Method for removing toxic pollutants in chromium metal smelting waste residues

Abstract

The invention discloses a method for removing toxic pollutants in metal chromium smelting waste slag, and relates to a method for removing toxic pollutants in smelting waste slag, which comprises the following steps of: firstly, crushing and sieving the smelting slag, and detecting that hexavalent chromium is dangerous solid waste according to the technical specification requirements of chromium slag pollution abatement and environmental protection; and adding a carbon, calcium, magnesium and aluminum mixed reducing agent, uniformly mixing by using a mixer, adding a binding agent, calcining in a roasting furnace, cooling, and detecting according to chromium slag pollution abatement and environmental protection technical specifications. According to the method, the chromium metal smelting slag is subjected to detoxification treatment, hexavalent chromium is reduced into trivalent chromium, the standard requirement of the chromium slag pollution abatement environmental protection technical specification (temporary) (HJ / T301-2007) is met, the limit values of total chromium in a leaching solution are smaller than 9 mg / L, hexavalent chromium is smaller than 3 mg / L, barium is smaller than 50 mg / L, and the chromium metal smelting slag is converted into common solid waste from dangerous solid waste.

Description

Technical Field

[0001] The invention relates to a method for removing toxic pollution from smelting waste slag, in particular to a method for removing toxic pollutants from metal chromium smelting waste slag. Background Art

[0002] Chromium metal is widely used as an additive in iron and steel metallurgy, high temperature alloys, resistance alloys, and precision alloys due to its high melting point, high strength, corrosion resistance, wear resistance, and other characteristics, especially its strong corrosion resistance at high temperatures. In particular, chromium metal is indispensable for the smelting of non-ferrous chromium-containing alloys, and chromium metal products are national strategic products.

[0003] At present, there are only three methods for producing metallic chromium. The first is the reduction method using chromium oxide and metallic aluminum, which is called metal thermal reduction in industry. This method is the main production method at home and abroad because of its low investment, low cost and good quality. The output of this method accounts for about 80% of the total output of metallic chromium. The second is the carbon reduction method, which uses chromium oxide and carbon to reduce chromium carbide under vacuum, and then mixes chromium carbide and chromium oxide to form columnar metallic chromium under vacuum. The third is to produce metallic chromium by electrolysis of chromium salt (chromic anhydride).

[0004] Aluminothermic reduction is the process of using aluminum to reduce chromium oxide to produce metallic chromium. The chemical reaction is as follows: Cr2O3+2AI=2Cr+ AI2O3 In this process, metallic aluminum is oxidized into alumina, and chromium oxide is reduced to metallic chromium and sinks to the bottom of the furnace. The floating layer is slag containing alumina and chromium oxide, which is the metallic chromium smelting slag.

[0005] The aluminothermic process produces a large amount of solid waste, chromium smelting slag. The production of 1 ton of chromium produces about 1.3 tons of chromium smelting slag. The smelting slag contains A12O3 and Cr2O3 components, of which the mass percentage of A12O3+Cr2O3 is generally greater than 97%. It contains 8% to 16% by weight of chromium oxide, as well as a small amount of impurities such as Na2CrO4, CaO, Fe2O3, Na2O, K2O and SiO2. Among them, Na2CrO4 is a soluble chromium salt, and the Cr (VI) contained in it is a type of hazardous waste that is banned by the state.

[0006] As the country pays more attention to the environment, especially the emission requirements of three wastes are becoming more stringent, enterprises must detoxify the hazardous solid wastes they emit before they can be reused. Summary of the invention

[0007] The object of the present invention is to provide a method for removing toxic pollutants from metal chromium smelting waste slag. The method detoxifies the metal chromium smelting slag, reduces hexavalent chromium to trivalent chromium, meets the standard requirements of the Technical Specification for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007), and the leachate limit values ​​of total chromium <9 mg / L, hexavalent chromium <3 mg / L, and barium <50 mg / L, thereby converting the metal chromium smelting slag from hazardous solid waste to ordinary solid waste.

[0008] The objective of the present invention is achieved through the following technical solutions: A method for removing toxic pollutants from metal chromium smelting waste slag, the method comprising the following treatment process: The smelting slag is crushed and sieved, and the hexavalent chromium is detected in the leaching liquid according to the requirements of the technical specifications for environmental protection of chromium slag pollution control to determine whether it is a hazardous solid waste; then, a mixed reducing agent of carbon, calcium, magnesium and aluminum is added, mixed evenly with a mixer, a binder is added, and the mixture is placed in a roasting furnace for calcination, and after cooling, the mixture is tested according to the technical specifications for environmental protection of chromium slag pollution control; When powdered carbon, calcium, magnesium and aluminum are added as reducing agents to powdered chromium smelting slag containing hexavalent chromium, the following reactions occur under calcination conditions in a roasting furnace: The main reaction is: 3C+2CrO3 = Cr2O3+3CO↑ 3Ca+2CrO3= Cr2O3+3CaO 3Mg+2CrO3= Cr2O3+3MgO 2AI+2CrO3= Cr2O3+ AI 2O3 The side reaction is: 3C+Cr2O3 = 2Cr+3CO↑ 3Ca+Cr2O3=2Cr+3CaO 3Mg+Cr2O3=2Cr+3MgO 2AI+Cr2O3= Cr2O3+ AI2O3.

[0009] The method for removing toxic pollutants from metal chromium smelting waste slag comprises crushing the smelting slag into particles with a size of 0 to 60 mm; preferably, crushing the smelting slag into particles with a size of 0-3 mm.

[0010] The method for removing toxic pollutants from metal chromium smelting waste slag comprises sampling and analyzing the total chromium, hexavalent chromium and barium contents, and adding the reducing agent dosage according to the hexavalent chromium content.

[0011] The method for removing toxic pollutants from metal chromium smelting waste slag has a calcination temperature of 600°C to 1850°C and an optimum temperature of 1400°C to 1600°C.

[0012] In the method for removing toxic pollutants from metal chromium smelting waste slag, the particle size of the reducing agent is 0.013 mm to 5 mm.

[0013] In the method for removing toxic pollutants from metal chromium smelting waste slag, the reducing agent is one of carbon, calcium, magnesium, and aluminum, or a mixture of multiple of the above, and the amount added is 0 to 15% of the weight of the metal chromium smelting slag.

[0014] The method for removing toxic pollutants from metal chromium smelting waste slag comprises adding a binder to press the mixture into blocks after the mixture is completed, and the volume density of the blocks after pressing is 1 g / cm3 to 6 g / cm3.

[0015] In the method for removing toxic pollutants from metal chromium smelting waste slag, the constant temperature time is 0 to 24 hours.

[0016] The advantages and effects of the present invention are: The present invention achieves the pollution control index limit values ​​(Table 5 index in the specification) of brick and block products produced by using chromium slag in the technical specification by controlling the process parameters such as the amount of reducing agent added, reaction temperature, and reaction time, with total chromium <0.3mg / L, hexavalent chromium <0.1mg / L, and barium <4.0mg / L. The smelting slag is crushed and sieved, and the hexavalent chromium is detected as hazardous solid waste in the leaching liquid according to the requirements of the Technical Specification for Environmental Protection of Chromium Slag Pollution Control (Provisional) (HJ / T301-2007). Then, carbon, calcium, magnesium, and aluminum are added as a mixed reducing agent, mixed evenly with a mixer, a binder is added, and the mixture is placed in a roasting furnace for calcination. After cooling, the mixture is tested according to the Technical Specification for Environmental Protection of Chromium Slag Pollution Control. All indicators are lower than the pollution control index limit values ​​of brick and block products produced by using chromium slag in the technical specification, thereby achieving the detoxification of metal chromium smelting waste slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a process flow chart of detoxification of metallic chromium smelting slag. DETAILED DESCRIPTION

[0018] The present invention will be described in detail below with reference to the embodiments of the accompanying drawings.

[0019] Example 1 105 kg of smelting slag was crushed and all passed through a 3mm sieve. The leaching solution was prepared for testing in accordance with the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The hexavalent chromium was 98 mg / L, which was a hazardous solid waste. Then carbon, calcium, magnesium, aluminum, and a variety of mixed reducing agents were added, and the weight of each reducing agent was 1% of the weight of the smelting slag. The particle size was under a 200-mesh sieve. The mixture was mixed evenly with a mixer, and a binder was added to press into 6 pieces, each with a size of 460 mm × 150 mm × 75 mm. The pieces were placed in a roasting furnace for calcination at a temperature of 1600°C for 12 hours. After cooling, the leaching solution was prepared for testing in accordance with the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007), with total chromium 0.1 mg / L, hexavalent chromium 0.05 mg / L, and barium 0.2 mg / L. All indicators were lower than the pollution control index limits for bricks and block products produced using chromium slag in the technical specifications. Example 2

[0020] 105 kg of smelting slag was crushed and all passed through a 3mm sieve. The leaching solution was prepared for testing in accordance with the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The hexavalent chromium content was 91 mg / L, which was a hazardous solid waste. Then, carbon and magnesium mixed reducing agents were added, and the weight of each reducing agent was 2% of the weight of the smelting slag. The particle size was all below the 200 mesh sieve. The mixture was mixed evenly with a mixer, and a binder was added to press into 6 pieces, each with a size of 460mm×150mm×75mm. The pieces were placed in a roasting furnace for calcination at a temperature of 1600℃ and kept at a constant temperature for 6 hours. After cooling, the leaching solution was prepared for testing in accordance with the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The total chromium content was 0.15 mg / L, the hexavalent chromium content was 0.09 mg / L, and the barium content was 0.2 mg / L. All indicators were lower than the pollution control index limit values ​​of bricks and blocks produced using chromium slag in the technical specifications. Example 3

[0021] 105 kg of smelting slag was crushed and all passed through a 3mm sieve. The leaching solution was prepared for testing in accordance with the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The hexavalent chromium was 102 mg / L, which is a hazardous solid waste. Then, magnesium powder reducing agent was added at 4% of the weight of the smelting slag, and the particle size was under a 200-mesh sieve. The mixture was mixed evenly with a mixer, and a binder was added to press it into 6 pieces, each with a size of 460 mm × 150 mm × 75 mm. The pieces were placed in a roasting furnace for calcination at a temperature of 1600°C and kept at a constant temperature for 6 hours. After cooling, the leaching solution was prepared for testing in accordance with the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The total chromium was 0.12 mg / L, the hexavalent chromium was 0.07 mg / L, and the barium was 0.2 mg / L. All indicators were lower than the pollution control index limit values ​​of bricks and blocks produced using chromium slag in the technical specifications. Example 4

[0022] 105 kg of smelting slag was crushed and all passed through a 3mm sieve. The leaching solution was prepared for testing in accordance with the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The hexavalent chromium content was 87 mg / L, which was a hazardous solid waste. Then calcium and aluminum mixed reducing agents were added, and the weight of each reducing agent was 2% of the weight of the smelting slag. The particle size was all below the 200 mesh sieve. The mixture was mixed evenly with a mixer, and a binder was added to press into 6 pieces, each with a size of 460mm×150mm×75mm. The pieces were placed in a roasting furnace for calcination at a temperature of 1400℃ and kept at a constant temperature for 8 hours. After cooling, the leaching solution was prepared for testing in accordance with the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The total chromium content was 0.1 mg / L, the hexavalent chromium content was 0.09 mg / L, and the barium content was 0.2 mg / L. All indicators were lower than the pollution control index limit values ​​of bricks and blocks produced using chromium slag in the technical specifications. Example 5

[0023] 105 kg of smelting slag was crushed and all passed through a 3mm sieve. The leaching solution was prepared for testing in accordance with the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007). The hexavalent chromium was 105 mg / L, which is a hazardous solid waste. Then, carbon, calcium, magnesium, and aluminum mixed reducing agents were added, and the weight of each reducing agent was 1% of the weight of the smelting slag. The particle size was under a 200 mesh sieve. The mixture was mixed evenly with a mixer, and a binder was added to press into 6 pieces, each of which was 460 mm × 150 mm × 75 mm in size. The pieces were placed in a roasting furnace for calcination at a temperature of 1400°C for 6 hours. After cooling, the leaching solution was prepared for testing in accordance with the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control (Interim) (HJ / T301-2007), with total chromium 0.1 mg / L, hexavalent chromium 0.08 mg / L, and barium 0.2 mg / L. All indicators were lower than the pollution control index limits for bricks and building blocks produced using chromium slag in the technical specifications.

Claims

1. A method for removing toxic pollutants from chromium smelting waste residue, characterized in that: The method comprises the following processing steps: First, the smelting slag is crushed and sieved, and the leaching liquid is tested according to the requirements of the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control to identify hexavalent chromium as hazardous solid waste; then, carbon, calcium, magnesium, and aluminum mixed reducing agents are added, mixed evenly with a mixer, a binder is added, and the mixture is placed in a roasting furnace for calcination. After cooling, the mixture is tested according to the Technical Specifications for Environmental Protection of Chromium Slag Pollution Control; When powdered carbon, calcium, magnesium and aluminum are added as reducing agents to powdered chromium smelting slag containing hexavalent chromium, the following reactions occur under calcination conditions in a roasting furnace: The main reaction is: 3C+2CrO3 = Cr2O3+3CO↑ 3Ca+2CrO3= Cr2O3+3CaO 3Mg+2CrO3= Cr2O3+3MgO 2AI+2CrO3= Cr2O3+ AI2O3 The side reaction is: 3C+Cr2O3 = 2Cr+3CO↑ 3Ca+Cr2O3=2Cr+3CaO 3Mg+Cr2O3=2Cr+3MgO 2AI+Cr2O3= Cr2O3+ AI2O3.

2. A method for removing toxic pollutants from metal chromium smelting waste slag according to claim 1, characterized in that: The method crushes the smelting slag into particles with a size of 0 to 60 mm; preferably, the smelting slag is crushed into particles with a size of 0-3 mm.

3. The method for removing toxic pollutants from chromium smelting waste slag according to claim 1, characterized in that: The sampling is performed to analyze the total chromium, hexavalent chromium and barium contents, and the amount of reducing agent is adjusted according to the hexavalent chromium content.

4. The method for removing toxic pollutants from chromium smelting waste slag according to claim 1, characterized in that: The calcination temperature is 600°C to 1850°C; the optimum temperature is 1400°C to 1600°C.

5. The method for removing toxic pollutants from chromium smelting waste slag according to claim 1, characterized in that: The reducing agent has a particle size of 0.013 mm to 5 mm.

6. The method for removing toxic pollutants from chromium smelting waste slag according to claim 1, characterized in that: The reducing agent is one of carbon, calcium, magnesium and aluminum, or a mixture of the above-mentioned agents, and the amount added is 0 to 15% of the weight of the metal chromium smelting slag.

7. The method for removing toxic pollutants from chromium smelting waste slag according to claim 1, characterized in that: After the mixing is completed, a binder is added to press the material into blocks, and the volume density of the blocks is 1 g / cm3 to 6 g / cm3.

8. The method for removing toxic pollutants from chromium smelting waste slag according to claim 1, characterized in that: The constant temperature time is from 0 hours to 24 hours.

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