A method for recovering iron from sulfuric acid slag

Abstract

The present invention relates to a method for recovering iron from sulfuric acid slag, the method comprising the following steps: mixing and fine-grinding the sulfuric acid slag with a reducing agent to obtain a mixture with a particle size of less than 300 μm; drying the mixture after shaping, then reducing it in a hydrogen atmosphere, and cooling it to obtain a reduced material; crushing the reduced material to a particle size of less than 200 μm, and recovering metallic iron by a mineral processing method. The method provided by the present invention uses hydrogen for reduction, the hydrogen has high selectivity, a clear reduction pathway, and a high metal recovery rate, and can reduce the complex iron components in the sulfuric acid slag to metallic iron, realizing resource utilization in the sulfuric acid slag while reducing carbon emissions, and the tailings after iron recovery can be further used to extract valuable metals, realizing the green and sustainable development of sulfuric acid slag utilization.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste recovery and relates to a method for recovering iron from iron-containing solid waste, and in particular to a method for recovering iron from sulfuric acid slag. Background Art

[0002] Sulfuric acid slag is a powdery tailing produced in the process of producing sulfuric acid using pyrite. 0.7-1.0t of slag is discharged for every ton of sulfuric acid produced. The main components of sulphuric acid slag are ferric oxide and silicon dioxide, generally containing 40%-55% iron and 1.5%-2.0% sulfur. In addition, it also contains trace amounts of metal elements such as Cu, Pb, Zn, As, Cd, Cr, Au, and Ag. At present, only a small amount of sulphuric acid slag is used as building materials and steel raw materials, and most of the rest is landfilled or piled up. With the consumption of iron ore sources, the large amount of valuable resources such as iron contained in sulphuric acid slag has attracted widespread attention, and its comprehensive utilization has become a focal issue. The stacking of sulphuric acid slag not only wastes resources and occupies a large amount of land, but also may cause pollution to the surrounding soil and water bodies.

[0003] There are many methods for comprehensive utilization of sulphuric acid slag. In addition to being used for building materials and steel raw materials, high-temperature reduction acid hydrolysis, chloride roasting, reduction roasting-magnetic separation and other methods are also used. These methods have a series of problems such as high energy consumption, high equipment corrosion, or low recycling rate. Each technology has its own advantages and limitations, and different methods need to be selected according to different material compositions and local environments.

[0004] At present, the extraction of iron from slag by carbon reduction roasting-magnetic separation is a method that has been widely studied, but this method has high energy consumption, large carbon emissions, and few industrial application cases. There are fewer reports on the use of hydrogen to reduce roasting sulfuric acid tailings. Hydrogen is not only a green and clean energy, its oxidation product only produces water, and it can replace carbon and be used for the reduction of iron in sulfuric acid slag. Hydrogen has high selectivity, a clear reduction pathway, and a high metal recovery rate under suitable reaction conditions. Driven by the dual carbon goals, the use of hydrogen has received more and more attention from society.

[0005] Therefore, the present invention aims at the problems of large-scale storage of sulfuric acid slag, low resource utilization rate, insufficient means of clean utilization, etc., and uses green hydrogen reduction to reduce the complex iron in the sulfuric acid slag into metallic iron, thereby recovering the resources in the slag. While increasing the resource utilization rate of roasting cyanidation tailings, carbon emissions are reduced, and green and sustainable development of sulfuric acid slag utilization is achieved.

[0006] Therefore, in order to address the problems of large-scale storage of sulfuric acid slag, low resource utilization rate and insufficient means for clean utilization, a method for recovering iron from sulfuric acid slag is provided, which reduces carbon emissions and realizes green utilization of sulfuric acid slag. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for recovering iron from sulfuric acid slag, which can reduce the complex iron components in the sulfuric acid slag into metallic iron, thereby realizing resource utilization in the sulfuric acid slag, reducing carbon emissions, and achieving green and sustainable development of sulfuric acid slag utilization.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for recovering iron from sulfuric acid slag, the method comprising the following steps:

[0010] The sulphuric acid slag is mixed with a reducing agent and finely ground to obtain a mixture with a particle size of less than 300 μm; the mixture is dried after being shaped, and then reduced in a hydrogen atmosphere and cooled to obtain a reduced material; the reduced material is crushed to a particle size of less than 200 μm, and the metallic iron is recovered by a mineral processing method.

[0011] The method provided by the present invention firstly mixes and finely grinds the sulfate slag with a reducing agent to ensure the subsequent hydrogen treatment effect; then hydrogen is used for reduction, and the hydrogen has high selectivity, a clear reduction pathway, and a high metal recovery rate, and can reduce the iron of complex components in the sulfate slag to metallic iron, thereby realizing resource utilization in the sulfate slag and reducing carbon emissions. Moreover, the tailings after iron recovery can be further used to extract valuable metals, thereby realizing the green and sustainable development of the utilization of the sulfate slag.

[0012] Preferably, the reduction temperature is 500°C-1000°C.

[0013] Preferably, the absolute pressure during the reduction is below 2 MPa.

[0014] Preferably, the reduction time does not exceed 24 hours.

[0015] Preferably, the cooling is performed in a protective atmosphere; the protective atmosphere comprises any one of hydrogen, nitrogen or an inert gas, or a combination of at least two of them.

[0016] Preferably, the terminal temperature of the cooling is below 200°C.

[0017] Preferably, the particle size of the sulfuric acid slag is less than 5 mm.

[0018] Preferably, the auxiliary reducing agent includes any one of calcium salt, magnesium salt, iron salt, manganese salt, potassium salt, sodium salt or alkali, or a combination of at least two thereof.

[0019] Preferably, the amount of the reducing agent does not exceed 15% of the mass of the sulfate slag.

[0020] Preferably, the shaping comprises mixing the mixed material, the binder and water, and then making balls, and the average diameter of the obtained balls is 10mm-30mm.

[0021] Preferably, the mass ratio of the mixture, the binder and water is 100:(0.5-5):(5-15).

[0022] Preferably, the binder includes an inorganic binder and / or an organic binder.

[0023] Preferably, the mineral processing method comprises any one of magnetic separation, gravity separation, air separation or centrifugation, or a combination of at least two thereof.

[0024] Preferably, the method comprises the following steps:

[0025] (1) screening the sulfuric acid slag to obtain sulfuric acid slag with a particle size of less than 5 mm;

[0026] (2) mixing and finely grinding the sulfuric acid slag and the reducing agent to obtain a mixture with a particle size of less than 300 μm; the amount of the reducing agent used is not more than 15% of the mass of the sulfuric acid slag;

[0027] (3) mixing a binder, water and a mixed material in a mass ratio of 100:(0.5-5):(5-15), and then forming pellets, wherein the average diameter of the obtained pellets is 10 mm to 30 mm;

[0028] (4) then reducing in a hydrogen atmosphere at a temperature of 500° C. to 1000° C., an absolute pressure of less than 2 MPa and a time period of no more than 24 h; cooling to less than 200° C. in a protective atmosphere to obtain a reduced material;

[0029] (5) The raw materials are crushed to a particle size of less than 200 μm, and the metallic iron is recovered by a mineral processing method.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The method provided by the present invention firstly mixes and finely grinds the sulfate slag with a reducing agent to ensure the subsequent hydrogen treatment effect; then hydrogen is used for reduction, and the hydrogen has high selectivity, a clear reduction pathway, and a high metal recovery rate, and can reduce the iron of complex components in the sulfate slag to metallic iron, thereby realizing resource utilization in the sulfate slag and reducing carbon emissions. Moreover, the tailings after iron recovery can be further used to extract valuable metals, thereby realizing the green and sustainable development of the utilization of the sulfate slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A process flow chart of the method is provided for Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0034] A certain embodiment of the present invention provides a method for recovering iron from sulfuric acid slag, the method comprising the following steps:

[0035] The sulphuric acid slag is mixed with a reducing agent and finely ground to obtain a mixture with a particle size of less than 300 μm; the mixture is dried after being shaped, and then reduced in a hydrogen atmosphere and cooled to obtain a reduced material; the reduced material is crushed to a particle size of less than 200 μm, and the metallic iron is recovered by a mineral processing method.

[0036] The method provided by the present invention firstly mixes and finely grinds the sulfuric acid slag with a reducing agent to ensure the subsequent hydrogen treatment effect; then hydrogen is used for reduction, and the hydrogen has high selectivity, a clear reduction pathway, and a high metal recovery rate, and can reduce the iron of complex components in the sulfuric acid slag to metallic iron, thereby realizing resource utilization in the sulfuric acid slag and reducing carbon emissions. Almost no harmful gases such as SO2 are generated during the process, and the tailings after iron recovery can be further used to extract valuable metals, thereby realizing the green and sustainable development of sulfuric acid slag utilization.

[0037] Optionally, the present invention uses fine grinding to make the particle size of the mixture less than 300 μm, which means that the finely ground mixture passes through a 50-mesh sieve, and the undersize is a mixture with a particle size of less than 300 μm. Further, the mixture is the undersize of a 60-mesh sieve; further, the undersize of an 80-mesh sieve; further, the undersize of a 150-mesh sieve; further, the undersize of a 180-mesh sieve; further, the undersize of a 300-mesh sieve, and further, the undersize of a 3000-mesh sieve.

[0038] In certain embodiments, the fine grinding is performed using at least one fine grinding device selected from the group consisting of a ball mill, a roller mill, a vibration mill, a stirring mill, a sand mill, or a tower mill.

[0039] Binders and other materials are used when the mixture is shaped. Reduction is usually carried out at a higher temperature. Under the reduction temperature conditions, the auxiliary materials used for shaping decompose to produce gas, thereby creating holes that are conducive to the passage of hydrogen, making it easier for hydrogen to reduce the iron oxide and ferroferric oxide inside the mixture.

[0040] In some embodiments, the reduction temperature is 500°C-1000°C, for example, it can be 500°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C or 1000°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] The present invention does not specifically limit the method of controlling the reduction temperature, as long as the reduction temperature is 500°C-1000°C. Exemplarily, the method of controlling the reduction temperature includes at least one of hydrogen heating, electric heating, gas heating or carbon heating.

[0042] In certain embodiments, the absolute pressure during reduction is below 2 MPa, for example, 1 MPa, 1.2 MPa, 1.5 MPa, 1.6 MPa, 1.8 MPa or 2 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] In certain embodiments, the reduction time does not exceed 24 hours, for example, it can be 0.5 hours, 1.1 hours, 2.3 hours, 5.7 hours, 8 hours, 11 hours, 13 hours, 16.2 hours, 22 hours or 24 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] In certain embodiments, the cooling is performed in a protective atmosphere; the protective atmosphere includes any one of hydrogen, nitrogen or an inert gas or a combination of at least two of them, typical but non-limiting combinations include a combination of hydrogen and nitrogen, a combination of nitrogen and an inert gas, a combination of hydrogen and an inert gas, or a combination of hydrogen, nitrogen and an inert gas.

[0045] In some embodiments, the terminal temperature of the cooling is below 200°C, for example, it can be 25°C, 48°C, 60°C, 77°C, 87°C, 100°C, 104°C, 123°C, 163°C, 195°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] In some embodiments, the particle size of the sulfuric acid slag is less than 5 mm.

[0047] The sulphuric acid slag in the present invention includes tailings obtained by roasting pyrite to produce acid, roasting cyanide tailings and other high-iron oxidation tailings. The present invention does not specifically limit the crushing method, as long as the particle size of the sulphuric acid slag can be less than 5 mm, that is, as long as the sulphuric acid slag is crushed and passed through a 5-mesh sieve, the sieve under is taken.

[0048] In certain embodiments, the auxiliary reducing agent includes any one of calcium salt, magnesium salt, iron salt, manganese salt, potassium salt, sodium salt or base, or a combination of at least two thereof.

[0049] Excessive use of the reducing agent will cause the raw material to be molten, resulting in a low iron grade, which is not conducive to separation, and will also increase the amount of raw materials used and increase costs. Therefore, it is necessary to optimize the amount of the reducing agent used.

[0050] In some embodiments, the amount of the reducing agent does not exceed 15% of the mass of the sulfate slag, for example, it can be 1%, 3%, 5%, 8%, 10%, 12% or 15%, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable.

[0051] In some embodiments, the shaping includes mixing the mixture, the binder and water, and then forming balls.

[0052] In some embodiments, the mass ratio of the mixture, binder and water is 100:(0.5-5):(5-15), for example, it can be 100:0.5:5, 100:3:10, 100:5:15, 100:0.5:15 or 100:5:5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] In certain embodiments, the binder includes an inorganic binder and / or an organic binder.

[0054] In certain embodiments, the binder includes any one of slaked lime, quicklime, diatomaceous earth or modified starch, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of slaked lime and modified starch, a combination of quicklime and modified starch, a combination of quicklime and diatomaceous earth, a combination of slaked lime and quicklime, or a combination of slaked lime, quicklime and modified starch.

[0055] In certain embodiments, the mineral processing method includes any one of magnetic separation, gravity separation, air separation or centrifugation, or a combination of at least two thereof.

[0056] In some embodiments, the method comprises the steps of:

[0057] (1) screening the sulfuric acid slag to obtain sulfuric acid slag with a particle size of less than 5 mm;

[0058] (2) mixing and finely grinding the sulfuric acid slag and the reducing agent to obtain a mixture with a particle size of less than 300 μm; the amount of the reducing agent used is not more than 15% of the mass of the sulfuric acid slag;

[0059] (3) mixing a binder, water and a mixed material in a mass ratio of 100:(0.5-5):(5-15), and then forming pellets, wherein the average diameter of the obtained pellets is 10 mm to 30 mm;

[0060] (4) then reducing in a hydrogen atmosphere at a temperature of 500° C. to 1000° C., an absolute pressure of less than 2 MPa and a time period of no more than 24 h; cooling to less than 200° C. in a protective atmosphere to obtain a reduced material;

[0061] (5) The raw materials are crushed to a particle size of less than 200 μm, and the metallic iron is recovered by a mineral processing method.

[0062] Example 1

[0063] This embodiment provides a method for recovering iron from sulfuric acid slag. The process flow chart of the method is as follows: Figure 1 As shown, including:

[0064] (1) screening the sulfuric acid slag to obtain sulfuric acid slag with a particle size of less than 5 mm and an iron content of 42%;

[0065] (2) mixing and finely grinding the sulfuric acid slag and sodium hydroxide to obtain a mixture that passes through an 80-mesh sieve; the amount of the sodium hydroxide used is 10% of the mass of the sulfuric acid slag;

[0066] (3) The modified starch (CH4020 (LYG)), water and the mixed material were mixed in a mass ratio of 100:2:5, and then pelletized. The average diameter of the obtained pellets was 30 mm.

[0067] (4) then reducing in a hydrogen atmosphere at a temperature of 900° C., an absolute pressure of 0.5 MPa and a time of 6 h; cooling to 80° C. in a hydrogen atmosphere to obtain a reduced material;

[0068] (5) The raw materials are crushed, passed through an 80-mesh sieve, and the metallic iron is recovered by magnetic separation; the tailings after the iron is recovered are used to extract valuable elements.

[0069] Example 2

[0070] This embodiment provides a method for recovering iron from sulfuric acid slag, the method comprising:

[0071] (1) screening the sulfuric acid slag to obtain sulfuric acid slag with a particle size of less than 2 mm and an iron content of 50%;

[0072] (2) mixing and finely grinding the sulfuric acid slag and calcium hydroxide to obtain a mixture that passes through an 80-mesh sieve; the amount of calcium hydroxide used is 5% of the mass of the sulfuric acid slag;

[0073] (3) mixing slaked lime, water and the mixed material in a mass ratio of 100:5:7, and then forming balls, wherein the average diameter of the obtained balls is 25 mm;

[0074] (4) then reducing in a hydrogen atmosphere at a temperature of 850° C., an absolute pressure of 1 MPa and a time of 3 h; cooling to 60° C. in a nitrogen atmosphere to obtain a reduced material;

[0075] (5) The raw materials are crushed, passed through an 80-mesh sieve, and the metallic iron is recovered by magnetic separation; the tailings after the iron is recovered are used to extract valuable elements.

[0076] Example 3

[0077] This embodiment provides a method for recovering iron from sulfuric acid slag, the method comprising:

[0078] (1) screening the sulfuric acid slag to obtain sulfuric acid slag with a particle size of less than 2 mm and an iron content of 38%;

[0079] (2) mixing and finely grinding the sulphuric acid slag and potassium hydroxide to obtain a mixture that passes through a 200-mesh sieve; the amount of potassium hydroxide used is 5% of the mass of the sulphuric acid slag;

[0080] (3) mixing slaked lime, water and the mixed material in a mass ratio of 100:2:5, and then forming balls, wherein the average diameter of the obtained balls is 10 mm;

[0081] (4) then reducing in a hydrogen atmosphere at a temperature of 650° C., an absolute pressure of 0.5 MPa and a time of 6 h; cooling to 80° C. in a nitrogen atmosphere to obtain a reduced material;

[0082] (5) The raw materials are crushed, passed through an 80-mesh sieve, and the metallic iron is recovered by magnetic separation; the tailings after the iron is recovered are used to extract valuable elements.

[0083] Example 4

[0084] This embodiment provides a method for recovering iron from sulfuric acid slag, the method comprising:

[0085] (1) providing the sulphuric acid slag in Example 1;

[0086] (2) mixing and finely grinding the sulfuric acid slag and sodium hydroxide to obtain a mixture that passes through an 80-mesh sieve; the amount of the sodium hydroxide used is 10% of the mass of the sulfuric acid slag;

[0087] (3) The modified starch (CH4020 (LYG)), water and the mixed material were mixed in a mass ratio of 100:0.5:5, and then pelletized. The average diameter of the obtained pellets was 30 mm.

[0088] (4) then reducing in a hydrogen atmosphere at a temperature of 500° C., an absolute pressure of 0.5 MPa and a time of 6 h; cooling to 80° C. in a hydrogen atmosphere to obtain a reduced material;

[0089] (5) The raw materials are crushed, passed through an 80-mesh sieve, and the metallic iron is recovered by magnetic separation; the tailings after the iron is recovered are used to extract valuable elements.

[0090] Example 5

[0091] This embodiment provides a method for recovering iron from sulfuric acid slag, the method comprising:

[0092] (1) providing the sulphuric acid slag in Example 1;

[0093] (2) mixing and finely grinding the sulfuric acid slag and sodium hydroxide to obtain a mixture that passes through an 80-mesh sieve; the amount of the sodium hydroxide used is 10% of the mass of the sulfuric acid slag;

[0094] (3) The modified starch (CH4020 (LYG)), water and the mixed material were mixed in a mass ratio of 100:5:15, and then pelletized. The average diameter of the obtained pellets was 30 mm.

[0095] (4) then reducing in a hydrogen atmosphere at a temperature of 1000° C., an absolute pressure of 0.5 MPa and a time of 6 h; cooling to 80° C. in a hydrogen atmosphere to obtain a reduced material;

[0096] (5) The raw materials are crushed, passed through an 80-mesh sieve, and the metallic iron is recovered by magnetic separation; the tailings after the iron is recovered are used to extract valuable elements.

[0097] Example 6

[0098] This embodiment provides a method for recovering iron from sulfuric acid slag, which is the same as that of Embodiment 1 except that the reduction temperature is 450°C.

[0099] Example 7

[0100] This embodiment provides a method for recovering iron from sulfuric acid slag, which is the same as that of Embodiment 1 except that the reduction temperature is 1250°C.

[0101] Comparative Example 1

[0102] This comparative example provides a method for recovering iron from sulfuric acid slag, which is the same as Example 1 except that no reducing agent is used.

[0103] Characterization

[0104] The recovery rate of iron and the quality of iron recovered in the above-mentioned embodiment and comparative example are shown in Table 1.

[0105] Table 1

[0106] Recovery rate (%) Taste (wt%) Example 1 85 95 Example 2 88 90 Example 3 80 88 Example 4 78 92 Example 5 81 90 Example 6 30 85 Example 7 75 80 Comparative Example 1 70 90

[0107] In summary, the method provided by the present invention first mixes the sulfate slag with the reducing agent and grinds them finely to ensure the subsequent hydrogen treatment effect; then hydrogen is used for reduction, and hydrogen has high selectivity, a clear reduction pathway, and a high metal recovery rate. It can reduce the complex iron components in the sulfate slag to metallic iron, thereby realizing resource utilization in the sulfate slag and reducing carbon emissions. Moreover, the tailings after iron recovery can be further used to extract valuable metals, thereby realizing the green and sustainable development of the utilization of sulfate slag.

[0108] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering iron from sulfuric acid slag, characterized in that: The method comprises the following steps: The sulphuric acid slag is mixed with a reducing agent and finely ground to obtain a mixture with a particle size of less than 300 μm; the mixture is dried after being shaped, and then reduced in a hydrogen atmosphere and cooled to obtain a reduced material; the reduced material is crushed to a particle size of less than 200 μm, and the metallic iron is recovered by a mineral processing method.

2. The method according to claim 1, characterized in that The reduction temperature is 500°C-1000°C; And / or, the absolute pressure during the reduction is below 2 MPa; And / or, the reduction time does not exceed 24 hours.

3. The method according to claim 1, characterized in that The cooling is carried out in a protective atmosphere; the protective atmosphere includes any one of hydrogen, nitrogen or an inert gas or a combination of at least two thereof; And / or, the cooling end point temperature is below 200°C.

4. The method according to claim 1, characterized in that: The particle size of the sulfuric acid slag is less than 5 mm.

5. The method according to claim 1, characterized in that The auxiliary reducing agent includes any one of calcium salt, magnesium salt, iron salt, manganese salt, potassium salt, sodium salt or alkali, or a combination of at least two thereof; And / or, the amount of the reducing agent does not exceed 15% of the mass of the sulfate slag.

6. The method according to claim 1, characterized in that The shaping comprises mixing the mixed material, the binder and water, and then making balls, wherein the average diameter of the balls is 10 mm to 30 mm.

7. The method according to claim 6, characterized in that The mass ratio of the mixture, the binder and water is 100:(0.5-5):(5-15).

8. The method according to claim 6 or 7, characterized in that: The binder includes an inorganic binder and / or an organic binder.

9. The method according to claim 1, characterized in that: The ore dressing method includes any one of magnetic separation, gravity separation, air separation or centrifugation, or a combination of at least two of them.

10. The method according to claim 1, characterized in that The method comprises the following steps: (1) screening the sulfuric acid slag to obtain sulfuric acid slag with a particle size of less than 5 mm; (2) mixing and finely grinding the sulfuric acid slag and the reducing agent to obtain a mixture with a particle size of less than 300 μm; the amount of the reducing agent used is not more than 15% of the mass of the sulfuric acid slag; (3) mixing a binder, water and a mixed material in a mass ratio of 100:(0.5-5):(5-15), and then forming pellets, wherein the average diameter of the obtained pellets is 10 mm to 30 mm; (4) then reducing in a hydrogen atmosphere at a temperature of 500° C. to 1000° C., an absolute pressure of less than 2 MPa and a time period of no more than 24 h; cooling to less than 200° C. in a protective atmosphere to obtain a reduced material; (5) The raw materials are crushed to a particle size of less than 200 μm, and the metallic iron is recovered by a mineral processing method.

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