A two-stage leaching method for zinc oxide concentrate to realize efficient separation of iron and zinc

Abstract

This application discloses a two-stage leaching method for zinc oxide concentrate to achieve efficient iron-zinc separation, belonging to the field of hydrometallurgical technology. Addressing the problem of unstable iron valence state and difficulty in precipitation and separation due to residual sulfides in zinc oxide concentrate, this application employs a neutral-acid two-stage coupled leaching process, including slurry preparation, neutral leaching, two-stage acid leaching, pressure filtration, and leaching residue washing steps. In the neutral leaching stage, the addition of hydrogen peroxide is determined based on the iron concentration in the slurry: when the iron concentration is ≤1 g / L, iron separation is achieved using the system itself; when the iron concentration is >1 g / L, hydrogen peroxide is added quantitatively for the portion exceeding the baseline value, and the reaction time is adjusted to allow for sufficient hydrolysis and precipitation of iron ions, thereby achieving effective separation of iron and zinc. This application significantly reduces oxidant consumption, increases zinc recovery rate, and improves liquid-solid separation performance.

Description

Technical Field

[0001] This application relates to the field of hydrometallurgical technology, and in particular to a two-stage leaching method for zinc oxide concentrate to achieve efficient separation of iron and zinc. Background Technology

[0002] Zinc oxide concentrate is a raw material supplied to smelters for direct hydrometallurgical processing after the ore has undergone flotation to separate sulfide and oxide ores at the concentrator. The oxide portion is then treated with decarbonization. Compared to flotation zinc oxide concentrate, zinc oxide concentrate, despite undergoing oxygen-sulfur separation and decarbonization, has a higher grade and lower organic matter content. However, due to limitations in the oxygen-sulfur separation process, zinc oxide concentrate still contains some sulfides (S₂O₃). 2- During the wet leaching process, the iron components associated with zinc oxide concentrate, in addition to zinc, are dissolved simultaneously. The dissolved ferric ions are rapidly reduced to ferrous ions (2Fe2+) by sulfides. 3+ +S 2- =2Fe 2+ (+S↓), while ferrous ions do not hydrolyze and precipitate under neutral pH conditions, forming a vicious cycle of oxidation-reduction, resulting in ineffective iron separation and its entry into subsequent processes with the solution. Therefore, how to effectively separate iron in the presence of residual sulfides, while ensuring efficient zinc leaching and recovery, based on the mineralogical characteristics of zinc oxide concentrate, is a technical problem that urgently needs to be solved in this field.

[0003] In the prior art, CN1477217C discloses a leaching process for zinc oxide ore, employing a two-stage coupled leaching process: the neutral leaching stage has an initial pH of 3.0-3.5 and an ending pH of 5-5.2, while the low-acid leaching stage has a pH of 1.5-3.0, with the leaching waste liquid returned to the neutral stage for recycling. This process achieves the hydrolysis and precipitation of iron and silicon in the neutral stage, and further recovers residual zinc in the low-acid stage. However, this process is designed for zinc oxide ore powder, which contains virtually no sulfides. The precipitation process of iron in the neutral stage is not affected by sulfide reduction, and hydrolysis and iron removal can be achieved simply by controlling the pH. It does not address the issue of the cyclic transformation of iron valence states in the presence of sulfides.

[0004] CN113528816A discloses a method for direct acid leaching and flotation of zinc oxide concentrate, employing a process route of single-stage high-acid leaching followed by neutralization with zinc-containing substances. This method is designed for flotation of zinc oxide concentrate, where the raw material is essentially free of sulfides; however, the use of high-acid leaching leads to the dissolution of a large amount of iron, and it does not address the issue of the cyclic transformation of iron valence states in the presence of sulfides.

[0005] In summary, while existing neutral-acid two-stage leaching processes can achieve zinc leaching and partial iron removal, they do not address the technical problem of iron valence instability caused by residual sulfides in zinc oxide concentrate. Therefore, there is an urgent need to develop a neutral-acid two-stage coupled leaching method specifically tailored to the mineralogical characteristics of zinc oxide concentrate to solve the problem of effective iron separation in the presence of residual sulfides. Summary of the Invention

[0006] To address or partially address the problems existing in related technologies, a neutral-acid two-stage coupled leaching method suitable for zinc oxide concentrate is provided, which achieves effective separation of iron and efficient recovery of zinc in the presence of residual sulfides.

[0007] A two-stage leaching method for zinc oxide concentrate to achieve efficient separation of iron and zinc includes the following steps: (1) Slurry preparation: Zinc oxide concentrate is slurried with slurry preparation solution under stirring at 30-40℃ to obtain slurry; (2) Neutral leaching: The slurry is heated to 55-65℃ under stirring, and acidified to pH 0.5-3.0 using acidic solution. When the pH reaches the above range, hydrogen peroxide is added according to the iron concentration in the slurry: no hydrogen peroxide is added when the iron concentration is ≤1g / L, and when the iron concentration is >1g / L, 0.001L of hydrogen peroxide is added per cubic meter of slurry for every 0.001g / L increase in iron concentration, based on 1g / L. The reaction continues for 2-3 hours until the pH value at the end of the reaction is 5.2-5.4 and the iron concentration in the slurry is ≤1g / L. Leaching is then stopped to obtain neutral leaching slurry. Solid-liquid separation is then carried out to obtain neutral supernatant and thick underflow. (3) Second stage acid leaching: The thickened underflow is heated to 55-65℃ under stirring, and the pH is adjusted to 1.5-4.0 with acidic solution to obtain acid leaching slurry; (4) Pressure filtration separation: The acid leaching slurry is subjected to solid-liquid separation to obtain the filter press liquid and leaching residue; (5) Leaching residue washing: The leaching residue is washed with washing liquid at a temperature of 50-60℃, and then filtered by pressure to obtain washing residue.

[0008] Preferably, the liquid-solid ratio of the slurry to the zinc oxide concentrate in step (1) is L:S=3-4:1.

[0009] Preferably, the liquid-to-solid ratio of the washing liquid and the leaching residue in step (5) is L:S=3-4:1.

[0010] Preferably, in step (1), the slurry preparation liquid is selected as water or the filtrate from step (4). During the process start-up stage, water is used for slurry preparation; after the filtration separation process in step (4) is running normally, the filtrate is used for circulating slurry preparation.

[0011] Preferably, the washing solution in step (5) is water or zinc precipitation solution. The zinc precipitation solution is obtained by washing the leaching residue with water to obtain the washing residue solution, then subjecting the washing residue solution to lime alkaline zinc precipitation and solid-liquid separation to finally obtain a solution with a zinc content ≤0.5 g / L. During the process start-up phase, water is used as the washing solution; after the process is running stably and the zinc precipitation solution is produced, the zinc precipitation solution is used for washing to achieve system solution circulation and zinc recovery.

[0012] Preferably, the acidic liquid mentioned in steps (2) and (3) is selected from: H2SO4 with a concentration of 98%, or waste electrolytic liquid with an H2SO4 concentration of 100-130 g / L.

[0013] Preferably, in step (2), the solid-liquid separation method includes: allowing the neutral leaching slurry to flow by gravity into a thickening tank, adding flocculant thereto, and obtaining a neutral supernatant and a thickened underflow after sedimentation separation.

[0014] Preferably, the flocculant is added at a rate of 0.01 m³ per cubic meter of slurry. 3 The flocculant solution is added in a specific ratio; the concentration of the flocculant solution is 1.5‰.

[0015] Preferably, the flocculant has a molecular weight ≥12 million, intrinsic viscosity ≤800mL / g, degree of hydrolysis <3%, dissolution rate ≤30min, solid content ≥93%, and Cl ≤0.05%.

[0016] Preferably, the stirring in steps (1), (2) and (3) is mechanical stirring, and the stirring speed is 80-85 r / min.

[0017] The technical solution provided in this application may include the following beneficial effects: (1) This solves the problem that the continuous reduction of ferric iron by residual sulfides in zinc oxide concentrate leads to an unstable valence state of iron and makes it difficult to precipitate and separate in the neutral stage. Although the existing technology CN1477217C adopts a neutral-low acid two-stage coupled leaching process, which controls the gradual increase of pH to hydrolyze and precipitate iron in the neutral stage, it is aimed at zinc oxide ore powder without sulfides, where the valence state of iron is relatively stable.

[0018] The raw material for this application is zinc oxide concentrate, in which residual sulfides will continuously reduce Fe... 3+ Reduced to Fe 2+ This disrupts the conditions for hydrolysis and iron removal. In step (2), hydrogen peroxide is added under initial acid pH conditions of 0.5-3.0, utilizing the abundant H+ in the acidic environment. + The rapid oxidation of ferrous ions to ferric ions is specifically reflected as follows: 2Fe 2+ +H₂O₂ + 2H += 2Fe 3+ +2H₂O reduces the effect of sulfides on Fe under neutral conditions. 3+ The reduction occurs; subsequently, within 2-3 hours, as the basic oxide (ZnO) continues to consume acid, the pH gradually rises to 5.2-5.4, and iron ions undergo hydrolysis and precipitation (Fe). 3+ +3H₂O=Fe(OH)₃↓+3H + The process generates ferric hydroxide, which precipitates together with impurities such as silicon, thus achieving effective separation of iron and zinc. Then, solid-liquid separation is performed, and the iron content of the neutral supernatant is ≤20 mg / L.

[0019] (2) This application sets a baseline value for resistance to sulfide reduction: iron concentration in the slurry = 1 g / L. Below this threshold, even if sulfides continuously reduce Fe... 3+ Under natural hydrolysis conditions, iron can still be suppressed; however, beyond this baseline, the reduction of sulfides is amplified, necessitating the artificial addition of oxidants. Specifically: In step (2), when the iron concentration in the slurry is ≤1 g / L, the iron load of the system is at a low level, and the sulfides in the zinc oxide concentrate are residual, limiting their ability to reduce iron ions; even if the sulfides continuously reduce some of the Fe... 3+ Reduced to Fe 2+ Remaining Fe 3+ It can still be fully hydrolyzed and precipitated under pH 5.2-5.4 conditions. Meanwhile, under conditions of 55-65℃ and mechanical stirring, dissolved oxygen has a spontaneous oxidation effect on ferrous ions (4Fe₂O₃). 2+ +O2+ 4H + = 4Fe 3+ + 2H2O), continuously replenishing Fe 3+ With a working time of 2-3 hours, the pH gradually increases from the initial acidity of 0.5-3.0 to 5.2-5.4, and the Fe... 3+ Hydrolyzed and precipitated, specifically: Fe 2+ →Fe 3+ →Fe(OH)3↓, relying on hydrolysis and precipitation, iron impurities can be effectively separated without the need for additional hydrogen peroxide.

[0020] When the iron concentration is greater than 1 g / L, the reduction of sulfides exceeds the system's self-equilibrium capacity, requiring the addition of hydrogen peroxide to rapidly oxidize ferrous ions to ferric ions (2Fe²⁺). 2+ + H2O2 + 2H + = 2Fe 3++ 2H2O); at this point, the oxidation rate of hydrogen peroxide is much faster than that of dissolved oxygen, and the oxidation reaction is no longer the bottleneck. However, it is still necessary to control the working time to 2-3 hours: firstly, to ensure that the alkaline oxide (ZnO) continuously consumes acid so that the pH gradually increases rather than suddenly; secondly, to provide sufficient flocculation and aging time for Fe(OH)3 flocs to form easily settling large particles; and thirdly, to ensure the full dissolution of zinc. Only the portion exceeding the 1 g / L benchmark value is calculated at 0.001 L / (m 3 By adding hydrogen peroxide at a ratio of ·mg / L, a precise match between oxidant consumption and raw material iron load was achieved. Detailed Implementation

[0021] The embodiments illustrate implementations of this application; however, 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.

[0022] Example 1 (1) Mixing the pulp The zinc oxide concentrate contains 23.6% zinc and 2.5% sulfides. 95% of the zinc oxide concentrate has a particle size of -300 mesh. The zinc oxide concentrate and water are added to a mixing tank at a liquid-solid ratio of L:S=3:1 and mixed at 40℃ and mechanical stirring speed of 85 r / min to obtain the slurry.

[0023] (2) Neutral leaching The slurry is pumped to the leaching tank (leaching tank volume: 90m³). 3 The stirring speed was maintained at 85 r / min, and the temperature was raised to 60℃. The pH was adjusted to 1.5 using 98% concentrated sulfuric acid. In this embodiment, hydrogen peroxide was added after the pH reached the predetermined range. Hydrogen peroxide is relatively more stable in strongly acidic to weakly acidic environments; adding it too early may lead to ineffective decomposition. Adding hydrogen peroxide after the pH reaches the predetermined range serves to oxidize ferrous ions (Fe2+) in the solution. 2+ At the set acidic pH, iron exists primarily in ionic form, which is conducive to the efficient oxidation reaction. The goal of oxidation is to produce Fe. 3+ This prepares the ground for subsequent neutralization and hydrolysis to completely precipitate the substance.

[0024] The iron concentration in the slurry was found to be 1.65 g / L (>1 g / L). Using 1 g / L as a baseline, the excess is 0.65 g / L (i.e., 650 mg / L). Based on the ratio of 0.001 L of hydrogen peroxide added per cubic meter of slurry exceeding the 1 mg / L iron concentration limit, the required amount of hydrogen peroxide (H2O2 concentration 27.5%) to be added is: 650 mg / L × 0.001 L / (m 3(mg / L)×90 m 3 =58.5L Immediately add 58.5 L of hydrogen peroxide to each leaching tank and control the operation time for 3 hours. As the alkaline oxides consume acid and the hydrogen peroxide oxidizes and consumes H⁺, the pH gradually rises to 5.2. At this point, the iron concentration is measured at 12 mg / L, which meets the requirement of <20 mg / L for this stage. Leaching is then stopped, yielding a neutral leaching slurry. The neutral leaching slurry flows by gravity to a thickening tank, where 1.5‰ flocculant is added. Based on the volume required per leaching tank, each leaching tank requires 0.9 m³ of... 3 Flocculant solution, 1.35 kg flocculant, The flocculant was polyacrylamide (molecular weight ≥ 12 million, intrinsic viscosity ≤ 800 mL / g, degree of hydrolysis < 3%, dissolution rate ≤ 30 min, solid content ≥ 93%, Cl ≤ 0.05%). After sedimentation separation, a neutral supernatant (Zn 115 g / L, Fe 12 mg / L, pH 5.2, solid content 1.5%) and a concentrated underflow were obtained.

[0025] By controlling the operation time to 3 hours, the pH is gradually increased from the initial acid 1.5 to the final 5.2. The ferric hydroxide generated by the hydrolysis of iron ions has sufficient time for flocculation and aging, forming large flocs of moderate size that are easy to settle. After the neutral leaching is completed, flocculant is added for solid-liquid separation. The solid content of the neutral supernatant is <2%, the sedimentation speed is fast, and the separation effect is good.

[0026] If the pH rises rapidly, or if the amount of hydrogen peroxide added is correct but the reaction time is too short, then Fe 3+ The ferric hydroxide generated by instantaneous hydrolysis does not have enough time to fully flocculate and grow, remaining suspended in the slurry as fine colloidal particles. This makes flocculation and sedimentation difficult, leading to difficulties in thickening and separation, turbidity of the supernatant, and incomplete iron removal. In this example, the hydrogen peroxide dosage is 58.5 L / L of Fe produced in the leaching tank. 3+ The amount of water was matched with the 3-hour reaction time, ensuring the timing coordination of the three stages of oxidation-hydrolysis-flocculation and avoiding the above-mentioned problems.

[0027] (3) Two-stage acid leaching The thickened underflow was pumped into the acid leaching tank, stirred at 80 r / min, heated to 60℃, and acidified to pH 3.5 with waste electrolytic solution of 100 g / L H2SO4. The reaction was carried out for 3 h to obtain the acid leaching slurry.

[0028] (4) Pressure filtration separation The acid-leached slurry is pumped to a filter press for filtration separation, yielding a filtrate (Zn 85 g / L, Fe 800 mg / L, pH 3.5) and leaching residue (Zn 7%, water content 30%). The filtrate is returned to the slurry preparation process for recycling.

[0029] (5) Washing of leaching residue The leaching residue was washed with water at 60℃ and a liquid-to-solid ratio of L:S = 3:1. After washing, the residue was filtered to obtain a washing liquid and a washing residue containing 3% zinc and 28% water. The washing liquid was subjected to lime-based zinc precipitation and solid-liquid separation to obtain a zinc-precipitated liquid containing 0.4 g / L zinc, which was returned for subsequent washing of the leaching residue.

[0030] Lime is added to the washing liquid. The amount of lime added is determined according to the zinc concentration in the washing liquid. The lime is added at a ratio of 1.5 g of lime per cubic meter of washing liquid for every 1 g / L of zinc. After stirring and reacting, the solid and liquid are separated to obtain the zinc-precipitated liquid.

[0031] In this embodiment, the overall zinc recovery rate is 93%, the iron content in the neutral supernatant is 12 mg / L, and the zinc content in the washing residue is 3%. The hydrogen peroxide consumption per leaching tank is 58.5 L, which is precisely matched with the iron load, reducing reagent costs by approximately 48% compared to the full oxidation solution.

[0032] This embodiment achieves a two-stage synergistic leaching process of neutral and acidic leaching, ensuring efficient zinc recovery while removing iron. In step (2), the neutral leaching stage controls the endpoint pH to 5.2-5.4, allowing iron and silicon impurities to fully precipitate into the concentrated underflow, while zinc remains stably in the solution as zinc sulfate. In step (3), the second-stage acid leaching stage further leaches the residual zinc from the concentrated underflow under low acid conditions. With the synergistic effect of the two stages, the overall zinc recovery rate is ≥93%, and the final washing residue in step (5) contains 3% zinc.

[0033] Example 2 (1) Mixing the pulp Zinc oxide concentrate (containing 25.4% zinc and 1.8% sulfides) and water were added to a mixing tank at a liquid-to-solid ratio of L:S=4:1. The mixture was then prepared by mixing at 35°C and a mechanical stirring speed of 80 r / min to obtain a slurry.

[0034] (2) Neutral leaching The slurry was pumped into the leaching tank, with the stirring speed maintained at 80 r / min. The temperature was raised to 65℃, and the pH was adjusted to 2.5 using waste electrolytic electrolyte with a H2SO4 concentration of 130 g / L. The iron concentration in the slurry was measured to be 0.8 g / L (≤1 g / L), and no hydrogen peroxide was added. The leaching time was controlled at 2.5 h. As alkaline minerals such as zinc oxide in the slurry continuously consumed acid, the pH gradually rose to 5.4. At this point, the iron concentration was measured to be 15 mg / L, at which point leaching was stopped, resulting in a neutral leached slurry. The neutral leached slurry flowed by gravity to the thickening tank, where a flocculant with a solubility of 1.5‰ (the same flocculant as in Example 1) was added. After sedimentation and separation, a neutral supernatant (Zn 118 g / L, Fe 15 mg / L, pH 5.4, solids content 1.6%) and a thickened underflow were obtained.

[0035] (3) Two-stage acid leaching The thickened underflow was pumped into the acid leaching tank, stirred at 85 r / min, heated to 65℃, and acidified to pH 3.0 using waste electrolytic solution. The reaction was carried out for 4 h to obtain the acid leaching slurry.

[0036] (4) Pressure filtration separation The acid-leached slurry is pumped to a filter press for filtration separation, yielding a filtrate (Zn 90 g / L, Fe 400 mg / L, pH 3.2) and a leaching residue (Zn 5.5%, water content 30%). The filtrate is returned to the slurry preparation process for recycling.

[0037] (5) Washing of leaching residue The leaching residue was washed with water at 55℃ and a liquid-to-solid ratio of L:S = 4:1. After washing, it was filtered under pressure to obtain a washing residue containing 2.5% zinc and 28% water. The washing liquid was subjected to lime-based zinc precipitation and solid-liquid separation to obtain a zinc-precipitated liquid containing 0.2 g / L zinc, which was returned for subsequent washing.

[0038] In this embodiment, the overall zinc recovery rate was 94%, the iron content in the neutral supernatant was 15 mg / L, and the zinc content in the washing residue was 2.5%. Comparative Example The same zinc oxide concentrate and process conditions as in Example 1 were used, but the amount of hydrogen peroxide added and the reaction time were not matched, as detailed below: Zinc oxide concentrate and water were added to a mixing tank at a liquid-solid ratio of L:S=3:1, and the mixture was prepared at 40℃ and mechanical stirring speed of 85 r / min to obtain a slurry.

[0039] The slurry is pumped to the leaching tank (leaching tank volume: 90m³). 3 The stirring speed was maintained at 85 r / min, and the temperature was raised to 60℃. The pH was adjusted to 1.5 using 98% concentrated sulfuric acid. The iron concentration in the slurry was measured to be 1.65 g / L (>1 g / L). Using 1 g / L as a baseline, the excess was 0.65 g / L (i.e., 650 mg / L), calculated at 0.001 L / (m³). 3 Based on the ratio of ·mg / L, 58.5 L of hydrogen peroxide (H2O2 concentration 27.5%) was added to each leaching tank.

[0040] However, the reaction time was only controlled to 0.5 h. Hydrogen peroxide rapidly decomposes Fe under acidic conditions. 2+ Oxidized to Fe 3+ A large amount of Fe is generated within 0.5 h. 3+ However, since the basic oxide (ZnO) requires a certain amount of time to consume acid, the pH only rose to about 3.0 after 0.5 h, which did not yet reach the Fe... 3+ The optimal pH range for complete hydrolysis and precipitation is 5.2-5.4. At this pH, the Fe content in the slurry is...3+ The concentration was extremely high, but it did not precipitate effectively and a large amount remained in the solution.

[0041] To force the target pH to be reached, an alkaline solution was subsequently used to rapidly adjust the pH from 3.0 to 5.4. This rapid pH increase resulted in a large amount of Fe... 3+ Instant hydrolysis results in ferric hydroxide that does not have enough time to fully flocculate and grow, forming extremely fine colloidal particles that are suspended in the slurry and are difficult to settle.

[0042] After the reaction, solid-liquid separation was performed to obtain a neutral supernatant (Zn 80 g / L, Fe 200 mg / L, pH 5.4, solid content 5%). Due to the severely excessive iron content and extremely high solid content, the liquid-solid separation of the neutral supernatant was severely deteriorated, and it needed to be returned to the process for reprocessing.

[0043] The concentrated underflow was subjected to two-stage acid leaching and pressure filtration to obtain leaching residue (Zn 10.8%, water content 36%). The leaching residue was washed with water at 60℃ and a liquid-to-solid ratio of 3:1, and then filtered to obtain washed residue (Zn 5.5%, water content 35%).

[0044] When the iron concentration was >1 g / L, although hydrogen peroxide was added in the correct proportion, the reaction time was only 0.5 h, leading to two problems: first, the alkaline oxides did not have enough time to consume the acid, and the pH failed to rise naturally to 5.2-5.4; second, the Fe... 3+ The precipitation could not be fully hydrolyzed; secondly, the subsequent rapid artificial adjustment of alkali caused a pH jump, and Fe... 3+ Instantaneous hydrolysis produces fine-particle colloids. Both factors contribute to incomplete iron removal and deterioration of liquid-solid separation. If the reaction time is controlled according to Example 1, the Fe produced by hydrogen peroxide... 3+ The amount of Fe was matched with the rate of gradual increase in pH. 3+ It can hydrolyze, flocculate, and grow simultaneously as the pH gradually increases, forming large particles that are easy to settle.

[0045] 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 two-stage leaching method for zinc oxide concentrate to achieve efficient separation of iron and zinc, characterized in that: Includes the following steps: (1) Slurry preparation: Zinc oxide concentrate is slurried with slurry preparation solution under stirring at 30-40℃ to obtain slurry; (2) Neutral leaching: The slurry is heated to 55-65℃ under stirring, and acidified to pH 0.5-3.0 using acidic solution. When the pH reaches the above range, hydrogen peroxide is added according to the iron concentration in the slurry: no hydrogen peroxide is added when the iron concentration is ≤1g / L, and when the iron concentration is >1g / L, 0.001L of hydrogen peroxide is added per cubic meter of slurry for every 0.001g / L increase in iron concentration, based on 1g / L. The reaction continues for 2-3 hours until the pH value at the end of the reaction is 5.2-5.4 and the iron concentration in the slurry is ≤1g / L. Leaching is then stopped to obtain neutral leaching slurry. Solid-liquid separation is then carried out to obtain neutral supernatant and thick underflow. (3) Second stage acid leaching: The thickened underflow is heated to 55-65℃ under stirring, and the pH is adjusted to 1.5-4.0 with acidic solution to obtain acid leaching slurry; (4) Pressure filtration separation: The acid leaching slurry is subjected to solid-liquid separation to obtain the filter press liquid and leaching residue; (5) Leaching residue washing: The leaching residue is washed with washing liquid at a temperature of 50-60℃. After washing, it is filtered to obtain washing residue and washing liquid.

2. The two-stage leaching method for zinc oxide concentrate to achieve efficient separation of iron and zinc according to claim 1, characterized in that: The liquid-solid ratio of the slurry to the zinc oxide concentrate in step (1) is L:S=3-4:

1.

3. The two-stage leaching method for zinc oxide concentrate to achieve efficient separation of iron and zinc according to claim 1, characterized in that: In step (5), the liquid-to-solid ratio of the washing liquid and the leaching residue is L:S=3-4:

1.

4. A two-stage leaching method for zinc oxide concentrate to achieve efficient iron-zinc separation according to claim 1 or 2, characterized in that: In step (1), the slurry is selected as water or the filtrate from step (4).

5. A two-stage leaching method for zinc oxide concentrate to achieve efficient iron-zinc separation according to claim 1 or 3, characterized in that: The washing liquid in step (5) is water or zinc precipitation liquid. The zinc precipitation liquid is obtained by washing the leaching residue with water to obtain the washing residue liquid, and then performing lime alkaline zinc precipitation and solid-liquid separation on the washing residue liquid to finally obtain a solution with a zinc content ≤0.5 g / L.

6. A two-stage leaching method for zinc oxide concentrate to achieve efficient iron-zinc separation according to any one of claims 1, 2, or 3, characterized in that: The acidic liquid mentioned in steps (2) and (3) is selected from H2SO4 with a concentration of 98% or waste electrolytic liquid with an H2SO4 concentration of 100-130 g / L.

7. A two-stage leaching method for zinc oxide concentrate to achieve efficient iron-zinc separation according to any one of claims 1, 2, or 3, characterized in that: In step (2), the solid-liquid separation method includes: allowing the neutral leaching slurry to flow by gravity to a thickening tank, adding flocculant to it, and obtaining a neutral supernatant and a thickened underflow after sedimentation separation.

8. The two-stage leaching method for zinc oxide concentrate to achieve efficient separation of iron and zinc according to claim 7, characterized in that: The flocculant is added at a rate of 0.01 m³ per cubic meter of slurry. 3 The flocculant solution is added in a specific ratio; the concentration of the flocculant solution is 1.5‰.

9. A two-stage leaching method for zinc oxide concentrate to achieve efficient separation of iron and zinc according to claim 7 or 8, characterized in that: The flocculant has a molecular weight ≥12 million, intrinsic viscosity ≤800mL / g, degree of hydrolysis <3%, dissolution rate ≤30min, solid content ≥93%, and Cl ≤0.05%.

10. A two-stage leaching method for zinc oxide concentrate to achieve efficient iron-zinc separation according to any one of claims 1, 2, or 3, characterized in that: The stirring described in steps (1), (2) and (3) is mechanical stirring, and the stirring speed is 80-85 r / min.