Method for enriching noble metal in low-grade noble metal iron alloy by using ferric chloride solution to selectively dissolve iron under pressure

Abstract

This invention relates to a method for selectively leaching and enriching precious metals in low-grade precious metal ferroalloys using a pressurized ferric chloride solution, belonging to the field of rare and precious metal secondary resource recovery technology. The method involves crushing and finely grinding the low-grade precious metal ferroalloy, followed by oxidative roasting at 450-600℃ to remove carbon and sulfur impurities, yielding pretreated low-grade precious metal ferroalloy powder. This pretreated powder is then added to a pure ferric chloride solution and mixed thoroughly. The mixture is then placed in a pressure vessel and leached under inert atmosphere and stirring for 60-240 minutes. Solid-liquid separation yields a leachate and a precious metal enrichment residue. The leachate is then oxidized and regenerated to obtain a ferric chloride solution. Using pure ferric chloride solution as the leaching agent, and through precise control of high temperature, high pressure, and redox potential, Fe... 3+ The oxidant selectively dissolves the iron matrix without adding acid or generating hydrogen gas throughout the process. The iron dissolution rate is ≥96%, the precious metal dissolution rate is <0.3%, the precious metals are completely enriched in the leaching residue, and the leaching agent can be oxidized and regenerated in a closed-loop cycle.

Description

Technical Field

[0001] This invention relates to a method for selectively dissolving iron in ferric chloride solution under pressure to enrich precious metals in low-grade precious metal ferroalloys, belonging to the field of rare and precious metal secondary resource recovery technology. Background Technology

[0002] In the fields of industrial production and solid waste recycling, there are a large amount of low-grade ferroalloy materials with precious metal content of 0.1%~5% and iron content ≥90%. These materials mainly originate from ferroalloy capture materials produced by pyrometallurgical capture of precious metals from spent automotive exhaust catalysts or petrochemical catalysts, as well as iron-containing precious metal alloy materials by-products from non-ferrous metallurgy. These materials have low precious metal content, are dispersed, and have precious metals encapsulated within an iron matrix, making efficient enrichment difficult to achieve using conventional processes. They are among the most difficult precious metal-containing materials to process in the industry.

[0003] The current mainstream treatment process in the industry is conventional strong acid leaching under normal pressure, using hydrochloric acid and sulfuric acid as leaching agents. The reaction principle is Fe + 2H+. + =Fe 2+ +H2↑, this process has four major defects: (1) extremely high safety risk: the reaction produces a large amount of flammable and explosive hydrogen gas, which is easy to cause an explosion and cannot meet the safety requirements of continuous industrial production; (2) low iron removal efficiency: the iron dissolution rate is less than 70% under normal pressure, a large amount of iron remains, and the enrichment ratio of precious metals is extremely low; (3) dispersion and loss of precious metals: during the acid dissolution process, some precious metals dissolve with iron under oxidizing conditions and enter the liquid phase, which is difficult to recover and the recovery rate of precious metals is low; (4) high environmental protection cost: a large amount of high-concentration waste acid is generated, which is difficult to treat and costly, and is easy to cause environmental pollution. Summary of the Invention

[0004] To address the problems of existing low-grade precious metal ferroalloy recycling processes, such as significant safety hazards, low iron removal rates, dispersed precious metals, and poor environmental performance, this invention proposes a method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution. This method uses pure ferric chloride solution as the leaching agent and employs precise control of high temperature, high pressure, and redox potential to extract Fe... 3+ The oxidant selectively dissolves the iron matrix without adding acid or generating hydrogen gas throughout the process. The iron dissolution rate is ≥96%, the precious metal dissolution rate is <0.3%, the precious metals are completely enriched in the leaching residue, and the leaching agent can be oxidized and regenerated in a closed-loop cycle.

[0005] A method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution, the specific steps of which are as follows: (1) The low-grade precious metal ferroalloy is crushed and finely ground to 80~200 mesh, and then placed at a temperature of 450~600℃ for 30~90 min to remove carbon impurities and sulfur impurities, so as to obtain pretreated low-grade precious metal ferroalloy powder. (2) Dissolve ferric chloride in deionized water to obtain a ferric chloride solution; (3) Add the pretreated low-grade precious metal ferroalloy powder to the ferric chloride solution and mix evenly. Then place it in a pressure vessel and leach under pressure for 60-240 minutes in an inert atmosphere with stirring. Separate the solid and liquid to obtain the leachate and the precious metal enrichment residue. The leachate is then oxidized and regenerated to obtain the ferric chloride solution.

[0006] Preferably, in step (1), the content of precious metals in the low-grade precious metal ferroalloy is 0.1~5 wt.%, and the content of iron is not less than 85 wt.%.

[0007] Preferably, the concentration of the ferric chloride solution in step (2) is 100~300g / L.

[0008] Preferably, the solid-liquid ratio (g:mL) of the pretreated low-grade precious metal ferroalloy powder and ferric chloride solution in step (3) is 1:5~10.

[0009] Preferably, the stirring speed of the pressurized leaching in step (3) is 300~600 rpm, the pressure is 0.2~4 MPa, the temperature is 110~250℃, and the oxidation-reduction potential is 350~500 mV.

[0010] Preferably, the method for oxidizing and regenerating the ferric chloride solution in step (3) is as follows: adding hydrogen peroxide solution and hydrochloric acid solution to the leachate, wherein the amount of hydrogen peroxide added is 0.6 to 1.2 times the molar amount of ferrous ions in the leachate, and the amount of hydrochloric acid is 1.05 to 1.2 times the molar amount of ferrous ions in the leachate, and FeCl2 is oxidized to FeCl3 under stirring conditions.

[0011] The mechanism of selective iron dissolution and enrichment of noble metals in low-grade precious metal ferroalloys using ferric chloride solution under pressure in this invention is as follows: ① By moderately roasting, C and S are removed from the low-grade precious metal ferroalloys, increasing the leaching performance of the material; ② Using ferric chloride solution, under high-temperature and high-pressure enhanced reaction conditions, elemental Fe in the alloy is selectively dissolved, 2Fe 3+ +Fe→3Fe 2+ This achieves the enrichment of precious metals; ③ The main component of the ferric chloride solution after leaching is FeCl2, which is regenerated into FeCl3 under the action of hydrogen peroxide and 2Fe 2+ +[O]→2Fe 3+ +O 2- The regeneration process introduces no additional impurities, achieving a green closed-loop use of the leaching agent.

[0012] The beneficial effects of this invention are: (1) The present invention uses a pure ferric chloride system, without adding hydrochloric acid or sulfuric acid, so that no hydrogen is generated, completely eliminating the safety hazards of flammability and explosion, and meeting the requirements of industrial safety production; (2) The reaction kinetics are enhanced by high temperature and pressure in this invention, and the iron dissolution rate reaches 96%~99%, which is much higher than the iron dissolution rate of 70%~85% by acid dissolution under normal pressure; (3) The present invention has zero loss of precious metals and low leaching rate of precious metals <0.3%, with all precious metals enriched in the leaching residue. The subsequent purification process is simplified and the total recovery rate of precious metals is increased by 5% to 10%. (4) The leachate of this invention is recycled in a closed loop with a utilization rate of ≥98%, with no waste acid or wastewater discharge, and the environmental treatment cost is reduced by more than 50%. (5) The wet pressing temperature (110~250℃) of the present invention is much lower than that of oxidation blowing (above 1200℃), and the energy consumption is greatly reduced. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0015] Example 1: In this example, the total precious metal content of the low-grade precious metal ferroalloy is 2.1 wt.%, of which Pt content is 0.24 wt.%, Pd content is 1.66 wt.%, Rh content is 0.2 wt.%, iron content is 92.3 wt.%, C content is 1.2 wt.%, and S content is 0.4 wt.%. A method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution (see...) Figure 1 The specific steps are as follows: (1) The low-grade precious metal ferroalloy is crushed and finely ground to 80~120 mesh, and then placed at 450℃ for oxidative roasting for 90 min to remove carbon impurities and sulfur impurities, thus obtaining pretreated low-grade precious metal ferroalloy powder. (2) Dissolve ferric chloride in deionized water to obtain a ferric chloride solution with a concentration of 180 g / L; (3) The pretreated low-grade precious metal ferroalloy powder was added to the ferric chloride solution and mixed evenly. The solid-liquid ratio of the pretreated low-grade precious metal ferroalloy powder to the ferric chloride solution was 1:7 g:mL. Then, it was placed in a pressure vessel and leached under an inert atmosphere (nitrogen) and a stirring speed of 300 rpm for 120 min. The pressure of the pressure leaching was 0.2 MPa, the temperature was 120 °C, and the redox potential was 420 mV. The solid and liquid were separated to obtain the leachate and the precious metal enrichment residue. H2O2 solution (concentration of 30%) and hydrochloric acid solution were added to the leachate and oxidized at a stirring speed of 300 rpm for 30 min to obtain the ferric chloride solution. The amount of H2O2 added was 0.75 times the molar amount of ferrous ions in the leachate, and the amount of HCl added to the hydrochloric acid solution was 1.1 times the molar amount of ferrous ions in the leachate. The test results showed that the total precious metal content in the precious metal enrichment slag was 23.5 wt.%, of which Pt content was 2.74 wt.%, Pd content was 18.56 wt.%, Rh content was 2.20 wt.%, and iron content was 22.8 wt.%. In this example, the Fe leaching rate reached 97.8%, while the precious metal leaching rate was only 0.21%.

[0016] Example 2: In this example, the total precious metal content of the low-grade precious metal ferroalloy is 0.8 wt.%, of which Pt content is 0.09 wt.%, Pd content is 0.63 wt.%, Rh content is 0.08 wt.%, iron content is 95.6 wt.%, C content is 2.3 wt.%, and S content is 0.4 wt.%. A method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution (see...) Figure 1 The specific steps are as follows: (1) The low-grade precious metal ferroalloy is crushed and finely ground to 150~180 mesh, and then placed at 600℃ for 30 min to remove carbon and sulfur impurities, thus obtaining pretreated low-grade precious metal ferroalloy powder. (2) Dissolve ferric chloride in deionized water to obtain a ferric chloride solution with a concentration of 220 g / L; (3) The pretreated low-grade precious metal ferroalloy powder was added to the ferric chloride solution and mixed evenly. The solid-liquid ratio of the pretreated low-grade precious metal ferroalloy powder to the ferric chloride solution was 1:8 g:mL. Then, it was placed in a pressure vessel and leached under an inert atmosphere (nitrogen) and a stirring speed of 600 rpm for 150 min. The pressure of the pressure leaching was 0.6 MPa, the temperature was 150 °C, and the redox potential was 450 mV. The solid and liquid were separated to obtain the leachate and the precious metal enrichment residue. H2O2 solution (concentration of 30%) and hydrochloric acid solution were added to the leachate and oxidized at a stirring speed of 300 rpm for 35 min to obtain the ferric chloride solution. The amount of H2O2 added was 1 times the molar amount of ferrous ions in the leachate, and the amount of HCl added to the hydrochloric acid solution was 1.2 times the molar amount of ferrous ions in the leachate. The test results showed that the total precious metal content in the precious metal enrichment slag was 12.3 wt.%, of which Pt content was 1.42 wt.%, Pd content was 9.73 wt.%, Rh content was 1.15 wt.%, and iron content was 51.5 wt.%. In this example, the Fe leaching rate reached 96.5%, while the precious metal leaching rate was only 0.18%.

[0017] Example 3: In this example, the total precious metal content in the low-grade precious metal ferroalloy enrichment is 4.2 wt.%, of which Pt content is 0.49 wt.%, Pd content is 3.32 wt.%, Rh content is 0.39 wt.%, iron content is 90.1 wt.%, C content is 3.1 wt.%, and S content is 0.1 wt.%. A method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution (see...) Figure 1 The specific steps are as follows: (1) The low-grade precious metal ferroalloy enriched material is crushed and finely ground to 100~120 mesh, and then placed at 600℃ for oxidative roasting for 90 min to remove carbon impurities and sulfur impurities, so as to obtain pretreated low-grade precious metal ferroalloy enriched powder. (2) Dissolve ferric chloride in deionized water to obtain a ferric chloride solution with a concentration of 250 g / L; (3) The pretreated low-grade precious metal ferroalloy powder was added to the ferric chloride solution and mixed evenly. The solid-liquid ratio of the pretreated low-grade precious metal ferroalloy powder to the ferric chloride solution was 1:6 g:mL. Then, it was placed in a pressure vessel and leached under an inert atmosphere (nitrogen) and a stirring speed of 300 rpm for 180 min. The pressure of the pressure leaching was 1.1 MPa, the temperature was 180 °C, and the redox potential was 380 mV. The solid and liquid were separated to obtain the leachate and the precious metal enrichment residue. H2O2 solution (concentration of 30%) and hydrochloric acid solution were added to the leachate and oxidized at a stirring speed of 300 rpm for 40 min to obtain the ferric chloride solution. The amount of H2O2 added was 0.6 times the molar amount of ferrous ions in the leachate, and the amount of HCl added to the hydrochloric acid solution was 1.1 times the molar amount of ferrous ions in the leachate. The test results showed that the total precious metal content in the precious metal enrichment slag was 40.1 wt.%, of which Pt content was 4.68 wt.%, Pd content was 31.75 wt.%, Rh content was 3.67 wt.%, and iron content was 15.5 wt.%. In this example, the Fe leaching rate reached 98.2%, while the precious metal leaching rate was only 0.25%.

[0018] Example 4: In this example, the total precious metal content in the low-grade precious metal ferroalloy enrichment is 4.7 wt.%, of which Pt content is 0.55 wt.%, Pd content is 3.71 wt.%, Rh content is 0.44 wt.%, iron content is 88.3 wt.%, C content is 3.5 wt.%, and S content is 0.4 wt.%. A method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution (see...) Figure 1 The specific steps are as follows: (1) The low-grade precious metal ferroalloy enriched material is crushed and finely ground to 80~100 mesh, and then placed at 500℃ for oxidative roasting for 90 min to remove carbon impurities and sulfur impurities, so as to obtain pretreated low-grade precious metal ferroalloy enriched powder. (2) Dissolve ferric chloride in deionized water to obtain a ferric chloride solution with a concentration of 280 g / L; (3) The pretreated low-grade precious metal ferroalloy powder was added to the ferric chloride solution and mixed evenly. The solid-liquid ratio of the pretreated low-grade precious metal ferroalloy powder to the ferric chloride solution was 1:10 g:mL. Then, it was placed in a pressure vessel and leached under an inert atmosphere (nitrogen) and a stirring speed of 450 rpm for 240 min. The pressure of the pressure leaching was 2.3 MPa, the temperature was 220 °C, and the redox potential was 360 mV. The solid and liquid were separated to obtain the leachate and the precious metal enrichment residue. H2O2 solution (concentration of 30%) and hydrochloric acid solution were added to the leachate and oxidized at a stirring speed of 300 rpm for 50 min to obtain the ferric chloride solution. The amount of H2O2 added was 0.8 times the molar amount of ferrous ions in the leachate, and the amount of HCl added to the hydrochloric acid solution was 1.2 times the molar amount of ferrous ions in the leachate. The test results showed that the total precious metal content in the precious metal enrichment slag was 38.5 wt.%, of which Pt content was 4.42 wt.%, Pd content was 30.47 wt.%, Rh content was 3.61 wt.%, and iron content was 10.87 wt.%. In this example, the Fe leaching rate reached 98.5%, while the precious metal leaching rate was only 0.23%.

[0019] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution, characterized in that, The specific steps are as follows: (1) The low-grade precious metal ferroalloy is crushed and finely ground to 80~200 mesh, and then placed at a temperature of 450~600℃ for 30~90 min to remove carbon impurities and sulfur impurities, so as to obtain pretreated low-grade precious metal ferroalloy powder. (2) Dissolve ferric chloride in deionized water to obtain a ferric chloride solution; (3) Add the pretreated low-grade precious metal ferroalloy powder to the ferric chloride solution and mix evenly. Then place it in a pressure vessel and leach under pressure for 60-240 minutes in an inert atmosphere with stirring. Separate the solid and liquid to obtain the leachate and the precious metal enrichment residue. The leachate is then oxidized and regenerated to obtain the ferric chloride solution.

2. The method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution according to claim 1, characterized in that: Step (1) The content of precious metals in the low-grade precious metal ferroalloy is 0.1~5wt., and the content of iron is not less than 85wt..

3. The method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution according to claim 1, characterized in that: Step (2) The concentration of ferric chloride solution is 100~300g / L.

4. The method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution according to claim 1, characterized in that: Step (3) The solid-liquid ratio of the low-grade precious metal ferroalloy powder to the ferric chloride solution is 1:5~10 g:mL.

5. The method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution according to claim 1, characterized in that: Step (3) The stirring speed for pressurized leaching is 300~600 rpm, the pressure is 0.2~4 MPa, the temperature is 110~250℃, and the oxidation-reduction potential is 350~500 mV.

6. The method for selectively dissolving and enriching precious metals in low-grade precious metal ferroalloys under pressure using ferric chloride solution according to claim 1, characterized in that: The method for oxidizing and regenerating ferric chloride solution in step (3) is as follows: add hydrogen peroxide solution and hydrochloric acid solution to the leachate. The amount of hydrogen peroxide added is 0.6 to 1.2 times the molar amount of ferrous ions in the leachate, and the amount of HCl added to the hydrochloric acid solution is 1.05 to 1.2 times the molar amount of ferrous ions in the leachate. Under stirring conditions, FeCl2 is oxidized to FeCl3.

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