertical axis represents the percentage of adsorption, and the horizontal axis represents the concentration of hydrochloric acid. Show. In the figure, black diamonds indicate Au (III), white circles indicate Cu (II), white diamonds indicate Fe (III), and white squares indicate Ni (II). The white triangle mark indicates Pd (II), the black square mark indicates Pt (IV), and the white triangle mark indicates Zn (II).

As is clear from FIG. 1, gold and palladium were adsorbed on the adsorbent by 70% or more in the range of hydrochloric acid concentration of 0.5-4 mol / l. In this hydrochloric acid concentration range, the adsorption percentage of platinum was 20%. % Or less. On the other hand, base metal ions were not adsorbed at all in the hydrochloric acid concentration range.
The above results show that the present adsorbent can selectively separate and recover gold and palladium from base metal ions.

(B. Examination of selectivity of adsorbent with immobilized dimethylamine functional group)
FIG. 2 is a graph showing the relationship between the adsorption percentage of metal ions and the hydrochloric acid concentration using an adsorbent in which a functional group of dimethylamine is immobilized. The vertical axis represents the adsorption percentage, and the horizontal axis represents the hydrochloric acid concentration. Show. The adsorption test was performed in the same manner as described above for the adsorbent in which the functional group of iminodiacetic acid was immobilized. In the figure, the black diamond mark is Au (III), the white circle is Cu (II), the black triangle is Fe (III), the black circle is Ni (II), White square marks indicate Pd (II), white triangle marks indicate Pt (IV), and white diamond marks indicate Zn (II).
As is apparent from FIG. 2, gold, palladium, and platinum were adsorbed approximately 100% in the hydrochloric acid concentration range of 0.5-4 mol / l.

On the other hand, in the case of base metal ions, copper was adsorbed to the present adsorbent by about 20% at a hydrochloric acid concentration of 2 mol / l or less, but was hardly adsorbed in other concentration ranges. Further, in the case of base metals other than copper, the adsorbent was hardly adsorbed in any hydrochloric acid concentration range.
The above results indicate that the present adsorbent can selectively adsorb gold, palladium, and platinum from base metals.

(C. Examination of saturated adsorption amount of adsorbent with iminodiacetic acid functional group fixed)
20 mg of adsorbent immobilizing the functional group of iminodiacetic acid was collected in a dry mass and put into a flask with a stopper, and a 1 mol / l hydrochloric acid solution containing gold (III) ions or palladium (II) ions with different concentrations. After injecting 15 ml and shaking at 30 ° C. for 60 hours, the adsorption amount of gold (III) ion or palladium (II) ion was measured to determine the saturated adsorption amount of both ions.

FIG. 3 is a graph showing the results of studying saturated adsorption amounts of gold (III) ions and palladium (II) ions on an adsorbent in which the functional group of iminodiacetic acid is immobilized. In the figure, the vertical axis indicates the dry mass. The number of moles of metal ions adsorbed with respect to the adsorbent per kg, and the horizontal axis indicate the metal concentration of the hydrochloric acid solution after the adsorption operation.
In the figure, black diamonds indicate gold (III), and black triangles indicate palladium (II).

As is apparent from FIG. 3, the so-called Langmuir type adsorption curve is shown for any metal, and the saturated adsorption of the present adsorbent is obtained from the value of the adsorption amount in a region where the adsorption amount is constant regardless of the concentration. The amount was determined to be 3.30 mol / kg for gold ions and 1.42 mol / kg for palladium ions.
Therefore, in this adsorbent, 660 kg of gold can be adsorbed per 1 kg of the adsorbent.

(D. Examination of saturated adsorption amount of adsorbent with dimethylamine functional group immobilized)
Using the adsorbent in which the functional group of dimethylamine was immobilized, the same test as above was performed for gold ion, platinum ion, and palladium ion, and the saturated adsorption amount of each ion was determined.

FIG. 4 is a graph showing the results of examining the saturated adsorption amount of gold (III) ion, platinum (IV) ion and palladium (II) ion on the adsorbent in which the functional group of dimethylamine is immobilized, The vertical axis represents the number of moles of metal ions adsorbed to the adsorbent per kg of dry mass, and the horizontal axis represents the metal concentration of the hydrochloric acid solution after the adsorption operation.
In the figure, black diamonds indicate gold (III), black squares indicate platinum (IV), and black triangles indicate palladium (II).

As is apparent from FIG. 4, each metal ion also showed a Langmuir type adsorption curve even in this adsorbent. From each graph, the saturated adsorption amount of this adsorbent is 4.6 mol / kg for gold ions, 2.1 mol / kg for platinum ions, and 0.9 mol / kg for palladium ions. I was asked.
Therefore, in this adsorbent, 906 kg of gold ions can be adsorbed per 1 kg of the adsorbent.

C. Study on recovery of precious metals by column method (a. Adsorption test)
FIG. 5 is a schematic diagram showing an apparatus configuration used for an adsorption test by the column method, in which 1 is a column packed with an adsorbent. FIG. 6 is an enlarged view of the column 1 shown in FIG.
As shown in FIGS. 5 and 6, the column 1 is a double cylinder, and constant temperature water is supplied to the outer cylinder 11 by the second pump 3. Further, an adsorbent region 22 filled with an adsorbent is disposed at substantially the center in the inner cylinder 12 of the column 1, and the adsorbent region 22 is a glass bead region 21 disposed on both ends thereof. , 21. A glass filter 25 is disposed at the bottom of the inner cylinder 12, and the filler in the inner cylinder 12 is carried by the glass filter 25.

  The supply liquid stored in the inner cylinder 12 from the supply liquid reservoir 4 is supplied from the bottom of the inner cylinder 12 by the first pump 2, and the supply liquid flowing through the inner cylinder 12 is supplied. Is discharged from the head of the inner cylinder 12 and is separated into a plurality of fractions by a fractionator 5 that dispenses a predetermined amount.

  The column 1 of such an apparatus was filled with an adsorbent in which a functional group of dimethylamine was immobilized to form an adsorbent region 22. The inner cylinder 12 had an inner diameter of 8 mm and a length of 20 cm, and the inner cylinder 12 was filled with an adsorbent to a dry weight of 100 mg.

In a 1 mol / l hydrochloric acid solution, copper (II), gold (III), platinum (IV), and palladium (II) are dissolved at 20 mg / l, 24 mg / l, 21 mg / l, and 19 mg / l, respectively. The metal solution was stored in the supply liquid reservoir 4 described above, and the metal solution was passed through the inner cylinder 12 of the column 1 at a flow rate of 6 ml / hour.
Then, the concentration of each metal in the solution flowing out from the column 1 was detected over time.

FIG. 7 is a graph showing the results of detecting the concentration of each metal in the solution flowing out from the column through which the metal solution passed, with the vertical axis representing the concentration of each metal and the horizontal axis representing the flow. The time since the start is shown. Note that the concentration of each metal in the outflowed solution is shown as a ratio to the concentration of each metal in the metal solution.
In the figure, the white diamond mark indicates palladium, the white square mark indicates platinum, the white triangle mark indicates gold, and the white circle mark indicates copper.

As is apparent from FIG. 7, in copper, detection started immediately after the start of flow, and after about 5 hours from the start of flow, the concentration was the same as the concentration in the flowed metal solution. .
On the other hand, in the case of gold, platinum, and palladium, the detection starts about 30 hours after the start of flow, and the concentration is the same as the concentration in the metal solution passed after about 70 to 80 hours. was detected.

(B. Desorption test)
Next, the noble metal was desorbed from the adsorbent on which the noble metal was adsorbed in this way.
FIG. 8 is a graph showing the result of detecting the concentration of the noble metal desorbed from the adsorbent adsorbing the noble metal as shown in FIG. 7, with the vertical axis representing the concentration of each metal and the horizontal axis representing the result. Each time after starting desorption is shown. The concentration of each metal in the outflowed solution is shown as a ratio to the concentration of each metal in the metal solution passed through the adsorbent.

In the figure, the white diamond mark indicates palladium, the white square mark indicates platinum, the white triangle mark indicates gold, and the white circle mark indicates copper.
As the desorption solution, a mixed solution of 0.1 mol / l thiourea and 1 mol / l hydrochloric acid was used, and the mixed solution was passed at a flow rate of 6 ml / hour.

As is clear from FIG. 8, copper was not detected in the solution discharged by the desorption operation at any time point.
From these results and the results shown in FIG. 8, it can be seen that copper is not adsorbed by the present adsorbent.

On the other hand, in the case of gold, platinum, and palladium, there is a relatively sharp peak between about 1 hour and a half after the start of desorption and 4 hours after the start of desorption. The concentration was higher than the concentration of the metal solution passed through the adsorbent.
Here, the concentration of thiourea in the mixed solution described above is preferably 0.1 mol / l or more and 5 mol / l or less. When the concentration of thiourea is less than 0.1 mol / l, the desorption rate of the noble metal decreases, and when it exceeds 5 mol / l, sulfur is deposited.

  The concentration of hydrochloric acid in the mixed solution is preferably 1.0 mol / l or more and 10 mol / l or less. When the concentration of hydrochloric acid is less than 1.0 mol / l, the desorption rate of the noble metal decreases, and when it exceeds 10 mol / l, it is difficult to handle the mixed solution and to separate the mixed solution after the desorption operation. .

(C. Repeat test)
Next, a test in which the adsorption test and the desorption test were repeated was performed.
Except that the metal solution does not contain copper, the conditions are the same as those of the adsorption test and desorption test described above, and the operation of adsorbing the noble metal to the adsorbent and the operation of desorbing the noble metal from the adsorbent are repeated three times. The amount of precious metal adsorbed and desorbed each time and the recovery rate determined from these were determined. The results are shown in Table 1 below.

As is clear from Table 1, the adsorption amount of the second time was smaller than the adsorption amount of the first time in any noble metal, but no difference was observed between the adsorption amount of the second time and the third time.
The recovery rate was 85% or more from the second time on for any precious metal.
From the above results, it was confirmed that by using a mixed solution of thiourea and hydrochloric acid as the desorption solution, the precious metal can be desorbed from the adsorbent and the adsorbent can be regenerated.

(D. X-ray diffraction and microscopic observation)
X-ray diffraction analysis and electron microscope observation are performed on the adsorbent that has been subjected to the noble metal adsorption test described above and the adsorbent that has been subjected to the noble metal desorption test.
FIG. 9 is a graph showing the results of X-ray diffraction after adsorbing gold on an adsorbent having a functional group of dimethylamine immobilized thereon.

As is clear from FIG. 9, four sharp peaks peculiar to elemental gold were observed in the diffraction pattern after adsorption. In addition, although X-ray diffraction was implemented also about the adsorption agent before making gold | metal | money adsorb | suck, this peak was not observed.
Therefore, it is considered that the adsorbed gold is attached to the adsorbent surface as elemental gold.
In the case of the adsorbent in which the functional group of iminodiacetic acid was immobilized, the pattern was the same as in FIG.

On the other hand, FIG. 10 is an electron micrograph of a sample in which gold is adsorbed on an adsorbent in which a functional group of dimethylamine is immobilized.
In the electron micrograph shown in FIG. 10, the white portion is elemental gold.
Such a result was consistent with the result shown in FIG.

11 and 12 are photomicrographs of an adsorbent in which a functional group of dimethylamine is immobilized, FIG. 11 is a graph showing adsorbed gold, and FIG. 12 is a sample for desorption in which thiourea and hydrochloric acid are mixed. This is after the gold is removed using the solution.
As is apparent from FIG. 11, elemental gold particles were observed before the desorption operation, but as is clear from FIG. 12, such particles were not removed after the desorption operation. Not observed, gold was desorbed from the adsorbent by the desorption solution.

The results of determining the relationship between the crystallinity of cellulose contained in the adsorbent substrate and the amount of functional groups introduced will be described.
Used paper and microcrystalline cellulose (Merck) were used as the substrate.
These substrates were pretreated and chlorinated by the method described in Example 1, and then fixed with dimethylamine as a functional group. And the crystallinity degree of the cellulose contained in the base | substrate before and behind fixation of a functional group was measured using the X-ray measuring method mentioned above.
The following Table 2 shows the results.

  As is clear from Table 2, the crystallinity of the substrate using waste paper is 65.2%, which is lower than 70%, and the crystallinity of the present adsorbent with dimethylamine fixed on the waste paper as substrate is 7.3%. Met. And when the quantity of the functional group fixed to this base was calculated | required, the functional group of 3.6 mol / l was fixed per 1g of dry mass of a base | substrate.

On the other hand, the crystallinity of the substrate using microcrystalline cellulose is 82.1%, which is higher than 70%, and the crystallinity of the comparative adsorbent in which dimethylamine is fixed using microcrystalline cellulose as the substrate is 58.8%. there were. And when the quantity of the functional group fixed to this base was calculated | required, the functional group of 0.7 mol / l was fixed per 1 g of dry mass of a base | substrate.
For the latter comparative adsorbent, that is, an adsorbent in which dimethylamine is fixed using microcrystalline cellulose as a substrate, the adsorption characteristics of noble metals were examined.

FIG. 13 is a graph showing the results.
In the figure, open circles indicate gold (III), open triangles indicate palladium (II), and open squares indicate platinum (IV). The detailed conditions of this test are shown in FIG. It is the same as the conditions described for.
As is clear from FIG. 13, in the adsorbent in which dimethylamine was fixed using microcrystalline cellulose as a base, gold and platinum could be slightly adsorbed, but palladium could hardly be adsorbed.

On the other hand, as shown in FIG. 2 described above, in the adsorbent in which dimethylamine was fixed using waste paper as a base, noble metals such as gold, platinum, and palladium were adsorbed approximately 100%.
From the above results, when the crystallinity of cellulose contained in the substrate exceeds about 70%, functional groups that bind to noble metals can hardly be introduced inside the cellulose crystals, and the functional groups are introduced into the cellulose. Since the rate is remarkably low, the recovery efficiency of noble metals is low.

  On the other hand, when a substrate containing cellulose having a degree of crystallinity of about 70% or less is used, the crystalline part becomes amorphous in an avalanche during the operation of introducing the functional group into the cellulose. Is introduced, and the rate of introduction of functional groups into cellulose increases dramatically. As a result, the amount of adsorption of the noble metal per unit mass of the adsorbent increases, so that the collection efficiency of the noble metal is dramatically improved.

  By the way, when the crystallinity of cellulose contained in the substrate is low, handling of the adsorbent becomes difficult, and there is a possibility that part of the cellulose flows out of the adsorbent, but in the adsorbent using the above-mentioned waste paper, Since hemicellulose and lignin are contained, even if the degree of crystallinity is as low as 7.3%, the adsorbent is collected as a whole. There is no risk of spilling from the adsorbent.

It is the graph which showed the relationship between the adsorption percentage of a metal ion using the adsorption agent which fixed the functional group of iminodiacetic acid, and hydrochloric acid concentration. It is the graph which showed the relationship between the adsorption percentage of a metal ion using the adsorption agent which fixed the functional group of dimethylamine, and hydrochloric acid concentration. It is a graph which shows the result of having examined the saturated adsorption amount of the gold (III) ion and palladium (II) ion with respect to the adsorption agent which fixed the functional group of iminodiacetic acid. It is a graph which shows the result of having examined the saturated adsorption amount of the gold (III) ion, platinum (IV) ion, and palladium (II) ion with respect to the adsorption agent which fixed the functional group of dimethylamine. It is a schematic diagram which shows the apparatus structure used for the adsorption test by the column method. FIG. 6 is an enlarged view of the column shown in FIG. 5. It is a graph which shows the result of having detected the density | concentration of each metal in the solution flowed out from the column which let the metal solution flowed over time. It is a graph which shows the result of having detected the concentration of the noble metal desorbed from the adsorbent which adsorbed the noble metal with time. It is a graph which shows the result of having performed X-ray diffraction, after making gold adsorb | suck to the adsorbent which fixed the functional group of dimethylamine. It is an electron micrograph of the sample which made gold adsorb | suck to the adsorbent which fixed the functional group of dimethylamine. It is a microscope picture of the adsorption agent which fixed the functional group of dimethylamine. It is a microscope picture of the adsorption agent which fixed the functional group of dimethylamine. It is a graph which shows the result of having examined the adsorption characteristic of a noble metal about the adsorption agent which fixed dimethylamine using microcrystalline cellulose as a substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Column 2 1st pump 3 2nd pump 5 Preparator 11 Outer cylinder 12 Inner cylinder 21 Glass bead area 22 Adsorbent area

Claims (5)

Iminodiacetic acid or dialkylamine is bonded to cellulose contained in the substrate as a functional group that adsorbs noble metals,
The crystallinity of the cellulose is about 70% or less,
The adsorbent characterized in that the substrate contains an appropriate amount of hemicellulose and / or lignin.   The adsorbent according to claim 1, wherein when iminodiacetic acid is bound as the functional group, the amount of the functional group bound per dry mass of the substrate is 1.0 mol / l to 4.0 mol / l.   The adsorbent according to claim 1, wherein when dialkylamine is bonded as the functional group, the amount of the functional group bonded per dry mass of the substrate is 1.0 mol / l to 5.0 mol / l. In the method of recovering the noble metal by bringing the solution into contact with an adsorbent formed by bonding a functional group that adsorbs the noble metal to cellulose contained in the substrate, and adsorbing the noble metal contained in the solution to the adsorbent,
Adsorption containing iminodiacetic acid or dialkylamine as the functional group to the cellulose, the crystallinity of the cellulose is about 70% or less, and the substrate contains an appropriate amount of hemicellulose and / or lignin A method for recovering a noble metal, characterized by using an agent.   The method for recovering a noble metal according to claim 4, wherein after the noble metal is adsorbed on the adsorbent, the adsorbent is brought into contact with a mixed solution of thiourea and hydrochloric acid to desorb the noble metal from the adsorbent.

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