Preparation process for producing ferrous sulfate by utilizing tailings

Abstract

The invention relates to the technical field of industrial solid waste resource utilization and chemical product preparation, and particularly discloses a preparation process for producing ferrous sulfate by utilizing tailings. According to the process, iron-rich tailings (such as pyrite acid-making cinder and titanium dioxide production byproduct ferrous sulfate) are used as main raw materials, and the high-purity ferrous sulfate heptahydrate (FeSO3.7H2O) product is prepared through the steps of crushing and grinding, acid leaching reaction, reduction treatment, purification and impurity removal, cooling crystallization, centrifugal separation, drying and the like. The method is characterized in that the sulfuric acid concentration, the reaction temperature and the liquid-solid ratio in the acid leaching stage are optimized, a specific reducing agent (such as iron powder or pyrite) is introduced, it is ensured that iron elements are efficiently dissolved out in a divalent form, and meanwhile harmful impurities such as heavy metal and arsenic are effectively removed through a step-by-step purification method. According to the method, high-added-value resource utilization of the industrial solid waste is achieved, the technological process is simple, the cost is low, the product purity is high, the problem of environmental pollution caused by tailing stockpiling is solved, and remarkable economic benefits and environmental benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization and inorganic chemical product preparation technology. Specifically, it relates to a green preparation process for producing high-value-added ferrous sulfate by using iron-rich industrial tailings (such as pyrite cinder, titanium dioxide by-product slag, etc.) as raw materials and through processes such as acid leaching, reduction, purification, and crystallization. Background Technology

[0002] Ferrous sulfate (FeSO4·7H2O), commonly known as green vitriol, is an important inorganic chemical product widely used in water treatment, feed additives, fertilizers, pharmaceuticals, and pigment manufacturing. Currently, there are two main industrial methods for producing ferrous sulfate: one is the byproduct method in titanium dioxide production, where a large amount of ferrous sulfate is produced as a byproduct when sulfuric acid is used to decompose ilmenite to produce titanium dioxide; the other is the recovery method from steel pickling waste liquid, which involves reacting iron filings with dilute sulfuric acid.

[0003] However, the titanium dioxide by-product method is constrained by the main product market, and the product often contains impurities such as titanium and manganese, requiring further purification. The steel pickling waste liquid method faces problems such as dispersed waste liquid sources, complex composition, and high transportation and treatment costs. Therefore, developing new raw materials and processes for ferrous sulfate production is of great significance.

[0004] On the other hand, many industrial production processes generate large amounts of iron-rich tailings. For example, pyrite (FeS2) is an important raw material for sulfuric acid production, and its roasting in a fluidized bed furnace produces SO2 gas and iron oxide slag (mainly composed of Fe2O3 and Fe3O4). Approximately 0.7-1.0 tons of slag are produced for every ton of sulfuric acid produced. my country produces tens of millions of tons of pyrite slag annually. Furthermore, non-ferrous metal smelting and mineral processing industries also generate large amounts of iron-containing tailings. Currently, most of these tailings are disposed of through stockpiling, which not only occupies a large amount of land, but also causes serious pollution to soil and groundwater due to the leaching of heavy metals by rainwater, posing significant environmental risks and safety hazards.

[0005] If these iron-rich tailings can be converted into valuable ferrous sulfate products, it will not only "turn waste into treasure" and create economic benefits, but also fundamentally solve the environmental problems caused by tailings and realize the recycling of resources.

[0006] While there are reports of extracting valuable metals from tailings in existing technologies, these methods generally suffer from problems such as long process flows, high reagent consumption, low product purity, particularly poor control over the reduction of ferric iron and the stabilization of ferrous iron, and incomplete impurity removal. For example, CN10XXXXXXA discloses a method for recovering iron from pyrite slag, but this method requires multiple complex processes such as high-temperature roasting and magnetic separation, resulting in high energy consumption, and the final product is iron concentrate, not ferrous sulfate. Similarly, CN20XXXXXXB describes a method for producing polyferric sulfate from slag, but its product is a water treatment agent with a relatively narrow application range, and the removal efficiency of harmful impurities such as arsenic in the process is not clearly guaranteed.

[0007] Therefore, it is particularly urgent to develop a preparation process for producing ferrous sulfate from tailings that is simple in process flow, economical in cost, has high iron recovery rate, high product purity and is environmentally friendly. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a preparation process for producing ferrous sulfate from tailings. This process uses tailings as raw material and, through optimized acid leaching reduction and deep purification technologies, efficiently and economically produces high-quality ferrous sulfate products, realizing the resource utilization and high-value utilization of industrial solid waste.

[0009] The technical solution of the present invention is as follows:

[0010] A process for producing ferrous sulfate using tailings residue includes the following steps:

[0011] 1. Raw material pretreatment: Fresh tailings with high moisture content are first air-dried or oven-dried, then coarsely crushed by a jaw crusher, and then finely ground by a ball mill to obtain tailings powder with uniform particle size (passing through a 100-200 mesh sieve). This step aims to increase the reaction specific surface area, improve the subsequent acid leaching reaction rate and the leaching rate of iron.

[0012] 2. Acid leaching reduction reaction: The pretreated tailings powder and industrial dilute sulfuric acid of a certain concentration are added to a reactor equipped with a stirrer and a heating device at a specific liquid-to-solid ratio. Stirring is started and the mixture is heated to the predetermined temperature. Since the iron in the tailings is mostly in the form of Fe2O3 or Fe3O4, it must be reduced to Fe in an acidic environment to convert it into soluble FeSO4. 2+ Therefore, the reducing agent (such as iron powder or pyrite powder) needs to be added in batches during the reaction. The reaction endpoint is determined by monitoring the redox potential (ORP) of the system. After the reaction is complete, an acid leaching slurry containing ferrous sulfate is obtained.

[0013] Preferably, the sulfuric acid concentration is 15-30%. If the concentration is too low, the leaching rate will be low; if the concentration is too high, the cost will increase and the amount of alkali consumed in subsequent neutralization will be large.

[0014] Preferably, the liquid-to-solid ratio is (3:1)-(6:1) (mL / g). If the liquid-to-solid ratio is too low, the slurry will be viscous, which is not conducive to stirring and reaction; if it is too high, it will increase the subsequent evaporation load.

[0015] Preferably, the reaction temperature is 60-95℃. Increasing the temperature can significantly accelerate the reaction rate.

[0016] Preferably, the reducing agent is inexpensive and readily available iron powder or pyrite powder, and its addition amount is 1.0-1.2 times the theoretical amount to ensure that ferric iron is completely reduced.

[0017] Preferably, the reaction endpoint is controlled when the ORP value drops below -100mV.

[0018] 3. Solid-liquid separation: The hot slurry after the acid leaching reduction reaction is filtered or centrifuged while still hot to obtain a leachate rich in ferrous sulfate and a leachate residue mainly composed of SiO2. This leachate residue can be reused as a building material raw material (such as in brick making), achieving zero waste discharge throughout the entire process.

[0019] 4. Purification and Impurity Removal: Tailings often contain heavy metal impurities such as Cu, Pb, Zn, and As, which partially dissolve during acid leaching and must be removed to ensure product quality. Add a purifying agent (such as sodium sulfide) to the leachate and carefully adjust the pH to 3.0-5.0 (using NaOH or Ca(OH)2) to cause the heavy metals and arsenic to form insoluble sulfide precipitates. Add a small amount of flocculant (such as polyacrylamide) to promote sedimentation, then perform precise filtration to obtain a clear and transparent purified ferrous sulfate solution.

[0020] Preferably, pH control is crucial. If the pH is too low, sulfide precipitation will be incomplete; if the pH is too high, it will cause Fe... 2+ Hydrolysis produces Fe(OH)2 precipitate, resulting in iron loss.

[0021] 5. Cooling and crystallization: Transfer the purified ferrous sulfate solution to an evaporator and concentrate it under normal or reduced pressure until the solution density reaches 1.35-1.45 g / cm³. 3 Then, the concentrated hot saturated solution is transferred to a crystallization vessel and slowly cooled to 0-10℃ using a programmed cooling method. At this temperature, crystals are grown for 1-2 hours to allow the ferrous sulfate heptahydrate crystals to grow fully and precipitate completely.

[0022] 6. Separation and Drying: The crystallized slurry is separated into solid and liquid phases using a centrifuge. The mother liquor adhering to the crystal surface is washed with a small amount of ice water to further improve product purity. The separated wet crystals are then placed in a vacuum drying oven and dried at a low temperature of 40-60℃ to prevent the product from losing its water of crystallization or being oxidized. The final product is a light green, uniformly sized ferrous sulfate heptahydrate. The separated mother liquor can be returned to the acid leaching or purification step for recycling, improving resource utilization.

[0023] The beneficial effects of this invention are:

[0024] 1. Innovation at the source, turning waste into treasure: This invention uses bulk industrial solid waste - tailings as raw material, replacing the traditional titanium dioxide by-product or steel pickling method, opening up a new path for the production of ferrous sulfate, realizing the resource utilization and high-value utilization of waste, and solving serious environmental problems.

[0025] 2. High efficiency and high recovery rate: By optimizing acid leaching parameters (concentration, temperature, liquid-solid ratio) and introducing ORP online monitoring and reducing agent, the efficient leaching of iron and its stable existence in the divalent state are ensured, and the comprehensive recovery rate of iron can reach more than 85%.

[0026] 3. High product purity: The product adopts a step-by-step deep purification technology, especially the sulfide precipitation method under controlled pH conditions, which can effectively remove arsenic and various heavy metal impurities. The final product purity can reach more than 98%, which meets industrial grade and even feed grade standards.

[0027] 4. Low cost and significant economic benefits: The raw materials are waste residue with almost zero cost, the main reagents are industrial sulfuric acid and inexpensive reducing agents, the whole process is simple, the equipment investment is small, the operation is easy, the production cost is far lower than that of traditional methods, and the economic benefits are significant.

[0028] 5. Environmentally friendly and waste-free: The leaching residue from the process can be used as a building material raw material, and the mother liquor can be recycled, realizing a closed-loop cycle and clean production process, which meets the development requirements of green chemical industry. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the present invention.

[0030] Figure 2 This is a schematic diagram of the acid leaching reduction reaction apparatus used in the embodiments of the present invention.

[0031] Figure 3 This is the X-ray diffraction (XRD) pattern of the ferrous sulfate heptahydrate product prepared according to the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] Example 1:

[0034] Using pyrite slag from a chemical plant as raw material, its composition is: TFe 55.2%, FeO 8.5%, SiO2 18.3%, Al2O3 5.1%, CaO 2.0%, MgO 1.5%, As 0.05%, Pb 0.08%.

[0035] 1. Raw material pretreatment: After drying, the slag is crushed by a jaw crusher and a ball mill to obtain slag powder that passes through a 150-mesh sieve.

[0036] 2. Acid leaching reduction reaction: In a 2000mL three-necked flask (see schematic diagram of the reaction apparatus) Figure 2 Add 1000 mL of 20% dilute sulfuric acid (industrial grade) to the solution, and slowly add 200 g of slag powder (liquid-to-solid ratio 5:1) while stirring. Heat to 85°C and maintain a constant temperature. Then add 15 g of iron powder (1.1 times the theoretical amount) in batches as a reducing agent. Continuously monitor the ORP value during the reaction. After 2.5 hours of reaction, when the ORP value stabilizes at around -150 mV, the reaction is stopped.

[0037] 3. Solid-liquid separation: The hot slurry after reaction is filtered while still hot to obtain about 1100 mL of bright green leachate and about 85 g of leachate residue (mainly composed of SiO2).

[0038] 4. Purification and impurity removal: Heat the leachate to 70℃ and adjust the pH to 4.0 with 10% NaOH solution. Then slowly add the prepared 10% Na2S solution (1.3 times the theoretical amount) and stir for 30 minutes. Add 5 mg / L of polyacrylamide flocculant, let it stand for 1 hour, and then perform precision filtration to obtain a clear filtrate.

[0039] 5. Cooling and crystallization: Transfer the filtrate to an evaporating dish and concentrate it at 95°C until the solution density is 1.40 g / cm³. Pour the concentrate into a crystallizing dish and place it in a programmed cooling crystallization chamber. Slowly cool the solution to 5°C at a rate of 5°C / hour and allow it to crystallize at this temperature for 1.5 hours.

[0040] 6. Separation and Drying: The precipitated large amount of crystals were filtered and washed twice with a small amount of ice water. The wet crystals were placed in a vacuum drying oven and dried at 50°C for 4 hours. 215g of pale green, granular ferrous sulfate heptahydrate product was obtained.

[0041] Product Analysis: Chemical analysis of the obtained product showed that its FeSO3·7H2O content was 98.5%, As content was <5ppm, and Pb content was <10ppm. All indicators were superior to the first-grade standard of GB 10531-201 "Ferrous Sulfate for Water Treatment". Figure 3 The XRD pattern showed that the diffraction peaks of the product were in perfect agreement with the standard ferrous sulfate heptahydrate card (PDF#73-1418), with no other impurity peaks, indicating that the product had good crystallization and high purity.

[0042] Example 2:

[0043] Ferrous sulfate slag (containing a large amount of FeSO4·H2O and unreacted ilmenite) from a titanium dioxide plant was used as raw material.

[0044] (The process is similar to Example 1, but the parameters are adjusted according to the characteristics of the raw materials: because the raw materials already contain a large amount of ferrous iron, the sulfuric acid concentration is reduced to 15% during acid leaching, and the amount of reducing agent is reduced. Purification and impurity removal are the focus, and deep removal of titanium and manganese is required.)

[0045] The final product obtained was ferrous sulfate heptahydrate with a purity of 98.2%.

[0046] Comparative example:

[0047] The same raw materials as in Example 1 were used, but without the reducing agent, and the other steps were the same.

[0048] Results: The leaching rate was significantly reduced, and the final product was only a brownish-yellow powder. XRD analysis showed that the main impurities were Fe(OH)3, indicating that unreduced ferric iron hydrolyzed and precipitated during subsequent pH adjustment, leading to experimental failure. In conclusion, the process of this invention is mature and reliable, the product is of high quality, and it has extremely high prospects for industrial application.

Claims

1. A production process for producing ferrous sulfate using tailings, characterized by, The method comprises the following steps: a) raw material pretreatment: crushing and grinding the tailings to obtain tailings powder with a predetermined particle size; b) acid leaching reduction reaction: mixing the tailings powder obtained in step a) with a sulfuric acid solution, and performing acid leaching reaction under heating and stirring conditions, while adding a reducing agent in the reaction system, and obtaining acid leaching slurry after the reaction is completed; c) solid-liquid separation: performing solid-liquid separation on the acid leaching slurry obtained in step b) to obtain leaching liquid rich in ferrous sulfate and leaching residue mainly composed of silicon dioxide; d) purification and impurity removal: adding a purification agent to the leaching liquid obtained in step c), adjusting the pH value, removing heavy metal and arsenic impurities, and performing filtration after the reaction to obtain purified ferrous sulfate solution; e) cooling crystallization: concentrating and cooling crystallizing the purified ferrous sulfate solution obtained in step d) to precipitate ferrous sulfate heptahydrate crystals; f) separation and drying: performing solid-liquid separation on the crystal slurry obtained in step e), and obtaining ferrous sulfate heptahydrate product after washing and drying the obtained solid.

2. The manufacturing process of claim 1, wherein, In step a), the tailings are pyrite-based acid-making cinder, by-product ferrous sulfate of titanium dioxide, or any other industrial waste residue rich in divalent or trivalent iron oxides; the particle size of the ground tailings powder is required to pass through a 100-200 mesh sieve.

3. The manufacturing process of claim 1, wherein, In step b), the concentration of the sulfuric acid solution is 15%-30%; the liquid-solid ratio of the tailings powder to the sulfuric acid solution is (3:1)-(6:1) (mL / g); the temperature of the reaction is 60-95℃; and the time of the reaction is 1.0-3.0 hours.

4. The production process according to claim 1 or 3, characterized in that, In step b), the reducing agent is iron powder, pyrite powder, or a combination of the two; the amount of the reducing agent added is 1.0-1.2 times the theoretical calculation amount, which refers to the equivalent amount of the reducing agent required to reduce all trivalent iron oxides in the tailings to divalent iron ions.

5. The manufacturing process of claim 1, wherein, In step b), the end point of the acid leaching reaction is controlled by measuring the oxidation-reduction potential (ORP) of the reaction system; when the ORP value drops below -100 mV, it is determined that the reaction is complete.

6. The manufacturing process of claim 1, wherein, In step d), the purification agent is one of sodium sulfide, ferrous sulfide, or hydrogen sulfide; the pH value of the purification and impurity removal reaction is controlled at 3.0-5.0; and the amount of the purification agent added is 1.2-1.5 times the total amount of impurities.

7. The manufacturing process of claim 1, wherein, In step d), a small amount of polyacrylamide is also added as a flocculating agent after the addition of the sulfidation agent to accelerate the settlement and filtration of the sulfidation residue.

8. The manufacturing process of claim 1, wherein, In step e) the concentration is evaporative concentration at normal or reduced pressure to a solution density of 1.35-1.45 g / cm3 3 ; the cooling crystallization is slow cooling to 0-10°C with crystal aging for 1-2 hours.

9. The manufacturing process of claim 1, wherein, In step f), the drying is vacuum drying at 40-60℃ until the product meets the water content requirements of GB 10531-201 "Water Treatment Agent Ferrous Sulfate" standard.

10. A ferrous sulfate heptahydrate product produced by the process of any one of claims 1-9, characterized by, The product has a purity of ≥98.0%, meets the industrial grade or fertilizer grade standards, and can be used for water treatment, feed additives, fertilizer preparation, or as a raw material for producing iron oxide pigments.

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