A method for recovering low-concentration platinum by electro-chemical composite adsorption in a short process

Abstract

The present invention discloses a method for recovering low-concentration platinum by short-process electro-chemical composite adsorption, comprising the following steps: using an electrode plate modified by cationic polymer-modified activated carbon as a cathode to construct an electrode system; placing the electrode system and a platinum-containing leachate in an electrolytic cell, and using the electrode system to recover the platinum-containing leachate by electro-chemical composite adsorption. The present invention proposes an electro-chemical composite adsorption technology, which combines the good adsorption performance of cationic polymer-modified activated carbon materials for anions and the interception effect of anion exchange membranes on impure metal cations under the conditions of an applied current and a disturbance device, thereby achieving direct reduction and efficient recovery of low-concentration / trace platinum, simplifying the steps of recovering platinum ions in traditional methods, and reducing the energy consumption and cost of the recovery process.

Description

Technical Field

[0001] The invention belongs to the technical field of platinum group metal recovery, and in particular relates to a method for recovering low-concentration platinum through a short process of electro-chemical composite adsorption. Background Art

[0002] Platinum group metals have excellent physical and chemical properties such as high stability, high temperature resistance and good catalytic activity. They are widely used in the fields of automobiles, petroleum, electronics and electrical appliances, chemicals, aerospace and environmental protection. They are called "strategic reserve metals" and "primary high-tech metals". However, platinum group metal resources are scarce and unevenly distributed. my country's platinum group metal mineral resources are very scarce, with reserves of only about 300t (accounting for 0.4% of the world). Since 2009, my country has become the world's largest consumer of platinum group metals, with demand accounting for about 30% to 35% of the global total, while the output of raw ore is only about 3t, and the contradiction between supply and demand is very prominent. Catalysts are the largest consumer of platinum group metals, such as waste automobile exhaust purification catalysts, waste petrochemical catalysts, waste pharmaceutical and fine chemical homogeneous catalysts. As the catalysts fail and are scrapped, a large amount of secondary resources will be generated. The total amount of platinum group metals in the above wastes is 35 to 40t. Recovering platinum group metals from secondary resources has significant economic benefits.

[0003] In the hydrometallurgical process, reagents such as cyanide, aqua regia, sulfuric acid, hydrogen peroxide or cupric chloride are often used to extract platinum group metals through an oxidation-acid leaching system. The main methods for recovering platinum group metals from solutions include chemical precipitation, solvent extraction, membrane separation technology, adsorption and electrodeposition. Chemical precipitation is a simple and widely used method, however, disadvantages such as the generation of wastewater and sludge, slow kinetics, and poor selectivity have triggered the demand for new technologies; solvent extraction technology is simple to operate and can be used to treat solutions with high content of platinum group metal compounds. Platinum group metals can be recovered graded through multiple extractions and stripping, but the volatilization of toxic and flammable solvents will cause safety hazards and environmental pollution; compared with traditional solvent extraction, membrane separation technology has the advantages of high separation concentration factor, strong mass transfer capacity, simple one-step operation and low organic consumption, but long-term stability and membrane fouling are key challenges for the large-scale application of membrane separation technology. Adsorption is simple to operate, low cost and high efficiency, and is considered to be a promising method. The adsorption capacity of metal ions in the adsorption process is directly affected by the metal ion concentration around the adsorbent. However, for industrial-grade waste catalysts, the content of platinum group metals is relatively low. For example, the FR20 semi-regenerated reforming catalyst produced by Nantong Yangzi Co., Ltd. in China contains 0.28% platinum, and the platinum-containing catalyst used for paint exhaust gas treatment contains only 0.012% platinum, which results in a low concentration of platinum in the waste catalyst leachate. Therefore, the traditional adsorption process has limited recovery capacity for low-concentration platinum group metals. Electrodeposition, as a clean recovery technology, has the advantages of controllability, simplicity, no need for additional reagents, and low equipment requirements. It has been used for the effective reduction of platinum group metals, but it requires a complex enrichment process before the electrodeposition reduction of metals, and the recovery and reduction efficiency of low-concentration platinum group metals is low; because there are often multiple metals in the actual leachate, a large amount of impurity metal ions will compete with platinum group metals for reduction during the electrodeposition process, thereby affecting the recovery and reduction efficiency and purity of platinum group metals.

[0004] Chinese patent CN108277350A proposes a method for recovering platinum from spent alumina-based platinum-rhenium catalysts. The method uses a "roasting-acid leaching-adsorption enrichment-desorption" process to enrich the concentration of platinum in the desorption solution to 30-40 g / L, and then conducts a current density of 500-600 A / m 2 , the effective reduction of platinum was achieved under the conditions of 50-60mm interelectrode spacing, pH 7.0-8.0, and temperature 50-65℃. This method has the problems of only being applicable to the recovery of high-concentration platinum, lengthy process, and high energy consumption. Therefore, driven by economic and environmental protection, a faster, cleaner, and more economical low-concentration / trace platinum group metal recovery technology is needed. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for recovering low-concentration platinum by a short process using electro-chemical composite adsorption, thereby solving the current problem that low-concentration / trace amounts of platinum group metals cannot be effectively recovered by a short process.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for recovering low-concentration platinum by electro-chemical composite adsorption short process, comprising the following steps:

[0008] S1: The electrode plate modified by cationic polymer-modified activated carbon is used as the cathode to construct the electrode system;

[0009] S2: placing the electrode system and the platinum-containing leaching solution in an electrolytic cell, and utilizing the electrode system to perform electro-chemical composite adsorption recovery on the platinum-containing leaching solution.

[0010] Preferably, the preparation method of cationic polymer modified activated carbon comprises:

[0011] mixing the cationic polymer with activated carbon, ammonium chloride and deionized water to obtain a mixed solution;

[0012] The mixed solution is heated and stirred in an inert gas atmosphere, aged, filtered and washed to obtain cationic polymer modified activated carbon.

[0013] Preferably, the mass ratio of the cationic polymer to the activated carbon is (2.5-10):1; the heating temperature is 40-70°C, and the aging time is 10-12h.

[0014] Preferably, the cationic polymer is at least one of polydiallyldimethylammonium chloride, cationic polyacrylamide, and a copolymer of diallyldimethylammonium chloride and acrylamide.

[0015] Preferably, the preparation method of the cathode comprises: mixing the cationic polymer modified activated carbon with the conductive material and the binder uniformly, and then coating the mixture on the surface of the electrode plate.

[0016] Preferably, the anode of the electrode system is an electrode plate modified with activated carbon.

[0017] Preferably, the concentration of platinum complex ions in the platinum-containing leaching solution is 1-15 mg / L.

[0018] Preferably, the applied voltage of the electrode system is 0.4-1.6V.

[0019] Preferably, an anion exchange membrane is provided in the electrolytic cell, which divides the electrolytic cell into a cathode chamber and an anode chamber; the cathode of the electrode system is placed in the cathode chamber, and the anode is placed in the anode chamber; an electrolyte solution is added to the cathode chamber, and a platinum-containing leaching solution is added to the anode chamber.

[0020] Preferably, a convection disturbance device is provided inside the anode chamber or outside the anode chamber.

[0021] The beneficial effects of the present invention are:

[0022] The present invention proposes an electro-chemical composite adsorption technology, which combines the adsorption method with the electrochemical method, realizes the short-process recovery of low-concentration / trace platinum metal, and reduces the energy consumption and cost of the recovery process.

[0023] The present invention adopts an electrode plate modified by cationic polymer modified activated carbon as the cathode, which has good adsorption performance for anions and accelerates the adsorption of platinum complex ions (PtCl6 2- or PtCl4 2- ) mass transfer process, thereby improving the efficient recovery of low-concentration platinum in the solution. When the cathode is modified with activated carbon, the recovery rate of platinum is 72.90%, and after modification with modified activated carbon, the recovery rate is increased to 93.98%. Compared with the electrodeposition technology, the platinum recovery rate is increased by nearly 15 times, which has the advantages of economy, environmental protection, simplicity, high efficiency and low energy consumption.

[0024] The present invention arranges an anion exchange membrane in the electrolytic cell so that the target ions move toward the cathode through the anion exchange membrane, while the impurity metal cations in the leachate are intercepted in the anode chamber because they cannot pass through the anion exchange membrane, thereby avoiding competitive reduction between the impurity metal cations and the target metal ions, thereby improving the recovery rate of the platinum group metals; and by arranging a convection disturbance device, the movement of the target ions toward the cathode is accelerated, thereby improving the recovery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The SEM and EDS images of the cathode material after electro-chemical composite adsorption and recovery of platinum in Example 1;

[0026] Figure 2 Example 1: Recovery effect diagram of platinum recovery by electro-chemical composite adsorption at different times;

[0027] Figure 3 1 is a graph showing the recovery effect of platinum under different conditions for Example 1 and Comparative Examples 1 to 3;

[0028] Figure 4 is a diagram showing the recovery effect of platinum under different voltages in Example 2;

[0029] Figure 5 This is a graph showing the recovery effect of platinum by conventional electrodeposition method in comparative example 4. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The present invention provides a method for recovering low-concentration platinum by short-process electro-chemical composite adsorption, comprising the following steps:

[0032] S1: The electrode plate modified by cationic polymer-modified activated carbon is used as the cathode to construct the electrode system;

[0033] The cathode preparation method includes:

[0034] S1.1. Mix the cationic polymer with activated carbon, ammonium chloride and deionized water to obtain a mixed solution; the mass ratio of the cationic polymer to the activated carbon is (2.5-10):1. Heat and stir the mixed solution at 40-70°C in an inert gas atmosphere, age it for 10-12 hours, filter and wash it, and obtain a cationic polymer modified activated carbon. The cationic polymer is at least one of polydiallyldimethylammonium chloride (Mw 20000-35000), cationic polyacrylamide (Mw 20000-35000), and a copolymer of diallyldimethylammonium chloride and acrylamide.

[0035] S1.2, after evenly mixing the cationic polymer modified activated carbon with the conductive material and the binder, apply it on the surface of the electrode plate, and dry it to obtain the cathode. The conductive material includes but is not limited to conductive carbon black, acetylene carbon black, etc.; the binder includes but is not limited to PVDF.

[0036] S2: Placing the electrode system and the platinum-containing leaching solution in an electrolytic cell, and using the electrode system to perform electro-chemical composite adsorption recovery on the platinum-containing leaching solution. The platinum complex ion in the platinum-containing leaching solution can be PtCl6 2- or PtCl4 2- The concentration is ppm or ppb, preferably 1-15 mg / L. The anode of the electrode system is preferably an electrode plate modified with activated carbon; and the applied voltage of the electrode system is preferably 0.4-1.6V.

[0037] Further, in some embodiments, an anion exchange membrane is provided in the electrolytic cell, and the anion exchange membrane divides the electrolytic cell into a cathode chamber and an anode chamber; the cathode of the electrode system is placed in the cathode chamber, and the anode is placed in the anode chamber; an electrolyte solution is added to the cathode chamber, and a platinum-containing leaching solution is added to the anode chamber. The anion exchange membrane is commercially available, and the model may be EDA1S, FAA-3-50, AEM8040 or AMI-7001S. The purpose of the anion exchange membrane is to prevent the diffusion of high-concentration impurity cations in the anode chamber to the cathode chamber.

[0038] The electrolyte solution includes but is not limited to sodium chloride, potassium chloride, etc. A convection disturbance device is provided inside or outside the anode chamber. The convection disturbance device can be a circulation pump or a stirrer, and the disturbance flow rate is 2-10L / h; the purpose of adding the convection disturbance device is to accelerate the diffusion of the target ions in the anode chamber to the cathode.

[0039] The present invention is described in detail below with reference to specific embodiments.

[0040] The platinum-containing leaching solution in the following examples is a PtCl6-containing solution obtained by oxidation-acid leaching of waste platinum-containing catalysts used for the treatment of waste gas from color steel spray painting. 2- The activated carbon was purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade. The anion exchange membrane was commercially available, model EDA1S, and the convection disturbance device was a magnetic stirrer purchased from Shanghai Meiyingpu Instrument Manufacturing Co., Ltd., model: H01-1B.

[0041] The platinum recovery rate is calculated as follows:

[0042] Recovery rate = (C0-C e ) / C0*100%

[0043] Where C0 is the initial concentration of platinum ions in the cathode chamber solution, mg / L; C e is the concentration of platinum ions in the cathode chamber solution after 24 hours of reaction.

[0044] Example 1

[0045] (1) Leaching of waste catalyst: 5M HCl was used as the leaching agent and 1% v / v H2O2 was used as the oxidant to carry out the leaching experiment of waste catalyst (the waste catalyst was provided by the waste gas treatment workshop of the color steel spray painting). The effective volume was 100mL, the solid-liquid ratio was 1:10, the temperature was maintained at 70°C, the rotation speed was 900 rpm, and the leaching time was 9 hours. After the leaching was completed, the samples were sampled and filtered, and the platinum ions (PtCl6 2- ) concentration is 9.43 mg / L.

[0046] (2) Preparation of cationic polymer modified activated carbon: First, 100 mL of 10 wt% polydiallyldimethylammonium chloride (Mw 20000-35000) was added dropwise to 100 mL of an aqueous solution containing 2 g of activated carbon and 0.2 g of ammonium chloride and mixed evenly; the mixed solution was heated and stirred for 5 h (temperature was 60°C) under a nitrogen atmosphere, and after aging for 10-12 h, it was washed and filtered with ethanol and water to remove the cationic polymer on the surface of the modified activated carbon, and then dried to obtain a cationic polymer modified activated carbon material.

[0047] (3) Preparation of electrodes: Two 6 cm × 4 cm titanium plates were selected as substrates. Before use, they were polished with sandpaper to make their surfaces smooth and flat, washed with ultrapure water, and then dried in a vacuum drying oven at 60°C for use;

[0048] Cationic polymer modified activated carbon, conductive carbon black and PVDF are mixed and fully ground in a mass ratio of 8:1:1, sprayed evenly on a dry titanium plate, and dried in a vacuum drying oven at 60°C; after drying, the electrode plate coated with the modified activated carbon material is soaked in ultrapure water for 24 hours to remove the modified activated carbon that fails to effectively adhere to the titanium plate, and finally the soaked electrode plate is placed in a vacuum drying oven at 60°C and dried again to obtain a cathode.

[0049] Using activated carbon as the electrode material, the anode was prepared in the same preparation method as the cathode. Specifically, activated carbon, conductive carbon black and PVDF were mixed and ground in a mass ratio of 8:1:1, sprayed evenly on a dry titanium plate, and dried in a vacuum drying oven at 60°C; after drying, the electrode plate coated with activated carbon material was soaked in ultrapure water for 24 hours to remove the activated carbon that failed to effectively adhere to the titanium plate, and finally the soaked electrode plate was placed in a vacuum drying oven at 60°C and dried again to obtain the anode.

[0050] (4) Electrochemical composite adsorption of PtCl6 2- Experiment: First, fix the anion exchange membrane in the electrolytic cell, which is divided into a cathode chamber and an anode chamber; then, pour 100 mL of the oxidation-acid leaching solution obtained in step (1) and 100 mL of 1% sodium chloride solution into the acid-resistant anode chamber and cathode chamber respectively, then insert the cathode plate modified by cationic polymer-modified activated carbon into the cathode chamber, and insert the anode plate modified by activated carbon into the anode chamber, so that the plate materials face each other, and use an external power supply to apply a voltage of 0.8 V to the electrode plates. During the reaction, the solution in the anode chamber is disturbed by a stirrer to accelerate ion mass transfer. During the reaction, under the disturbance of the external flow and the adsorption of the cathode material, the PtCl6 2- The anion exchange membrane reaches the cathode, where platinum particles (such as Figure 1After 24 hours, the electrolyte was filtered to separate the platinum particles, and the platinum ion content in the filtrate was detected. The platinum recovery rate was calculated to be 93.98% (as shown in Figure 2 shown).

[0051] Comparative Example 1

[0052] The same apparatus and method as in Example 1 were used to recover platinum from the oxidation-acid leaching solution, except that the cathode and anode were prepared in the same manner and the electrode materials used were both activated carbon. Figure 3 As shown in the figure, it can be seen that when the activated carbon modified by cationic polymer is used as the cathode material, the recovery rate of platinum increases by 1.28 times, indicating that the addition of cationic polydiallyldimethylammonium chloride promotes the recovery of PtCl6 2- Diffusion and enrichment to the cathode. In the oxidation-acid leaching solution, due to Cl - The concentration is much higher than PtCl6 2- The concentration of Cl - Under the action of the electric field force, the impurity metal cations are enriched at the anode, and at the same time, the impurity metal cations migrate toward the cathode. The anion exchange membrane intercepts these impurity cations in the anode chamber, avoiding the competitive reduction of the impurity metal cations and the platinum complex ions, and realizing the PtCl6 2- Separation of impurity cations. In addition, anions in the anode and cathode compartments (such as PtCl6 2- and Cl - ) There is a concentration gradient, and the adsorption of cationic polydiallyldimethylammonium chloride on anions causes the platinum complex ions to move to the cathode and enrich. The force generated by adsorption and diffusion will be greater than the electric field force on the electromigration of platinum complex ions. Therefore, under the action of solution disturbance, the platinum complex ions will pass through the anion exchange membrane and be enriched in the cathode chamber.

[0053] Comparative Example 2

[0054] The same apparatus and method as in Example 1 were used to recover platinum from the oxidation-acid leaching solution, except that no anion exchange membrane was provided in the electrolytic cell. Figure 3 As shown, it can be seen that when the electrolytic cell is provided with an anion exchange membrane, the recovery efficiency of platinum is 93.33%, while when the anion exchange membrane is not provided, the recovery efficiency of platinum drops significantly to 71.98%, indicating that the introduction of the anion exchange membrane hinders the competitive reduction of impurity metal cations and platinum complex ions, thereby improving the recovery efficiency of low concentration / trace platinum complex ions.

[0055] Comparative Example 3

[0056] The same apparatus and method as in Example 1 were used to recover platinum from the oxidation-acid leaching solution, except that no anion exchange membrane was provided in the electrolytic cell and the cathode material was activated carbon. Figure 3 As shown, the concentration of platinum ions in the solution was sampled and tested for 24 hours, and the calculated recovery rate was 54.37%. Compared with the case where an anion exchange membrane was set and the cathode material was modified activated carbon, or no anion exchange membrane was set and the cathode material was modified activated carbon, or anion exchange membrane was set and the cathode material was activated carbon, the recovery efficiency was significantly reduced, indicating that the introduction of cationic polydiallyldimethylammonium chloride and / or anion exchange membrane accelerated the recovery of platinum ions.

[0057] Example 2

[0058] The same apparatus and method as in Example 1 were used to recover platinum from the oxidation-acid leaching solution, except that the voltages applied by the external power source were 0.4 V, 0.8 V, 1.2 V and 1.6 V, respectively. Figure 4 As shown, it can be seen that with the increase of voltage, the recovery of platinum first increases and then decreases. Under the condition of low voltage 0.8V, the recovery efficiency of platinum is as high as 93.98%.

[0059] Comparative Example 4

[0060] The conventional electrodeposition method was used to recover platinum from the oxidation-acid leaching solution. The difference from Example 1 was that the cathode and anode of the electrolysis device were both ordinary smooth titanium plates. Electrodeposition was performed to recover PtCl6 at voltages of 0.8 V and 4 V, respectively. 2- The results are as follows. Figure 5 As shown, it can be seen that after 24 hours under low voltage conditions, the recovery rate of platinum is only 6.25%; even if the electrodeposition recovery is carried out under high voltage, the effect is still lower than the cationic polymer modified activated carbon electro-chemical composite adsorption method under low voltage of the present invention.

[0061] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0062] The above-mentioned embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recovering low-concentration platinum by short-process electrochemical composite adsorption, characterized in that: The steps include: S1: An electrode plate modified with activated carbon modified by a cationic polymer is used as a cathode to construct an electrode system; the cationic polymer is at least one of polydiallyldimethylammonium chloride, cationic polyacrylamide, and a copolymer of diallyldimethylammonium chloride and acrylamide; S2: placing the electrode system and the platinum-containing leaching solution in an electrolytic cell, and using the electrode system to perform electro-chemical composite adsorption recovery on the platinum-containing leaching solution; the concentration of platinum complex ions in the platinum-containing leaching solution is at the ppm level or the ppb level; The electrolytic cell is provided with an anion exchange membrane, which divides the electrolytic cell into a cathode chamber and an anode chamber; the cathode of the electrode system is placed in the cathode chamber, and the anode is placed in the anode chamber; an electrolyte solution is added to the cathode chamber, and a platinum-containing leaching solution is added to the anode chamber; The preparation method of the cationic polymer modified activated carbon comprises: mixing the cationic polymer with activated carbon, ammonium chloride and deionized water to obtain a mixed solution; the mass ratio of the cationic polymer to the activated carbon is (2.5-10):1; The mixed solution is heated and stirred in an inert gas atmosphere, aged, filtered and washed to obtain the cationic polymer modified activated carbon; the heating temperature is 40-70°C.

2. The method for recovering low-concentration platinum by electro-chemical composite adsorption short process according to claim 1, characterized in that: The preparation method of the cathode comprises: mixing the cationic polymer modified activated carbon with the conductive material and the binder uniformly, and then coating the mixture on the surface of the electrode plate.

3. The method for recovering low-concentration platinum by electro-chemical composite adsorption short process according to claim 1, characterized in that: The anode of the electrode system is an electrode plate modified with activated carbon.

4. The method for recovering low-concentration platinum by electro-chemical composite adsorption short process according to claim 1, characterized in that: The concentration of platinum complex ions in the platinum-containing leaching solution is 1-15 mg / L.

5. The method for recovering low-concentration platinum by electro-chemical composite adsorption short process according to claim 1, characterized in that: The applied voltage of the electrode system is 0.4-1.6 V.

6. The method for recovering low-concentration platinum by electro-chemical composite adsorption short process according to claim 1, characterized in that: A convection disturbance device is arranged inside the anode chamber or outside the anode chamber.

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