Optimization method for recovering iron and improving activity by synergistically magnetizing and roasting iron tailings and coal gangue

Abstract

The invention belongs to the technical field of solid waste treatment, and particularly discloses an iron tailing and coal gangue synergistic magnetizing roasting iron recovery and activity improvement optimization method which comprises the following steps: S1, taking coal gangue doping amount, carbon powder doping amount, heating temperature and heating time in magnetizing roasting as influence factors; designing a response surface test scheme by taking the iron grade and the iron recovery rate of the reduced iron powder and the tailing activity index as response values; s2, iron tailings, coal gangue and carbon powder are mixed, magnetization reduction roasting, ball milling and magnetic separation are conducted, reduced iron powder is recovered, and the iron grade and the iron recovery rate of the reduced iron powder are tested; s3, testing the activity index of the tailings; s4, establishing a response surface model of three response values, and verifying the reliability of the model; and S5, obtaining an optimization technical scheme which simultaneously meets the multi-objective optimization demand conditions of the three response surface models. The application value of the reduced iron powder of the iron tailings and the application value of the tailings are synergistically improved, the overall income of iron tailing treatment products is improved, and solid waste co-treatment is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization, and in particular relates to a method for optimizing iron recovery and activity enhancement by coordinated magnetization roasting of iron tailings and coal gangue. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Iron tailings refer to the solid waste remaining after roughing or concentrating in the iron ore mining process. my country's iron ore resources are of low grade and have many associated ores. For every ton of iron concentrate produced, 2.5 to 3.0 tons of iron tailings are discharged. The total amount of iron tailings is large and the comprehensive utilization rate is low. The main resource utilization methods of iron tailings include the following two: (1) The total proportion of SiO2, Al2O3, Fe2O3 and CaO in iron tailings is more than 70%, which has a certain volcanic ash activity and can be used as a building material. However, the activity of untreated iron tailings is low, with an activity index of only about 60%. It can only be used as an inactive mineral admixture to fill cement and concrete, and its application value is low. The activity of iron tailings can be stimulated by mechanical grinding and high-temperature heating, making it an active mineral admixture that can be used to prepare solid waste-based cementitious materials, but these activity stimulation methods require a lot of energy and are costly. The above reasons limit the application scale of iron tailings as building materials.

[0004] (2) Since iron tailings contain a large amount of weakly magnetic iron oxide, some studies have attempted to recover the iron component through magnetization reduction roasting. The main method is: the iron tailings are roasted at high temperature in a reducing atmosphere such as H2 or CO to reduce the weakly magnetic Fe2O3 to the strongly magnetic Fe3O4, and then the reduced iron powder rich in the strongly magnetic Fe3O4 in the iron tailings roasting product is recovered through a weak magnetic separation process. The remaining tailings can be used as building materials. However, the process parameters of this method are based on the iron grade and iron recovery rate of the reduced iron powder. The value of the recovered reduced iron powder is mainly considered, and the application value of the tailings that account for more than 70% of the total weight of the iron tailings is not taken into account. The activity of the tailings produced by this method is between 60% and 70%, and its application value as a building material is still low. Most of the tailings can only be abandoned, which greatly reduces the overall benefits of iron tailings.

[0005] In summary, the two main current methods of resource utilization of iron tailings only focus on the single benefits of using them for building materials or recycling iron, and fail to achieve the coordinated improvement of the application value of iron tailings for building materials and recycling iron from an overall perspective. As a result, the current treatment cost of iron tailings is high, the overall benefits are low, and some treatment products (tailings) cannot be used at a high value and can only be abandoned, which limits the large-scale and full-scale application of iron tailings. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for recovering iron and improving activity by synergistic magnetic roasting of iron tailings and coal gangue.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions: The method for recovering iron and improving activity by coordinated magnetization roasting of iron tailings and coal gangue comprises the following steps: S1: Taking the gangue content, carbon powder content, heating temperature and heating time in magnetic roasting as influencing factors, and the iron grade and iron recovery rate of reduced iron powder and tailings activity index as response values, a response surface test plan was designed.

[0008] S2: Mix the iron tailings, coal gangue and carbon powder in proportion, carry out magnetization reduction roasting, ball milling and magnetic separation, recover the reduced iron powder, and test the iron grade and iron recovery rate of the reduced iron powder.

[0009] S3: Test the activity index of tailings.

[0010] S4: Establish a response surface model with three response values ​​and verify the reliability of the model.

[0011] S5: Obtain an optimization technical solution that simultaneously meets the multi-objective optimization requirements of the three response surface models.

[0012] Gangue is solid waste generated during coal mining and coal processing. Currently, there are more than 7.5 billion tons of gangue stockpiled nationwide. The main components of gangue are silicon-aluminum oxides and are rich in carbon. This patent proposes a technical method for the coordinated magnetic roasting of iron tailings and gangue, mainly based on two reasons: first, the coordinated heating of iron tailings and silicon-aluminum materials can significantly improve the activity of iron tailings and enhance the application value of iron tailings as building materials; second, the carbon component in gangue can be used as a reducing agent, which can reduce the amount of reducing agents such as carbon powder; third, the coordinated disposal of iron tailings and gangue is achieved to achieve waste treatment. However, studies have shown that excessive addition of high silicon-aluminum materials will cause iron oxides to react with silicon-aluminum oxides to generate iron spinel compounds, which will hinder the reduction of weakly magnetic iron oxide and reduce the iron recovery rate of reduced iron powder. Therefore, it is necessary to accurately control the amount of gangue added. In addition, the three important technical parameters of carbon powder dosage, heating temperature and heating time in magnetic roasting will also have different effects on the iron grade of reduced iron powder, iron recovery rate of reduced iron powder and activity index of tailings.

[0013] Based on the above reasons, this patent constructs a response surface model between influencing factors (gangue dosage, carbon powder dosage, heating temperature, heating time) and response values ​​(iron grade of reduced iron powder, iron recovery rate of reduced iron powder, tailings activity index), accurately quantifies the influence of gangue dosage, carbon powder dosage, heating temperature and heating time on the iron grade of reduced iron powder, iron recovery rate of reduced iron powder and tailings activity index under the coupling of multiple influencing factors, and performs multi-objective optimization to obtain an optimization technical solution that simultaneously meets the multi-objective optimization requirements of the three response surface models, so as to solve the problem that the traditional iron tailings resource utilization method only focuses on the single benefit of using it for building materials or recovering iron, realizes the synergistic improvement of the application value of reduced iron powder and tailings of iron tailings, and improves the overall benefit of iron tailings treatment products.

[0014] In some embodiments, in step S1, the Box-Benhnken model of the response surface methodology is used to design the experimental scheme.

[0015] Preferably, the amount of coal gangue added is the mass ratio of coal gangue to iron tailings; the amount of carbon powder added is the mass ratio of carbon powder to iron tailings.

[0016] Further preferably, the mass ratio of iron tailings, coal gangue and carbon powder is 100:(10-30):(2-4).

[0017] More preferably, the heating temperature is 600° C. to 800° C. and the heating time is 30 min to 90 min.

[0018] Preferably, the influencing factors are set to three factor levels, represented by -1, 0, and 1 respectively.

[0019] In some embodiments, in step S2, iron tailings, coal gangue and carbon powder are mixed according to a designed ratio and then roasted in a closed environment at a designed heating temperature and a designed heating time; After the roasting is completed, the roasted product is water-quenched and dried; The dried calcined product is ball-milled and magnetically separated to recover the reduced iron powder, and the iron grade and iron recovery rate of the reduced iron powder are tested. Preferably, in step S3, according to the national standard "Pozzolanic mixed materials used in cement" GB / T 2847-2022, the tailings remaining after recovering the reduced iron powder replace 30% of the cement to prepare cement mortar specimens, and the 28-day compressive strength of the cement mortar specimens mixed with tailings and the pure cement mortar specimens are tested, and the tailings activity index is obtained by calculating the ratio of the 28-day compressive strength of the two.

[0020] In some embodiments, in step S4, a response surface model is established between the influencing factors (coal gangue dosage, carbon powder dosage, heating temperature, heating time) and the response values ​​(iron grade of reduced iron powder, iron recovery rate of reduced iron powder, tailings activity index), and the response surface model is expressed by a quadratic polynomial regression equation as follows: ; Where: Y is the response value; X i as influencing factors; k is the number of influencing factors. In the present invention, k =4; α 0. α i , α ii and α ij is an undetermined coefficient and is determined through experiments.

[0021] In some embodiments, in step S5, the multi-objective optimization requirements of the three response surface models are: (1) the iron grade of the reduced iron powder is above 50% (in order to ensure the ironmaking efficiency of the reduced iron powder and reduce the energy consumption of ironmaking); (2) the activity index of the tailings should be more than 80% (in building material applications, to ensure the application effect); (3) when both (1) and (2) are met, the iron recovery rate of the reduced iron powder takes the maximum value.

[0022] The beneficial effects achieved by one or more embodiments of the present invention are as follows: (1) By adding coal gangue during the magnetization roasting process of iron tailings, the activity of iron tailings can be significantly improved, thereby enhancing the application value of iron tailings as building materials; the carbon component in coal gangue can be used as a reducing agent, reducing the amount of reducing agents such as carbon powder; and the coordinated disposal of iron tailings and coal gangue can be achieved, thus achieving waste treatment with waste.

[0023] (2) By constructing a response surface model for the iron grade of reduced iron powder, the iron recovery rate of reduced iron powder, and the activity index of tailings, the effects of coal gangue dosage, carbon powder dosage, heating temperature, and heating time on the iron grade of reduced iron powder, the iron recovery rate of reduced iron powder, and the activity index of tailings under the coupling effect of multiple influencing factors are accurately quantified, and multi-objective optimization is performed to obtain an optimization technical solution that simultaneously meets the multi-objective optimization requirements of the three response surface models. This solves the problem that traditional methods for the resource utilization of iron tailings only focus on the single benefit of using them for building materials or recovering iron, and achieves a synergistic improvement in the application value of reduced iron powder and tailings in iron tailings, thereby improving the overall benefits of iron tailings treatment products. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 The process flow chart of an embodiment of the present invention.

[0026] Figure 2 Response surface diagrams of the influencing factors in the embodiment on the iron grade of reduced iron powder; wherein, (a) is a response surface diagram of the interaction between gangue content and carbon powder content on the iron grade of reduced iron powder; (b) is a response surface diagram of the interaction between gangue content and heating temperature on the iron grade of reduced iron powder; (c) is a response surface diagram of the interaction between gangue content and heating time on the iron grade of reduced iron powder; (d) is a response surface diagram of the interaction between carbon powder content and heating temperature on the iron grade of reduced iron powder; (e) is a response surface diagram of the interaction between carbon powder content and heating time on the iron grade of reduced iron powder; (f) is a response surface diagram of the interaction between heating temperature and heating time on the iron grade of reduced iron powder.

[0027] Figure 3 The figures are response surface diagrams of the influencing factors in the embodiments on the iron recovery rate of reduced iron powder; wherein, (a) is a response surface diagram of the interaction between the amount of coal gangue and the amount of carbon powder on the iron recovery rate of reduced iron powder; (b) is a response surface diagram of the interaction between the amount of coal gangue and the heating temperature on the iron recovery rate of reduced iron powder; (c) is a response surface diagram of the interaction between the amount of coal gangue and the heating time on the iron recovery rate of reduced iron powder; (d) is a response surface diagram of the interaction between the amount of carbon powder and the heating temperature on the iron recovery rate of reduced iron powder; (e) is a response surface diagram of the interaction between the amount of carbon powder and the heating time on the iron recovery rate of reduced iron powder; (f) is a response surface diagram of the interaction between the heating temperature and the heating time on the iron recovery rate of reduced iron powder.

[0028] Figure 4 Response surface diagrams of the influencing factors in the embodiment on the activity index of tailings; wherein, (a) is a response surface diagram of the interaction between gangue content and carbon powder content on the activity index of tailings; (b) is a response surface diagram of the interaction between gangue content and heating temperature on the activity index of tailings; (c) is a response surface diagram of the interaction between gangue content and heating time on the activity index of tailings; (d) is a response surface diagram of the interaction between carbon powder content and heating temperature on the activity index of tailings; (e) is a response surface diagram of the interaction between carbon powder content and heating time on the activity index of tailings; (f) is a response surface diagram of the interaction between heating temperature and heating time on the activity index of tailings. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0030] The present invention will be further described below in conjunction with the embodiments.

[0031] The method for recovering iron and improving activity by coordinated magnetization roasting of iron tailings and coal gangue comprises the following steps: S1: The coal gangue content, carbon powder content, heating temperature and heating time in magnetic roasting are taken as four influencing factors, and the iron grade of reduced iron powder, iron recovery rate of reduced iron powder and tailings activity index are taken as three response values. The Box-Benhnken model of response surface methodology is used for experimental design. The influencing factors are set at three factor levels, and the influencing factors are coded as shown in Table 1.

[0032] Table 1 Coding and level of influencing factors

[0033] The response surface experiment scheme includes 29 experimental combinations, as shown in Table 2.

[0034] Table 2 Coding and level of influencing factors

[0035] S2: First, the iron tailings, coal gangue and carbon powder are mixed evenly in proportion and then loaded into a covered steel can. The covered steel can is placed in a muffle furnace and heated at a set temperature for a certain time. The amount of coal gangue, the amount of carbon powder, the heating temperature and the heating time are carried out according to the parameters in Table 2. The chemical compositions of iron tailings, coal gangue and carbon powder are shown in Tables 3 to 5. Secondly, the covered steel can is taken out from the muffle furnace, the roasted product is quickly quenched with water, and filtered and dried. Then, the roasted product is wet-milled by a planetary ball mill at a 50% slurry concentration, and the grinding fineness is -300 mesh accounting for more than 90%. Finally, the ball-milled roasted product is wet-magnetically separated by an electromagnetic cylinder weak magnetic separator to recover the reduced iron powder. The magnetic field strength is 80kA / m. The reduced iron powder and tailings separated by magnetic separation are filtered and dried, and the iron grade and iron recovery rate of the reduced iron powder are tested. The iron grade is determined according to the national standard "Determination of total iron content of iron ore - Titanium trichloride reduction potassium dichromate titration method (conventional method)" GB / T6730.65-2009. The iron recovery rate is calculated according to the following formula:

[0036] Where: η is the iron recovery rate (%); β is the iron grade of reduced iron powder (%); αis the iron grade of iron tailings (%); γ is the mass ratio of reduced iron powder to iron tailings (%).

[0037] Table 3 Main chemical components of iron tailings (%)

[0038] Table 4 Main chemical components of coal gangue (%)

[0039] Table 5 Main components of carbon powder (%)

[0040] S3: According to the national standard "Pozzolanic mixed materials used in cement" GB / T 2847-2022, 30% of cement was replaced by tailings to prepare cement mortar specimens, and the 28-day compressive strength of the cement mortar specimens mixed with tailings and the pure cement mortar specimens was tested. The tailings activity index was calculated by the following formula.

[0041]

[0042] Where: A is the tailings activity index (unit: %); S 1 is the 28-day compressive strength of the tailings-added cement mortar specimen (unit: MPa); S 1 is the 28-day compressive strength of pure cement mortar specimen (unit: MPa).

[0043] The iron grade of reduced iron powder, iron recovery rate of reduced iron powder and tailings activity index corresponding to the 29 groups of tests obtained are shown in Table 6.

[0044] Table 6 Test results of iron grade, iron recovery rate and tailings activity index of reduced iron powder

[0045] S4: Establish a response surface model between influencing factors and response values, and the iron grade of reduced iron powder ( Y 1) Iron recovery rate of reduced iron powder ( Y 2) Tailings activity index ( Y 3) The quadratic polynomial regression equation of the measured value response surface model is as follows: Y 1=13.292+0.152 X 1+2.567 X 2+0.0908 X 3+0.0611 X 4-0.03 X 1 X 2+1×10-4 X 1 X 3+8×10 - 4 X 1 X 4+7×10 -4 X 2 X 3+0.00167 X 2 X 4-3.333×10 -5 X 3 X 4-0.00904 X 1²-0.467 X 2²-6.167×10 -5 X 3²-5.6×10 -4 X 4²； Y 2=23.40+0.194 X 1+1.242 X 2+0.131 X 3+0.186 X 4-0.0075 X 1 X 2-1.75×10 -4 X 1 X 3+0.00142 X 1 X 4+0.00225 X 2 X 3-8.33×10 -4 X 2 X 4-1.75×10 -4 X 3 X 4-0.00904 X 1²-0.479 X 2²-8.29×10 -5 X 3²-8.38×10 -4 X 4²； Y 3=61.946-0.133 X 1-1.217 X 2+0.0342 X 3 - 0.0958 D -0.01 X 1 X 2+8.25×10-4 X 1 X 3+7.5×10 -4 X 1 X 4-9.89×10 -18 X 2 X 3+0.0167 X 2 X 4+1.33×10 -4 X 3 X 4-0.00475 X 1²+0.15 X 2²-2.625×10 -5 X 3²-2.92×10 -4 X 4².

[0046] The response surface model was subjected to variance analysis, and the results are shown in Tables 7 to 9. The response surface model was represented by a 3D response surface, and the results are shown in Figure 2~Figure 4 shown.

[0047] Table 7 ANOVA results of the response surface model for iron grade of reduced iron powder

[0048] Note: P <0.05 indicates significant difference, indicated by *; P <0.01 indicates a very significant difference, indicated by **.

[0049] It can be seen from Table 7 that the iron grade response surface model of reduced iron powder P The value is <0.0001, which is extremely significant; the lack of fit term is not significant, which means that the proportion of abnormal errors in the process of fitting the quadratic polynomial regression equation with the test data is small, and the iron grade response surface model of reduced iron powder is credible; R 2 , after adjustment R 2 All of them exceeded 0.9 and were very close to 1, indicating that the proportion of response value changes explained by the influencing factors of the iron grade response surface model of reduced iron powder was very high, and the model had a high degree of fitting; after adjustment R 2 With the predicted value R 2 The difference between them is less than 0.2, indicating that there is a high correlation between the predicted value of the iron grade response surface model of reduced iron powder and the measured value. The signal-to-noise ratio is 27.0479, which is much greater than 4, indicating that the influence of accidental error of the iron grade response surface model of reduced iron powder is very low.P The values ​​are all <0.01, and the carbon powder content P The value is <0.05, indicating that the amount of coal gangue, heating temperature and heating time have a very significant effect on the iron grade of reduced iron powder, and the amount of carbon powder has a significant effect on the iron grade of reduced iron powder. Figure 2 Response surface diagram of the influence factors on the iron grade of reduced iron powder in the embodiment. Figure 2 From a, we can see that under the interaction between the amount of coal gangue and the amount of carbon powder, as the amount of coal gangue decreases, the iron grade of the reduced iron powder gradually increases; as the amount of carbon powder increases, the iron grade of the reduced iron powder first increases and then decreases. Figure 2 As shown in Figure b, under the interaction between the amount of coal gangue and the heating temperature, as the amount of coal gangue decreases, the iron grade of the reduced iron powder gradually increases; as the heating temperature increases, the iron grade of the reduced iron powder first increases and then decreases. Figure 2 It can be seen from Figure c that under the interaction between the amount of coal gangue and the heating time, as the amount of coal gangue decreases, the iron grade of the reduced iron powder gradually increases; as the heating time increases, the iron grade of the reduced iron powder first increases and then decreases. Figure 2 It can be seen from Figure d that under the interaction between the carbon powder content and the heating temperature, with the increase of carbon powder content and the increase of heating temperature, the iron grade of reduced iron powder first increases and then decreases. Figure 2 It can be seen from Figure 5 that under the interaction between carbon powder content and heating time, with the increase of carbon powder content and heating time, the iron grade of reduced iron powder first increases and then decreases. Figure 2 It can be seen from Figure 5 that under the interaction of heating temperature and heating time, with the increase of heating temperature and heating time, the iron grade of reduced iron powder first increases and then decreases.

[0050] Table 8 Results of variance analysis of the response surface model for iron recovery of reduced iron powder

[0051] Note: P <0.05 indicates significant difference, indicated by *; P <0.01 indicates a very significant difference, indicated by **.

[0052] It can be seen from Table 8 that the iron recovery rate response surface model of reduced iron powder P The value is <0.0001, which is extremely significant; the lack of fit term is not significant, indicating that the proportion of abnormal errors in the process of fitting the quadratic polynomial regression equation of the test data is small, and the response surface model of iron recovery rate of reduced iron powder is credible; R 2 , after adjustment R 2All of them exceeded 0.9 and were very close to 1, indicating that the proportion of response value changes explained by the influencing factors of the iron recovery rate response surface model of reduced iron powder was very high, and the model had a high degree of fitting; after adjustment R 2 With the predicted value R 2 The difference between them is less than 0.2, indicating that there is a high correlation between the predicted value of the iron recovery rate response surface model of reduced iron powder and the measured value. The signal-to-noise ratio is 25.6567, which is much greater than 4, indicating that the influence of accidental error of the iron recovery rate response surface model of reduced iron powder is very low. P The values ​​are all <0.01, and the carbon powder content P The value is <0.05, indicating that the amount of coal gangue, heating temperature and heating time have a very significant effect on the iron recovery rate of reduced iron powder, and the amount of carbon powder has a significant effect on the iron recovery rate of reduced iron powder.

[0053] Figure 3 Response surface diagram of the influence factors on the iron recovery rate of reduced iron powder in the embodiment. Figure 3 From a, we can see that under the interaction between the amount of coal gangue and the amount of carbon powder, as the amount of coal gangue decreases, the iron recovery rate of reduced iron powder gradually increases; as the amount of carbon powder increases, the iron recovery rate of reduced iron powder first increases and then decreases. Figure 3 As shown in Figure b, under the interaction between the amount of coal gangue and the heating temperature, as the amount of coal gangue decreases, the iron recovery rate of the reduced iron powder gradually increases; as the heating temperature increases, the iron recovery rate of the reduced iron powder first increases and then decreases. Figure 3 It can be seen from Figure c that under the interaction between the amount of coal gangue and the heating time, as the amount of coal gangue decreases, the iron recovery rate of the reduced iron powder gradually increases; as the heating time increases, the iron recovery rate of the reduced iron powder first increases and then decreases. Figure 3 It can be seen from Figure d that under the interaction between the carbon powder content and the heating temperature, with the increase of carbon powder content and the increase of heating temperature, the iron recovery of reduced iron powder first increases and then decreases. Figure 3 It can be seen from Figure 5 that under the interaction between carbon powder dosage and heating time, with the increase of carbon powder dosage and heating time, the iron recovery of reduced iron powder first increases and then decreases. Figure 3 It can be seen from Figure 5 that under the interaction of heating temperature and heating time, with the increase of heating temperature and heating time, the iron recovery of reduced iron powder first increases and then decreases.

[0054] Table 9 Results of variance analysis of the response surface model for tailings activity index

[0055] Note: P<0.05 indicates significant difference, indicated by *; P <0.01 indicates a very significant difference, indicated by **.

[0056] It can be seen from Table 9 that the response surface model of tailings activity index P The value is <0.0001, which is extremely significant; the lack of fit term is not significant, which means that the proportion of abnormal errors in the process of fitting the quadratic polynomial regression equation with the test data is small, and the response surface model of the tailings activity index is credible; R 2 , after adjustment R 2 All of them exceeded 0.9 and were very close to 1, indicating that the proportion of response value changes explained by the influencing factors of the response surface model of tailings activity index was very high, and the model had a high degree of fitting; after adjustment R 2 With the predicted value R 2 The difference between them is less than 0.2, indicating that there is a high correlation between the predicted value of the response surface model of the tailings activity index and the measured value. The signal-to-noise ratio is 18.4800, which is much greater than 4, indicating that the influence of the accidental error of the response surface model of the tailings activity index is very low. P The values ​​are all <0.01, and the carbon powder content P The value is <0.05, indicating that the influence of coal gangue content, heating temperature and heating time on the activity index of tailings is extremely significant, and the influence of carbon powder content on the activity index of tailings is significant.

[0057] Figure 4 Response surface diagram of the influence factors on the tailings activity index in the embodiment. Figure 4 From a, we can see that under the interaction between the amount of coal gangue and the amount of carbon powder, the activity index of tailings gradually increases with the increase of the amount of coal gangue and the increase of the amount of carbon powder. Figure 4 As shown in Figure b, under the interaction between the amount of coal gangue and the heating temperature, the activity index of tailings gradually increases with the increase of coal gangue amount and the increase of heating temperature. Figure 4 It can be seen from Figure c that under the interaction between the amount of coal gangue and the heating time, the activity index of tailings gradually increases with the increase of coal gangue amount and the increase of heating time. Figure 4 It can be seen from Figure d that under the interaction between the carbon powder content and the heating temperature, the activity index of the tailings gradually increases with the increase of the carbon powder content and the increase of the heating temperature. Figure 4 It can be seen from Figure 5 that under the interaction between carbon powder content and heating time, the activity index of tailings gradually increases with the increase of carbon powder content and heating time. Figure 4It can be seen from Figure 5 that under the interaction of heating temperature and heating time, the activity index of tailings gradually increases with the increase of heating temperature and heating time.

[0058] Based on the results of variance analysis and response surface diagram analysis of the three response surface models, it can be seen that the four influencing factors have significant or extremely significant effects on the iron grade of reduced iron powder, the iron recovery rate of reduced iron powder and the activity index of tailings. The three response surface models of iron grade of reduced iron powder, iron recovery rate of reduced iron powder and activity index of tailings are highly reliable and can effectively simulate the actual test results.

[0059] S5: The recovered reduced iron powder is mainly used for ironmaking, and the tailings are mainly used as active mineral admixtures for cement or concrete, or for the preparation of solid waste-based cementitious materials. In order to improve the application value of reduced iron powder and tailings, three response surface models were optimized by multi-objective optimization, and the multi-objective optimization requirements were formulated as follows: (1) In order to ensure the ironmaking efficiency of reduced iron powder and reduce the energy consumption of ironmaking, the iron grade of reduced iron powder used as ironmaking raw material should be above 50%; (2) In building material applications, to ensure the application effect, the tailings activity index should exceed 80%; (3) When both (1) and (2) are met, the iron recovery rate of reduced iron powder takes the maximum value. The multi-objective optimization requirements of the three response surface models are shown in Table 10.

[0060] Table 10 Multi-objective optimization requirements

[0061] Considering that the application value of reduced iron powder and tailings is equally important, the weights of the three response values ​​of iron grade of reduced iron powder, iron recovery rate of reduced iron powder and activity index of tailings are all set to 1. Based on the "Optimization-Numerical" module of the response surface analysis Box-Benhnken model of the experimental design software DesignExpert (version 11), the demand conditions in Table 10 are input, and the optimization technical solution that simultaneously meets the multi-objective optimization demand conditions is obtained: the coal gangue content is 15.9%, the carbon powder content is 3.2%, the heating temperature is 797.8℃, and the heating time is 52.8min. Under these conditions, according to the response surface model, the predicted value of the iron grade of reduced iron powder is 53.0%, the predicted value of the iron recovery rate of reduced iron powder is 79.4%, and the predicted value of the activity index of tailings is 80.0%.

[0062] In order to verify the reliability of the optimized technical scheme, the iron tailings and coal gangue were co-magnetized and roasted, ball milled and magnetically separated again according to the optimized technical scheme, the reduced iron powder was recovered, the iron grade and iron recovery rate of the reduced iron powder were tested, and the activity index of the tailings was tested. The test results are shown in Table 11.

[0063] Table 11 Test verification results of the optimized technical solution

[0064] It can be seen from Table 11 that the deviations between the predicted values ​​and the measured values ​​of the three response values ​​under the optimization technical scheme are very small, and the measured values ​​also meet the requirements of multi-objective optimization, which verifies the reliability of the response surface model and the optimization technical scheme.

[0065] In summary, the present invention significantly improves the activity of iron tailings by adding coal gangue during the magnetization roasting process of iron tailings, improves the application value of iron tailings as building materials, and reduces the amount of carbon powder. By adopting the response surface method of 4 factors and 3 levels to design the experimental scheme, the response surface model of the iron grade of reduced iron powder, the iron recovery rate of reduced iron powder, and the tailings activity index is constructed, and multi-objective optimization is performed to obtain an optimization technical solution that simultaneously satisfies the multi-objective optimization requirements of the three response surface models, solves the drawback that the traditional iron tailings resource utilization method only focuses on the single benefit of building materials or iron recovery, realizes the synergistic improvement of the application value of the reduced iron powder and tailings of the iron tailings, improves the overall benefit of the iron tailings treatment product, realizes the high-value full-quantity utilization of iron tailings and coal gangue, and the coordinated disposal of iron tailings and coal gangue, with significant economic and social benefits.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for recovering iron and improving activity by synergistic magnetization roasting of iron tailings and coal gangue, characterized in that: The steps include: S1: Taking the gangue content, carbon powder content, heating temperature and heating time in magnetic roasting as influencing factors, and the iron grade and iron recovery rate of reduced iron powder and tailings activity index as response values, a response surface test scheme is designed; S2: Mix the iron tailings, coal gangue and carbon powder in proportion, perform magnetization reduction roasting, ball milling and magnetic separation, recover the reduced iron powder, and test the iron grade and iron recovery rate of the reduced iron powder; S3: test tailings activity index; S4: Establish a response surface model with three response values ​​and verify the reliability of the model; S5: Obtain an optimization technical solution that simultaneously meets the multi-objective optimization requirements of the three response surface models.

2. The method for optimizing iron recovery and activity enhancement by coordinated magnetization roasting of iron tailings and coal gangue according to claim 1, characterized in that: In step S1, the Box-Benhnken model of the response surface methodology is used to design the experimental scheme.

3. The method for optimizing iron recovery and activity enhancement by coordinated magnetization roasting of iron tailings and coal gangue according to claim 2, characterized in that: The coal gangue content is the mass ratio of coal gangue to iron tailings; the carbon powder content is the mass ratio of carbon powder to iron tailings.

4. The method for optimizing iron recovery and activity enhancement by coordinated magnetization roasting of iron tailings and coal gangue according to claim 2, characterized in that: The mass ratio of iron tailings, coal gangue and carbon powder is 100:(10~30):(2~4).

5. The method for recovering iron and improving activity by coordinated magnetization roasting of iron tailings and coal gangue according to claim 2, characterized in that: The heating temperature is 600° C. to 800° C., and the heating time is 30 min to 90 min.

6. The method for optimizing iron recovery and activity enhancement by coordinated magnetization roasting of iron tailings and coal gangue according to claim 2, characterized in that: The influencing factors are set to three factor levels, represented by -1, 0, and 1 respectively.

7. The method for recovering iron and improving activity by coordinated magnetization roasting of iron tailings and coal gangue according to claim 1, characterized in that: In step S2, iron tailings, coal gangue and carbon powder are mixed according to a designed ratio, and then roasted in a closed environment at a designed heating temperature and a designed heating time; After the roasting is completed, the roasted product is water-quenched and dried; The dried calcined product is ball-milled and magnetically separated to recover the reduced iron powder, and the iron grade and iron recovery rate of the reduced iron powder are tested.

8. The method for recovering iron and improving activity by coordinated magnetization roasting of iron tailings and coal gangue according to claim 1, characterized in that: In step S3, the tailings remaining after the recovery of the reduced iron powder are used to replace 30% of cement to prepare cement mortar specimens, and the 28-day compressive strength of the cement mortar specimens mixed with tailings and the pure cement mortar specimens are tested. The tailings activity index is obtained by calculating the ratio of the 28-day compressive strengths of the two.

9. The method for recovering iron and improving activity by coordinated magnetization roasting of iron tailings and coal gangue according to claim 1, characterized in that: In step S4, a response surface model between influencing factors and response values ​​is established, and the response surface model is expressed by a quadratic polynomial regression equation as follows: ； Where: Y is the response value; X i as influencing factors; k is the number of influencing factors, k =4; α 0. α i , α ii and α ij is an undetermined coefficient and is determined through experiments.

10. The method for recovering iron and improving activity by coordinated magnetization roasting of iron tailings and coal gangue according to claim 1, characterized in that: In step S5, the multi-objective optimization requirements of the three response surface models are: (1) the iron grade of the reduced iron powder is above 50%; (2) the activity index of the tailings exceeds 80%; (3) when both (1) and (2) are met, the iron recovery rate of the reduced iron powder takes the maximum value.

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