A method for preparing magnetite using electrolytic manganese residue

Abstract

The present invention relates to a method for preparing ferric oxide from electrolytic manganese residue, comprising the following steps: Step 1) Grinding and activation; Step 2) Oxidative roasting: mixing the manganese residue powder obtained in Step 1) with an oxidation aid evenly, and roasting it in a furnace; Step 3) Reductive roasting: adding biomass carbon to the roasted product obtained in Step 2) and mixing evenly to obtain a mixture, and performing anaerobic roasting on the mixture in a furnace; Step 4) Magnetic separation. The advantages of the present invention are that ferrous sulfides FeS and FeS2 are converted into Fe2O3 through oxidative roasting, and then Fe2O3 is transformed into Fe3O4 and MnO2 is converted into Mn3O4 through reductive roasting, effectively separating iron and manganese. The product is ferric oxide, solving the technical problems of low recycling value of manganese residue and difficulty in separating iron and manganese from other substances.

Description

Technical Field

[0001] The present invention relates to the field of harmless treatment and resource utilization of metallurgical solid waste, and particularly to a method for preparing magnetite from electrolytic manganese slag. Background Art

[0002] Electrolytic manganese slag is the acid leaching waste residue generated during the preparation of manganese sulfate solution by acid leaching of rhodochrosite in the electrolytic manganese production process, and it is an industrial solid waste with excessive sulfate. The electrolytic manganese slag has a complex composition, containing a large amount of soluble salts and free heavy metal ions such as manganese, iron, and ammonia nitrogen, which are easily diffused into the environment, causing serious harm to the surrounding ecological environment and then affecting the physical health of residents.

[0003] In China, rhodochrosite is a lean ore with an average grade of about 12%. About 8 - 10 tons of electrolytic manganese slag are produced for every 1 ton of metallic manganese electrolytically produced. The annual new increase of electrolytic manganese slag in the country is about 10 million tons. By the end of 2022, the stockpile of electrolytic manganese slag in China exceeded 100 million tons, and its comprehensive utilization rate was less than 10%. Its harmlessness, reduction, and resource utilization have become key problems urgently needed to be solved in the electrolytic manganese industry.

[0004] Iron in electrolytic manganese slag mainly exists in the forms of FeS, FeS2, etc., and has a high recycling value.

[0005] Patent document CN116173703A discloses a method for mineralizing CO2 in electrolytic manganese slag to co-cure metal ions Mn 2+ / Mg 2+ The method includes the following steps: mixing electrolytic manganese slag powder and a neutral salt solution according to a predetermined liquid-solid ratio, leaching for a first time period at a first temperature and a first stirring speed to obtain a first solid-liquid mixture; filtering the first solid-liquid mixture to obtain the leaching solution and leaching residue of electrolytic manganese slag; mixing the leaching solution with concentrated ammonia water according to a predetermined ratio, and simultaneously introducing CO2 gas at a first rate, and stirring and reacting at a second temperature for a second time period to obtain a second solid-liquid mixture; filtering the second solid-liquid mixture to obtain a filter cake and a filtrate; washing and drying the filter cake to obtain a mineralized product.

[0006] Patent document CN116043040A discloses a method for extracting manganese from electrolytic manganese slag, including the following steps: S1, co-ball milling the electrolytic manganese slag, pyrite, and a leaching agent to obtain a ball-milled product; wherein, the mass ratio of the pyrite to the electrolytic manganese slag is not higher than 5%; the ball-milling rate is not less than 200 rpm / min, and the ball-milling duration is not less than 30 min; S2, performing solid-liquid separation on the ball-milled product to obtain a manganese-containing extraction solution.

[0007] Patent document CN116005013A discloses a method for recovering manganese from electrolytic manganese slag, which includes the following steps: S1. Treating the electrolytic manganese slag: drying the electrolytic manganese slag in a constant-temperature drying oven, putting it into a ball mill for ball milling after drying (the ball milling particle size is 200 mesh), after ball milling, passing through a vibrating screen, and sealing for standby; S2. Oxalic acid leaching: dissolving 20-100 parts of oxalic acid in 20-500 parts of deionized water, preparing an oxalic acid solution according to the liquid-solid ratios of 1, 2, 3, 4, and 5, weighing 6-10 parts of electrolytic manganese slag, pouring the weighed manganese slag and the prepared oxalic acid solution into a conical flask, placing the conical flask on a horizontal oscillator to oscillate, allowing it to react fully to obtain a suspension of manganese slag and oxalic acid; S3. Vacuum filtration: filtering the obtained suspension of manganese slag and oxalic acid with a vacuum filter to separate the manganese slag solid particles from the suspension; S4. Drying: putting the manganese slag solid particles in step S3 into a constant-temperature drying oven for drying, and that's it.

[0008] Therefore, the above patent has an unsatisfactory treatment effect on manganese slag, the recovered manganese slag has low value, and it is difficult to completely separate iron and manganese. Summary of the Invention

[0009] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing magnetite from electrolytic manganese slag. The difficult-to-treat electrolytic manganese slag is subjected to grinding activation - oxidation roasting - reduction roasting to convert the iron sulfide in the manganese slag into magnetite, and the recovery of iron is achieved through magnetic separation, thereby realizing the complete separation of iron and manganese.

[0010] The present invention is realized through the following technical solutions: On the one hand, a method for preparing magnetite from electrolytic manganese slag includes the following steps:

[0011] Step 1) Grinding activation;

[0012] Step 2) Oxidation roasting: mixing the manganese slag powder obtained in step 1) with an oxidation aid evenly, and roasting it in a furnace;

[0013] Step 3) Reduction roasting: adding biomass carbon to the roasted product obtained in step 2) and mixing evenly to obtain a mixture, and performing anaerobic roasting on the mixture in a furnace;

[0014] Step 4) Magnetic separation.

[0015] Through the above technical solutions, the present invention converts the iron sulfides FeS and FeS2 into Fe2O3 through oxidation roasting, and then converts Fe2O3 into Fe3O4 through reduction roasting, and converts MnO2 into Mn3O4 to effectively separate iron and manganese. The product is Fe3O4, which solves the technical problems of low value of manganese slag and difficulty in separating iron and manganese.

[0016] Further, in step 1), the crushed electrolytic manganese slag is ground and activated with a grinding aid; the mass percentage of the grinding aid in the electrolytic manganese slag is 1% - 5%.

[0017] Specifically, the crushed electrolytic manganese slag is the manganese slag obtained by drying and crushing the electrolytic manganese slag;

[0018] Furthermore, the grinding aid is any mixture of glycerol and any one of citric acid, oxalic acid, and acetic acid.

[0019] Preferably, the mass percentages of citric acid, oxalic acid, and acetic acid in the grinding aid are 5% - 10% respectively.

[0020] Through the above technical solution, the purpose of grinding is to increase the dispersibility of the electrolytic manganese slag. The function of adding glycerol is lubrication, and the purpose of adding citric acid, oxalic acid, and acetic acid is to absorb the ammonia gas generated during the grinding process.

[0021] Further, in step 2), the mass percentage of the oxidation aid in the manganese slag powder is 1% - 5%.

[0022] Furthermore, the oxidation aid is any mixture of calcium fluoride and any one of sodium peroxide, potassium peroxide, calcium peroxide, and barium peroxide.

[0023] Furthermore, the mass percentage of calcium fluoride in the oxidation aid is 1% - 10%.

[0024] Further, in step 2), the roasting temperature is 600 - 1000 °C, and the roasting time is 1 - 4 h. Preferably, the roasting time is 1 - 3 h.

[0025] Through the above technical solution, the function of adding calcium fluoride is mineralization, which further improves the dispersibility of the material; the function of adding peroxides is to catalyze and strengthen the oxidation process of iron sulfide.

[0026] In step 2), the main chemical reactions are as follows:

[0027] 2FeS + 3.5O2 → Fe2O3 + 2SO2

[0028] 2FeS2 + 5.5O2 → Fe2O3 + 4SO2

[0029] Further, in step 3), the biochar is obtained by anaerobic carbonization of pine needles, peanut shells, and walnut shells, and the addition amount of biochar is 1.0 - 2.0 times the theoretical requirement for the reduction of Fe2O3 to Fe3O4.

[0030] Through the above technical solution, the use of agricultural and forestry waste such as pine needles, peanut shells, and walnut shells more effectively improves the carbon source and realizes co - treatment.

[0031] Further, in step 3), the roasting temperature is 500 - 900 °C, and the roasting time is 2 - 5 h. Preferably, the roasting time is 2 - 4 h.

[0032] Preferably, in step 4), the magnetic separation field strength is 500 - 2000 G.

[0033] Through the above technical solution, the main chemical reactions occurring in step 3) are as follows:

[0034] 3Fe2O3 + 4C → 2Fe3O4 + 4CO2

[0035] The beneficial effects of the present invention are as follows: By oxidative roasting, the iron sulfides FeS and FeS2 are converted into Fe2O3, and then through reduction roasting, Fe2O3 is transformed into Fe3O4, and MnO2 is converted into Mn3O4, effectively separating iron and manganese, solving the technical problems of low value of manganese slag and difficult separation of iron and manganese. At the same time, agricultural and forestry waste pine needles / peanut shells / walnut shells are utilized to achieve co-treatment. The grinding process avoids the release of ammonia, which is environmentally friendly; the lubricating effect of glycerol is also utilized during the grinding process to avoid material adhesion; during the oxidative roasting process, the peroxide releases oxygen, which plays a catalytic role and shortens the reaction time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the appearance transformation morphology diagram of the raw materials and products of the present invention; wherein, (a) manganese slag powder; (b) oxidation product; (c) reduction product; (d) magnetic separation product;

[0037] Figure 2 It is the XRD spectrum diagram of the manganese slag raw material and product of the present invention;

[0038] Figure 3 It is the XRD spectrum diagram of the product after magnetic separation of the present invention;

[0039] Figure 4 It is the appearance diagram of the product after magnetic separation of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the invention embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions or parts are by weight.

[0041] The main element composition of the electrolytic manganese residue used in the following examples is shown in Table 1.

[0042] Table 1 Main element composition of electrolytic manganese residue (wt%)

[0043] Element O Fe S Ca Si Al Mn Mg K N Content / % 48.13 12.91 10.67 8.35 7.26 4.12 4.98 1.53 0.91 1.02

[0044] Example 1

[0045] A method for preparing magnetite from electrolytic manganese residue, comprising the following steps:

[0046] Step 1) Grinding activation: After drying the electrolytic manganese residue, it is crushed, and 1% of a grinding aid (a mixture of glycerol and citric acid, with the mass ratio of citric acid in the grinding aid being 10%) is added, followed by grinding activation to obtain manganese residue powder (see Figure 1 (d));

[0047] Step 2) Oxidative roasting: The manganese residue powder obtained in Step 1 is added with 5% of an oxidation aid (a mixture of calcium fluoride and sodium peroxide, with the mass ratio of calcium fluoride in the oxidation aid being 1%), mixed evenly, and the mixture is placed in a furnace and roasted at 600 °C for 3 hours in an air atmosphere to obtain an oxidation product;

[0048] Step 3) Reduction roasting: The oxidation product obtained in Step 2 is added with 1.0 times the theoretically required amount of pine needle-based biomass carbon for reacting with iron oxide, mixed evenly, and the mixture is placed in a furnace and roasted at 500 °C for 4 hours in an anaerobic atmosphere to obtain a reduction product;

[0049] Step 4): Magnetic separation: The reduction product obtained in Step 3 is subjected to magnetic separation to obtain magnetite (see Figure 4 a).

[0050] Example 2:

[0051] A method for preparing magnetite from electrolytic manganese residue, comprising the following steps:

[0052] Step 1) Grinding activation: After drying the electrolytic manganese residue, it is crushed, and 3% of a grinding aid (a mixture of glycerol and oxalic acid, with the mass ratio of oxalic acid in the grinding aid being 7%) is added, followed by grinding activation to obtain manganese residue powder;

[0053] Step 2) Oxidative roasting: The manganese residue powder obtained in Step 1 is added with 3% of an aid (a mixture of calcium fluoride and potassium peroxide, with the mass ratio of calcium fluoride in the aid being 5%), mixed evenly, and the mixture is placed in a furnace and roasted at 800 °C for 2 hours in an air atmosphere to obtain an oxidation product (see Figure 1 (b));

[0054] Step 3) Reduction roasting: Add peanut shell-based biochar, which is 1.5 times the theoretical requirement for reacting with iron oxide, to the oxidized product obtained in Step 2), mix evenly, place the mixture in a furnace, and roast it at 700 °C for 2.5 hours in an oxygen-free atmosphere to obtain a reduced product;

[0055] Step 4) Magnetic separation: Perform magnetic separation on the reduced product obtained in Step 3) to obtain high-purity magnetite (see Figure 4 a).

[0056] Example 3:

[0057] A method for preparing magnetite using electrolytic manganese residue, comprising the following steps:

[0058] Step 1) Grinding activation: Crush the dried electrolytic manganese residue, add 5% grinding aid (a mixture of glycerol and acetic acid, and the mass ratio of acetic acid in the grinding aid is 3%), and perform grinding activation to obtain manganese residue powder;

[0059] Step 2) Oxidation roasting: Add 1% additive (a mixture of calcium fluoride and calcium peroxide, and the mass ratio of calcium fluoride in the additive is 10%) to the manganese residue powder obtained in Step 1), mix evenly, place the mixture in a furnace, and roast it at 1000 °C for 1 hour in an air atmosphere to obtain an oxidized product;

[0060] Step 3) Reduction roasting: Add walnut shell-based biochar, which is 2.0 times the theoretical requirement for reacting with iron oxide, to the oxidized product obtained in Step 2), mix evenly, place the mixture in a furnace, and roast it at 900 °C for 2 hours in an oxygen-free atmosphere to obtain a reduced product;

[0061] Step 4) Magnetic separation: Perform magnetic separation on the reduced product obtained in Step 3) to obtain magnetite (its XRD is shown in Figure 3 .

[0062] Comparative Example 1:

[0063] A method for preparing magnetite using electrolytic manganese residue, comprising the following steps:

[0064] (1) Crush and grind the dried electrolytic manganese residue to obtain manganese residue powder (see Figure 1 (c)), add 5% oxidation additive (a mixture of calcium fluoride and sodium peroxide, and the mass ratio of calcium fluoride in the additive is 1%), mix evenly, place the mixture in a furnace, and roast it at 600 °C for 3 hours in an air atmosphere to obtain an oxidized product;

[0065] (2) Add pine needle-based biochar, which is 1.0 times the theoretical requirement for reacting with iron oxide, to the oxidized product obtained in step (1), mix evenly, place the mixture in a furnace, and roast it at 500 °C for 4 hours in an oxygen-free atmosphere to obtain a reduced product;

[0066] (3) Magnetic separation. The reduced product obtained in step (2) is subjected to magnetic separation to obtain magnetite.

[0067] Compared with Example 1, the manganese slag powder obtained without adding a grinding aid is sticky, and an ammonia smell can be smelled during the grinding process.

[0068] Comparative Example 2:

[0069] A method for preparing magnetite from electrolytic manganese slag, comprising the following steps:

[0070] (1) The dried electrolytic manganese slag is crushed, 3% of a grinding aid (a mixture of glycerol and oxalic acid, and the mass ratio of oxalic acid in the grinding aid is 7%) is added, and grinding activation is carried out to obtain manganese slag powder;

[0071] (2) Oxidative roasting. The manganese slag powder obtained in step (1) is placed in a furnace and roasted at 800 °C for 2 hours in an air atmosphere to obtain an oxidation product (see Figure 1 (a));

[0072] (3) Reductive roasting. The oxidation product obtained in step (2) is added with 1.5 times the theoretical requirement for reacting with iron oxide of peanut shell-based biomass carbon, mixed evenly, and the mixture is placed in a furnace and roasted at 700 °C for 2.5 hours in an anaerobic atmosphere to obtain a reduced product;

[0073] (4) Magnetic separation. The reduced product obtained in step (3) is subjected to magnetic separation to obtain magnetite with a lower purity ( Figure 4 b).

[0074] It can be seen from the comparison with Example 2 that the oxidation product obtained without adding an oxidation aid has a lighter color, indicating a low degree of oxidation, which in turn leads to a low yield of magnetite in the subsequent process.

[0075] Comparative Example 3:

[0076] A method for preparing magnetite from electrolytic manganese slag, comprising the following steps:

[0077] Step 1) Grinding: The dried electrolytic manganese slag is crushed, 5% of a grinding aid (a mixture of glycerol and acetic acid, and the mass ratio of acetic acid in the grinding aid is 3%) is added, and grinding activation is carried out to obtain manganese slag powder;

[0078] Step 2) Oxidative roasting: 1% of an additive (a mixture of calcium fluoride and calcium peroxide, and the mass ratio of calcium fluoride in the additive is 10%) is added to the manganese slag powder obtained in step 1 and mixed evenly. The mixture is placed in a furnace and roasted at 1000 °C for 1 hour in an air atmosphere to obtain an oxidation product;

[0079] Step 3) Reduction roasting: Place the oxidation product obtained in Step 2 in a furnace and roast it at 900 °C for 2 hours in an oxygen-free atmosphere to obtain a reduction product (the XRD pattern of which is shown in Figure 2 the reduction roasted product in

[0080] Step 4) Magnetic separation: Perform magnetic separation on the reduction product obtained in Step 3 to obtain magnetite.

[0081] Effect examples

[0082] Characterize the magnetite prepared in the above Examples 1-3 and Comparative Examples 1-3. The specific data are shown in the following table:

[0083] Example 1 Comparative Example 1 Example 2 Comparative Example 2 Example 3 Comparative Example 3 Manganese slag 1000 1000 1000 1000 1000 1000 Fe content 129.1 129.1 129.1 129.1 129.1 129.1 <![CDATA[Yield of Fe3O4]]> 97.6％ 90.0％ 98.1％ 75.3％ 98.8％ 40.5％

[0084] As can be seen from the above table, in combination with the Figure 1 - Figure 4 of the present invention, compared with the traditional method, the preparation method of the present invention has the following advantages: by adding a grinding aid, the yield of Fe3O4 can be increased by 7.6%; by adding an oxidation aid, the yield of Fe3O4 can be increased by 22.8%; by adding biomass carbon, the yield of Fe3O4 can be increased by 58.3%, which is significantly better than the existing yield value and has achieved remarkable technical effects.

[0085] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing magnetite using electrolytic manganese residue, characterized in that, It includes the following steps: Step 1) Grinding and activation; Step 2) Oxidative roasting: Mix the manganese slag powder obtained in Step 1) with an oxidation aid evenly, and place it in a furnace for roasting; Step 3) Reductive roasting: Add biomass carbon to the roasted product obtained in Step 2) and mix evenly to obtain a mixture, and carry out anaerobic roasting of the mixture in a furnace; Step 4) Magnetic separation; Among them, in Step 1), the crushed electrolytic manganese slag is ground and activated with a grinding aid; the mass percentage of the grinding aid in the electrolytic manganese slag is 1% - 5%; the grinding aid is any mixture of glycerol and citric acid, oxalic acid, and acetic acid; In Step 2), the mass percentage of the oxidation aid in the manganese slag powder is 1% - 5%; the oxidation aid is any mixture of calcium fluoride and sodium peroxide, potassium peroxide, calcium peroxide, and barium peroxide; the mass percentage of calcium fluoride in the oxidation aid is 1% - 10%.

2. The method for preparing magnetite using electrolytic manganese residue according to claim 1, characterized in that, In Step 2), the roasting temperature is 600 - 1000 °C, and the roasting time is 1 - 4 h.

3. The method for preparing magnetite using electrolytic manganese residue according to claim 1, characterized in that, In Step 3), the biomass carbon is obtained by anaerobic carbonization of pine needles, peanut shells, and walnut shells, and the addition amount of biomass carbon is 1.0 - 2.0 times the theoretical requirement for the reduction of Fe2O3 to Fe3O4.

4. The method for preparing magnetite using electrolytic manganese residue according to claim 1, characterized in that, In Step 3), the roasting temperature is 500 - 900 °C, and the roasting time is 2 - 5 h.

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