Titanium-rich coal gangue graded gradient utilization co-production titanium dioxide and polysilicate aluminum iron process

Abstract

This invention discloses a process for the graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferric silicate, belonging to the field of solid waste resource utilization technology. The process includes: roasting and activating coal gangue; selectively leaching aluminum ferric silicate with dilute sulfuric acid to obtain leachate and titanium-rich silicon filter residue; mixing the titanium-rich silicon filter residue with concentrated sulfuric acid for acid hydrolysis reaction, followed by water leaching, reduction to remove iron, sedimentation and filtration to separate silicon-rich filter residue, freezing and crystallizing the filtrate to obtain titanium oxysulfate solution and by-product ferrous sulfate, hydrolyzing and calcining the titanium oxysulfate solution to prepare titanium dioxide, oxidizing the by-product ferrous sulfate and adding it to the leachate; alkali dissolving the silicon-rich filter residue to obtain sodium silicate solution and tailings; polymerizing the leachate with sodium silicate to obtain polyaluminum ferric silicate, and recycling acid mist and wastewater in a closed loop. This invention can be used to extract valuable elements from coal gangue and co-produce high-purity titanium dioxide and polyaluminum ferric silicate flocculant. It can solve the problems of difficult element separation, insufficient iron source for direct production of polyaluminum ferric silicate, and large emissions of waste gas, wastewater, and solid waste in the current utilization of coal gangue.

Description

Technical Field

[0001] This invention relates to a process for the graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate, belonging to the field of solid waste resource utilization technology. Background Technology

[0002] Coal gangue is a large-scale industrial solid waste generated during coal mining and washing. my country's annual emissions reach hundreds of millions of tons. Long-term stockpiling not only occupies significant land resources but also easily causes environmental problems such as dust pollution, acid leaching, and groundwater pollution, thus creating a high demand for solid waste disposal. The main chemical components of coal gangue are SiO2, Al2O3, Fe2O3, and TiO2, and it is also rich in valuable elements such as aluminum, iron, titanium, and silicon, demonstrating significant potential for resource utilization.

[0003] Currently, the utilization of coal gangue resources is mainly divided into two paths: one is the low-value-added utilization path of large-scale consumption, which mainly includes brick making, cement admixture, coal-fired power generation, etc., and is the mainstream consumption method of coal gangue; the other is the utilization path of extracting valuable elements. This type of process usually involves first crushing and grinding the coal gangue, then roasting and activating it to remove organic matter and destroy the mineral lattice to enhance the acid dissolution reaction activity, and then extracting valuable elements through the acid leaching process.

[0004] However, low-value-added utilization pathways do not fully extract valuable elements from coal gangue, resulting in low element utilization efficiency and insufficient high-value utilization. For processes involving the extraction of valuable elements, co-dissolution of elements such as aluminum and iron is common, leading to difficulties in subsequent element separation and low purity of the final product. Some processes use hydrochloric acid systems, which are highly volatile, cause severe equipment corrosion, and create a poor operating environment, making it difficult to achieve synergistic high-value utilization of multiple elements. Furthermore, coal gangue itself generally has a low iron content; when directly using its acid leaching solution as a raw material to prepare polyaluminum ferric silicate, it is difficult to meet the iron content requirements of the product, easily leading to unstable product performance. Summary of the Invention

[0005] (a) Purpose of the invention

[0006] Based on the above, this invention provides a process for the graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferric silicate. This process achieves efficient cascaded separation of multiple elements such as aluminum, iron, titanium, and silicon. The ferrous sulfate generated during the reduction of iron powder in the titanium dioxide production process is oxidized to supplement the iron source required for the preparation of polyaluminum ferric silicate, thereby improving the added value and environmental benefits of coal gangue resource utilization.

[0007] (II) Technical Solution

[0008] A process for the graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate includes the following steps:

[0009] S1. Titanium-rich coal gangue is crushed, ground, roasted, and activated to obtain activated coal gangue powder.

[0010] S2. Activated coal gangue powder is mixed with dilute sulfuric acid for selective leaching, and solid-liquid separation is performed to obtain aluminum-iron leaching solution and titanium-rich silicon filter residue.

[0011] S3. The titanium-rich silicon filter residue is mixed with concentrated sulfuric acid for acid hydrolysis. After water immersion, iron is removed by reduction, sedimentation and filtration are performed to separate the silicon-rich filter residue. The filtrate is frozen and crystallized to obtain by-product ferrous sulfate and titanium oxysulfate filtrate. The titanium oxysulfate filtrate is hydrolyzed and filtered to obtain metatitanic acid, which is then calcined to prepare titanium dioxide.

[0012] S4. The ferrous sulfate byproduct of step S3 is oxidized to ferric sulfate under acidic conditions and added to the aluminum-iron leaching solution to supplement the iron source, thereby obtaining an iron-supplemented aluminum-iron leaching solution.

[0013] S5. The silica-rich filter residue is treated with alkali to obtain a sodium silicate solution;

[0014] S6. The iron-added aluminum-iron leaching solution is mixed and polymerized with sodium silicate solution to prepare polyaluminum-iron silicate flocculant;

[0015] S7. The acid mist generated by the recycling process is used to prepare dilute sulfuric acid for reuse, and the purified washing wastewater is reused in the production process, realizing a closed loop of acid and water media.

[0016] Preferably, in step S2, the mass concentration of dilute sulfuric acid is 10-50%, the liquid-solid ratio of activated coal gangue powder to dilute sulfuric acid is 3-8:1, the leaching temperature is 50-100℃, and the leaching time is 1-8h.

[0017] Preferably, in step S3, the mass concentration of concentrated sulfuric acid is 80-98%, the mass ratio of titanium-rich silicon filter residue to concentrated sulfuric acid is 1:1.2-2.5, the acidolysis temperature is 150-220℃, and the acidolysis time is 1-5h.

[0018] Preferably, in step S4, the oxidation reaction of ferrous sulfate is carried out in an acidic system with pH ≤ 2, and the oxidant used is hydrogen peroxide or oxygen.

[0019] Preferably, in step S3, the hydrolysis temperature of the titanium oxysulfate solution is 90~120℃, the acidity coefficient F during the hydrolysis process is controlled to be 1.7~2.2, the calcination temperature is 800~1000℃, and the purity of the obtained titanium dioxide is ≥95%.

[0020] Preferably, in step S5, the alkaline dissolution treatment uses a NaOH solution with a mass concentration of 10-40%, the liquid-solid ratio of the silica-rich filter residue to the NaOH solution is 2-10:1, the alkaline dissolution temperature is 50-120℃, and the alkaline dissolution time is 1-8h.

[0021] Preferably, in step S5, part of the tailings generated by alkali dissolution is returned to the roasting process in step S1 or the acid hydrolysis process in step S3 for recycling, and part is used as fertilizer and building material additives.

[0022] Preferably, in step S6, the pH value of the mixed polymerization is 2.0~4.5, the polymerization temperature is 40~70℃, the polymerization time is 1~5h, and the basicity of the obtained polyaluminum silicate flocculant is 30~70%.

[0023] (III) Beneficial Effects

[0024] This invention employs a graded leaching process using dilute sulfuric acid for selective leaching of aluminum and iron, and concentrated sulfuric acid for acid hydrolysis to extract titanium. It utilizes the differences in the leaching characteristics of aluminum, iron, titanium, and silicon by different concentrations of sulfuric acid. First, low-concentration dilute sulfuric acid preferentially dissolves aluminum and iron, while titanium and silicon remain in the solid filter residue. Then, high-concentration concentrated sulfuric acid is used to acid hydrolyze the titanium-rich silicon filter residue, causing titanium to dissolve into the liquid phase while silicon remains in the solid phase. This achieves the stepwise leaching of different elements, thus solving the problems of current single-acid leaching systems that easily lead to the co-dissolution of aluminum, iron, and titanium, resulting in difficulties in subsequent element separation and low product purity.

[0025] This invention employs an internal iron source recycling process that utilizes the oxidation and reuse of ferrous sulfate, a byproduct of titanium dioxide extraction. The ferrous sulfate, obtained during the reduction and iron removal process in titanium dioxide production, is oxidized to ferric salt under acidic conditions and directly incorporated into the aluminum-iron leaching solution obtained from dilute sulfuric acid extraction. This provides iron supplementation for the subsequent production of polyaluminum-iron silicate, thus solving the problem of insufficient iron source and unstable product performance when directly preparing polyaluminum-iron silicate due to the low iron content of coal gangue. Compared with traditional processes, this invention eliminates the need for additional external iron raw materials, reducing the production cost of polyaluminum-iron silicate. Furthermore, the basicity of the product is stably controlled within the range of 30-70%, resulting in good product performance consistency.

[0026] This invention employs a fully closed-loop process design involving tailings recycling and acid and water media. This design returns a portion of the tailings generated from alkali leaching and silicon extraction to the upstream roasting or acidolysis process for further extraction of valuable elements. The acid mist generated during the process is recovered to prepare dilute sulfuric acid for reuse in the leaching process. The washing wastewater is purified and reused in the water leaching and washing processes. This invention solves the problems of large emissions of waste gas, wastewater, and solid waste and low resource utilization rate in coal gangue resource utilization processes.

[0027] Furthermore, this invention uses a sulfuric acid system as the leaching medium, avoiding the problems of high volatility, severe equipment corrosion, and poor operating environment associated with traditional hydrochloric acid systems. The equipment used in the process is all general-purpose chemical equipment, the process conditions are mild, and it is easy to achieve industrial-scale promotion. In this invention, titanium-rich coal gangue refers to coal gangue with a TiO2 content of 3% or higher. Attached Figure Description

[0028] Figure 1This is a flowchart of the process flow of the present invention. Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0030] Example 1

[0031] The chemical composition (mass fraction) of coal gangue raw material is: Al2O3 32%, SiO2 52%, TiO2 5.5%, Fe2O3 4.2%, with the remainder being carbonaceous matter and impurities.

[0032] S1 Pretreatment and Activation: After the coal gangue raw material is crushed by a jaw crusher, it is fed into a ball mill and ground until it passes through a 200-mesh sieve. The ground coal gangue is then fed into a rotary roasting furnace and roasted at 900℃ for 1.5 hours to obtain activated coal gangue powder.

[0033] S2 Selective Leaching of Aluminum and Iron with Dilute Sulfuric Acid: Activated coal gangue powder is mixed with 30% (w / w) dilute sulfuric acid at a liquid-to-solid ratio of 4:1 (L / kg). The dilute sulfuric acid can be regenerated dilute sulfuric acid prepared by acid mist recovery. The dilute sulfuric acid is pumped into a reactor and preheated to 95°C. Activated coal gangue powder is then added, and the mixture is kept at this temperature and stirred for 4 hours. After this process, solid-liquid separation is performed to obtain an aluminum-iron leachate and titanium-rich silicon filter residue.

[0034] S3. Titanium Extraction and Titanium Dioxide Preparation via Concentrated Sulfuric Acid Acid Hydrolysis: Titanium-rich silicon filter residue is mixed with 95% concentrated sulfuric acid at a mass ratio of 1:1.5. The concentrated sulfuric acid can be obtained by diluting 98% concentrated sulfuric acid or by recycling waste concentrated sulfuric acid from the titanium dioxide production system. The titanium-rich silicon filter residue and concentrated sulfuric acid are premixed and fed into an acidification reactor at 190℃ for 2 hours. Afterward, it is transferred to a hydrolysis reactor and soaked in water at a liquid-to-solid ratio of 3:1 (L / kg) with 5% dilute sulfuric acid for 1 hour. Reduced iron powder is added to reduce ferric iron to ferrous iron. Plate and frame filter press separation yields a titanium oxysulfate solution and the silicon-rich filter residue. The titanium conversion rate is 90%.

[0035] Titanium dioxide preparation: The ferrous sulfate byproduct was separated by cooling the titanium oxysulfate solution to 15℃ to obtain purified titanium liquid; the purified titanium liquid was hydrolyzed at 90–120℃ to generate metatitanic acid, and the acidity coefficient of the titanium liquid was strictly controlled to be 1.9. The metatitanic acid was generated by hydrolysis at 105℃. After washing with water to remove impurities, it was sent to a calcining furnace and calcined at 850℃ for 2 hours to obtain titanium dioxide with a purity of 97.2%.

[0036] S4 Internal Iron Source Circulation: The ferrous sulfate obtained from the above crystallization separation is dissolved in dilute sulfuric acid, and the pH of the system is adjusted to 1.5. 27% (w / w) industrial hydrogen peroxide is added as an oxidant. Using an oxidation reactor equipped with an aeration device, hydrogen peroxide is added while stirring at 300 rpm. The reaction is continued for 30 minutes until no ferrous iron residue remains, yielding a ferric sulfate solution. This solution is directly incorporated into the aluminum-iron leaching solution obtained in S2 to replenish the iron source.

[0037] S5 Alkali dissolution for silicon extraction and tailings recycling: The silicon-rich filter residue is mixed with a 20% NaOH solution at a liquid-to-solid ratio of 5:1 (L / kg), and alkali dissolved at 105℃ for 4 hours. The solid and liquid are separated to obtain sodium silicate solution and tailings. The tailings are returned to the roasting process of S1 for recycling.

[0038] Preparation of S6 polyaluminum ferric silicate: The aluminum ferric leachate after iron supplementation was mixed with sodium silicate solution at an aluminum:iron:silicon molar ratio of 1:1:1.2. The pH of the system was adjusted to 3.5 with dilute NaOH, and polymerization was carried out at 60℃ for 2 hours. After aging at room temperature, polyaluminum ferric silicate flocculant with a basicity of 45% was obtained.

[0039] S7 Closed-loop media circulation: Acid mist generated in the leaching and acidolysis processes is recovered by an absorption tower to prepare dilute sulfuric acid, and washing wastewater is purified and reused in the water leaching and washing processes, realizing a complete closed loop of acid and water media with no wastewater discharge.

[0040] The resource recovery rates were as follows: 88% for aluminum, 83% for iron, 90% for titanium, and 90.5% for coal gangue.

[0041] Example 2

[0042] This embodiment is the same as embodiment 1, with the main difference being:

[0043] S1 pretreatment activation: calcination temperature adjusted to 700℃, calcination time 1.5h;

[0044] S2 dilute sulfuric acid selective leaching of aluminum and iron: leaching temperature adjusted to 90℃;

[0045] S3 concentrated sulfuric acid acid hydrolysis for titanium extraction and titanium dioxide preparation: the acid hydrolysis temperature was adjusted to 180℃, and the titanium liquid hydrolysis temperature was adjusted to 110℃.

[0046] Testing revealed that titanium dioxide with a purity of 96.2% and polyaluminum ferrosilicon with a basicity of 55% were obtained. The resource recovery rates were: aluminum recovery rate 86%, iron recovery rate 82%, titanium recovery rate 89%, and coal gangue utilization rate 89.2%.

[0047] Example 3

[0048] This embodiment is the same as embodiment 1, with the main difference being:

[0049] S1 pretreatment activation: Grind to pass through 100 mesh, calcinate at 800℃ for 1 hour;

[0050] S2 selective leaching of aluminum and iron with dilute sulfuric acid: dilute sulfuric acid concentration 40%, liquid-solid ratio 5:1, leaching at 100℃ for 5 hours;

[0051] S3 concentrated sulfuric acid acid hydrolysis for titanium extraction and titanium dioxide preparation: concentrated sulfuric acid concentration 98%, filter residue to concentrated sulfuric acid mass ratio 1:1.8, acid hydrolysis reaction at 200℃ for 1.5h, calcination temperature 1000℃;

[0052] S4 Internal Iron Source Circulation: Ferrous sulfate is oxidized by oxygen to ferric sulfate for reuse;

[0053] S5 Alkali Dissolution Silicon Extraction and Tailings Recycling: 30% NaOH solution is used;

[0054] Preparation of S6 polyaluminum iron silicate: polymerization temperature 65℃, polymerization time 1.5h.

[0055] Testing revealed that 97.1% rutile titanium dioxide and 52% basicity polyaluminum iron silicate were obtained. The resource recovery rates were: 80% aluminum recovery, 80% iron recovery, 87% titanium recovery, and 87.5% coal gangue utilization.

[0056] Comparative Example 1

[0057] The internal iron supplementation step, i.e. step S4, is omitted. Polyaluminum ferric silicate is prepared directly using the aluminum-iron leaching solution obtained in S2. The remaining steps are completely consistent with those in Example 1.

[0058] Test results:

[0059] Table 1 Performance Comparison of Various Schemes

[0060]

[0061] This invention utilizes a process design for the oxidation and reuse of ferrous sulfate, a byproduct of titanium extraction, under pH ≤ 2 conditions. This design enables the basicity of polyaluminum ferric silicate to reach a stable 45%, eliminating the need for additional external iron sources. Compared to Comparative Example 1, this invention effectively addresses the shortcomings of insufficient iron content in coal gangue and unstable performance of polyaluminum ferric silicate.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A process for the graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate, characterized in that, Includes the following steps: S1. Titanium-rich coal gangue is crushed, ground, roasted, and activated to obtain activated coal gangue powder. S2. Activated coal gangue powder is mixed with dilute sulfuric acid for selective leaching, and solid-liquid separation is performed to obtain aluminum-iron leaching solution and titanium-rich silicon filter residue. S3. The titanium-rich silicon filter residue is mixed with concentrated sulfuric acid for acid hydrolysis. After water immersion, iron is removed by reduction, sedimentation and filtration are used to separate the silicon-rich filter residue. The filtrate is frozen and crystallized to obtain by-product ferrous sulfate and titanium oxysulfate filtrate. The titanium oxysulfate filtrate is hydrolyzed and filtered to obtain metatitanic acid. The calcination is then used to prepare titanium dioxide, with ferrous sulfate as a by-product. S4. The ferrous sulfate byproduct of step S3 is oxidized to ferric sulfate under acidic conditions and added to the aluminum-iron leaching solution to supplement the iron source, thereby obtaining an iron-supplemented aluminum-iron leaching solution. S5. The silica-rich filter residue is treated with alkali to obtain a sodium silicate solution; S6. The iron-added aluminum-iron leaching solution is mixed and polymerized with sodium silicate solution to prepare polyaluminum-iron silicate flocculant; S7. The acid mist generated by the recycling process is used to prepare dilute sulfuric acid for reuse, and the purified washing wastewater is reused in the production process, realizing a closed loop of acid and water media.

2. The process for graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate according to claim 1, characterized in that, In step S2, the mass concentration of dilute sulfuric acid is 10-50%, the liquid-solid ratio of activated coal gangue powder to dilute sulfuric acid is 3-8:1, the leaching temperature is 50-100℃, and the leaching time is 1-8h.

3. The process for graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate according to claim 1, characterized in that, In step S3, the mass concentration of concentrated sulfuric acid is 80-98%, the mass ratio of titanium-rich silicon filter residue to concentrated sulfuric acid is 1:1.2-2.5, the acidolysis temperature is 150-220℃, and the acidolysis time is 1-5h.

4. The process for graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate according to claim 1, characterized in that, In step S4, the oxidation reaction of ferrous sulfate is carried out in an acidic system with pH ≤ 2, and the oxidant used is hydrogen peroxide or oxygen.

5. The process for graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate according to claim 1, characterized in that, In step S3, the hydrolysis temperature of the titanium oxysulfate solution is 90~120℃, the acidity coefficient F is controlled to be 1.7~2.2 during the hydrolysis process, the calcination temperature is 800~1000℃, and the purity of the obtained titanium dioxide is ≥95%.

6. The process for graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate according to claim 1, characterized in that, In step S5, the alkaline dissolution treatment uses a NaOH solution with a mass concentration of 10~40%, the liquid-solid ratio of the silica-rich filter residue to the NaOH solution is 2~10:1, the alkaline dissolution temperature is 50~120℃, and the alkaline dissolution time is 1~8h.

7. The process for graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate according to claim 1, characterized in that, In step S5, the tailings produced by alkali dissolution are partially returned to the roasting process in step S1 or the acid hydrolysis process in step S3 for recycling, and partially used as fertilizer and building material additives.

8. The process for graded and cascaded utilization of titanium-rich coal gangue to co-produce titanium dioxide and polyaluminum ferrosilicate according to claim 1, characterized in that, In step S6, the pH value of the mixed polymerization is 2.0~4.5, the polymerization temperature is 40~70℃, the polymerization time is 1~5h, and the basicity of the obtained polyaluminum silicate iron flocculant is 30~70%.

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