A method for preparing low-zinc magnetite, a micro-entrained flow reactor and application thereof

Abstract

This invention provides a method for preparing low-zinc magnetite, a micro-entrapment reactor, and its application. The micro-entrapment reactor includes a cross-shaped connector, a liquid inlet assembly, and a reaction microchannel. The cross-shaped connector has a first sample inlet, a second sample inlet, an alkali inlet, and an outlet. The first and second sample inlets are arranged opposite to each other, and the alkali inlet and the outlet are arranged opposite to each other. The liquid inlet assembly includes a first sample pipeline, a second sample pipeline, and an alkali pipeline. The outlet end of the first sample pipeline is connected to the first sample inlet, the outlet end of the second sample pipeline is connected to the second sample inlet, and the outlet end of the alkali pipeline is connected to the alkali inlet. The inlet end of the reaction microchannel is connected to the outlet. This invention can obtain high-quality low-zinc magnetite while reducing the alkali concentration.

Description

Technical Field

[0001] This invention relates to the preparation of low-zinc magnetite, and more particularly to a method for preparing low-zinc magnetite, a micro-entrainment reactor, and its applications. Background Technology

[0002] Iron and zinc are indispensable industrial raw materials in industrial production and are widely distributed around the world. Iron is widely used in the manufacture of steel, metal alloys, machinery, and building materials. Meanwhile, zinc plays a crucial role in the manufacture of galvanized steel, batteries, and alloys. The demand for iron and zinc in industrial production has remained stable over the long term, and they have broad application prospects in high-tech industries.

[0003] my country is a major zinc smelting country globally. The hydrometallurgical zinc refining process generates large quantities of iron- and zinc-containing leachate, which ultimately results in hazardous iron slag during the iron precipitation process. Therefore, recovering and extracting iron and zinc from this slag has significant industrial value. Traditional heavy metal recovery technologies typically employ a combined pyrometallurgical and hydrometallurgical process, which suffers from high energy consumption, significant secondary pollution risks, and environmental unfriendliness. Furthermore, the actual iron precipitation process in hydrometallurgical zinc refining involves multiple complex stages, including nucleation, growth, and the formation of intermediate products. In addition, heavy metals such as zinc in the leachate readily co-precipitate with iron minerals, resulting in inclusions within the iron mineral crystal structure and increasing processing difficulty. To address these bottlenecks, it is necessary to introduce emerging microfluidic technologies to reduce zinc inclusions in the iron slag during the iron precipitation process.

[0004] Chinese invention patent application CN117085607A (the applicant's previous application) discloses a microchannel reactor, a method for iron precipitation based on an iron-zinc mixture, and its application. The microchannel reactor in this patent application includes a delivery mechanism and a reaction mechanism; the delivery mechanism includes a first delivery component and a second delivery component; the reaction mechanism includes a first preheating microchannel, a second preheating microchannel, a mixing connector, and a reaction microchannel; the mixing connector has a first inlet passage, a second inlet passage, and an outlet passage; the first inlet passage and the outlet of the first preheating microchannel are connected; the second inlet passage and the outlet of the second preheating microchannel are connected; the outlet passage and the inlet of the reaction microchannel are connected.

[0005] While this patent application can avoid polymetallic co-precipitation to some extent and yielded a low-zinc iron-precipitated product with a content of only 2.83% under 9M-35s conditions, the 9M alkali concentration increases reagent dosage and cost, and also increases the difficulty of equipment operation. Therefore, it is necessary to explore how to obtain high-quality low-zinc magnetite while reducing the alkali concentration. It should be noted that while reducing the zinc content, it is necessary to avoid the increase of impurity iron phases and to ensure the uniformity of magnetite morphology in order to ensure the acquisition of high-quality low-zinc magnetite.

[0006] Therefore, it is necessary to provide a method for preparing low-zinc magnetite, a micro-entrapment reactor, and its application, in order to solve or at least alleviate the aforementioned technical problem of how to obtain high-quality low-zinc magnetite while reducing the concentration of alkali solution. Summary of the Invention

[0007] The main objective of this invention is to provide a method for preparing low-zinc magnetite, a micro-entrapment reactor, and its application, aiming to solve the aforementioned technical problem of how to obtain high-quality low-zinc magnetite while reducing the concentration of alkali solution.

[0008] To achieve the above objectives, the present invention provides a micro-clamp reactor, comprising a cross joint, a liquid inlet assembly, and a reaction microchannel;

[0009] The cross-shaped connector has a first sample inlet, a second sample inlet, an alkali inlet, and an outlet; the first sample inlet and the second sample inlet are arranged opposite to each other and are interconnected along a first passage; the alkali inlet and the outlet are arranged opposite to each other and are interconnected along a second passage; the first passage and the second passage intersect and are perpendicular to each other, and are interconnected at the intersection;

[0010] The liquid inlet assembly includes a first sample liquid pipeline, a second sample liquid pipeline, and an alkali liquid pipeline; the outlet end of the first sample liquid pipeline is connected to the first sample liquid inlet, the outlet end of the second sample liquid pipeline is connected to the second sample liquid inlet, and the outlet end of the alkali liquid pipeline is connected to the alkali liquid inlet.

[0011] The inlet and outlet of the reaction microchannel are connected.

[0012] Furthermore, the micro-clamp reactor also includes a first sample injection unit, a second sample injection unit, and an alkali injection unit;

[0013] The first sample injection unit is connected to the inlet end of the first sample pipeline, the second sample injection unit is connected to the inlet end of the second sample pipeline, and the alkali injection unit is connected to the inlet end of the alkali pipeline.

[0014] Furthermore, both the first path and the second path are straight paths; the middle of the first path and the middle of the second path intersect.

[0015] Furthermore, the inner diameters of the first sample solution pipeline, the second sample solution pipeline, the alkali solution pipeline, and the reaction microchannel are all 0.8-1.2 mm; the length of the reaction microchannel is 2-12 m.

[0016] The present invention also provides an application of the micro-entrainment reactor as described above in the acquisition of low-zinc magnetite.

[0017] This invention also provides a method for preparing low-zinc magnetite based on an iron-zinc mixture, using a micro-entrainment reactor as described above; the method includes:

[0018] Take an iron-zinc mixture and an alkaline solution, and divide the iron-zinc mixture into a first part and a second part;

[0019] The iron-zinc mixture in the first part is controlled to be injected into the first passage sequentially through the first sample solution pipeline and the first sample solution inlet; the iron-zinc mixture in the second part is controlled to be injected into the first passage sequentially through the second sample solution pipeline and the second sample solution inlet; the alkali solution is controlled to be injected into the second passage sequentially through the alkali solution pipeline and the alkali solution inlet;

[0020] The iron-zinc mixture described in Part 1, the iron-zinc mixture described in Part 2, and the alkaline solution are combined in the cross joint to obtain a reaction solution;

[0021] The reaction solution is controlled to enter the reaction microchannel through the outlet, and the suspension generated by the reaction is collected at the outlet of the reaction microchannel;

[0022] The suspension was separated into solid and liquid components to obtain low-zinc magnetite.

[0023] Furthermore, in the iron-zinc mixture, the total concentration of ferrous ions and ferric ions is 0.01-0.2 mol / L, and the concentration of zinc ions is 0.01-0.2 mol / L; the molar ratio of iron to zinc is 5-1:1-3.

[0024] Furthermore, the concentration of alkaline substances in the alkaline solution is 4-8 mol / L.

[0025] Furthermore, the flow rate of the iron-zinc mixture in the first sample solution pipeline is 1-5 ml / min, the flow rate of the iron-zinc mixture in the second sample solution pipeline is 1-5 ml / min, the flow rate of the alkali solution in the alkali solution pipeline is 2-10 ml / min, and the residence time of the reaction solution in the reaction microchannel is 12-88 s.

[0026] Furthermore, the cross-shaped connector, the liquid inlet assembly, and the reaction microchannel are all located in an environment of 50-90°C.

[0027] Compared with the prior art, the present invention has at least the following advantages:

[0028] 1. The micro-junction reactor provided by the present invention can enhance fluid mixing and mass transfer effects while reducing the concentration of alkali solution, and efficiently form the target product; and can precisely control the formation process of magnetite, ultimately avoiding the formation of impurity phases and multi-metal doping.

[0029] 2. The micro-entrainment reactor provided by this invention accelerates the transformation of amorphous intermediates into magnetite through a specific micro-entrainment mixing method, reduces the formation of impurity iron phases, and obtains magnetite with uniform morphology and size, thus providing a foundation for obtaining high-quality low-zinc magnetite.

[0030] 3. The method for preparing low-zinc magnetite provided by the present invention involves injecting the reaction solution into the alkali solution pipeline and two sample solution pipelines through each injection unit, then rapidly mixing the solution in a cross-shaped micro-interface using an iron-alkali mixture, and then reacting in the reaction microchannel to form a black suspension which flows into a pre-cooled collection container. After solid-liquid separation, low-zinc magnetite is obtained. The present invention can obtain high-quality low-zinc magnetite at an alkali solution concentration of about 7 mol / L, and can reduce the zinc doping rate in the magnetite to 2.84%. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the micro-entrapment mixing method in this invention;

[0033] Figure 2 This is a reaction scenario diagram for the preparation of low-zinc magnetite in this invention;

[0034] Figure 3 These are X-ray diffraction patterns of the solid phases in Embodiment 1, Comparative Examples 1, and 3-4 of the present invention;

[0035] Figure 4 The doping rate of zinc in the solid phase is shown in Embodiment 1, Comparative Examples 1, 3-4, and 7-8 of this invention.

[0036] Figure 5 The graph shows the percentage iron content in Examples 1, 1, 3-4, and 7-8 of this invention.

[0037] Figure 6 The doping rate of zinc in the solid phase is shown in Embodiment 2, Comparative Examples 2, 5-6, and 9-10 of the present invention.

[0038] Figure 7The graph shows the percentage iron content in Examples 2, 2, 5-6, and 9-10 of the present invention.

[0039] Figure 8 These are transmission electron microscope images of Embodiments 1-2 and Comparative Example 10 of the present invention;

[0040] Figure 9 The Fourier transform infrared spectra of the solid phases in Embodiment 1, Comparative Examples 1, and 3-4 of this invention are shown below.

[0041] Figure 10 The Fourier transform infrared spectra of the solid phases in Embodiment 2 and Comparative Example 6 of the present invention are shown.

[0042] Reference numerals in the attached drawings: 1. First sample injection unit; 2. Alkali injection unit; 3. Second sample injection unit; 4. First sample line; 5. Alkali line; 6. Second sample line; 7. Cross connector; 8. Reaction microchannel; 9. Collection device.

[0043] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. It should be noted that the data in the embodiments and comparative examples of the present invention are all average values ​​after multiple tests, and have stability and reliability; and the zinc doping rate in the present invention is the mass concentration ratio of zinc in the iron precipitate product.

[0046] Currently, preliminary research has been conducted on the separation of heavy metals using the magnetite method in macroscopic mixed systems. However, this traditional method suffers from problems such as easy doping by multiple metals, a variety of intermediate products, slow nucleation and conversion rates, and the influence of other impurity elements. Furthermore, at the macroscopic scale, the solution mixing process easily creates regions with excessively high concentrations or temperatures, leading to uneven mass or heat transfer and directly affecting the formation efficiency of magnetite. Moreover, macroscopic mixed systems cannot achieve precise control over the magnetite formation process, resulting in the formation of more impurity phases and intermediate states, increasing the difficulty of controlling impurity elements. Therefore, the application of this method in this field is limited.

[0047] While the applicant's previous application (Chinese invention patent application publication number CN117085607A) provided a microchannel reactor, a method for iron precipitation based on an iron-zinc mixture, and its application, in practical industrial applications, it is necessary to minimize the concentration of the alkali solution to reduce the amount of raw materials added and simplify equipment operation. Therefore, developing a micro-entrapment mixing method for controlling the formation of low-zinc magnetite while reducing the concentration of the alkali solution is of great significance.

[0048] like Figure 1-2 As shown, the present invention provides a micro-clamp reactor, including a cross joint, a liquid inlet assembly, and a reaction microchannel.

[0049] The cross connector is a cross-shaped four-way micro connector, and the cross connector has a first sample liquid inlet, a second sample liquid inlet, an alkali liquid inlet, and an outlet; the first sample liquid inlet, the second sample liquid inlet, the alkali liquid inlet, and the outlet are respectively located on the four end faces of the cross connector.

[0050] To ensure the formation of the micro-fluid mixing method in this invention, the first sample liquid inlet and the second sample liquid inlet are arranged opposite to each other, and the first sample liquid inlet and the second sample liquid inlet are interconnected along the first passage; the alkali liquid inlet and the liquid outlet are arranged opposite to each other, and the alkali liquid inlet and the liquid outlet are interconnected along the second passage.

[0051] As a specific description of the cross-shaped connector, the cross-shaped connector has a first passage and a second passage inside, both of which are straight passages, that is, the extension paths of the first passage and the second passage are both straight lines; to ensure that a cross-shaped channel is formed inside the cross-shaped connector; the first sample liquid inlet is located at one end of the first passage, and the second sample liquid inlet is located at the other end of the first passage; the alkali liquid inlet is located at one end of the second passage, and the liquid outlet is located at the other end of the second passage; the first passage and the second passage intersect and are arranged perpendicularly, and the first passage and the second passage are interconnected at the intersection, and the middle part of the first passage and the middle part of the second passage intersect, that is, the first passage and the second passage form a cross shape after intersecting.

[0052] In addition, the orifice diameter of the cross connector can be 0.5-1.0 mm; that is, the orifice diameters of the first sample liquid inlet, the second sample liquid inlet, the alkali liquid inlet and the liquid outlet are all 0.5-1.0 mm, and the inner diameters of the first passage and the second passage are both 0.5-1.0 mm.

[0053] To form three liquid streams and converge them within the cross joint, the liquid inlet assembly includes a first sample liquid line, a second sample liquid line, and an alkali liquid line; the outlet of the first sample liquid line is connected to the first sample liquid inlet, the outlet of the second sample liquid line is connected to the second sample liquid inlet, and the outlet of the alkali liquid line is connected to the alkali liquid inlet.

[0054] To control the flow rate and velocity of the three liquid streams and achieve continuous liquid supply, the micro-clamp reactor further includes a first sample injection unit, a second sample injection unit, and an alkali injection unit. The first sample injection unit is connected to the inlet end of the first sample pipeline, the second sample injection unit is connected to the inlet end of the second sample pipeline, and the alkali injection unit is connected to the inlet end of the alkali pipeline. Each of the first sample injection unit, the second sample injection unit, and the alkali injection unit may include or be an injection pump.

[0055] To ensure the reaction solution obtained after the three liquid streams converge continues to react within the microchannel, the inlet and outlet of the reaction microchannel are connected. For example, two equal parts of an iron-zinc mixture and one part of an alkaline solution are injected into the cross-shaped connector. When the iron-zinc mixture and the alkaline solution converge within the mixing connector, a reaction begins, and the solution enters the reaction microchannel from the outlet to continue the iron deposition reaction.

[0056] In this invention, in order to ensure the normal progress of the reaction and to avoid particle blockage of the pipeline, the inner diameter of the first sample liquid pipeline, the second sample liquid pipeline, the alkaline solution pipeline and the reaction microchannel can all be 0.8-1.2 mm; the outer diameter can all be 1.5-2.0 mm.

[0057] In this invention, the first sample liquid pipeline, the second sample liquid pipeline, the alkali liquid pipeline, and the reaction microchannel can all be spiral structures, thereby reducing the footprint while further ensuring that the fluid has microscale effects, orderly flow behavior, and uniform mass and heat transfer, achieving enhanced mixing and precise fluid control in a microscale space; the inner diameter of the spiral structure can be 2-6 cm, and the inner diameter refers to the diameter between the inner walls of the spiral tube.

[0058] In this invention, in order to ensure the stable formation of low-zinc magnetite, the length of the reaction microchannel can be 2-12m, preferably 5-10m.

[0059] In this invention, in order to achieve temperature control of the liquid inlet assembly, the cross joint, and the reaction microchannel, and to further ensure the reaction, the micro-clamp reactor may also include a temperature control device to preheat the liquid inlet assembly and maintain the temperature of the liquid flow in the cross joint and the reaction microchannel; specifically, the temperature control device is a water bath heater, and the liquid inlet assembly, the cross joint, and the reaction microchannel are all placed in the water bath heater to achieve heating operation.

[0060] In this invention, to ensure sufficient preheating, the lengths of the first sample liquid pipeline, the second sample liquid pipeline, and the alkali solution pipeline can all be 2-5m. It should be noted that the lengths of the first sample liquid pipeline, the second sample liquid pipeline, the alkali solution pipeline, and the reaction microchannel all refer to the total length of the spiral structure after it has been unfolded.

[0061] The present invention also provides an application of the micro-entrainment reactor as described above in the acquisition of low-zinc magnetite; wherein the low-zinc magnetite is processed in an iron-zinc mixture.

[0062] The present invention also provides a method for preparing low-zinc magnetite based on an iron-zinc mixture, using a micro-entrainment reactor as described in the present invention.

[0063] The method for preparing low-zinc magnetite includes:

[0064] Take an iron-zinc mixture and an alkaline solution, and divide the iron-zinc mixture into a first part and a second part; the amounts of the first part and the second part of the iron-zinc mixture can be equal.

[0065] The first sample injection unit controls the first portion of the iron-zinc mixture to be injected into the first passage sequentially through the first sample pipeline and the first sample inlet; the second sample injection unit controls the second portion of the iron-zinc mixture to be injected into the first passage sequentially through the second sample pipeline and the second sample inlet; the alkali injection unit controls the alkali solution to be injected into the second passage sequentially through the alkali solution pipeline and the alkali solution inlet.

[0066] The iron-zinc mixture described in Part 1, the iron-zinc mixture described in Part 2, and the alkaline solution are combined in the cross joint to obtain a reaction solution.

[0067] The reaction solution is controlled to enter the reaction microchannel sequentially through the second passage and the outlet, and the resulting suspension is collected at the outlet of the reaction microchannel using a collecting device (e.g., a collecting container). To prevent the suspension from continuing to react in the collecting device, the collecting device can be placed in a temperature environment of approximately 0°C; for example, the collecting container can be placed in a cooling tank containing ice water.

[0068] The suspension was separated into solid and liquid components to obtain low-zinc magnetite.

[0069] In this invention, the iron-zinc mixture can be obtained by mixing ferrous sulfate, ferric sulfate, zinc sulfate, and a sulfuric acid solution with pH=1. The iron-zinc mixture can be derived from zinc leaching solutions, such as hydrometallurgical zinc leaching solutions. In the iron-zinc mixture, the total concentration of ferrous ions and ferric ions is 0.01-0.2 mol / L, and the zinc ion concentration is 0.01-0.2 mol / L. The molar ratio of ferrous ions to ferric ions can be 1:1-5; the molar ratio of iron (the sum of ferrous and ferric ions) to zinc (zinc ions) can be 5-1:1-3. In the alkaline solution of this invention, the concentration of the alkaline substance can be 0.5-9 mol / L; to further reduce the concentration of the alkaline substance, the concentration is 4-8 mol / L, preferably 6.5-7.5 mol / L; the alkaline substance may include sodium hydroxide.

[0070] It should be noted that, before the reaction, nitrogen gas can be bubbled into the iron-zinc mixture and the alkaline solution for 30 minutes to prevent the ferrous iron in the solution from being oxidized.

[0071] To ensure the acquisition of low-zinc magnetite, the flow rate of the first part of the iron-zinc mixture in the first sample solution pipeline can be 1-5 ml / min, the flow rate of the second part of the iron-zinc mixture in the second sample solution pipeline can be 1-5 ml / min, and the flow rate of the alkali solution in the alkali solution pipeline can be 2-10 ml / min; the residence time of the reaction solution in the reaction microchannel can be 12-88 s, preferably 20-38 s. The flow rates of the first part of the iron-zinc mixture in the first sample solution pipeline and the second part of the iron-zinc mixture in the second sample solution pipeline can be the same, and the flow rate of the first part of the iron-zinc mixture in the first sample solution pipeline can be half the flow rate of the alkali solution in the alkali solution pipeline.

[0072] To facilitate the reaction, the cross-shaped connector, the liquid inlet assembly, and the reaction microchannel are all kept in an environment of 50-90°C.

[0073] Specifically, this invention can be understood as follows: two identical iron-zinc mixtures and one alkaline solution are injected into pipelines through an injection unit for a continuous process of preheating, mixing, and reaction; wherein, the two iron-zinc mixtures flow into the cross-shaped micro-interface from the bottom and top respectively, and the alkaline solution flows into the cross-shaped micro-interface from the left, rapidly mixing to form a reaction solution, which flows into the reaction microchannel to continue the reaction, and finally, the suspension of the precipitated iron product flows into a pre-cooled collection device to complete the low-zinc magnetite preparation process by the entrained mixing method.

[0074] This invention utilizes a cross-shaped microjoint design for a mixed-flow process, significantly reducing the zinc doping rate in the magnetite crystal structure of the iron precipitation product, improving the purity of the target product, and effectively solving the problem of multi-metal co-precipitation in traditional iron precipitation techniques. This invention innovates the iron precipitation process in complex leaching solutions of hydrometallurgical zinc refining by leveraging the characteristics of microfluidic technology, contributing to iron slag reduction and recycling from the source. This invention rapidly precipitates iron from hydrometallurgical zinc leaching solutions in the form of magnetite, while reducing zinc doping, avoiding the formation of impurity phases, and ensuring the morphology of the magnetite. Compared to traditional macroscopic mixing systems, this method improves the efficiency and purity of obtaining the target product, while significantly reducing zinc doping during the iron precipitation process.

[0075] This invention not only specifies the mixing joint as a cross joint, but also optimizes the micro-entrapment method and parameters. Specifically, the advantages of micro-entrapment in this invention include: the fluid at the confluence is first squeezed and then diffused, resulting in two contact interfaces, which increases the fluid contact area and enhances the fluid mixing effect.

[0076] It should be noted that the micro-entrapment mixing method provided by this invention features microscale space and microfluidic effects, both of which enhance the mixing and mass and heat transfer of the reaction solution, reduce the formation of intermediate products, accelerate the transformation of amorphous intermediates into magnetite, and reduce the chance of iron-containing phases combining with zinc. The ordered fluid flow behavior and uniform mass and heat transfer in the microscale space ensure the uniformity of magnetite morphology and size. Furthermore, a 9M alkali concentration significantly increases reagent dosage, cost, and equipment operation difficulty. Therefore, this invention optimizes and controls parameters while reducing the alkali concentration to ensure stable equipment operation and the quality of low-zinc magnetite.

[0077] The following are specific examples of the present invention:

[0078] Comparative Example 1: Iron-alkali mixture 7.5m-3M (35s-3M)

[0079] This comparative example was implemented in a microchannel, and the methods used in this comparative example for controlling the formation of low-zinc magnetite include:

[0080] Ferrous sulfate, ferric sulfate, zinc sulfate, and a sulfuric acid solution with pH=1 were mixed to obtain an iron-zinc mixture. Sodium hydroxide was mixed with water to obtain an alkaline solution. Both reaction solutions were continuously purged with nitrogen for 30 minutes to prevent the oxidation of ferrous sulfate.

[0081] Two syringes were used to draw 25 mL of the iron-zinc mixture into each of two syringes and place them into a dual-channel syringe pump. Then, a syringe was used to draw 50 mL of the alkali solution and place it into a single-channel syringe pump. The iron-zinc mixture contained 0.0167 mol / L of ferrous ions, 0.0334 mol / L of ferric ions, and 0.05 mol / L of zinc ions. The alkali solution (sodium hydroxide solution) had a concentration of 3 mol / L, and the reaction microchannel length was 7.5 m.

[0082] The inner diameter of the first sample liquid pipeline, the second sample liquid pipeline, the alkali solution pipeline, and the reaction microchannel is 1.0 mm, and the outer diameter is 1.6 mm. The length of the first sample liquid pipeline, the second sample liquid pipeline, and the alkali solution pipeline is 2.5 m. The first sample liquid pipeline, the second sample liquid pipeline, the alkali solution pipeline, and the reaction microchannel are all spiral structures with an inner diameter of 4 cm. The mixing connector is a cross-shaped four-way connector with an aperture of 0.51 mm. Two equal portions of iron-zinc mixture enter from the upper and lower ports of the cross-shaped four-way connector, respectively, and the alkali solution enters from the left port of the cross-shaped four-way connector.

[0083] Two equal portions of an iron-zinc mixture were injected at a flow rate of 2.5 ml / min into the first and second sample lines, respectively, using a dual-channel syringe pump. The mixture then entered a cross-shaped four-way connector (inlet from both the top and bottom). A single-channel syringe pump was used to inject an alkali solution at a flow rate of 5 ml / min into the alkali solution line, which then entered a cross-shaped four-way connector (inlet from the left side). The resulting reaction solution (exiting from the right side of the connector) after mixing the iron-zinc mixture and the alkali solution at the cross-shaped four-way connector continued to react in a 7.5 m reaction microchannel. The residence time of the reaction solution in the microchannel was 35 s. All components—the first sample line, the second sample line, the alkali solution line, the cross-shaped four-way connector, and the reaction microchannel—were placed in a 60°C water bath.

[0084] A collection device is set at the outlet of the reaction microchannel. The collection device is equipped with a cooling component to achieve a temperature of about 0°C. The collection container is placed in the pre-cooled collection device to collect the suspension of precipitated iron product. After the reaction is completed, the solid and liquid are separated. The solid phase is freeze-dried under vacuum to obtain the precipitated iron product. X-ray diffraction and transmission electron microscopy analysis are performed on it, and the zinc doping rate and iron content are determined and calculated.

[0085] The determination and calculation process of zinc doping rate and iron content is as follows: Weigh 0.02g of the precipitated iron product, dissolve it in concentrated hydrochloric acid, make up to 50mL in a colorimetric tube, dilute and then determine by ICP-OES; the calculated ratio of zinc mass concentration in the precipitated iron product is the zinc doping rate, and the ratio of iron mass concentration in the precipitated iron product is the iron content.

[0086] like Figure 3 As shown, the X-ray spectrum of the iron-laden product (iron-alkali 7.5m-3M) in this comparative example has characteristic peaks at 2θ of 29.64°, 35.39°, 42.85°, 56.85°, and 62.30°, which correspond to the (220), (311), (400), (511), and (440) crystal planes, respectively. This is consistent with the PDF card (PDF#19-0629) of magnetite, indicating that the main phase of the iron-laden product is magnetite and the crystal form is good.

[0087] like Figure 4 As shown, in this comparative example, the zinc doping rate in magnetite is 15.34%. Compared with Comparative Examples 3 and 7, the zinc doping rate is reduced, indicating that the iron-alkali sandwich mixing method helps to reduce zinc doping, and the zinc doping rate is reduced by 30.74% compared with the traditional method.

[0088] like Figure 5 As shown, the iron content in magnetite in this comparative example is 45.09%. Compared with comparative examples 3 and 7, the iron content is increased, indicating that the iron-alkali intercalation mixing mode is conducive to the formation of magnetite.

[0089] like Figure 9As shown, the Fourier transform infrared spectrum of the iron precipitation product (iron-alkali 7.5m-3M) in this comparative example is at a wavenumber of 537cm⁻¹. -1 The characteristic peak of magnetite was identified at 1638 cm⁻¹. -1 The OH tensile vibration is attributed to tetragonal fibrous ore. Wavenumber is around 1050 cm⁻¹. -1 The nearby absorption peaks correspond to the OH stretching vibration of fibrous ferrite, and the signal of the characteristic peaks is weaker compared to Comparative Example 3. The wavenumbers are in the range of 1780-950 cm⁻¹. -1 The range contains characteristic peaks of the impurity iron phase.

[0090] Example 1: Iron-alkali mixture 7.5m-7M (35s-7M)

[0091] Compared to Comparative Example 1, this embodiment only adjusts the concentration of the alkali solution to 7 mol / L, while keeping other conditions unchanged.

[0092] like Figure 3 As shown, the X-ray spectrum of the iron-laden product (iron-alkali 7.5m-7M) in this embodiment has characteristic peaks at 2θ of 29.64°, 35.39°, 42.85°, 56.85°, and 62.30°, which correspond to the (220), (311), (400), (511), and (440) crystal planes, respectively. This is consistent with the PDF card (PDF#19-0629) of magnetite, indicating that the main phase of the iron-laden product is magnetite and the crystal form is good.

[0093] like Figure 4 As shown, in this embodiment, the zinc doping rate in magnetite is 3.36%. Compared with Comparative Examples 4 and 8, the zinc doping rate is reduced, indicating that the micro-junction mixing method of iron-alkali mixture helps to reduce zinc doping, and the zinc doping rate is reduced by 54.0% compared with the conventional method.

[0094] like Figure 5 As shown, in this embodiment, the iron content in the magnetite is 54.39%. Compared with Comparative Examples 4 and 8, the iron content is increased, indicating that the iron-alkali intercalation mixing mode is conducive to the formation of magnetite.

[0095] like Figure 8 As shown in the upper left portion (7.5m-7M iron-alkali intercalation), in this embodiment, the magnetite morphology is uniformly distributed, appearing as uniformly sized flakes. Compared to Comparative Example 10, the particle size is smaller and the uniformity is higher.

[0096] like Figure 9 As shown, the Fourier transform infrared spectrum of the iron precipitation product (iron-alkali 7.5m-7M) in this embodiment is at a wavenumber of 537 cm⁻¹. -1 The characteristic peaks of magnetite were identified at the time; wavenumber 1638 cm⁻¹. -1 The value is attributed to the OH tensile vibration of tetragonal fibrous ore. 1340cm-1 The OH tensile vibrations, attributed to ferrohydride, have a wavenumber of 1050 cm⁻¹. -1 The nearby absorption peaks correspond to the OH stretching vibration of fibrous ferrite, and the signal of the characteristic peaks is weaker compared to Comparative Example 4. The wavenumbers are in the range of 1780-950 cm⁻¹. -1 The range contains characteristic peaks of the impurity iron phase.

[0097] Comparative Example 2: Iron-alkali mixture 5m-1M (24s-1M)

[0098] Compared to Example 1, the concentration of the alkali solution in this comparative example was adjusted to 1 mol / L, and the length of the reaction microchannel was adjusted to 5 m. At this time, the residence time of the reaction solution in the reaction microchannel was 24 s, while other conditions remained unchanged.

[0099] like Figure 6 As shown, in this comparative example, the zinc doping rate in magnetite is 24.20%. Compared to Comparative Examples 5 and 9, the zinc doping rate is lower, indicating that the micro-junction mixing mode of iron-alkali mixture helps to reduce zinc doping.

[0100] like Figure 7 As shown, the iron content in magnetite in this comparative example is 36.97%. Compared with comparative examples 5 and 9, the iron content is increased, indicating that the iron-alkali intercalation mixing mode is conducive to the formation of magnetite.

[0101] Example 2: Iron-alkali mixture 5m-7M (24s-7M)

[0102] Compared to Comparative Example 2, this embodiment only adjusts the concentration of the alkali solution to 7 mol / L, while keeping other conditions unchanged.

[0103] like Figure 6 As shown, in this embodiment, the zinc doping rate in magnetite is 2.84%. Compared to Comparative Example 10, the zinc doping rate is reduced by 60.0% compared to the conventional method, indicating that the micro-junction mixing method of iron-alkali mixture helps to reduce zinc doping.

[0104] like Figure 7 As shown, in this embodiment, the iron content in the magnetite is 54.35%. Compared with Comparative Examples 6 and 10, the iron content is increased, indicating that the iron-alkali intercalation mixing mode is conducive to the formation of magnetite.

[0105] like Figure 8 As shown in the upper right part (5m-7m of iron-alkali inclusions), in this embodiment, the magnetite morphology is uniformly distributed, consisting of uniformly sized flakes. Compared to Comparative Example 10, the particle size is smaller and the uniformity is higher.

[0106] like Figure 10 As shown, the Fourier transform infrared spectrum of the iron precipitation product (iron-alkali 5m-7M) in this embodiment is at a wavenumber of 537 cm⁻¹. -1The characteristic peak of magnetite was identified at 1638 cm⁻¹. -1 OH tensile vibrations belonging to tetragonal lepidocrocite. 1340cm -1 The OH tensile vibrations, attributed to ferrohydride, have a wavenumber of 1050 cm⁻¹. -1 The nearby absorption peaks correspond to the OH stretching vibration of fibrous ferrite, and the characteristic peak signals of the impurity iron phase are significantly weakened compared to Comparative Example 6. The wavenumbers are in the range of 1780-950 cm⁻¹. -1 The range contains characteristic peaks of the impurity iron phase.

[0107] Comparative Example 3: Alkali with Iron 7.5m-3M (35s-3M)

[0108] Ferrous sulfate, ferric sulfate, zinc sulfate, and a sulfuric acid solution with pH=1 were mixed to obtain an iron-zinc mixture. Sodium hydroxide was mixed with water to obtain an alkaline solution. Both reaction solutions were continuously purged with nitrogen for 30 minutes to prevent the oxidation of ferrous sulfate.

[0109] Two syringes were used to draw 25 mL of alkaline solution into each of two syringes and place them into a dual-channel syringe pump. Then, a syringe was used to draw 50 mL of an iron-zinc mixture and place it into a single-channel syringe pump. The iron-zinc mixture contained 0.0167 mol / L ferrous ions, 0.0334 mol / L ferric ions, and 0.05 mol / L zinc ions. The alkaline solution (sodium hydroxide solution) had a concentration of 3 mol / L, and the reaction microchannel length was 7.5 m.

[0110] The inner diameter of the first alkali solution pipeline, the second alkali solution pipeline, the sample solution pipeline, and the reaction microchannel is 1.0 mm, and the outer diameter is 1.6 mm. The length of the first alkali solution pipeline, the second alkali solution pipeline, and the sample solution pipeline is 2.5 m. The first alkali solution pipeline, the second alkali solution pipeline, the sample solution pipeline, and the reaction microchannel are all spiral structures with an inner diameter of 4 cm. The mixing connector is a cross-shaped four-way connector with an aperture of 0.51 mm. The alkali solution enters from the upper and lower ports of the cross-shaped four-way connector, and the iron-zinc mixture enters from the left port of the cross-shaped four-way connector.

[0111] Two equal portions of alkaline solution were injected into the first and second alkaline solution lines at a flow rate of 2.5 ml / min using a dual-channel syringe pump, and then into a cross-shaped four-way connector (inlet from both the top and bottom). An iron-zinc mixture was injected into the sample solution line at a flow rate of 5 ml / min using a single-channel syringe pump, and then into a cross-shaped four-way connector (inlet from the left side). The reaction solution obtained after the iron-zinc mixture and alkaline solution were mixed at the cross-shaped four-way connector (exiting from the right side of the connector) continued to react in a 7.5 m reaction microchannel, with a residence time of 35 s. The first alkaline solution line, the second alkaline solution line, the sample solution line, the cross-shaped four-way connector, and the reaction microchannel were all placed in a 60°C water bath.

[0112] A collection device is set at the outlet of the reaction microchannel. The collection device is equipped with a cooling component to achieve a temperature of about 0°C. The collection container is placed in the pre-cooled collection device to collect the suspension of precipitated iron product. After the reaction is completed, the solid and liquid are separated. The solid phase is freeze-dried under vacuum to obtain the precipitated iron product. X-ray diffraction and transmission electron microscopy analysis are performed on it, and the zinc doping rate and iron content are determined and calculated.

[0113] The determination and calculation process of zinc doping rate and iron content is as follows: Weigh 0.02g of the precipitated iron product, dissolve it in concentrated hydrochloric acid, make up to 50mL in a colorimetric tube, dilute and then determine by ICP-OES; the calculated ratio of zinc mass concentration in the precipitated iron product is the zinc doping rate, and the ratio of iron mass concentration in the precipitated iron product is the iron content.

[0114] like Figure 3 As shown, the X-ray spectrum of the iron-laden product (alkali-containing iron 7.5m-3M) in this comparative example has characteristic peaks at 2θ of 29.64°, 35.39°, 42.85°, 56.85°, and 62.30°, which correspond to the (220), (311), (400), (511), and (440) crystal planes, respectively. This is consistent with the PDF card (PDF#19-0629) of magnetite, indicating that the iron-laden product is magnetite with a good crystal form.

[0115] like Figure 4 As shown, in this comparative example, the zinc doping rate in magnetite is 17.72%.

[0116] like Figure 5 As shown, in this comparative example, the iron content in magnetite is 42.41%.

[0117] like Figure 9 As shown, the Fourier transform infrared spectrum of the iron precipitation product (alkali-containing iron 7.5m-3M) in this comparative example is at a wavenumber of 537cm⁻¹. -1 The characteristic peak of magnetite was identified at 1638 cm⁻¹. -1 OH tensile vibrations belonging to tetragonal lepidocrocite. 1340cm -1 The OH tensile vibrations, attributed to ferrohydride, have a wavenumber of 1099 cm⁻¹. -1 The nearby absorption peaks correspond to the OH stretching vibration of fibrous ore. Wavenumbers are in the range of 1780-950 cm⁻¹. -1 The range contains characteristic peaks of the impurity iron phase.

[0118] Comparative Example 4: Alkali-Iron Intercalation 7.5m-7M (35s-7M)

[0119] Compared to Comparative Example 3, this comparative example only changed the concentration of the alkali solution to 7 mol / L, while keeping all other conditions unchanged.

[0120] like Figure 3As shown, the X-ray spectrum of the iron-laden product (alkali-containing iron 7.5m-7M) in this comparative example has characteristic peaks at 2θ of 29.64°, 35.39°, 42.85°, 56.85°, and 62.30°, which correspond to the (220), (311), (400), (511), and (440) crystal planes, respectively. This is consistent with the PDF card (PDF#19-0629) of magnetite, indicating that the iron-laden product is magnetite with a good crystal form.

[0121] like Figure 4 As shown, in this comparative example, the zinc doping rate in magnetite is 3.73%.

[0122] like Figure 5 As shown, in this comparative example, the iron content in magnetite is 52.47%.

[0123] like Figure 9 As shown, the Fourier transform infrared spectrum of the iron precipitation product (alkali-impregnated iron 7.5m-7M) in this comparative example is at a wavenumber of 537 cm⁻¹. -1 The characteristic peak of magnetite was identified at 1638 cm⁻¹. -1 OH tensile vibrations belonging to tetragonal lepidocrocite. 1340cm -1 The OH tensile vibrations, attributed to ferrohydride, have a wavenumber of 1099 cm⁻¹. -1 The nearby absorption peaks correspond to the OH stretching vibration of fibrous ore. Wavenumbers are in the range of 1780-950 cm⁻¹. -1 The range contains characteristic peaks of the impurity iron phase.

[0124] Comparative Example 5: Alkali with Iron 5m-1M (24s-1M)

[0125] Compared to Comparative Example 3, the concentration of the alkali solution in this comparative example was adjusted to 1 mol / L, and the length of the reaction microchannel was adjusted to 5 m. At this time, the residence time of the reaction solution in the reaction microchannel was 24 s, while other conditions remained unchanged.

[0126] like Figure 6 As shown, in this comparative example, the zinc doping rate in magnetite is 27.82%.

[0127] like Figure 7 As shown, in this comparative example, the iron content in magnetite is 36.78%.

[0128] Comparative Example 6: Alkali-Iron Intercalation 5m-7M (24s-7M)

[0129] Compared to Comparative Example 5, this comparative example only changed the concentration of the alkali solution to 7 mol / L, while keeping all other conditions unchanged.

[0130] like Figure 6 As shown, in this comparative example, the zinc doping rate in magnetite is 3.65%.

[0131] like Figure 7 As shown, in this comparative example, the iron content in magnetite is 51.20%.

[0132] like Figure 10 As shown, the Fourier transform infrared spectrum of the iron precipitation product (alkali-containing iron 5m-7M) in this comparative example is at a wavenumber of 537 cm⁻¹. -1 The characteristic peak of magnetite was identified at 1638 cm⁻¹. -1 OH tensile vibrations belonging to tetragonal lepidocrocite. 1426 cm -1 The OH tensile vibrations, attributed to ferrohydride, have a wavenumber of 1120 cm⁻¹. -1 The nearby absorption peaks correspond to the OH stretching vibration of fibrous ore. Wavenumbers are in the range of 1780-950 cm⁻¹. -1 The range contains characteristic peaks of the impurity iron phase.

[0133] Comparative Example 7: Macroscopic Mixture 35s-3M

[0134] Ferrous sulfate, ferric sulfate, zinc sulfate, and a sulfuric acid solution with pH=1 were mixed to obtain an iron-zinc mixture. Sodium hydroxide was mixed with water to obtain an alkaline solution. Both reaction solutions were continuously purged with nitrogen for 30 minutes to prevent the oxidation of ferrous sulfate.

[0135] Measure 50 mL of the iron-zinc mixture into a glass bottle using a graduated cylinder, then quickly pour 50 mL of the alkaline solution into the glass bottle. Seal the bottle and stir at 200 rpm in a 60°C water bath for 35 seconds. After the reaction is complete, place the bottle in a pre-cooled container to cool. After cooling, filter the solution and vacuum dry the solid phase to obtain the precipitated iron product. Determine and calculate the zinc doping rate and iron content of the product.

[0136] The iron-zinc mixture contained 0.0167 mol / L of ferrous ions, 0.0334 mol / L of ferric ions, and 0.05 mol / L of zinc ions; the alkaline solution (sodium hydroxide solution) had a concentration of 3 mol / L.

[0137] The determination and calculation process of zinc doping rate is as follows: Weigh 0.02g of precipitated iron product, dissolve it in concentrated hydrochloric acid, make up to 50mL in a colorimetric tube, dilute and then determine by ICP-OES; the calculated ratio of zinc mass concentration in precipitated iron product is the zinc doping rate, and the ratio of iron mass concentration in precipitated iron product is the iron content.

[0138] like Figure 4 As shown, in this comparative example, the zinc doping rate in magnetite is 22.15%.

[0139] like Figure 5 As shown, in this comparative example, the iron content in magnetite is 40.86%.

[0140] Comparative Example 8: Macroscopic Mixture 35s-7M

[0141] Compared to Comparative Example 7, this comparative example only changed the concentration of the alkali solution to 7 mol / L, while keeping all other conditions unchanged.

[0142] like Figure 4 As shown, in this comparative example, the zinc doping rate in magnetite is 7.30%.

[0143] like Figure 5 As shown, in this comparative example, the iron content in magnetite is 50.74%.

[0144] Comparative Example 9: Macroscopic Mixture 24s-1M

[0145] Compared to Comparative Example 8, the concentration of the alkali solution in this comparative example was adjusted to 1 mol / L, and the reaction (stirring) time was shortened to 24 s, while other conditions remained unchanged.

[0146] like Figure 6 As shown, in this comparative example, the zinc doping rate in magnetite is 32.44%.

[0147] like Figure 7 As shown, in this comparative example, the iron content in magnetite is 30.23%.

[0148] Comparative Example 10: Macroscopic Mixture 24s-7M

[0149] Compared to Comparative Example 9, this comparative example only changed the concentration of the alkali solution to 7 mol / L, while keeping all other conditions unchanged.

[0150] like Figure 6 As shown, in this comparative example, the zinc doping rate in magnetite is 7.09%.

[0151] like Figure 7 As shown, in this comparative example, the iron content in magnetite is 49.61%.

[0152] like Figure 8 As shown in the lower part (macro-mixed 24s-7M), in this comparative example, the magnetite morphology is uneven and irregular, with various shapes such as octahedral, short columnar, and platy stacked together.

[0153] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing low-zinc magnetite based on an iron-zinc mixture, characterized in that, Low-zinc magnetite was prepared using a micro-entrapment reactor; the micro-entrapment reactor included a cross-shaped connector, a liquid inlet assembly, and a reaction microchannel. The cross-shaped connector has a first sample inlet, a second sample inlet, an alkali inlet, and an outlet; the first sample inlet and the second sample inlet are arranged opposite to each other and are interconnected along a first passage; the alkali inlet and the outlet are arranged opposite to each other and are interconnected along a second passage; the first passage and the second passage intersect and are perpendicular to each other, and are interconnected at the intersection; The liquid inlet assembly includes a first sample liquid pipeline, a second sample liquid pipeline, and an alkali liquid pipeline; the outlet end of the first sample liquid pipeline is connected to the first sample liquid inlet, the outlet end of the second sample liquid pipeline is connected to the second sample liquid inlet, and the outlet end of the alkali liquid pipeline is connected to the alkali liquid inlet. The inlet and outlet of the reaction microchannel are connected. The method for preparing low-zinc magnetite based on an iron-zinc mixture includes: Take an iron-zinc mixture and an alkaline solution, and divide the iron-zinc mixture into a first part and a second part; The iron-zinc mixture in the first part is controlled to be injected into the first passage sequentially through the first sample solution pipeline and the first sample solution inlet; the iron-zinc mixture in the second part is controlled to be injected into the first passage sequentially through the second sample solution pipeline and the second sample solution inlet; the alkali solution is controlled to be injected into the second passage sequentially through the alkali solution pipeline and the alkali solution inlet; The iron-zinc mixture described in Part 1, the iron-zinc mixture described in Part 2, and the alkaline solution are combined in the cross joint to obtain a reaction solution; The reaction solution is controlled to enter the reaction microchannel through the outlet, and the suspension generated by the reaction is collected at the outlet of the reaction microchannel; The suspension was separated into solid and liquid components to obtain low-zinc magnetite.

2. The method for preparing low-zinc magnetite based on an iron-zinc mixture according to claim 1, characterized in that, The micro-clamp reactor also includes a first sample injection unit, a second sample injection unit, and an alkali injection unit. The first sample injection unit is connected to the inlet end of the first sample pipeline, the second sample injection unit is connected to the inlet end of the second sample pipeline, and the alkali injection unit is connected to the inlet end of the alkali pipeline.

3. The method for preparing low-zinc magnetite based on an iron-zinc mixture according to claim 1, characterized in that, Both the first path and the second path are straight paths; the middle of the first path and the middle of the second path intersect.

4. The method for preparing low-zinc magnetite based on an iron-zinc mixture according to any one of claims 1-3, characterized in that, The inner diameters of the first sample solution pipeline, the second sample solution pipeline, the alkali solution pipeline, and the reaction microchannel are all 0.8-1.2 mm; the length of the reaction microchannel is 2-12 m.

5. The method for preparing low-zinc magnetite based on an iron-zinc mixture according to claim 1, characterized in that, In the iron-zinc mixture, the total concentration of ferrous and ferric ions is 0.01-0.2 mol / L, and the concentration of zinc ions is 0.01-0.2 mol / L; the molar ratio of iron to zinc is 5-1:1-3.

6. The method for preparing low-zinc magnetite based on an iron-zinc mixture according to claim 1, characterized in that, The concentration of alkaline substances in the alkaline solution is 4-8 mol / L.

7. The method for preparing low-zinc magnetite based on an iron-zinc mixture according to claim 1, characterized in that, The flow rate of the iron-zinc mixture in the first sample solution pipeline is 1-5 ml / min, the flow rate of the iron-zinc mixture in the second sample solution pipeline is 1-5 ml / min, the flow rate of the alkali solution in the alkali solution pipeline is 2-10 ml / min, and the residence time of the reaction solution in the reaction microchannel is 12-88 s.

8. The method for preparing low-zinc magnetite based on an iron-zinc mixture according to claim 1, characterized in that, The cross-shaped connector, the liquid inlet assembly, and the reaction microchannel are all located in an environment of 50-90°C.

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