CN-121992208-A - Supercritical CO of fly ash strategic metal2Membrane extraction process

Abstract

The invention provides a supercritical CO 2 membrane extraction method for fly ash strategic metals, and relates to the technical field of solid waste resource utilization and environmental protection. The invention adopts TBP and DEHCNPB composite chelating agent and ethanol-methanol composite modifier to obviously improve the compatibility of strategic metal ions and supercritical CO 2 and enhance complexation capability, uses supercritical CO 2 as extractant, and CO 2 can be recycled, has no solvent residue, and can be mechanically activated and pretreated to destroy the stable structure of strategic metal in fly ash, thereby greatly improving extraction efficiency, and the extraction rate of strategic metal such as rare earth element, lithium, gallium and the like can reach more than 90%, wherein the extraction rate of rare earth element such as Nd, eu and the like can exceed 97%. Through the selective screening effect of the polyimide graphene composite membrane, the precise fractionation of different strategic metals is realized, the separation purity reaches more than 98%, and the problems of poor selectivity and complicated subsequent separation in the traditional process are solved.

Inventors

• WANG BEN
• YANG WU
• BEI LEI
• DU JIAXING
• BAI MINGFENG

Assignees

• 华中科技大学

Dates

Publication Date

20260508

Application Date

20260304

Claims (10)

1. 1. The supercritical CO 2 membrane extraction method for the fly ash strategic metals is characterized by comprising the following steps: Step 1, pre-treating fly ash, namely crushing and screening the fly ash to 100-200 meshes to remove large-particle impurities, removing chloride and soluble impurities in the fly ash by adopting a multistage countercurrent water washing process, and performing vacuum drying after water washing is finished to obtain pre-treated fly ash; Step 2, preparing an extraction system, namely adding a chelating agent and a modifier into the extraction system by taking supercritical CO 2 as an extractant, and uniformly stirring the mixture to prepare a composite extraction system; Step 3, supercritical CO 2 membrane extraction, namely loading the pretreated fly ash into a supercritical extraction kettle, introducing the composite extraction system prepared in the step 2, controlling specific temperature, pressure and stirring rotation speed to perform extraction, and performing fractional separation of strategic metal complex by a polyimide-graphene composite membrane component connected with an outlet of the extraction kettle in the extraction process; step 4, metal analysis and purification, namely respectively introducing each component separated by the membrane into an analysis kettle, converting supercritical CO 2 into a gas state by a decompression and heating mode, recycling, adding an analysis agent into the analyzed metal-chelating agent complex solution, and performing analysis, precipitation, filtration and crystallization treatment to obtain a high-purity strategic metal compound; And 5, residue treatment, namely taking out the extraction residues left in the extraction kettle, and carrying out resource utilization or harmless landfill after detecting and confirming that the strategic metal content is lower than the emission standard, wherein the fly ash comprises waste incineration fly ash and coal-fired fly ash, and the strategic metal comprises one or more of rare earth elements, lithium, gallium, chromium, lead, zinc, copper and arsenic.
2. 2. The supercritical CO 2 membrane extraction method for fly ash strategic metals according to claim 1, wherein the specific parameters of the multistage countercurrent water washing process in step 1 are that the water-ash ratio is 3-5:1, the water washing temperature is 25-35 ℃, the water washing time is 30-60min, the dechlorination efficiency of the fly ash after water washing is more than or equal to 95%, and the chlorine content of the fly ash after dechlorination is less than or equal to 1%.
3. 3. The supercritical CO 2 membrane extraction method for fly ash strategic metals according to claim 1, wherein the specific parameters of the vacuum drying in the step 1 are that the drying temperature is 60-80 ℃, the drying time is 2-4h, and the water content of the fly ash after drying is less than or equal to 5%.
4. 4. The supercritical CO 2 membrane extraction process of flyash strategic metal according to claim 1, characterized in that, after the flyash is screened and before the water washing in step 1, the process further includes a mechanical activation pretreatment step, the mechanical activation time is 10-30min, and the mechanical force breaks the stable lattice structure of strategic metal in flyash.
5. 5. The supercritical CO 2 membrane extraction process of fly ash strategic metals according to claim 1, wherein the chelating agent in step 2 is a mixture of TBP (tributyl phosphate) and DEHCNPB (bis (2-ethylhexyl) cyanophosphonate) and the modifier is a mixture of ethanol and methanol.
6. 6. The method for supercritical CO 2 membrane extraction of fly ash strategic metals according to claim 5, wherein the chelating agent in step 2 is added in an amount of 0.5% -5% by mass of supercritical CO 2 , the mass ratio of TBP to DEHCNPB is 1:0.5-2, the modifier is added in an amount of 1% -10% by mass of supercritical CO 2 , and the volume ratio of ethanol to methanol is 1:1-3.
7. 7. The supercritical CO 2 membrane extraction method for fly ash strategic metals according to claim 1, wherein the specific parameters of the supercritical CO 2 membrane extraction in the step3 are that the extraction temperature is 40-80 ℃, the extraction pressure is 15-30MPa, the stirring rotation speed is 200-500r/min, and the extraction time is 60-180min.
8. 8. The method for supercritical CO 2 membrane extraction of fly ash strategic metals according to claim 1, wherein the pore diameter of the polyimide-graphene composite membrane in the step 3 is 5-20nm, and the separation purity is not less than 98% according to the molecular size precise fractionation of strategic metal complex.
9. 9. The supercritical CO 2 membrane extraction method for fly ash strategic metals according to claim 1, wherein the specific parameters of the analysis in the step 4 are that the analysis agent is hydrochloric acid or nitric acid with the concentration of 0.5-2mol/L, the analysis temperature is 40-60 ℃, the analysis time is 30-60min, the analysis rate of metal ions after the analysis is more than or equal to 99%, and the recycling rate of the CO 2 is more than or equal to 95% after the recovery, compression and cooling treatment.
10. 10. The method for supercritical CO 2 membrane extraction of fly ash strategic metals according to claim 1, wherein the recycling way of the extraction residues in step 5 is as building material raw materials, including building bricks and cement raw materials, and the harmless treatment way is harmless landfill.

Description

Supercritical CO 2 membrane extraction method for fly ash strategic metals Technical Field The invention relates to the technical field of solid waste recycling and environmental protection, in particular to a supercritical CO 2 membrane extraction method for fly ash strategic metals. Background Fly ash is a main solid waste produced in industrial processes of coal-fired power plants, garbage incineration plants and the like, the annual production amount of China is up to hundreds of millions of tons, the accumulated accumulation and storage amount is huge, a large amount of land resources are occupied, and the substances such as heavy metals, strategic metals and the like which are enriched in the fly ash are easy to cause soil and water pollution, so that ecological environment and human health are threatened. The waste incineration fly ash is rich in heavy metals such as chromium, lead, zinc and the like, part of coal-fired fly ash is also rich in scattered strategic metals such as lithium, gallium and the like, and the strategic metals are key raw materials in the modern industrial fields such as aerospace, electronic information, new energy and the like, and have extremely high recovery value. At present, the recovery method of strategic metals in fly ash mainly comprises traditional processes such as wet leaching and pyrometallurgy, but the methods have the problems of low selectivity, high energy consumption, serious environmental pollution, limited extraction efficiency and the like. The wet leaching method needs a large amount of acid-base reagents, is easy to produce secondary pollution, has the defects of high energy consumption, low metal recovery rate, easy element volatilization loss and the like in the pyrometallurgy, and is difficult to realize the efficient and green recovery of strategic metals. The supercritical CO 2 extraction technology is used as a green and efficient separation technology, has the advantages of good environmental compatibility, strong permeability, high extraction efficiency, recycling and the like, and has been widely applied to the extraction of heavy metals and rare earth elements in soil and sludge. Supercritical CO 2 can penetrate through pores and cracks of the solid matrix to be fully contacted with target metal, and the compatibility of metal ions and CO 2 can be effectively improved by adding a chelating agent and a modifying agent, so that the extraction efficiency is improved. However, the existing supercritical CO 2 extraction technology still has obvious defects in the recovery of the strategic metals of the fly ash, namely, the fly ash substrate is complex, contains a large amount of impurities such as silicon, aluminum, calcium and the like, is easy to cause the invalidation of an extractant, increases the mass transfer resistance, reduces the extraction selectivity and efficiency, is difficult to realize the precise separation of different strategic metals by single supercritical CO 2 extraction, has complicated subsequent separation and purification steps, and has lower content of part of strategic metals (such as rare earth elements) in the fly ash, and is mostly in the form of stable compounds, the direct extraction difficulty is high, the complex pretreatment process is needed, and the recovery cost and the environmental burden are further increased. The membrane separation technology has the characteristics of high separation efficiency, low energy consumption, simple operation, no secondary pollution and the like, and can realize the accurate fractionation of substances. The membrane separation technology is combined with the supercritical CO 2 extraction technology, and the problems of poor selectivity and high separation difficulty of the single extraction technology can be effectively solved by utilizing the selective screening effect of the membrane. However, there is no report on how to optimize the process parameters and screen the adaptive membrane materials and extraction system to realize the efficient, green and accurate recovery of the strategic metals in the fly ash, which is a technical problem to be solved currently. Therefore, a supercritical CO 2 membrane extraction method of fly ash strategic metals is provided. Disclosure of Invention Aiming at the problems of low selectivity, high energy consumption, serious environmental pollution, high separation difficulty and the like of the existing fly ash strategic metal recovery technology, the invention provides the fly ash strategic metal supercritical CO 2 membrane extraction method, which combines the efficient extraction capability of supercritical CO 2 and the precise separation advantage of a membrane by optimizing a pretreatment process and screening an adaptive extraction system and a membrane material, realizes the efficient extraction and the grading separation of strategic metals in the fly ash, takes the recovery efficiency and the environmental friendliness into considerat