Method for recovering high-purity platinum metal from waste three-way catalyst

Abstract

The invention relates to a method for recovering high-purity platinum metal from a waste three-way catalyst. The method comprises the following steps: crushing the three-way catalyst, and heating in air or oxygen at a high temperature to obtain metal-containing powder mainly comprising metal and metal compounds; the metal-containing powder is put into hydrochloric acid, soluble metal and oxide thereof are dissolved, then filtering is conducted, and insoluble filter residues are obtained; putting the insoluble filter residues into aqua regia to dissolve platinum, removing nitrate by hydrochloric acid, filtering, and separating the filter residues from filtrate; gradually adding solid ammonium chloride into the filtrate and stirring; separating the precipitate from the filtrate, adding water into the precipitate for slurrying, adding ammonium oxalate according to a preset proportion, heating to nearly boiling, gradually dissolving the precipitate, and filtering when the precipitate is not dissolved any more to obtain the filtrate; adjusting the pH value of the filtrate with hydrochloric acid, and adding hydrogen peroxide while stirring until no precipitate is generated in the filtrate; and calcining the precipitate, and then re-melting the ingot.

Description

Technical Field

[0001] The invention relates to the technical field of precious metal recovery, and in particular to a method for recovering high-purity platinum metal from a waste three-way catalyst. Background Art

[0002] The carrier component of the three-way catalytic converter is a porous ceramic material installed in a special exhaust pipe. It is called a carrier because it does not participate in the catalytic reaction itself, but is covered with a layer of precious metals such as platinum, rhodium, and palladium. It can turn HC and CO in the exhaust gas into water and CO2, and decompose NOx into nitrogen and oxygen. Platinum, rhodium, palladium and other precious metals with catalytic effects are three-way catalysts.

[0003] The three-way catalyst has a certain service life. After the service life is exceeded, the catalyst becomes ineffective or the catalytic efficiency decreases, resulting in exhaust gas purification failing to meet the standards and needs to be replaced. This part of the catalyst is called the spent three-way catalyst. The platinum group metals in the spent three-way catalyst have a high recycling value. The three-way catalyst contains 0.08-0.12% platinum.

[0004] During the purification and refining process of platinum in the three-way catalyst, potassium oxalate is mainly used as a reducing agent to redissolve ammonium chloroplatinate precipitate to generate water-soluble potassium chloroplatinite. The filtrate is oxidized to generate potassium chloroplatinate precipitate that is slightly soluble in water. This double salt precipitate cannot be directly calcined into sponge platinum. It needs to be reduced and cleaned with hydrazine hydrate first, and then calcined after removing potassium and sodium ions. Therefore, the production cycle is long and the labor intensity of operators is high. At the same time, due to the addition of hydrazine hydrate reduction of potassium chloroplatinate and cleaning steps, the reagent costs of the reducing agent hydrazine hydrate and sodium hydroxide are increased. Summary of the invention

[0005] In view of this, it is necessary to provide a method for recovering high-purity platinum metal from waste three-way catalysts, improve the refining efficiency and quality of platinum, and reduce labor intensity and cost.

[0006] A method for recovering high-purity platinum metal from a spent three-way catalyst comprises the following steps:

[0007] Step S1: After the three-way catalyst is crushed, it is heated at high temperature in air or oxygen to remove the residual carbon and organic compounds in the three-way catalyst to obtain a metal-containing powder mainly composed of metals and metal compounds;

[0008] Step S2: putting the metal-containing powder into hydrochloric acid to dissolve the soluble metal and its oxide, and then filtering to obtain a hardly soluble filter residue;

[0009] Step S3: putting the insoluble filter residue into aqua regia to dissolve the platinum, and then using hydrochloric acid to drive out the nitrate, filtering and separating the filter residue and the filtrate;

[0010] Step S4: gradually adding solid ammonium chloride to the filtrate and stirring to dissolve the solid ammonium chloride and generate a precipitate. When the precipitate is complete, stop adding the solid ammonium chloride;

[0011] Step S5: separating the precipitate from the filtrate, adding water to the precipitate to slurry it, adding ammonium oxalate in a predetermined ratio, heating to near boiling, so that the precipitate gradually dissolves, and filtering when the precipitate no longer dissolves to obtain a filtrate;

[0012] Step S6: adjusting the pH value of the filtrate with hydrochloric acid, and adding hydrogen peroxide while stirring until no more precipitation is produced in the filtrate;

[0013] Step S7: repeating steps S5 to S6 until the platinum content in the precipitate reaches more than 99.995% of the total metal;

[0014] Step S8: calcining the precipitate and then remelting the ingot.

[0015] Beneficial effects: The present invention uses ammonium oxalate instead of potassium oxalate as a precipitant, and can directly calcine and recover platinum, eliminating the need for reduction and cleaning of hydrazine hydrate, thereby reducing production costs. At the same time, the operation process is simplified, the production cycle is shortened, and the labor intensity is reduced. No metal ions are introduced, thereby increasing the purity of platinum. Compared with potassium oxalate, the price of ammonium oxalate is relatively cheap, which can save production costs. DETAILED DESCRIPTION

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the embodiments will be introduced below. Obviously, for ordinary technicians in this field, other implementation methods can be obtained based on the embodiments described below without paying any creative work.

[0017] A method for recovering high-purity platinum metal from a spent three-way catalyst comprises the following steps:

[0018] Step S1: crushing the three-way catalyst and heating it at high temperature in air or oxygen to remove the residual carbon and organic compounds in the three-way catalyst to obtain a metal-containing powder mainly composed of metals and metal compounds;

[0019] In a preferred embodiment, the metal-containing powder has a mesh size of 100 to 200.

[0020] Step S2: putting the metal-containing particles into hydrochloric acid to dissolve the soluble metals and their oxides, and then filtering to obtain insoluble filter residues;

[0021] Step S3: putting the insoluble filter residue into aqua regia to dissolve the platinum, then adding a predetermined amount of hydrochloric acid, filtering and separating the filter residue and the filtrate;

[0022] In a preferred embodiment, the pH of the filtrate is 1.5-2.

[0023] After the filter residue is dissolved in aqua regia, platinum exists in the solution in the form of H2PtCl6, and the remaining insoluble filter residue can be filtered to obtain the filtrate.

[0024] The reactions that occur during platinum dissolution are:

[0025] 3Pt+4HNO3+18HCl=3H2PtCl6+8H2O+4NO;

[0026] Step S4: gradually adding solid ammonium chloride to the filtrate and stirring to dissolve the solid ammonium chloride and generate a precipitate. When the precipitate is complete, stop adding the solid ammonium chloride;

[0027] After solid ammonium chloride is added, it quickly dissolves in the solution due to its high solubility. At the same time, ammonium chloride reacts with chloroplatinic acid to form a precipitate, ammonium chloroplatinate.

[0028] Furthermore, in step S4, the ammonium chloroplatinate precipitate is rinsed to remove acidic soluble substances on the surface of the precipitate.

[0029] Step S5: separating the precipitate from the filtrate, adding water to the precipitate to slurry it, adding ammonium oxalate in a predetermined ratio, heating to near boiling, so that the precipitate gradually dissolves, and filtering when the precipitate no longer dissolves to obtain a filtrate;

[0030] After adding water to slurry, the solid matter is suspended in water. After adding ammonium oxalate and heating, the ammonium chloroplatinate in the solid matter dissolves to form ammonium chloroplatinate. Other impurities do not react with ammonium oxalate, so they still exist in the form of precipitation. After filtering, an ammonium chloroplatinate solution can be obtained, thereby further purifying the platinum element. The reactions that occur in this process are:

[0031] (NH4)2PtCl6+(NH4)2C2O4——Δ→(NH4)2PtCl4+2NH4Cl+2CO2;

[0032] In a preferred embodiment, the filter residue is washed 2 to 3 times, and the washing liquid is mixed with the filtrate to collect the ammonium chloroplatinite attached to the surface of the filter residue.

[0033] Step S6: adjusting the pH value of the filtrate with hydrochloric acid, and adding hydrogen peroxide while stirring until no more precipitation is produced in the filtrate;

[0034] After adding hydrogen peroxide, ammonium chloroplatinite is oxidized to generate ammonium chloroplatinate precipitate. Steps S5 to S6 are repeated according to actual conditions until the platinum content in the precipitate reaches more than 99.995% of the total metal components.

[0035] In a preferred embodiment, steps S5-S6 are repeated 2-3 times.

[0036] In a preferred embodiment, the ammonium chloroplatinate precipitate is rinsed to clean the soluble impurities on the surface of the ammonium chloroplatinate precipitate.

[0037] Step S8: calcining the precipitate and then remelting the ingot.

[0038] In a preferred embodiment, the waste liquid after precipitation and washing is collected and then neutralized to prevent acid contamination.

[0039] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for recovering high-purity platinum metal from a waste three-way catalyst, characterized in that: The following steps are involved: Step S1: After the three-way catalyst is crushed, it is heated at high temperature in air or oxygen to remove the residual carbon and organic compounds in the three-way catalyst to obtain a metal-containing powder mainly composed of metals and metal compounds; Step S2: putting the metal-containing powder into hydrochloric acid to dissolve the soluble metal and its oxide, and then filtering to obtain a hardly soluble filter residue; Step S3: putting the insoluble filter residue into aqua regia to dissolve the platinum, and then using hydrochloric acid to drive out the nitrate, filtering and separating the filter residue and the filtrate; Step S4: gradually adding solid ammonium chloride to the filtrate and stirring to dissolve the solid ammonium chloride and generate a precipitate. When the precipitate is complete, stop adding the solid ammonium chloride; Step S5: separating the precipitate from the filtrate, adding water to the precipitate to slurry it, adding ammonium oxalate in a predetermined ratio, heating to near boiling, so that the precipitate gradually dissolves, and filtering when the precipitate no longer dissolves to obtain a filtrate; Step S6: adjusting the pH value of the filtrate with hydrochloric acid, and adding hydrogen peroxide while stirring until no more precipitation is produced in the filtrate; Step S7: repeating steps S5 to S6 until the platinum content in the precipitate reaches more than 99.995% of the total metal; Step S8: calcining the precipitate and then remelting the ingot.

2. The method for recovering high-purity platinum metal from a waste three-way catalyst as claimed in claim 1, characterized in that: In step S1, the metal-containing powder has a mesh size of 100-200.

3. The method for recovering high-purity platinum metal from a waste three-way catalyst as claimed in claim 1, characterized in that: In step S3, the pH of the filtrate is 1.5-2.

4. The method for recovering high-purity platinum metal from a waste three-way catalyst as claimed in claim 1, characterized in that: In step S4, the ammonium chloroplatinate precipitate is rinsed to remove acidic soluble substances on the surface of the precipitate.

5. The method for recovering high-purity platinum metal from a waste three-way catalyst as claimed in claim 1, characterized in that: In step S5, the filter residue is washed 2 to 3 times, and the washing liquid is mixed with the filtrate to collect the ammonium chloroplatinite attached to the surface of the filter residue.

6. The method for recovering high-purity platinum metal from a waste three-way catalyst as claimed in claim 1, characterized in that: Steps S5-S6 are repeated 2-3 times.

7. The method for recovering high-purity platinum metal from a waste three-way catalyst as claimed in claim 1, characterized in that: In step S7, the ammonium chloroplatinate precipitate is rinsed to clean the soluble impurities on the surface of the ammonium chloroplatinate precipitate.

8. The method for recovering high-purity platinum metal from a waste three-way catalyst as claimed in claim 1, characterized in that: The waste liquid after precipitation and cleaning is collected and neutralized to prevent acid contamination.