Method for producing palladium from silver mud

Abstract

One embodiment of the present disclosure discloses a method for producing palladium from silver mud, the method comprising: a gold separation process of introducing silver mud into an acidic solution to produce a separated effluent containing leached palladium; a neutralization process of adding a neutralizing agent to the separation effluent to produce a neutralized precipitate containing palladium oxide; a hydrochloric acid leaching process of adding hydrochloric acid to the effluent containing the neutralized precipitate to produce a hydrochloric acid leachate containing leached palladium and platinum; a chloride precipitation process of adding a precipitating agent to the hydrochloric acid leachate to produce a palladium-containing chloride precipitate; and a purification process for recovering palladium from the chloride precipitate.

Description

Technical Field

[0001] This disclosure relates to a method for producing palladium (Pd) from silver (Ag) slime. More specifically, this disclosure relates to a method for producing high-grade palladium by recovering palladium from silver slime produced during a silver electrolysis process. Background Technology

[0002] To recover palladium (Pd) from the silver sludge produced during the silver electrolysis process, a palladium leaching process is performed using hydrochloric acid (HCl). During this leaching process, most of the platinum (Pt) is also leached out, and the leached platinum is retained until subsequent purification processes. Therefore, to produce high-grade palladium (Pd) with a purity of 99.9% or higher from silver sludge, three or more purification processes are typically performed.

[0003] As the number of purification processes increases, there is an increase in palladium (Pd) loss, which leads to a decrease in palladium recovery and an increase in the auxiliary materials required for the purification process. Summary of the Invention

[0004] Technical issues

[0005] This disclosure aims to provide a method for producing palladium from silver mud, wherein the leaching rate of palladium is kept at a high level while the leaching rate of platinum is reduced during the hydrochloric acid leaching step, thereby reducing the number of purification processes required.

[0006] Technical solution

[0007] According to one embodiment of this disclosure, a method for producing palladium from silver mud is provided, comprising: a gold separation process of introducing silver mud into an acidic solution to produce a separation effluent containing leached palladium; a neutralization process of adding a neutralizing agent to the separation effluent to produce a neutralized precipitate containing palladium oxide; a hydrochloric acid leaching process of adding hydrochloric acid to the effluent containing the neutralized precipitate to produce a hydrochloric acid leaching solution containing leached palladium and platinum; a chloride precipitation process of adding a precipitating agent to the hydrochloric acid leaching solution to produce a chloride precipitate containing palladium; and a purification process for recovering palladium from the chloride precipitate.

[0008] According to one embodiment of this disclosure, during the hydrochloric acid leaching process, the amount of hydrochloric acid added is 9 to 11 equivalents relative to the palladium content in the neutralized precipitate.

[0009] According to one embodiment of this disclosure, the amount of hydrochloric acid added is 10 equivalents relative to the palladium content in the neutralized precipitate.

[0010] According to one embodiment of this disclosure, the concentration of hydrochloric acid is 30% to 40%.

[0011] According to one embodiment of this disclosure, the hydrochloric acid leaching process is carried out at a reaction temperature of 50°C to 70°C.

[0012] According to one embodiment of this disclosure, the neutralization process further includes evaporating a portion of the separated effluent before adding the neutralizing agent.

[0013] According to one embodiment of this disclosure, the purification process includes repeatedly leaching palladium from the chloride precipitate and precipitating the leached palladium.

[0014] Beneficial effects

[0015] According to this disclosure, the leaching rate of platinum, which is the main impurity, can be reduced while maintaining a high leaching rate of palladium.

[0016] Therefore, this disclosure can reduce the number of repetitions of the purification process required to obtain the final palladium, thereby minimizing palladium loss and reducing the amount of auxiliary materials required in the purification process. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a method for producing palladium from silver mud according to an embodiment of this disclosure. Detailed Implementation

[0018] The embodiments disclosed herein are intended to illustrate the technical concept of this disclosure. The scope of this disclosure is not limited to the embodiments described below or a detailed description of such embodiments.

[0019] Figure 1 This is a flowchart illustrating a method for producing palladium from silver mud according to an embodiment of this disclosure.

[0020] See Figure 1 The method (S1) for producing palladium from silver mud may include: a gold separation process (S100) in which a leaching agent is added to the silver mud to separate gold in cake form and palladium is leached into a separation effluent; a neutralization process (S200) in which a neutralizing agent is added to the separation effluent to produce a neutralized precipitate containing palladium oxide; a hydrochloric acid leaching process (S300) in which hydrochloric acid is added to the neutralized precipitate to produce a hydrochloric acid leaching solution containing leached palladium and platinum; a chloride precipitation process (S400) in which a precipitating agent is added to the hydrochloric acid leaching solution to produce a chloride precipitate containing palladium; and a purification process (S500) in which palladium is recovered from the chloride precipitate.

[0021] According to embodiments of this disclosure, a method for producing palladium from silver mud involves producing high-quality palladium from impure silver mud. Silver mud can be produced, for example, during silver electrolysis. In this regard, in addition to silver (Ag), silver mud may contain various metallic elements such as palladium (Pd), platinum (Pt), gold (Au), bismuth (Bi), tellurium (Te), copper (Cu), and lead (Pb). According to embodiments of this disclosure, the method for producing palladium from silver mud focuses on reducing the number of purification processes by maintaining a high leaching rate of palladium while reducing the leaching rate of platinum.

[0022] Gold separation process (S100)

[0023] In the gold separation process (S100), gold (Au) can be separated from silver (Ag) mud. Specifically, in the gold separation process (S100), silver mud is introduced into nitric acid (HNO3) to leach metals including palladium, while the gold not leached into the solution is separated in the form of a cake. The leachate may also contain silver (Ag), bismuth (Bi), platinum, tellurium, copper, and lead, as well as metals such as palladium. The solution from which palladium and other metals are leached and separated from the gold-containing cake is called the "separation effluent". The leaching reaction in the gold separation process can be represented by the following [reaction formula 1]:

[0024] [Reaction Formula 1]

[0025] M+2HNO3→M(NO3)2+H2(g), (M: Pd, Ag, Pt, Bi, Te, Cu, etc.)

[0026] Preferably, the gold separation process (S100) can be carried out at a reaction temperature of 60°C to 80°C for a reaction time of 3 to 5 hours.

[0027] Neutralization process (S200)

[0028] In the neutralization process (S200), the separation effluent is neutralized to produce a precipitate containing palladium oxide (PdO), while silver remains in the solution and can be separated.

[0029] In one embodiment, in the neutralization process (S200), prior to neutralizing the separated effluent, an evaporation process may be performed to evaporate a portion of the separated effluent generated in the gold separation process (S100). This evaporation aims to remove acids (e.g., nitric acid) contained in the separated effluent, thereby reducing the amount of neutralizing agent required in the neutralization process (S200).

[0030] Furthermore, in the neutralization process (S200), the effluent can be diluted with water before the addition of the neutralizing agent. Neutralizing agents such as Na2CO3 or NaOH can be used. Through the neutralization process (S200), palladium is precipitated as palladium oxide (PdO), while silver is not precipitated and silver is mainly separated into the liquid. The precipitate containing palladium oxide is called the "neutralized precipitate". The chemical reaction in the neutralization process can be represented by the following [reaction formula 2]:

[0031] [Reaction 2]

[0032] Pd(NO3)2+ Na2CO3→PdO+2NaNO3+CO2

[0033] Preferably, the neutralization reaction in the neutralization process (S200) can be carried out at a reaction temperature of 60°C to 80°C for a reaction time of 1 hour to 3 hours.

[0034] Hydrochloric acid leaching process (S300)

[0035] In the hydrochloric acid leaching process (S300), hydrochloric acid is used to leach the precipitate after neutralization. During this process (S300), while palladium and platinum are leached into the solution, silver (Ag) that was not removed in the neutralization process (S200) can be precipitated as silver chloride (AgCl). This allows for further separation of silver after the neutralization process (S200). The leachate from this process (S300), containing the leached palladium and platinum, is called the "hydrochloric acid leachate". In the hydrochloric acid leaching process (S300), the leaching reaction can be represented by [Reaction 3], while the precipitation reaction is represented by [Reaction 4]:

[0036] [Reaction 3]

[0037] PdO + 2HCl → PdCl₂ + H₂O

[0038] [Reaction 4]

[0039] AgNO3 + HCl → AgCl + HNO3

[0040] Preferably, when the hydrochloric acid concentration is 30-40%, the hydrochloric acid leaching process is carried out at a reaction temperature of 60-80°C for 2-4 hours (S300).

[0041] The inventors have discovered that by adjusting the amount of hydrochloric acid or the reaction temperature during the hydrochloric acid leaching process, the leaching rate of platinum, the main impurity, can be reduced while maintaining a high leaching rate of palladium. Reducing the platinum leaching rate in the hydrochloric acid leaching process (S300) reduces the number of repetitions required in the subsequent purification process (S500), thereby increasing the palladium yield. For example, a single purification process (S500) may result in the loss of approximately 10% of palladium; therefore, reducing the platinum leaching rate in the hydrochloric acid leaching process (S300) before the purification process is crucial. Furthermore, reducing the platinum leaching rate reduces the amount of auxiliary materials required in repeated purification processes, thereby improving the economic efficiency of palladium production.

[0042] In the implementation scheme, the amount of hydrochloric acid is determined based on the palladium content in the neutralized precipitate (oxidized palladium sludge), but is limited to an amount below a predetermined stoichiometric amount of palladium content. Preferably, the amount of hydrochloric acid used can reach 11 equivalents (eq) relative to the palladium content in the neutralized precipitate formed in the neutralization process (S200). This is because if the amount of hydrochloric acid exceeds 11 equivalents relative to the palladium content in the neutralized precipitate, it may increase the leaching rate of the platinum to be removed. Furthermore, preferably, the amount of hydrochloric acid can be at least 9 equivalents relative to the palladium content, because if the amount of hydrochloric acid is less than 9 equivalents, it may reduce the leaching rate of palladium, which is the target for recovery. Therefore, limiting the amount of hydrochloric acid to 9 to 11 equivalents relative to the palladium content in the neutralized precipitate can achieve optimal results by reducing the leaching rate of platinum while maintaining a high palladium leaching rate.

[0043] In this embodiment, the reaction temperature in the hydrochloric acid leaching process (S300) can be limited to a predetermined temperature. If the reaction temperature exceeds a certain limit, although a high palladium leaching rate can be maintained, the platinum leaching rate may also increase. Preferably, the reaction temperature in the hydrochloric acid leaching process (S300) can be as high as 70°C. Furthermore, the reaction temperature can also preferably be at least a certain temperature (e.g., 50°C), because if the reaction temperature is below a certain level, although it can reduce the platinum leaching rate, it will also reduce the palladium leaching rate, resulting in a lower recovery rate.

[0044] Therefore, according to embodiments of the present invention, the method for producing palladium from silver mud reduces the leaching rate of platinum while effectively maintaining a high palladium leaching rate by limiting the stoichiometry of hydrochloric acid or the reaction temperature to an appropriate range.

[0045] Chloride precipitation process (S400)

[0046] In the chloride precipitation process (S400), palladium can be precipitated and recovered in the form of palladium chloride (PdCl2) by adding a chloride precipitant to the hydrochloric acid leachate (containing leached palladium and platinum) from which silver chloride precipitate has been removed. Ammonium chloride (NH4Cl) and sodium hypochlorite (NaOCl) are examples of precipitants that can be introduced simultaneously. In this case, the precipitation reaction in the chloride precipitation process (S400) can be represented by the following [Reaction Formula 5]. Preferably, the amount of ammonium chloride introduced in the chloride precipitation process (S400) is 2.0 to 3.0 equivalents relative to the palladium content in the hydrochloric acid leachate, while the amount of sodium hypochlorite is 0.5 to 1.5 equivalents relative to the palladium content. In Reaction Formula 5, both ammonium chloride and sodium hypochlorite participate directly in the reaction. The role of sodium hypochlorite is to increase the ORP (oxidation-reduction potential) value of the solution, thereby promoting the reaction. The precipitate containing palladium is called "chloride precipitate", and the precipitate may also contain impurities such as platinum.

[0047] [Reaction 5]

[0048] 2PdCl2+4NH4Cl+4NaOCl+2H2O=2(NH4)2PdCl6+4NaOH+O2(g)

[0049] Preferably, the neutralization reaction in the chloride precipitation process (S400) can be carried out at room temperature for a reaction time of 2 to 4 hours.

[0050] Purification process (S500)

[0051] The purification process (S500) involves repeated leaching and precipitation of the chloride precipitate generated in the chloride precipitation process (S400) to remove impurities such as platinum and ultimately recover high-purity palladium. Specifically, the chloride precipitate is first introduced into ammonium hydroxide (NH4OH) to selectively leach palladium in an ammonium reaction process (S510), followed by the introduction of a precipitant (such as hydrochloric acid (HCl)) to precipitate palladium in a hydrochloric acid reaction process (S520). These processes can be repeated as needed. The reactions in the purification process (S500) can be represented by [Reaction 6] for the ammonium reaction process (S510) and [Reaction 7] for the hydrochloric acid reaction process (S520):

[0052] [Reaction Formula 6]

[0053] (NH4)2PdCl6+2NH4OH=Pd(NH3)4Cl2+H2(g)+2Cl2+2H2O

[0054] [Reaction Formula 7]

[0055] Pd(NH3)4Cl2+2HCl=2Pd(NH3)2Cl2+H2(g)

[0056] Preferably, the ammonium reaction process (S510) in the purification process (S500) can be carried out for 2 to 4 hours at room temperature and pH value of 10 to 11, with a solid density of 80 g / L to 120 g / L.

[0057] The hydrochloric acid reaction process (S520) can be carried out for 2 to 4 hours at room temperature and pH 1 to 2.

[0058] In the embodiments, the purification process (S500) can be repeated as needed to produce high-purity palladium. In this regard, according to embodiments of the present disclosure, the method for producing palladium from silver mud can significantly reduce the number of iterations in the purification process (S500) by limiting the amount of hydrochloric acid and the reaction temperature in the hydrochloric acid leaching process (S300), thereby substantially reducing the leaching rate of platinum. For example, conventional techniques may require three or more iterations of the purification process (S500), while the method according to embodiments of the present disclosure requires only one iteration to produce high-purity palladium. This method minimizes palladium loss and also reduces the amount of auxiliary materials such as leaching agents and precipitants used.

[0059] The following example illustrates a method for producing palladium from silver mud according to this disclosure.

[0060] In the following examples and comparative examples, experiments were conducted using silver (Ag) mud having the following composition.

[0061] Table 1

[0062]

[0063] Gold separation process (S100)

[0064] In the gold separation process (S100), multiple silver mud samples with the same composition were leached with nitric acid (HNO3) under the same conditions. The reaction was carried out at 70°C and a solid density of 250 g / L for 4 hours. The concentrations of metals in the resulting effluent are detailed in the table below.

[0065] Table 2

[0066]

[0067] Neutralization process (S200)

[0068] In the neutralization process (S200), before using sodium carbonate (Na2CO3) as a neutralizing agent for the neutralization reaction, the effluent is evaporated and concentrated, then diluted with distilled water. The reaction is maintained at 70°C for 2 hours, with sodium carbonate added until the final pH reaches 4. After the neutralization reaction, silver (Ag) does not precipitate, thus most of the silver separates into the liquid. The composition of the palladium oxide-containing neutralized precipitate (palladium oxide sludge) is as follows:

[0069] Table 3

[0070]

[0071] Hydrochloric acid leaching process (S300)

[0072] In the hydrochloric acid leaching process (S300), hydrochloric acid was added to the neutralized precipitate to produce a leachate containing leached palladium and platinum. To compare the leaching rates of palladium and platinum under different acid dosages and temperature settings, multiple experiments were conducted. The reaction time was 3 hours, the solid density was 150 g / L, and the hydrochloric acid (HCl) concentration was 35% for all experiments. The measurements of palladium and platinum content in the hydrochloric acid leachate are as follows.

[0073] 1. Relative to the palladium content in the neutralized precipitate, the hydrochloric acid dosage is 16 equivalents of the leachate, and the reaction temperature varies. Spend

[0074] Table 4

[0075]

[0076] 2. The hydrochloric acid dosage is 13 equivalents of the leachate relative to the palladium content in the neutralized precipitate, and the reaction temperature varies. Spend

[0077] Table 5

[0078]

[0079] 3. The hydrochloric acid dosage is 11 equivalents of the leachate relative to the palladium content in the neutralized precipitate, and the reaction temperature varies. Spend

[0080] Table 6

[0081]

[0082] 4. The hydrochloric acid dosage is 10 equivalents of the leachate relative to the palladium content in the neutralized precipitate, and the reaction temperature varies. Spend

[0083] Table 7

[0084]

[0085] 5. The hydrochloric acid dosage is 9 equivalents of the leachate relative to the palladium content in the neutralized precipitate, and the reaction temperature varies.

[0086] Table 8

[0087]

[0088] 6. The hydrochloric acid dosage is 7 equivalents of the leachate relative to the palladium content in the neutralized precipitate, and the reaction temperature varies.

[0089] Table 9

[0090]

[0091] In studying the effect of hydrochloric acid dosage on the leaching of palladium and platinum from the neutralized precipitate in Examples 1, 2, 3 and Comparative Examples 5, 6, and 7, it was found that when the hydrochloric acid dosage exceeded 11 equivalents relative to the palladium content in the neutralized precipitate, the leaching rate of palladium did not significantly change, remaining above 99%. However, the leaching rate of platinum showed a significant difference, increasing to over 60%. On the other hand, in Examples 7, 8, 9 and Comparative Examples 11, 12, and 13, when the hydrochloric acid dosage was less than 9 equivalents relative to the palladium content, the leaching rate of platinum was higher, but the leaching rate of palladium decreased significantly, leading to increased palladium loss. Therefore, to optimally ensure both high palladium leaching rate and low platinum leaching rate simultaneously, it is preferable to control the hydrochloric acid dosage within the range of 9 to 11 equivalents relative to the palladium content. Within this range, a hydrochloric acid dosage of 10 equivalents relative to the palladium content was found to be most suitable for achieving the optimal leaching rates of palladium and platinum.

[0092] Further analysis of Examples 3, 6, and 9 and Comparative Examples 9, 10, and 11 showed that when the reaction temperature of the hydrochloric acid leaching process (S300) exceeded 70°C, the leaching rate of palladium did not change significantly, but the leaching rate of platinum increased sharply. Therefore, maintaining the reaction temperature at or below 70°C during the hydrochloric acid leaching process (S300) ensured a high palladium leaching rate while significantly reducing the leaching rate of the impurity platinum. Notably, lowering the reaction temperature to 50°C did not significantly affect the palladium leaching rate, but the platinum leaching rate decreased significantly compared to palladium. Therefore, setting the reaction temperature to 50°C maintained the optimal palladium leaching rate while minimizing platinum leaching, thus achieving optimal process efficiency.

[0093] Chloride precipitation process (S400)

[0094] In the chloride precipitation process (S400), only Comparative Example 1 and Example 4 were performed, which showed a stark contrast in platinum leaching rates. Ammonium chloride (NH4Cl) and sodium hypochlorite (NaOCl) were introduced to precipitate palladium and platinum. The reaction was maintained at 25°C for 5 hours. The amount of ammonium chloride added was 2.5 equivalents relative to the palladium content in the previous step (hydrochloric acid leaching process), and the amount of sodium hypochlorite added was 1.0 equivalent relative to the palladium content. The composition of the resulting chloride precipitate (Cl2 precipitate cake) is as follows:

[0095] Table 10

[0096]

[0097] Purification process (S500)

[0098] In the purification process (S500), ammonium hydroxide (NH4OH) was introduced into the chloride precipitate produced by the chloride precipitation process (S400) in Comparative Example 1 and Example 4 to selectively leach palladium. The reaction conditions were maintained at 25°C and a solid density of 150 g / L for 3 hours. The amount of ammonium hydroxide added was 9.0 equivalents relative to the palladium content. The palladium and platinum contents in the leachate after the reaction are as follows.

[0099] Table 11

[0100]

[0101] Subsequently, hydrochloric acid was added to the leachate to selectively precipitate palladium. The reaction was maintained at 25°C for 5 hours, with the amount of hydrochloric acid added being 17 equivalents relative to the palladium content. The masses of palladium and platinum in the precipitate after the reaction are as follows:

[0102] Table 12

[0103]

[0104] As described above, according to the method for producing palladium from silver mud of this disclosure, by setting the hydrochloric acid dosage or reaction temperature to a predetermined value, the leaching of platinum during the hydrochloric acid leaching process (S300) can be effectively suppressed. Therefore, a single purification process can minimize the content of impurities (platinum).

[0105] The technical concept of this disclosure has been described through some embodiments and examples shown in the accompanying drawings. However, it should be understood that those skilled in the art to which this disclosure pertains can make various substitutions, modifications, and variations without departing from the technical concept and scope of this disclosure. Furthermore, it should be understood that such substitutions, modifications, and variations all fall within the scope of the appended claims.

Claims

1. A method for producing palladium from silver mud, the method comprising: A gold separation process in which silver mud is introduced into an acidic solution to produce a separation effluent containing leached palladium. A neutralizing process involves adding a neutralizing agent to the separated effluent to produce a neutralized precipitate containing palladium oxide. A hydrochloric acid leaching process in which hydrochloric acid is added to the effluent containing the neutralized precipitate to produce a hydrochloric acid leaching solution containing leached palladium and platinum; A chloride precipitation process in which a precipitant is added to the hydrochloric acid leachate to produce a chloride precipitate containing palladium; as well as The purification process for recovering palladium from the chloride precipitate.

2. The method according to claim 1, wherein the amount of hydrochloric acid added during the hydrochloric acid leaching process is 9 to 11 equivalents relative to the palladium content in the neutralized precipitate.

3. The method according to claim 2, wherein the amount of hydrochloric acid added is 10 equivalents relative to the palladium content in the neutralized precipitate.

4. The method according to any one of claims 1 to 3, wherein the concentration of the hydrochloric acid is 30% to 40%.

5. The method according to claim 1, wherein the hydrochloric acid leaching process is carried out at a reaction temperature of 50°C to 70°C.

6. The method of claim 1, wherein the neutralization process further comprises evaporating a portion of the separated effluent before adding the neutralizing agent.

7. The method of claim 1, wherein the purification process comprises repeatedly leaching palladium from the chloride precipitate and precipitating the leached palladium.

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