A sequential palladium and selective silver precipitation process for silver nitrate leach solutions

Abstract

The present application relates to the technical field of rare and precious metal hydrometallurgy, and particularly relates to a method for sequentially precipitating palladium and selectively precipitating silver from silver nitrate leaching solution, which comprises the following steps: filtering and removing impurities from the silver nitrate leaching solution, adjusting the pH value of the leaching solution to 1.0-2.0, and controlling the temperature to be 30-40 DEG C; adding N-phenyl thiourea chelate palladium precipitating reagent to the pretreated silver nitrate leaching solution, and controlling the reaction time to be 1.0-2.0 h, the pH value to be 1.0-2.0 during the reaction process, and the temperature to be 30-40 DEG C; filtering after the reaction is completed to obtain palladium chelate precipitate and palladium-precipitated solution; adding composite reduction silver precipitating reagent to the palladium-precipitated solution, adjusting the pH value to be 2.5-3.5, controlling the temperature to be 45-55 DEG C, and controlling the reaction time to be 0.8-1.5 h; filtering after the reaction is completed to obtain elemental silver precipitate and silver-precipitated solution; washing and roasting the palladium chelate precipitate, acid dissolving and refining after cooling to obtain palladium products with a purity of greater than or equal to 99.97%; and washing the elemental silver precipitate to neutral, drying to obtain silver products with a purity of greater than or equal to 99.95%. The present application realizes efficient sequential separation of silver and palladium from the silver nitrate leaching solution, and no chlorine-containing reagent is needed in the whole process.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology for rare and precious metals, specifically to a method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution. Background Technology

[0002] In the field of rare and precious metal extraction and resource recovery, nitric acid leachate is a highly valuable intermediate product with a wide range of sources, including silver anode mud, silver-containing spent catalysts, silver-containing minerals, and electronic waste. The silver and palladium ions enriched in the leachate are high-value rare and precious metals, and their efficient separation and purification directly determine resource utilization and economic benefits. However, silver and palladium have similar chemical properties and readily form complexes of similar stability in the nitric acid system, making their selective separation extremely difficult and becoming a key technological bottleneck restricting the industry's development.

[0003] Currently, the main industrial techniques for separating silver and palladium from silver nitrate leachates include chemical precipitation, solvent extraction, ion exchange, and electrochemical separation. However, each method has significant drawbacks. Solvent extraction relies on large amounts of specialized organic extractants, which is not only costly but also causes environmental pollution due to extractant loss and degradation. Furthermore, the subsequent back-extraction and washing processes are cumbersome, resulting in significant reagent consumption and making it unsuitable for large-scale industrial continuous production. While ion exchange is gentler, the limited adsorption capacity of specialized resins leads to low efficiency in treating high-concentration leachates. Frequent resin regeneration results in high costs for regenerator consumption and wastewater treatment, making it economically infeasible. Electrochemical separation requires demanding equipment, necessitating precise control of parameters such as electrode potential and current density. It is also susceptible to interference from impurity ions in the solution, leading to fluctuations in product purity and limiting its industrial application.

[0004] Chemical precipitation has become the most widely used separation technology in industry due to its advantages such as simple operation, low equipment investment, and fast reaction rate. However, traditional chemical precipitation methods have many insurmountable problems: the palladium precipitation stage often uses traditional chelating agents such as dimethylglyoxime and dimethylglyoxime. These reagents have insufficient specific chelating ability for palladium ions and are prone to side reactions with silver ions and impurity ions such as copper and iron in the solution, resulting in low purity of palladium precipitation and increased difficulty in subsequent purification; the silver precipitation stage often relies on chlorine-containing reagents such as chlorides. Although silver precipitation can be achieved, it will generate insoluble silver chloride precipitate, requiring additional reduction and smelting processes, which are lengthy and energy-intensive. At the same time, the use of chlorine-containing reagents will cause serious corrosion to production equipment and pipelines, increasing equipment maintenance costs and safety risks; in addition, the reaction efficiency of a single precipitation reagent is limited, and problems such as incomplete separation of silver and palladium and low recovery rate are easy to occur, making it difficult to balance separation efficiency and product purity.

[0005] Patent CN102041393A discloses a method for recovering silver and palladium from a nitric acid solution containing silver and palladium. This method employs a process route of first precipitating silver with hydrochloric acid, followed by precipitating palladium with an amine reagent. While this achieves preliminary separation of silver and palladium, it still has significant technical shortcomings: Firstly, relying on chloride precipitation inevitably produces silver chloride precipitate, requiring subsequent reduction with hydrazine hydrate to obtain metallic silver, making the process cumbersome and increasing reducing agent consumption. Secondly, the amine reagent for palladium precipitation has poor selectivity and is easily interfered with by nitrate ions and impurity metal ions in the nitric acid system, resulting in a palladium recovery rate of only about 95%. Furthermore, the precipitate contains numerous impurities, affecting subsequent refining effects. Simultaneously, the use of a chlorine-containing system cannot avoid equipment corrosion and chlorine-containing wastewater treatment issues, which is inconsistent with the current trend of green and low-carbon industrial development. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution includes the following steps:

[0009] (1) Pretreatment: The silver nitrate leaching solution is filtered to remove impurities, the pH value of the leaching solution is adjusted to 1.0-2.0, and the temperature is controlled at 30-40℃;

[0010] (2) Sequential palladium precipitation: N-phenylthiourea chelating palladium precipitation reagent is added to the pretreated silver nitrate leaching solution. The molar ratio of the palladium precipitation reagent to palladium ions in the leaching solution is 1.3-1.8:1. The stirring rate is 180-250 r / min. The reaction time is 1.0-2.0 h. The pH value during the reaction is 1.0-2.0. After the reaction is completed, the solution is filtered to obtain palladium chelate precipitate and palladium precipitation solution.

[0011] (3) Selective silver precipitation: Add a composite reducing silver precipitation reagent to the palladium precipitation solution obtained in step (2). The composite reducing silver precipitation reagent includes sodium bisulfite and sodium metabisulfite. The mass ratio of sodium bisulfite to sodium metabisulfite is 2-3:1. The molar ratio of the composite reducing silver precipitation reagent to silver ions in the silver precipitation solution is 1.2-1.5:1. Adjust the pH value to 2.5-3.5, the temperature to 45-55℃, the stirring rate to 150-200r / min, and the reaction time to 0.8-1.5h. After the reaction is completed, filter to obtain silver elemental precipitate and silver precipitation solution.

[0012] (4) Product purification: The palladium chelate precipitate obtained in step (2) is washed with hydrochloric acid solution 2-3 times, calcined at 650-750℃ for 1.5-2.5h, cooled and then refined by acid dissolution to obtain a palladium product with a purity ≥99.97%; the silver elemental precipitate obtained in step (3) is washed with deionized water until neutral, and dried to obtain a silver product with a purity ≥99.95%.

[0013] Furthermore, in step (1), the silver nitrate leaching solution is a nitric acid system leaching solution containing silver and palladium, with a silver ion concentration of 50-80 g / L and a palladium ion concentration of 0.5-2.0 g / L.

[0014] Further, in step (2), the N-phenylthiourea chelating palladium precipitating reagent is p-methylphenylthiourea or p-chlorophenylthiourea.

[0015] Furthermore, in step (3), the composite reduction silver precipitate reagent is added by dropping, with a dropping rate of 5-10 mL / min.

[0016] Further, in step (4), the concentration of the hydrochloric acid solution used to wash the palladium chelate precipitate is 0.5-1.0 mol / L, and the washing temperature is 30-40℃.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention provides a method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solutions. Through a step-by-step process design of pretreatment-sequential palladium precipitation-selective silver precipitation-product purification, it utilizes N-phenylthiourea-based specific chelating palladium precipitation reagents and sodium bisulfite-sodium metabisulfite composite reducing silver precipitation reagents. Combined with precise control of parameters such as pH, temperature, and stirring rate, it achieves highly efficient sequential separation of silver and palladium in silver nitrate leaching solutions. The entire process requires no chlorine-containing reagents, completely avoiding silver chloride precipitation and equipment corrosion problems, and simplifying subsequent processing. The palladium precipitation reagent... It exhibits extremely high selectivity for palladium ions and outstanding resistance to impurity interference, with palladium recovery rate ≥99.5% and product purity ≥99.97%. The composite reduction silver precipitation reagent synergistically enhances the silver ion reduction efficiency and precipitation purity, with silver recovery rate ≥99% and product purity ≥99.5%. The process is simple to operate, with mild reaction conditions, requiring no high-temperature or high-pressure equipment, reasonable reagent consumption, and a concise product purification process, making it suitable for large-scale industrial production. At the same time, it reduces waste liquid discharge and environmental treatment pressure, taking into account efficient resource recovery, high product purity, low production cost, and environmental friendliness. Attached Figure Description

[0019] The embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

[0020] Figure 1 A process flow diagram of the present invention is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Reference Appendix Figure 1 A method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution includes the following steps:

[0023] (1) Pretreatment: The silver nitrate leaching solution is filtered to remove impurities, the pH value of the leaching solution is adjusted to 1.0-2.0, and the temperature is controlled at 30-40℃;

[0024] (2) Sequential palladium precipitation: N-phenylthiourea chelating palladium precipitation reagent is added to the pretreated silver nitrate leaching solution. The molar ratio of palladium precipitation reagent to palladium ions in the leaching solution is 1.3-1.8:1. The stirring rate is 180-250 r / min. The reaction time is 1.0-2.0 h. The pH value during the reaction is 1.0-2.0. After the reaction is completed, the solution is filtered to obtain palladium chelate precipitate and palladium precipitation solution.

[0025] (3) Selective silver precipitation: Add a composite reducing silver precipitation reagent to the palladium precipitation solution obtained in step (2). The composite reducing silver precipitation reagent includes sodium bisulfite and sodium metabisulfite. The mass ratio of sodium bisulfite to sodium metabisulfite is 2-3:1. The molar ratio of the composite reducing silver precipitation reagent to silver ions in the silver precipitation solution is 1.2-1.5:1. Adjust the pH value to 2.5-3.5, the temperature to 45-55℃, the stirring rate to 150-200r / min, and the reaction time to 0.8-1.5h. After the reaction is completed, filter to obtain silver element precipitate and silver precipitation solution.

[0026] (4) Product purification: The palladium chelate precipitate obtained in step (2) is washed with hydrochloric acid solution 2-3 times, calcined at 650-750℃ for 1.5-2.5h, cooled and then refined by acid dissolution to obtain a palladium product with a purity ≥99.97%; the silver elemental precipitate obtained in step (3) is washed with deionized water until neutral, and dried to obtain a silver product with a purity ≥99.95%.

[0027] In one embodiment of the present invention, in step (1), the silver nitrate leaching solution is a nitric acid system leaching solution containing silver and palladium, with a silver ion concentration of 50-80 g / L and a palladium ion concentration of 0.5-2.0 g / L.

[0028] In one embodiment of the present invention, in step (2), the N-phenylthiourea chelating palladium precipitation reagent is p-methylphenylthiourea or p-chlorophenylthiourea.

[0029] In one embodiment of the present invention, in step (3), the composite reduction silver precipitate reagent is added by dropping, with a dropping rate of 5-10 mL / min.

[0030] In one embodiment of the present invention, in step (4), the concentration of the hydrochloric acid solution used to wash the palladium chelate precipitate is 0.5-1.0 mol / L, and the washing temperature is 30-40℃.

[0031] Example 1

[0032] A method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution includes the following steps:

[0033] (1) Pretreatment: Take silver nitrate leaching solution (a nitric acid system leaching solution containing 50 g / L silver and 0.5 g / L palladium), filter it to remove insoluble solid particles, adjust the pH of the leaching solution to 1.0, and control the system temperature to 30℃.

[0034] (2) Sequential palladium precipitation: p-methylphenylthiourea was added to the pretreated silver nitrate leaching solution. The molar ratio of the palladium precipitating reagent to palladium ions in the leaching solution was 1.3:1. The stirring rate was set to 180 r / min, the reaction time was 1.0 h, and the pH was maintained at 1.0 during the reaction. After the reaction was completed, the solution was filtered to obtain palladium chelate precipitate and palladium precipitation solution.

[0035] (3) Selective silver precipitation: A composite reducing silver precipitation reagent (sodium bisulfite to sodium metabisulfite mass ratio 2:1) was added to the palladium precipitation solution. The molar ratio of the composite reducing silver precipitation reagent to silver ions in the silver precipitation solution was 1.2:1. The pH of the system was adjusted to 2.5, the temperature was controlled at 45℃, the stirring rate was 150 r / min, and the reaction time was 0.8 h. After the reaction was completed, the mixture was filtered to obtain elemental silver precipitate and the silver precipitation solution.

[0036] (4) Product purification: The palladium chelate precipitate was washed twice with 0.5 mol / L hydrochloric acid solution at 30°C, then calcined at 650°C for 1.5 h, cooled and refined by acid dissolution to obtain the palladium product with a purity of 99.97% and a palladium recovery rate of 99.5%; the silver element precipitate was washed with deionized water until neutral, dried and obtained the silver product with a purity of 99.96% and a silver recovery rate of 99.1%.

[0037] Example 2

[0038] A method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution includes the following steps:

[0039] (1) Pretreatment: Take silver nitrate leaching solution (a nitric acid system leaching solution containing 80 g / L silver and 2.0 g / L palladium), filter it to remove impurities and insoluble solid particles, adjust the pH value of the leaching solution to 2.0, and control the system temperature to 40℃.

[0040] (2) Sequential palladium precipitation: p-chlorophenylthiourea was added to the pretreated silver nitrate leaching solution. The molar ratio of the palladium precipitation reagent to palladium ions in the leaching solution was 1.8:1. The stirring rate was 250 r / min, the reaction time was 2.0 h, and the pH was maintained at 2.0 during the reaction. After the reaction was completed, the solution was filtered to obtain palladium chelate precipitate and palladium precipitation solution.

[0041] (3) Selective silver precipitation: Add a composite reducing silver precipitation reagent (sodium bisulfite to sodium metabisulfite mass ratio 3:1) to the palladium precipitation solution. The molar ratio of the composite reducing silver precipitation reagent to silver ions in the silver precipitation solution is 1.5:1. Adjust the pH to 3.5, control the temperature at 55℃, the stirring rate at 200 r / min, and the reaction time at 1.5 h. After the reaction is complete, filter to obtain elemental silver precipitate and silver precipitation solution.

[0042] (4) Product purification: The palladium chelate precipitate was washed three times with 1.0 mol / L hydrochloric acid solution at 40°C, calcined at 750°C for 2.5 h, cooled and then refined by acid dissolution to obtain the palladium product with a purity of 99.98% and a palladium recovery rate of 99.7%; the silver element precipitate was washed with deionized water until neutral, dried and then the silver product was obtained with a purity of 99.97% and a silver recovery rate of 99.3%.

[0043] Example 3

[0044] A method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution includes the following steps:

[0045] (1) Pretreatment: Take silver nitrate leaching solution (a nitric acid system leaching solution containing 65 g / L silver and 1.2 g / L palladium), filter it to remove insoluble solid particles, adjust the pH value of the leaching solution to 1.5, and control the system temperature to 35℃.

[0046] (2) Sequential palladium precipitation: p-methylphenylthiourea was added to the pretreated silver nitrate leaching solution. The molar ratio of the palladium precipitation reagent to palladium ions in the leaching solution was 1.5:1. The stirring rate was 220 r / min, the reaction time was 1.5 h, and the pH was maintained at 1.5 during the reaction. After the reaction was completed, the solution was filtered to obtain the palladium chelate precipitate and the palladium precipitation solution.

[0047] (3) Selective silver precipitation: A composite reducing silver precipitation reagent (sodium bisulfite to sodium metabisulfite mass ratio 2.5:1) was added to the palladium precipitation solution. The molar ratio of the composite reducing silver precipitation reagent to silver ions in the silver precipitation solution was 1.3:1. The pH was adjusted to 3.0, the temperature was controlled at 50℃, the stirring rate was 180 r / min, and the reaction time was 1.2 h. The composite reducing silver precipitation reagent was added dropwise at a rate of 8 mL / min. After the reaction was completed, the mixture was filtered to obtain elemental silver precipitate and the silver precipitation solution.

[0048] (4) Product purification: The palladium chelate precipitate was washed three times with 0.8 mol / L hydrochloric acid solution at 35°C, calcined at 700°C for 2.0 h, cooled and then refined by acid dissolution to obtain the palladium product with a purity of 99.97% and a palladium recovery rate of 99.5%; the silver element precipitate was washed with deionized water until neutral, dried and then the silver product was obtained with a purity of 99.95% and a silver recovery rate of 99.5%.

[0049] This invention provides a method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solutions. Through a step-by-step process design of pretreatment-sequential palladium precipitation-selective silver precipitation-product purification, it utilizes N-phenylthiourea-based specific chelating palladium precipitation reagents and sodium bisulfite-sodium metabisulfite composite reducing silver precipitation reagents. Combined with precise control of parameters such as pH, temperature, and stirring rate, it achieves highly efficient sequential separation of silver and palladium in silver nitrate leaching solutions. The entire process requires no chlorine-containing reagents, completely avoiding silver chloride precipitation and equipment corrosion problems, and simplifying subsequent processing. The palladium precipitation reagent... It exhibits extremely high selectivity for palladium ions and outstanding resistance to impurity interference, with palladium recovery rate ≥99.5% and product purity ≥99.97%. The composite reduction silver precipitation reagent synergistically enhances the silver ion reduction efficiency and precipitation purity, with silver recovery rate ≥99% and product purity ≥99.5%. The process is simple to operate, with mild reaction conditions, requiring no high-temperature or high-pressure equipment, reasonable reagent consumption, and a concise product purification process, making it suitable for large-scale industrial production. At the same time, it reduces waste liquid discharge and environmental treatment pressure, taking into account efficient resource recovery, high product purity, low production cost, and environmental friendliness.

[0050] The foregoing descriptions have outlined some exemplary embodiments of the present invention. It is understood that these embodiments are merely illustrative and do not constitute a limitation on the scope of protection of the present invention. Features in these embodiments can be rearranged in suitable ways, and the resulting solutions remain within the scope of protection claimed by the present invention. All other embodiments obtained by those skilled in the art based on the foregoing embodiments without inventive effort, i.e., all modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution, characterized in that, Includes the following steps: (1) Pretreatment: The silver nitrate leaching solution is filtered to remove impurities, the pH value of the leaching solution is adjusted to 1.0-2.0, and the temperature is controlled at 30-40℃; (2) Sequential palladium precipitation: N-phenylthiourea chelating palladium precipitation reagent is added to the pretreated silver nitrate leaching solution. The molar ratio of the palladium precipitation reagent to palladium ions in the leaching solution is 1.3-1.8:

1. The stirring rate is 180-250 r / min. The reaction time is 1.0-2.0 h. The pH value during the reaction is 1.0-2.

0. After the reaction is completed, the solution is filtered to obtain palladium chelate precipitate and palladium precipitation solution. (3) Selective silver precipitation: Add a composite reducing silver precipitation reagent to the palladium precipitation solution obtained in step (2). The composite reducing silver precipitation reagent includes sodium bisulfite and sodium metabisulfite. The mass ratio of sodium bisulfite to sodium metabisulfite is 2-3:

1. The molar ratio of the composite reducing silver precipitation reagent to silver ions in the silver precipitation solution is 1.2-1.5:

1. Adjust the pH value to 2.5-3.5, the temperature to 45-55℃, the stirring rate to 150-200r / min, and the reaction time to 0.8-1.5h. After the reaction is completed, filter to obtain silver elemental precipitate and silver precipitation solution. (4) Product purification: The palladium chelate precipitate obtained in step (2) is washed with hydrochloric acid solution 2-3 times, calcined at 650-750℃ for 1.5-2.5h, cooled and then refined by acid dissolution to obtain a palladium product with a purity ≥99.97%; the silver elemental precipitate obtained in step (3) is washed with deionized water until neutral, and dried to obtain a silver product with a purity ≥99.95%.

2. The method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution according to claim 1, characterized in that, In step (1), the silver nitrate leaching solution is a nitric acid system leaching solution containing silver and palladium, with a silver ion concentration of 50-80 g / L and a palladium ion concentration of 0.5-2.0 g / L.

3. The method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution according to claim 1, characterized in that, In step (2), the N-phenylthiourea chelating palladium precipitating reagent is p-methylphenylthiourea or p-chlorophenylthiourea.

4. The method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution according to claim 1, characterized in that, In step (3), the composite reduction silver precipitation reagent is added by dropping, with a dropping rate of 5-10 mL / min.

5. The method for sequential palladium precipitation and selective silver precipitation of silver nitrate leaching solution according to claim 1, characterized in that, In step (4), the concentration of the hydrochloric acid solution used to wash the palladium chelate precipitate is 0.5-1.0 mol / L, and the washing temperature is 30-40℃.

Images