Method for recycling multi-metal ion-containing waste acid

Abstract

The present application belongs to the technical field of valuable metal recovery from industrial waste acid, and discloses a method for resource utilization of waste acid containing multi-metal ions, which adopts a treatment process of "stepwise directional separation-high value recovery", and realizes stepwise separation through three-stage pH regulation: first, the pH of the waste acid is adjusted to 1-2, and the first filter residue is separated, and titanium dioxide is prepared through alkali leaching and calcination; the pH of the first filtrate is adjusted to 2-8, so that iron and aluminum ions are co-precipitated to obtain an iron-aluminum mixture, which can be treated by alkali dissolution and pyrolysis to obtain iron powder; the second filtrate is adjusted to pH greater than or equal to 9 to separate and recover calcium carbonate precipitate, and the third filtrate is evaporated and crystallized to obtain sodium chloride. The present application simultaneously realizes efficient separation and resource utilization of iron, aluminum, titanium and calcium, significantly reduces the risk of secondary pollution, and successfully converts the valuable components in the waste acid containing multi-metal ions into high-purity titanium dioxide, calcium carbonate, sodium chloride and iron powder.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste acid recovery of valuable metals, specifically relating to a method for the resource utilization of waste acid containing polymetallic ions. Background Technology

[0002] The amount of waste acid containing polymetallic ions discharged from industries such as metallurgy, chemical engineering, and surface treatment is increasing daily. This type of wastewater has a high chloride ion concentration and contains components such as iron, aluminum, titanium, calcium, and silicates, characterized by complex composition, strong acidity, and high corrosiveness. Currently, neutralization is commonly used, which is simple to operate but makes it difficult to recover valuable metals, leading to resource waste and secondary pollution. In addition, Chinese patent CN120330482A discloses a method for recovering valuable metals from waste acid from the sulfuric acid process for titanium dioxide production using steel slag. This method separates iron, scandium, titanium, and vanadium through crystallization, extraction, and neutralization steps, and uses vanadium-rich slag to prepare an electrolyte, achieving the recovery of valuable metals. However, this process is complex, has low product conversion efficiency, and poor economic viability.

[0003] Polymetallic ion-containing waste acids typically contain high concentrations of hydrochloric acid, which in turn contains high concentrations of chloride ions (Cl). - and various metal ions, such as Fe 2+ / Fe 3+ TiO 2+ Ca 2+ Mg 2+ Al 3+ These ions interact complexly in acidic environments, readily forming various complex ions (such as FeCl4). - AlCl4 - (etc.), increasing the difficulty of separation. Under conditions of high acidity and multiple coexistence, hydrolysis competition and co-precipitation phenomena easily occur, affecting the selective recovery of the target metal. For example, Fe 3+ It can be hydrolyzed and precipitated at lower pH, while Al 3+ TiO 2+ The presence of plasma interferes with the hydrolysis of iron, resulting in precipitates with complex composition and low purity. High concentrations of Cl... - It will also exacerbate equipment corrosion and adversely affect subsequent extraction, crystallization and other processes.

[0004] Therefore, given the unique characteristics of polymetallic ion-containing waste acid, developing efficient, economical, and environmentally friendly technologies for separating and recovering waste acid from valuable metals is of great significance for achieving resource recycling and reducing environmental impact. Summary of the Invention

[0005] In view of the aforementioned defects and shortcomings of existing technologies, this invention provides a method for the resource utilization of waste acid containing polymetallic ions. This method can efficiently separate and convert the main valuable components such as titanium, iron, calcium, and sodium in polymetallic ion waste acid into high-value products such as titanium dioxide, iron concentrate, calcium carbonate, and sodium chloride, thereby truly realizing the high-value, reduced-volume, and resource-based utilization of waste acid containing polymetallic ions. This method is applicable to waste acid containing iron, aluminum, titanium, calcium, and high concentrations of chloride emitted from industries such as metallurgy, chemical engineering, and surface treatment. - Strongly acidic and complex waste acid.

[0006] The technical solution adopted by this invention to solve the technical problem is: This invention provides a method for the resource utilization of waste acid containing polymetallic ions, comprising the following steps: (1) Add an alkaline agent to the waste acid containing polymetallic ions to adjust the pH to 1-2, and filter to separate the first filter residue and the first filtrate; (2) Wash the first filter residue with water until neutral, and soak the first filter residue in 0.25-1.25 mol / L sodium hydroxide solution at 60-150℃ for 30-90 min with a solid-liquid ratio of 0.1-0.25 g / mL. Filter to obtain sodium silicate solution and metatitanic acid precipitate. (3) The metatitanic acid precipitate was washed with sulfuric acid solution, then washed with water, dried and calcined to obtain titanium dioxide; (4) The first filtrate is stirred at 60-100℃ while an alkaline agent is added to adjust the pH value to 2-8, and the solid and liquid are separated to obtain an aluminum-iron mixture and a second filtrate. (5) The aluminum-iron mixture is boiled and leached with a sodium hydroxide solution of 1.25-6.25 mol / L at a solid-liquid ratio of 0.1-0.2 g / mL, and filtered to obtain sodium aluminate solution and iron hydroxide precipitate. The iron hydroxide precipitate is then pyrolyzed to obtain iron concentrate. (6) Add sodium carbonate to the second filtrate to adjust the pH to ≥9, and separate the solid and liquid to obtain calcium carbonate precipitate and the third filtrate; (7) Evaporate the third filtrate to precipitate sodium chloride crystals.

[0007] Preferably, the waste acid contains iron, aluminum, titanium, calcium, silicon, and chloride ions.

[0008] Preferably, the alkaline agent is sodium hydroxide or sodium carbonate. More preferably, the alkaline agent is sodium carbonate.

[0009] The reaction that occurs in step (1) is as follows: .

[0010] Preferably, in step (1), an alkali agent is added to adjust the pH to between 1 and 2 because the pH range for the precipitation of metatitanic acid is <2, and silicic acid is stable under acidic conditions. Therefore, a pH range of 1 to 2 can satisfy the requirement that titanium in waste acid containing polymetallic ions is completely converted into metatitanic acid precipitate and silicon is converted into silicic acid, which is beneficial for the subsequent deep separation of iron, calcium, and sodium. The preferred pH condition is 1.3 to 2.

[0011] The reaction that occurs in step (2) is as follows: .

[0012] Preferably, the washing process is performed 3-6 times. The purpose of the washing is to remove residual acid from the first filter residue, thus saving the amount of sodium hydroxide solution added in the subsequent alkaline leaching process. During the alkaline leaching process, silicic acid is converted into sodium silicate, and metatitanic acid is obtained through filtration and separation, achieving silicon-titanium separation. Sodium silicate is commonly used in the preparation of water glass (sodium silicate aqueous solution).

[0013] Preferably, in step (3), the concentration of the sulfuric acid solution is 0.5-1 mol / L, the number of water washes is 3-6, the drying temperature is 90-150℃, the calcination temperature is 500-900℃, and the calcination time is 30-90 min.

[0014] The reaction that occurs in step (3) is as follows: .

[0015] Specifically, during the alkaline leaching process, some amphoteric metal impurities (such as aluminum (Al) and silicon (Si) will react with oxyacid radicals (such as AlO2). - SiO3 2- The impurities dissolve in the alkaline solution and adsorb onto the surface of the metatitanic acid particles in the form of sulfuric acid. Sulfuric acid, a strong acid, effectively converts these impurity ions into a more acid-soluble form, which is then removed by washing, preventing them from entering the final product and affecting its purity. After sulfuric acid washing, the precipitate will contain a large amount of soluble sulfate impurities and excess free sulfuric acid. Water washing can effectively and thoroughly remove these water-soluble impurities. Subsequently, during the calcination process, the metatitanic acid loses its bound water and undergoes a crystal transformation to produce anatase titanium dioxide pigment, i.e., titanium dioxide.

[0016] Preferably, the stirring rate is 85-200 r / min, and the concentration of the alkali is 0.1-0.5 mol / L. The reaction that occurs in step (4) is as follows: ; .

[0017] Specifically, the purpose of adding an alkali is to adjust the pH and reduce the Fe content in the system. 3+ And Al 3+ A hydroxide precipitate forms. Fe is detected during the reaction process. 3+The concentration of the alkali was adjusted by regulating the dropping rate to keep it below 0.018 mol / L, maintaining a stable concentration. During the reaction, the pH gradually increased, and Fe... 3+ A large amount of precipitate begins to form when pH > 3, Al 3+ Precipitation is basically complete when pH > 6, and aluminum and iron hydroxides are completely precipitated when pH reaches 6-8.

[0018] Preferably, the boiling leaching time is 0.5-3 h, the ferric hydroxide precipitate pyrolysis temperature is 300-800℃, and the pyrolysis time is 30-90 min; The reaction that occurs in step (5) is as follows: , .

[0019] Specifically, Al(OH)3 is converted into soluble NaAlO2 in a strong alkali, while iron exists as FeOOH precipitate, thus achieving effective separation of iron and aluminum. The resulting sodium aluminate solution can be recycled as an alkali agent added during the alkali leaching process.

[0020] The reaction that occurs in step (6) is as follows: .

[0021] Specifically, sodium carbonate is added to adjust the pH to ≥ 9, causing carbonate ions to react with calcium ions to form calcium carbonate precipitate. The calcium carbonate precipitate is then washed with deionized water to remove surface-adsorbed impurity ions (such as chloride ions, sodium ions, etc.) and improve the purity of the calcium carbonate.

[0022] This invention employs a "stepwise directional separation-high-value recovery" process for the resource recovery of waste acid containing polymetallic ions. It utilizes a three-stage pH gradient control, with the first stage being acidic (pH 1-2): employing Ti... 4+ The hydrolysis reaction produces metatitanic acid precipitate, and based on the differences in precipitation thresholds of various ions, Fe... 3+ Ca 2+ Na + It remains stable in solution in an ionic state. Under these conditions, silicic acid remains dissolved and does not form colloidal interference, achieving the directional separation of titanium from other metal ions (especially iron and calcium). The second stage controls the pH to 2-8, initially controlling it to acidic to neutral (pH 2-6) to ensure the Fe in the solution... 3+ And Al 3+The hydrolysis reaction generates Fe(OH)3 and Al(OH)3 precipitates. The pH range is further increased (pH 6-8) to ensure complete precipitation of aluminum and iron hydroxides. The aim is to deeply recover iron and aluminum resources, reduce subsequent alkali consumption and processing load, and further purify the solution. The third stage is controlled alkaline (pH ≥ 9): utilizing CO32-. 2- With Ca 2+ The specific reaction generates calcium carbonate precipitate, with the aim of achieving deep removal and resource recovery of calcium, obtaining high-purity calcium carbonate products, and completing the comprehensive separation and high-value recovery of multiple metals.

[0023] Compared with the prior art, this application has the following advantages and beneficial effects: 1. It achieves efficient synergistic recovery and deep separation of multiple components, resulting in a high degree of resource utilization. By precisely controlling the pH gradient of the system, the technical challenge of efficiently separating titanium, iron, aluminum, calcium, and sodium, which have similar properties, in hydrochloric acid media has been successfully solved. This transforms a complex system, traditionally considered waste, into various high-value-added products, including titanium dioxide, iron concentrate, calcium carbonate, and sodium chloride, essentially achieving full component recovery of waste acid and near-zero solid waste discharge.

[0024] 2. The core products are of excellent quality, resulting in a significant increase in economic value. High-purity titanium dioxide: Through "directional titanium extraction" technology, the purity of the obtained titanium dioxide product reaches ≥92%, meeting the national standard A2 for anatase titanium dioxide pigment.

[0025] Qualified iron concentrate: The "tiered and graded iron extraction" process effectively inhibits the co-precipitation of impurities such as silicon and aluminum. The TFe grade of the obtained iron concentrate fully meets the industry standards for ironmaking raw materials, realizing the high-value utilization of iron.

[0026] High-purity byproducts: The calcium carbonate obtained from deep separation meets the standards for ordinary industrial precipitated calcium carbonate, and the sodium chloride can be purified to industrial salt standards, completely changing the situation where the traditional neutralization method produces mixed hazardous waste, turning waste into treasure. Attached Figure Description

[0027] Figure 1 The flowchart illustrates a method for the resource utilization of waste acid containing polymetallic ions provided by this invention. Detailed Implementation

[0028] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the following detailed description of the present invention, some specific details are described in detail, but well-known methods, processes, procedures, and elements are not described in detail in order to avoid obscuring the essence of the present invention.

[0029] Unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as encompassing rather than being exclusive or exhaustive; that is, meaning "including but not limited to."

[0030] In the description of this invention, "content" refers to a percentage by mass.

[0031] Example 1 In this embodiment, the waste acid containing polymetallic ions was selected from the acid leaching solution of high-iron red mud after aluminum and iron removal. The main chemical components in the acid leaching solution were measured by conventional chemical determination methods as shown in Table 1 below, and its pH was 0.45. Table 1. Composition of acid leaching solution of high-iron red mud in Example 1

[0032] A method for the resource utilization of waste acid containing polymetallic ions includes the following steps: (1) Sodium carbonate was added to the acid leaching solution to adjust the pH to 2. The solution was filtered to separate the first filter residue and the first filtrate. The following reaction occurred: ; (2) The first filter residue was washed with water to remove surface acid until neutral, resulting in a silicon-titanium mixture. Then, the silicon-titanium mixture was alkali-impregnated with 1.25 mol / L sodium hydroxide solution at a solid-liquid ratio of 0.125 g / mL in a water bath at 100°C for 30 min. After filtration, sodium silicate solution and metatitanic acid precipitate were obtained, and the following reaction occurred: ; (3) Metatitanic acid precipitate was washed with 0.5 mol / L sulfuric acid solution, washed three times with water, and dried at 105℃ to obtain metatitanic acid. The calcination temperature was set at 650℃ and the calcination time was 30 min to obtain titanium dioxide product. The reaction was as follows: .

[0033] (4) The first filtrate was stirred at 200 r / min at 90℃, and the pH was adjusted to 6 by adding 0.4 mol / L sodium carbonate solution. Solid-liquid separation was performed to obtain an aluminum-iron mixture and a second filtrate. The reaction was as follows: ; .

[0034] (5) The aluminum-iron mixture was boiled and leached with 1.25 mol / L sodium hydroxide solution at a solid-liquid ratio of 0.2 g / mL for 1 hour. The mixture was then filtered to obtain sodium aluminate solution and ferric hydroxide precipitate. The ferric hydroxide precipitate was pyrolyzed at 700℃ for 40 min to obtain iron concentrate, and the following reaction occurred: ; ; (6) Add sodium carbonate to the second filtrate to adjust the pH to 9, and separate the solid and liquid to obtain calcium carbonate precipitate and the third filtrate. The reaction is as follows: ; (7) Evaporate the third filtrate to precipitate sodium chloride crystals.

[0035] The products obtained in Example 1 were analyzed and tested, and the results are shown in Table 2. Table 2 shows that the TiO2 content in the titanium dioxide is 95.06%, which meets the national standard (GB / T 1706-2006) for anatase titanium dioxide pigment type A2; the Fe2O3 content in the iron concentrate is 90.81%, which is equivalent to 63.51% TFe, and the Al2O3 content is <1.2%, meeting the chemical composition requirements (GB / T36704-2018). Referring to the hematite quality standard, the iron concentrate obtained in the experiment is superior to the H63 grade; the CaCO3 content in the calcium carbonate crystals is 97.32%, meeting the standard for ordinary industrial precipitated calcium carbonate (HG / T 2226-2019); and the NaCl content in the sodium chloride crystals is 99.5%, meeting the requirements for superior grade in the "Industrial Salt" standard (GB / T 5462-2015).

[0036] Table 2 Chemical composition (%) of the product in Example 1

[0037] Example 2 In this embodiment, the waste acid containing polymetallic ions was selected from the pickling solution produced by the hydrochloric acid method of titanium dioxide. The main chemical components in the pickling solution were measured by conventional chemical determination methods as shown in Table 3 below, and its pH was 0.53. Table 3. Composition (%) of pickling solution in titanium dioxide production using hydrochloric acid process

[0038] A method for the resource utilization of waste acid containing polymetallic ions includes the following steps: (1) The content of trivalent titanium in the pickling solution was found to be 0.023 mol / L. Sodium carbonate was added to adjust the pH to 1.5, and the first filter residue and the first filtrate were obtained by filtration. (2) The first filter residue was washed with water to remove surface residual acid until neutral, and a silicon-titanium mixture was obtained. Then, the silicon-titanium mixture was soaked in 0.5 mol / L sodium hydroxide solution at a solid-liquid ratio of 0.25 g / mL in a water bath at 80°C for 60 min. The mixture was then filtered to obtain sodium silicate solution and metatitanic acid precipitate. (3) The metatitanic acid precipitate was washed with 1 mol / L sulfuric acid solution, washed with water 5 times, and dried at 90℃ to obtain metatitanic acid. The calcination temperature was set at 550℃ and the calcination time was 60 min to obtain titanium dioxide. (4) The first filtrate was stirred at 150 r / min at 80℃, and 0.3 mol / L sodium carbonate solution was added to adjust the pH to 6.5. The solid and liquid were separated to obtain an aluminum-iron mixture and a second filtrate. (5) The aluminum-iron mixture was boiled and leached with 6.25 mol / L sodium hydroxide solution at a solid-liquid ratio of 0.1 g / mL for 1 hour, and filtered to obtain sodium aluminate solution and ferric hydroxide precipitate. The ferric hydroxide precipitate was pyrolyzed at 600℃ for 60 min to obtain iron concentrate. (6) Add sodium carbonate to the second filtrate to adjust the pH to 9.5, and separate the solid and liquid to obtain calcium carbonate precipitate and the third filtrate; (7) Evaporate the third filtrate to precipitate sodium chloride crystals.

[0039] Table 4 Chemical composition (%) of the product in Example 2

[0040] The products obtained in Example 2 were analyzed and tested, and the results are shown in Table 4. According to Table 4, the TiO2 content in the titanium dioxide is 92.9%, which meets the national standard (GB / T 1706-2006) for anatase titanium dioxide pigment type A2; the Fe2O3 content in the iron concentrate is 90.06%, which is equivalent to 62.98% TFe, and the Al2O3 content is <1.2%, which meets the requirements of the chemical composition standard (GB / T36704-2018). Referring to the quality standard of hematite, the iron concentrate obtained in the test is superior to the H60 grade; the CaCO3 content in the calcium carbonate crystals is 97.01%, which meets the standard of ordinary industrial precipitated calcium carbonate (HG / T 2226-2019); the NaCl content in the sodium chloride crystals is 99.1%, which meets the requirements of the superior grade in the "Industrial Salt" standard (GB / T 5462-2015).

[0041] Comparative Example 1 The only difference from Example 1 is that step (1) adjusts the pH to 5.

[0042] Comparative Example 2 The only difference from Example 1 is that step (4) adjusts the pH to 10.

[0043] Comparative Example 3 The only difference from Example 1 is that step (6) adjusts the pH to 8.

[0044] The products prepared in Comparative Examples 1-3 were analyzed and tested, as shown in Tables 5-7.

[0045] Table 5 Chemical composition (%) of the product in Comparative Example 1

[0046] Table 6 Chemical composition (%) of the products in Comparative Example 2

[0047] Table 7 Chemical composition (%) of the products in Comparative Example 3

[0048] As can be seen from Table 5, in Comparative Example 1, adjusting the pH to 5 in step (1) resulted in an iron-titanium mixture, but the iron and titanium could not be completely separated.

[0049] As can be seen from Table 6, in Comparative Example 2, adjusting the pH to 10 in step (4) resulted in an iron-calcium mixture, but the iron and calcium could not be completely separated.

[0050] As shown in Table 7, in Comparative Example 3, adjusting the pH to 8 in step (6) resulted in a small amount of calcium in the prepared sodium chloride product. The NaCl content in the sodium chloride crystals was 93.11%, which does not meet the requirements for superior grade in the "Industrial Salt" standard (GB / T 5462-2015). This is because when the pH is adjusted to 8, calcium ions are not completely precipitated, and some calcium ions still exist in the third solution, leading to the generation of calcium ion impurities during the subsequent evaporation and crystallization of sodium chloride.

[0051] It should be understood that the above embodiments are merely exemplary and not restrictive. Various obvious or equivalent modifications or substitutions that can be made by those skilled in the art regarding the above details without departing from the basic principles of the present invention will be included within the scope of the claims of the present invention.

Claims

1. A method for the resource utilization of waste acid containing polymetallic ions, characterized in that, The method includes the following steps: (1) Sodium carbonate is added to the acid leaching solution to adjust the pH to 2, and the first filter residue and the first filtrate are obtained by filtration and separation. The acid leaching solution is the acid leaching solution of high iron red mud after aluminum and iron removal, and the pH value is 0.

45. (2) Wash the first filter residue with water to remove surface acid until neutral to obtain a silicon-titanium mixture. Then, immerse the silicon-titanium mixture in a water bath at 100°C for 30 min with a 1.25 mol / L sodium hydroxide solution at a solid-liquid ratio of 0.125 g / mL. Filter to obtain sodium silicate solution and metatitanic acid precipitate. (3) The metatitanic acid precipitate was washed with 0.5 mol / L sulfuric acid solution, washed with water 3 times, and dried at 105℃ to obtain metatitanic acid. The calcination temperature was set at 650℃ and the calcination time was 30 min to obtain titanium dioxide product. (4) The first filtrate was stirred at 200 r / min at 90℃, and 0.4 mol / L sodium carbonate solution was added to adjust the pH to 6. The solid and liquid were separated to obtain an aluminum-iron mixture and a second filtrate. (5) The aluminum-iron mixture was boiled and leached with 1.25 mol / L sodium hydroxide solution at a solid-liquid ratio of 0.2 g / mL for 1 hour. The mixture was filtered to obtain sodium aluminate solution and iron hydroxide precipitate. The iron hydroxide precipitate was pyrolyzed at 700℃ for 40 min to obtain iron concentrate. (6) Add sodium carbonate to the second filtrate to adjust the pH to 9, and separate the solid and liquid to obtain calcium carbonate precipitate and the third filtrate; (7) Evaporate the third filtrate to precipitate sodium chloride crystals. A three-stage pH gradient control is employed: the first stage controls the pH to 2, utilizing Ti... 4+ Hydrolysis produces metatitanic acid precipitate. Based on the differences in precipitation thresholds for each ion, Fe... 3+ Ca 2+ Na + It exists stably in solution in an ionic state, enabling the directional separation of titanium from other metal ions; the second stage controls the pH to 6, allowing Fe... 3+ and Al 3+ Hydrolysis generates hydroxide precipitate for deep recovery of iron and aluminum resources, further purifying the solution; the third stage controls the pH to 9 and utilizes CO32-. 2- With Ca 2+ The specific reaction generates calcium carbonate precipitate, achieving deep removal and high-value recovery of calcium. The titanium dioxide obtained in step (3) has a TiO2 content of 95.06%; the iron concentrate obtained in step (5) has a TFe content of 63.15% and an Al2O3 content of <1.2%; the calcium carbonate precipitate obtained in step (6) has a CaCO3 content of 97.32%; and the sodium chloride crystals obtained in step (7) have a NaCl content of 99.5%, thus completing the comprehensive separation and high-value recovery of multiple metals.

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