HK1183066B - Method and apparatus for extracting precious metal from an inorganic granular waste catalyst - Google Patents

Abstract

In the circulation of electrolyte in a vertical-cylinder-type electrolyzer having a three-dimensional filling cathode made of active carbon granules and a fixed granular catalyst layer, the leaching and precipitation of a precious metal occur in the same phase. Since electrochemical leaching and sorption take place simultaneously, electric energy may be saved, and the use of equipment may be facilitated. An apparatus for extracting a precious metal from an inorganic granular waste catalyst of the present invention includes a vertical electrolyzer, a conduit line, an electrolyte circulation pump, a device automatically maintaining the acidity required for the circulation of electrolyte, a filter filtering out active carbon particles from the electrolyte, a control valve, and a stop valve. The electrolyzer includes a heat exchanger heating the circulating electrolyte, an infusible anode, and a three-dimensional filling cathode made of active carbon granules.

Description

Method and device for extracting precious metals from inorganic granular waste catalyst

Technical Field

The present invention relates to electrochemical hydrometallurgy for the reduction of precious metal waste, and in particular to a method and apparatus for the extraction of precious metals from inorganic particulate spent catalysts.

Background

The method for extracting noble metals from inorganic particulate spent catalysts refers to a method of: the method comprises the following steps: electrochemically leaching precious metals in an electrolytic cell; precipitating the noble metal at the cathode; and subsequently separating the noble metal from the cathode using conventional methods.

In a prior art method for dissolving and extracting precious metals from a spent catalyst (prior art document 1: U.S. Pat. No. 4,775,452, 1988, "method for dissolving and recovering precious metals" (Process for dissolution and recovery of precious metals) "), leaching is performed in an anode chamber of a horizontal type electrolytic cell. The horizontal electrolytic cell comprises a fluorine resin based anion exchange membrane dividing the electrolytic cell into two chambers: an anode chamber and a cathode chamber. The bottom of the anode chamber includes a diffusion grid. In the first step of extracting the noble metals, a particulate spent catalyst fixed bed is introduced into the anode chamber, and the electrolyte is circulated upward through the diffusion grid. Hydrochloric acid, nitric acid, sulfuric acid, or an acidic compound is used as the electrolyte. Preferably, 5% to 35% hydrochloric acid is used. Herein, the anode film and the cathode film are positioned along one side of the electrolytic cell parallel to the flow direction of the electrolyte.

The dimensionally stable porous anode is made of titanium coated with noble metal oxides. The cathode is made of titanium. The cell has a length of 85mm, a width of 115mm to 250mm and a depth of 200mm to 1000 mm. In a second step after leaching the precious metals, the electrolyte is diluted 6 to 50 times and the precious metals are precipitated, thereby separating the precious metals into activated carbon particles present in a fluid state in the cathode space of a second electrolytic cell comprising a cationic membrane.

The drawback of this extraction method is that the efficiency for extracting the noble metal decreases with increasing distance between the anode and the cathode. This is because the hydrochloric acid oxide moves upward parallel to the anodic film by the electrolyte flow and its concentration decreases as it moves from the surface of the anodic film toward the cathode. For this reason, the leaching of the precious metals is mainly carried out on the anode bed close to the spent catalyst.

Since the electrolyte is pumped through the electrolytic cell at one time, a large amount of solution flows out, so that additional equipment is required, thereby increasing economic loss.

The apparatus used to implement the extraction method according to prior art document 1 is energy intensive, has low precious metal extraction efficiency and requires the use of high concentrations (5% to 35%) of acid (mainly hydrochloric acid).

Prior art for extracting precious metals from inorganic spent catalysts, sludge, concentrates, or other metals [ prior art document 2: russian patent No. 21199646, 1997, "method for extracting precious metals and apparatus for carrying out the method" ] is characterized in that during the circulation of the electrolyte, the leaching of the precious metals and the precipitation of the packed cathode are carried out simultaneously in the same step, by means of a fixed filter bed or fluidized bed of leached particles.

The extraction of precious metals is performed simultaneously by means of an electrolytic cell comprising a leaching block and a filled cathode. A 10% to 25% aqueous sodium chloride solution containing the required amounts of hydrochloric acid and base was used as the electrolyte. Herein, the noble metal is deposited on the filled cathode. The leaching block comprises one or more reactors provided with conventional units for introducing and discharging leaching material. The leaching block comprises an electrolytic cell provided with a pH measuring chamber and an automatic discharge control unit.

After the precious metals have been deposited, the filled cathode is separated from the electrolytic cell and sent to a recovery process. To extract the metals, the filled cathode is incinerated. It is also possible to carry out metal extraction without separating the cathode from the electrolytic cell. In this case, the noble metal is dissolved by passing a current of opposite polarity through the cathode, thereby obtaining a chloride solution of high concentration.

The method according to prior art document 2 has the disadvantage that the leaching process is complicated and the functional blocks are spaced apart from each other making it difficult to design the device.

Prior art for extracting precious metals from inorganic spent catalysts, concentrates and other metals [ prior art document 3: russian patent No. 21989477, 9/12/2000, "method for extracting precious metals" ] is the closest prior art to the present invention, and the method comprises: leaching in an electrolyte; circulating an electrolyte through the fill material along a closed loop; precipitating metal in the electrolytic cell; and subsequently separating the noble metal from the cathode according to conventional methods, wherein the metal treated in a packed form is placed in the space between the electrodes of the electrolytic cell. The electrochemical leaching of the noble metal can be activated by reversing the polarity of the electrode beforehand. For this purpose, these electrodes are transformed into large capacity multipolar electrodes, which allow the metal to be dissolved at the anode, independently of the amount of material. At the same time, hydrated anionic chlorine compounds of the noble metals formed during leaching of the filler material are prevented from being burned out by the cathode by suppressing the formation of brown clouds on the cathode, and the electrolyte is circulated from the anode to the cathode at a rate suitable for such conditions. Herein, acidic water containing 0.3% to 4.0% hydrochloric acid is used as the electrolyte.

In order to investigate the efficiency of the noble metal extraction method and examine its defects, the present inventors constructed a document [3 ] corresponding to the prior art]Description of the corresponding electrolytic cell (figure 1). As in prior art document [3]The cell has a horizontal configuration, and the effective cross-sectional area of the cell is 1600cm²(40 cmx40 cm) and the length of the filler material was 100 cm. The filling material in the space between the electrodes is fixed with a dielectric grid. Parameters of the experiment and Prior Art document [3]Those parameters described in (1) are consistent.

According to the studies conducted by the present inventors using the prototype, the influence of the polarity inversion on the leaching rate and depth was negligible. The leaching time increases the time required for polarity reversal. In addition, the noble metal is not formed as a dense foil on the surface of the titanium cathode and is precipitated in the form of black gold, which can be easily separated from the cathode surface by rising hydrogen bubbles. Hydrogen bubbles separated from the surface of the cathode film rise to the surface of the electrolyte and form convection. Thus, the noble metal black gold in a fluidized bed state is placed in the cathode space of the electrolytic cell. Such conditions cause the noble metal black gold to return to the packing material of the spent catalyst through the grid holes. In addition, the precious metal black gold is moved to the anode space of the electrolytic cell by the positive circulating electrolyte flow. A sample of the packing material was analysed after the experiment was carried out and it can be seen that the leaching of the precious metal at the bottom of the packing was incomplete. This is because the circulation rate of the electrolyte from the anode to the cathode is not constant along the cross-section of the cell. The circulation rate of the electrolyte is slower in the lower part than in the upper part of the electrolyte. This can be clearly explained because the spent catalyst particles in the lower part of the cell are subjected to the pressure of the particles in the upper part. This reduces the amount of free space in which electrolyte circulation between the particles in the lower part of the cell occurs. Such conditions impose limitations on increasing the depth of the cell in order to use the cell in industrial applications. In addition, the area of evaporation of the electrolyte in the electrolytic cell is large. If the above process is carried out at 70 c, the electrolyte and anodic hydrochloric acid oxide are strongly evaporated, so that an additional device is required for reducing negative effects on the environment. In addition, since hydrochloric acid is used to partially dissolve the catalyst during electrolysis, the acidity of the solution is reduced. It has been found that when the acidity (pH) of the solution is greater than 1, the rate of leaching is significantly reduced.

In order to maintain acidity at a constant level, electrolyte needs to be periodically drained from the cell and hydrochloric acid needs to be replenished to the desired concentration.

Disclosure of Invention

Technical problem

The object of the present invention is to develop an efficient method for extracting noble metals from particulate spent catalysts by leaching and to construct an apparatus which is easily used to implement the method.

Technical scheme

This object is achieved by the method of the invention for extracting precious metals from inorganic particulate spent catalysts and other substances, which method comprises leaching the precious metals in the space between the electrodes of a vertical electrolytic cell. Leaching is performed by the electrolyte which is circulated from the anode, through the filled catalyst, up the closed circuit to the cathode. The precipitation of the noble metal is carried out in a three-dimensional cathode filled with activated carbon particles. Unlike the prototype, hydrochloric acid having an acidity (pH) of 1 was used as the electrolyte and contained aluminum chloride (AlCl) at a concentration of 0.1% to 5%₃). The leaching of the noble metal and its precipitation in the three-dimensionally packed cathode are carried out simultaneously in the same step. The noble metal is separated from the cathode by burning activated carbon or dissolving the precipitated metal in the anode.

Advantageous effects

The electrolytic cell according to the present invention allows the spent catalyst to be electrolyzed in a particulate form without being pulverized. The present invention can greatly improve the yield of extraction of platinum group metals from a particulate catalyst containing metal compounds to extract almost the entire amount of metals, reduce power consumption and extraction time, and improve ecological compatibility. Furthermore, the present invention has improved work efficiency because it can minimize the amount of waste liquid to be recovered and allow a large amount of waste catalyst to be introduced and leached. In addition, the reliability and electrical safety of the electrolytic cell can be improved and the repair and maintenance of the electrolytic cell is simple and convenient.

Drawings

Figure 1 is a cross-sectional view of an electrolytic cell according to the prior art.

Fig. 2 is a sectional view of an apparatus for extracting noble metals according to the present invention.

Figure 3 is a cross-sectional view of a vertical electrolytic cell according to the present invention.

Detailed Description

In the present invention, an apparatus for extracting noble metals from inorganic particulate catalysts and other substances (fig. 2) has a vertical flow type electrolytic cell 1 including an insoluble anode 3 and a three-dimensionally filled cathode 4. The charging block 18 is used to charge the vertical flow cell. The anode space and the cathode space are connected by a pipeline. The electrolyte is circulated by a pump 6, the pump 6 being operated at a predetermined speed controlled by a flow meter 7. In order to prevent the activated carbon powder from permeating into the anode space from the three-dimensionally packed cathode, a filter press 19 is disposed in the circulation line. The acidity of the solution in the circulation line is measured by an acidity meter 21 and maintained at a constant level by an automatic hydrochloric acid discharge controller 24. The device further comprises a shut-off valve 8, a shut-off valve 9, a shut-off valve 10, a shut-off valve 11, a shut-off valve 12 and a shut-off valve 13.

The apparatus for extracting noble metals operates in the following manner.

The vertical flow cell is filled with particulate spent catalyst from which the organic mixture has been removed. The noble metal content in the catalyst should be in a regenerated (metallic) state in the range of 0.05% to 5%. The cork (valve) 10 and cork 13 are opened, the valves 8, 11 and 12 are closed and the automatic drain controller 24 is inactive and in this state comprises hydrochloric acid solution at pH 1 and aluminium chloride (AlCl) at a concentration of 0.1% to 5%₃) Is fed into the cell through inlet 16. The electrolyte is fed along a high-speed electrolyte pumping line 15. After the electrolyte is fed into the apparatus, the electrolyte is heated at a predetermined temperature by the pipe heater 25. When the electrolyte reaches a predetermined temperature, the valve 10 is closed and the valve 12 is opened. At this time, the electrolyte is circulated at a predetermined rate by the flow meter 7. The charging block 18 is used to set the current value of the cell. Hydrochloric acid in an amount required to maintain the acidity of the electrolyte at a pH of 1 is discharged to the vertical direction by the automatic discharge controller 24The space in front of the anodes of the electrolytic cell. The conditions set for performing the process can be maintained using conventional automated control systems. After a sufficient amount of extracted precious metals have been precipitated in the three-dimensional packed carbon cathode 4, the cathode is dismantled from the vertical electrolytic cell and incinerated. In case the precipitated noble metal dissolves in the anode, the process is stopped, the electrolyte is poured out of the cell and the filled cathode is dismantled and washed with warm water. After washing, the cathode was placed in a tube containing a titanium electrode, the tube was filled with hydrochloric acid or nitric acid, and then an anodic polarity was applied to the three-dimensional carbon electrode supported with a noble metal. In this process, the polarity is changed and the metal deposited on the activated carbon particles is gradually dissolved.

Figure 3 shows a cross-sectional view of an electrolytic cell according to the present invention.

The vertical flow cell comprises a vertical cylindrical body 101 of three-dimensional multi-polar electrodes comprising regenerated catalyst particles, and a distributor 103 for distributing the electrolyte flow, wherein the distributor is provided with an electric heater 104 for maintaining a predetermined temperature of the solution. In this context, the upward circulating direction of the electrolyte flow has the same axis as the direction of the electromagnetic field in the space of the electrolytic cell.

As the precious metal is leached from the three-dimensional multi-polar electrode chamber 108, the chlorine gas formed on the horizontally disposed anode 106 is distributed through the upward flow of electrolyte over the entire dielectric metal oxide quality packed particulate spent catalyst. The right angle outlet 110 is placed on the underside of the cylindrical body structure of the electrolytic cell, whereby the particulate catalyst can be discharged in a simple and fast manner after the metal leaching process.

The lower end of the outlet 110 is located on the same plane as the protective/supporting dielectric grid 109 placed on the anode 106 of the multi-electrode chamber, whereby labor can be reduced and the granular catalyst can be completely discharged.

The corrosion-resistant dielectric support grid 105 acts as a barrier to the packed particulate catalyst, preventing the particulate catalyst of the multi-polar electrodes of the electrolytic cell (the space between the electrodes) from penetrating (flowing out) of the vertical cylindrical body into the conical electrolyte flow distributor 103 (the space in front of the anode), wherein the corrosion-resistant dielectric support grid 105 has mechanical rigidity and is placed between the electrolyte flow distributor 103 and the cylindrical body 101.

The anode 106, which is horizontally disposed and made of a titanium grid, evenly distributes the total flux density of the oxidant formed on the anode throughout the multi-polar electrode. For use with iridium dioxide (IrO)₂) The protective film of the titanium anode produced prevents anodic oxidation (formation of titanium dioxide (TiO) due to oxo acid anions)₂) Dielectric layer of (a) or to prevent galvanic corrosion caused by oxidation of oxygen-free acid anions.

The protective/supporting dielectric grid 109 is interposed between the titanium grid of the anode and the regenerated particulate catalyst (three-dimensional multipolar electrode) and is made of a material (polytetrafluoroethylene) having corrosion resistance, heat resistance and mechanical rigidity. Which is protected from iridium dioxide (IrO)₂) The coating of the finished anode is mechanically destroyed by the abrasive material used for the particulate catalyst.

The membrane (made of polypropylene) 114 separating the cathode space of the cell from the three-dimensional multi-polar electrode chamber minimizes the precipitation of materials such as aluminum oxide on the cathode surface, allowing the dissolved metal to be more completely removed from the cell by the electrolyte flow.

A pair of dielectric supports 113 placed horizontally between the anode chamber of the electrolytic cell and the three-dimensional multipolar electrode containing the regenerated particulate catalyst, fixes the spacing between the anode and the cathode, allows the electromagnetic field to be distributed uniformly in the three-dimensional multipolar electrode, and keeps the cathode chamber in the upper part of the cylindrical space of the electrolytic cell.

Since the current is applied to the horizontally placed anode 106 through the metal rod 107 passing through the multi-polar electrode chamber, the sealability of the electrolytic cell is ensured and the electrical safety and convenience of use of the electrolytic cell are improved.

The center of the conical flow distributor 103 is provided with an inlet 117 so that the leached electrolyte is directly supplied to the heat source. The rising thermal convection of the electrolyte flow forms a thermal buffer in the space near the anode in a state where the flow rate is not high, thereby preventing cold electrolyte from penetrating into the cylindrical chamber 108 of the three-dimensional multi-polar electrode including the regenerated particulate catalyst.

An overflow outlet 118 placed in the upper part of the cylindrical cathode 111 of the vertical flow type electrolytic cell discharges the noble metal salt solution and determines the maximum amount of electrolyte in the electrolytic cell to prevent the electrolyte from overflowing.

The insulation 119 surrounding the cylindrical and conical portions of the cell minimizes heat loss and reduces energy consumption when performing the electrochemical leaching process.

The temperature of the cell cover 120 is lower than the steam temperature of the acid electrolyte, which causes the steam to condense on the inner surface of the cell cover 120. This reduces electrolyte loss and heat loss and increases the environmental safety of the electrochemical leaching process.

The outlet 121 disposed at the cell cover 120 removes hydrogen gas formed in the cathode and prevents the hydrogen gas from being accumulated in the body of the electrolytic cell not filled with the electrolyte, thereby improving the operational stability of the electrolytic cell.

The cell comprises a cylindrical body 101, the cylindrical body 101 being placed on a support 102 and being connected to a conical flow distributor 103 (in the space in front of the anode). The conical flow distributor 103 is provided with an electric heater 104. The cylindrical body is separated from the conical flow distributor by a corrosion-resistant dielectric support grid 105 having mechanical rigidity. On the supporting grid 105 an anode 106 made of a titanium grid made of iridium dioxide (IrO)₂) And (4) coating and protecting. An electric current is applied to the anode 106 through a metal rod 107, which metal rod 107 passes through a multi-polar electrode chamber 108. Disposed on the anode 106 is a material having corrosion resistance, heat resistance, and mechanical rigidity (e.g., aluminum alloy material)E.g., teflon) to protect/support the dielectric grid 109. The lower part of the cylindrical multi-electrode chamber structure of the cell is provided with an outlet 110 for discharging the particulate catalyst, and the lower end of the outlet 110 is placed on the same plane as the protective/supporting dielectric grid 109 on the anode. A cathode space block 111, placed in the upper cylindrical section of the vertical flow cell, is arranged on a pair of dielectric supports 112 arranged horizontally between the cathode chamber of the cell and a three-dimensional porous electrode containing regenerated particulate catalyst. The cathode body is made of a cylindrical dielectric material. The bottom of the cylindrical body consists of a porous bottom 113, on which bottom 113 a porous membrane 114 is arranged. A titanium cathode 115 is provided on the diaphragm, and an electric current is supplied to the titanium cathode 115 through a metal rod 116. The cell comprises an inlet 117 for introducing leached electrolyte, an outlet 118 for discharging a noble metal salt solution, and a thin dielectric cover 120 comprising an outlet 121 for discharging gas.

Example 1: working example of vertical electrolytic cell

To leach out the inorganic (metal oxide) dielectric particulate spent catalyst containing precious metals (e.g., 0.02% to 0.03% palladium-aluminum catalyst), the catalyst is introduced through the top of the cylindrical portion 101 of the electrolytic cell. The cathode compartment 111 is removed from the cell before the catalyst is introduced. The leaching electrolyte (e.g. 3% aqueous HCl) is introduced into the conical flow distributor 103 through the lower inlet 117, and the inside of the distributor is heated to a predetermined temperature by the electric heater 104. The heated electrolyte laminar flow passes through the dielectric support grid cells 105, is oxidized in the horizontal anode grid 106, and passes through the porous protection/support grid 109 to the three-dimensional porous electrode comprising the regenerated particulate catalyst. During the passage of the oxidized electrolyte solution through the bed of particulate catalyst, the noble metal is leached from the particles and enters the electrolyte solution in the form of a salt. This leaching process occurs when the overvoltage is significantly reduced due to the reduction in current density because the working area of the three-dimensional multipolar electrode is large. After the noble metal salt solution is discharged from the particulate spent catalyst bed, it is discharged from the vertical flow cell body through overflow outlet 118. When the cell is initially filled with electrolyte, the cathode space is filled with electrolyte through the porous separator. The membrane controls the movement of noble metal ions to the cathode space, thereby reducing the amount of noble metal ions that precipitate on the cathode. The evaporated electrolyte condenses on the cold wall of the thin cover 120 of the cell and the hydrogen gas separated from the cathode is removed from the space of the cylindrical part of the cell, which is not filled with electrolyte, through the outlet 121. After the leaching process is completed, the electrolyte is discharged through the lower outlet 118, and the particulate catalyst is discharged through the outlet 110.

After the above examples were performed, the particulate catalyst was inspected. As a result, it was found that the amount of platinum group metal remaining in the particulate catalyst after being subjected to electrochemical leaching was not more than 1ppm in the lower part of the electrolytic cell and 1ppm to 10ppm in the upper part.

INDUSTRIAL APPLICABILITY

The electrolytic cell according to the present invention allows the spent catalyst to be electrolyzed in a particulate form without being pulverized. The present invention can greatly improve the yield of extraction of platinum group metals from a particulate catalyst containing metal compounds to extract almost the entire amount of metals, reduce power consumption and extraction time, and improve ecological compatibility. Furthermore, the present invention has improved work efficiency because it can minimize the amount of waste liquid to be recovered and allow a large amount of waste catalyst to be introduced and leached. In addition, the reliability and electrical safety of the electrolytic cell can be improved and the repair and maintenance of the electrolytic cell is simple and convenient.

Claims (15)

1. A vertical flow electrolytic cell for electrochemically leaching platinum group metals from a particulate catalyst containing platinum group metals, the electrolytic cell comprising: an electrolyte flow distributor (103) having an electrolyte inlet (117); and a cylindrical body (1) disposed on the electrolyte flow distributor, wherein the cylindrical body (101) includes a horizontally disposed anode (106), a multi-electrode chamber (108) filled with the granular catalyst, and a cathode space block (111), the anode, the multi-electrode chamber, and the cathode space block are sequentially stacked from the bottom, a granular catalyst outlet (110) and an electrolyte overflow outlet (118) are provided on a side surface of the cylindrical body (101), and the electrolyte flow is upward.

2. The vertical flow electrolysis cell of claim 1 wherein the electrolyte flow distributor (103) further comprises at least one heat source.

3. The vertical flow cell according to claim 1, wherein the granular catalyst outlet (110) is placed at the side of the lower part of the multi-polar electrode chamber (108).

4. The vertical flow cell according to claim 1, wherein the electrolyte overflow outlet (118) is placed at the side of the cylindrical body (1) at a height higher than the multipolar electrode chamber (108).

5. The vertical flow cell according to claim 1, further comprising a corrosion resistant dielectric grid (105) on one side of the anode (106).

6. The vertical flow cell according to claim 1, further comprising a protective/supporting dielectric grid (109) on one side of the anode (106).

7. The vertical flow electrolysis cell according to claim 1 wherein the cathode space block (111) comprises a horizontally placed cathode (115).

8. The vertical flow cell according to claim 7, comprising at least one of a porous membrane (114) or a cathode space support (113) with small pores below the cathode (115).

9. The vertical flow cell of claim 1, further comprising a support member (112) on the multi-polar electrode chamber (108) filled with the particulate catalyst.

10. The vertical flow cell according to claim 1, further comprising a thin dielectric cover (120) on the cylindrical body (101).

11. The vertical flow electrolysis cell according to claim 10 further comprising an outlet (121) for separated gases at the thin dielectric cover (120).

12. The vertical flow cell according to claim 1, wherein the anode (106) is made of a titanium grid.

13. The vertical flow cell according to claim 1, wherein the anode (106) is coated with iridium dioxide (IrO)₂）。

14. The vertical flow cell according to claim 1, wherein the anode (106) is supplied with electric current by a metal rod (107), the metal rod (107) passing through the multi-polar electrode chamber (108).

15. The vertical flow cell according to claim 1, further comprising a thermally insulating material (119) on the outer surface of the electrolyte flow distributor (3) and the cylindrical body (1).