A method for simultaneously recovering lead oxide and preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore

Abstract

This application discloses a method for simultaneously preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore to recover lead oxide, belonging to the field of non-ferrous metal metallurgy and inorganic functional material preparation technology. This method achieves high-value utilization of the oxygen-sulfur mixed ore through dilute acid decalcification pretreatment, oxidative roasting conversion, deep desilication with hot alkali, selective lead leaching, sodium carbonate precipitation-thermal decomposition to recover lead oxide, Fe2O3-enhanced solid-phase synthesis, and dilute acid refining. Experiments show that under these process conditions, lead oxide can be successfully separated and recovered from low-grade ore, while simultaneously producing nano-zinc ferrite. This process synergistically achieves desilication, metal recovery, and high-value utilization of low-grade oxygen-sulfur mixed lead-zinc ore, demonstrating significant economic and environmental benefits.

Description

Technical Field

[0001] This application belongs to the field of non-ferrous metal metallurgy and inorganic functional material preparation technology, specifically relating to a method for recovering lead oxide from low-grade oxygen-sulfur mixed lead-zinc ore while preparing nano-zinc ferrite. Background Technology

[0002] Lead-zinc concentrate is the core raw material for the lead-zinc smelting industry. With the long-term depletion of easily beneficiated high-grade ores, my country's lead-zinc resource supply is gradually shifting towards complex ores that are difficult to beneficiate and contain multiple metals. Among these, low-grade oxygen-sulfur mixed lead-zinc ores, due to the close association of sulfide and oxide phase minerals, fine particle size, and complex composition, generally suffer from lengthy processes, low overall recovery rates, and high processing costs in conventional beneficiation and hydrometallurgical processes. This results in large quantities of such resources remaining in stockpiles or "stagnant" for extended periods, failing to achieve large-scale economic utilization. Therefore, developing a new process that can directly target such low-grade complex ores and synergistically recover valuable components and produce high-value-added materials in the same process is of significant industrial demand and practical importance.

[0003] Zinc ferrite (ZnFe2O4) is a composite oxide with a spinel structure and has been widely used in photocatalysis, gas-sensitive materials, magnetic adsorbents, and gas sensors. Existing preparation methods mainly include co-precipitation, hydrothermal methods, sol-gel methods, and high-purity oxide solid-phase methods. Although these methods produce high-purity products, they are expensive and have limited raw material sources, making them unsuitable for resource utilization using industrial by-products or low-grade ores as raw materials.

[0004] Therefore, there is an urgent need for a method that can utilize low-grade complex ores to recover valuable metal lead while simultaneously preparing ZnFe2O4, in order to solve the problem of resource waste from low-grade ores and realize the resource utilization and high-value utilization of waste residue. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of existing lead-zinc ore processing technologies, such as complex processes and limited resource utilization, and to provide a method for simultaneously recovering lead oxide and preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore, comprising the following steps: (1) After acid washing with dilute hydrochloric acid, the low-grade oxygen-sulfur mixed lead-zinc ore is separated into solid and liquid to obtain decalcified ore; the concentration of dilute hydrochloric acid is 0.2-0.5 mol / L, and the solid-liquid ratio is 1g:8-15mL; (2) After drying the decalcified ore obtained in step (1), it is subjected to oxidative roasting to obtain roasted ore; the oxidative roasting temperature is 850-1050℃, the oxygen flow rate is 100-300mL / min, and the holding time is 1-4h. (3) The roasted ore obtained in step (2) is subjected to hot alkaline leaching with alkaline solution, and solid-liquid separation is performed to obtain desiliconized residue; the solid-liquid ratio of roasted ore to NaOH solution is 1g:6-15mL; (4) The desilication residue obtained in step (3) is leached with a mixed solution of NaCl and NaClO. After solid-liquid separation, a lead-containing solution and zinc-rich iron residue are obtained; the NaCl concentration is 1-3 mol / L and the NaClO concentration is 0.05-0.10 mol / L. (5) Add sodium carbonate solution to the lead-containing solution obtained in step (4), control the endpoint pH to 7-9, generate a precipitate, separate the solid and liquid, wash and dry to obtain lead carbonate, calcine the lead carbonate at 300-400℃ to obtain lead oxide; the concentration of sodium carbonate solution is 1-2 mol / L, the addition method is slow dropwise, and the precipitation temperature is 50-70℃. (6) After drying the zinc-rich iron residue obtained in step (4), Fe2O3 is added according to the Fe / Zn molar ratio of 1:1-1:2, and the mixture is ball-milled to obtain a ball-milled mixture; (7) The ball-milled mixture obtained in step (6) is calcined at 800-1100℃ to obtain crude zinc ferrite; (8) The crude zinc ferrite obtained in step (7) is purified by acid washing with dilute hydrochloric acid, solid-liquid separation is performed, and the product is dried to obtain nano zinc ferrite.

[0006] Furthermore, in step (3), the alkaline solution is a NaOH solution with a concentration of 5wt%-20wt%, the hot alkaline leaching temperature is 90-120℃, and the time is 1-2h.

[0007] Furthermore, in step (8), the concentration of dilute hydrochloric acid is 0.1-0.5 mol / L, the purification temperature is 30-60℃, the solid-liquid ratio is 1g:5-15mL, and the leaching time is 1-2h.

[0008] Furthermore, in step (6), the molar ratio of Fe2O3 to zinc in the zinc-rich iron residue is 1:1-1:2, and the ball milling time is 30-60 min.

[0009] Furthermore, in step (5), the thermal decomposition temperature is 300-400℃ and the thermal decomposition time is 1-2h.

[0010] Furthermore, in step (4), the leaching temperature is 50-70℃ and the time is 0.5-2h.

[0011] Furthermore, the pickling time in step (1) is 10-30 min.

[0012] Furthermore, the roasting time in step (7) is 1-6 hours.

[0013] Furthermore, when the proportion of zinc carbonate in the low-grade oxygen-sulfur mixed lead-zinc ore in step (1) is ≥15wt%, the ore should be pre-roasted at 300-400℃ for 0.5-1.5h before proceeding to step (1).

[0014] Beneficial effects

[0015] 1. Strong raw material adaptability: It can directly process low-grade oxygen-sulfur mixed lead-zinc ore (Zn 5-10wt%, Pb 1-5wt%, Fe 5-10wt%, SiO2 5-15wt%) without pre-enrichment or sorting. Zinc in the ore mainly exists in the form of zinc sulfide and is not leached during the decalcification process, resulting in minimal process loss. For raw materials with high zinc carbonate content, an optional pre-roasting step can be used to convert it into zinc oxide, effectively suppressing zinc leaching loss during decalcification.

[0016] 2. Clean recovery of lead: Lead is selectively leached using a NaCl-NaClO system, with lead as PbCl4. 2- The zinc and iron are introduced into the solution in a form that minimizes zinc and iron loss. Lead oxide is then obtained through sodium carbonate precipitation followed by thermal decomposition. The lead precipitation mother liquor can be recycled. The entire process is clean and waste-free with low reagent consumption.

[0017] 3. Pre-treatment desilication to eliminate interference: Hot alkaline desilication is performed immediately after oxidative roasting to effectively remove silicate impurities, avoiding interference from silicon in subsequent zinc ferrite synthesis and ensuring product purity. The hot alkaline desilication solution can be neutralized and precipitated to recover lead, further reducing the loss of valuable metals.

[0018] 4. Dual-purpose acid with precise separation via kinetic window: Dilute hydrochloric acid plays a dual role in this process. In step (1), it preferentially removes calcium carbonate using a short reaction window (10-30 min), effectively inhibiting the simultaneous dissolution of zinc oxide. In step (8), it utilizes a long reaction window (1-2 h) and moderate heating (30-60 °C) to directionally dissolve unreacted residual free zinc oxide and other acid-soluble impurities, while zinc ferrite with a spinel structure is almost unaffected by corrosion under the same conditions. This stepwise control strategy, which utilizes the difference in reaction kinetics to first selectively remove calcium carbonate and inhibit zinc loss in step (1), and then selectively dissolves free zinc oxide in step (8) while retaining zinc ferrite, is an important technical innovation of this application.

[0019] 5. Significant synergistic effect of steps: Each step is combined in a specific order, with each step creating favorable conditions for the next, and together achieving the value enhancement of the entire process from complex low-grade ore to nano-functional materials and lead oxide products.

[0020] 6. Metallurgical-material integration: The preparation of nano-zinc ferrite and the recovery of lead oxide are realized simultaneously in the same process, realizing the high-value utilization of resources and having good economic and environmental benefits.

[0021] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0022] The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the basic process of the method described in this application.

[0024] Figure 2 This is a graph showing the decomposition characteristics of NaClO at different temperatures.

[0025] Figure 3 This is a photograph of the lead oxide product obtained in Example 3.

[0026] Figure 4 The image shows the XRD pattern of the lead oxide product obtained in Example 3.

[0027] Figure 5 This is a photograph of the nano zinc ferrite product obtained in Example 3.

[0028] Figure 6 The image shows the XRD pattern of the nano zinc ferrite product obtained in Example 3.

[0029] Figure 7 The image shows the XRD pattern of the zinc ferrite product obtained in Comparative Example 1.

[0030] Figure 8 The image shows the XRD pattern of the zinc ferrite product obtained in Comparative Example 2.

[0031] Figure 9 The image shows the XRD pattern of the zinc ferrite product obtained in Comparative Example 3.

[0032] Figure 10 The XRD pattern of the zinc ferrite product obtained in Comparative Example 4 is shown.

[0033] Figure 11 The XRD pattern of the zinc ferrite product obtained in Comparative Example 5 is shown. Detailed Implementation

[0034] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0035] A method for the co-preparation of nano-zinc ferrite and the recovery of lead oxide from low-grade oxygen-sulfur mixed lead-zinc ore ((Zn 5-10wt%, Pb 1-5wt%, Fe 5-10wt%, SiO2 5-15wt%)) is described below: Step (0) Optional pre-roasting step: When the proportion of zinc carbonate in the raw material to the total zinc is ≥15wt%, the ore is pre-roasted at 300-400℃ for 0.5-1.5h to decompose the zinc carbonate into zinc oxide (ZnCO3→ZnO+CO2↑). The purpose of this step is to convert the acid-soluble zinc carbonate into zinc oxide, which has a lower dissolution rate in dilute acid, thereby effectively inhibiting the leaching loss of zinc during the subsequent decalcification process.

[0036] It should be noted that within the pre-roasting temperature zone (300-400℃) described in step (0), the calcium carbonate in the ore raw material does not decompose significantly (the significant thermal decomposition temperature of CaCO3 usually exceeds 800℃), and the activity of CaO in the system is extremely low. Simultaneously, the oxidation rate of sulfides is slow within this temperature zone, and the amount of SO2 produced is negligible. Therefore, there are no thermodynamic and kinetic conditions in this step for the large-scale combination of CaO and SO2 to form difficult-to-remove calcium sulfate, and this will not adversely affect the subsequent oxidative roasting desulfurization and zinc ferrite synthesis.

[0037] Step (1) Decalcification Pretreatment: The low-grade oxygen-sulfur mixed lead-zinc ore or the pre-roasted ore obtained in step (0) is acid-washed with 0.2-0.5 mol / L dilute hydrochloric acid at a solid-liquid ratio of 1:8-15 g / ml, stirred for 10-30 min, filtered, and separated to reduce the calcium carbonate content in the ore, thus obtaining decalcified ore. It should be noted that in the low-grade oxygen-sulfur mixed lead-zinc ore targeted in this application, zinc mainly exists in the form of zinc sulfide (ZnS), which does not dissolve under the dilute hydrochloric acid conditions. If the zinc carbonate content in the raw material is high and has not undergone pre-roasting treatment in step (0), a large amount of zinc carbonate will dissolve in this step, causing serious zinc loss; therefore, for raw materials with high zinc carbonate content, the pre-roasting treatment described in step (0) should be given priority. The acid washing waste liquid generated during decalcification can be recycled multiple times, enriched with zinc concentration, and then incorporated into the subsequent recovery system to avoid zinc loss.

[0038] Step (2) Oxidative roasting: After drying the decalcified ore at 50-80℃ for 3-6 hours, place it in a tube furnace or rotary kiln, introduce oxygen (100-300 mL / min), and roast at 850-1050℃ for 1-4 hours to convert sulfides such as lead sulfide and zinc sulfide into oxides, controlling the sulfur content in the roasted product to <0.5 wt%. The purpose of this step is to activate the mineral, converting sulfides into oxides, providing active oxide precursors for subsequent leaching and solid-phase synthesis. After oxidative roasting, the mineral phase exhibits a porous structure, which is beneficial for the full penetration and reaction of the subsequent hot alkaline desilication process.

[0039] Step (3) Desilication: The roasted ore is leached with a 5wt%-20wt% NaOH solution at 90-120℃ for 1-2 hours, with a solid-liquid ratio of 1:6-15 g / mL. The leaching is then filtered to achieve deep desilication. The purpose of this step is to remove silicate impurities and eliminate their interference with the subsequent synthesis of zinc ferrite. It should be noted that a small amount of lead will enter the alkaline solution in the form of sodium leadate in this step. The lead in the alkaline solution can be recovered after neutralization and precipitation, further reducing the loss of valuable metals. Step (3) Desilication must be performed after step (2) oxidative roasting. If desilication is performed before roasting, the silicates coated with sulfides cannot effectively contact the alkaline solution; while the oxidized ore phase after roasting has a porous structure, allowing the hot alkali to fully penetrate, significantly improving the desilication efficiency.

[0040] Step (4) Selective lead leaching: The desilication residue is leached with a mixed solution of 1-3 mol / L NaCl and 0.05-0.10 mol / L NaClO at 50-70℃ for 0.5-2 hours, so that the lead is treated as PbCl4. 2- The complexed ions selectively enter the solution, while zinc and iron are almost insoluble under neutral to weakly alkaline conditions. Solid-liquid separation yields a lead-containing solution and a zinc- and iron-rich residue. NaClO has a half-life >5 hours at 25-50℃ and exhibits good stability. Figure 2 As shown, leaching occurs rapidly above 70℃, leading to a decrease in chlorine utilization. Therefore, the leaching temperature should be controlled between 50-70℃ to balance oxidation efficiency and NaClO stability.

[0041] Step (5) Lead precipitation and thermal decomposition: Add 1-2 mol / L sodium carbonate solution slowly to the lead-containing solution obtained in step (4) at 50-70℃ with stirring, controlling the final pH to 7-9 to generate lead carbonate precipitate, followed by solid-liquid separation. Wash the lead carbonate precipitate with distilled water, dry it, and then calcine it at 300-400℃ for 1-2 hours, undergoing a thermal decomposition reaction PbCO3→PbO+CO2↑ to obtain lead oxide product. The lead precipitation filtrate from this step is mainly composed of NaCl solution, which can be recycled back to step (4), further reducing reagent consumption and wastewater discharge. Compared to the iron powder replacement method or electrolytic deposition method, the sodium carbonate precipitation-thermal decomposition method for recovering lead oxide has comprehensive advantages such as low reagent cost, high product purity, and the ability to sell the product directly as a chemical raw material.

[0042] Step (6) Iron Supplementation and Ball Milling: After drying the zinc-rich iron residue, determine the zinc content. Calculate the required amount of Fe2O3 to be added based on an Fe / Zn molar ratio of 1:1-2. Then add the corresponding amount of Fe2O3 and place it in a planetary ball mill. Use zirconia balls as the medium, with a ball-to-material ratio of 1-50:1, a rotation speed of 250-450 r / min, and ball mill for 30-60 min. The purpose of this step is to adjust the iron-zinc stoichiometric ratio to the target ratio and to promote the subsequent solid-phase reaction through mechanical activation.

[0043]

[0044] Step (7) Solid-phase synthesis: The ball-milled mixture is calcined at 800-1100℃ for 1-6 hours to undergo a solid-phase reaction ZnO+Fe2O3→ZnFe2O4, thus synthesizing crude zinc ferrite.

[0045] Step (8) Acid washing and purification: Crude zinc ferrite is acid washed and purified with 0.1-0.5 mol / L dilute hydrochloric acid at 30-60℃ for 1-2 h, with a solid-liquid ratio of 1:5-1:15 g / mL. After filtration, it is dried at 50-80℃ for 3-6 h to obtain nano zinc ferrite product with a purity ≥90%, a Zn / Fe molar ratio ≈1:2, and a particle size of 10-60 nm. Zinc ferrite has a stable spinel structure and is almost unaffected by corrosion within the dilute hydrochloric acid concentration range. Unreacted ZnO, residual free Fe2O3, and a small amount of CaO are removed by acid washing, thereby achieving purification.

[0046] It should be noted that although both steps (8) and (1) use dilute hydrochloric acid, their operational objectives and reaction conditions are fundamentally different. The decalcification pretreatment in step (1) is carried out at room temperature for a short time (10-30 min). At this time, calcium carbonate is preferentially removed due to its excellent acid solubility, while zinc oxide dissolves relatively slowly under these conditions, and zinc loss is controllable. The acid washing purification in step (8) is carried out for a longer time (1-2 h) and under moderate heating (30-60℃), so that unreacted free ZnO is fully dissolved into the acid solution and removed. Zinc ferrite (ZnFe2O4) has a stable spinel lattice structure and is almost unaffected by the dilute hydrochloric acid concentration and reaction conditions, thus achieving selective purification. The synergistic cooperation of the two is one of the key technical points of this application: step (1) achieves selective removal of calcium carbonate and reduces zinc loss during the short-term decalcification pretreatment process, and step (8) achieves removal of free ZnO during the long-term acid washing purification process to reduce impurities in zinc ferrite, thus jointly ensuring the purity of the final product.

[0047] The steps in this application exhibit a clear synergistic effect: Step (1) decalcification provides clean raw materials for step (2) oxidative roasting, preventing CaO from reacting with SiO2 at high temperatures to form low-melting-point silicates, thus avoiding the adhesion of the furnace charge; Step (2) oxidative roasting creates a porous structure for step (3) desiliconization, allowing the alkaline solution to fully penetrate; Step (3) desiliconization removes SiO2, which consumes oxidant and produces silica gel precipitates, for step (4), ensuring the selectivity of the lead leaching system; After lead leaching in step (4), Zn and Fe are enriched in the zinc-rich iron residue, providing suitable precursors for the synthesis of zinc ferrite in steps (6)-(8). The steps are used in combination according to the specific order described above, jointly achieving a full-process value enhancement from complex low-grade ore to nano-functional materials and lead oxide products.

[0048] Product characterization method: In this application, the phase of the zinc ferrite product was identified by X-ray diffraction (XRD). The test conditions were Cu Kα radiation and the scanning range was 2θ = 10°-80°. The obtained spectrum was compared with the standard card JCPDS No. 89-7412 to confirm the spinel structure.

[0049] Chemical composition was determined using inductively coupled plasma optical emission spectrometry (ICP-OES, GB / T23942-2009), which included the contents of major elements Fe and Zn, as well as impurity elements such as Pb, Ca, and Si. Assuming XRD confirmed the product to be pure-phase spinel-type ZnFe2O4, the mass fraction of ZnFe2O4 was calculated from the Zn and Fe content measured by ICP-OES, and this was used as the product purity.

[0050] The particle size of the product was determined using a specific surface area analyzer (BET method, referring to GB / T19587-2017), and the average particle size was calculated using the formula d=6 / (ρ·S), where ρ is taken as the theoretical density of ZnFe2O4, which is 5.33 g / cm³. 3 .

[0051] The lead oxide product was identified by X-ray diffraction (XRD) and compared with the characteristic diffraction peaks of the PbO standard card (JCPDS No. 05-0561), confirming that the obtained product was lead oxide (PbO).

[0052] Example 1 A method for simultaneously preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore and recovering lead oxide includes the following steps: (1) Decalcification pretreatment: Take 100g of mineral sample (composition as shown in Table 1), wash with 0.3mol / L dilute hydrochloric acid, solid-liquid ratio 1:10g / ml, stir for 30min, filter with medium speed qualitative filter paper to obtain decalcified mineral.

[0053] (2) Oxidative roasting: The decalcified ore is dried at 60℃ for 6 hours, placed in a tube furnace, oxygen is introduced at 200 mL / min, and roasted at 950℃ for 3 hours to obtain roasted ore.

[0054] (3) Desilication treatment: The roasted ore was leached with 15wt% NaOH solution at 100℃ for 1.5h with a solid-liquid ratio of 1:10g / mL. After filtration, the desilication residue was obtained.

[0055] (4) Selective lead leaching: The desiliconized residue was leached with a mixed solution of 2 mol / L NaCl + 0.05 mol / L NaClO at a solid-liquid ratio of 1:10 g / mL, at a temperature of 60℃, for 1 h. The solution was filtered with medium-speed qualitative filter paper to obtain a lead-containing solution and zinc-rich iron residue.

[0056] (5) Precipitation of lead and thermal decomposition: The lead-containing solution was heated to 60°C, and 1.5 mol / L Na2CO3 solution was slowly added with stirring until the pH reached 8. Stirring was continued for 30 min, and the solution was filtered to obtain lead carbonate precipitate. The precipitate was washed three times with distilled water, dried at 60°C for 6 h, and then calcined at 350°C for 1.5 h to obtain lead oxide product.

[0057] (6) Iron supplementation and ball milling: The zinc-rich iron residue obtained in step (4) is dried at 60℃ for 6 hours. Take 15g and add 4.40g of Fe2O3 according to the Fe / Zn molar ratio of 1:1.2. Place it in a ball mill jar with a ball-to-material ratio of 15:1 and a rotation speed of 400r / min for 1 hour.

[0058] (7) Solid-phase synthesis: The ball-milled mixture was calcined at 1000℃ for 5h to obtain crude zinc ferrite.

[0059] (8) Acid washing and purification: Crude zinc ferrite was purified with 0.3 mol / L dilute hydrochloric acid at 45℃ for 1 h, with a solid-liquid ratio of 1:10 g / ml. After filtration, it was dried at 60℃ for 6 h to obtain the zinc ferrite product. The purity of ZnFe2O4 was calculated based on the Zn and Fe main element contents measured by ICP-OES and is shown in Table 2.

[0060] Formula for calculating the purity of zinc ferrite: The Fe element content measured by ICP-OES is calculated according to the following formula:

[0061] The value of 0.4633 represents the theoretical mass fraction of Fe in pure ZnFe₂O₄ (46.33%). The measured Zn mass fraction is used for verification. If the Zn / Fe molar ratio deviates from the theoretical value by 1:2, the Fe standard shall prevail.

[0062] Table 1 shows the main chemical composition of the low-grade oxygen-sulfur mixed lead-zinc ore used in the examples.

[0063]

[0064] Example 2 A method for simultaneously preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore and recovering lead oxide includes the following steps: (1) Decalcification pretreatment: Same as in Example 1, except the solid-liquid ratio is changed to 1:15 g / ml.

[0065] (2) Oxidative roasting: oxygen flow rate 300 mL / min, the rest is the same as in Example 1.

[0066] (3) Desilication treatment: NaOH concentration 20wt%, solid-liquid ratio 1:15g / ml, the rest is the same as in Example 1.

[0067] (4) Selective lead immersion: NaCl 3mol / L + NaClO 0.08mol / L, solid-liquid ratio 1:10g / mL, the rest is the same as in Example 1.

[0068] (5) Lead precipitation and thermal decomposition: Same as in Example 1.

[0069] (6) Iron supplementation and ball milling: Fe / Zn molar ratio 1:1.5, add 5.96g Fe2O3, and ball mill for 2h.

[0070] (7) Solid-phase synthesis: Same as in Example 1.

[0071] (8) Acid washing and purification: temperature 55℃, solid-liquid ratio 1:15g / ml, the rest is the same as in Example 1, to obtain zinc ferrite product. The purity of ZnFe2O4 calculated by the Zn and Fe main element content measured by ICP-OES is shown in Table 2.

[0072] Example 3 A method for simultaneously preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore and recovering lead oxide includes the following steps: (1) Decalcification pretreatment: Same as in Example 1.

[0073] (2) Oxidative roasting: oxygen flow rate 300 mL / min, the rest is the same as in Example 1.

[0074] (3) Desiliconization treatment: NaOH concentration 20wt%, the rest is the same as in Example 1.

[0075] (4) Selective lead immersion: NaCl 3mol / L + NaClO 0.10mol / L, solid-liquid ratio 1:10g / mL, temperature 55℃, time 0.5h, the rest is the same as in Example 1.

[0076] (5) Lead precipitation and thermal decomposition: Same as in Example 1, see product sample. Figure 3 XRD patterns can be found Figure 4 .

[0077] (6) Iron supplementation and ball milling: Fe / Zn molar ratio 1:1.8, 7.52g Fe2O3 added, ball-to-material ratio 20:1, ball milling for 2h.

[0078] (7) Solid-phase synthesis: Same as in Example 1.

[0079] (8) Acid washing and purification: HCl concentration 0.5 mol / L, temperature 55℃, solid-liquid ratio 1:15 g / ml, time 1 h, filtration, drying at 60℃ for 6 h to obtain the final product. XRD analysis showed that the characteristic diffraction peaks of the product matched the spinel structure ZnFe2O4 standard card (JCPDS No. 89-7412), confirming that the obtained product was pure phase spinel type zinc ferrite. The purity of ZnFe2O4 was calculated based on the Zn and Fe main element contents measured by ICP-OES, as shown in Table 2. The particle size of the product was determined by the BET method, and the specific surface area S BET It is 53.35m 2 / g, converted to an average particle size of 21.1nm, see product sample. Figure 5 XRD patterns can be found Figure 6 The particle size calculation results are shown in Table 3.

[0080] Average particle size formula (assuming particles are spherical or cubic): d = 6000 / (ρ × S) BET ) d: average particle size, nm; ρ: true density of sample, g / cm³ 3 S BET : BET specific surface area.

[0081] Table 2 shows the calculated purity results of zinc ferrite in Examples 1-7.

[0082] Table 3 shows the BET test results for particle size in Example 3.

[0083] Example 4 A method for recovering lead oxide and preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore is presented, demonstrating the effectiveness of using a different combination of process parameters than in Example 1, and includes the following steps: (1) Decalcification pretreatment: Take 100g of the same mineral sample as in Example 1, wash with 0.5mol / L dilute hydrochloric acid, solid-liquid ratio 1:15g / mL, stir for 10min, filter, and obtain decalcified ore.

[0084] (2) Oxidative roasting: The decalcified ore is dried at 80℃ for 3 hours, placed in a tube furnace, oxygen is introduced at 100 mL / min, and roasted at 1050℃ for 1 hour to obtain roasted ore.

[0085] (3) Desilication treatment: The roasted ore was leached with 5wt% NaOH solution at 90℃ for 2 hours with a solid-liquid ratio of 1:6 g / mL. After filtration, the desilication residue was obtained.

[0086] (4) Selective lead leaching: The desiliconized residue was leached with a mixed solution of 1 mol / L NaCl + 0.05 mol / L NaClO, with a solid-liquid ratio of 1:10 g / mL, a temperature of 50℃, and a time of 2 h. After filtration, a lead-containing solution and zinc-rich iron residue were obtained.

[0087] (5) Lead precipitation and thermal decomposition: Same as in Example 1.

[0088] (6) Iron supplementation and ball milling: After drying the zinc-rich iron residue, Fe2O3 is added at a Fe / Zn molar ratio of 1:1, the ball-to-material ratio is 50:1, the rotation speed is 250 r / min, and the ball milling is performed for 30 min.

[0089] (7) Solid-phase synthesis: The ball-milled mixture was calcined at 800℃ for 6 hours to obtain crude zinc ferrite.

[0090] (8) Acid washing and purification: Crude zinc ferrite was purified with 0.1 mol / L dilute hydrochloric acid at 30℃ for 2 h with a solid-liquid ratio of 1:5 g / mL. After filtration, it was dried at 50℃ for 6 h to obtain the zinc ferrite product. The purity of ZnFe2O4 was calculated based on the Zn and Fe main element contents measured by ICP-OES and is shown in Table 2.

[0091] Example 5 A method for recovering lead oxide and simultaneously preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore demonstrates the effectiveness of another set of process parameter combinations, including the following steps: (1) Decalcification pretreatment: Same as in Example 1, except the solid-liquid ratio is changed to 1:8 g / mL, and the mixture is stirred for 15 min.

[0092] (2) Oxidative roasting: Same as in Example 1, roasting temperature 850℃, roasting time 4h.

[0093] (3) Desilication treatment: Same as in Example 1, except that the NaOH concentration is changed to 10wt%, the temperature is 110℃, and the time is 1h.

[0094] (4) Selective lead impregnation: Same as in Example 1.

[0095] (5) Lead precipitation and thermal decomposition: Same as in Example 1.

[0096] (6) Iron supplementation and ball milling: Fe / Zn molar ratio 1:2, Fe2O3 added, ball-to-material ratio 20:1, rotation speed 450r / min, ball milling for 45min.

[0097] (7) Solid-phase synthesis: calcined at 1100℃ for 1h.

[0098] (8) Acid washing and purification: Same as in Example 1, zinc ferrite product was obtained. The purity of ZnFe2O4 calculated from the Zn and Fe main element contents measured by ICP-OES is shown in Table 2.

[0099] Example 6 A method for recovering lead oxide and simultaneously preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore is demonstrated, showcasing the effectiveness of using sodium carbonate lead precipitation and another set of process parameters, including the following steps: (1) Decalcification pretreatment: Same as in Example 1, except that the concentration of dilute hydrochloric acid was changed to 0.2 mol / L and stirred for 20 min.

[0100] (2) Oxidative roasting: Same as in Example 1.

[0101] (3) Desiliconization treatment: Same as in Example 1.

[0102] (4) Selective lead impregnation: Same as in Example 1.

[0103] (5) Precipitation of lead and thermal decomposition: Slowly add 1 mol / L Na2CO3 solution to the lead-containing solution at 50℃ until pH=7, filter after precipitation, wash, and calcine at 300℃ for 2h to obtain lead oxide product.

[0104] (6) Iron supplementation and ball milling: Same as in Example 1.

[0105] (7) Solid-phase synthesis: Same as in Example 1.

[0106] (8) Acid washing and purification: Same as in Example 1, zinc ferrite product was obtained. The purity of ZnFe2O4 calculated from the Zn and Fe main element contents measured by ICP-OES is shown in Table 2.

[0107] Example 7 A method for recovering lead oxide and preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore, demonstrating the effectiveness of pre-roasting, includes the following steps: (0) Pre-roasting: Take 200g of ore sample and pre-roast at 350℃ for 1h to obtain pre-roasted ore. (1) Oxidative roasting: Take 100g of pre-roasted ore sample and roast it in the same way as in Example 3.

[0108] (2) Oxidative roasting: Same as in Example 3.

[0109] (3) Desiliconization treatment: Same as in Example 3.

[0110] (4) Selective lead impregnation: Same as Example 3.

[0111] (5) Lead precipitation and thermal decomposition: Same as in Example 3.

[0112] (6) Iron supplementation and ball milling: Same as in Example 3.

[0113] (7) Solid-phase synthesis: Same as in Example 3.

[0114] (8) Acid washing and purification: Same as in Example 3, zinc ferrite product was obtained. The purity of ZnFe2O4 calculated from the Zn and Fe main element contents measured by ICP-OES is shown in Table 2.

[0115] Comparative Analysis of the Effects of Examples A comparison of Examples 1-7 shows that different combinations of process parameters have a significant impact on the purity of zinc ferrite products. Examples 1-3 employed progressively optimized iron supplementation molar ratios (Fe / Zn increasing from 1:1.2 to 1:1.5 and 1:1.8) and NaClO concentrations in the lead leaching system (increasing from 0.05 mol / L to 0.08 mol / L and 0.10 mol / L), resulting in a significant increase in product purity from 89.75% to 90.18% and 94.55%, respectively. This indicates that appropriately increasing the iron supplementation ratio and NaClO concentration is beneficial for the full reaction of zinc and the efficient removal of lead, thereby obtaining zinc ferrite with higher purity. In Example 4, the oxidative roasting temperature was increased to 1050℃ and the solid-phase synthesis temperature was decreased to 800℃, resulting in a decrease in purity to 87.64%. This is because excessively high roasting temperatures may lead to mineral sintering, affecting subsequent leaching efficiency, while a lower solid-phase synthesis temperature (800℃) results in slow reaction kinetics and incomplete reaction between ZnO and Fe2O3, leading to a decrease in purity. Example 5, using a lower oxidative roasting temperature (850℃) and a higher solid-phase synthesis temperature (1100℃), achieved a purity of 92.13%. This indicates that a slightly lower oxidative roasting temperature can still yield good results, but an excessively high solid-phase synthesis temperature may cause particle growth, resulting in a slightly inferior overall effect compared to Example 3. Example 6 adjusted the final pH of lead precipitation to 7 (below the preferred range of 7-9), achieving a purity of 85.91%, the lowest among all examples. This demonstrates that a low pH during lead precipitation leads to incomplete lead precipitation, and residual lead interferes with subsequent zinc ferrite synthesis; therefore, controlling the pH between 7 and 9 is necessary. Example 7, performed on high-zinc carbonate ore after pre-roasting, achieved a purity of 93.57%, close to the 94.55% of Example 3. This proves that the pre-roasting step effectively suppresses zinc loss, allowing high-purity products to be obtained from high-zinc carbonate ore. Taking all factors into consideration, the preferred combination of process parameters for this invention is as follows: decalcification hydrochloric acid concentration 0.3 mol / L, oxidative roasting 950℃, desilication NaOH concentration 20%, lead immersion NaCl 3 mol / L + NaClO 0.10 mol / L, solid-liquid ratio 1:10 g / mL, iron molar ratio 1:1.8, solid-phase synthesis 1000℃, and acid washing purification HCl concentration 0.5 mol / L (as shown in Example 3). Under these conditions, a nano-zinc ferrite product with a purity of 94.55% and a particle size of 21.1 nm can be obtained, while effectively recovering lead oxide.

[0116] Comparative Example 1 Same as Example 3, except that step (1) decalcification pretreatment is omitted. The resulting product has a purity of 72.58%, and XRD shows the presence of CaSiO3 impurity peaks. Its XRD pattern is shown below. Figure 7 .

[0117] Comparative Example 2 Same as Example 3, except that step (3) desilication treatment is omitted. The purity of the obtained product is 65.61%, and XRD shows the presence of CaO and CaSiO3 impurity peaks. Its XRD pattern is shown in [reference needed]. Figure 8 .

[0118] Comparative Example 3 Same as Example 3, except that Fe2O3 is not added in step (6). The purity of the obtained product is 59.52%, and XRD shows residual peaks of ZnO and Fe2O3. Its XRD pattern is shown in [reference needed]. Figure 9 .

[0119] Comparative Example 4 Same as Example 3, except that step (8) acid washing and purification is omitted. The purity of the obtained product is 90.08%, and XRD shows that there are still a small amount of elutable impurities remaining.

[0120] Comparative Example 5 Same as Example 3, except for the addition of step (0) pre-calcination. The resulting product had a purity of 92.74%, and XRD showed a peak of pure zinc ferrite.

[0121] The XRD phase identification results of the products obtained from each comparative example are summarized in Table 4.

[0122] Table 4 summarizes the XRD phase identification results of the products obtained from each comparative example.

[0123]

[0124] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for simultaneously preparing nano-zinc ferrite from low-grade oxygen-sulfur mixed lead-zinc ore, characterized in that, Includes the following steps: (1) After acid washing with dilute hydrochloric acid, the low-grade oxygen-sulfur mixed lead-zinc ore is separated into solid and liquid to obtain decalcified ore; the concentration of dilute hydrochloric acid is 0.2-0.5 mol / L, and the solid-liquid ratio is 1g:8-15mL; (2) After drying the decalcified ore obtained in step (1), it is subjected to oxidative roasting to obtain roasted ore; the oxidative roasting temperature is 850-1050℃, the oxygen flow rate is 100-300mL / min, and the holding time is 1-4h. (3) The roasted ore obtained in step (2) is subjected to hot alkaline leaching with alkaline solution, and solid-liquid separation is performed to obtain desiliconized residue; the solid-liquid ratio of roasted ore to NaOH solution is 1g:6-15mL; (4) The desilication residue obtained in step (3) is leached with a mixed solution of NaCl and NaClO. After solid-liquid separation, a lead-containing solution and zinc-rich iron residue are obtained; the NaCl concentration is 1-3 mol / L and the NaClO concentration is 0.05-0.10 mol / L. (5) Add sodium carbonate solution to the lead-containing solution obtained in step (4), control the endpoint pH to 7-9, generate a precipitate, separate the solid and liquid, wash and dry to obtain lead carbonate, calcine the lead carbonate at 300-400℃ to obtain lead oxide; the concentration of sodium carbonate solution is 1-2 mol / L, the addition method is slow dropwise, and the precipitation temperature is 50-70℃. (6) After drying the zinc-rich iron residue obtained in step (4), Fe2O3 is added according to the Fe / Zn molar ratio of 1:1-1:2, and the mixture is ball-milled to obtain a ball-milled mixture; (7) The ball-milled mixture obtained in step (6) is calcined at 800-1100℃ to obtain crude zinc ferrite; (8) The crude zinc ferrite obtained in step (7) is purified by acid washing with dilute hydrochloric acid, solid-liquid separation is performed, and the product is dried to obtain nano zinc ferrite.

2. The method according to claim 1, characterized in that, In step (3), the alkaline solution is a NaOH solution with a concentration of 5wt%-20wt%, the hot alkaline leaching temperature is 90-120℃, and the time is 1-2h.

3. The method according to claim 1, characterized in that, In step (8), the concentration of dilute hydrochloric acid is 0.1-0.5 mol / L, the purification temperature is 30-60℃, the solid-liquid ratio is 1g:5-15mL, and the leaching time is 1-2h.

4. The method according to claim 1, characterized in that, In step (6), the molar ratio of Fe2O3 to zinc in the zinc-rich iron residue is 1:1-1:2, and the ball milling time is 30-60 min.

5. The method according to claim 1, characterized in that, In step (5), the thermal decomposition temperature is 300-400℃ and the thermal decomposition time is 1-2h.

6. The method according to claim 1, characterized in that, In step (4), the leaching temperature is 50-70℃ and the time is 0.5-2h.

7. The method according to claim 1, characterized in that, The pickling time in step (1) is 10-30 min.

8. The method according to claim 1, characterized in that, The roasting time in step (7) is 1-6 hours.

9. The method according to claim 1, characterized in that, When the proportion of zinc carbonate in the low-grade oxygen-sulfur mixed lead-zinc ore in step (1) is ≥15wt%, the ore should be pre-roasted at 300-400℃ for 0.5-1.5h before proceeding to step (1).

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