Method for treating iron-containing solid waste and carbon-based waste with joule heat

Abstract

The application discloses a method for treating iron-containing solid waste and carbon-based waste by means of Joule heat, and belongs to the technical field of solid waste resource utilization. The method comprises the steps of crushing and mixing, loading, passing in a carrier gas and reacting, grinding and magnetic separation. The method utilizes the superfast heating characteristics of the Joule heat technology, greatly shortens the reaction time compared with the traditional roasting process, and significantly reduces the energy consumption. Meanwhile, H2, CO and small molecular hydrocarbons generated by pyrolysis of the carbon-based waste under a high-temperature and water vapor atmosphere are used as in-situ reducing agents to reduce high-valence iron oxides such as Fe2O3 in the iron-containing solid waste into magnetic iron which is easy to be separated by magnetic separation, so that the synergistic disposal effect of "waste treatment by waste" is realized. The process flow is short, the reaction efficiency is high, and the method can meet the treatment requirements of various complex iron-containing solid wastes such as red mud and blast furnace gas ash, and difficult-to-degrade organic solid wastes such as waste tires and plastics.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically relating to a method for co-processing iron-containing solid waste and carbon-based waste using Joule heating. Background Technology

[0002] Iron in iron-containing solid waste is usually found in the crystal lattice of iron minerals, making extraction and utilization difficult. Traditional iron extraction processes typically involve blast furnace smelting or rotary kiln magnetization roasting, which suffer from high energy consumption, long reaction times (usually several hours), and large equipment footprint.

[0003] On the other hand, carbon-based wastes such as straw and waste plastics are mostly disposed of through landfill or incineration, which easily causes serious secondary pollution. If carbon-based wastes can be used as reducing agents and heat sources for the reduction and iron extraction of iron-containing solid waste, resource utilization through "waste treatment" can be achieved. For example, the paper "Toward carbon-neutral iron recovery: Red mud upcycling through optimized carbothermic reduction with calcium activation at 825℃" discloses iron extraction through red mud roasting within a time range of 30-90 minutes, with an iron recovery rate of 53.87%-81.8%. However, this method suffers from long reaction time and low iron extraction efficiency. Therefore, it is essential to develop a new technology that can synergistically achieve the reduction and recovery of iron-containing solid waste and the harmless disposal of carbon-based waste in a very short time. Summary of the Invention

[0004] To address the problems of long reaction times and low iron extraction efficiency in existing treatment technologies, the present invention aims to provide a method for the synergistic treatment of iron-containing solid waste and carbon-based waste using Joule heating. By utilizing Joule heating instantaneous high-temperature technology, the method achieves efficient recovery of iron resources from iron-containing solid waste and simultaneously converts the remaining components into high-value soil conditioners or soil-like matrices, thereby realizing the synergistic resource utilization of multi-source solid waste.

[0005] The objective of this invention is achieved by including the following steps: S1. Crush the iron-containing solid waste and carbon-based waste separately, and then mix the crushed iron-containing solid waste, carbon-based waste and calcium oxide evenly to obtain mixed reaction raw materials; S2. Place the mixed reaction materials into the Joule heating reactor; S3. Introduce a carrier gas containing water vapor into the Joule heating reactor, turn on the Joule heating reactor, rapidly raise the temperature and carry out the heat preservation reaction to accelerate the decomposition of inorganic and organic minerals, and use the reducing gas (hydrogen, carbon monoxide, carbon-containing gas, etc.) generated by the pyrolysis of carbon-based waste to reduce the iron component in iron-containing solid waste to magnetic iron. S4. After the reaction is completed, the mixture is allowed to cool naturally. The reaction products are then ground and separated by magnetic separation to obtain iron-rich iron smelting raw materials. The remainder is a soil conditioner.

[0006] Joule heating technology is a novel heating technology that utilizes electric current passing through conductive materials to generate high temperatures. It boasts advantages such as extremely rapid heating rates, high energy efficiency, and precise controllability. It enables the synergistic reduction and recovery of iron-containing solid waste with the harmless disposal and resource utilization of carbon-based waste in a very short time.

[0007] Preferably, the iron-containing solid waste in step S1 is one or more of red mud, steel slag, copper slag, pyrite slag, and blast furnace gas ash; the carbon-based waste is one or more of waste plastics, waste rubber, straw, wood chips, polychlorinated biphenyls, and perfluoroalkyl substances.

[0008] Preferably, in step S1, the mass ratio of iron-containing solid waste to carbon-based waste is 1:0.5~2, and the amount of calcium oxide added is 1%~5% of the total mass of iron-containing solid waste and carbon-based waste.

[0009] Preferably, in step S1, the particle size of the iron-containing solid waste is 50 mesh to 200 mesh, and the particle size of the carbon-based waste is 1 mm to 5 mm.

[0010] Preferably, the Joule heating apparatus includes a quartz tube, a graphite plate, a graphite felt, and a graphite rope. A quartz boat, with an open top, is placed inside the quartz tube. The graphite felt is laid on the quartz boat and has pores in its center. The graphite plate is positioned at both ends of the graphite felt, pressing it tightly. Electrodes are electrically connected to the graphite plate. The graphite rope fixes the center of the graphite felt to the quartz boat. One end of the quartz tube has an air inlet, and the other end has an air outlet. The quartz boat is chosen as the carrier, utilizing the excellent high-temperature resistance and electrical insulation properties of quartz material. In the Joule heating reaction, the current flows directly through the graphite felt, generating temperatures as high as several thousand degrees Celsius, ensuring that the current path is concentrated on the graphite felt, thus improving energy utilization efficiency. Meanwhile, the boat-shaped structure and the graphite felt laid on it form a semi-enclosed micro-reaction chamber, facilitating the loading of powder precursors and allowing the heat generated by the graphite felt to directly act on the sample over a very short distance through thermal radiation and conduction, greatly reducing heat loss. A graphite plate clamps both ends of the graphite felt and connects to the electrodes, solving the problem of excessive contact resistance that easily occurs when flexible carbon materials are in direct contact with metal electrodes. The graphite plate, as a rigid medium, compresses the graphite felt, significantly reducing contact resistance and preventing arcing or localized overheating and melting at the electrodes due to poor contact under high current impact. Graphite ropes are used to bind and fix the graphite felt to the quartz boat to address the thermal expansion problem caused by Joule thermal shock. Because the graphite felt expands in volume during rapid heating, it is easy for the felt to arch and detach from the sample surface if not fixed. Graphite ropes have a similar coefficient of thermal expansion to the graphite felt and are resistant to ultra-high temperatures, ensuring the stability of the system under severe thermal shock.

[0011] Preferably, in step S3, the temperature is increased to 800℃~1400℃ in 10s~30s, and the reaction is held at this temperature for 1min~10min.

[0012] Preferably, the carrier gas in step S3 is nitrogen, the volume percentage of water vapor in the carrier gas is 1% to 5%, and the carrier gas flow rate is 10 mL / min to 50 mL / min.

[0013] Preferably, the magnetic field strength of the magnetic separation in step S4 is 0.1T~0.5T.

[0014] Compared with the prior art, the present invention has the following technical effects: 1. This invention utilizes the ultra-fast heating characteristics of Joule heating technology, which significantly shortens the reaction time and reduces energy consumption compared to traditional roasting processes. Simultaneously, it uses H2, CO, and small-molecule hydrocarbons generated from the pyrolysis of carbon-based waste under high temperature and steam atmosphere as in-situ reducing agents to reduce high-valence iron oxides such as Fe2O3 in iron-containing solid waste to easily separated magnetic iron (Fe3O4, Fe...). 0 This achieved the synergistic disposal effect of "treating waste with waste"; 2. By introducing water vapor and calcium oxide, this invention not only promotes the reforming and gasification reaction of carbon-based waste in a high-temperature system, increasing the yield and utilization rate of reducing gas; at the same time, calcium oxide, as a flux and stabilizer, can react with the aluminosilicate components in solid waste, improving the properties of the reaction residue. This makes the tailings after magnetic separation rich in nutrients such as calcium and silicon, non-toxic and harmless, and usable as a high-quality soil conditioner, realizing the full utilization of solid waste resources and avoiding secondary pollution.

[0015] 3. The process of this invention is short and has high reaction efficiency, which can meet the treatment needs of various complex iron-containing solid wastes such as red mud and blast furnace gas ash, as well as recalcitrant organic solid wastes such as waste tires and plastics. This invention achieves efficient recovery of iron resources (converting them into high-value-added iron smelting raw materials) by precisely controlling the Joule heating temperature field and atmosphere, and solves the bottleneck problems of high energy consumption, long treatment cycle and low resource recovery rate in traditional solid waste treatment technologies, which has significant economic and environmental benefits. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 This is a schematic diagram of a Joule heating apparatus. Figure 3 The images show the XRD patterns before and after the reaction in Example 1. In the diagram: 1-quartz tube, 2-graphite plate, 3-graphite felt, 4-graphite rope, 5-mixed reaction raw materials, 6-air inlet, 7-air outlet, 8-quartz boat. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention. Example 1

[0018] This embodiment uses Bayer process red mud as iron-containing solid waste and waste polypropylene (PP) plastic as carbon-based waste; as shown in the attached... Figure 1 ~Appendix Figure 2 The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating as shown in this embodiment includes the following steps: S1. Crush the iron-containing solid waste and carbon-based waste separately. The crushing particle size of the iron-containing solid waste is 150 mesh, and the crushing particle size of the carbon-based waste is 3 mm. Then, mix 2g of crushed iron-containing solid waste, 2g of carbon-based waste and 0.15g of calcium oxide evenly to obtain mixed reaction raw materials. S2. The Joule heating reaction apparatus includes a quartz tube 1, a graphite plate 2, a graphite felt 3, and a graphite rope 4. A quartz boat 8 is placed inside the quartz tube 1. The graphite felt 3 is laid on the quartz boat 8 and has pores in the middle. The graphite plate 2 is placed at both ends of the graphite felt 3 to press it tightly. The electrode is electrically connected to the graphite plate 2. The graphite rope 4 fixes the middle part of the graphite felt 3 to the quartz boat 8. One end of the quartz tube 1 has an air inlet 6 and the other end has an air outlet 7. The mixed reaction raw material 5 is placed in the quartz boat 8, the graphite felt 3 is laid on it and pressed tightly by the graphite plate 2, and the graphite rope 4 is tied tightly. S3. A carrier gas (nitrogen) containing water vapor is introduced into the Joule heating reactor. The carrier gas passes through the pores of the graphite felt 3 and comes into contact with the mixed reaction raw materials 5. The volume ratio of water vapor in the carrier gas is 3%, the carrier gas flow rate is 20 mL / min, and the system pressure is maintained at 1 atm. The Joule heating reactor is turned on, and the reaction temperature is raised to 1200℃ in 30s by high current discharge through the electrodes and the reaction is held at this temperature for 3min. During this process, the PP plastic pyrolysis produces a large amount of H2 and CO, which reduces the iron oxide in the red mud to metallic iron powder. S4. After the reaction is completed, the mixture is allowed to cool naturally. The reaction products are then ground and separated by magnetic separation with a magnetic field strength of 0.1T to obtain iron-rich iron smelting raw materials. The remainder is a soil conditioner. Testing showed that the iron recovery rate in this embodiment was 93.2%, and the resulting iron-rich smelting raw materials were of excellent quality. The pH value of the remaining soil conditioner dropped to 8.4, achieving deep dealkalization, and the matrix structure was loose, making it suitable for subsequent soil improvement. Example 2

[0019] In this embodiment, steel slag is selected as iron-containing solid waste and waste tires are selected as carbon-based waste. The method of co-processing iron-containing solid waste and carbon-based waste by Joule heating in this embodiment is based on Example 1, but differs from Example 1 in the following ways: In step S1, the particle size of the iron-containing solid waste is 150 mesh, the particle size of the carbon-based waste is 1 mm, the iron-containing solid waste is 2 g, the carbon-based waste is 1 g, and the calcium oxide is 0.1 g; In step S3, the carrier gas flow rate is 30 mL / min, the reaction temperature is raised to 1400℃ in 30 s and the reaction is held at this temperature for 1 min; In step S4, the magnetic field strength is 0.25 T. The results showed that the stable calcium ferrite (CaFe2O5) in the steel slag underwent reduction decomposition at high temperature, and the recovery rate of metallic iron reached 89.5%. At the same time, the sulfur component in the waste tires was efficiently solidified into CaS by calcium oxide and entered into the soil conditioner, reducing gaseous pollution. The density of the resulting matrix was significantly lower than that of the original steel slag. Example 3

[0020] In this embodiment, red mud is selected as iron-containing solid waste and wood chips as carbon-based waste. The method of co-processing iron-containing solid waste and carbon-based waste by Joule heating in this embodiment is based on Example 1, but differs from Example 1 in the following ways: In step S1, the particle size of the iron-containing solid waste is 50-200 mesh, the particle size of the carbon-based waste is 1-5 mm, the iron-containing solid waste is 2 g, the carbon-based waste is 4 g, and the calcium oxide is 0.25 g; In step S3, the carrier gas flow rate is 50 mL / min, the reaction temperature is raised to 800℃ in 30 s and the reaction is held at that temperature for 10 min; In step S4, the magnetic field strength is 0.5 T. In this embodiment, the reaction was carried out at a relatively low temperature, and the main reduction product was magnetic Fe3O4, with a magnetic separation recovery rate of 78.4%. Due to the high amount of sawdust added, the synergistic effect of CO2 and water vapor generated by pyrolysis was extremely strong, resulting in a dealkalization rate of up to 96.1% for the soil conditioner. In addition, the soil conditioner is rich in microporous carbon formed by biomass pyrolysis, which significantly improves its organic matter content and water-holding capacity as a soil conditioner. Example 4

[0021] In this embodiment, copper slag with a high iron olivine content (Fe2SiO4) is selected as iron-containing solid waste, and waste polyethylene (PE) plastic is selected as carbon-based waste. The method of co-processing iron-containing solid waste and carbon-based waste by Joule heating in this embodiment is based on Example 1, but differs from Example 1 in the following ways: In step S1, 2g of iron-containing solid waste, 2g of carbon-based waste, and 0.2g of calcium oxide are used; In step S3, the volume ratio of water vapor in the carrier gas is 1%, the carrier gas flow rate is 35mL / min, the reaction temperature is raised to 1300℃ in 30s and the reaction is held at this temperature for 2min; In step S4, the magnetic field strength is 0.15T. High-temperature Joule heating effectively disrupted the silicate phase structure of fir olivine in copper slag, and the addition of calcium oxide promoted phase transformation; the iron recovery rate reached 91.0%, and some metallic copper in the copper slag was recovered along with the iron phase into iron-rich smelting raw materials. The remaining soil conditioner was porous, and its density decreased significantly after the removal of the iron component, meeting the characteristics of lightweight soil-like materials, and can be used as soil conditioner. Example 5

[0022] In this embodiment, pyrite slag is selected as iron-containing solid waste and corn stalks are selected as carbon-based waste. The method of co-processing iron-containing solid waste and carbon-based waste by Joule heating in this embodiment is based on Example 1, but differs from Example 1 in the following ways: In step S1, the particle size of the iron-containing solid waste is 50 mesh, the particle size of the carbon-based waste is 1 mm, the mass ratio of iron-containing solid waste to carbon-based waste is 1:0.5, and the amount of calcium oxide added is 1% of the total mass of iron-containing solid waste and carbon-based waste; In step S3, the volume ratio of water vapor in the carrier gas is 1%, the carrier gas flow rate is 10 mL / min, the reaction temperature is raised to 800℃ in 10 s and the reaction is held at this temperature for 1 min; In step S4, the magnetic field strength is 0.1 T. Example 6

[0023] In this embodiment, blast furnace gas ash is selected as iron-containing solid waste and wood chips are selected as carbon-based waste. The method of co-processing iron-containing solid waste and carbon-based waste by Joule heating in this embodiment is based on Example 1, but differs from Example 1 in the following ways: In step S1, the particle size of the iron-containing solid waste is 200 mesh, the particle size of the carbon-based waste is 5 mm, the mass ratio of iron-containing solid waste to carbon-based waste is 1:2, and the amount of calcium oxide added is 5% of the total mass of iron-containing solid waste and carbon-based waste; In step S3, the volume ratio of water vapor in the carrier gas is 5%, the carrier gas flow rate is 50 mL / min, the reaction temperature is raised to 1400℃ in 30 s and the reaction is held at that temperature for 10 min; In step S4, the magnetic field strength is 0.5 T. Example 7

[0024] In this embodiment, red mud, steel slag, copper slag, pyrite slag, and blast furnace gas ash are mixed in a mass ratio of 1:1:1:1:1 as iron-containing solid waste, and waste PP plastic, waste rubber, corn stalks, and wood chips are mixed in a mass ratio of 1:1:1:1 as carbon-based waste. The method of co-processing iron-containing solid waste and carbon-based waste with Joule heating in this embodiment is based on Example 1, but differs from Example 1 in the following ways: In step S1, the particle size of the iron-containing solid waste is 125 mesh, the particle size of the carbon-based waste is 3 mm, the mass ratio of iron-containing solid waste to carbon-based waste is 1:1.25, and the amount of calcium oxide added is 3% of the total mass of iron-containing solid waste and carbon-based waste; In step S3, the volume ratio of water vapor in the carrier gas is 3%, the carrier gas flow rate is 30 mL / min, the reaction temperature is raised to 1100℃ in 20 s and the reaction is held at that temperature for 5.5 min; In step S4, the magnetic field strength is 0.3 T.

Claims

1. A method for co-processing iron-containing solid waste and carbon-based waste using Joule heating, characterized in that... Includes the following steps: S1. Crush the iron-containing solid waste and carbon-based waste separately, and then mix the crushed iron-containing solid waste, carbon-based waste and calcium oxide evenly to obtain mixed reaction raw materials; S2. Place the mixed reaction materials into the Joule heating reactor; S3. Introduce a carrier gas containing water vapor into the Joule heating reactor, turn on the Joule heating reactor, rapidly raise the temperature and carry out the heat preservation reaction, accelerate the decomposition of inorganic and organic minerals, and use the reducing gas generated by the pyrolysis of carbon-based waste to reduce the iron component in iron-containing solid waste to magnetic iron. S4. After the reaction is completed, the mixture is allowed to cool naturally. The reaction products are then ground and separated by magnetic separation to obtain iron-rich iron smelting raw materials. The remainder is a soil conditioner.

2. The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating according to claim 1, characterized in that... The iron-containing solid waste mentioned in step S1 is one or more of red mud, steel slag, copper slag, pyrite slag, and blast furnace gas ash; the carbon-based waste is one or more of waste plastics, waste rubber, straw, wood chips, polychlorinated biphenyls, and perfluoroalkyl substances.

3. The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating according to claim 1, characterized in that... In step S1, the mass ratio of iron-containing solid waste to carbon-based waste is 1:0.5~2, and the amount of calcium oxide added is 1%~5% of the total mass of iron-containing solid waste and carbon-based waste.

4. The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating according to claim 1, characterized in that... In step S1, the particle size of the iron-containing solid waste is 50-200 mesh, and the particle size of the carbon-based waste is 1-5 mm.

5. The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating according to claim 1, characterized in that... The Joule heating apparatus includes a quartz tube (1), a graphite plate (2), a graphite felt (3), and a graphite rope (4). A quartz boat (8) is installed inside the quartz tube (1). The graphite felt (3) is laid on the quartz boat (8) and has pores in the middle. The graphite plate (2) is located at both ends of the graphite felt (3) to press the graphite felt (3) tightly. The electrode is electrically connected to the graphite plate (2). The graphite rope (4) fixes the middle part of the graphite felt (3) to the quartz boat (8). One end of the quartz tube (1) is provided with an air inlet (6), and the other end is provided with an air outlet (7).

6. The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating according to claim 1, characterized in that... In step S3, the temperature is increased to 800℃~1400℃ in 10s~30s, and the reaction is held at this temperature for 1min~10min.

7. The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating according to claim 1, characterized in that... In step S3, the carrier gas is nitrogen, with water vapor accounting for 1% to 5% of the volume, and the carrier gas flow rate is 10 mL / min to 50 mL / min.

8. The method for co-processing iron-containing solid waste and carbon-based waste using Joule heating according to claim 1, characterized in that... The magnetic field strength of the S4 step magnetic separation is 0.1T~0.5T.

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