Waste iron scrap reduction-low-temperature arsenic fixation and copper removal method

Abstract

The invention provides a waste iron scrap reduction-low-temperature arsenic fixation and copper removal method which can comprise the following steps: drying and sieving arsenic-containing anode slime to obtain anode slime powder; the anode slime powder and the scrap iron are mixed and subjected to reactive smelting in the inert atmosphere at the temperature of 500-600 DEG C till the reaction is finished, a reduction smelting product is obtained, and the reduction smelting product is composed of a slag layer containing elemental copper and a metal layer containing elemental arsenic; and the metal layer is subjected to vacuum distillation, and metal contained in the arsenic-containing anode slime is recycled. According to the method disclosed by the invention, highly toxic and volatile arsenic oxide is reduced and elemental arsenic is fixed at low temperature by utilizing the scrap iron, so that secondary pollution of arsenic is avoided from the source, and harmless treatment is realized.

Description

Technical Field

[0001] This invention relates to the field of resource recycling, and more specifically, to a method for reducing waste iron scraps and removing copper by low-temperature arsenic fixation. Background Technology

[0002] Copper and lead anode sludge are important byproducts of copper and lead electrolytic refining processes, rich in valuable metals such as gold, silver, platinum, and palladium, and possess extremely high comprehensive recycling value. However, anode sludge often contains large amounts of arsenic, frequently existing as arsenic oxides (such as As₂O₃ and As₂O₅). Arsenic is a highly toxic element; if not effectively controlled during treatment, it will not only seriously harm the ecological environment and human health but also affect the recovery efficiency of valuable metals and product quality, increasing the cost of subsequent environmental remediation.

[0003] Currently, the mainstream methods for treating arsenic-containing anode sludge include pyrometallurgical processes and hydrometallurgical processes. Traditional pyrometallurgical processes, such as roasting-smelting, are typically carried out at high temperatures, resulting in high energy consumption and a high risk of arsenic entering the flue gas as volatile arsenic trioxide, causing arsenic dispersion and secondary pollution, placing enormous pressure on dust collection and flue gas purification systems. While hydrometallurgical processes avoid the high-temperature volatilization problem to some extent, they often require the use of strong oxidants or reducing agents (such as SO2, Na2S, etc.) in the arsenic removal stage, resulting in a longer process flow and the potential generation of complex arsenic-containing waste liquid or hazardous waste residue, making subsequent treatment still challenging. Regardless of whether it is a pyrometallurgical or hydrometallurgical process, how to achieve efficient, stable, and safe solidification of arsenic, ultimately forming an environmentally friendly stable product, remains a technical challenge in the industry.

[0004] On the other hand, industries such as machining generate a large amount of scrap iron every year. Its clean surface and high reactivity make it a potential low-cost source of iron. However, current utilization methods for scrap iron are relatively limited, mostly using it only as a raw material for steelmaking or for simple disposal, failing to fully explore its application potential in high-value-added environmental protection technologies.

[0005] Therefore, there is an urgent need in this field to develop an innovative technology that can solve the two problems mentioned above at the same time: to achieve both efficient reduction and stable solidification of arsenic in anode mud under mild conditions, and to realize the high-value resource utilization of waste iron filings. Summary of the Invention

[0006] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a method for reducing and fixing arsenic and removing copper from arsenic-containing anode mud at low temperatures.

[0007] This invention provides a method for reducing and removing copper from waste iron scrap using low-temperature arsenic fixation, which may include the following steps: drying and sieving arsenic-containing anode mud to obtain anode mud powder; mixing the anode mud powder with waste iron scrap and reacting and smelting it under an inert atmosphere at 500℃~600℃ until the reaction is completed to obtain a reduction smelting product, wherein the reduction smelting product consists of a slag layer containing elemental copper and a metal layer containing elemental arsenic; and vacuum distilling the metal layer to recover the metal contained in the arsenic-containing anode mud.

[0008] Furthermore, the reduction smelting time can be 2 to 3 hours.

[0009] Furthermore, the mass percentage of elemental iron in the scrap iron can be 70% to 85%, and the mass percentage of ferrous oxide can be 10% to 20%.

[0010] Furthermore, the amount of scrap iron added can be 7% to 15% of the mass of the anode mud powder.

[0011] Furthermore, it may also include adding metallic lead to the mixture of anode mud powder and scrap iron.

[0012] Furthermore, metallic lead can be 30% to 40% of the mass of the anode mud powder.

[0013] Furthermore, the arsenic-containing anode mud is at least one of lead anode mud and copper anode mud.

[0014] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0015] (1) The method of the present invention utilizes waste iron filings to reduce highly toxic and volatile arsenic oxide at low temperature and fix elemental arsenic, thereby eliminating secondary pollution of arsenic from the source and achieving harmless treatment.

[0016] (2) The waste iron filings in the method of the present invention serve as a reducing agent, an arsenic fixation agent and a copper removal agent. By generating a matte phase, copper removal and selenium and tellurium enrichment are completed in one step, replacing the traditional complex wet copper removal process and greatly shortening the process. The pre-treatment of arsenic and copper reduces the interference of subsequent precious metal recovery. The matte phase enrichment creates favorable conditions for the recovery of copper, selenium and tellurium, and is expected to improve the overall recovery rate.

[0017] (3) The method of the present invention transforms waste iron filings into an effective medium for treating hazardous anode mud, realizing the synergistic resource utilization of the two types of waste, which is in line with the concept of green circular economy. Attached Figure Description

[0018] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 This is the XRD pattern of lead anode mud.

[0020] Figure 2 This is a SEM image of lead anode mud.

[0021] Figure 3 The XRD pattern of the smelting product in Example 1 is shown.

[0022] Figure 4 The XRD pattern of the smelting product is shown in Example 2.

[0023] Figure 5 The XRD pattern of the reduced smelting product is shown in Comparative Example 1.

[0024] Figure 6 The XRD pattern of the reduced smelting product is shown in Comparative Example 2. Detailed Implementation

[0025] In the following, a method for reducing waste iron scraps to remove copper at low temperature and solidifying arsenic will be described in detail according to the present invention, in conjunction with the accompanying drawings and exemplary embodiments.

[0026] Specifically, this invention provides an innovative method for treating copper / lead anode mud using scrap iron. This invention cleverly utilizes the active components in scrap iron (mainly elemental iron and ferrous oxide) as a multifunctional reaction medium to simultaneously achieve arsenic reduction and fixation, as well as the separation of valuable metals, in an integrated process. On one hand, this invention uses elemental iron (Fe) and ferrous oxide (FeO) in scrap iron as highly efficient reducing agents, selectively reducing highly toxic arsenic oxides (such as As₂O₃) in the anode mud to low-toxicity elemental arsenic at a relatively low smelting temperature of 500℃~600℃. Compared with traditional high-temperature pyrometallurgical processes, this process significantly inhibits arsenic volatilization, avoiding secondary pollution at the source. On the other hand, scrap iron not only acts as a reducing agent, but the iron source it provides can also react with the generated elemental arsenic to form stable intermetallic compounds or solid solutions, thereby firmly fixing the elemental arsenic. This achieves arsenic stabilization / solidification, greatly reducing the environmental risk of the product and providing possibilities for the safe disposal or subsequent resource utilization of arsenic. Furthermore, in the reducing smelting environment of this invention, the iron components in the scrap iron can undergo a sulfidation reaction with sulfides (such as Cu2S) in the anode mud to generate FeS. The generated FeS floats to the surface and forms a very thin matte phase. This matte phase has excellent trapping ability and can efficiently enrich valuable elements such as copper (Cu), selenium (Se), and tellurium (Te) in the anode mud, thereby achieving copper removal from the anode mud and preliminary separation of valuable elements in a single step within the pyrometallurgical system. This process completely eliminates the traditional complex wet copper removal process that generates large amounts of copper-containing wastewater, simplifying the process and reducing environmental pressure.

[0027] This invention provides a method for reducing and removing copper from waste iron scrap using low-temperature arsenic fixation. In some embodiments, the method may include the following steps:

[0028] Step S01: Dry the arsenic-containing anode mud, sieve it, and obtain anode mud powder;

[0029] Step S02: Mix the anode mud powder with waste iron filings and smelt them in an inert atmosphere at 500℃~600℃ until the reaction is complete to obtain a reduction smelting product, wherein the reduction smelting product consists of a slag layer containing elemental copper and a metal layer containing elemental arsenic.

[0030] Step S03: Vacuum distillation is performed on the metal layer to recover the metal contained in the arsenic-containing anode mud.

[0031] In some implementations, the arsenic-containing anode mud can be at least one of copper anode mud and lead anode mud produced during the electrolytic refining of copper and lead.

[0032] In some implementations, arsenic-containing anode slime can be dried in a vacuum chamber. The drying temperature must be controlled during the process to prevent the volatilization of arsenic oxide. For example, the drying temperature is 120°C to 170°C. The dried anode slime is then sieved to obtain anode slime powder.

[0033] In some implementations, the scrap iron can be crushed and then mixed with anode mud powder. For example, the scrap iron can be crushed, mixed evenly with anode mud powder, placed in an alumina crucible, covered with an alumina lid, placed in a sealed reactor, and then placed in a muffle furnace. The reactor is then subjected to a gas washing operation, and inert gas is introduced. When the pressure gauge shows positive pressure (one atmosphere), the reaction temperature is set to 500℃~600℃, and the reduction time is 2h~3h. After the reaction and smelting are completed, a reaction product is obtained with a slag layer on top and a metal layer on the bottom. Because the FeS generated during the reaction will float to the surface and form a very thin matte phase, this matte phase has excellent capturing ability and can efficiently enrich valuable elements such as copper (Cu), selenium (Se), and tellurium (Te) in the anode mud. Therefore, the slag layer contains valuable elements such as copper (Cu), selenium (Se), and tellurium (Te), and the separation and recovery of valuable elements such as copper, selenium, and tellurium can be achieved using traditional copper smelting processes. The metal layer contains elements such as arsenic and precious metals. Different substances within the metal layer can be separated and recovered through processes such as vacuum distillation. In some embodiments, the reaction melting temperature can be 520℃~580℃, and the reduction time can be 2.1h~2.8h. For example, the reaction melting temperature can be 540℃~570℃, and the reduction time can be 2.3h~2.5h. Yet another example is a reaction melting temperature of 550℃~560℃, and a reduction time of 2.4h~2.6h.

[0034] In some implementation schemes, the mass ratio of elemental iron to ferrous oxide in the scrap iron is 70%–85% iron and 10%–20% ferrous oxide. The scrap iron contains a suitable amount of elemental iron as the main agent for reduction and arsenic fixation, while also containing an appropriate amount of ferrous oxide to regulate slag fluidity and assist the reaction. If Fe is too high and FeO is too low: the reduction and arsenic fixation capabilities are strong, but it may lead to a viscous melt, poor separation effect, and increased energy consumption. If FeO is too high and Fe is too low: the slag fluidity is good, but the reduction and arsenic fixation capabilities are insufficient, and the risk of arsenic volatilization loss increases. For example, the mass ratio of elemental iron to ferrous oxide in the scrap iron is 72%–79% iron and 12%–15% ferrous oxide. Another example is a mass ratio of 74%–77% iron and 13%–14% ferrous oxide.

[0035] In some implementations, in order to completely reduce and fix the arsenic in the anode mud, the amount of waste iron filings added can be 7% to 15% of the mass of the anode mud powder. For example, the amount of waste iron filings added can be a combination of 8% to 14%, 9% to 13%, 10% to 12% or more of the mass of the anode mud powder.

[0036] In some implementations, metallic lead is added to the mixture of anode mud powder and scrap iron. Because metallic lead has a low melting point and the reduction reaction between the anode mud powder and scrap iron is more complete in the molten lead environment, the lead melt encapsulates the anode mud for reduction smelting and arsenic fixation. This further lowers the reduction smelting and arsenic fixation temperature and ensures a more complete reaction, guaranteeing that all oxides in the anode mud are reduced. For example, the addition of metallic lead can achieve the reduction of arsenic and other metals at a reaction smelting temperature of 400℃ to 600℃.

[0037] In some implementations, the mass of metallic lead is 30-40% of the mass of the anode mud powder. With this amount of lead, the anode mud can be completely coated with lead, placing it in a molten environment to lower the temperature for arsenic reduction. Through the synergistic effect of iron filings and lead, arsenic reduction can be achieved by reducing and smelting at 400℃~600℃ for 2-3 hours. For example, the amount of lead added can be a combination of 32%~38%, 34%~37%, 35%~36% or more of the mass of the anode mud powder.

[0038] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0039] Example 1

[0040] A method for reducing scrap iron filings and removing copper by low-temperature arsenic fixation may include the following steps:

[0041] Step 1: Weigh 50g of lead anode mud (content detection results are shown in Table 1, XRD results are shown in Table 1). Figure 1 As shown, the SEM results are as follows: Figure 2 (As shown) The sample was placed in a vacuum drying oven and dried. The drying temperature of the vacuum drying oven was set to 150℃, the pressure to 1000Pa, and the drying time to 20h, resulting in 41g of dried anode mud.

[0042] Step 2: Crush the scrap iron filings (content analysis shown in Table 2). Add 4g of scrap iron filings to the dried anode mud and mix thoroughly. Place the mixture into an alumina crucible, cover it, and place it in the reactor. Place the reactor in a muffle furnace and perform a gas purging operation. Then, purge the reactor with nitrogen gas until the pressure gauge reads one atmosphere, at which point the purging is stopped. Set the heating program, setting the reduction melting temperature to 520℃ and the reduction time to 2 hours. Once the furnace temperature has cooled to room temperature, remove the reactor and collect the product. Perform ICP analysis on the product; the results are shown in Table 3. XRD results are shown below. Figure 3 As shown.

[0043] Table 1 Composition of lead anode mud

[0044]

[0045] Table 2 Composition of scrap iron

[0046]

[0047] Table 3 Composition of the product from Example 1

[0048]

[0049] From Table 3 and Figure 3 As can be seen, through the method of the present invention, the arsenic oxide in the lead anode mud is effectively reduced by the iron source in the waste iron filings and exists in the reduction product in the form of elemental arsenic, thus avoiding environmental pollution. The arsenic fixation rate can reach about 84%, and the copper content in the product is reduced to 0.01%, thus achieving copper removal from the anode mud.

[0050] Example 2

[0051] A method for reducing scrap iron filings and removing copper by low-temperature arsenic fixation may include the following steps:

[0052] Step 1: Weigh 50g of lead anode mud (content detection results are shown in Table 1, XRD results are shown in Table 1). Figure 1 As shown, the SEM results are as follows: Figure 2 (As shown) The sample was placed in a vacuum drying oven and dried. The drying temperature of the vacuum drying oven was set to 150℃, the pressure to 1000Pa, and the drying time to 20h, resulting in 41g of dried anode mud.

[0053] Step 2: Crush the scrap iron (content analysis shown in Table 2). Add 4g of scrap iron fragments and 13g of metallic lead to the dried anode mud and mix thoroughly. Place the mixture into an alumina crucible, cover it, and place it in the reactor. Place the reactor in a muffle furnace and perform a gas purging operation. Then, purge the reactor with nitrogen gas until the pressure gauge reads one atmosphere, at which point stop the purging. Set the heating program, setting the reduction melting temperature to 450℃ and the reduction time to 2 hours. Start the heating program. After the furnace temperature cools to room temperature, remove the reactor and recover the product. Perform XRD analysis on the product as follows: Figure 4 As shown, the results indicate that arsenic exists in the reduction products in the form of elemental form, and the reduction and fixation of arsenic in anode mud were achieved at a lower temperature.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that the reduction melting temperature in step 2 is 450°C; all other aspects are the same. ICP analysis was performed on the product after reduction melting, and the results are shown in Table 4. The XRD pattern of the product is shown below. Figure 5 As shown in Table 4 and Figure 5 It can be seen that, under the reduction smelting conditions of 450℃, arsenic oxide still exists in the product of lead anode mud, the reduction is incomplete, and the copper content is high, thus failing to achieve the purpose of copper removal.

[0056] Table 4. Composition of Product from Comparative Example 1

[0057]

[0058] Comparative Example 2

[0059] The difference between this comparative example and Example 2 is that the reduction melting temperature in step 2 is 650°C; all other aspects are the same. ICP analysis was performed on the product after reduction melting, and the results are shown in Table 5. The XRD pattern of the product is shown in... Figure 6 As shown in Table 5 and Figure 6 It can be seen that the product of reduction smelting at 650℃ contains only elemental arsenic, indicating that the arsenic oxides in the anode mud are completely reduced to arsenic. However, the arsenic content in the reduction product is low. Arsenic and arsenic oxide volatilize at high temperatures, resulting in poor arsenic fixation effect.

[0060] Table 5. Composition of the product of Comparative Example 2

[0061]

[0062] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for reducing waste iron filings and removing copper by low-temperature arsenic fixation, characterized in that, Includes the following steps: The arsenic-containing anode mud was dried and sieved to obtain anode mud powder. Anode mud powder is mixed with waste iron filings and smelted in an inert atmosphere at 500℃~600℃ until the reaction is completed to obtain a reduction smelting product, which consists of a slag layer containing elemental copper and a metal layer containing elemental arsenic. The metal layer is vacuum distilled to separate and recover the metal contained in the arsenic-containing anode mud.

2. The method for reducing waste iron scraps and removing copper at low temperature by arsenic fixation according to claim 1, characterized in that, The reduction smelting time is 2 to 3 hours.

3. The method for reducing waste iron scraps and removing copper at low temperature by arsenic fixation according to claim 1 or 2, characterized in that, The mass percentage of elemental iron in scrap iron is 70% to 85%, and the mass percentage of ferrous oxide is 10% to 20%.

4. The method for reducing waste iron scraps and removing copper at low temperature by arsenic fixation according to claim 1 or 2, characterized in that, The scrap iron filings account for 7% to 15% of the mass of the anode mud powder.

5. The method for reducing waste iron scraps and removing copper at low temperature by arsenic fixation according to claim 1 or 2, characterized in that, This also includes adding metallic lead to a mixture of anode mud powder and scrap iron.

6. The method for reducing waste iron scraps and removing copper at low temperature by arsenic fixation according to claim 5, characterized in that, Metallic lead accounts for 30% to 40% of the mass of the anode mud powder.

7. The method for reducing waste iron scraps and removing copper at low temperature by arsenic fixation according to claim 1, 2, or 6, characterized in that, Arsenic-containing anode mud is at least one of lead anode mud and copper anode mud.

Images