Use of metal-organic particles for the adsorption of germanium ions in aqueous solutions and method for adsorbing germanium ions

Abstract

The present invention relates to the field of adsorbent materials, and specifically to the use of metal-organic particles (MOF), intended for the selective adsorption of germanium ions in aqueous solutions. The invention also relates to a method for adsorbing Ge ions.

Description

[0001] USE OF METAL-ORGANIC PARTICLES FOR THE ADSORPTION OF GERMANIUM IONS IN AQUEOUS SOLUTIONS AND METHOD FOR THE ADSORPTION OF GERMANIUM IONS

[0002] DESCRIPTION

[0003] The present invention relates to the field of adsorbent materials, and specifically to the use of metal-organic framework (MOF) particles for the selective adsorption of germanium ions in aqueous solutions. It also relates to a method for adsorbing germanium ions.

[0004] Background of the invention

[0005] In the context of the growing need for efficient and selective methods for the recovery and removal of valuable metals, such as germanium, from aqueous solutions, various adsorbent materials and processes have been developed that enable effective separation. Germanium is a critical element in several technological industries, and its recovery and purification are essential for both resource sustainability and environmental protection.

[0006] There are numerous methods for the removal and recovery of inorganic ions present in aqueous solutions, including ion exchange, adsorption, chemical precipitation, solvent extraction, and electrochemical methods, among others.

[0007] Various techniques have been developed for the recovery of germanium, allowing for its extraction and concentration. One of the oldest methods, still in use, is based on the precipitation of germanium as sulfide or mixtures of hydroxides. This precipitate is then redissolved in hydrochloric acid, and through a fractional distillation process, high-purity germanium tetrachloride (GeCl4) is obtained.

[0008] Among the methods applicable at an industrial level, liquid-liquid extraction stands out, employing specific agents to maximize germanium recovery efficiency. Examples of these agents include 8-hydroxyquinoline and tartaric acid, among others.

[0009] Other relevant solutions are described in patent CN113019342B, which details a method for germanium recovery using a composite magnetic adsorbent. This method employs an adsorbent material with magnetic properties for the efficient extraction of germanium, leveraging both the material's adsorption capacity and its response to external magnetic fields to facilitate recovery. This approach offers advantages in terms of ease of handling and separation of the adsorbent after use, thus optimizing the germanium recovery process.

[0010] Furthermore, patent DE102021212510 addresses a method for treating water that removes germanium from aqueous solutions containing it. In this method, the germanium-containing solution is passed through an adsorbent material containing iron hydroxide. The adsorbent material, in this case, is inorganic and has a granular structure with an average grain size ranging from 0.2 mm to 2.0 mm. Additionally, the adsorbent material may be composed of FeOOH and / or Fe(OH)3, which gives it a high affinity for adsorbing germanium ions in aqueous media.

[0011] Despite these advances in germanium adsorption technology, there is a need to develop new composite materials that combine high adsorption capacity, stability, and selectivity for germanium ions.

[0012] Description of the invention

[0013] The recovery of germanium from aqueous solutions faces several significant technical obstacles. First, the low concentrations of germanium in these solutions make its recovery unprofitable when using conventional techniques.

[0014] The invention involves the use of metal-organic framework (MOF) particles, specifically Fe-MIL-88C, for the adsorption of germanium (Ge) ions present in aqueous solutions. This material offers high capacity and selectivity for germanium ion capture, providing an efficient solution for water purification and the recovery of this valuable metal in industrial processes.

[0015] The invention also relates to a method for adsorbing germanium ions in aqueous solutions by adding Fe-MIL-88C particles to the aqueous solution containing Ge. This method enables the effective capture of germanium ions through the specific interaction between the particles and the ions in the solution, improving efficiency and allowing its application in water treatment and metal recovery processes.

[0016] The term “metal-organic framework (MOF) particles” refers to a class of advanced materials consisting of metal atoms coordinated with organic molecules to form highly porous structures, enabling the adsorption and storage of small molecules, such as ions. In iron-based MOFs, the iron is typically in the (III) oxidation state.

[0017] The Fe-MIL-88C particles have the chemical formula Fe6O45.2C89.2H88, 8.

[0018] The term germanium ions refers to germanium atoms that gain or lose electrons, thus acquiring an electrical charge. Germanium is a chemical element with atomic number 32. Examples of cations include Ge 2+ and Ge 4+ .

[0019] The different aspects of the invention have the following preferred embodiments.

[0020] Preferably, the particles are distributed in polymeric nanofibers in the form of a composite material.

[0021] The term “composite material” refers to a material formed by the combination of two or more different components, which when integrated produce a material with improved properties and characteristics superior to those of each individual component.

[0022] The invention introduces a nanofibrous composite material comprising polymeric nanofibers doped with Fe-MIL-88C particles, which efficiently adsorbs germanium (Ge) ions from aqueous solutions. The nanofibers exhibit high surface area and porosity (increasing contact with the solution; more adsorption sites equal more adsorption, with a low pressure rise in the adsorption process), are flexible, non-woven, and form a network (which can be useful for implementation in any shape or module), eliminate the need for phase separation (often used in industry with aggressive solvents), and are reusable in a continuous flow system (which could be helpful in an industrial process).

[0023] The composite nanofibers are synthesized through an electrospinning process, allowing precise control over the incorporation of Fe-MIL-88C particles within the polymer matrix. The electrospinning parameters are optimized to achieve a uniform distribution of the Fe-MIL-88C particles within the nanofibers, ensuring a larger surface area and high reactivity for ion adsorption. The final nanofiber structure exhibits high porosity and a large specific surface area, crucial for effective ion adsorption. Furthermore, they are flexible, non-woven materials, allowing their integration into various formats or modules. The adsorption in the present invention is selective ion adsorption, which refers to a process by which an adsorbent material captures and retains specific ions from a solution mixture, based on properties such as the size, charge, or chemical affinity of the ions.Adsorption is selective because the adsorbent material exhibits a preference for certain ions over others, allowing the separation or extraction of particular ions within a complex mixture.

[0024] Composite nanofibers are designed for the selective adsorption of Ge ions in aqueous solutions, especially at high pH levels. When introduced into aqueous solutions containing Ge ions, the Fe-MIL-88C particles act as active sites, selectively adsorbing Ge through ionic interactions. The term “nanofibers” refers to polymeric nanofibers, fibers with a diameter in the nanometer range, between 50 and 900 nanometers, manufactured from specific polymers. These fibers are distinguished by their high surface-to-volume ratio and their versatility in terms of chemical modification and functionalization.

[0025] Preferably, the metal-organic framework (MOF) particles, Fe-MIL-88C, are in a proportion of between 15% and 20% by weight relative to the weight of the polymeric nanofibers.

[0026] All the nanofibers evaluated showed stability at both pH levels, and PAN and PVDF-HFP were selected for the development of nanofiber composite materials due to their ease of electrospinning and high chemical resistance. PAN nanofibers retain more water, while PVDF-HFP nanofibers are more hydrophobic, which helps reduce water retention. Specifically, the polymeric nanofibers are polyacrylonitrile nanofibers (PAN).

[0027] Water stability is an extremely important property for the proper functioning of the adsorbent particle. The adsorbent material must also withstand low and high pH levels, especially under specific alkaline solution conditions.

[0028] Preferably, the adsorption of Ge ions is carried out in aqueous solutions where the pH of the aqueous solution is between 9 and 12.

[0029] EXAMPLES

[0030] The following examples are for illustrative purposes only and should not be interpreted in a limiting sense.

[0031] Synthesis and Stability of Fe-MIL-88C: FeC₂-6H₂O (2.56 g) and 2,6-naphthalenedicarboxylic acid (2.08 g) were dispersed in 100 mL of DMF. The mixture was transferred to a 250 mL round-bottom flask and heated to 130 °C under continuous stirring for 18 h. The product was collected by centrifugation, washed three times with pure DMF, and dried under vacuum. 1.41 g of Fe-MIL-88C was obtained.

[0032] The stability experiments consisted of analyzing the metal adsorbent content of a sample after prolonged contact time in an aqueous medium at pH 3 and 12. Specifically, 40 mg of the adsorbent under study were added to 40 mL of aqueous solution at pH 3, and the same amount at pH 12. After 24 h of immersion with continuous rotation, an aliquot of this solution was taken and filtered through a 0.45 µm PVDF syringe filter, which was designed to retain all solid adsorbent particles. The aliquots were then analyzed by inductively coupled plasma mass spectrometry, or ICP-MS (ICP-MS model 7500CX, Agilent Technologies), searching for metal ions that are precursors to the MOF clusters under study. If metal is detected, it is most likely that the metal-organic structure of the MOF is breaking down with the solution environment and, therefore, the adsorbent is not stable.

[0033] Fe-MIL-88C is stable at pH 3 and pH 12.

[0034] Example 2. Synthesis of nanofibers and synthesis of the MOF nanofiber composite material

[0035] The nanofibers were prepared by electrospinning. In electrospinning, the polymer solution is pumped through a needle, and a high voltage is applied between the needle and the collector to overcome the surface tension of the solution and form an electrified jet. As the solvent evaporates, the polymer fiber is deposited on the collector.

[0036] First, different polymeric nanofibers were developed and their stability was evaluated at pH 3 and 12. The stability tests performed were similar to those used for particle stability. The PAN and PVDF-HFP nanofibers were found to be stable at pH 3 and pH 12.

[0037] Synthesis of MOF nanofiber composite material.

[0038] Electrospinning was performed with a polymer solution containing MOF particles dispersed in a solution.

[0039] The experimental methodology followed for the development of the composite materials consisted, first, of calculating all the quantities necessary for preparing the electrospinning solution. Two-thirds of the solvent solution was used for the preliminary dissolution of the polymer, and the other third for particle dispersion. Polymer dissolution was aided by heating to 50 °C while stirring. Particle dispersion was performed using a VCX750 ultrasonic processor (SONICS) for 10 minutes at a 1:1 pulse ratio.

[0040] The PAN solution was set at 10% by weight due to its ease of electrospinning and the good results obtained in previous work. The PVDF-HFP solution was set at 17.5% by weight. The adsorbent mass content ranged between 5% and 20% by weight relative to the polymer weight in most cases.

[0041] Table 1: Summary of the different composite materials developed

[0042] Adsorption experiments were performed in batches by contacting aqueous solutions of metal ions with a constant amount of adsorbent material at room temperature under rotary stirring. The pH of the metal solutions was controlled with standardized solutions of 0.1 M HCl or 1.0 M NaOH, and the pH was confirmed with a pH meter. The initial metal concentration in the solution was set at 100 ppm. Four pH values—3, 6, 10, and 12—were initially selected as the pH of interest. Stock solutions of 100 ppm Ge(IV) were prepared by dissolving the appropriate amount of Ge₂ (500 mL, 72.03 mg, pH 10 and 12). All reagents were purchased from Sigma-Aldrich.

[0043] After 24 h under rotary stirring, as the stipulated contact time to ensure adsorption saturation, the solid phase (adsorbent material) was removed, stored and allowed to dry in glass vials, while an aliquot of the aqueous phase was filtered and stored to determine the analyte content of interest by ICP-MS (model 7500CX, Agilent Technologies) or ICP-AES (model ICAP 6300, Thermo).

[0044] The adsorption capacity (q, mmol / g) was obtained from the initial (Cin¡ , mmol / L) and final concentration of the metal (Cf¡ n , mmol / L) for each experiment and following the equation:

[0045] Where V a ds is the volume of solution used in the experiment ym ads is the amount of adsorbent used (g). The solution volume was set at 40 mL for each pH. The amount of adsorbent used was set at 40 mg per experiment (metal and pH). Aliquots were filtered using a 0.45 µm syringe filter or a 0.22 PVDF filter to separate the adsorbent material from the solution to be analyzed. The final metal concentrations in the aliquots were analyzed by ICP-MS or ICP-AES.

[0046] Table 2: Results of the adsorption capacity in mg / g of the tested adsorbents for Ge at both pH.

Claims

CLAIMS 1. Use of metal-organic framework (MOF) particles, Fe-MIL-88C; for the adsorption of Ge ions in aqueous solutions.

2. Use of metal-organic framework (MOF) particles, Fe-MIL-88C; according to claim 1 characterized in that the particles are distributed in the polymer nanofibers forming a composite material.

3. Use of metal-organic framework (MOF) particles, Fe-MIL-88C according to claim 2 characterized in that the metal-organic framework (MOF) particles, Fe-MIL-88C, are in a proportion of between 15% and 20% by weight relative to the weight of the polymeric nanofibers.

4. Use of metal-organic framework (MOF) particles, Fe-MIL-88C according to claim 2 or 3 characterized in that the polymeric nanofibers are polyacrylonitrile (PAN) nanofibers.

5. Use according to any of claims 1 to 4 characterized by the adsorption of Ge ions in aqueous solutions where the pH of the aqueous solution is between 9 and 12.

6. Method of adsorption of Ge ions in aqueous solutions comprising the addition of Fe-MIL-88C particles in the aqueous solution.

7. Ge ion adsorption method according to claim 6 characterized in that the particles are distributed in the polymeric nanofibers forming a composite material.

8. Ge ion adsorption method according to claim 7 characterized in that the metal-organic framework (MOF) particles, Fe-MIL-88C, are in a proportion of between 15% and 20% by weight relative to the weight of the polymeric nanofibers.

9. Method for adsorption of Ge ions according to claim 7 or 8 characterized in that the polymeric nanofibers are polyacrylonitrile (PAN) nanofibers.

10. Method for adsorbing Ge ions according to any one of claims 6 to 9 characterized by the adsorption of Ge ions in aqueous solutions where the pH of the aqueous solution is between 9 and 12

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