A method for preparing zero-valent iron from iron tailings based on liquid-phase reduction

Abstract

The present invention discloses a method for preparing zero-valent iron from iron tailings based on liquid-phase reduction, comprising the following steps: S1, preparation of a soluble iron salt solution; S2, pretreatment of the soluble iron salt; S3, preparation of zero-valent iron. The present invention utilizes waste iron tailings as resources, prepares soluble iron salts therefrom, and conducts a liquid-phase reduction reaction on the soluble salts to generate zero-valent iron. Before the reduction reaction, the soluble iron salt is complexed with phosphate and citrate, and the iron ions in the complexed state are reduced to zero-valent iron under the action of a dispersant and a reducing agent, thereby preparing zero-valent iron with good dispersibility, uniform particle size, and good antioxidant property.

Description

Technical Field

[0001] The present invention relates to the technical field of iron tailings methods, and specifically relates to a method for preparing zero-valent iron from iron tailings based on liquid-phase reduction. Background Art

[0002] Zero-valent iron refers to iron that has lost its charge in certain chemical reactions and becomes an atom with zero charge or free electrons. Zero-valent iron has a relatively large electronegativity and strong reducibility. It is used to treat certain trace organic pollutants in water bodies and can act as a catalyst to accelerate the reaction process. Zero-valent iron has high reaction activity and chemical stability, so it is widely used in many environmental and industrial applications, such as the remediation of contaminated soil and groundwater, wastewater treatment, catalysts, etc.

[0003] Iron tailings are the waste after ore dressing and are the main component of industrial solid waste. According to incomplete statistics, the annual discharge of tailings and waste rocks worldwide is more than 10 billion tons. There are more than 8,000 state-owned mines and more than 110,000 township collective mines in China. The stockpiled tailings volume is nearly 5 billion tons, and the annual discharge of tailings is as high as more than 500 million tons, of which the annual discharge of tailings from ferrous metallurgy mines reaches 150 million tons. Acid leaching reduction experiments are carried out on the waste iron tailings to extract iron resources from the tailings and use them as raw materials to prepare zero-valent iron.

[0004] Currently, a variety of physical and chemical methods have been developed for the preparation of zero-valent iron, mainly including high-energy ball milling method, electro-deposition method, chemical vapor deposition method, sol-gel method, co-precipitation method, thermal decomposition of iron carbonyl method, and chemical liquid-phase reduction method, etc. In terms of efficiency, complexity, and cost, these methods are different from each other. Among them, the thermal decomposition of iron carbonyl method and the chemical liquid-phase reduction method are two important widely used methods. The thermal decomposition of iron carbonyl method can produce fine and high-purity iron nanoparticles with a uniform particle size distribution, but it has large heat energy loss, strong raw material toxicity, high cost, and limited output, which cannot meet the large-scale demand, and there are certain limitations from the perspective of cost-benefit. In comparison, the chemical liquid-phase reduction method is more simple, economical, safe, and efficient. This method usually uses a chemical reducing agent to reduce Fe 2+ or Fe 3+ in an aqueous solution to prepare zero-valent iron nanoparticles. The main bottleneck of the liquid-phase reduction method is that it is easy to cause non-uniform particle shape and size during the preparation process, and agglomeration is likely to occur between particles. Zero-valent iron has poor antioxidant properties and is easily oxidized when exposed to air, affecting the reaction activity of zero-valent iron.

[0005] Therefore, there is a need to design a method for preparing zero-valent iron from iron tailings based on liquid-phase reduction. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for preparing zero-valent iron from iron tailings based on liquid-phase reduction.

[0007] A method for preparing zero-valent iron from iron tailings based on liquid-phase reduction, comprising the following steps:

[0008] S1. Preparation of soluble iron salt solution:

[0009] Use iron tailings to prepare soluble iron salts;

[0010] S2. Pretreatment of soluble iron salts:

[0011] Weigh 12 - 18 ml of soluble iron salt with a concentration of 0.15 mol·L -1 and mix it with a buffer. Among them, mix according to the molar ratio of Fe 3+ to the buffer of 1:1.5 - 3.5. The buffer is composed of phosphate and citrate in a mass ratio of 2:4, and adjust the pH value of the solution to 4.5 - 6.5. When the pH value rises to 4.5, start adding 15 - 20% / +0.2pH of citrate. When the pH value rises to 5.0, start adding 6 - 10% / +0.1pH of phosphate. When the pH value rises to 5.8, add the remaining phosphate, add distilled water to form a pretreatment solution with a concentration of 0.02 - 0.04 mol·L -1 Then add tetrahydrofuran. The addition amount of tetrahydrofuran to the volume of distilled water is 8 - 3:2;

[0012] S3. Preparation of zero-valent iron:

[0013] Add a dispersant to the pretreatment solution obtained in step S2 and mix, then dropwise add a reducing agent and stir. The molar ratio of the soluble iron salt to the reducing agent is 1:2.2 - 3.8. After the addition of the reducing agent is completed, continue to stir. After the reaction is complete, filter, wash the filter residue with deionized water and dry it, then wash it with anhydrous ethanol and acetone in turn, and finally vacuum dry it after suction filtration to finally obtain zero-valent iron.

[0014] Note: By utilizing waste iron tailings, soluble iron salts are prepared from them, and the soluble salts are subjected to liquid-phase reduction reaction to generate zero-valent iron. Before the reduction reaction of the soluble iron salt, it is complexed with phosphate and citrate. The iron ions in the complexed state are reduced to zero-valent iron under the action of a dispersant and a reducing agent, thereby preparing zero-valent iron with good dispersion, uniform particle size, and good antioxidant property.

[0015] Furthermore, the preparation method of the soluble iron salt solution:

[0016] S1-1. Grinding iron tailings:

[0017] Grind and crush the iron tailings and pass through a 100-mesh sieve to obtain the finely ground iron tailings;

[0018] S1-2, Acid Leaching:

[0019] Weigh 50 g of the fine iron tailings obtained in step S1-2 into a beaker. Place the beaker on a constant-temperature heating magnetic stirrer. When heated to 80 - 110 °C, add a strong acid for acid leaching, where the volume-mass ratio of the strong acid to the fine iron tailings is 7 ml / 1 g;

[0020] S1-3, Purification:

[0021] Perform ion exchange on the iron ion solution obtained in step S1-2 using an ion exchange resin to obtain an FeCl3 solution. The ion exchange resin selected is polystyrene sulfonic acid resin, and the mass ratio of the iron ion solution to the polystyrene sulfonic acid resin is 20 - 13:1;

[0022] Note: First, grind the iron tailings to improve the subsequent acid leaching efficiency and the leaching rate of iron ions. Use hydrochloric acid, a strong reducing agent, to perform acid leaching on the fine iron tailings, leach out iron ions from the fine iron tailings, and then purify the iron ion solution to remove other impurities and other components, finally obtaining a soluble FeCl3 solution.

[0023] Further, in step S1-2, the strong acid includes hydrochloric acid with a concentration of 9 - 12 mol·L -1 and hydrochloric acid with a concentration of 14 - 20 mol·L -1 , and the mass ratio of the two is 1:1. During acid leaching, first add hydrochloric acid with a concentration of 9 - 12 mol·L -1 and leach for 2 - 3 h. Subsequently, add hydrochloric acid with a concentration of 14 - 20 mol·L -1 and leach for 2.5 - 4 h to obtain an iron ion solution.

[0024] Note: First add hydrochloric acid with a concentration of 9 - 12 mol·L -1 for acid leaching. As the reaction time increases, the leaching rate of iron ions continuously increases. When the time reaches 2 - 3 h, the leaching rate of iron ions weakens. Then add hydrochloric acid with a concentration of 14 - 20 mol·L -1 again for acid leaching, which can effectively improve the leaching rate of iron ions.

[0025] Further, the reducing agent is one of hydrazine hydrate, sodium borohydride, or potassium borohydride.

[0026] Description: It is an inorganic compound with the chemical formula N2H4·H2O. It is a colorless, transparent and fuming liquid with a faint ammonia smell. It smokes in humid air, has strong alkalinity and hygroscopicity. Hydrazine hydrate has strong reducing ability, low cost, and the zero-valent iron particles prepared with it have fewer impurities. Hydrazine hydrate can reduce ferric ions in soluble ferric salt solutions to prepare zero-valent iron. Sodium borohydride alkaline solution is brownish-yellow and stable at normal temperature and pressure. It is one of the most commonly used reducing agents. It is relatively stable to water vapor and oxygen in the air, and is easy to operate and handle. It can be used as a reducing agent to reduce ferric ions in soluble ferric salt solutions to zero-valent iron. Potassium borohydride is a white, loose powder or crystal, stable in air, not hygroscopic, easily soluble in water, soluble in liquid ammonia, slightly soluble in methanol and ethanol, and has strong reducibility. It can reduce ferric ions in soluble ferric salt solutions to prepare zero-valent iron.

[0027] Further, the dispersant is composed of sodium acrylate and polyvinylpyrrolidone in a mass ratio of 1:3 - 8.

[0028] Description: Sodium acrylate has good water solubility and ionic stability, and can form a polymer colloid in aqueous solution. The polymer colloid of sodium acrylate can form a three-dimensional network structure in the liquid state to form a dispersion system, which can disperse solid particles in water and prevent them from aggregating. The polymer colloid of sodium acrylate can also attach colloidal particles to the solid surface through adsorption to form stable colloidal particles, having good dispersion effect. It can also reduce the surface tension of the solution, making it easier for solid particles to be dispersed in water. Polyvinylpyrrolidone is a non-ionic polymer compound. Polyvinylpyrrolidone is a hydrophilic, easy-flowing white or almost white powder with a slight odor. As a synthetic water-soluble polymer compound, polyvinylpyrrolidone has the general properties of water-soluble polymer compounds, such as colloid protection, film-forming property, adhesiveness, hygroscopicity, solubilization or aggregation, excellent solubility and physiological compatibility. The zero-valent iron particles prepared using the above dispersant have good dispersibility and stability.

[0029] Further, the mass ratio of the dispersant to the soluble ferric salt is 0.2 - 0.8:1.

[0030] Description: Before liquid-phase reduction of the pretreatment solution, adding an appropriate amount of dispersant can improve the dispersibility and stability of the prepared zero-valent iron, reduce the occurrence of agglomeration phenomenon, and increase antioxidant property.

[0031] Further, in step S3, while adding a reducing agent, an antioxidant is added, and the mass ratio of the antioxidant to the soluble ferric salt is 0.06 - 1:90.

[0032] Description: Adding an antioxidant can improve the antioxidant property and reaction activity of zero-valent iron.

[0033] Further, the antioxidant is composed of 80 - 90% tea extract and the balance being chitosan. The tea extract is a green tea extract with a certain concentration. The preparation method of the antioxidant is as follows: Add 2.5 g of dried green tea into 100 ml of boiling water, heat for 0.5 h to obtain the green tea extract, and then add chitosan to obtain the antioxidant.

[0034] Explanation: The tea extract has better adsorption and reduction ability and the characteristic of maintaining activity for a long time, and has strong antioxidant effect, making the prepared zero-valent iron have high antioxidant property. Chitosan is a natural polysaccharide that widely exists in nature, which is renewable, non-toxic, has good biocompatibility and degradability. Due to the special structure of chitosan, it contains active -OH and -NH2, and other groups can be introduced on N or O to improve its solubility and biological activity, and can improve the antioxidant property of the prepared zero-valent iron.

[0035] Further, in step S3, the stirring rate is 150 r / min, and after the reducing agent is completely added, continue to stir for 30 - 50 min.

[0036] Explanation: The pretreatment liquid is continuously stirred during the liquid-phase reduction process, so that the reducing agent is fully contacted with the iron ions in the pretreatment liquid. After the reducing agent is completely added, continue to stir to make the reduction reaction more complete and increase the amount of the prepared zero-valent iron.

[0037] The beneficial effects of the present invention are as follows:

[0038] (1) By resource utilization of waste iron tailings, the present invention prepares soluble iron salts therefrom, and conducts a liquid-phase reduction reaction on the soluble salts to generate zero-valent iron. Before the reduction reaction of the soluble iron salts, they are complexed with phosphates and citrates, and the iron ions in the complexed state are reduced to zero-valent iron under the action of a dispersant and a reducing agent, thereby preparing zero-valent iron with good dispersibility, uniform particle size and good antioxidant property.

[0039] (2) The present invention first grinds the iron tailings to improve the subsequent acid leaching efficiency and the leaching rate of iron ions, uses strong reducing agent hydrochloric acid to acid leach the fine iron tailings, leaches out iron ions from the fine iron tailings, and then purifies the iron ion-containing solution to remove other impurities and other components, and finally obtains a soluble FeCl3 solution, obtaining a soluble iron salt with high iron ion content and high purity.

[0040] (3) The present invention mixes the tea extract and chitosan as an antioxidant to further improve the antioxidant property of zero-valent iron. Specific Embodiments

[0041] The following further describes the present invention in detail in combination with specific embodiments to better reflect the advantages of the present invention.

[0042] Example 1

[0043] A method for preparing zero-valent iron from iron tailings based on liquid-phase reduction, comprising the following steps:

[0044] S1. Preparation of soluble iron salt solution:

[0045] Use iron tailings to prepare soluble iron salt;

[0046] S1-1. Grinding iron tailings:

[0047] Grind and crush the iron tailings and pass through a 100-mesh sieve to obtain the finely ground iron tailings;

[0048] S1-2. Acid leaching:

[0049] Weigh 50 g of the finely ground iron tailings obtained in step S1-2 into a beaker, place the beaker on a constant-temperature heating magnetic stirrer, heat to 95 °C, and add strong acid for acid leaching, where the volume-mass ratio of the strong acid to the finely ground iron tailings is 7 ml / g;

[0050] The strong acid consists of hydrochloric acid with a concentration of 11 mol·L -1 and hydrochloric acid with a concentration of 17 mol·L -1 , and the mass ratio of the two is 1:1. During acid leaching, first add hydrochloric acid with a concentration of 11 mol·L -1 and leach for 2.1 h, then add hydrochloric acid with a concentration of 17 mol·L -1 and leach for 2.8 h to obtain a solution containing iron ions;

[0051] S1-3. Purification:

[0052] Ion-exchange the solution containing iron ions obtained in step S1-2 using ion-exchange resin to obtain FeCl3 solution. The ion-exchange resin is selected as polystyrene sulfonic acid resin, and the mass ratio of the solution containing iron ions to the polystyrene sulfonic acid resin is 18:1;

[0053] S2. Pretreatment of soluble iron salt:

[0054] Weigh 15 ml of soluble iron salt with a concentration of 0.15 mol·L -1 and buffer agent and mix them. Among them, according to Fe 3+Mix with a molar ratio of 1:2.5 of the buffer agent. The buffer agent is composed of sodium dihydrogen phosphate and sodium citrate with a mass ratio of 2:4, and adjust the pH value of the solution to 6.2. When the pH value rises to 4.5, start adding 18% / +0.2pH of citrate. When the pH value rises to 5.0, start adding 8% / +0.1pH of phosphate. When the pH value rises to 5.8, add all the remaining phosphate, and add distilled water to form a pretreatment solution with a concentration of 0.03mol·L -1 of the pretreatment solution, and then add tetrahydrofuran. The addition amount of tetrahydrofuran and the volume ratio of distilled water is 5:2;

[0055] S3. Preparation of zero-valent iron:

[0056] Add a dispersant to the pretreatment solution obtained in step S2 and mix, and then dropwise add a reducing agent and stir. The molar ratio of the soluble iron salt to the reducing agent is 1:3. After the addition of the reducing agent is completed, continue to stir at a stirring rate of 150r / min for 40min after the addition of the reducing agent;

[0057] After the reaction is complete, filter, wash the filter residue with deionized water and drain, then wash with absolute ethanol and acetone in turn, and finally vacuum dry after suction filtration to finally obtain zero-valent iron;

[0058] While adding the reducing agent, add an antioxidant. The mass ratio of the antioxidant to the soluble iron salt is 0.5:90;

[0059] The antioxidant is composed of 85% of tea extract and the balance of chitosan. The tea extract is a green tea extract with a concentration. The preparation method of the antioxidant is: add 2.5g of dried green tea to 100ml of boiling water, heat for 0.5h to obtain green tea extract, and then add chitosan to obtain the antioxidant;

[0060] The reducing agent is hydrazine hydrate;

[0061] The dispersant is composed of sodium acrylate and polyvinylpyrrolidone with a mass ratio of 1:5;

[0062] The mass ratio of the dispersant to the soluble iron salt is 0.5:1.

[0063] Example 2

[0064] The difference between this example and Example 1 is that in step S2, 12ml of a soluble iron salt with a concentration of 0.15mol·L -1 is weighed and mixed with the buffer agent. Among them, according to Fe 3+Mix with a buffer in a molar ratio of 1:2.5. The buffer is composed of sodium dihydrogen phosphate and sodium citrate in a mass ratio of 2:4, and adjust the pH value of the solution to 6.2. When the pH value rises to 4.5, start adding 18% / +0.2pH of citrate. When the pH value rises to 5.0, start adding 8% / +0.1pH of phosphate. When the pH value rises to 5.8, add all the remaining phosphate, and add distilled water to form a pretreatment solution with a concentration of 0.02mol·L -1 Subsequently, add tetrahydrofuran. The addition amount of tetrahydrofuran and the volume ratio of distilled water is 4:1.

[0065] Example 3

[0066] The difference between this example and Example 1 is that in step S2, weigh 18 ml of a soluble iron salt with a concentration of 0.15mol·L -1 and mix it with a buffer. Among them, mix according to the molar ratio of Fe 3+ and the buffer is 1:2.5. The buffer is composed of sodium dihydrogen phosphate and sodium citrate in a mass ratio of 2:4, and adjust the pH value of the solution to 6.2. When the pH value rises to 4.5, start adding 18% / +0.2pH of sodium citrate. When the pH value rises to 5.0, start adding 8% / +0.1pH of sodium dihydrogen phosphate. When the pH value rises to 5.8, add all the remaining sodium dihydrogen phosphate, and add distilled water to form a pretreatment solution with a concentration of 0.04mol·L -1 Subsequently, add tetrahydrofuran. The addition amount of tetrahydrofuran and the volume ratio of distilled water is 3:2.

[0067] Example 4

[0068] The difference between this example and Example 1 is that in step S2, mix according to the molar ratio of Fe 3+ and the buffer is 1:1.5. The buffer is composed of sodium dihydrogen phosphate and sodium citrate in a mass ratio of 2:4, and adjust the pH value of the solution to 5.8. When the pH value rises to 4.5, start adding 20% / +0.2pH of sodium citrate. When the pH value rises to 5.0, start adding 10% / +0.1pH of sodium dihydrogen phosphate. When the pH value rises to 5.8, add the remaining sodium dihydrogen phosphate.

[0069] Example 5

[0070] The difference between this example and Example 1 is that among them, according to Fe 3+Mix with a buffer in a molar ratio of 1:3.5. The buffer is composed of sodium dihydrogen phosphate and sodium citrate in a mass ratio of 2:4, and adjust the pH value of the solution to 6.5. When the pH value rises to 4.5, start adding sodium citrate of 15% / +0.2pH. When the pH value rises to 5.0, start adding sodium dihydrogen phosphate of 6% / +0.1pH. When the pH value rises to 5.8, add the remaining sodium dihydrogen phosphate.

[0071] Example 6

[0072] The difference between this example and Example 1 is that the molar ratio of the soluble iron salt to the reducing agent is 1:2.2.

[0073] Example 7

[0074] The difference between this example and Example 1 is that the molar ratio of the soluble iron salt to the reducing agent is 1:3.8.

[0075] Example 8

[0076] The difference between this example and Example 1 is that the reducing agent is sodium borohydride.

[0077] Example 9

[0078] The difference between this example and Example 1 is that the reducing agent is potassium borohydride.

[0079] Example 10

[0080] The difference between this example and Example 1 is that the dispersant is composed of sodium acrylate and polyvinylpyrrolidone in a mass ratio of 1:3.

[0081] Example 11

[0082] The difference between this example and Example 1 is that the dispersant is composed of sodium acrylate and polyvinylpyrrolidone in a mass ratio of 1:8.

[0083] Example 12

[0084] The difference between this example and Example 1 is that the mass ratio of the dispersant to the soluble iron salt is 0.2:1.

[0085] Example 13

[0086] The difference between this example and Example 1 is that the mass ratio of the dispersant to the soluble iron salt is 0.8:1.

[0087] Example 14

[0088] The difference between this embodiment and Embodiment 1 lies in that in step S3, the antioxidant consists of 80% tea extract and the balance being peptidoglycan, and the mass ratio of the antioxidant to the soluble iron salt is 0.06:90.

[0089] Embodiment 15

[0090] The difference between this embodiment and Embodiment 1 lies in that in step S3, the antioxidant consists of 90% tea extract and the balance being peptidoglycan, and the mass ratio of the antioxidant to the soluble iron salt is 1:90.

[0091] Embodiment 16

[0092] The difference between this embodiment and Embodiment 1 lies in that in step S1-2, the strong acid consists of hydrochloric acid with a concentration of 9 mol·L -1 and hydrochloric acid with a concentration of 14 mol·L -1 in a mass ratio of 1:1. During acid leaching, hydrochloric acid with a concentration of 9 mol·L -1 is first added and leached for 2.1 h, and then hydrochloric acid with a concentration of 14 mol·L -1 is added and leached for 2.8 h to obtain a solution containing iron ions.

[0093] Embodiment 17

[0094] The difference between this embodiment and Embodiment 1 lies in that in step S1-2, the strong acid consists of hydrochloric acid with a concentration of 12 mol·L -1 and hydrochloric acid with a concentration of 20 mol·L -1 in a mass ratio of 1:1. During acid leaching, hydrochloric acid with a concentration of 12 mol·L -1 is first added and leached for 2.1 h, and then hydrochloric acid with a concentration of 20 mol·L -1 is added and leached for 2.8 h to obtain a solution containing iron ions.

[0095] Embodiment 18

[0096] The difference between this embodiment and Embodiment 1 lies in that in step S1-2, the strong acid consists of hydrochloric acid with a concentration of 9 mol·L -1 and hydrochloric acid with a concentration of 14 mol·L -1 in a mass ratio of 1:1. During acid leaching, hydrochloric acid with a concentration of 9 mol·L -1 is first added and leached for 3 h, and then hydrochloric acid with a concentration of 14 mol·L -1 is added and leached for 4 h to obtain a solution containing iron ions.

[0097] Embodiment 19

[0098] The difference between this embodiment and Embodiment 1 lies in that in step S1-2, the strong acid consists of hydrochloric acid with a concentration of 12 mol·L -1 and hydrochloric acid with a concentration of 20 mol·L -1 in a mass ratio of 1:1. During acid leaching, first add hydrochloric acid with a concentration of 12 mol·L -1 and leach for 3 h, then add hydrochloric acid with a concentration of 20 mol·L -1 and leach for 4 h to obtain a solution containing iron ions.

[0099] Experimental Example

[0100] For the zero-valent iron prepared in each embodiment, its physical properties were measured, and the specific exploration is as follows:

[0101] Explore the effects of raw materials with different ratios and different processes on zero-valent iron.

[0102] Take Embodiments 1-5, 10-13 as experimental examples for comparison;

[0103] At the same time, set Comparative Example 1: In step S2, the buffer is sodium dihydrogen phosphate, and other conditions remain unchanged;

[0104] Comparative Example 2: In step S2, the buffer is sodium citrate, and other conditions remain unchanged;

[0105] Comparative Example 3: In step S2, the buffer is composed of phosphate and citrate in a mass ratio of 2:4. When the pH value rises to 4.5, start to slowly add the buffer, and other conditions remain unchanged;

[0106] Comparative Example 4: In step S1-2, the strong acid is hydrochloric acid with a concentration of 11 mol·L -1 and the leaching time is 4 h, and other conditions remain unchanged;

[0107] Comparative Example 5: In step S3, no antioxidant is added, and other conditions remain unchanged;

[0108] Comparative Example 6: In step S3, the antioxidant is tea extract, and other conditions remain unchanged;

[0109] The performance of zero-valent iron is shown in Table 1:

[0110] Table 1 Performance test table of the flow channels prepared from the castables under various ingredients

[0111]

[0112]

[0113] As can be seen from the results in Table 1 above, exploring raw materials with different ratios and different processes has a certain impact on the performance of zero-valent iron; the zero-valent iron prepared in the above Examples 1-19 has a particle size between 8-18 nm and a specific surface area between 80-90 m 2 / g, and there is no iron oxide on the surface of the zero-valent iron particles, and no oxidation phenomenon occurs. The particle size of the zero-valent iron prepared in Comparative Examples 1-3 is between 8-25 nm, and the specific surface area is between 70-90 m 2 / g. There is no iron oxide on the surface of the zero-valent iron particles. Oxidation occurs on the surface of the zero-valent iron particles prepared in Comparative Example 5, and slight oxidation occurs on the surface of the zero-valent iron particles prepared in Comparative Example 6. Among them, the zero-valent iron particles prepared in Example 1 are more uniform, have a large specific surface area, and good antioxidant performance;

[0114] Taking Examples 1 and 16-19 as experimental examples for comparison and comparing with Comparative Example 4, it can be seen that the iron leaching rates of Examples 1, 16, 17, 18, and 19 are 98%, 92%, 98.5%, 93.4%, and 95% respectively, and the iron leaching rate of Comparative Example 4 is 89.7%. The concentration of hydrochloric acid has a certain impact on the iron leaching rate. From Examples 1 and 16-19, it can be seen that as the reaction time prolongs, the iron leaching rate increases; when the leaching time reaches 2.1 h and the reaction time is further prolonged, the increase in the iron leaching rate is small and tends to be stable. If the reaction time is too long, the production efficiency will decrease and the energy consumption will also increase. From Examples 1 and Comparative Example 4, it can be seen that choosing the acid leaching method of Example 1 can effectively improve the iron leaching rate.

Claims

1. A method for preparing zero-valent iron from iron tailings based on liquid-phase reduction, characterized in that, It includes the following steps: S1. Preparation of soluble iron salt solution: Use iron tailings to prepare soluble iron salt; S2. Pretreatment of soluble iron salt: Weigh 12 - 18 ml of soluble iron salt with a concentration of 0.15 mol·L -1 and buffer and mix them. Among them, mix according to the molar ratio of Fe 3+ to buffer of 1:1.5 - 3.

5. The buffer is composed of phosphate and citrate in a mass ratio of 2:4, and adjust the pH value of the solution to 4.5 - 6.

5. When the pH value rises to 4.5, start adding citrate with 15 - 20% / +0.2pH. When the pH value rises to 5.0, start adding phosphate with 6 - 10% / +0.1pH. When the pH value rises to 5.8, add the remaining phosphate, add distilled water to form a pretreatment solution with a concentration of 0.02 - 0.04 mol·L -1 . Subsequently, add tetrahydrofuran, and the addition amount of tetrahydrofuran to the volume of distilled water is 8 - 3:2; S3. Preparation of zero-valent iron: Add a dispersant and mix it into the pretreatment liquid obtained in step S2, then dropwise add a reducing agent and stir. The molar ratio of the soluble iron salt to the reducing agent is 1:2.2 - 3.

8. After the addition of the reducing agent is completed, continue to stir. After the reaction is complete, filter. The filter residue is rinsed with deionized water and dried, then rinsed successively with absolute ethanol and acetone, and finally vacuum dried after suction filtration to finally obtain zero-valent iron; In step S1, the preparation method of the soluble iron salt solution: S1-1. Grinding of iron tailings: Grind and crush the iron tailings and pass through a 100-mesh sieve to obtain the finely ground iron tailings; S1-2. Acid leaching: Weigh 50 g of the finely ground iron tailings obtained in step S1-2 into a beaker, place the beaker on a constant-temperature heating magnetic stirrer, heat to 80 - 110 °C, and add a strong acid for acid leaching. The volume-mass ratio of the strong acid to the finely ground iron tailings is 7 ml / 1 g; S1-3. Purification: Ion exchange the iron ion solution obtained in step S1-2 using an ion exchange resin to obtain an FeCl3 solution. The ion exchange resin is polystyrene sulfonic acid resin, and the mass ratio of the iron ion solution to the polystyrene sulfonic acid resin is 20 - 13:1; In step S1-2, the strong acid includes hydrochloric acid with a concentration of 9-12 mol·L -1 and hydrochloric acid with a concentration of 14-20 mol·L -1 . The mass ratio of the two is 1:

1. During acid leaching, first add hydrochloric acid with a concentration of 9-12 mol·L -1 and leach for 2-3 h. Subsequently, add hydrochloric acid with a concentration of 14-20 mol·L -1 and leach for 2.5-4 h to obtain a solution containing iron ions; The reducing agent is one of hydrazine hydrate, sodium borohydride, or potassium borohydride; The dispersant is composed of sodium acrylate and polyvinylpyrrolidone with a mass ratio of 1:3 - 8; In step S3, while adding the reducing agent, add an antioxidant. The mass ratio of the antioxidant to the soluble iron salt is 0.06 - 1:90; The antioxidant is composed of 80 - 90% of tea extract and the balance is chitosan. The tea extract is green tea extract. The preparation method of the antioxidant is: add 2.5 g of dry green tea to 100 ml of boiling water, heat for 0.5 h to obtain the green tea extract, and then add chitosan to obtain the antioxidant.

2. The method for preparing zero-valent iron from iron tailings based on liquid-phase reduction according to claim 1, wherein The mass ratio of the dispersant to the soluble iron salt is 0.2 - 0.8:

1.

3. A method for preparing zero-valent iron from iron tailings based on liquid-phase reduction according to claim 1, characterized in that, The stirring rate in step S3 is 150 r / min, and continue to stir for 30 - 50 min after the addition of the reducing agent is completed.

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