Method for synergistically extracting lithium, iron, gallium and germanium from coal fly ash of a thermal power plant

Abstract

The application relates to a method for synergistically extracting lithium, iron, gallium and germanium from fly ash of a thermal power plant. The method comprises the following steps: sequentially performing first-stage acid leaching and second-stage acid leaching containing choline chloride-urea on the fly ash to obtain first-stage filtrate and second-stage filtrate; combining the first-stage filtrate with the second-stage filtrate after removing choline chloride-urea from the second-stage filtrate to obtain combined leaching liquid; extracting lithium, iron and gallium by using a phosphoric acid tributyl ester organic solution and sequentially stripping to obtain lithium product liquid, iron product liquid and gallium product liquid; and performing complex extraction and stripping on germanium in the first-stage raffinate to obtain germanium product liquid. The application can realize gradient recovery of various valuable metals in the fly ash and improve the comprehensive recovery degree of the various valuable metals in the fly ash.

Description

Technical Field

[0001] This application belongs to the field of technology for the recycling and utilization of fly ash resources in thermal power plants, specifically relating to a method for the synergistic extraction of lithium, iron, gallium and germanium from fly ash in thermal power plants. Background Technology

[0002] Fly ash is a major solid waste generated by the thermal power industry, containing valuable metals such as lithium, iron, gallium, and germanium. With the increasing demand for related metal resources from new energy batteries, semiconductors, optoelectronic materials, and basic industries, extracting valuable metals from fly ash has become an important direction for its resource utilization. Existing research typically employs methods such as magnetic separation and acid leaching-precipitation for iron recovery, while lithium extraction often utilizes methods such as acid leaching followed by adsorption or membrane separation. Rare and dispersed metals such as gallium and germanium are mostly enriched and separated using methods such as solvent extraction and ion exchange.

[0003] However, existing technologies mostly focus on the recovery of single metals or a few components, making it difficult to simultaneously release, effectively enrich, and grade and separate multiple valuable metals in fly ash. Due to the mineral structure of fly ash and the coexistence of various impurities, the leaching and separation behaviors of different metals vary significantly. Individual treatment processes tend to result in long process chains, high reagent consumption, increased metal loss, and insufficient comprehensive utilization. Therefore, there is an urgent need for a resource-based treatment method that can synergistically recover lithium, iron, gallium, and germanium multimetallic systems from fly ash. Summary of the Invention

[0004] This application addresses the technical problem in existing fly ash resource recovery processes where multiple valuable metals such as lithium, iron, gallium, and germanium are difficult to leach simultaneously, co-enrich, and grade and separate, resulting in a fragmented process flow and insufficient comprehensive metal recovery. It provides a method for the co-extraction of lithium, iron, gallium, and germanium from fly ash in thermal power plants.

[0005] To achieve the above objectives, this application adopts the following technical solution: This application provides a method for the co-extraction of lithium, iron, gallium, and germanium from fly ash of thermal power plants, comprising the following steps: S1, the fly ash from the thermal power plant is subjected to a first-stage acid leaching with a first acid solution, and after solid-liquid separation, it is washed with water to obtain a first filtrate and a first filter residue; the first filter residue is subjected to a second-stage acid leaching with a mixture of a second acid solution and choline chloride-urea, and after solid-liquid separation, a second filtrate and a second filter residue are obtained. S2, remove choline chloride-urea from the second filtrate, combine the treated second filtrate with the first filtrate to obtain a combined leachate; extract the combined leachate with an organic solution composed of tributyl phosphate and a diluent to obtain a first organic phase rich in lithium, iron and gallium and a first raffinate; S3, the first organic phase is back-extracted using a third acid solution to obtain a lithium product solution and a second organic phase; S4, the second organic phase is back-extracted using a mixed solution containing a reducing agent and a salting-out agent to obtain an iron product liquid and a third organic phase; S5, the third organic phase is back-extracted using the fourth acid solution to obtain gallium product solution and regenerated organic phase; S6, add a complexing agent to the first raffinate to obtain a complexing solution, add a quaternary ammonium salt extractant to the complexing solution for extraction, and obtain a germanium-rich organic phase and a second raffinate; S7. The germanium-rich organic phase is back-extracted using the fifth acid solution to obtain a germanium product solution.

[0006] Further, in step S1, the first acid solution is a hydrochloric acid solution with a concentration of 2~5 mol / L, the solid-liquid ratio of the fly ash from the thermal power plant to the first acid solution is 1:(4~7) g / mL, and the temperature of the first acid leaching is 60~100℃, and the time is 3~5h; The second acid solution is a hydrochloric acid solution with a concentration of 2~8 mol / L. The solid-liquid ratio of the first filter residue to the mixture composed of the second acid solution and choline chloride-urea is 1:(4~7) g / mL. The temperature of the secondary acid leaching is 45~85℃ and the time is 1~3h. The volume ratio of the second acid solution to the choline chloride-urea solution is (2~5):1, and the molar ratio of choline chloride to urea in the choline chloride-urea solution is 1:(0.5~2).

[0007] Furthermore, in step S2, the concentration of tributyl phosphate in the organic solution is 1-4 mol / L; the diluent includes at least one of dichloromethane, trichloromethane, and carbon tetrachloride. The volume ratio of organic solution to combined leachate is 1:(0.5~5).

[0008] Furthermore, in step S3, the third acid solution is a hydrochloric acid solution with a concentration of 4~8 mol / L, and the volume ratio of the first organic phase to the third acid solution during back-extraction is 1:1.

[0009] Further, in step S4, the mixed solution contains hydrochloric acid, sodium sulfite, and sodium chloride. The sodium sulfite is used as a reducing agent with a concentration of 0.3~0.8 mol / L, and the sodium chloride is used as a salting-out agent with a concentration of 4~8 mol / L. The pH of the mixed solution is 1.5~3.0, and the redox potential is 250~300 mV. During back-extraction, the volume ratio of the second organic phase to the mixed solution is 1:(0.5~5).

[0010] Furthermore, in step S5, the fourth acid solution is a hydrochloric acid solution with a concentration of 0.1~2 mol / L; during back-extraction, the volume ratio of the third organic phase to the fourth acid solution is 1:(0.5~5).

[0011] Furthermore, the regenerated organic phase obtained in step S5 is returned to the combined leachate in step S2 for mixing.

[0012] Furthermore, in step S6, the complexing agent is tartaric acid, and the molar ratio of tartaric acid to germanium in the first raffinate is 2:1. The volume ratio of the complexing solution to the quaternary ammonium salt extractant is 1:1; The quaternary ammonium salt extractant is an organic solution containing trioctylmethylammonium chloride, wherein the volume fraction of trioctylmethylammonium chloride in the organic solution is 0.2% to 0.5%.

[0013] Furthermore, in step S7, the fifth acid solution is a hydrochloric acid solution with a concentration of 0.1~2 mol / L; the volume ratio of the germanium-rich organic phase to the fifth acid solution is 1:(0.5~5).

[0014] Furthermore, in step S2, choline chloride-urea in the second filtrate is removed and recovered by vacuum distillation, and the recovered choline chloride-urea is recycled for secondary acid leaching in step S1.

[0015] Compared with the prior art, this application has the following beneficial effects: This application employs a combination of primary and secondary acid leaching to leach lithium, iron, gallium, and germanium from fly ash in thermal power plants in stages, allowing multiple valuable metals to enter the leachate. By removing choline chloride-urea from the second filtrate and combining the treated second filtrate with the first filtrate, the metal leachates obtained from both acid leaching stages enter the same subsequent separation process. Further, this application uses an organic solution composed of tributyl phosphate and a diluent to extract the combined leachate, causing lithium, iron, and gallium to co-transfer into the first organic phase, while germanium remains in the first raffinate. Then, the first, second, and third organic phases are sequentially back-extracted using a third acid solution, a mixed solution containing a reducing agent and a salting-out agent, and a fourth acid solution to obtain lithium, iron, and gallium product solutions, respectively. Simultaneously, this application performs complexation extraction and back-extraction on the germanium in the first raffinate to obtain a germanium product solution. Therefore, this application can integrate the leaching, co-enrichment and stepwise separation of lithium, iron, gallium and germanium in fly ash from thermal power plants into the same process flow, reducing the need for separate processing flow for different metals and improving the comprehensive recovery of multiple valuable metals in fly ash. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating the method for the co-extraction of lithium, iron, gallium, and germanium from fly ash in thermal power plants, as described in this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] In one embodiment of this application, a method for the synergistic extraction of lithium, iron, gallium, and germanium from fly ash from thermal power plants is provided. This method uses fly ash from thermal power plants as the raw material to be processed. First, the fly ash is leached in stages using a hydrochloric acid system. Then, based on the differences in the speciation of lithium, iron, gallium, and germanium in the leachate, stepwise extraction and back-extraction are performed to obtain lithium product solution, iron product solution, gallium product solution, and germanium product solution, respectively. Figure 1 As shown, the specific steps include: S1, the fly ash from the thermal power plant is subjected to a first-stage acid leaching with a first acid solution, and after solid-liquid separation, it is washed with water to obtain a first filtrate and a first filter residue; the first filter residue is subjected to a second-stage acid leaching with a mixture of a second acid solution and choline chloride-urea, and after solid-liquid separation, a second filtrate and a second filter residue are obtained. S2, remove choline chloride-urea from the second filtrate, combine the treated second filtrate with the first filtrate to obtain a combined leachate; extract the combined leachate with an organic solution composed of tributyl phosphate and a diluent to obtain a first organic phase rich in lithium, iron and gallium and a first raffinate; S3, the first organic phase is back-extracted using a third acid solution to obtain a lithium product solution and a second organic phase; S4, the second organic phase is back-extracted using a mixed solution containing a reducing agent and a salting-out agent to obtain an iron product liquid and a third organic phase; S5, the third organic phase is back-extracted using the fourth acid solution to obtain gallium product solution and regenerated organic phase; S6. Add a complexing agent to the first raffinate to convert germanium into anionic complexes, and extract with a quaternary ammonium salt extractant to obtain a germanium-rich organic phase and a second raffinate. S7. The germanium-rich organic phase is back-extracted using the fifth acid solution to obtain a germanium product solution.

[0020] This application utilizes a two-stage acid leaching process to increase the extent to which lithium, iron, gallium, and germanium from fly ash in thermal power plants enter the leachate. The treated second filtrate is then combined with the first filtrate to obtain a combined leachate. Subsequently, an organic solution composed of tributyl phosphate and a diluent is used to extract the combined leachate, causing lithium, iron, and gallium to co-transfer into the first organic phase in a hydrochloric acid system, while germanium mainly remains in the first raffinate. After sequential back-extraction of the first organic phase, lithium, iron, and gallium can be separated and recovered stepwise within the same co-extraction system, reducing the need for multiple independent separation processes. Furthermore, the first raffinate undergoes complexation extraction and back-extraction to transfer germanium into the aqueous phase, yielding a germanium product solution. This application enables the sequential leaching, co-enrichment, and stepwise separation of lithium, iron, gallium, and germanium in fly ash, achieving the cascade recovery of multiple valuable metals from fly ash.

[0021] In some embodiments of this application, the fly ash from thermal power plants can be dried, crushed, or screened first to improve the uniformity of contact between the fly ash and the acid leaching system. The pretreated fly ash is then subjected to primary acid leaching with a first acid solution. The concentration of the first acid solution is 2-5 mol / L, the solid-liquid ratio of the fly ash to the first acid solution is 1 g:(4-7) mL, the temperature of the primary acid leaching is 60-100℃, and the leaching time is 3-5 h. By controlling the concentration of the first acid solution, the solid-liquid ratio, the leaching temperature, and the leaching time, readily acid-soluble elements such as lithium, iron, gallium, and germanium in the fly ash can be introduced into the first filtrate.

[0022] After the first-stage acid leaching is completed, the first-stage acid leaching system is subjected to solid-liquid separation, and the resulting solid is washed with water. The washing solution can be combined with the first-stage acid leaching filtrate as part of the first filtrate to reduce the loss of valuable metals carried over in the filter residue.

[0023] In some embodiments of this application, the first filter residue is subjected to a two-stage acid leaching with a mixture of a second acid solution and choline chloride-urea. The concentration of the second acid solution is a hydrochloric acid solution of 2-8 mol / L, the solid-liquid ratio of the first filter residue to the mixture is 1 g:(4-7) mL, the temperature of the two-stage acid leaching is 45-85°C, and the leaching time is 1-3 h. In the above two-stage acid leaching system, the second acid solution provides a chlorination environment and acidic leaching conditions, and choline chloride-urea is used to form a eutectic system containing choline chloride and urea. Controlling the volume ratio of the second acid solution to choline chloride-urea to (2-5):1 is beneficial for balancing the acidity required for the acid leaching reaction and the promoting effect of the eutectic system on the release of metals from the filter residue. Controlling the molar ratio of choline chloride to urea to 1:(0.5-2) is beneficial for maintaining the compositional stability of the choline chloride-urea system.

[0024] After the secondary acid leaching, solid-liquid separation is performed to obtain a second filtrate and a second filter residue. The second filtrate contains lithium, iron, gallium, germanium, and choline chloride-urea released during the secondary acid leaching. To facilitate subsequent solvent extraction and reduce interference from eutectic components entering the subsequent extraction system, in some embodiments of this application, the second filtrate is subjected to distillation to remove choline chloride-urea. Optionally, choline chloride-urea in the second filtrate can be removed and recovered by vacuum distillation, and the recovered choline chloride-urea can be recycled back to the secondary acid leaching step. By recovering choline chloride-urea, the consumption of secondary acid leaching aids can be reduced, and the content of non-target components in the subsequent extraction system can be decreased.

[0025] The treated second filtrate was combined with the first filtrate to obtain a combined leachate. This combined leachate served as the aqueous phase for the co-extraction of lithium, iron, and gallium. The combined leachate was extracted using an organic solution composed of tributyl phosphate (TBP) and a diluent. The concentration of TBP in the organic solution was 1–4 mol / L, and the diluent included at least one of dichloromethane, trichloromethane, and carbon tetrachloride. The volume ratio of the organic solution to the combined leachate was 1:(0.5–5). In the hydrochloric acid system, iron and gallium could form chloride complex anions, and lithium could also be co-extracted in the TBP system, thereby allowing lithium, iron, and gallium to enter the first organic phase, while germanium remained in the first raffinate. By controlling the concentration of TBP and the volume ratio of the organic solution to the combined leachate, the extraction phase capacity and interphase mass transfer conditions could be adjusted, allowing lithium, iron, and gallium to be enriched in the organic phase in the same extraction step.

[0026] The first organic phase obtained from extraction is then subjected to sequential back-extraction of lithium, iron, and gallium. First, the first organic phase is back-extracted using a third acid solution. The third acid solution is a hydrochloric acid solution with a concentration of 4–8 mol / L, and the volume ratio of the first organic phase to the third acid solution during back-extraction is 1:1. This allows lithium from the first organic phase to enter the aqueous phase, thus yielding a lithium product solution and a second organic phase. The acidity and volume ratio of the third acid solution are used to regulate the distribution of lithium between the organic and aqueous phases, preferentially transferring lithium from the first organic phase to the aqueous phase.

[0027] Then, the second organic phase is back-extracted using a mixed solution containing hydrochloric acid, sodium sulfite, and sodium chloride. Sodium sulfite is used as a reducing agent at a concentration of 0.3–0.8 mol / L; sodium chloride is used as a salting-out agent at a concentration of 4–8 mol / L; the pH of the mixed solution is 1.5–3.0, and the redox potential is 250–300 mV; the volume ratio of the second organic phase to the mixed solution during back-extraction is 1:(0.5–5). In this step, hydrochloric acid is used to adjust the pH and chloride ion environment of the back-extraction system, sodium sulfite is used to adjust the redox state of iron, and sodium chloride is used to adjust the salt concentration in the aqueous phase. By jointly controlling the pH, redox potential, reducing agent concentration, and salting-out agent concentration, iron can be facilitated to enter the aqueous phase from the second organic phase, yielding an iron product solution and a third organic phase.

[0028] Subsequently, the third organic phase was back-extracted using a fourth acid solution. The fourth acid solution was a hydrochloric acid solution with a concentration of 0.1–2 mol / L, and the volume ratio of the third organic phase to the fourth acid solution during back-extraction was 1:(0.5–5). This step was used to transfer gallium from the third organic phase into the aqueous phase, yielding a gallium product solution and a regenerated organic phase.

[0029] The regenerated organic phase obtained in step S5 can be reused for extraction of the combined leachate. Since lithium, iron, and gallium have been removed from the organic phase through stepwise back-extraction, the regenerated organic phase can still be used as the extraction phase in the extraction process of the next batch of combined leachate. By recycling the regenerated organic phase, the consumption of tributyl phosphate and diluent can be reduced, improving process continuity and resource utilization efficiency.

[0030] In some embodiments of this application, tartaric acid is added to the first raffinate as a complexing agent, with a molar ratio of tartaric acid to germanium in the first raffinate of 2:1. Tartaric acid and germanium combine to form a complex solution, which converts germanium into an anionic complex more suitable for extraction with quaternary ammonium salt extractants. Subsequently, a quaternary ammonium salt extractant is used to extract the germanium in the complex solution. In some embodiments of this application, the quaternary ammonium salt extractant is an organic solution containing trioctylmethylammonium chloride, with a volume fraction of 0.2% to 0.5% in the organic solution. The volume ratio of the complex solution to the quaternary ammonium salt extractant is 1:1. Through the combination of tartaric acid complexation and trioctylmethylammonium chloride extraction, the germanium in the first raffinate can be transferred into a germanium-rich organic phase, yielding a second raffinate.

[0031] The germanium-rich organic phase is then back-extracted using a fifth acid solution. The fifth acid solution is a hydrochloric acid solution with a concentration of 0.1–2 mol / L, and the volume ratio of the germanium-rich organic phase to the fifth acid solution is 1:(0.5–5). The fifth acid solution is used to disrupt or weaken the extraction state of germanium in the organic phase, allowing germanium to re-enter the aqueous phase, thus yielding a germanium product solution. Therefore, based on the synergistic extraction and stepwise back-extraction of lithium, iron, and gallium, this application further performs complexation extraction and back-extraction on germanium in the raffinate, achieving a stepwise recovery of the four metals.

[0032] In the process of this application, the first and second acid solutions are used together for graded leaching of valuable metals from fly ash; tributyl phosphate is used for the co-extraction of lithium, iron, and gallium from the combined leachate; the third acid solution, a mixed solution containing a reducing agent and a salting-out agent, and the fourth acid solution are used sequentially for the back-extraction of lithium, iron, and gallium; tartaric acid and trioctylmethylammonium chloride are used in combination for the complexation extraction of germanium; and the fifth acid solution is used for the back-extraction of germanium. The above steps are performed in the order of leaching, co-extraction, stepwise back-extraction, complexation extraction, and back-extraction of germanium, so that different metals are recovered separately according to their distribution differences in the acidic chlorination system, the tributyl phosphate system, and the quaternary ammonium salt extraction system.

[0033] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading this description, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0034] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under standard conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications in the art, unless otherwise stated.

[0035] Example 1 S1, Primary Acid Leaching: Take fly ash from a thermal power plant and mix it with 3 mol / L hydrochloric acid solution at a solid-liquid ratio of 1 g: 6 mL. Perform primary acid leaching at 80℃ for 4 hours. After primary acid leaching is completed, filter the reaction system and wash the filter residue with water to obtain the first filtrate and the first filter residue.

[0036] S2, Secondary Acid Leaching: Choline chloride and urea are mixed at a molar ratio of 1:1 to obtain a choline chloride-urea system; a 6 mol / L hydrochloric acid solution is mixed with the choline chloride-urea system at a volume ratio of 3:1 to obtain a secondary acid leaching solution. The first filter residue is mixed with the solution at a solid-liquid ratio of 1 g:4 mL, and secondary acid leaching is carried out at 55°C for 2 hours. After the secondary acid leaching is completed, the mixture is filtered to obtain a second filtrate and a second filter residue.

[0037] S3, Recovery of the eutectic system and combination of leachates: The second filtrate is subjected to vacuum distillation at 60℃ and 5kPa to remove and recover choline chloride-urea from the second filtrate. The treated second filtrate is combined with the first filtrate to obtain the combined leachate.

[0038] S4, Co-extraction of lithium, iron, and gallium: An organic solution consisting of tributyl phosphate and a diluent is prepared, wherein the concentration of tributyl phosphate in the organic solution is 2 mol / L, and the diluent is dichloromethane. The organic solution is mixed with the combined leachate at a volume ratio of 1:1 and extracted. After phase separation, a first organic phase rich in lithium, iron, and gallium and a first raffinate are obtained.

[0039] S5, Back-extraction of lithium: Using 6 mol / L hydrochloric acid solution as the third acid solution, the first organic phase and the third acid solution are mixed at a volume ratio of 1:1 and back-extracted. After phase separation, lithium product liquid and second organic phase are obtained.

[0040] S6, Iron back-extraction: Prepare a mixed solution containing hydrochloric acid, sodium sulfite, and sodium chloride, wherein the concentration of sodium sulfite is 0.5 mol / L, the concentration of sodium chloride is 6 mol / L, the pH of the mixed solution is 2.0, and the redox potential is 272 mV. Mix the second organic phase with the mixed solution at a volume ratio of 1:2 and perform back-extraction. After phase separation, an iron product solution and a third organic phase are obtained.

[0041] S7, Gallium back-extraction: Using a 1 mol / L hydrochloric acid solution as the fourth acid solution, the third organic phase and the fourth acid solution are mixed at a volume ratio of 1:1 and back-extracted. After phase separation, gallium product solution and regenerated organic phase are obtained. The regenerated organic phase can be returned to step S4 for extraction of the next batch of combined leachate.

[0042] S8, Complex extraction of germanium: Tartaric acid was added to the first raffinate, the amount of tartaric acid being twice the molar amount of germanium in the first raffinate, to convert germanium into an anionic complex, yielding a complex solution. Subsequently, extraction was performed using a quaternary ammonium salt extractant containing trioctylmethylammonium chloride, with a volume fraction of 0.2% in the quaternary ammonium salt extractant. The complex solution and the quaternary ammonium salt extractant were mixed at a volume ratio of 1:1 and extracted. After phase separation, a germanium-rich organic phase and a second raffinate were obtained.

[0043] S9, Germanium back-extraction: Using 2 mol / L hydrochloric acid solution as the fifth acid solution, the germanium-rich organic phase and the fifth acid solution are mixed at a volume ratio of 1:1 and back-extracted. After phase separation, the germanium product liquid is obtained.

[0044] The recovery rates of lithium, iron, gallium, and germanium in this embodiment were 67.17%, 70.57%, 89.55%, and 94.34%, respectively. This result indicates that by combining primary hydrochloric acid leaching with secondary acid leaching using a second acid solution / choline chloride-urea, multiple valuable metals in fly ash can be transferred into the leachate. By synergistic extraction of the combined leachate with tributyl phosphate, followed by stepwise back-extraction in the order of lithium, iron, and gallium, and by subjecting the germanium residue in the first extraction solution to tartrate complexation, trioctylmethylammonium chloride extraction, and acid back-extraction, lithium, iron, gallium, and germanium product solutions can be obtained, respectively.

[0045] Example 2 The difference from Example 1 is as follows: In the first-stage acid leaching, the concentration of the first acid solution was 2 mol / L, the solid-liquid ratio of the fly ash from the thermal power plant to the first acid solution was 1 g: 5 mL, the first-stage acid leaching temperature was 75 ℃, and the first-stage acid leaching time was 5 h. In the secondary acid leaching, the concentration of the second acid solution was 6 mol / L, the solid-liquid ratio of the first filter residue to the mixture of the second acid solution and choline chloride-urea was 1 g:4 mL, the secondary acid leaching temperature was 65 ℃, and the secondary acid leaching time was 1 h; the volume ratio of the second acid solution to choline chloride-urea was 2:1, and the molar ratio of choline chloride to urea in the choline chloride-urea mixture was 1:1.5. The concentration of tributyl phosphate in the organic solution was 3 mol / L, and the volume ratio of the organic solution to the combined leachate was 1:2. The third acid solution used for lithium back-extraction is an 8 mol / L hydrochloric acid solution, and the volume ratio of the first organic phase to the third acid solution is 1:1. In the mixed solution used for iron back-extraction, the concentration of sodium sulfite is 0.4 mol / L, the concentration of sodium chloride is 7 mol / L, the pH of the mixed solution is 2.0, the redox potential is 260 mV, and the volume ratio of the second organic phase to the mixed solution is 1:0.5. The fourth acid solution used for gallium back-extraction is a 1.5 mol / L hydrochloric acid solution, and the volume ratio of the third organic phase to the fourth acid solution is 1:3. In germanium complex extraction, the molar ratio of tartaric acid to germanium in the first raffinate is 2:1, and the volume fraction of trioctylmethylammonium chloride in the organic phase used for extraction is 0.2%. The fifth acid solution used for germanium back-extraction is a 1 mol / L hydrochloric acid solution, and the volume ratio of the germanium-rich organic phase to the fifth acid solution is 1:5.

[0046] The remaining steps are the same as in Example 1.

[0047] Example 3 The difference from Example 1 is as follows: In the first-stage acid leaching, the concentration of the first acid solution was 4 mol / L, the solid-liquid ratio of the fly ash from the thermal power plant to the first acid solution was 1 g:7 mL, the first-stage acid leaching temperature was 60 ℃, and the first-stage acid leaching time was 4 h. In the secondary acid leaching, the concentration of the second acid solution was 3 mol / L, the solid-liquid ratio of the first filter residue to the mixture of the second acid solution and choline chloride-urea was 1 g:6 mL, the secondary acid leaching temperature was 85 ℃, and the secondary acid leaching time was 2 h; the volume ratio of the second acid solution to choline chloride-urea was 5:1, and the molar ratio of choline chloride to urea in the choline chloride-urea mixture was 1:0.5. The concentration of tributyl phosphate in the organic solution was 1 mol / L, and the volume ratio of the organic solution to the combined leachate was 1:4. The third acid solution used for lithium back-extraction is a 5 mol / L hydrochloric acid solution, and the volume ratio of the first organic phase to the third acid solution is 1:1. In the mixed solution used for iron back-extraction, the concentration of sodium sulfite is 0.7 mol / L, the concentration of sodium chloride is 4 mol / L, the pH of the mixed solution is 2.5, the redox potential is 290 mV, and the volume ratio of the second organic phase to the mixed solution is 1:2. The fourth acid solution used for gallium back-extraction is a 0.5 mol / L hydrochloric acid solution, and the volume ratio of the third organic phase to the fourth acid solution is 1:5. In germanium complex extraction, the molar ratio of tartaric acid to germanium in the first raffinate is 2:1, and the volume fraction of trioctylmethylammonium chloride in the organic phase used for extraction is 0.4%. The fifth acid solution used for germanium back-extraction was a 2 mol / L hydrochloric acid solution, and the volume ratio of the germanium-rich organic phase to the fifth acid solution was 1:0.5.

[0048] The remaining steps are the same as in Example 1.

[0049] Example 4 The difference from Example 1 is as follows: In the first-stage acid leaching, the concentration of the first acid solution was 5 mol / L, the solid-liquid ratio of the fly ash from the thermal power plant to the first acid solution was 1 g: 4 mL, the first-stage acid leaching temperature was 90 ℃, and the first-stage acid leaching time was 3 h. In the secondary acid leaching, the concentration of the second acid solution was 8 mol / L, the solid-liquid ratio of the first filter residue to the mixture of the second acid solution and choline chloride-urea was 1 g:5 mL, the secondary acid leaching temperature was 45 ℃, and the secondary acid leaching time was 3 h; the volume ratio of the second acid solution to choline chloride-urea was 3:1, and the molar ratio of choline chloride to urea in the choline chloride-urea mixture was 1:2. The concentration of tributyl phosphate in the organic solution was 4 mol / L, and the volume ratio of the organic solution to the combined leachate was 1:0.5. The third acid solution used for lithium back-extraction is a 6 mol / L hydrochloric acid solution, and the volume ratio of the first organic phase to the third acid solution is 1:1. In the mixed solution used for iron back-extraction, the concentration of sodium sulfite is 0.8 mol / L, the concentration of sodium chloride is 5 mol / L, the pH of the mixed solution is 1.5, the redox potential is 300 mV, and the volume ratio of the second organic phase to the mixed solution is 1:4. The fourth acid solution used for gallium back-extraction is a 2 mol / L hydrochloric acid solution, and the volume ratio of the third organic phase to the fourth acid solution is 1:1. In germanium complex extraction, the molar ratio of tartaric acid to germanium in the first raffinate is 2:1, and the volume fraction of trioctylmethylammonium chloride in the organic phase used for extraction is 0.5%. The fifth acid solution used for germanium back-extraction was a 0.1 mol / L hydrochloric acid solution, and the volume ratio of the germanium-rich organic phase to the fifth acid solution was 1:3.

[0050] The remaining steps are the same as in Example 1.

[0051] Example 5 The difference from Example 1 is as follows: In the first-stage acid leaching, the concentration of the first acid solution was 3 mol / L, the solid-liquid ratio of the fly ash from the thermal power plant to the first acid solution was 1 g: 6 mL, the first-stage acid leaching temperature was 100 ℃, and the first-stage acid leaching time was 3.5 h. In the secondary acid leaching, the concentration of the second acid solution was 2 mol / L, the solid-liquid ratio of the first filter residue to the mixture of the second acid solution and choline chloride-urea was 1 g:7 mL, the secondary acid leaching temperature was 75 ℃, and the secondary acid leaching time was 1.5 h; the volume ratio of the second acid solution to choline chloride-urea was 4:1, and the molar ratio of choline chloride to urea in the choline chloride-urea mixture was 1:1. The concentration of tributyl phosphate in the organic solution was 2 mol / L, and the volume ratio of the organic solution to the combined leachate was 1:5. The third acid solution used for lithium back-extraction is a 4 mol / L hydrochloric acid solution, and the volume ratio of the first organic phase to the third acid solution is 1:1. In the mixed solution used for iron back-extraction, the concentration of sodium sulfite is 0.5 mol / L, the concentration of sodium chloride is 8 mol / L, the pH of the mixed solution is 3.0, the redox potential is 270 mV, and the volume ratio of the second organic phase to the mixed solution is 1:5. The fourth acid solution used for gallium back-extraction is a 0.1 mol / L hydrochloric acid solution, and the volume ratio of the third organic phase to the fourth acid solution is 1:0.5. In germanium complex extraction, the molar ratio of tartaric acid to germanium in the first raffinate is 2:1, and the volume fraction of trioctylmethylammonium chloride in the organic phase used for extraction is 0.3%. The fifth acid solution used for germanium back-extraction was a 1.5 mol / L hydrochloric acid solution, and the volume ratio of the germanium-rich organic phase to the fifth acid solution was 1:2.

[0052] The remaining steps are the same as in Example 1.

[0053] Comparative Example 1 The difference between this comparative example and Example 1 is that a secondary acid leaching is not performed. That is, the first filter residue obtained after the primary acid leaching is not subjected to a secondary acid leaching with a mixture of the second acid solution and choline chloride-urea. The remaining extraction, back-extraction and germanium recovery steps are performed as in Example 1.

[0054] Compared with Example 1, this comparative example lacks the secondary acid leaching process involving the second acid solution and choline chloride-urea. This difference is mainly used to illustrate the role of secondary acid leaching in increasing the release of residual lithium, iron, gallium, and germanium from fly ash.

[0055] Comparative Example 2 The difference between this comparative example and Example 1 is that choline chloride-urea is not added to the mixed solution used for the secondary acid leaching, and only the second acid solution is used to perform secondary acid leaching on the first filter residue. The remaining steps are the same as in Example 1.

[0056] Compared to Example 1, this comparative example retains the secondary acid leaching with hydrochloric acid, but does not contain the eutectic system components of choline chloride-urea. This difference is mainly used to illustrate the role of choline chloride-urea in promoting further leaching of residual metals in the first filter residue.

[0057] The elemental content of the lithium, iron, gallium, and germanium product solutions obtained in the examples or comparative examples was tested, and the recovery rate of the corresponding metal was calculated based on the content of each metal in the original fly ash of the thermal power plant and the metal content in each product solution. The test results are shown in Table 1.

[0058] Table 1. Recovery rate test results of various elements in the examples and comparative examples.

[0059] As can be seen from the data in Table 1, in the embodiments of this application, the recovery rates of Li, Fe, Ga and Ge in fly ash are all not less than 35%. This process can simultaneously complete the extraction and stepwise recovery of multiple valuable metals such as Li, Fe, Ga and Ge in the same process, which helps to simplify the process and improve the overall recovery level.

[0060] The above-described embodiments are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A method for the synergistic extraction of lithium, iron, gallium, and germanium from fly ash of thermal power plants, characterized in that, Includes the following steps: S1, the fly ash from the thermal power plant is subjected to a first-stage acid leaching with a first acid solution, and after solid-liquid separation, it is washed with water to obtain a first filtrate and a first filter residue; the first filter residue is subjected to a second-stage acid leaching with a mixture of a second acid solution and choline chloride-urea, and after solid-liquid separation, a second filtrate and a second filter residue are obtained. S2, remove choline chloride-urea from the second filtrate, combine the treated second filtrate with the first filtrate to obtain a combined leachate; extract the combined leachate with an organic solution composed of tributyl phosphate and a diluent to obtain a first organic phase rich in lithium, iron and gallium and a first raffinate; S3, the first organic phase is back-extracted using a third acid solution to obtain a lithium product solution and a second organic phase; S4, the second organic phase is back-extracted using a mixed solution containing a reducing agent and a salting-out agent to obtain an iron product liquid and a third organic phase; S5, the third organic phase is back-extracted using the fourth acid solution to obtain gallium product solution and regenerated organic phase; S6, add a complexing agent to the first raffinate to obtain a complexing solution, add a quaternary ammonium salt extractant to the complexing solution for extraction, and obtain a germanium-rich organic phase and a second raffinate; S7. The germanium-rich organic phase is back-extracted using the fifth acid solution to obtain a germanium product solution.

2. The method for co-extracting lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S1, the first acid solution is a hydrochloric acid solution with a concentration of 2~5 mol / L, the solid-liquid ratio of the fly ash from the thermal power plant to the first acid solution is 1:(4~7) g / mL, and the temperature of the first acid leaching is 60~100℃ and the time is 3~5h. The second acid solution is a hydrochloric acid solution with a concentration of 2~8 mol / L. The solid-liquid ratio of the first filter residue to the mixture composed of the second acid solution and choline chloride-urea is 1:(4~7) g / mL. The temperature of the secondary acid leaching is 45~85℃ and the time is 1~3h. The volume ratio of the second acid solution to the choline chloride-urea solution is (2~5):1, and the molar ratio of choline chloride to urea in the choline chloride-urea solution is 1:(0.5~2).

3. The method for co-extracting lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S2, the concentration of tributyl phosphate in the organic solution is 1-4 mol / L; the diluent includes at least one of dichloromethane, trichloromethane, and carbon tetrachloride. The volume ratio of organic solution to combined leachate is 1:(0.5~5).

4. The method for co-extracting lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S3, the third acid solution is a hydrochloric acid solution with a concentration of 4~8 mol / L, and the volume ratio of the first organic phase to the third acid solution during back-extraction is 1:

1.

5. The method for co-extracting lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S4, the mixed solution contains hydrochloric acid, sodium sulfite, and sodium chloride. The sodium sulfite is used as a reducing agent with a concentration of 0.3~0.8 mol / L, and the sodium chloride is used as a salting-out agent with a concentration of 4~8 mol / L. The pH of the mixed solution is 1.5~3.0, and the redox potential is 250~300 mV. During back-extraction, the volume ratio of the second organic phase to the mixed solution is 1:(0.5~5).

6. The method for co-extracting lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S5, the fourth acid solution is a hydrochloric acid solution with a concentration of 0.1~2 mol / L; during back-extraction, the volume ratio of the third organic phase to the fourth acid solution is 1:(0.5~5).

7. The method for synergistic extraction of lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, The regenerated organic phase obtained in step S5 is returned to the combined leachate in step S2 for mixing.

8. The method for co-extracting lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S6, the complexing agent is tartaric acid, and the molar ratio of tartaric acid to germanium in the first raffinate is 2:

1. The volume ratio of the complexing solution to the quaternary ammonium salt extractant is 1:1; The quaternary ammonium salt extractant is an organic solution containing trioctylmethylammonium chloride, wherein the volume fraction of trioctylmethylammonium chloride in the organic solution is 0.2% to 0.5%.

9. The method for co-extracting lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S7, the fifth acid solution is a hydrochloric acid solution with a concentration of 0.1~2 mol / L; the volume ratio of the germanium-rich organic phase to the fifth acid solution is 1:(0.5~5).

10. The method for synergistic extraction of lithium, iron, gallium, and germanium from fly ash of thermal power plants according to claim 1, characterized in that, In step S2, choline chloride-urea in the second filtrate is removed and recovered by vacuum distillation, and the recovered choline chloride-urea is recycled for secondary acid leaching in step S1.

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