KR100367709B1 - Recovery method of platinum group metals from waste water - Google Patents

Abstract

The present invention relates to a method for effectively recovering a platinum group metal from various precious metal-containing waste liquids containing a large amount of impurities.

In the present invention, in order to recover the platinum group metal in the state containing only a small amount of impurities electrochemically, after the production and installation of an electrolysis recovery system, the activated carbon powder is added to the electrolytic solution to increase the electrolytic efficiency and the recovery rate of the platinum group metal. Can increase. In addition, in the present invention, by adding and filtering 0.01 to 1% by weight of activated carbon powder and a polymer flocculant to the electrochemical recovery solution, it is possible to prevent leakage of fine noble metal particles and to shorten the time required for filtration.

Description

Recovery method of platinum group metal from waste liquid {RECOVERY METHOD OF PLATINUM GROUP METALS FROM WASTE WATER}

The present invention relates to a method for recovering platinum group metals from waste liquids, and more particularly, to a method for effectively recovering and separating platinum group metals from various precious metal-containing waste liquids containing a large amount of impurities.

Platinum group metals (PGM), such as platinum (Pt), palladium (Pd) and rhodium (Rh), have a very high melting temperature, excellent corrosion resistance to chemical erosion, and unique chemical properties such as reduction catalysis. Have The average annual production of platinum group metals is around 200 tonnes, with more than 90% produced in South Africa and the former Soviet Union, and about 6% in Canada, in South America, the United States, Australia and Japan. These platinum group metals are almost used as catalysts for automobiles and petrochemical industries except for electric and electronic industries such as platinum group metal circuits.

These catalysts and components are degraded over time and eventually discarded at the end of their lifetime, but especially since platinum group metals are expensive and imported in their entirety, it is not only economically advantageous to recover and reuse them. It can play a big role in the effective use of resources.

Various methods have been reported for the recovery of precious metals supported on a catalyst carrier, but each has technical advantages and disadvantages. In particular, the platinum group metal has a very high ionization potential, making it difficult to dissolve the metal itself, and it is more difficult to extract and separate the platinum group metal due to the catalyst carrier and other catalyst components and contamination. In addition, when the recovered solution containing the recovered platinum group metal is filtered as it is, fine metal particles pass through various filter papers or filter cloths, and at the same time, it takes a long time to filter.

Various methods for recovering a precious metal have been proposed. For example, there is a water repellent method in which a supporting material on which a precious metal or the like is supported is dissolved in aqua regia and the like is separated by an analytical chemical method. This method has a low purity of recovered precious metals, extremely limited selection of equipment and materials, and a large amount of waste acid is produced, which leads to many difficulties in reprocessing it. In addition, a method of adsorbing a solution containing a noble metal to an ion adsorbent or the like with an ion exchange resin and incineration to obtain a noble metal oxide has also been proposed. However, when two or more kinds of noble metals are contained, it is difficult to recover a single noble metal.

In addition, as a method of adding a reducing agent to a solution containing a noble metal, a method of injecting a reducing gas to precipitate a noble metal ion as a reducing metal has been proposed, but most impurities together with the noble metal are recovered by precipitation together to effectively recover the noble metal. I can't.

In addition, a method of recovering a noble metal by electrolysis of a noble metal-containing solution has been proposed. In this method, an electron is supplied from a power source at a cathode, and in a solution, a cation diffuses to an electrode surface, whereby a cation is received and reduced to an electrochemical reduction. The platinum group metal is recovered by the negative electrode adhesion method by the reaction. However, the platinum group recovery by the electrochemical reduction is limited because the reduction process occurs only on the surface of the electrode (cathode), it requires several reactors for mass production. In addition, since the platinum group metal is reduced and deposited on the surface of the cathode, the electrolytic metal must be separated (peeled) from the surface of the cathode, and current efficiency also has a disadvantage in that the current efficiency is greatly reduced. In addition, there are problems such as temperature rise of the electrolyte and electrode corrosion.

SUMMARY OF THE INVENTION An object of the present invention is to provide a more efficient method for recovering platinum group metals, which improves the problems of separation efficiency of precious metals, temperature rise of electrolyte solution, electrode corrosion and the like in the electrochemical recovery method.

1 is a schematic diagram of an electrolytic apparatus applied to the present invention.

* Explanation of symbols for main parts of the drawings

1. membrane, 2. rectifier,

3. anode electrode, 4. cathode electrode,

5. electrolyzer, 6. anode chamber,

7. Cathode chamber.

The method for recovering the platinum group metal of the present invention is an electrochemical recovery method for recovering the platinum group metal from various waste liquids containing the platinum group metal, using a membrane to separate the positive electrode and the negative electrode and using an HCl solution as the electrolyte of the positive electrode. Electrochemical recovery is performed by the precipitation method.

Specifically, in the present invention, as shown in FIG. 1, a membrane, preferably a liquid-permeable neutral membrane 1, is provided in the center of the electrolytic cell 5 to convert the electrolytic cell 5 into an anode including the anode electrode 3. Platinum groups are recovered by conducting electrolysis using a separate electrolytic cell separated into a cathode chamber 7 including the chamber 6 and the cathode electrode 4.

It is preferable to use a platinum electrode or a carbon electrode as the anode electrode 3 and the cathode electrode 4, and both electrodes are more preferable because the electrode corrosion problem can be solved.

An HCl solution, preferably 5 to 36% HCl solution, is charged as an electrolyte into the anode chamber 6 of the separated electrolytic cell configured as described above, and a platinum group waste solution is introduced into the cathode chamber 7 to automatically adjust the rectifier 2. Electrolysis is initiated while maintaining a current density of 15 to 60 A / dm ² , preferably a current density of 15 to 16 A / dm ² , a voltage of 3 to 10 V, preferably 4 to 5 V, and a temperature of 40 to 70 ° C. Underlying, the platinum group metal precipitates and precipitates at the bottom of the cathode chamber 7. Since the electrolyte of the anode may evaporate due to the temperature rise of the electrolyte during the electrolysis process, the concentration of HCl may change. Therefore, it is desirable to continuously check the HCl concentration to maintain the above constant concentration. It varies depending on the spacing, the number of electrodes, and the concentration of electrolyte in the positive and negative electrodes. The closer the electrode is, the higher the current density at the same voltage, and the higher the concentration of the electrolyte, the lower the voltage at the same current density. Increasing the number of cathodes to a certain number of anodes lowers the current density at the same voltage. In the electrolytic recovery method of the present invention, the adjustment range of the voltage and the current density is free. However, when the current density is lower than 15A / dm ² , the electrolytic recovery time is 1.5 to 2.0 times or more than 30A / dm ² or more, which is uneconomical. The higher the current density, the shorter the recovery time. However, if the current density is higher than 60A / dm ² , the temperature of the anode electrolyte increases and the rate of evaporation, concentration, and decomposition of the cathode electrolyte is 3-4 times faster than that of 30A / dm ² . The electrolyte must be replenished. In this case, automatic replenishment of the electrolyte is required, or 24 hours of continuous monitoring and replenishment is uneconomical. The current density and the voltage range that can solve the above problems are 15 ~ 60A / dm ² and 3 ~ 10V, respectively. If the temperature of the electrolyte is lower than 40 ℃, the current density and voltage are outside the proper electrolytic conditions. It takes a long time to decompose and it is uneconomical. When the temperature of electrolyte rises higher than 70 ℃, excessive voltage is supplied to maintain a constant current density.

In the recovery method of the present invention, the concentration of the HCl solution is preferably 5 to 36%, when the concentration of the HCl solution is less than 5% the current rises, the temperature of the electrolyte rises, the concentration of the HCl solution 36% It is difficult to produce more than.

In addition, when the activated carbon powder is added and electrolyzed into the platinum group metal-containing waste liquid, the electrolytic efficiency can be increased, which is more preferable. At this time, it is preferable to add 0.01 to 1% by weight of activated carbon powder in the amount of waste liquid to the platinum group metal waste liquid.In the case where the activated carbon powder is less than 0.01% by weight, the effect of the present invention is insignificant. In the process, there is a problem that the filtration equipment and the like become large.

When the electrolysis is completed and the platinum group metal precipitate is precipitated at the bottom of the cathode chamber 7, the filtrate and the platinum group metal precipitate are separated using a filtration means, and then dried and calcined to obtain a mixture of the platinum group metal.

As in the present invention, when using a separate electrolytic cell in which the anode chamber and the cathode chamber are separated by using a membrane, a problem that may occur when using a single electrolytic cell, that is, when the reduction of the platinum group metal in the cathode of the single electrolytic cell occurs in the positive electrode Oxidation is generated from hydrochloric acid to generate chlorine gas, thereby preventing the deposition of platinum group metal at the cathode, thereby greatly reducing the current density efficiency. In addition, when the separation electrolyzer by the membrane is used, the reduced platinum group metal can be prevented from entering and dissolving again into the anode chamber, thereby increasing the recovery efficiency.

As in the present invention, when a platinum electrode or a carbon electrode is used as an electrode in a separate electrolytic cell, and the electrolysis is performed at the current density, voltage, and temperature conditions as described above, the platinum group metal is formed on the surface of the negative electrode as in the negative electrode attachment method. Since the platinum group metal is recovered in the form of precipitation in the cathode chamber (cathode precipitation method), the problem of peeling of the metal attached to the electrode, which is a disadvantage of the cathode attachment method, and the metal attached to the surface of the cathode, It is possible to completely solve the problem of decreasing the current density efficiency and the problem of difficult mass production, and recover the platinum group metal with a low content of impurities.

On the other hand, when filtering the recovery solution containing the platinum group metal as it is, fine metal particles not only can pass through the filter means such as various filter papers or filter cloth, but also takes a lot of time filtration, in the present invention, the recovery in the electrolytic cell is completed electrochemical recovery After the polymer coagulant is added to the solution, the activated carbon powder is added and filtered. In this case, fine metal particles can be prevented from leaking and the filtration time can be shortened. The amount of the polymer flocculant and the activated carbon powder is preferably 0.01 to 1% by weight of the waste liquid, and when the amount of the polymer flocculant and the activated carbon is less than 0.01% by weight, no precipitate is formed and the effect is insufficient. Exceeding this may cause filtration problems. The polymer coagulant may be a conventional anionic, nonionic, cationic polymer coagulant, specifically, anionic polymer coagulants such as K-305A, K-310A, K-320A of Besfloc, Nonionic polymer flocculants, such as K-300N, and cationic polymer flocculants, such as K-505C, K-520C, and K-550C, can be used.

In addition, in the present invention, in order to prevent the temperature rise of the electrolytic cell, an electrolytic cell may be further circulated by continuously separating the electrolytic cell with a separate electrolytic cell equipped with an electrode and a separate auxiliary electrolytic cell capable of circulating.

In the present invention, the measurement of the platinum group metal content and the recovery rate of the platinum group metal in the platinum group-containing waste liquid for recovering the platinum group metal is measured by atomic absorption spectrometry (AAS), ion chromatography, and inductively coupled plasma emission spectrometry (ICPS). Ordinary methods, etc. are applicable, and those skilled in the art will be able to easily select and implement.

The present invention will be described in detail through the following examples. However, these examples are for illustrative purposes only, and the present invention is not limited thereto.

Comparative Example 1

After eluting the platinum group metal containing a large amount of impurities, the waste liquid containing the platinum group metal was fixed at a current density of 16 A / dm ² and a voltage of 6 V in a single electrolytic cell using a carbon anode plate and a Ti cathode plate, and 0.1 N as the electrolyte solution. The hydrochloric acid solution was continuously added to maintain Pt / Pd / Rh electrochemically by the negative electrode attachment method while maintaining the concentration in the range of 5 to 36%. Quantitative analysis was performed by peeling off a mixture of platinum group metals attached to the Ti negative electrode plate surface. In the present embodiment, the quantitative analysis of the platinum group metal was carried out using an atomic absorption spectrophotometer (AAS). The results are shown in Table 1.

Hours (hr) 0 One 2 3 4 5 6 7 8 Recovery rate Voltage (v) 6 6 6 6 6 6 6 6 6 - Temperature (℃) 26 60 70 70 70 66 70 70 70 - Concentration in solution (ppm) Pt 299 134 36 13 11 13 13 12 13 96 Pd 443 99 17 6 9 10 8 8 7 98 Rh 314 140 14 7 9 9 6 6 7 98 Ni 685 667 829 829 937 686 657 571 714 - Cu 1,032 357 56 33 38 33 23 24 24 - Zn 1,021 931 1,005 1,041 1,154 1,092 1,200 1,017 1,158 - Fe 4,465 4,465 4,750 4,900 5,300 4,716 4,657 4,716 4,836 -

As can be seen in Table 1, the recovery of the platinum group metal was 96% platinum, 98% palladium, 98% rhodium. However, the platinum group recovery by the electrochemical reduction performed using a single electrolyzer, the platinum group metal was reduced and deposited on the surface of the negative electrode, and the current efficiency was also significantly decreased with time. In addition, the temperature of the electrolyte was increased, and electrode corrosion occurred.

Example 1

In the single electrolytic cell of Comparative Example 1, in order to prevent the platinum group metal from adhering to the cathode and re-dissolving the recovered platinum group metal, the anode chamber and the cathode chamber are separated using a membrane (liquid permeable neutral membrane). In addition, both the positive electrode and the negative electrode were recovered with Pt / Pd / Rh by a cathode precipitation method at a voltage of 6V using a carbon electrode, and the electrolytic conditions and results are shown in Table 2.

PGM concentration in solution (ppm) Remarks Pt Pd Rh Current density time Solution temperature One Before reduction 111 82 27 16 A / dm ² 4 hours 30 minutes Up to 60 ℃ After reduction 7 2 One % Recovery 93.7 97.56 96.3 2 Before reduction 111 82 27 16 A / dm ² 8 hours Up to 60 ℃ After reduction 6 One 0.5 % Recovery 94.6 98.78 98.15 3 Before reduction 114 102 26 21 A / dm ² 5 hours 30 minutes Up to 60 ℃ After reduction 4.3 1.4 0.4 % Recovery 96.2 98.6 98.4 4 Before reduction 178 233 63 20 A / dm ² 4 hours Up to 65 ℃ After reduction 8 2 One % Recovery 95.5 99.14 94.41 5 Before reduction 178 233 63 20 A / dm ² 6 hours 30 minutes 67 ℃ After reduction 7 2 0.2 % Recovery 96.06 99.14 99.68

As can be seen in Table 2, by using the separation electrolytic cell according to the method of the present invention by recovering by the negative electrode precipitation method, while showing a recovery level equivalent to Comparative Example 1 using a single electrolytic cell, adhered to the electrode which is a disadvantage of Comparative Example 1 The problem of exfoliation of precious metals was completely solved.

Example 2

In the same manner as in Example 1, in order to prevent the temperature rise of the electrolytic solution during the electrochemical recovery, after further installing an auxiliary electrolytic cell, the activated carbon powder in the waste liquid while continuously circulating the waste liquid containing precious metal into the electrolytic cell and then electrochemical Was recovered, and the results are shown in Table 3.

PGM concentration in solution (ppm) Remarks Pt Pd RH Current density time Solution temperature One Before reduction 17 221 12 15 A / dm ² 12 hours Up to 25 ℃ After reduction ND 1.4 ND % Recovery 100 99.3 100 2 Before reduction 91 140 19 20 A / dm ² 12 hours Up to 25 ℃ After reduction One ND ND % Recovery 98.9 100 100 3 Before reduction 67 246 26 20 A / dm ² 12 hours Up to 25 ℃ After reduction ND 0.2 ND % Recovery 100 99.9 100

Example 3

In Example 2, in order to filter and separate the platinum group metal from the recovered solution, activated carbon powder and a polymer flocculant (K-305A: manufactured by Besfloc) were added to the recovered solution and filtered, and the filtration time was measured. The results are shown in Table 4.

Recovery Solution (kg) Activated carbon Polymer flocculant Filtration time (h) One 1800ℓ 0.01 wt% of solution amount added Add 0.1% by weight of solution 24 2 1800ℓ Add 0.05% by weight of solution 0.2 wt% of solution 4 3 1800ℓ Add 0.1% by weight of solution 0.2 wt% of solution One

As can be seen from the above, according to the recovery method of the present invention, the platinum group metal can be effectively recovered and separated from the waste liquid, and the current density efficiency decreases over time due to the metal attached to the electrode, the metal attached to the electrode. The problem of peeling, temperature rise of electrolyte solution and electrode corrosion can be solved.

Claims (8)

In an electrochemical recovery method for recovering platinum group metals from various waste liquids containing platinum group metals, a HCl solution is used as an electrolyte solution of a positive electrode in a separate electrolytic cell in which a cathode chamber and a cathode chamber are separated using a membrane, and the platinum group metal containing waste liquid is used as a cathode. A method for recovering a platinum group metal, which is introduced into a chamber, and the platinum group metal is precipitated and precipitated by electrolysis, followed by filtration. 2. A method for recovering a platinum group metal according to claim 1, wherein electrolysis is performed at a current density of 15 to 60 A / dm ² , a voltage of 3 to 10 V, and a temperature of 40 to 70 ° C. The method of recovering a platinum group metal according to claim 1, wherein a platinum electrode or a carbon electrode is used as an anode and a cathode. The method for recovering platinum group metals according to claim 3, wherein both the anode and the cathode electrodes are used as carbon electrodes. The method of claim 1 wherein the concentration of HCl solution is 5 to 36%. The method for recovering platinum group metals according to claim 1, wherein the platinum group metal waste solution is charged with 0.01 to 1% by weight of activated carbon powder in an amount of waste liquid. The method of recovering a platinum group metal according to claim 1, wherein in order to prevent the temperature rise of the electrolytic cell, electrolysis is further performed by providing an electrolytic cell in which an electrode is installed and an auxiliary electrolytic cell capable of circulation. The method according to claim 1, wherein 0.01 to 1% by weight of a polymer flocculant is added to a recovered solution containing a precipitate of platinum group metal, followed by filtering by adding 0.01 to 1% by weight of activated carbon powder. Method for recovering platinum group metals.