A method for treating tin-bearing iron ore by suspension magnetization roasting

Abstract

The application belongs to the technical field of mineral processing, and discloses a tin-containing iron ore suspension magnetization roasting treatment method. After dry grinding of tin-containing iron ore, decomposition roasting and magnetization roasting are carried out, efficient and reasonable separation of iron and tin in the tin-containing iron ore is realized, and tin metal can be recycled. The method has the advantages of simple process, high separation efficiency, low cost, environmental friendliness and the like.

Description

Technical Field

[0001] This application belongs to the field of mineral processing technology, specifically relating to a method for suspension magnetization roasting of tin-containing iron ore. Background Technology

[0002] Iron ore is a vital resource for my country's steel industry and a major strategic necessity for the country.

[0003] Difficult-to-process tin-bearing iron ore refers to high-iron, low-tin iron concentrates or high-iron, low-tin ores. The tin in these ores generally exists primarily as cassiterite, with extremely fine particles distributed disseminated within the iron minerals, making it difficult to concentrate and recover using beneficiation methods. Furthermore, the tin grade of these tin-bearing iron ores often exceeds the permissible content for ironmaking raw materials, or they may contain other harmful elements. Therefore, to be used as raw material for ironmaking, processing is necessary to prevent the tin and other impurities in the ore from causing harm in the blast furnace. According to national standards, the limit for the harmful element Sn in iron concentrate entering the blast furnace is Sn ≤ 0.08%. Tin is easily reduced and dissolves in molten iron to form alloys with pig iron during blast furnace smelting. During steelmaking, tin also enters the steel; when this amount exceeds a certain level, it causes hot brittleness in the steel and has a detrimental effect on the ductility and toughness of the steel.

[0004] Currently, the main methods for recycling tin-containing iron minerals both domestically and internationally include sulfidation volatilization, chlorination volatilization, and weak reduction roasting volatilization.

[0005] The sulfidation volatilization method is currently the most effective technology in the world for processing tin middlings, lean tin concentrate, or lean tin smelting slag, and can effectively separate Sn from other elements. Its principle is based on the volatility of SnS to recover tin. When applied to processing tin middlings, the Sn volatilization rate is consistently above 98%, and the Sn content in the waste slag is below 0.07%. However, this method has disadvantages: the sulfidation temperature is relatively high, requiring 1180℃~1300℃; the roasting time is relatively long, requiring 60~90 minutes; and the flue gas contains a large amount of SO2 gas, which must be treated before emission to avoid secondary pollution.

[0006] The chlorination roasting method involves mixing Sn-containing materials with a chlorinating agent, grinding, pelletizing, drying, and then feeding them together with a carbonaceous reducing agent into a rotary kiln. The mixture is then roasted at approximately 1000°C. During roasting, Sn and almost all other non-ferrous metals in the pellets volatilize as chlorides, which are then recovered in a dust collection system. This high-temperature chlorination volatilization method has been developed to handle low-grade, high-impurity (especially arsenic and iron) tin-poor materials that cannot be processed by conventional tin smelting methods, and is one of the effective means for the comprehensive recovery of complex polymetallic minerals. However, due to the strong chemical reactivity of chlorine and hydrogen chloride, their high corrosiveness to industrial equipment, and their environmental hazards, the widespread application of this method is greatly limited.

[0007] The reduction roasting and volatilization method. The patent "A method for separating and recovering tin from tin-bearing tailings in mineral processing (Patent No.: 201210453731.2)" employs a weak reduction roasting method to treat tin-bearing tailings that are difficult to process using traditional mineral processing techniques. This method achieves a tin volatilization rate of over 70% in the tin-bearing tailings, enabling efficient separation and recovery of tin from low-grade tin-bearing tailings. The technical principle is that under high-temperature conditions, SnO2 is easily reduced to SnO, and SnO has a high vapor pressure, thus achieving SnO volatilization and recovery. However, this method does not consider the separation and recovery of iron from the tailings. Furthermore, the material preparation before roasting is complex, requiring not only pelletizing but also drying, which is not conducive to industrial-scale production. Patent CN201410347175 discloses a method for preparing iron concentrate for iron smelting from tin-containing iron ore. The method involves grinding tin-containing iron ore and sodium carbonate separately, then mixing them uniformly in a certain mass ratio. The mixture is then lumped together and subjected to reduction roasting. After reduction roasting, the product is cooled, and then ball-milled and leached in water to obtain a mixed slurry. The resulting slurry is then magnetically separated to obtain magnetite concentrate, while the remaining non-magnetic material is filtered to separate sodium stannate solution and filter residue. This method can be used to process tin-containing iron ore and tin-containing iron tailings resources. However, the preparation of roasting materials is relatively cumbersome, and it suffers from drawbacks such as long reduction roasting time, high temperature, and high energy consumption.

[0008] In summary, current technological methods are insufficient for the efficient separation and effective recovery of iron and tin from my country's abundant tin-iron ore reserves and low-grade tin-bearing tailings. Therefore, given the dwindling resources of high-quality iron and tin ore in my country, there is an urgent need to develop an efficient, environmentally friendly, and economically viable method for utilizing tin-bearing iron ore. Summary of the Invention

[0009] Objective of the Invention: To address the shortcomings of existing technologies, this application provides a method for suspension magnetization roasting of tin-bearing ore. This method involves dry grinding, followed by decomposition roasting and magnetization roasting of the tin-bearing ore, achieving efficient and rational separation of iron and tin in the ore while simultaneously recovering tin metal. The method described in this application has advantages such as simple process, high separation efficiency, low cost, and environmental friendliness.

[0010] Technical solution: The suspension magnetization roasting method for tin-bearing iron ore described in this application includes the following steps:

[0011] Step 1: Crush the tin-iron ore raw material, grind it to -1mm using a high-pressure roller mill, and then continuously feed it into a cyclone preheater for preheating via a screw feeder;

[0012] Step 2: The preheated material is fed into the suspension heating furnace. The bottom of the suspension heating furnace is connected to the burner. Natural gas and air are introduced into the burner for combustion to form high-temperature flue gas. The preheated material is in a suspended state under the action of the high-temperature flue gas, forming heated material and undergoing a pre-oxidation reaction. The heated material and high-temperature flue gas are fed into the first cyclone separator through the pipe at the top of the suspension heating furnace. After gas-solid separation, the heated material is discharged from the lower outlet of the first cyclone separator.

[0013] Step 3: The above-mentioned heated material is continuously fed into the suspension magnetization roasting furnace. A mixture of nitrogen and reducing gas is introduced into the furnace. Under weak reducing atmosphere conditions, the heated material and the reducing gas mixture undergo a reduction reaction to carry out suspension magnetization roasting. The roasted magnetized material is fed into the second cyclone separator through the outlet of the suspension magnetization roasting furnace. The strongly magnetic Fe2O3 is oxidized to the more strongly magnetic γ-Fe2O3 and releases latent heat. The sensible heat and latent heat can be recovered through the waste heat recovery device.

[0014] Step 4: After gas-solid separation by the second cyclone separator, the high-temperature tin-containing waste gas and dust are fed into a water-cooled heat exchanger for cooling and then enter the dust collection system. The magnetized solid material is cooled to 180~220℃ under nitrogen protection and then air-cooled.

[0015] Step 5: The air-cooled magnetized material is passed through a water-cooled heat exchanger. The secondary cooled material after water cooling is fed into a stirred mill for fine grinding. The finely ground material discharged from the stirred mill outlet is fed into a weak magnetic separator for magnetic separation to obtain high-grade iron concentrate.

[0016] In step 2 above, the main reaction formula during the pre-oxidation reaction of the preheated material is:

[0017] Fe₂O₃•nH₂O=αFe₂O₃+nH₂O (1)

[0018] 4FeCO3 + O2 = 2αFe2O3 + 4CO2 (2)

[0019] 3FeCO3 = Fe3O4 + 2CO2 + CO (3)

[0020] Specifically, in step 2, the high-temperature flue gas after gas-solid separation in the first cyclone separator is fed into the cyclone preheater to preheat the raw materials.

[0021] Specifically, in step 2, the temperature of the material after preheating by the first cyclone preheater is 300~450℃, the residence time of the preheated material in the suspension heating furnace is 5~15min, and the oxidation reaction temperature of the heated material is 700~1000℃.

[0022] In step 3 above, the main reaction equation when the reducing gas and the heated material react is:

[0023] SnO2 + CO = SnO + CO2 (4)

[0024] 3Fe₂O₃ + CO = 2Fe₃O₄ + CO₂ (5)

[0025] 3Fe2O3+H2=2Fe3O4+H2O (6).

[0026] Specifically, in step 3, the reducing gas mixture used is a mixture of nitrogen and reducing gas (CO, H2).

[0027] Specifically, in step 3, the ratio of the reducing gas mixture introduced into the furnace is N2 / (CO+H2) = 1.5~3.5, the reaction temperature of the heated material and the reducing gas in the suspension magnetized roasting furnace is 600~850℃, and the roasting time is 15~30min. Further research found that the process conditions during reduction have a significant impact on the iron grade and tin content in the final product. Further optimization yielded the following results: reduction reaction temperature: 750~800℃; gas concentration ratio: N2 / (CO+H2) = 2~3; reduction time: 20~30 minutes. The optimal process conditions are: reduction reaction temperature: 760℃; gas concentration ratio: N2 / (CO+H2) = 2.3; reduction time: 25 minutes.

[0028] In step 4 above, the main reaction formula for the disproportionation reaction of SnO is:

[0029] 2SnO=SnO2+Sn(7).

[0030] In step 4 above, the main reaction formula for the oxidation of strongly magnetic Fe2O3 to more strongly magnetic γ-Fe2O3 is:

[0031] 4Fe3O4+O2=6γFe2O3(8).

[0032] Specifically, in step 4, the strongly magnetic Fe2O3 is oxidized to the more strongly magnetic γ-Fe2O3 and releases latent heat. The sensible heat and latent heat are recovered by a waste heat recovery device.

[0033] Specifically, in step 4, the temperature of the material cooled after heat exchange in the cooler is ≤200℃. At high temperatures, SnO products volatilize into the flue gas in gaseous form. When the flue gas temperature decreases, SnO2 and Sn are generated, thus allowing for further recovery of tin from the tin-containing dust in the dust collection system.

[0034] Specifically, in step 4, the flue gas from the second cyclone separator enters the dust collection system. After being cooled (below 80°C, at which point gaseous tin and its oxides do not exist in the dust collection system), the exhaust gas after dust collection is discharged through the chimney. The remaining tin-containing dust is collected and the tin in it is further processed.

[0035] Specifically, in step 5, the temperature of the secondary cooled material after heat exchange by the water-cooled heat exchanger is ≤80℃.

[0036] Specifically, in step 5, the particle size of the material after fine grinding by the stirred mill is -0.074mm, accounting for 60~95%.

[0037] Specifically, in step 5, a wet magnetic separator performs weak magnetic separation (600-1500 Oe), with the iron concentrate having a TFe grade ≥65% and Sn ≤0.08%.

[0038] This invention provides a new technology for energy-saving and efficient separation of tin-iron ore, which reduces the process production cost of tin-iron ore, revitalizes tin-iron ore resources, and achieves effective recovery of tin metal while obtaining iron concentrate with high iron grade and recovery rate and low tin content, which can be used as raw material for blast furnace ironmaking, thereby realizing the comprehensive utilization of tin-iron ore resources.

[0039] Beneficial effects: This invention uses suspension magnetization roasting for staged roasting, achieving precise control of various iron minerals during the roasting process, ultimately generating strong magnetic γ-Fe2O3 with low coercivity, which can significantly reduce the occurrence of magnetic agglomeration and significantly improve the quality of iron concentrate. At the same time, it can recover and reuse the sensible and latent heat of the cooling process and the preheating of flue gas, significantly reducing energy consumption compared with traditional roasting equipment such as rotary kilns and vertical shaft furnaces.

[0040] This invention uses a high-pressure roller mill to perform multi-layer crushing of materials, which increases the number of microcracks in the particles. This helps to improve the internal and external diffusion efficiency of reducing gas and gaseous products at the gas-solid interface, thereby increasing the reaction rate to achieve a stronger reduction effect. Furthermore, the product after grinding does not need to be dried and can be directly fed into the roasting system.

[0041] This invention utilizes preheating and multi-stage suspension roasting to ensure controllable and adjustable product output at each stage, thereby achieving efficient separation and effective recovery of iron and tin elements in tin-iron ore. Furthermore, the equipment and technology are mature, with high heat utilization, making it easily scalable for industrial application. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0043] Figure 2 This is a flowchart illustrating the present invention.

[0044] In the diagram: 1-High-pressure roller mill; 2-Screw feeder; 3-Cyclone preheater; 4-Suspension heating furnace; 5-Burner; 6-First cyclone separator; 7-Suspension magnetized roasting furnace; 8-Second cyclone separator; 9-Waste heat recovery device; 10-Water-cooled heat exchanger; 11-Stirred mill; 12-Weak magnetic separator; 13-Dust collection system. Detailed Implementation

[0045] The technical solution of this application will be described in detail below through embodiments, but the protection scope of this application is not limited to the embodiments described. The process is as follows: Figure 1 and Figure 2 As shown.

[0046] Example 1

[0047] The refractory tin-bearing iron ore used in this embodiment of the invention contains 35.62% TFe and 0.74% Sn by weight.

[0048] The tin-containing iron ore raw material, which is crushed and ground to -1mm by a high-pressure roller mill, is continuously fed into a cyclone preheater through the first screw feeder for preheating. The temperature of the preheated material is 350℃.

[0049] The preheated material is fed into a suspension heating furnace, the bottom of which is connected to a burner. Natural gas and air are introduced into the burner for combustion, forming high-temperature flue gas. The preheated material is in a suspended state under the action of the high-temperature flue gas and is heated to 800°C to form heated material and undergo a pre-oxidation reaction. The residence time of the heated material in the suspension heating furnace is 5 minutes. The heated material and the high-temperature flue gas are fed into the first cyclone separator through the pipe at the top of the suspension heating furnace. After gas-solid separation, the high-temperature flue gas is fed into the cyclone preheater to preheat the raw material. The heated material is discharged from the lower outlet of the first cyclone separator.

[0050] A reducing gas mixture consisting of nitrogen and reducing gas (CO, H2) is fed into the second screw feeder. The sulfiding agent from the second screw feeder and the heated material discharged from the lower outlet of the first cyclone separator are continuously fed into the suspension magnetization roasting furnace. The ratio of the reducing gas mixture introduced into the furnace is N2 / (CO+H2) = 3. The heated material and the reducing gas undergo a reduction reaction in the suspension magnetization roasting furnace at a reaction temperature of 700℃. Suspension sulfidation roasting is carried out for 20 minutes. The magnetized material after roasting is fed into the second cyclone separator through the outlet of the suspension magnetization roasting furnace.

[0051] After gas-solid separation in the second cyclone separator, the high-temperature tin-containing waste gas is fed into the suspension heating furnace to heat the furnace body, and the magnetized material is fed into the cooler. In the cooler, the magnetized material and the fed nitrogen gas exchange heat in a countercurrent manner. The primary cooled material, which is cooled to 185°C by heat exchange, is fed into the third cyclone separator for gas-solid separation.

[0052] After gas-solid separation, the primary cooled material is passed through a water-cooled heat exchanger. The secondary cooled material, cooled to 80°C by water cooling, is fed into a stirred mill for fine grinding. The finely ground material discharged from the stirred mill outlet has a particle size of -0.074mm, accounting for 65%. The finely ground material is then fed into a weak magnetic separator for magnetic separation. The magnetic separator uses an electric field strength of 1000 Oe, resulting in an iron concentrate with extremely low tin content. The iron concentrate contains 66.1% TFe and 0.073% tin by mass percentage.

[0053] The flue gas from the second cyclone separator enters the dust collection system. After being cooled (below 80℃, at which point gaseous tin and its oxides are no longer present in the dust collection system), the exhaust gas after dust collection is discharged through the chimney. The remaining tin-containing dust is collected for further processing of the tin.

[0054] Example 2

[0055] The method is the same as in Example 1, except that:

[0056] (1) The refractory tin-bearing iron ore used in the embodiments of the present invention contains 29.44% TFe and 0.91% Sn by weight.

[0057] (2) The temperature of the material after being heated in the suspension heating furnace is 850℃, and the residence time of the preheated material in the suspension heating furnace is 7min;

[0058] (3) The mixing ratio of nitrogen and reducing gas (CO, H2) in the mixed reducing gas is 3.5, the reaction temperature of the heated material and the reducing gas in the suspension magnetization roasting furnace is 750℃, and the roasting time is 30min;

[0059] (4) The temperature of the material after primary cooling via heat exchange in the cooler is 170℃;

[0060] (5) The temperature of the material after secondary cooling after heat exchange in the first water-cooled heat exchanger is 70℃;

[0061] (6) The particle size of the material after fine grinding by the stirred mill is -0.074mm, accounting for 85%. The iron concentrate contains 65.21% TFe by mass percentage and 0.07% tin.

[0062] Example 3

[0063] The system and steps are the same as in Example 1, except that:

[0064] (1) The refractory tin-bearing iron ore used in the embodiments of the present invention contains 40.67% TFe and 0.71% Sn by weight.

[0065] (2) The temperature of the material after being heated in the suspension heating furnace is 850℃, and the residence time of the preheated material in the suspension heating furnace is 10min;

[0066] (3) The mixing ratio of nitrogen and reducing gas (CO, H2) in the mixed reducing gas is 3, the reaction temperature of the heated material and the reducing gas in the suspension magnetization roasting furnace is 800℃, and the roasting time is 15min;

[0067] (4) The temperature of the material after primary cooling via heat exchange in the cooler is 150℃;

[0068] (5) The temperature of the material after secondary cooling after heat exchange in the first water-cooled heat exchanger is 65℃;

[0069] (6) The particle size of the material after fine grinding by the stirred mill is -0.074mm, accounting for 70%. The iron concentrate contains 67.31% TFe by mass percentage and 0.06% tin.

[0070] Example 4

[0071] The system and steps are the same as in Example 1, except that:

[0072] (1) The refractory tin-bearing iron ore used in the embodiments of the present invention contains 35.44% TFe and 0.69% Sn by weight.

[0073] (2) The temperature of the material after being heated in the suspension heating furnace is 850℃, and the residence time of the preheated material in the suspension heating furnace is 10min;

[0074] (3) The mixing ratio of nitrogen and reducing gas (CO, H2) in the mixed reducing gas is 2.5, the reaction temperature of the heated material and the reducing gas in the suspension magnetization roasting furnace is 730℃, and the roasting time is 25min;

[0075] (4) The temperature of the material after primary cooling via heat exchange in the cooler is 150℃;

[0076] (5) The temperature of the material after secondary cooling after heat exchange in the first water-cooled heat exchanger is 60℃;

[0077] (6) The particle size of the material after fine grinding by the stirred mill is -0.074mm, accounting for 80%. The iron concentrate contains 65.36% TFe by mass percentage and 0.07% tin.

[0078] Example 5

[0079] The system and steps are the same as in Example 1. The process conditions selected are: reduction reaction temperature: 760℃; gas concentration ratio: N2 / (CO+H2) = 2.3; reduction time: 25 minutes. This example uses a tin-containing iron ore from Yunnan, which contains 36.1% TFe and 0.9% Sn by weight. Through the experimental operation in Example 5, the technical indicators of the iron concentrate containing 67.85% TFe and 0.067% tin by weight were obtained.

[0080] Based on the above embodiments, the preferred process conditions of this application are a calcination-reduction temperature of 750℃~800℃, a reducing gas concentration of N2 / (CO+H2) = 2~3, and a reduction-calcination time of 20~30 minutes. The optimal conditions are: reduction reaction temperature of 760℃; gas concentration ratio of N2 / (CO+H2) = 2.3; and reduction time of 25 minutes.

[0081] The above description is merely a preferred embodiment of this application and is not intended to limit this application.

Claims

1. A process for the suspension magnetization roasting of tin-bearing iron ores, characterized in that, It comprises the following steps: Step 1, crushing the cassiterite raw material, grinding to-1mm with high-pressure roller mill, continuously feeding into the cyclone preheater through the screw feeder for preheating; Step 2, the preheated preheating material is fed into the suspension heating furnace, the bottom of the suspension heating furnace is connected with the burner, natural gas and air are introduced into the burner for combustion to form high-temperature flue gas, the preheating material is in a suspended state under the action of the high-temperature flue gas, the heated material is formed and the pre-oxidation reaction occurs, the heated material and the high-temperature flue gas are fed into the first cyclone separator through the pipeline at the top of the suspension heating furnace, after gas-solid separation, the heated material is discharged from the lower discharge port of the first cyclone separator; Step 3, the above heated material is continuously fed into the suspension magnetization roasting furnace, nitrogen and reducing gas mixed gas are introduced into the furnace body, the heated material and the reducing gas mixed gas occur reduction reaction under the condition of weak reducing atmosphere, suspension magnetization roasting, the magnetized material after roasting is fed into the second cyclone separator through the discharge port of the suspension magnetization roasting furnace, Fe2O3 with strong magnetism is oxidized to γ-Fe2O3 with relatively strong magnetism and releases latent heat, which can be recovered by waste heat recovery device; Step 4, after gas-solid separation in the second cyclone separator, high-temperature tin-containing waste gas and smoke dust are cooled in the water-cooled heat exchanger and enter the dust collection system, and the magnetized solid material is cooled to 180-220℃ under the protection of nitrogen and then air-cooled; Step 5, the air-cooled magnetized material passes through the water-cooled heat exchanger, the secondary cooled material after water-cooled heat exchange is fed into the stirring mill for fine grinding, the fine ground material discharged from the discharge port of the stirring mill is fed into the low-intensity magnetic separator for magnetic separation to obtain high-grade iron concentrate; In step 2, the temperature of the material preheated by the first cyclone preheater is 300-450℃, the residence time of the preheated material in the suspension heating furnace is 5-15min, and the oxidation reaction temperature of the heated material is 700-1000℃; In step 3, the proportion of reducing gas mixed gas introduced into the furnace is N2 / (CO+H2)=1.5-3.5, the reaction temperature of the heated material and the reducing gas in the suspension magnetization roasting furnace is 600-850℃, and the roasting time is 15-30min.

2. The tin-bearing iron ore suspension magnetization roasting process according to claim 1, characterized in that, In step 2, the high-temperature flue gas after gas-solid separation in the first cyclone separator is fed into the cyclone preheater to preheat the raw material.

3. The tin-bearing iron ore suspension magnetization roasting process according to claim 1, characterized in that, In step 4, the temperature of the once-cooled material after heat exchange in the heat exchanger is ≤200℃; wherein the SnO product at high temperature volatilizes into the flue gas in the form of gas, when the flue gas temperature decreases, SnO2 and Sn are generated, so the tin can be further recovered from the tin-containing smoke dust in the dust collection system.

4. The tin-bearing iron ore suspension magnetization roasting process according to claim 1, characterized in that, In step 4, the flue gas of the second cyclone separator enters the dust collection system, the tail gas after cooling and dust collection is discharged through the chimney, and the remaining tin-containing dust is collected for further recovery and treatment of tin.

5. The tin-bearing iron ore suspension magnetization roasting process according to claim 1, characterized in that, In step 5, the temperature of the secondary cooled material after heat exchange in the water-cooled heat exchanger is ≤80℃.

6. The tin-bearing iron ore suspension magnetization roasting process according to claim 1, characterized in that, In step 5, the particle size of the material after fine grinding in the stirring mill is-0.074mm, accounting for 60-95%.

7. The tin-bearing iron ore suspension magnetization roasting process according to claim 1, characterized in that, In step 5, the wet magnetic separator is used for low-intensity magnetic separation, the TFe grade of the iron concentrate is ≥65%, and the tin content is ≤0.08%.

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