A method for enriching rare metals in sodium aluminate mother liquor based on microfluidics technology

Abstract

This invention discloses a method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology, comprising: providing a strongly alkaline sodium aluminate mother liquor containing target rare and dispersed metal ions; preparing highly active iron-based adsorbent wet powder using a microreactor: pumping an iron salt solution and an alkaline solution into the microreactor for a spray reaction, controlling the theoretical pH value of the mixture, and separating the solid and liquid phases after the reaction to obtain the iron-based adsorbent wet powder; washing the iron-based adsorbent wet powder and adding it to the sodium aluminate mother liquor for a heterogeneous adsorption reaction to form a slurry; performing solid-liquid separation on the adsorbed slurry, washing the obtained solid product and drying it overnight to obtain the final product enriched with rare and dispersed metals. This invention utilizes microfluidic technology to eliminate the defects of macroscopic mixing inhomogeneity, and the prepared adsorbent has a higher specific surface area and surface activity, significantly shortening the adsorption equilibrium time and significantly reducing the aluminum loss rate in the mother liquor, with advantages such as short process, high efficiency, and good selectivity.

Description

Technical Field

[0001] This invention relates to the fields of hydrometallurgy and microchemical technology, and in particular to a method for enriching rare dispersed metals in sodium aluminate mother liquor based on microfluidic technology. Background Technology

[0002] Rare and dispersed metals (Rb, Ga, Ge, V, etc.) are important strategic resources in modern industry and are often found in the sodium aluminate mother liquor produced in the alumina industry. Due to the strong alkalinity, high salt content, and complex composition of the mother liquor, the efficient extraction of trace rare and dispersed metals from it has always been a challenge for the industry.

[0003] Traditional heterogeneous adsorption methods often use adsorbents prepared by ordinary chemical precipitation. Due to the low macroscopic mixing efficiency, the adsorbent particles are prone to agglomeration and have few active sites, resulting in a long adsorption equilibrium time (often more than 20 hours). Furthermore, during long-term adsorption, there will be a serious precipitation loss of aluminum and silicon resources in the mother liquor.

[0004] Microfluidics technology, with its excellent mass transfer and mixing characteristics at the micrometer scale, enables the controllable preparation of adsorbents. However, its applications are currently mostly concentrated in the treatment of heavy metal ion wastewater, and its application in the enrichment of rare and dispersed metals in strongly alkaline high-salt sodium aluminate mother liquor systems is still rare.

[0005] Therefore, in order to overcome the shortcomings of traditional adsorption methods, such as long reaction time, low adsorbent activity, and large loss of main resources, developing a process for rapidly preparing adsorbents with extremely high adsorption activity has important engineering application value. Summary of the Invention

[0006] In view of this, the present invention provides a method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology. It proposes a method for preparing adsorbents with good dispersibility and fully exposed active sites using microfluidic technology, which can efficiently enrich rare and dispersed metals in sodium aluminate mother liquor, shorten the adsorption equilibrium time, and reduce the precipitation loss of aluminum and silicon resources.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for enriching rare dispersed metals in sodium aluminate mother liquor based on microfluidic technology includes the following steps:

[0009] (1) Provide a strongly alkaline sodium aluminate mother liquor containing the target rare metal ions;

[0010] (2) Preparation of highly active iron-based adsorbent wet powder by microreactor spraying: Iron salt solution as phase A and alkaline solution as phase B are pumped into microreactor for spraying reaction, the theoretical pH value of the mixed system is controlled, and the iron-based adsorbent wet powder is obtained by solid-liquid separation after reaction.

[0011] (3) After washing the wet powder of the iron-based adsorbent, add it to the sodium aluminate mother liquor in step (1), stir to carry out heterogeneous adsorption reaction, and form a slurry;

[0012] (4) The adsorbed slurry is subjected to solid-liquid separation. The resulting solid product is washed and dried overnight to obtain the final product enriched with rare dispersed metals.

[0013] Preferably, in step (1), the prepared iron salt solution and sodium hydroxide solution are rapidly mixed by spraying through a microreactor system at a volume ratio of 1:1 to 1:2.

[0014] The reaction equation is:

[0015]

[0016] or

[0018] Preferably, in step (1), the sodium aluminate mother liquor is a seed mother liquor from the industrial alumina production process; the target rare dispersed metal includes at least one or more of gallium (Ga), rubidium (Rb), germanium (Ge), and vanadium (V).

[0019] Preferably, in step (2), the iron salt includes, but is not limited to, one or more of ferric sulfate, ferric chloride, ferric nitrate, or organic iron salts;

[0020] Fe 3+ with Fe 2+ The molar ratio is (0-2):1;

[0021] The alkaline solution is a sodium hydroxide solution, wherein the amount of sodium hydroxide is controlled according to the pH of the system.

[0022] Preferably, in step (2), the theoretical pH value is 11-13, and the actual pH value after spraying is 11-14.

[0023] Preferably, in step (2), the channel characteristic size of the microchannel reactor is 0.5-1.5 mm, the total fluid residence time is less than 1 second, turbulence is formed, and the iron-based adsorbents Fe(OH)2 and Fe3O4 are instantly and uniformly nucleated and grown.

[0024] Preferably, in step (2), the microreactor spray preparation process achieves continuous, large-scale industrial in-situ preparation of adsorbent precursors by combining multiple microchannel mixing modules in parallel (Numbering-up).

[0025] Preferably, in step (3), the adsorption time is 30 min to 3 h.

[0026] Preferably, the cleaning step before addition in step (3) is as follows: the wet powder of the adsorbent is cleaned 3-4 times with deionized water and anhydrous ethanol;

[0027] The washing step of the obtained solid product in step (4) is as follows: wash 2-3 times with deionized water or hot water at 30-60℃, and then rinse 2-3 times with low temperature water.

[0028] Preferably, in step (4), the product is dried overnight at 60°C.

[0029] The present invention achieves the following technical effects compared to the prior art:

[0030] (1) Adsorption kinetics are significantly improved:

[0031] The adsorbent prepared by the present invention using a microreactor has extremely high activity, which shortens the traditional adsorption time of more than 20 hours to 1-3 hours, thus greatly improving production efficiency.

[0032] (2) Excellent aluminum loss control:

[0033] Compared with traditional long-term adsorption, this invention effectively suppresses the loss of aluminum resources through short-term heterogeneous adsorption. Experimental data show that the Fe3O4 adsorbent prepared by this invention captures rare and dispersed metals while the Al content in the product is significantly lower than that of traditional methods, effectively preserving the main aluminum resources.

[0034] (3) The preparation process is continuous and controllable:

[0035] The microreactor preparation process of this invention can be easily scaled up through parallel connection, and can precisely control the stability of product quality. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of the present invention;

[0037] Figure 2 This is a bar chart showing the loss rate of Al in Embodiments 1, 2 and 3 of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] This invention discloses a method for enriching rare dispersed metals in sodium aluminate mother liquor based on microfluidic technology, comprising the following steps:

[0040] (1) Provide a strongly alkaline sodium aluminate mother liquor containing the target rare metal ions;

[0041] (2) Preparation of highly active iron-based adsorbent wet powder by microreactor spraying: Iron salt solution as phase A and alkaline solution as phase B are pumped into microreactor for spraying reaction, the theoretical pH value of the mixed system is controlled, and the iron-based adsorbent wet powder is obtained by solid-liquid separation after reaction.

[0042] (3) After washing the wet powder of the iron-based adsorbent, add it to the sodium aluminate mother liquor in step (1), stir to carry out heterogeneous adsorption reaction, and form a slurry;

[0043] (4) The adsorbed slurry is subjected to solid-liquid separation. The resulting solid product is washed and dried overnight to obtain the final product enriched with rare dispersed metals.

[0044] In step (1), the prepared iron salt solution and sodium hydroxide solution are rapidly mixed by spraying through a microreactor system at a volume ratio of 1:1 to 1:2.

[0045] The reaction equation is:

[0046]

[0047] or

[0049] In step (1), the sodium aluminate mother liquor is a seed mother liquor in the industrial alumina production process; the target rare dispersed metal includes at least one or more of gallium (Ga), rubidium (Rb), germanium (Ge), and vanadium (V).

[0050] In step (2), the iron salt includes, but is not limited to, one or more of ferric sulfate, ferric chloride, ferric nitrate, or organic iron salts;

[0051] Fe 3+ with Fe 2+ The molar ratio is (0-2):1;

[0052] The alkaline solution is a sodium hydroxide solution, wherein the amount of sodium hydroxide is controlled according to the pH of the system.

[0053] In step (2), the theoretical pH value is 11-13, and the actual pH value after spraying is 11-14.

[0054] In step (2), the channel characteristic size of the microchannel reactor is 0.5-1.5 mm, the total fluid residence time is less than 1 second, turbulence is formed, which promotes the instantaneous and uniform nucleation and growth of iron-based adsorbents Fe(OH)2 and Fe3O4.

[0055] In step (2), the microreactor spray preparation process achieves continuous, large-scale industrial in-situ preparation of adsorbent precursors by combining multiple microchannel mixing modules in parallel (Numbering-up).

[0056] In step (3), the adsorption time is 30 min to 3 h.

[0057] The specific cleaning steps before addition in step (3) are as follows: use deionized water and anhydrous ethanol to clean the wet powder of the adsorbent 3-4 times;

[0058] The washing steps for the obtained solid product in step (4) are as follows: wash 2-3 times with deionized water or hot water at 30-60℃, and then rinse 2-3 times with low temperature water.

[0059] In step (4), the product is dried overnight at 60°C.

[0060] Example 1:

[0061] Weigh 5.34g NaOH and add it to 100ml of deionized water to prepare phase A solution, and weigh 18.56g FeSO4·7H2O and add it to 100ml of deionized water to prepare phase B solution.

[0062] Phases A and B are simultaneously pumped into a Y-type micro-mixer at a flow rate ratio of 1:1 for instantaneous burst nucleation. The mixing time is <10ms, the Reynolds number is >2000, and turbulence is formed. At this point, the theoretical pH of the reaction endpoint is 11 (the actual pH is 11.86).

[0063] After completion, centrifugation was performed immediately at a speed of 8000 r / min for 5 min.

[0064] Subsequently, the solid product was washed 3-4 times with anhydrous ethanol and deionized water to remove the sulfate (SO4) ions covering its surface. 2- ), yielding 6.32g of wet powder. 3g of the wet powder was added to industrial sodium aluminate mother liquor and stirred for 1 hour to adsorb, resulting in a gray-black mixed slurry.

[0065] Subsequently, the mixed slurry was washed 3-4 times with deionized water and anhydrous ethanol, and then immediately centrifuged at 8000 r / min for 5 min to obtain a composite product with an actual weight of about 4.67 g, denoted as A1-B2-C3.

[0066] Example 2:

[0067] The preparation method is the same as in Example 1, except that the ratio of iron salt and NaOH is changed according to the reaction equation. While keeping the total molar amount constant, Fe is taken... 2+: Fe 3+The ratio of FeSO4·7H2O to Fe(NO3)3·9H2O is 1:1, with excess Fe... 2+ Ensure Fe 2+ It is not completely oxidized.

[0068] The actual weight of the wet powder was 6.43g. 2g of the wet powder was added to the industrial sodium aluminate mother liquor and stirred for 1h for adsorption. After centrifugation and washing, 2.53g of black mixed slurry was obtained, which was denoted as Fe3O4-1.

[0069] Comparative Example 1: The actual sodium aluminate mother liquor (containing elements such as Si, Al, K, Cl, Ga, Ge, Rb, and V) mentioned above is denoted as Mother Liquor-1. The initial contents of rare and dispersed metals, as well as aluminum and silicon, in Mother Liquor-1 are shown in Table 1.

[0070] Table 1: Content of rare and precious metals and Al and Si in mother liquor

[0071]

[0072] Comparative Example 2: The preparation method is the same as in Example 1, except that L9(3) was used. 3 An orthogonal experimental design was used to investigate three key factors affecting the enrichment effect of Fe(OH)₂ adsorbent: the endpoint pH of the adsorbent, adsorption time, and wet powder dosage. Factor A is denoted as the endpoint pH of the adsorbent (11, 12, 13), factor B as the adsorption time (1h, 2h, 3h), and factor C as the wet powder dosage (1g, 2g, 3g). Specific results are shown in Tables 2 and 3.

[0073] Table 2: Original Data and Range Analysis of Orthogonal Experiments

[0074]

[0075] Table 3: Proportion of each element in the adsorbed rare metal product

[0076]

[0077] Results and conclusions:

[0078] Figure 1 The process flow diagram of the present invention is shown in Table 2. Meanwhile, in conjunction with L9(3) in Table 2... 3Orthogonal experimental results and range analysis show that the influence of each factor on the adsorption effect of the Fe(OH)₂ system is in the following order: Factor C (wet powder dosage, range R = 2.9967) > Factor B (adsorption time, range R = 0.5594) > Factor A (adsorbent endpoint pH, range R = 0.2609). The wet powder dosage plays an absolutely dominant role, which further confirms that the iron-based adsorbent prepared by microfluidics is driven by its extremely large specific surface area and abundant surface hydroxyl active sites, a typical surface physicochemical-dominated process.

[0079] Based on this, the key sample extracted from the orthogonal experiment and Fe3O4-1 in Example 2 were subjected to ICP-MS / OES multi-element precision testing, and the results are shown in Table 3.

[0080] The results showed that the Fe3O4-1 prepared in Example 2 had the highest adsorption cutoff for Ga (reaching 0.0318%), which was significantly better than the Fe(OH)2 system under optimal conditions (0.029% for Al-B2-C3).

[0081] Furthermore, when the heterogeneous adsorption time of the Fe(OH)₂ system adsorbent was extended from 2 hours (A1-B2-C3) to 3 hours (A2-B3-C3), the solid-phase retention of the target rare metals (Ga, Rb) not only did not increase, but a catastrophic desorption and loss occurred (Ga decreased sharply from 0.029% to 0.0088%). The underlying metallurgical mechanism of this anomaly lies in the fact that prolonged stirring in a strongly alkaline, high-salt sodium aluminate mother liquor disrupts the metastable state of the mother liquor, causing the adsorbed ions to be "squeezed out" again. This fully demonstrates that the traditional adsorption process, which often lasts 20 hours, is not only inefficient but also extremely harmful.

[0082] This invention utilizes a highly active precursor prepared by microfluidics, which perfectly matches the kinetic window of "short-term rapid adsorption (1-2 hours)," allowing it to "exit" before a large amount of aluminum and silicon are precipitated, thus achieving efficient retention of rare dispersed metals and extreme suppression of aluminum loss.

[0083] Figure 2This is a bar chart showing the Al loss rate in Examples 1, 2, and 3 of this invention. Based on material balance results, the process of this invention successfully overcomes the bottleneck of severe loss of main resources caused by traditional heterogeneous adsorption while achieving targeted enrichment of rare and dispersed metals. Data shows that the aluminum loss rate of the system exhibits a high degree of responsiveness to key process parameters (especially the adsorbent dosage): at the low dosage boundary (such as sample A2-B2-C1), the aluminum loss rate can be suppressed to a maximum of 1.60%; while within the optimal process range that takes into account the optimal adsorption capacity of rare and dispersed metals, the aluminum loss rates of the Fe3O4 system (Fe3O4-1) and the Fe(OH)2 system (A1-B2-C3) remain stably controlled at low levels of 4.02% and 5.51%, respectively. Conversely, if the dosage is blindly increased and the adsorption time is extended to 3 hours, the aluminum loss rate significantly increases to 6.64%. This strategy cleverly utilizes the kinetic time difference between the rapid chemical adsorption of rare and dispersed metals and the nucleation and precipitation of amorphous aluminosilicates, effectively avoiding the induction period of large-scale co-precipitation of silica and aluminum in the mother liquor. This precise suppression of aluminum loss ensures that the impurity removal process does not disrupt the metastable state of the Bayer process seed liquor, highly meeting the stringent requirements of industrial systems for alkali and water balance, and demonstrating extremely strong engineering conversion potential.

[0084] Therefore, this invention innovatively introduces microfluidic spraying technology, overcoming the bottleneck of limited mass transfer in traditional batch synthesis, and successfully prepares highly active iron-based wet powder adsorbents (Fe(OH)2 and Fe3O4) with huge specific surface areas and abundant active sites. When these adsorbents are directly applied to a heterogeneous adsorption system of strongly alkaline sodium aluminate mother liquor, efficient and specific enrichment of rare and dispersed metals such as gallium (Ga), rubidium (Rb), germanium (Ge), and vanadium (V) is achieved within an extremely short kinetic window of 1 to 2 hours. Simultaneously, this ultra-fast, short-process technology successfully cuts off the reaction pathway of large-scale hydrolysis and co-precipitation of aluminum and silicon in the mother liquor, suppressing the loss of main aluminum resources to an extremely low level. Without interfering with the Bayer process's main production flow, it achieves a win-win situation of high-value rare and dispersed metal extraction and resource preservation, demonstrating outstanding industrial conversion potential and economic benefits.

[0085] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for enriching rare dispersed metals in sodium aluminate mother liquor based on microfluidic technology, characterized in that, Includes the following steps: (1) Provide a strongly alkaline sodium aluminate mother liquor containing the target rare metal ions; (2) Preparation of highly active iron-based adsorbent wet powder by microreactor spraying: Iron salt solution as phase A and alkaline solution as phase B are pumped into microreactor for spraying reaction, the theoretical pH value of the mixed system is controlled, and the iron-based adsorbent wet powder is obtained by solid-liquid separation after reaction. (3) After washing the wet powder of the iron-based adsorbent, add it to the sodium aluminate mother liquor in step (1), stir to carry out heterogeneous adsorption reaction, and form a slurry; (4) The adsorbed slurry is subjected to solid-liquid separation. The resulting solid product is washed and dried overnight to obtain the final product enriched with rare dispersed metals.

2. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (1), the prepared iron salt solution and sodium hydroxide solution are rapidly mixed by spraying through a microreactor system at a volume ratio of 1:1 to 1:

2. The reaction equation is: or .

3. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (1), the sodium aluminate mother liquor is a seed mother liquor in the industrial alumina production process; the target rare dispersed metal includes at least one or more of gallium (Ga), rubidium (Rb), germanium (Ge), and vanadium (V).

4. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (2), the iron salt includes, but is not limited to, one or more of ferric sulfate, ferric chloride, ferric nitrate, or organic iron salts; Fe 3+ with Fe 2+ The molar ratio is (0-2):1; The alkaline solution is a sodium hydroxide solution, wherein the amount of sodium hydroxide is controlled according to the pH of the system.

5. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (2), the theoretical pH value is 11-13, and the actual pH value after spraying is 11-14.

6. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (2), the microchannel reactor has a channel characteristic size of 0.5-1.5 mm and a total fluid residence time of less than 1 second, forming turbulence and promoting the instantaneous and uniform nucleation and growth of iron-based adsorbents Fe(OH)2 and Fe3O4.

7. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (2), the microreactor spray preparation process achieves continuous, large-scale industrial in-situ preparation of adsorbent precursors by combining multiple microchannel mixing modules in parallel (Numbering-up).

8. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (3), the adsorption time is 30 min to 3 h.

9. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, The cleaning step before adding the adsorbent in step (3) is as follows: use deionized water and anhydrous ethanol to clean the wet powder of the adsorbent 3-4 times; The washing step of the obtained solid product in step (4) is as follows: wash 2-3 times with deionized water or hot water at 30-60℃, and then rinse 2-3 times with low temperature water.

10. The method for enriching rare and dispersed metals in sodium aluminate mother liquor based on microfluidic technology according to claim 1, characterized in that, In step (4), the product is dried overnight at 60°C.

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