Hematite seed crystal optimized pressure leaching iron removal process and seed crystal preparation method

Abstract

According to the pressure leaching iron removal process based on hematite seed crystal optimization and the seed crystal preparation method, the crystallinity and the purity of hematite are remarkably improved by regulating and controlling the temperature, the pressure, the pH and the liquid-solid ratio and combining internal source seed crystal acid pickling purification. The process has the iron removal rate of more than or equal to 95%, is high in nickel and copper recovery rate, and is suitable for an industrial hydrometallurgy system.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, specifically to a pressure leaching process for iron removal and a method for preparing hematite seed crystals, which is particularly suitable for the efficient removal and recovery of iron in the process of processing non-ferrous metal minerals such as nickel and cobalt. Background Technology

[0002] In hydrometallurgical processes, iron is one of the most common impurity elements, and its efficient separation is crucial for ensuring subsequent metal purification and recovery. The hematite method (Fe2O3) is currently one of the mainstream iron removal technologies, precipitating iron as hematite under high temperature and pressure conditions. However, this process still has significant problems in practical industrial applications: First, the hematite produced under traditional process conditions has poor crystallinity and incomplete crystal form, with the iron content in the seed crystals generally only 10%-15%, making it difficult to effectively guide the selective precipitation of iron, resulting in low iron removal efficiency; second, the reaction system's pH value and chloride ion (Cl) are also problematic. - If key parameters such as concentration are not strictly controlled, impurities such as goethite, ferrous sulfate, and amorphous ferric hydroxide are easily produced as byproducts. This not only reduces the purity of iron precipitation but also increases the difficulty of subsequent solid-liquid separation and affects the filtration performance of the slag. In addition, existing technologies mostly rely on the addition of seed crystals, which not only increases the cost of raw materials but also introduces the risk of external impurities, making it difficult to guarantee the complexity and stability of operation.

[0003] Therefore, there is an urgent need in this field for a new pressurized leaching process for iron removal that can generate high-purity, high-crystallinity hematite seed crystals in situ and achieve efficient iron precipitation and impurity suppression, so as to improve the overall metal recovery rate, reduce processing costs and promote the development of green smelting technology. Summary of the Invention

[0004] The existing hydrometallurgical hematite removal process has the following drawbacks: (1) It requires the addition of hematite seed crystals from external sources, which is costly and complicated to operate; (2) The hematite seed crystals that spontaneously form in the high-pressure leaching environment have poor crystallinity and low purity (the iron content is usually only 10-15%), which cannot effectively promote the precipitation of the hematite phase. (3) Improper control of leaching conditions can easily generate a large amount of byproducts such as ferrous sulfate and goethite, leading to difficulties in subsequent solid-liquid separation, poor slag filtration performance, and loss of valuable metals such as nickel and copper. Based on this, the present invention aims to solve the above problems and provide a pressure leaching process and seed preparation method for achieving efficient and economical iron removal by endogenously generating and optimizing hematite seed crystals.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: In a first aspect, the present invention provides a pressure leaching process for removing iron from hematite seeds, comprising the following steps: (1) First-stage pressure leaching: The iron-containing raw material is reacted for no less than 5 hours under the conditions of temperature 180-200℃, pressure 0.70-0.85MPa, pH value 2.5-3.0 and liquid-solid ratio 9:1-10:1 to obtain a first-stage leaching residue; (2) Seed preparation: The first leaching residue is acid washed and dried to obtain hematite seed crystals with an iron content ≥70%; (3) Second-stage pressure leaching: Add the hematite seed crystals obtained in step (2) to the leaching system. The amount added is 1-3% of the total mass of the system. The reaction is carried out for no less than 4 hours under the conditions of temperature 170-190℃, pressure 0.70-0.85MPa, and pH value 2.5-3.0.

[0006] Preferably, the pickling in step (2) uses dilute sulfuric acid with a concentration of 5-10% and the pickling time is 30-60 minutes.

[0007] Preferably, the Cl⁻ concentration in the leachate is controlled to be ≤0.02 g / L, which is preferably achieved through ion exchange resin pretreatment.

[0008] Preferably, after adding the seed crystal in step (3), the generation of by-products can be suppressed, reducing the amount of jaundice by ≥80% and / or the amount of goethite by ≥70%.

[0009] Secondly, the present invention provides a hematite seed crystal for the above-mentioned iron removal process. The seed crystal is prepared by a method including the following steps: acid washing and drying of a section of pressure leaching residue, and the resulting seed crystal has an iron content of ≥70% and a crystallinity of ≥90%.

[0010] Preferably, the pickling uses dilute sulfuric acid with a concentration of 5-10% and the pickling time is 30-60 minutes.

[0011] Preferably, the iron content in the pressure leaching residue is ≥12%.

[0012] Thirdly, the present invention provides a method for preparing hematite seed crystals, comprising the following steps: Obtain a section of pressurized leaching residue; The leaching residue is acid-washed with 5-10% dilute sulfuric acid for 30-60 minutes; dried to obtain hematite seed crystals with an iron content ≥70% and a crystallinity ≥90%.

[0013] Compared with the prior art, the present invention has the following significant advantages: High-efficiency utilization of endogenous seed crystals has been achieved: high-performance seed crystals are prepared in situ by simple acid washing and purification of a leaching residue, completely eliminating the dependence on expensive exogenous seed crystals and significantly reducing production costs and process complexity.

[0014] Significantly improved iron removal efficiency and metal recovery rate: The optimized high-purity (Fe≥70%) and high-crystallinity (≥90%) seed crystals greatly promoted the heterogeneous nucleation and growth of the hematite phase, enabling the iron removal rate to stably reach ≥95%, and effectively reducing impurity entrainment, thereby increasing the leaching recovery rates of nickel and copper to ≥95% and ≥90%, respectively.

[0015] Side reactions were effectively suppressed: By strictly controlling the Cl⁻ concentration and combining it with the addition of highly efficient seed crystals, the formation of unfavorable byproducts such as ferrous sulfate and goethite was suppressed thermodynamically and kinetically, with their formation reduced by more than 80% and 70% respectively, thereby improving the properties of the leaching residue.

[0016] Improved subsequent processing performance: The generated hematite slag has large crystals and high purity, which greatly improves the solid-liquid separation performance, increases the filtration rate of leaching residue by about 40%, and reduces overall energy consumption by about 15% due to optimized reaction conditions and reduced slag volume. Attached Figure Description

[0017] Figure 1 Flowchart of hematite seed crystal preparation process; Figure 2 Comparison of hematite crystallinity at different temperatures; Figure 3 Comparison chart of iron removal rates between optimized and traditional processes; Figure 4 Comparison of XRD patterns before (a) and after (b) seed crystal addition (significant enhancement of hematite characteristic peaks). Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described in conjunction with the preferred embodiments and comparative examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0020] The detection method used in this invention is as follows: Iron, nickel, and copper content: determined by inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0021] Phase analysis: X-ray diffraction (XRD) was used for analysis, and the relative crystallinity and phase content of hematite were calculated using Jade software.

[0022] Filtration rate: The time required to filter a fixed volume of slurry under a vacuum of 0.4 MPa was measured, and the rate was calculated.

[0023] Example 1 (1) First-stage pressure leaching: Take 100g of a nickel concentrate (composition: Fe 12.5%, Ni 8.2%, Cu 4.1%) and place it in a 1L high-pressure reactor. Add 900ml of sulfuric acid leaching solution (liquid-solid ratio 9:1). Adjust the initial pH to 2.8 with concentrated sulfuric acid. Raise the temperature to 190℃ and maintain the system pressure at 0.80MPa. Stir the reaction for 6 hours.

[0024] (2) Seed crystal preparation: After the reaction, a leaching residue was obtained by filtration. The leaching residue (Fe content of 35%) was placed in an 8% dilute sulfuric acid solution and acid-washed at 80°C for 45 minutes with a liquid-to-solid ratio of 5:1. After acid washing, it was filtered, washed with deionized water until neutral, and dried at 105°C for 2 hours to obtain hematite seed crystals. XRD analysis showed that the main phase of the seed crystals was hematite, with an Fe content of 72% and a crystallinity of 92%.

[0025] (3) Two-stage pressure leaching: Take another 100g of the same nickel concentrate, prepare a slurry with a liquid-to-solid ratio of 9:1 and place it in a high-pressure reactor, and adjust the pH to 2.7. Add 2g of the seed crystals prepared in step (2) (the amount added is 2% of the total mass of the system). React at a temperature of 180℃ and a pressure of 0.75MPa for 5 hours.

[0026] (4) Results Detection: After the reaction, the slurry had excellent filtration performance. The leachate and the final leaching residue were analyzed, and the results were as follows: iron removal rate 96.5%, nickel leaching rate 95.8%, and copper leaching rate 91.2%. XRD analysis showed that hematite content in the leaching residue accounted for more than 85%, while goethite and ferrous sulfate were not detected.

[0027] Example 2 The difference between this embodiment and embodiment 1 is that the temperature of the first stage of pressure leaching in step (1) is adjusted to 180°C, while the rest of the steps and parameters are exactly the same.

[0028] Results: The final hematite seed crystals had an Fe content of 70% and a crystallinity of 88%. After two-stage leaching, the iron removal rate was 94.2%, while the nickel and copper leaching rates decreased slightly but still reached 94.5% and 90.1%, respectively. The results indicate that the process of this invention still has excellent performance within the specified parameter range.

[0029] Example 3 The difference between this embodiment and embodiment 1 is that in step (2) seed preparation, the concentration of dilute sulfuric acid used for acid washing is 5%, and the acid washing time is 60 minutes. The remaining steps and parameters are exactly the same.

[0030] Results showed that the final seed crystals had an Fe content of 71% and a crystallinity of 90%. After two-stage leaching, the iron removal rate was 95.1%, proving that the present invention can effectively purify seed crystals within the specified acid washing concentration range.

[0031] Example 4 The difference between this embodiment and embodiment 1 is that in step (3) the amount of seed crystals added is adjusted to 1% (1g) in the two-stage pressure leaching, while the other steps and parameters are exactly the same.

[0032] Results showed that after two-stage leaching, the iron removal rate was 93.8%. This demonstrates that even with the minimum seed crystal addition (1%), the process of this invention can still achieve highly efficient iron removal.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that no seed crystals are added in the second stage of pressure leaching in step (3), while the remaining steps and parameters are exactly the same.

[0034] Results: The slurry after reaction was viscous and difficult to filter. The final iron removal rate was only 85.5%. XRD analysis showed that, in addition to hematite, the leaching residue contained approximately 15% goethite. The leaching rates of nickel and copper were also significantly reduced. This comparison demonstrates that adding the high-quality endogenous seed crystals prepared in this invention is crucial for improving iron removal efficiency and suppressing byproduct formation.

[0035] Comparative Example 2 This comparative example simulates a traditional process, using commercially available ordinary hematite powder (Fe content 65%, crystallinity <80%) as seed crystals. Referring to step (3) of Example 1, 2% of this externally sourced seed crystals were added for two-stage pressure leaching, and the reaction conditions were exactly the same as in Example 1.

[0036] Results showed that the final iron removal rate was 82.3%, which is significantly lower than that of the endogenous seed crystals (96.5%) prepared using the method of this invention. This indicates that not all hematite is suitable as seed crystals, and the high-purity, high-crystallinity endogenous seed crystals prepared by this invention through a specific acid washing process have irreplaceable and excellent catalytic induction properties.

[0037] In summary, this invention successfully prepared high-performance endogenous hematite seed crystals by optimizing the first-stage leaching conditions and combining them with an acid washing purification process. Applying these seed crystals to the second-stage leaching process significantly improved iron removal and valuable metal recovery rates, effectively suppressed the formation of impurity crystals, and improved operating conditions. This invention features a stable process, low cost, and significant effects, demonstrating promising prospects for industrial application.

Claims

1. A pressure leaching process for iron removal based on hematite seed crystals, characterized in that, Includes the following steps: (1) First-stage pressure leaching: under the conditions of temperature 180-200℃, pressure 0.70-0.85MPa, pH value 2.5-3.0 and liquid-solid ratio 9:1-10:1, the reaction shall be carried out for no less than 5 hours to obtain a first-stage leaching residue; (2) Seed preparation: The first leaching residue is acid washed and dried to obtain hematite seed crystals with an iron content ≥70%; (3) Second-stage pressure leaching: Add the hematite seed crystals obtained in step (2) to the leaching system. The amount added is 1-3% of the total mass of the system. The reaction is carried out for no less than 4 hours under the conditions of temperature 170-190℃, pressure 0.70-0.85MPa, and pH value 2.5-3.

0.

2. The pressure leaching iron removal process according to claim 1, characterized in that, The pickling in step (2) uses dilute sulfuric acid with a concentration of 5-10% and the pickling time is 30-60 minutes.

3. The pressure leaching iron removal process according to claim 1, characterized in that, Cl in the leachate - The concentration should be controlled at ≤0.02g / L.

4. The pressure leaching iron removal process according to claim 1, characterized in that, After the seed crystals are added, the amount of jaundice is reduced by ≥80%, and the amount of goethite is reduced by ≥70%.

5. A hematite seed crystal for use in the iron removal process of claim 1, characterized in that, Prepared by a method including the following steps: 1) Acid wash the pressure leaching residue in a section. The acid wash solution is 5-10% dilute sulfuric acid, and the acid wash time is 30-60 minutes. 2) Dry the slag after acid washing to obtain hematite seed crystals with a crystallinity ≥90% and an iron content ≥70%.

6. The hematite seed crystal according to claim 5, characterized in that, The iron content in the pressure leaching residue is ≥12%.

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