Method for synergetic resource utilization of red mud and arsenic-containing hazardous waste

Abstract

The invention belongs to the technical field of metallurgical engineering, and discloses a red mud and arsenic-containing hazardous waste collaborative resource utilization method which comprises the following steps: pretreating red mud by adopting roasting and magnetic separation processes, mixing the pretreated red mud with sodium carbonate, a reducing agent and non-ferrous smelting arsenic removal slag, and carrying out reduction smelting to obtain arsenic-iron alloy and sodium carbonate slag; the arsenic-iron alloy can be used as a counterweight material; the furnace slag can be reused as an arsenic removal agent. According to the method, the red mud is pretreated through roasting and magnetic separation, the valuable element iron is enriched from the red mud in a high-selectivity mode and cooperates with the colored arsenic-removed slag to carry out reduction smelting, the harmful element arsenic is converted into a novel material, synergistic resource utilization of the red mud and the arsenic-containing hazardous waste is achieved by using waste to treat waste, and the method has great significance.

Description

Technical Field

[0001] The present invention relates to the field of resource utilization of red mud and arsenic-containing hazardous waste, and in particular to a method for co-processing red mud and arsenic-containing hazardous waste, specifically a method for preparing arsenic-iron alloy and sodium carbonate molten salt by co-reducing and smelting the pre-treated red mud with arsenic-removing slag. Background Art

[0002] Red mud is a solid waste produced in the Bayer aluminum production process. Depending on the smelting process, 1.0 to 1.8 tons of red mud will be produced for every ton of alumina produced. my country is a major aluminum smelting country. As of 2023, my country's alumina production has reached 35 million tons, and red mud has also produced 35 to 63 million tons. So far, only 2 to 3% of red mud has been comprehensively utilized, and the rest of the red mud is still treated by stockpiling. Because red mud contains a large amount of alkaline substances, it is easy to seep into the ground during long-term storage, causing water pollution and irreversible environmental damage. It is worth noting that red mud contains a large amount of iron. The use of appropriate processes to recover iron from red mud can not only reduce the storage of red mud, but also realize its resource utilization, which is of great significance. Non-ferrous smelting, such as antimony smelting (antimonite), copper smelting (chalcopyrite), and lead smelting (galena) usually use sodium carbonate and sodium hydroxide as arsenic removal agents, and use oxidation refining to convert arsenic into Na3AsO4 to remove impurities from the metal. This arsenic removal slag can easily seep into groundwater, causing serious arsenic pollution. Arsenic is also an important non-ferrous metal, and it is of great significance to use resource processing technology to recycle arsenic removal slag.

[0003] Red mud contains not only Fe2O3 but also a large amount of CaO and SiO2. If red mud is directly mixed with arsenic removal slag, reduction smelting will cause a large amount of CaO and SiO2 to enter the smelting slag, resulting in an increase in the melting point and viscosity of the smelting slag, which is not conducive to the development of reduction smelting. In addition, the addition of CaO and SiO2 is not conducive to the reuse of smelted regenerated Na2CO3 as an arsenic removal agent. Summary of the invention

[0004] The purpose of the present invention is to solve the existing problems in the treatment of red mud and arsenic-containing hazardous wastes, adopt the idea of ​​treating waste with waste, and aim to provide a simple and easy-to-operate method to convert red mud and non-ferrous smelting arsenic-removing slag into arsenic-iron alloy.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for collaborative resource utilization of red mud and arsenic-containing hazardous waste, comprising the following steps:

[0007] (1) mixing red mud and a reducing agent, pre-roasting, and treating roasted sand with a magnetic separation process to obtain pre-treated red mud;

[0008] (2) The pretreated red mud obtained in step (1), the non-ferrous smelting arsenic removal slag, sodium carbonate and a reducing agent are mixed and reduction smelting is performed. After the reduction smelting is completed, the melt is allowed to stand and the reduction smelting slag and the alloy obtained by smelting are separated.

[0009] In the method, the red mud comprises 20-50% CaO, 5-20% Fe2O3, 5-20% Al2O3 and 15-50% SiO2.

[0010] The method described herein, wherein the non-ferrous smelting arsenic removal slag refers to the arsenic removal slag obtained by using sodium carbonate or sodium hydroxide as arsenic removal agents in non-ferrous smelting and adopting an oxidative refining method to convert arsenic into Na3AsO4 to remove impurities from the metal.

[0011] The nonferrous smelting includes: antimony smelting (stibnite), copper smelting (chalcopyrite), and lead smelting (galena).

[0012] The arsenic removal slag usually contains 3-25% arsenic.

[0013] In the method described, the reducing agent is one or more of pulverized coal, biochar, metallurgical coke, waste engine oil, waste cooking oil, and natural gas. The amount of the reducing agent added in step (1) is 5 to 10% of the mass of the red mud; the amount of the reducing agent added in step (2) is 20 to 40% of the mass of the pretreated red mud.

[0014] In the method, in the step (1), the pre-baking temperature is 300-700° C. and the pre-baking time is 0.5-2 h.

[0015] In the method, in the step (1), the magnetic field intensity during the magnetic separation of roasted sand is 40 to 100 kA / m.

[0016] The method, in step (2), the amount of arsenic added needs to be less than 65% of the mass of iron in the pretreated red mud;

[0017] The method, in step (2), the ratio of the mass of sodium carbonate to the mass of arsenic removal slag is 1:4 to 3:4;

[0018] In the method, in the step (2), the reduction smelting temperature is 1000-1200° C., the reduction smelting time is 1-3 hours, and the standing time after smelting is 30-60 minutes.

[0019] In the method, the alloy obtained by smelting is an arsenic-iron alloy; and the reduced smelting slag is reused as an arsenic removal agent.

[0020] The present invention adopts a process scheme of treating waste with waste, and while utilizing red mud as a resource, it also realizes the resource utilization of arsenic removal slag from non-ferrous smelting. The inventor found that pre-baking and magnetic separation processes are crucial to the invention. The pre-baking process can transform Fe2O3 in red mud into Fe3O4. Fe3O4 can be separated and enriched from red mud by magnetic separation, thereby avoiding a large amount of CaO and SiO2 in red mud from entering the reduction smelting system together, which increases the melting point and viscosity of the slag, and is not conducive to the development of reduction smelting. In addition, the pre-baking temperature and magnetic field strength are also crucial to the new process proposed by the present invention. When the baking temperature is lower than 300°C, the temperature is too low and the reducing agent cannot convert Fe2O3 into Fe3O4, so that the magnetic separation process cannot be used to achieve the separation and enrichment of iron; when the temperature is higher than 700°C, the temperature is too high, and the reducing agent reduces Fe2O3 to elemental iron. The fixed arsenic efficiency of elemental iron in the reduction smelting process is not as good as that of iron oxide, so that part of the arsenic in the reduction smelting volatilizes into the flue gas. Reducing the magnetic field strength is beneficial to improving the grade of Fe3O4 obtained by magnetic separation, but the iron recovery rate also decreases. In order to ensure the direct recovery rate of iron, the present invention proposes that the magnetic field strength should not be lower than 40kA / m; increasing the magnetic field strength is beneficial to improving the direct recovery rate of iron, but it will cause the grade of Fe3O4 to decrease, causing a large amount of CaO and SiO2 to enter the reduction smelting system. Therefore, the invention proposes that the magnetic field strength of magnetic separation is not higher than 100kA / m.

[0021] The inventors found that sodium carbonate is essential for reducing arsenic in smelting. Arsenic-containing hazardous waste from non-ferrous smelting mainly exists in the form of Na3AsO4, which has a melting point of up to 1390°C. Direct carbon reduction pretreatment of red mud and arsenic removal slag will cause a large amount of arsenic to volatilize, and the iron obtained by reduction cannot be fixed in the alloy phase. Adding sodium carbonate during the mixing process can change the melting point of the mixed material, inhibit the volatilization of arsenic obtained by reduction, promote arsenic to enter the alloy phase, and enhance the arsenic fixation effect of iron.

[0022] The smelting temperature of arsenic-iron alloy is about 1030°C. To ensure the smooth progress of reduction smelting, the reduction smelting temperature should be higher than the melting point of the alloy. In addition, the melt also needs to have a certain amount of superheat to ensure that the melt has good fluidity. Therefore, the present invention proposes that the reduction smelting temperature should not be lower than 1100°C.

[0023] Beneficial effects of the present invention:

[0024] The present invention proposes a pretreatment process for red mud, wherein Fe2O3 is transformed into Fe3O4 by magnetization roasting, and then separated from impurities such as CaO and SiO2 in the red mud by magnetic separation, thereby greatly reducing the impurity content entering the furnace during the reduction smelting process. Sodium arsenate can be reduced to a metallic state by carbon in a reducing atmosphere. In addition, the reduction process can also obtain sodium carbonate molten salt, which is located in the upper layer of the metal melt and can be returned to the non-ferrous metal arsenic removal refining as an arsenic removal agent. Iron can form intermetallic compounds such as FeAs, Fe2As, and Fe3As2 with arsenic. At the same time, in the Fe-As system, iron preferentially forms FeAs2 intermetallic compounds with As. As the temperature rises, FeAs2 is successively transformed into FeAs and Fe2As. Fe2As has a large density and low biological toxicity, and can be used as a counterweight in the field of equipment manufacturing. The method for resource utilization of red mud disclosed in the present invention adopts the idea of ​​treating waste with waste, and has the advantages of simple process, good raw material adaptability, high social and economic value, etc., and has great application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a process flow chart of the present invention;

[0026] Figure 2 The XRD diagram of smelting slag and arsenic-iron alloy is obtained for the present invention. DETAILED DESCRIPTION

[0027] The following examples are intended to further illustrate the present invention, but are not intended to limit the present invention.

[0028] Example 1

[0029] Step 1: Mix 1000 kg of red mud with a Fe2O3 content of 16.29%, a SiO2 content of 42.34%, a CaO content of 26.62% and an Al2O3 content of 9.43% with 80 kg of pulverized coal, and roast them at 300°C for 2 hours. After the roasted sand is cooled, it is magnetically separated at a magnetic field strength of 80 kA / m to obtain 120.33 kg of pretreated red mud containing 67.45% iron (mainly ferroferric oxide).

[0030] Step 2: Mix 120.33 kg of pretreated red mud obtained in step 1, 165 kg of arsenic-removing slag (chalcopyrite) containing 21.46% arsenic, 0.37% antimony and 4.32% copper, 40 kg of sodium carbonate and 30 kg of pulverized coal, and perform reduction smelting at 1100°C for 2 hours, and then let the melt stand for 30 minutes.

[0031] After smelting, 113.64 kg of arsenic-iron alloy was obtained, in which arsenic existed in the form of Fe2As, the alloy had an iron content of 69.64% and an arsenic content of 29.76%; 175.74 kg of smelting slag was obtained, which was mainly Na2CO3. The density of the obtained arsenic-iron alloy was 7.46 g / cm 3 , the HJ / T 299-2007 test method showed that the arsenic leaching concentration of the material was only 3.06 mg / L, which is lower than the limit of 5 mg / L.

[0032] Example 2

[0033] Step 1: Mix 1000 kg of red mud with a Fe2O3 content of 5.51%, a SiO2 content of 39.31%, a CaO content of 48.53% and an Al2O3 content of 5.44% with 50 kg of straw carbon, and roast them at 700°C for 0.5 h. After the roasted sand is cooled, it is magnetically separated at a magnetic field strength of 100 kA / m to obtain 41.27 kg of pretreated red mud with an iron content of 64.26%.

[0034] Step 2: Mix 41.27 kg of pretreated red mud obtained in step 1, 45 kg of arsenic-removing slag (chalcopyrite) containing 14.29% arsenic, 0.06% antimony and 4.68% copper; 35 kg of sodium carbonate and 16 kg of pulverized coal, and perform reduction smelting at 1200° C. for 1 hour, and then let the melt stand for 30 minutes.

[0035] After smelting, 31.57 kg of arsenic-iron alloy was obtained, in which arsenic existed in the form of Fe2As, the alloy had an iron content of 81.52% and an arsenic content of 16.23%; 77.06 kg of smelting slag was obtained, which was mainly Na2CO3. The density of the obtained arsenic-iron alloy was 7.55 g / cm 3 , the HJ / T 299-2007 test method showed that the arsenic leaching concentration of the material was only 2.88 mg / L, which is lower than the limit of 5 mg / L.

[0036] Example 3

[0037] Step 1: 1000 kg of the same red mud as in Example 1 was mixed with 100 kg of straw carbon, and roasted at 500° C. for 1 h. After the roasted sand was cooled, it was magnetically separated at a magnetic field strength of 40 kA / m to obtain 158.71 kg of pretreated red mud containing 71.04% iron.

[0038] Step 2: Mix 158.71 kg of pretreated red mud obtained in step 1, 155 kg of arsenic-removing slag (stibnite) containing 24.33% arsenic, 4.06% antimony and 0.18% copper; 75 kg of sodium carbonate and 55 kg of straw carbon, and perform reduction smelting at 1150°C for 1.5 hours, and then let the melt stand for 60 minutes.

[0039] After smelting, 148.82 kg of arsenic-iron alloy was obtained, in which arsenic existed in the form of Fe2As, the alloy had an iron content of 72.14% and an arsenic content of 23.96%; 203.74 kg of smelting slag was obtained, which was mainly Na2CO3. The density of the obtained arsenic-iron alloy was 7.42 g / cm 3 , the HJ / T 299-2007 test method showed that the arsenic leaching concentration of the material was only 2.94 mg / L, which is lower than the limit of 5 mg / L.

[0040] Comparative Example 1 (calcination temperature is too low)

[0041] Comparative Example 1 is basically the same as Example 1, except that the temperature of the pre-roasting of red mud in Comparative Example 1 is only 200°C. After magnetic separation, only 5.14 kg of magnetic separation product was obtained from the pre-roasted sand, and most of the iron was still retained in the magnetic separation tailings. The pre-roasting process failed to achieve the transformation of Fe2O3 into Fe3O4.

[0042] Comparative Example 2 (calcination temperature is too high)

[0043] Comparative Example 2 is substantially the same as Example 1, except that the calcination temperature of the red mud in Comparative Example 2 is 750° C. After reduction smelting of the pretreated red mud and the arsenic-removing slag, only 95.64 kg of alloy was obtained, and a large amount of metallic arsenic appeared in the smelting dust.

[0044] Comparative Example 3 (Magnetic Field Intensity Too Low)

[0045] Comparative Example 3 is substantially the same as Example 1, except that the magnetic field intensity is only 30 kA / m during the magnetic separation of roasted sand in Comparative Example 3. After magnetic separation, only 97.66 kg of magnetic separation product is obtained, and part of the iron is retained in the magnetic separation tailings.

[0046] Comparative Example 4 (magnetic field strength is too high)

[0047] Comparative Example 4 is basically the same as Example 1, except that the magnetic field intensity is as high as 110 kA / m during the magnetic separation of roasted sand in Comparative Example 4. After magnetic separation, 140.21 kg of magnetic separation products are obtained. The pre-treated red mud brings in a large amount of CaO and SiO2. During the reduction smelting process with the arsenic removal slag, the smelting slag fails to melt, deteriorating the furnace ore and making it difficult to separate the slag.

[0048] Comparative Example 5 (melting temperature is too low)

[0049] Comparative Example 5 is substantially the same as Example 1, except that, in the reduction smelting process, the smelting temperature of Comparative Example 5 is only 1050° C. When the temperature is too low, the fluidity of the slag and the alloy is poor, and it is difficult to separate the slag from the alloy.

[0050] Comparative Example 6 (Sodium carbonate was not used to assist smelting)

[0051] Comparative Example 6 is substantially the same as Example 1, except that no sodium carbonate was added to the mixture during the reduction smelting process in Comparative Example 6. Only 98.64 kg of alloy was obtained through reduction smelting, and part of the arsenic entered the flue gas and condensed to obtain metallic arsenic.

[0052] Comparative Example 7 (Too much arsenic in the arsenic removal slag)

[0053] Comparative Example 7 is basically the same as Example 1, except that the mass of arsenic removal slag added in Comparative Example 7 is 265 kg, and the mass of arsenic in the mixed material reaches 70.07% of the mass of iron, which is higher than 65%. After the smelting is completed, 132.96 kg of arsenic-iron alloy is obtained, in which the arsenic content is 39.64. The arsenic content in the alloy is only 52.71 kg, which is much lower than the mass of 56.81 kg of arsenic added to the arsenic removal slag. That is, part of the arsenic volatilizes into the flue gas during the reduction smelting process.

[0054] Comparative Example 8 (Insufficient amount of reducing agent)

[0055] Comparative Example 8 is basically the same as Example 1, except that the mass of pulverized coal added in Comparative Example 8 is only 20 kg, which is 16.62% of the mass of the pretreated red mud. After reduction smelting, the reduced slag has poor fluidity and contains a large amount of unreduced pretreated red mud. In addition, a large amount of metallic arsenic is found in the flue gas, and the solid arsenic rate of the alloy is not high.

Claims

1. A method for collaborative resource utilization of red mud and arsenic-containing hazardous waste, characterized in that: The following steps are involved: (1) mixing red mud and a reducing agent, pre-roasting, and treating roasted sand with a magnetic separation process to obtain pre-treated red mud; (2) The pretreated red mud obtained in step (1), the non-ferrous smelting arsenic removal slag, sodium carbonate and a reducing agent are mixed and reduction smelting is performed. After the reduction smelting is completed, the melt is allowed to stand and the reduction smelting slag and the alloy obtained by smelting are separated.

2. The method according to claim 1, characterized in that The red mud comprises 20-50% of CaO, 5-20% of Fe2O3, 5-20% of Al2O3 and 15-50% of SiO2.

3. The method according to claim 1 or 2, characterized in that: The non-ferrous smelting arsenic removal slag refers to the arsenic removal slag obtained by using sodium carbonate and sodium hydroxide as arsenic removal agents in non-ferrous smelting and adopting an oxidative refining method to convert arsenic into Na3AsO4 to remove impurities from the metal; the arsenic removal slag usually contains 3-25% arsenic.

4. The method according to claim 1, 2 or 3, characterized in that: The reducing agent is one or more of pulverized coal, biochar, metallurgical coke, waste engine oil, waste cooking oil, and natural gas. The amount of the reducing agent added in step (1) is 5 to 10% of the mass of the red mud; the amount of the reducing agent added in step (2) is 20 to 40% of the mass of the pretreated red mud.

5. The method according to claim 1, characterized in that: In the step (1), the pre-baking temperature is 300-700° C. and the pre-baking time is 0.5-2 h.

6. The method according to claim 1 or 4, characterized in that: In the step (1), the magnetic field intensity during the roasting sand magnetic separation is 40 to 100 kA / m.

7. The method according to claim 1, characterized in that In the step (2), the amount of arsenic added must be less than 65% of the mass of iron in the pretreated red mud.

8. The method according to claim 1 or 7, characterized in that: In the step (2), the ratio of the mass of sodium carbonate to the mass of the arsenic removal slag is 1:4 to 3:

4.

9. The method according to claim 1, 7 or 8, characterized in that: In the step (2), the reduction smelting temperature is 1000-1200°C, the reduction smelting time is 1-3 hours, and the standing time after smelting is 30-60 minutes.

10. The method according to claim 1 or 7 or 8 or 9, characterized in that: The alloy obtained by smelting is an arsenic-iron alloy; the reduced smelting slag is reused as an arsenic removal agent.

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