A method for synthesizing nanometer ferroferric oxide based on cyanide tailings derived ammonium ferric oxalate and ferrous oxalate

Abstract

This invention belongs to the interdisciplinary field of industrial solid waste resource utilization and inorganic functional material synthesis. It discloses a method for synthesizing nano-ferric oxide (Fe3O4) based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings. The method includes: preparing ferric ammonium oxalate and ferrous oxalate using cyanide tailings leachate; dissolving ferric ammonium oxalate in water to obtain an aqueous solution of ferric ammonium oxalate; adding ferrous oxalate to the aqueous solution of ferric ammonium oxalate to obtain a mixed raw material solution; adjusting the pH of the mixed raw material solution with commercially available ammonia water under continuous stirring, reacting and statically aging; filtering after the static aging process to obtain nano-ferric oxide and a filtrate containing ammonium oxalate; evaporating, concentrating, and crystallizing the filtrate containing ammonium oxalate, and then separating the liquid and solid to obtain crystalline ammonium oxalate and a crystallization mother liquor. This invention completely eliminates inorganic salt pollution, achieves a closed-loop cycle of the oxalic acid system, and efficiently prepares high-purity, controllable-size nano-ferric oxide.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of industrial solid waste resource utilization and inorganic functional material synthesis, and specifically relates to a method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings. Background Technology

[0002] Nano-iron oxide (Fe3O4) is a typical mixed-valence iron oxide, in which Fe... 2+ with Fe 3 + Strictly adhering to a 1:2 stoichiometric ratio, nano-ferric oxide possesses excellent magnetic response, chemical stability, and biocompatibility, making it valuable for applications in metallurgical catalysis, magnetic material preparation, advanced wastewater treatment, and biopharmaceutical carriers. The development of green and low-cost preparation technologies has been a research hotspot in both industry and academia. Currently reported methods for preparing nano-ferric oxide include co-precipitation, microemulsion, sol-gel, solvothermal, and high-temperature pyrolysis. Among these, co-precipitation has become the mainstream technology in industrial production due to its simplicity, ease of operation, and suitability for large-scale production.

[0003] However, the above-mentioned methods for preparing nano-ferric oxide generally suffer from the following problems: firstly, the raw materials are highly dependent on inorganic iron salts, resulting in high costs; secondly, the production process generates high-salt wastewater, leading to high wastewater treatment costs; and thirdly, a large amount of low-value inorganic sodium salts are produced as byproducts, resulting in a narrow resource utilization pathway and creating a dual dilemma of "resource waste and environmental pressure".

[0004] Specifically, the coprecipitation method uses soluble Cl-containing... - Or SO4 2- Inorganic ferrous / ferric salts are used as raw materials to synthesize nano-ferric oxide under alkaline conditions, but the reaction process will produce Fe... 2+ The process is prone to oxidation, generates large amounts of high-salinity wastewater, has high wastewater treatment costs, and the byproducts sodium chloride or sodium sulfate are difficult to utilize. While microemulsions can achieve precise morphology control, they rely on large amounts of organic surfactants and co-surfactants, resulting in high costs and potential secondary pollution. Although the sol-gel method attempts to use inexpensive iron salts instead of expensive metal alkoxides as raw materials, it still requires organic solvents such as propylene oxide, and environmental issues have not been fundamentally resolved. The solvothermal method uses ferric chloride as the iron source and ethylene glycol as both solvent and reducing agent, achieving Fe2+ oxidation in a closed autoclave under high temperature and pressure. 3+The reduction and crystallization of Fe3O4 can produce Fe3O4 with high crystallinity and purity, but it requires high-end equipment and its large-scale application is limited. High-temperature pyrolysis often uses organometallic compounds such as iron acetylacetone, iron pentacarbonyl, iron N-nitrosohydroxyaniline, and iron-oleic acid complexes as precursors. Pyrolysis in high-boiling-point organic media such as fatty acids, oleic acid, and hexadecylamine can yield well-dispersed nanoparticles, but the precursors are expensive, the conditions are harsh, and the products are usually hydrophobic, which limits its application. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings, so as to solve the technical problem that the existing preparation methods of nano-ferric oxide generally suffer from the dual dilemma of resource waste and environmental pressure.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings, comprising: Ferric ammonium oxalate and ferrous oxalate were prepared using cyanide tailings leachate. Ferrous ammonium oxalate is dissolved in water to obtain an aqueous solution of ferric ammonium oxalate; ferrous oxalate is added to the aqueous solution of ferric ammonium oxalate to obtain a mixed raw material solution; Under continuous stirring, commercially available ammonia water was used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the reaction to synthesize Fe3O4. Static aging was then carried out. After the static aging process was completed, the solution was filtered to obtain nano-Fe3O4 and a filtrate containing ammonium oxalate. The filtrate containing ammonium oxalate was evaporated, concentrated, and crystallized, and then separated by liquid-solid separation to obtain crystalline ammonium oxalate and crystallization mother liquor.

[0007] Furthermore, during the process of adding ferrous oxalate to an aqueous solution of ferric ammonium oxalate to obtain a mixed raw material solution, the molar ratio of ferrous oxalate to ferric ammonium oxalate is 1:2.

[0008] Furthermore, the commercially available ammonia solution has a mass fraction of 25%-28%; the pH of the mixed raw material solution is adjusted to 9.0-9.5 using commercially available ammonia solution.

[0009] Furthermore, under continuous stirring, commercially available ammonia water is used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the synthesis of Fe3O4. Static aging is then carried out. After the static aging process is completed, the mixture is filtered to obtain nano-Fe3O4 and ammonium oxalate-containing filtrate. The reaction temperature is 40-70℃ and the reaction time is 30-90min.

[0010] Furthermore, under continuous stirring, commercially available ammonia water is used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the reaction to synthesize Fe3O4. Static aging is then carried out. After the static aging process is completed, the mixture is filtered to obtain nano-Fe3O4 and ammonium oxalate-containing filtrate. The aging temperature is 90-100℃ and the aging time is 30-90 min.

[0011] Furthermore, under continuous stirring, commercially available ammonia water is used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the reaction to synthesize Fe3O4. Static aging is then carried out. After the static aging process is completed, the mixture is filtered to obtain nano-Fe3O4 and ammonium oxalate-containing filtrate. During this process, the stirring rate is 400-800 r / min and the stirring time is 30-90 min.

[0012] Furthermore, during the process of evaporating, concentrating, and crystallizing the filtrate containing ammonium oxalate, and then separating it into liquid and solid forms to obtain crystalline ammonium oxalate and crystallization mother liquor, the volatile ammonia gas generated during the evaporation process enters the process of preparing nano-ferric oxide.

[0013] Furthermore, crystalline ammonium oxalate is used in the iron removal process of cyanide tailings.

[0014] Furthermore, after evaporating, concentrating, and crystallizing the filtrate containing ammonium oxalate, and then performing liquid-solid separation to obtain crystalline ammonium oxalate and crystallization mother liquor, the process also includes: Regenerated oxalic acid is obtained from the crystallization mother liquor; the regenerated oxalic acid is used in the iron removal process of cyanide tailings.

[0015] Furthermore, the process of preparing ferric ammonium oxalate and ferrous oxalate using cyanide tailings leachate is as follows: Ferrous ammonium oxalate was obtained by subjecting the cyanide tailings leachate to a single evaporation, a single concentration, a single cooling crystallization, a redissolution, a second evaporation, a second concentration, and a second cooling crystallization; wherein the cyanide tailings leachate was the leachate produced during the iron removal and gold enrichment process of the cyanide tailings. Ferric ammonium oxalate was dissolved in water, and ammonia was added dropwise under stirring to induce an iron precipitation reaction, thereby reducing the Fe content in the ferric ammonium oxalate. 3+ Complete precipitation was achieved, and ferric hydroxide precipitate was obtained by filtration. An aqueous solution containing oxalic acid was mixed with ferric hydroxide precipitate to prepare a raw material solution containing ferric oxalate complex. Ascorbic acid was added to the raw material solution containing ferric oxalate complex as a reducing agent, and a stirring reduction reaction was carried out. After the reduction reaction was completed, liquid-solid separation, filter residue washing and drying were performed to obtain ferrous oxalate.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for synthesizing nano-ferric oxide (Fe3O4) from cyanide tailings-derived ferric ammonium oxalate and ferrous oxalate. Using ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings leachate as dual iron source raw materials, and precisely controlling the pH value of the mixed raw material solution with commercially available ammonia, this method effectively eliminates inorganic salt pollution, achieves a closed-loop cycle of the iron removal agent oxalic acid and ammonium oxalate system, and efficiently prepares high-purity, controllable-size nano-ferric oxide. This achieves multiple objectives of resource utilization, environmental protection and emission reduction, and high-performance products. Specifically, using ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings leachate as dual iron source raw materials, and precisely controlling the pH of the reaction system with commercially available ammonia, the method achieves the directional phase transformation of Fe(II) and Fe(III). Through the guiding effect of Fe(OH)3 template, nano-ferric oxide is synthesized in situ under mild alkaline conditions without introducing Cl-. - SO4 2- By using anions that readily form byproduct salts, this process avoids the problems of high-salt wastewater generation and the difficulty in resource utilization of low-value inorganic sodium salts produced by existing preparation technologies, thus constructing a clean preparation process without inorganic salt byproducts. Simultaneously, the synthesis of nano-ferric oxide achieves the regeneration of oxalic acid and ammonium oxalate, which can be directly reused in the leaching of cyanide tailings for iron removal, forming a complete closed loop of "cyanide tailings iron removal - intermediate (oxalic acid and ammonium oxalate) preparation - ferric oxide synthesis - iron removal agent regeneration and reuse." This significantly reduces the reagent costs for cyanide tailings iron removal and nano-ferric oxide synthesis, promoting the high-value utilization of cyanide tailings leachate derivatives. Furthermore, by precisely controlling the reaction conditions, high-purity, controllable-particle-size nano-ferric oxide can be prepared, effectively broadening its application areas and laying the foundation for the industrialization and promotion of oxalic acid and ammonium oxalate leaching iron removal technology, fundamentally solving the dilemma of resource waste and environmental pressure. Attached Figure Description

[0017] Figure 1 A flowchart of the method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings provided by the present invention. Figure 2 These are scanning electron microscope images of the nano-ferric oxide prepared in Examples 1-4; Figure 3 The X-ray diffraction patterns of the nano-Fe3O4 prepared in Examples 1-4 are shown. Figure 4 These are scanning electron microscope images of the nano-Fe3O4 prepared in Examples 5-8; Figure 5 The X-ray diffraction patterns of the nano-iron oxide prepared in Examples 5-8 are shown. Figure 6 These are scanning electron microscope images of the nano-ferric oxide prepared in Examples 9-12; Figure 7These are scanning electron microscope images of the nano-Fe3O4 prepared in Examples 13-16; Figure 8 This is a scanning electron microscope image of the nano-ferric oxide prepared in Example 17; Figure 9 The X-ray diffraction pattern of the nano-iron oxide prepared in Example 17; Figure 10 Hysteresis loop diagram of the nano-Fe3O4 prepared in Example 17 Figure 11 This is a scanning electron microscope image of the nano-Fe3O4 prepared in Example 18; Figure 12 The X-ray diffraction pattern of the nano-iron oxide prepared in Example 18; Figure 13 Scanning electron microscope (SEM) image of the nano-ferric oxide prepared in Example 19. Figure 14 The X-ray diffraction pattern of the nano-iron oxide prepared in Example 19 is shown. Detailed Implementation

[0018] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0019] As attached Figure 1 As shown, this invention provides a method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings, comprising the following steps: Step 1: Prepare ferric ammonium oxalate and ferrous oxalate using cyanide tailings leachate. Specifically, after leaching the cyanide tailings with a mixed oxalic acid-ammonium oxalate solution, liquid-solid separation is performed to obtain cyanide tailings leachate and leachate residue. The cyanide tailings leachate is evaporated, concentrated, cooled, and crystallized at room temperature to obtain ferric ammonium oxalate and crystallization mother liquor. The crystallization mother liquor is mixed with the leachate from the next cycle to continue preparing ferric ammonium oxalate. After dissolving ferric ammonium oxalate in water, the iron in it is precipitated with commercially available ammonia water, filtered, and ferric hydroxide precipitate and filtrate containing ammonium oxalate are obtained. Then, the ferric hydroxide precipitate is dissolved in oxalic acid to obtain a feed solution containing ferric oxalate complex. Ascorbic acid is added to the feed solution containing ferric oxalate complex to carry out a reduction reaction. After the reduction reaction, ferrous oxalate is obtained by filtration.

[0020] Step 2: Under stirring, dissolve ferric ammonium oxalate in water to obtain an aqueous solution of ferric ammonium oxalate; add ferrous oxalate to the aqueous solution of ferric ammonium oxalate to obtain a mixed raw material solution; wherein the molar ratio of ferrous oxalate to ferric ammonium oxalate is 1:2.

[0021] Step 3: Under continuous stirring, adjust the pH of the mixed raw material solution with commercially available ammonia water to carry out the phase transformation of Fe(II) and Fe(III) and the synthesis of Fe3O4, followed by static aging. After the static aging process, filter to obtain nano-Fe3O4 and a filtrate containing ammonium oxalate. The stirring rate is 500 r / min, and the stirring time is 30 min. The mass fraction of commercially available ammonia water is 25%-28%. The pH of the mixed raw material solution is adjusted to 9-9.5 with commercially available ammonia water. The reaction temperature is 40-70℃, and the reaction time is 30-90 min. The aging temperature is 90-100℃, and the aging time is 30-90 min.

[0022] Step 4: Evaporate, concentrate, and crystallize the filtrate containing ammonium oxalate, and then separate the liquid and solid to obtain crystalline ammonium oxalate and crystallization mother liquor; wherein, the crystallinity of ammonium oxalate is controlled according to the molar ratio of oxalic acid to ammonium oxalate in the iron removal process of cyanide tailings; the volatile ammonia gas generated during the evaporation process enters the process of preparing nano-ferric oxide in step 3; the crystalline ammonium oxalate is used in the iron removal process of cyanide tailings.

[0023] Step 5: Obtain regenerated oxalic acid using the crystallization mother liquor; the regenerated oxalic acid is used in the iron removal process of the cyanide tailings leaching. Specifically, lime is added to the crystallization mother liquor, and the reaction yields calcium oxalate and an ammonia solution; the ammonia solution and the volatilized ammonia gas enter the process of preparing ferric hydroxide precipitate using ferric ammonium oxalate; calcium oxalate is reacted with sulfuric acid solution to obtain calcium sulfate and oxalic acid; the obtained oxalic acid is used in the iron removal process of the cyanide tailings.

[0024] Preparation principle: In the above embodiments, ferric ammonium oxalate ((NH4)3[Fe(C2O4)3·3H2O]) and ferrous oxalate (FeC2O4·2H2O) derived from cyanide tailings leachate are used as dual iron source raw materials. Ferrous oxalate and ferric ammonium oxalate are converted into [Fe(C2O4)2] respectively at pH=9.0-9.5. 2- Based on the principle of Fe(OH)3 colloids, commercially available ammonia is used to precisely control the pH of the reaction system, achieving a directional phase transformation between Fe(II) and Fe(III). Nano-sized iron(III) oxide is synthesized in situ under mild alkaline conditions through the template-directed effect of Fe(OH)3. Specifically, the surface hydroxyl groups of Fe(OH)3 undergo deprotonation in an alkaline environment of pH 9.0-9.5, resulting in a negatively charged surface for the Fe(OH)3 colloid, while the liquid phase contains [Fe(C2O4)2]. 2- Both are negatively charged, and there is an electrostatic repulsion between them; the process of deprotonation reaction is shown in the following equation (1): (1) In the reaction raw material solution, C2O42- It overcomes this energy barrier by utilizing its strong bidentate chelating ability through an inner-loop ligand exchange mechanism: [Fe(C2O4)2] 2- One of the C2O4 2- Acting as a bridging ligand, its one-terminal carboxyl oxygen atom directly replaces the ≡Fe-O on the Fe(OH)3 surface. - The ligand -OH at the site - Or H2O, forming a stable inner-ring coordination bond (≡Fe(Ⅲ)-OC(O)-), the other end of which is still coordinated with the central Fe(II), and the other end is connected to the ≡Fe-O bond on the Fe(OH)3 surface through the aforementioned inner-ring coordination bond. - Fe in the site 3+ Coordination ultimately forms ≡Fe Ⅲ -O - -C2O4-Fe Ⅱ (C2O4) ternary interface bridging structure; this structure not only realizes the specific chemisorption of Fe(II) at the Fe(III) active site, but more importantly, it provides an atomic-level channel for interfacial electron transfer.

[0025] Under the alkaline conditions, [Fe(C2O4)2] adsorbed on the surface of Fe(OH)3 2- It transfers one electron to the ≡Fe on the surface. Ⅲ -O - The site itself is oxidized to [Fe Ⅲ (C2O4)2] - Surface Fe(III) accepts electrons and is reduced to Fe(II). This divalent iron surface intermediate rapidly reacts with OH-. - Its function is to form ≡Fe (OH)₂ species. The newly formed, atomically mixed Fe(II) / Fe(III) hydroxide species then undergo co-precipitation and dehydration recombination in an alkaline medium, ultimately transforming into magnetic iron(III) oxide with an anti-spinel structure. Therefore, oxalate-mediated specific adsorption and electron transfer are key precursor steps in the directed synthesis of iron(III) oxide under these pH conditions. Additionally, [Fe Ⅲ (C2O4)2] - Unstable, immediately reacts with C2O4 2- Coordination generates [Fe Ⅲ (C2O4)3] 3- [Fe Ⅲ (C2O4)3] 3-In a solution with pH = 9.0-9.5, it is immediately converted into fresh Fe(OH)3 colloid, and a new round of reaction for the synthesis of iron(III) oxide is carried out. Among them, the electron transfer reaction process is shown in equation (2) below, the chemical reaction of Fe(II) / Fe(III) hydroxide species is shown in equation (3) below, and [Fe Ⅲ (C2O4)2] - Converted to [Fe Ⅲ (C2O4)3] 3- The reaction formula (as shown in formula (4) below), [Fe Ⅲ (C2O4)3] 3- The reaction formula for converting to fresh Fe(OH)3 colloid is shown in equation (5) below, and the specific details are as follows: (2) (3) (4) (5) It should be noted that the nucleation process of Fe3O4 crystal nuclei does not rely on long-range diffusion of ions and supersaturation accumulation in solution; it is directly generated in situ on the Fe(OH)3 surface. At the nanoscale, iron atoms in amorphous Fe(OH)3 tend to form FeO6 octahedral coordination with surrounding oxygen / hydroxyl groups. This structure exhibits good lattice matching with the inverse spinel structure of Fe3O4 crystal nuclei, providing an ideal structural template for the in-situ nucleation of Fe3O4 with an inverse spinel structure. This significantly reduces the nucleation energy barrier, enabling the nucleation process to complete rapidly. Furthermore, the initial Fe(OH)3 particles formed under weakly alkaline conditions (pH 9.0-9.5) are amorphous colloidal precipitates. To reduce surface energy, they tend to form approximately spherical aggregates with high specific surface area and abundant surface hydroxyl active sites. Using this Fe(OH)3 as a "reaction template," it can be used for [Fe(C2O4)2] in the liquid phase. 2- It provides numerous heterogeneous nucleation sites, becoming a core carrier for liquid-solid interface reactions; [Fe(C2O4)2] 2- The liquid-solid interface reaction between Fe(OH)3 and Fe(OH)3 begins at the active sites on the surface of the colloidal particles. The iron(III) oxide crystal nuclei generated by electron transfer and dehydration condensation grow in situ along the outline of the original Fe(OH)3 colloidal particles. It can be seen that Fe(OH)3 colloidal particles have the dual role of morphological template and structure guiding agent, and are the core factor in regulating the morphology of the product.

[0026] Furthermore, the newly formed iron(III) oxide crystal nuclei are themselves highly active sites, and their fresh surfaces can further adsorb surrounding [Fe(C2O4)2]. 2-Like Fe(OH)3 particles, it achieves rapid growth of crystal nuclei through the same "coordination adsorption-interfacial electron transfer-dehydration condensation" cycle mechanism, until [Fe(C2O4)2] is formed in the system. 2- The iron-active sites are completely consumed; simultaneously, during ligand replacement, free C2O4 is released. 2- With high concentrations of NH4 in the solution + The reaction produces ammonium oxalate, which quickly leaves the reaction interface and enters the liquid phase, thereby driving the interfacial reaction to continue to the right, ensuring the continuity and efficiency of the entire nucleation-growth process.

[0027] Furthermore, using ammonia to adjust the pH of the reaction system to a weakly alkaline range of 9-9.5 provides an excellent environment for the in-situ nucleation and growth of ferric oxide; this weakly alkaline environment plays a dual crucial regulatory role in the entire reaction system, as detailed below: On the one hand, the system has a high OH content under weakly alkaline conditions. - Concentration promotes the release of Fe(II) after the dissolution of ferrous oxalate and the reaction of free C2O4 in the system. 2- They combine to form a stable [Fe(C2O4)2] 2- Complex ion; [Fe(C2O4)2] 2- The complex ion can effectively shield the active sites of Fe(II), preventing it from hydrolyzing into Fe(OH)2 precipitate under alkaline conditions or being oxidized into Fe(III) by dissolved oxygen. This ensures a quantitative supply of Fe(II) in the liquid phase, providing a stable precursor source for subsequent coordination adsorption and electron transfer steps with the Fe(OH)3 colloidal surface—which is also crucial for maintaining the Fe concentration in the system. 2+ :Fe 3+ The precise stoichiometric ratio of 1:2 is a core prerequisite for ensuring the purity of nano-ferric oxide products.

[0028] On the other hand, weakly alkaline conditions are a key step in the formation of Fe3O4 crystal nuclei; its role is mainly reflected in: (1) providing reaction sites: the alkaline environment promotes the deprotonation of hydroxyl groups on the Fe(OH)3 surface, significantly increasing the number of negatively charged surface active sites (≡Fe-O3). - (1) The quantity creates conditions for subsequent coordination and electron transfer; (2) Promotes crystal nucleus growth: the surface species after deprotonation (≡Fe-O) - It has higher nucleophilicity and reactivity, which can significantly reduce the kinetic energy barrier of dehydration condensation reaction, thereby accelerating the generation and growth of iron oxide crystal nuclei; within this pH range, the surface charge state and reactant morphology reach the best match, making the reaction rate of the entire conversion process the fastest.

[0029] In summary, the pH of the mixed feed solution not only directly determines the chemical form and stability of iron species (Fe(II) / Fe(III)) in the solution, but also affects the occurrence of dehydration condensation nucleation reaction. It is one of the core process parameters for regulating the formation of iron(II) oxide crystal nuclei, product particle size and dispersibility.

[0030] In this invention, ferric ammonium oxalate and ferrous oxalate, derivatives of cyanide tailings leachate, are used as dual iron sources for the synthesis of nano-ferric oxide. This precisely addresses the challenge of high-yield derivatives from cyanide tailings leachate, achieving diversification and high-value utilization of solid waste derivative resources. Commercially available ammonia is used to adjust the pH of the mixed raw material solution, disrupting the structural stability of ferric ammonium oxalate and ferrous oxalate, thus converting their product [Fe(C2O4)2]. 2- Further reaction with Fe(OH)3 produces ferric oxide; secondly, by constructing a closed-loop system of "ferric oxide removal from cyanide tailings - preparation of intermediates (oxalic acid and ammonium oxalate) - synthesis of ferric oxide - regeneration and reuse of iron removal agent", not only can ammonium oxalate be efficiently regenerated, but it can also be extended to the regeneration of oxalic acid, maximizing the reduction of reagent procurement costs in the cyanide tailings iron removal process and improving the overall economic efficiency and sustainability of the process; both ferric ammonium oxalate and ferrous oxalate contain C2O4. 2- This can guarantee Fe 2+ With Fe(C2O4)2 2- It exists in a stable form, preventing oxidation and ensuring the purity of the nano-iron oxide product; at the same time, the preparation process is simple to operate, requires no high-end equipment, and is easy to scale up for industrial production.

[0031] It should be noted that the preparation process does not produce Cl. - SO4 2- The inorganic salt byproducts can be used to regenerate oxalic acid and ammonium oxalate through simple treatment of the filtrate. The production process produces no wastewater, completely solving the byproduct pollution problem of traditional processes. At the same time, it diversifies the byproducts of cyanide tailings and reduces the environmental risk of solid waste accumulation. Replacing traditional inorganic iron salts with ferric ammonium oxalate and ferrous oxalate byproducts of cyanide tailings significantly reduces raw material procurement costs and significantly improves the process profitability of gold smelting enterprises. The preparation process is simple to operate, does not require harsh reaction conditions such as high temperature and high pressure, and can be completed in conventional reactors. The equipment investment cost is low and it is easy to achieve large-scale industrial promotion.

[0032] The following specific embodiments further explain the method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings provided by the present invention: Example 1 This embodiment 1 provides a method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings, including the following steps: Step 1: Prepare ferric ammonium oxalate and ferrous oxalate using the cyanide tailings leachate. Specifically, the steps are as follows: Step 11: Use an oxalic acid-ammonium oxalate mixed solution to leach the cyanide tailings. After leaching, perform liquid-solid separation to obtain cyanide tailings leachate; that is, the cyanide tailings leachate is the leachate produced during the iron removal and gold enrichment process of the cyanide tailings.

[0033] Step 12: The cyanide tailings leachate is subjected to one evaporation, one concentration, one cooling crystallization, redissolution, a second evaporation, a second concentration, and a second cooling crystallization to obtain ferric ammonium oxalate and crystallization mother liquor; wherein, the crystallization mother liquor is mixed with the cyanide tailings leachate of the next cycle to continue the preparation of ferric ammonium oxalate.

[0034] Step 13: Dissolve ferric ammonium oxalate in water, and add ammonia dropwise while stirring to carry out the iron precipitation reaction, so that the Fe in the ferric ammonium oxalate... 3+ After complete precipitation, ferric hydroxide precipitate was obtained by filtration.

[0035] Step 14: Mix the aqueous solution containing oxalic acid with the ferric hydroxide precipitate to prepare a raw material solution containing ferric oxalate complex; wherein the molar ratio of oxalic acid to ferric hydroxide is 2:1; add ascorbic acid as a reducing agent to the raw material solution containing ferric oxalate complex, and carry out a stirring reduction reaction. After the reduction reaction is completed, perform liquid-solid separation, filter residue washing, and drying to obtain ferrous oxalate and the reduced solution; wherein the molar ratio of ascorbic acid to ferric hydroxide is 1.5:1.

[0036] Step 2: Under stirring, dissolve ferric ammonium oxalate in water to obtain an aqueous solution of ferric ammonium oxalate; add ferrous oxalate to the aqueous solution of ferric ammonium oxalate to obtain a mixed raw material liquid system; wherein, the molar ratio of ferrous oxalate to ferric ammonium oxalate is 1:2, the concentration of ferric ammonium oxalate is 17.20 g / L, and the concentration of ferrous oxalate is 3.60 g / L.

[0037] Step 3: Under continuous stirring, the pH of the mixed raw material solution is adjusted using commercially available ammonia water to carry out the phase transformation of Fe(II) and Fe(III) and the synthesis of Fe3O4, followed by static aging. After the static aging process is completed, the mixture is filtered to obtain nano-Fe3O4 and a filtrate containing ammonium oxalate. The stirring rate is 500 r / min, the stirring time is 30 min, the mass fraction of commercially available ammonia water is 25%-28%, the pH of the mixed raw material solution is adjusted to 9 using ammonia water, the reaction temperature is 40℃, the aging temperature is 90℃, the aging time is 90 min, and the sum of the stirring time and aging time is 120 min.

[0038] Step 4: Evaporate, concentrate, and crystallize the filtrate containing ammonium oxalate, and then separate the liquid and solid to obtain crystalline ammonium oxalate and crystallization mother liquor; wherein, the crystallinity of ammonium oxalate is controlled according to the molar ratio of oxalic acid to ammonium oxalate in the iron removal process of cyanide tailings; the volatile ammonia gas generated during the evaporation process enters the process of preparing nano-ferric oxide in step 3; the crystalline ammonium oxalate is used in the iron removal process of cyanide tailings.

[0039] Step 5: Obtain regenerated oxalic acid using the crystallization mother liquor; the regenerated oxalic acid is used in the iron removal process of the cyanide tailings leaching. Specifically, lime is added to the crystallization mother liquor, and the reaction yields calcium oxalate and an ammonia solution; the ammonia solution and the volatilized ammonia gas enter the process of preparing ferric hydroxide precipitate using ferric ammonium oxalate in step 13; calcium oxalate is reacted with sulfuric acid solution to obtain calcium sulfate and oxalic acid; the obtained oxalic acid is used in the iron removal process of the cyanide tailings.

[0040] Example 2 This embodiment 2 is basically the same as embodiment 1 above, except that: In step 3, the reaction temperature is 50℃.

[0041] The other steps are the same as in Example 1, and will not be repeated here.

[0042] Example 3 This embodiment 3 is basically the same as embodiment 1 above, except that: In step 3, the reaction temperature is 60℃.

[0043] The other steps are the same as in Example 1, and will not be repeated here.

[0044] Example 4 This embodiment 4 is basically the same as embodiment 1 above, except that: In step 3, the reaction temperature is 70℃.

[0045] The other steps are the same as in Example 1, and will not be repeated here.

[0046] As attached Figure 2 As shown, attached Figure 2 The image shows scanning electron microscope (SEM) images of the nano-Fe3O4 prepared in Examples 1-4; in the appendix... Figure 2 In the figure, (a) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 1, (b) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 2, (c) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 3, and (d) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 4.

[0047] From the appendix Figure 2As can be seen, the reaction temperature has a significant impact on the particle size, morphology, and crystallinity of nano-Fe3O4. Specifically, with increasing reaction temperature, the particle size of nano-Fe3O4 generally increases, and the degree of agglomeration gradually intensifies. This is mainly because the reaction temperature simultaneously affects the particle size, morphology, and surface activity of the precursor Fe(OH)3, and also regulates the [Fe(C2O4)2] content. 2- The diffusion behavior to the Fe(OH)3 surface also affects the rate of coordination dissociation and electron transfer in the system. The synergistic effect of the above factors determines the final microstructure and crystallinity of the nano-Fe3O4 product.

[0048] Specifically, at a reaction temperature of 40℃, Fe(OH)3 has low solubility and high supersaturation, readily and rapidly forming a large number of fine-sized initial Fe(OH)3 colloidal particles. The surface of these initial Fe(OH)3 colloidal particles contains numerous highly active sites, which can be [Fe(C2O4)2]. 2- The directed adsorption provides ample reaction sites; however, the lower reaction temperature also significantly reduces the [Fe(C2O4)2] content. 2- The diffusion rate to the surface of Fe(OH)3 colloidal particles is slowed down, and ligand exchange and electron transfer at the interface are inhibited. The combined effect of these factors leads to a slower rate of nucleation site formation in Fe3O4, suppressing the kinetics of crystal growth. Ostwald ripening and oriented crystal growth are difficult to occur effectively, ultimately resulting in Fe3O4 particles with small size and low crystallinity. As the reaction temperature rises to 50℃, the particle size of Fe(OH)3 colloidal particles moderately increases, [Fe(C2O4)2] 2- The diffusion rate to its surface also increases accordingly, and the rates of ligand exchange and electron transfer also accelerate simultaneously, thereby promoting the increase in the reaction synthesis rate of Fe3O4. At the same reaction ripening time, Fe3O4 particles with uniform particle size distribution and relatively large size can be prepared at this temperature. When the reaction temperature continues to rise, the particle size of Fe(OH)3 colloidal particles further increases, [Fe(C2O4)2] 2- The diffusion rate to its surface and the reaction rates of coordination substitution and electron transfer in the system are further accelerated, and the synthesis reaction rate of Fe3O4 is also increased accordingly; among them, the higher the reaction temperature, the faster the product growth rate, and the particle size of the final Fe3O4 particles shows a continuous increasing trend.

[0049] As attached Figure 3 As shown, attached Figure 3 The X-ray diffraction patterns of the nano-ferric oxide prepared in Examples 1-4 are given in the appendix; Figure 3As can be seen, the products prepared at all temperatures were high-purity nano-Fe3O4 phase, and no characteristic diffraction peaks of impurity phases such as ferric oxide were detected, indicating that this reaction system can achieve the synthesis of pure nano-Fe3O4 phase. The successful preparation of pure phase nano-Fe3O4 phase is mainly related to the following two factors: firstly, the reaction process Fe 2+ Take [Fe(C2O4)2] 2- The system contains coordinated forms and free C2O4. 2- It can effectively inhibit Fe 2+ Oxidation, ensuring Fe in the reaction system 2+ with Fe 3+ The stability of the molar ratio; secondly, strict control of Fe during the experiment. 2+ with Fe 3+ The molar ratio is 1:2, which perfectly matches the stoichiometric ratio of Fe3O4 (FeO·Fe2O3), and is [Fe(C2O4)2]. 2- The quantitative reaction with Fe(OH)3 laid the foundation; further comparison of XRD characteristic diffraction peaks at different temperatures showed that the sharpness of the characteristic diffraction peaks of nano-Fe3O4 synthesized at 50℃ was better than that at other temperatures, indicating that the product at this temperature had higher crystallinity and a more complete crystal structure; therefore, combined with the attached... Figure 2 With appendix Figure 3 The characterization results show that the nano-iron oxide prepared at a reaction temperature of 50℃ has the excellent characteristics of uniform particle size, high crystallinity, and pure phase without impurities.

[0050] Example 5 This embodiment 5 is basically the same as embodiment 2 above, except that: In step 3, the stirring time is 30 minutes.

[0051] The other steps are the same as in Example 2, and will not be repeated here.

[0052] Example 6 This embodiment 6 is basically the same as embodiment 2 above, except that: In step 3, the stirring time is 45 minutes.

[0053] The other steps are the same as in Example 2, and will not be repeated here.

[0054] Example 7 This embodiment 7 is basically the same as embodiment 2 above, except that: In step 3, the stirring time is 75 minutes.

[0055] The other steps are the same as in Example 2, and will not be repeated here.

[0056] Example 8 This embodiment 8 is basically the same as embodiment 2 above, except that: In step 3, the stirring time is 90 minutes.

[0057] The other steps are the same as in Example 2, and will not be repeated here.

[0058] As attached Figure 4 As shown, attached Figure 4 The image shows scanning electron microscope (SEM) images of the nano-ferric oxide prepared in Examples 5-8; in the appendix... Figure 4 In the figures, (a) is a scanning electron microscope (SEM) image of the nano-ferric oxide prepared in Example 5, (b) is a scanning electron microscope (SEM) image of the nano-ferric oxide prepared in Example 6, (c) is a scanning electron microscope (SEM) image of the nano-ferric oxide prepared in Example 7, and (d) is a scanning electron microscope (SEM) image of the nano-ferric oxide prepared in Example 8. (See attached figures.) Figure 5 As shown, attached Figure 5 The X-ray diffraction patterns of the nano-iron oxide prepared in Examples 5-8 are given in the paper.

[0059] From the appendix Figure 4-5 As can be seen, with the extension of stirring time, the average particle size of the nano-Fe3O4 product shows a significant increasing trend, the particle agglomeration phenomenon becomes more prominent, and the dispersibility gradually deteriorates. Simultaneously, the XRD characteristic diffraction peaks of the product continue to broaden, indicating a decreasing trend in the crystallinity of Fe3O4. These changes indirectly affect the maturation and growth process of the Fe3O4 crystal nuclei by controlling the characteristics of the Fe(OH)3 colloidal template and the mass transfer efficiency of the system through stirring time. In this system, the crystal nucleation process of nano-Fe3O4 strictly relies on fresh Fe(OH)3 colloid as the reaction template, [Fe(C2O4)2]. 2- ≡Fe³ on the surface of Fe(OH)3 colloid + -O - Active site formation ≡Fe Ⅲ -O - -C2O4-Fe Ⅱ (C2O4) ternary bridged structure, then through C2O4 2- Mediated intramolecular superexchange electron transfer and interfacial Fe Ⅱ (OH)2 / Fe Ⅲ In-situ dehydration nucleation at the (OH)3 site is completed; due to the advantages of molecular-level interfacial contact and the low energy barrier of electron transfer, the nucleus generation process can be completed in a very short time. Therefore, the stirring time mentioned above does not dominate the generation of iron oxide nuclei. Its core regulatory role is concentrated in the grain growth and Ostwald ripening process after nucleus generation.

[0060] From the appendix Figure 4It can also be seen that extending the stirring time can significantly increase the collision frequency between Fe(OH) colloidal particles and primary iron oxide nuclei, while enhancing the liquid phase mass transfer efficiency, promoting the dissolution of thermodynamically unstable, high surface energy, and highly soluble fine primary iron oxide nuclei in the system; the dissolved iron species rapidly diffuse to the surface of large iron oxide particles with low surface energy and more stable thermodynamics through liquid phase mass transfer and redeposit, that is, the typical Ostwald ripening effect occurs, which is the direct reason for the increase in the average particle size of the product with the extension of stirring time.

[0061] Furthermore, the total stirring time and aging time were controlled at 120 min. Extending the stirring time inevitably leads to a shorter static aging time, while the liquid-phase mass transfer efficiency under dynamic stirring is much higher than that of the static aging process. This can accelerate the diffusion and redeposition of dissolved species, further promoting the full maturation process. Ultimately, the longer the stirring time, the larger the product particle size and the more obvious the tendency to agglomerate. Secondly, the nano-iron oxide crystal nuclei themselves have high surface energy. There is electrostatic repulsion between particles in the system to maintain dispersion, but continuous and long-term mechanical... The shear force generated by stirring can force particles to overcome the electrostatic repulsion barrier, triggering shear-induced agglomeration and forming secondary aggregates that are difficult to disperse. This is an important reason for the agglomeration phenomenon. At the same time, the amorphous Fe(OH)3 colloid, as the key morphological template for the in-situ growth of iron oxide crystal nuclei, is easily damaged by long-term mechanical stirring due to its loose flocculent structure, resulting in structural compaction or local agglomeration. When iron oxide particles grow along this deformed template, they will directly inherit the rough and agglomerated initial morphology of the template, further aggravating the degree of product agglomeration.

[0062] From the appendix Figure 5 As can be seen, the broadening of the XRD diffraction peaks of the nano-Fe3O4 product is closely related to the nucleation and grain growth characteristics under stirring: the dynamic mass transfer effect of stirring accelerates the nucleation process of nano-Fe3O4, resulting in the rapid formation of a large number of small primary nuclei in the early stage of the reaction; although the subsequent ripening process causes the overall particle size to increase, the size of the primary grains does not increase significantly, and the secondary aggregates formed by particle agglomeration will have a scattering effect on the XRD diffraction signal. Under the combined effect of these two factors, the XRD characteristic diffraction peaks of the nano-Fe3O4 product gradually broaden with the extension of stirring time.

[0063] Example 9 This embodiment 9 is basically the same as embodiment 2 above, except that: In step 2, the concentration of ferric ammonium oxalate is 8.60 g / L and the concentration of ferrous oxalate is 1.80 g / L.

[0064] The other steps are the same as in Example 2, and will not be repeated here.

[0065] Example 10 This embodiment 10 is basically the same as embodiment 2 above, except that: In step 2, the concentration of ferric ammonium oxalate is 12.90 g / L and the concentration of ferrous oxalate is 2.70 g / L.

[0066] The other steps are the same as in Example 2, and will not be repeated here.

[0067] Example 11 This embodiment 11 is basically the same as the above embodiment 2, except that: In step 2, the concentration of ferric ammonium oxalate is 21.50 g / L and the concentration of ferrous oxalate is 4.50 g / L.

[0068] The other steps are the same as in Example 2, and will not be repeated here.

[0069] Example 12 This embodiment 12 is basically the same as the above embodiment 2, except that: In step 2, the concentration of ferric ammonium oxalate is 25.80 g / L and the concentration of ferrous oxalate is 5.40 g / L.

[0070] The other steps are the same as in Example 2, and will not be repeated here.

[0071] As attached Figure 6 As shown, attached Figure 6 The accompanying image shows scanning electron microscope (SEM) images of the nano-Fe3O4 prepared in Examples 9-12; Figure 6 In the figure, (a) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 9, (b) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 10, (c) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 11, and (d) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 12.

[0072] From the appendix Figure 6 It can be seen that the concentrations of ferric ammonium oxalate and ferrous oxalate have a significant regulatory effect on the particle size and dispersibility of the nano-ferric oxide product. With the simultaneous increase of the concentrations of the two iron source materials, the average particle size of the nano-ferric oxide exhibits a non-monotonic trend of first increasing, then decreasing, and then increasing again. This is because the raw material concentration affects the formation and aggregation behavior of Fe(OH)3 colloids and [Fe(C2O4)2]. 2- It has a comprehensive regulatory effect on the adsorption amount and adsorption rate on the colloidal surface, as well as on the coordination adsorption-electron transfer-in-situ nucleation reaction pathway at the liquid-solid interface.

[0073] Specifically, when the raw material concentration is increased to the low to medium concentration range (i.e., ferric ammonium oxalate is 12.90 g / L and ferrous oxalate is 2.70 g / L), the concentration of Fe(OH)3 colloid generated increases synchronously, the collision frequency between colloidal particles increases significantly, resulting in a slight increase in the degree of colloid aggregation, and the overall size of the Fe(OH)3 colloidal template increases accordingly. Since the in-situ growth of iron oxide crystal nuclei depends on the morphology and size of the Fe(OH)3 colloidal template, using this large-sized Fe(OH)3 agglomerate as the reaction interface, the particle size of Fe3O4 particles subsequently generated through electron transfer and dehydration nucleation will also increase synchronously with the increase of template size.

[0074] It is worth noting that in the low to medium concentration range, the colloidal concentration is moderate, and the Fe(OH)3 particles can still maintain good dispersibility without serious agglomeration. Therefore, although the product particle size increases, the particle size distribution remains relatively concentrated. However, when the raw material concentration continues to rise to a higher concentration range (25.80 g / L for ferric ammonium oxalate and 5.40 g / L for ferrous oxalate), the system becomes excessively supersaturated, and the nucleation process of Fe(OH)3 becomes extremely vigorous, generating a large number of high surface energy Fe(OH)3 primary crystal nuclei in a short period of time. At the same time, the ionic strength of the high concentration system increases significantly, which compresses the surface of the Fe(OH)3 colloidal particles. The increased double-layer thickness weakens the electrostatic repulsion between particles, accelerating the collision and aggregation of primary nuclei, forming larger and denser Fe(OH)3 aggregates. The Fe3O4 nuclei undergo heterogeneous nucleation and growth along this large-sized aggregate template, inheriting the template's agglomeration morphology and reducing the uniformity of the interfacial reaction. This ultimately leads to a further increase in the average particle size of the product, exacerbating the agglomeration phenomenon. Furthermore, excessively high supersaturation can cause the nucleation and growth process of Fe(OH)3 to become uncontrolled, further intensifying colloidal agglomeration and product particle size inhomogeneity, ultimately affecting the structural integrity of the Fe3O4 product.

[0075] Example 13 This embodiment 13 is basically the same as the above embodiment 2, except that: In step 3, the stirring rate is 400 r / min.

[0076] The other steps are the same as in Example 2, and will not be repeated here.

[0077] Example 14 This embodiment 14 is basically the same as embodiment 2 above, except that: In step 3, the stirring rate is 600 r / min.

[0078] The other steps are the same as in Example 2, and will not be repeated here.

[0079] Example 15 This embodiment 15 is basically the same as embodiment 2 above, except that: In step 3, the stirring rate is 700 r / min.

[0080] The other steps are the same as in Example 2, and will not be repeated here.

[0081] Example 16 This embodiment 16 is basically the same as embodiment 2 above, except that: In step 3, the stirring rate is 800 r / min.

[0082] The other steps are the same as in Example 2, and will not be repeated here.

[0083] As attached Figure 7 As shown, attached Figure 7 The accompanying image shows scanning electron microscope (SEM) images of the nano-Fe3O4 prepared in Examples 13-16; (See attached image). Figure 7 In the figure, (a) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 13, (b) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 14, (c) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 15, and (d) is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 16.

[0084] From the appendix Figure 7 As can be seen, with the gradual increase of stirring speed, the average particle size of the nano-Fe3O4 product shows a trend of first decreasing and then slightly increasing, and the dispersibility simultaneously shows a pattern of first improving and then deteriorating; in particular, when the stirring speed is low, on the one hand, the reactant [Fe(C2O4)2]... 2- The mass transfer rate to the Fe(OH)3 colloid surface becomes the rate-determining step of the interfacial reaction, leading to [Fe(C2O4)2] 2- The adsorption distribution on the surface of Fe(OH)3 colloid is uneven, making it impossible to form a uniform ≡Fe III -O - -C2O4-Fe II The (C2O4) ternary interface bridging structure leads to uneven distribution of Fe3O4 nucleation sites, resulting in local overgrowth of grains. On the other hand, the newly generated high surface energy Fe(OH)3 colloidal particles, lacking sufficient fluid shear force for dispersion, are prone to collision under Brownian motion and form agglomerates through van der Waals interactions. These agglomerates serve as templates for heterogeneous nucleation and growth of Fe3O4, causing subsequent Fe3O4 particles growing along the template to inherit the agglomeration characteristics of the template, ultimately resulting in products with larger average particle size and obvious agglomeration.

[0085] Example 17 This embodiment 17 is basically the same as embodiment 1 above, except that: In step 2, the concentration of ferric ammonium oxalate is 8.6 g / L and the concentration of ferrous oxalate is 3.60 g / L.

[0086] In step 3, the stirring rate is 700 r / min and the stirring time is 30 min; the mass fraction of commercially available ammonia is 25%-28%; the pH of the mixed raw material solution is adjusted to 9 using commercially available ammonia; the reaction temperature is 50℃; the aging temperature is 90℃ and the aging time is 90 min.

[0087] The other steps are the same as in Example 1, and will not be repeated here.

[0088] As attached Figure 8-9 As shown, attached Figure 8 The attached image shows a scanning electron microscope (SEM) image of the nano-ferric oxide prepared in Example 17; from the appendix... Figure 8 As can be seen from the data, the nano-iron oxide prepared in Example 17 consists of spherical nanoparticles with a small amount of agglomeration and an average particle size of less than 20 nm.

[0089] As attached Figure 8-9 As shown, attached Figure 9 The X-ray diffraction pattern of the nano-ferric oxide prepared in Example 17 is given in Appendix 17; Figure 9 As can be seen from the data, the positions of all diffraction peaks of the nano-Fe3O4 prepared in Example 17 are consistent with those of the standard card (PDF#19-0629) for Fe3O4, and no impurity phase peaks are observed.

[0090] As attached Figure 10 As shown, attached Figure 10 The hysteresis loop diagram of the nano-Fe3O4 prepared in Example 17 is given in Appendix 17; Figure 10 In the figure, (a) shows the hysteresis loop of the nano-iron oxide prepared in Example 17 under a magnetic field strength of -20k to -20k, and (b) shows the hysteresis loop of the nano-iron oxide prepared in Example 17 under a low magnetic field strength.

[0091] From the appendix Figure 10 As can be seen from the data, the hysteresis loop of the nano-Fe3O4 prepared in Example 17 is a smooth S-shaped curve passing through the origin of the coordinate system, and its positive and negative magnetization curves almost completely coincide, confirming that the prepared Fe3O4 nanoparticles have typical superparamagnetism. The measured value of its saturation magnetization is 37.5 emu / g, which is significantly lower than the theoretical value of 92 emu / g for bulk Fe3O4. The decrease in saturation magnetization is related to the significant surface effect of the Fe3O4 nanoparticles.

[0092] It is worth noting that as the particle size of iron oxide decreases, the proportion of surface atoms increases sharply. The surface atoms are in a state of broken lattice symmetry and unsaturated chemical bonds, which leads to the disordered arrangement or tilting of surface spins, forming a magnetic disorder layer on the particle surface that contributes little or no to the total magnetic moment. The presence of the surface magnetic disorder layer reduces the overall average magnetic moment of the material, resulting in a lower measured value of saturation magnetization per unit mass than that of bulk iron oxide.

[0093] Example 18 This embodiment 18 is basically the same as the above embodiment 17, except that: In step 3, commercially available ammonia is used to adjust the pH of the mixed raw material solution to 9.5.

[0094] The other steps are the same as in Example 17, and will not be repeated here.

[0095] As attached Figure 11-12 As shown; Appendix Figure 11 The image provided is a scanning electron microscope (SEM) image of the nano-ferric oxide prepared in Example 18, with appended images. Figure 12 The X-ray diffraction pattern of the nano-iron oxide prepared in Example 18 is given in the figure.

[0096] From the appendix Figure 11-12 As can be seen, compared with Example 17, the Fe3O4 particle size obtained in Example 18 at pH 9.5 is larger. This is because the increase in pH promotes the deprotonation of hydroxyl groups (≡Fe-OH) on the surface of amorphous Fe(OH)3 colloids, generating more negatively charged surface-active species (≡Fe–O). - ); ≡Fe–O formed by deprotonation - It exhibits stronger nucleophilicity and higher reactivity, enabling it to react more effectively with [Fe(C2O4)2]. 2- Coordination occurs at the Fe(II) centers, significantly reducing interfacial electron transfer and subsequent Fe... 2+ / Fe 3+ The reaction kinetic energy barrier of interphase dehydration condensation is reduced, thereby accelerating the nucleation process of Fe3O4; rapid and synchronous nucleation allows a large number of crystal nuclei to form in a similar time period, thus having a relatively consistent growth time window, ultimately leading to an increase in the average particle size of the product and a more concentrated particle size distribution.

[0097] Example 19 This embodiment 19 is basically the same as the above embodiment 17, except that: In step 3, the aging temperature is 100℃.

[0098] The other steps are the same as in Example 19, and will not be repeated here.

[0099] As attached Figure 13-14 As shown; Appendix Figure 13 The image provided is a scanning electron microscope (SEM) image of the nano-Fe3O4 prepared in Example 19, with appended images. Figure 14 The X-ray diffraction pattern of the nano-iron oxide prepared in Example 19 is given in the figure.

[0100] From the appendix Figure 13-14 As can be seen from the data, compared with Example 17, the Fe3O4 obtained by aging at 100℃ in Example 19 has a significantly larger particle size and a more severe agglomeration phenomenon. This is because the increased aging temperature is conducive to the growth of ferrous oxalate crystal nuclei. Secondly, the characteristic diffraction peaks of ferrous oxalate prepared at an aging temperature of 100℃ are sharper, indicating that the ferrous oxalate crystals are better developed.

[0101] The present invention describes a method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings. Using ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings as raw materials, nano-ferric oxide is synthesized in situ in a green manner under mild alkaline conditions (pH 9.0-9.5) via a Fe(OH)3 template. Specifically, commercially available ammonia is used to precisely control the directional conversion of ferric ammonium oxalate and ferrous oxalate into a Fe(OH)3 and ferrous oxalate complex ([Fe(C2O4)2)). 2- ), without introducing Cl throughout the process - SO4 2- By eliminating anions that easily form byproduct salts, inorganic salt pollution can be prevented at the source, and a clean preparation process without inorganic salt byproduct Fe3O4 can be constructed.

[0102] In this invention, oxalic acid and ammonium oxalate are regenerated during the preparation of nano-ferric oxide. The regenerated oxalic acid and ammonium oxalate can be directly reused in the leaching of hematite from cyanide tailings, forming a complete closed loop of "iron removal from cyanide tailings - preparation of ferric ammonium oxalate and ferrous oxalate intermediates - synthesis of ferric oxide - regeneration and reuse of iron removal agent". This significantly reduces the reagent procurement cost of the iron removal process and the reagent cost of Fe3O4 synthesis. The high-purity, controllable-particle-size nano-ferric oxide prepared expands its application in magnetic recording materials, catalyst carriers, biomedicine and other fields. It effectively promotes the high-value and diversification of derivatives from cyanide tailings leachate, solves the problem of large quantities of intermediate derivatives, and clears the way for the industrialization and promotion of oxalic acid and ammonium oxalate leaching iron removal technology.

[0103] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A method for synthesizing nano-ferric oxide based on ferric ammonium oxalate derived from cyanide tailings and ferrous oxalate, characterized in that, include: Ferric ammonium oxalate and ferrous oxalate were prepared using cyanide tailings leachate. Ferric ammonium oxalate was dissolved in water to obtain an aqueous solution of ferric ammonium oxalate. Ferrous oxalate was added to an aqueous solution of ferric ammonium oxalate to obtain a mixed raw material solution; Under continuous stirring, commercially available ammonia water was used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the reaction to synthesize Fe3O4. Static aging was then carried out. After the static aging process was completed, the solution was filtered to obtain nano-Fe3O4 and a filtrate containing ammonium oxalate. The filtrate containing ammonium oxalate was evaporated, concentrated, and crystallized, and then separated by liquid-solid separation to obtain crystalline ammonium oxalate and crystallization mother liquor.

2. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, In the process of adding ferrous oxalate to an aqueous solution of ferric ammonium oxalate to obtain a mixed raw material solution, the molar ratio of ferrous oxalate to ferric ammonium oxalate is 1:

2.

3. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, Commercially available ammonia solution has a mass fraction of 25%-28%; commercially available ammonia solution is used to adjust the pH of the mixed raw material solution to 9.0-9.

5.

4. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, Under continuous stirring, commercially available ammonia water is used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the synthesis of Fe3O4. Static aging is then carried out. After the static aging process is completed, the mixture is filtered to obtain nano-Fe3O4 and ammonium oxalate-containing filtrate. The reaction temperature is 40-70℃ and the reaction time is 30-90min.

5. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, Under continuous stirring, commercially available ammonia water is used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the reaction to synthesize Fe3O4. Static aging is then carried out. After the static aging process is completed, the mixture is filtered to obtain nano-Fe3O4 and ammonium oxalate-containing filtrate. The aging temperature is 90-100℃ and the aging time is 30-90min.

6. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, Under continuous stirring, commercially available ammonia water is used to adjust the pH of the mixed raw material solution to carry out the phase transformation of Fe(II) and Fe(III) and the synthesis of Fe3O4. Static aging is then carried out. After the static aging process is completed, the mixture is filtered to obtain nano-Fe3O4 and ammonium oxalate-containing filtrate. During this process, the stirring rate is 400-800 r / min and the stirring time is 30-90 min.

7. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, In the process of evaporating, concentrating, crystallizing, and separating the filtrate containing ammonium oxalate to obtain crystalline ammonium oxalate and crystallization mother liquor, the volatile ammonia gas generated during the evaporation process enters the process of preparing nano-ferric oxide.

8. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, Crystalline ammonium oxalate is used in the iron removal process of cyanide tailings.

9. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, After evaporating, concentrating, and crystallizing the filtrate containing ammonium oxalate, and then performing liquid-solid separation to obtain crystalline ammonium oxalate and crystallization mother liquor, the process also includes: Regenerated oxalic acid is obtained from the crystallization mother liquor; the regenerated oxalic acid is used in the iron removal process of cyanide tailings.

10. The method for synthesizing nano-ferric oxide based on ferric ammonium oxalate and ferrous oxalate derived from cyanide tailings according to claim 1, characterized in that, The process for preparing ferric ammonium oxalate and ferrous oxalate using cyanide tailings leachate is as follows: Ferrous ammonium oxalate was obtained by subjecting the cyanide tailings leachate to a single evaporation, a single concentration, a single cooling crystallization, a redissolution, a second evaporation, a second concentration, and a second cooling crystallization; wherein the cyanide tailings leachate was the leachate produced during the iron removal and gold enrichment process of the cyanide tailings. Ferric ammonium oxalate was dissolved in water, and ammonia was added dropwise under stirring to induce an iron precipitation reaction, thereby reducing the Fe content in the ferric ammonium oxalate. 3+ Complete precipitation was achieved, and ferric hydroxide precipitate was obtained by filtration. An aqueous solution containing oxalic acid was mixed with ferric hydroxide precipitate to prepare a raw material solution containing ferric oxalate complex. Ascorbic acid was added to the raw material solution containing ferric oxalate complex as a reducing agent, and a stirring reduction reaction was carried out. After the reduction reaction was completed, liquid-solid separation, filter residue washing and drying were performed to obtain ferrous oxalate.

Images