Preparation method of laser-induced breakdown spectroscopy solid target and solid-phase laser-induced breakdown spectroscopy rapid detection method of salt lake brine

Abstract

The invention belongs to the technical field of analytical chemistry, and particularly relates to a preparation method of a laser-induced breakdown spectroscopy solid target and a solid-phase laser-induced breakdown spectroscopy rapid detection method of salt lake brine. The method comprises the following steps: mixing a salt lake brine sample with sodium carbonate to obtain a carbonate precipitate suspension; and filtering the carbonate precipitation suspension by using a functional modified film to obtain the laser-induced breakdown spectroscopy solid target. According to the method, the concentration of Li ions in the salt lake brine is detected by adopting a laser-induced breakdown spectroscopy solid target. According to the method, liquid sample analysis is converted into high-stability solid target analysis, rapid and high-sensitivity detection and quantitative analysis of mg / L level lithium ions in the salt lake brine are achieved, the RSD is about 2.0% within the interval of 20-50 mg / L, the detection stability and sensitivity under the liquid-phase LIBS condition are remarkably improved, and the method is suitable for on-site rapid monitoring of the salt lake.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of analytical chemistry, and particularly relates to a preparation method of a laser-induced breakdown spectroscopy solid target and a solid-phase laser-induced breakdown spectroscopy rapid detection method for salt lake brine. BACKGROUND

[0002] Emerging industries represented by electric vehicles (EVs) and energy storage systems have shown explosive growth in demand for lithium-ion batteries, making lithium resources increasingly strategic and earning the reputation of "white oil".

[0003] In recent years, significant breakthroughs have been made in lithium extraction from salt lakes, especially for high magnesium-lithium ratio salt lakes. Traditional "natural sun evaporation" has been replaced by industrialized continuous production technologies such as adsorption, extraction, and membrane separation, enabling the commissioning of multiple 10,000-ton lithium salt projects.

[0004] However, whether it is adsorption, extraction, or membrane separation process, the core lies in the real-time, accurate, and rapid monitoring of lithium ion concentration changes in brine, especially in the control of key nodes such as lithium extraction efficiency, concentration ratio, and eluent ratio. Traditional laboratory analysis methods such as atomic absorption spectrometry (AAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) require complex sample pretreatment and long analysis periods, making it difficult to meet the needs of on-site online or rapid detection.

[0005] Laser-induced breakdown spectroscopy (LIBS) has shown great application potential in geological exploration and mineral resource analysis due to its unique advantages of rapidity, in-situ analysis, no need for complex sample pretreatment, and simultaneous analysis of multiple elements, making it an ideal choice for realizing rapid on-site monitoring of lithium extraction from salt lakes.

[0006] However, there are fatal defects when LIBS is directly applied to salt lake brine (liquid): Unstable plasma: Laser ablation of the liquid surface leads to droplet splashing, resulting in poor reproducibility of spectral signals.

[0007] Severe matrix effect: High concentrations of salts in brine can strongly affect plasma characteristics, producing a large spectral background and interference.

[0008] Insufficient sensitivity: The detection limit of liquid LIBS is usually high, making it difficult to meet the monitoring needs of low-concentration lithium at the mg / L level in the lithium extraction process. SUMMARY

[0009] The application aims to provide a preparation method of a laser-induced breakdown spectroscopy solid target and a rapid detection method of salt lake brine by laser-induced breakdown spectroscopy of a solid target.

[0010] To achieve the above-mentioned purpose, the application provides the following technical scheme. The application provides a preparation method of a laser-induced breakdown spectroscopy solid target, comprising the following steps. Mixing a salt lake brine sample and sodium carbonate and reacting under the condition of pH>10 to obtain a carbonate precipitate suspension; Filtering the carbonate precipitate suspension by using a functionalized modified membrane to obtain the laser-induced breakdown spectroscopy solid target; the functionalized modified membrane comprises a base membrane and a natural high molecular material and a complexing agent loaded on the base membrane; the complexing agent has a multi-dentate carboxylic acid complexing structure; the base membrane is a microporous filter membrane; and the laser-induced breakdown spectroscopy solid target is enriched with the carbonate precipitate.

[0011] Preferably, the natural high molecular material comprises one or more of chitosan, a chitosan derivative, cyclodextrin, lignin, chitin and a chitin derivative.

[0012] Preferably, the complexing agent comprises one or more of ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid disodium salt, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid sodium salt and diethylenetriamine pentaacetic acid; and the mass of the complexing agent accounts for 10-20% of the mass of the natural high molecular material.

[0013] Preferably, the base membrane comprises a nylon membrane, a mixed cellulose ester (MCE) microporous filter membrane, a cellulose acetate membrane, a polyamide membrane, a polyvinylidene fluoride (PVDF) membrane or a polytetrafluoroethylene (PTFE) membrane; the diameter of the base membrane is 13-50 mm; and the pore size of the base membrane is 0.22-0.45 μm.

[0014] Preferably, the preparation method of the functionalized modified membrane comprises the following steps. Coating the surface of the base membrane with a functionalized solution, and then sequentially performing alkali neutralization, water washing and drying to obtain the functionalized modified membrane; the functionalized solution comprises a natural high molecular material, a complexing agent and a solvent; and the content of the natural high molecular material in the functionalized solution is 1-4%(w / v).

[0015] Preferably, the alkali neutralization is performed using a sodium hydroxide solution having a molar concentration of NaOH of 1-6 mol / L.

[0016] Preferably, the pH value of the reaction is 10.6-11; the molar ratio of carbonate ions in the sodium carbonate to lithium ions in the salt lake brine sample is 10-30:1; the reaction comprises sequentially performing a stirring reaction and standing, the stirring reaction time is 5-15 min, and the standing time is 5-10 min.

[0017] The application provides a solid-phase laser-induced breakdown spectroscopy rapid detection method for a salt lake brine, comprising the following steps: The laser-induced breakdown spectroscopy solid target prepared by the technical scheme is fixed on a laser-induced breakdown spectroscopy sample stage, laser ablation and spectrum acquisition are performed on the laser-induced breakdown spectroscopy solid target, and the laser-induced breakdown spectroscopy characteristic spectral line intensity of lithium in the salt lake brine sample is obtained. The laser-induced breakdown spectroscopy characteristic spectral line intensity of lithium is brought into a linear fitting curve or a linear fitting equation, and the concentration of lithium ions in the salt lake brine sample is obtained; the linear fitting curve or the linear fitting equation is a linear fitting relationship between the laser-induced breakdown spectroscopy characteristic spectral line intensity of lithium and the concentration of lithium ions.

[0018] Preferably, the linear fitting equation between the laser-induced breakdown spectroscopy characteristic spectral line intensity of lithium and the concentration of lithium ions is Y=kX+b, wherein X is the concentration of lithium ions, and Y is the laser-induced breakdown spectroscopy characteristic spectral line intensity.

[0019] Preferably, the detection wavelength of the laser-induced breakdown spectroscopy characteristic spectral line intensity of lithium in the salt lake brine sample is 670.78 nm.

[0020] The application provides a preparation method of a laser-induced breakdown spectroscopy solid target and a solid-phase laser-induced breakdown spectroscopy rapid detection method for a salt lake brine. + , Mg 2+ , Cl − and other coexisting ions, which greatly interfere with the detection of low-concentration lithium. The application creatively combines chemical precipitation enrichment, functional membrane solid-phase extraction (MSPE) and solid-phase laser-induced breakdown spectroscopy (LIBS) for efficient combination, and compared with the prior art, the application achieves the following beneficial effects: This invention introduces functional groups such as carboxyl and hydroxyl groups onto the surface of a base membrane through synergistic modification of natural polymer materials and complexing agents. The natural polymer materials form a cross-linked network framework structure on the base membrane surface, thereby fixing the complexing agent to the membrane surface (taking chitosan as an example, the hydroxyl groups on the chitosan molecular chain form intermolecular hydrogen bonds with the carboxyl groups of the complexing agent such as EDTA; therefore, the natural polymer materials fix the complexing agent molecules through both physical and chemical bonding). This prevents the complexing agent from being washed away during the adsorption of brine in salt lake treatment. By introducing functional groups from natural polymer materials and complexing agents onto the base membrane surface, this invention enables the functionalized modified membrane to filter carbonate precipitate suspensions. Based on physical retention, it achieves enhanced capture of carbonate precipitates (including Li precipitate particles) through electrostatic adsorption and multidentate complexation, ensuring the efficient enrichment of the target element (Li).

[0021] This invention transforms "liquid LIBS" into "solid LIBS": This invention significantly improves the fatal defects of traditional liquid LIBS, such as droplet splashing, plasma instability, and high salt matrix effect, by converting Li in the liquid sample into a highly stable solid target (enriched on the membrane surface) through precipitation.

[0022] This invention exhibits high sensitivity and high precision: it achieves a good linear relationship between net Li intensity and concentration, and reduces LOD to the mg / L level. Simultaneously, the RSD after enrichment with the functionalized modified membrane is extremely low (approximately 2.0%, 2.1–4.3% in the examples), indicating that this invention has good quantitative accuracy and reproducibility.

[0023] This invention features rapid, on-site monitoring capabilities: it replaces traditional, complex laboratory pretreatment processes (such as digestion, dilution, and ionization) with a simple precipitation-membrane filtration operation, followed by rapid solid-phase LIBS analysis. The entire analytical process can be completed within minutes, meeting the needs of the brine lithium extraction industry for on-site online or real-time rapid monitoring, thus helping to improve lithium extraction efficiency and reduce production costs.

[0024] In summary, this invention provides a simple and efficient solution for the rapid and sensitive detection of Li analyte in salt lake brine. Attached Figure Description

[0025] Figure 1 The linear fitting curve between the intensity of the characteristic spectral lines of the laser-induced breakdown spectrum of lithium and the lithium ion concentration was established for this invention. Figure 2 The flowchart shows the rapid detection method for solid-phase laser-induced breakdown spectroscopy of salt lake brine provided by the present invention. Detailed Implementation

[0026] This invention provides a method for preparing a laser-induced breakdown spectroscopy solid target, comprising the following steps: Salt lake brine samples were mixed with sodium carbonate and reacted under conditions of pH > 10 to obtain a carbonate precipitate suspension. The carbonate precipitate suspension is filtered using a functionalized modified membrane to obtain a laser-induced breakdown spectroscopy solid target. The functionalized modified membrane includes a base membrane and a natural polymer material and a complexing agent loaded on the base membrane. The complexing agent has a multidentate carboxylic acid complex structure. The base membrane is a microporous filter membrane. The laser-induced breakdown spectroscopy solid target is enriched with carbonate precipitate.

[0027] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0028] This invention involves mixing a salt lake brine sample with sodium carbonate and reacting it under conditions of pH > 10 to obtain a carbonate precipitate suspension. In this invention, the sodium carbonate can be used in the form of an aqueous sodium carbonate solution. The molar ratio of carbonate ions in the sodium carbonate to lithium ions in the salt lake brine sample is preferably 10-30:1, more preferably 15-25:1. The pH of the reaction is preferably 10.6-11. The reaction preferably includes sequential stirring and settling. The stirring time is preferably 5-15 min, and the settling time is preferably 5-10 min. The reaction promotes the formation of carbonate precipitates from lithium, magnesium, and other ions. By controlling the pH of the reaction and the conditions for carbonate ion enrichment, this invention forms a carbonate particle cluster mainly composed of magnesium carbonate / calcium carbonate, with Li₂CO₃ co-precipitated, which is beneficial for subsequent membrane enrichment and solid-phase LIBS analysis. This invention promotes the formation of carbonates and their subsequent filtration and enrichment by controlling the molar ratio of carbonate ions in the sodium carbonate and lithium ions in the brine sample from the salt lake, as well as the reaction operating conditions and time.

[0029] After obtaining the carbonate precipitate suspension, the present invention filters the carbonate precipitate suspension using a functionalized modified membrane to obtain a laser-induced breakdown spectroscopy solid target; the functionalized modified membrane includes a base membrane and a natural polymer material and a complexing agent loaded on the base membrane, the base membrane is a microporous filter membrane, the natural polymer material contains hydroxyl and / or carboxyl groups, and the laser-induced breakdown spectroscopy solid target is enriched with carbonate precipitate.

[0030] In this invention, the natural polymer material preferably includes one or more of chitosan, chitosan derivatives, cyclodextrin, lignin, chitin, and chitin derivatives. In the embodiments, it can be chitosan or cyclodextrin.

[0031] In this invention, the complexing agent preferably has a polydentate carboxylic acid complex structure. The complexing agent preferably includes one or more of ethylenediaminetetraacetic acid (EDTA), disodium EDTA, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), sodium DOTA, and diethylenetriaminepentaacetic acid (DTPA), and in the examples, it can be EDTA, disodium EDTA, or DTPA. The mass percentage of the complexing agent relative to the mass of the natural polymer material is preferably 10-20%, and in the examples, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0032] In this invention, the base membrane preferably includes a nylon membrane, a mixed cellulose ester (MCE) microporous filter membrane, a cellulose acetate membrane, a polyamide membrane, a polyvinylidene fluoride (PVDF) membrane, or a polytetrafluoroethylene (PTFE) membrane. The mixed cellulose ester microporous filter membrane is composed of cellulose acetate (CA) and cellulose nitrate (CN), and the mass ratio of CA to CN is preferably 30:70 to 70:30.

[0033] In this invention, the diameter of the base membrane is preferably 13-50 mm, and in the embodiments it can be 25 mm, 20 mm or 13 mm. The pore size of the base membrane is preferably 0.22-0.45 μm, and in the embodiments it can be 0.45 μm.

[0034] In this invention, the method for preparing the functionalized modified membrane preferably includes the following steps: The surface of the base membrane is coated with a functionalized solution, followed by alkali neutralization, water washing, and drying to obtain the functionalized modified membrane. In this invention, the functionalized solution preferably comprises a natural polymer material, a complexing agent, and a solvent. In this invention, when the natural polymer material is preferably chitosan, the solvent can be an aqueous solution of glacial acetic acid. The content of the natural polymer material in the functionalized solution is preferably 1-4% (w / v), and in the examples, it can be 1% (w / v), 2% (w / v), 3% (w / v), or 4% (w / v). The percentage of the complexing agent by mass of the natural polymer material is preferably 10-20%, and in the examples, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. The content of glacial acetic acid in the aqueous solution is preferably 1.5-3% (v / v), and in the examples, it can be 2% (v / v). The pH value of the functionalized solution is preferably 4-5.5.

[0035] In this invention, the preferred ratio of the volume of the functionalized solution to the diameter of the base membrane is (200~400) µL: (13~50) mm.

[0036] In this invention, the coating can be spin coating, which is performed using a spin coater. The preferred spin coating speed is 200-500 rpm, and in the embodiments, it can be 200 rpm, 300 rpm, 400 rpm, or 500 rpm. The spin coating time can be 20-40 seconds, and in the embodiments, it can be 30 seconds.

[0037] In this invention, the alkali neutralization is preferably performed using a sodium hydroxide solution. The molar concentration of NaOH in the sodium hydroxide solution is preferably 1-6 mol / L, and in the examples, it can be 3 mol / L. The volume ratio of the functionalized solution to the sodium hydroxide solution is preferably (0.1-1):(2-5). This invention enables the natural polymer material to solidify on the surface of the base film through alkali neutralization, and after solidification, the natural polymer material can be stably attached to the surface of the base film.

[0038] In this invention, deionized water is preferably used for the water washing. The preferred volume ratio of the sodium hydroxide solution to the deionized water is (2~5):(3~5). This invention preferably removes residual NaOH and acetic acid from the surface of the base film through the water washing.

[0039] In this invention, the functionalized modified membrane is rich in amino (derived from chitosan / complexing agent), carboxyl (derived from EDTA), and hydroxyl (derived from chitosan) functional groups.

[0040] In this invention, the amino, carboxyl, and hydroxyl functional groups on the surface of the functionalized membrane work synergistically during filtration to enhance the capture and adsorption of carbonate precipitate particles, thereby achieving efficient solid-phase enrichment and preparing a LIBS solid target.

[0041] This invention provides a rapid solid-phase laser-induced breakdown spectroscopy detection method for salt lake brine, comprising the following steps: The laser-induced breakdown spectroscopy solid target prepared by the above technical solution is fixed on the laser-induced breakdown spectroscopy sample stage, and laser ablation and spectral acquisition are performed on the laser-induced breakdown spectroscopy solid target to obtain the intensity of the laser-induced breakdown spectral characteristic lines of lithium in the salt lake brine sample. The intensity of the characteristic spectral lines of the laser-induced breakdown spectrum of lithium is substituted into a linear fitting curve or a linear fitting equation to obtain the concentration of lithium ions in the brine sample of the salt lake; the linear fitting curve or linear fitting equation is a linear fitting relationship between the intensity of the characteristic spectral lines of the laser-induced breakdown spectrum of lithium and the concentration of lithium ions.

[0042] In this invention, the linear fitting equation between the intensity of the characteristic spectral line of the laser-induced breakdown spectrum of lithium and the lithium ion concentration is: Y = kX + b, where X is the lithium ion concentration in mg / L, and Y is the intensity of the characteristic spectral line of the laser-induced breakdown spectrum. The fitting data of the linear fitting curve or linear fitting equation in this invention are shown in Table 1. The linear fitting curve between the intensity of the characteristic spectral line of the laser-induced breakdown spectrum of an element and the lithium ion concentration in this invention is shown in Table 1. Figure 1 As shown.

[0043] In embodiments of the present invention, the intensity of the lithium element spectral line shows a good linear relationship with the lithium ion concentration, with a correlation coefficient R. 2 ≈0.99 (e.g.) Figure 1 (As shown in Table 1), where X is the lithium ion concentration in mg / L and Y is the intensity of the characteristic spectral line of the laser-induced breakdown spectrum. In the embodiments of the present invention, the linear fitting equation between the intensity of the characteristic spectral line of the laser-induced breakdown spectrum of lithium and the lithium ion concentration is: Y = 871.2X - 192.7 (R² - 192.7)². 2 =0.9887).

[0044] In this invention, it should be noted that due to variations in samples and instruments between batches, it is recommended to re-establish a standard curve using samples of known concentrations before each measurement, and then perform the detection of unknown samples. This reduces errors caused by the instrument and the sample matrix itself, thereby establishing a standard curve that is more suitable for the current sample.

[0045] In this invention, the preferred detection wavelength for the intensity of the characteristic spectral lines of the laser-induced breakdown spectrum of lithium in the brine sample is 670.78 nm.

[0046] This invention provides a method for rapid quantitative analysis of lithium in salt lake brine based on functionalized membrane solid-phase extraction (MSPE) combined with laser-induced breakdown spectroscopy (LIBS). The detection method provided by this invention includes four main steps: preparation of functionalized modified membrane, sample pretreatment and precipitation formation, membrane solid-phase capture and enrichment, and rapid LIBS detection and quantitative analysis.

[0047] To further illustrate the present invention, the technical solutions provided by the present invention are described in detail below with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention. The following embodiments are based on... Figure 2 The flowchart is as follows.

[0048] Example 1 Step 1: Preparation of functionalized modified membranes: Preparation of functionalized solution: Chitosan was dissolved in a 2.0% (v / v) aqueous solution of glacial acetic acid to prepare a chitosan-acetic acid solution; then, disodium EDTA was added, wherein the mass of disodium EDTA accounted for 15% of the mass of chitosan. The mixture was stirred until completely dissolved to obtain a functionalized solution, wherein the chitosan content in the functionalized solution was 2% (w / v). This embodiment controls the amount of raw materials used in the functionalized solution to form a stable functionalized solution and ensure sufficient functional groups.

[0049] Coating and Curing: A base membrane (nylon membrane, 25 mm in diameter, 0.45 μm pore size; the base membrane selected in this embodiment has good mechanical strength and the ability to capture precipitated particles) was selected. 400 µL of the functionalized solution was pipetted and added dropwise to the center of the base membrane at 400 rpm using a spin coater. During this process, the functionalized solution was uniformly dispersed on the membrane surface under centrifugal force. The membrane was then kept rotating for 30 seconds, after which the spin coating process was stopped.

[0050] Neutralization and cleaning: After spin coating, 2-5 mL of NaOH aqueous solution (3 mol / L) is added to the surface of the base film for neutralization, so that chitosan is solidified on the surface of the base film. Finally, the surface of the base film is cleaned with 3-5 mL of deionized water and dried to obtain a functionalized modified film rich in amino (derived from chitosan), carboxyl (derived from EDTA) and hydroxyl functional groups.

[0051] Step 2: Sample Pretreatment and Precipitation Formation: Measure a certain volume (10 mL) of salt lake brine sample, add sodium carbonate aqueous solution, and Na2CO3 aqueous solution containing CO3. 2- Li in salt lake brine samples + The molar ratio was 15:1, and the pH of the system was adjusted to 10.6-11 to promote the formation of carbonate precipitates from lithium and magnesium ions. In this embodiment, enrichment was performed under the above pH and carbonate dosage conditions, resulting in a carbonate particle cluster mainly composed of magnesium carbonate / calcium carbonate with entrained Li₂CO₃ co-precipitates, which is beneficial for subsequent membrane enrichment and solid-phase LIBS analysis. The mixture was stirred for 15 min and then allowed to stand for 10 min to promote carbonate formation, resulting in a carbonate precipitate suspension.

[0052] Membrane solid-phase capture and enrichment: The carbonate precipitate suspension obtained in step 2 is filtered through the functionalized modified membrane prepared in step 1. The amino, carboxyl, and hydroxyl functional groups on the membrane surface work synergistically to enhance the capture and adsorption of carbonate precipitate particles, achieving efficient solid-phase enrichment and preparing a LIBS solid target.

[0053] Step 3: Rapid LIBS Detection: The LIBS solid target enriched with precipitate is fixed on the LIBS sample stage, and laser ablation and spectral acquisition are performed directly on the precipitate surface of the LIBS solid target. Quantitative Analysis: The characteristic spectral line intensities of lithium are collected, and the concentration of lithium ions in the brine sample is calculated using a pre-established calibration curve.

[0054] Example 2: Quantitative analysis of Li based on the EDTA / chitosan modified nylon membrane prepared in Example 1 The functionalized modified membrane prepared in Example 1 was used to enrich and quantitatively analyze simulated salt lake brine samples of different concentrations.

[0055] Sample preparation and enrichment: 5 groups of Li were prepared + Standard solutions: The simulated high-salinity brine contained 200 mg / L MgCl2, 10 mg / L NaCl, and LiCl concentrations as shown in Table 1, with concentrations of 1.0, 5.0, 10.0, 20.0, and 50.0 mg / L, respectively. After adding sodium carbonate as a precipitant and adjusting the pH, solid-phase capture and enrichment were performed using the functionalized modified membrane prepared in Example 1.

[0056] LIBS detection: LIBS detection was performed on the enriched LIBS solid target, and the intensity of the characteristic spectral line of Li(I) at 670.78 nm was collected. LOD was calculated as 3σ / k, where σ is the net intensity standard deviation of the blank sample (or low concentration sample), and k is the slope of the calibration curve. The results are shown in Table 1.

[0057] Table 1. Test results of simulated salt lake brine samples at different concentrations.

[0058] The results show that the net intensity of the LIBS spectral line of Li has a good linear relationship with the Li concentration, and the correlation coefficient R0 is low. 2 With a relative standard deviation (RSD) of approximately 0.99, accurate quantitative analysis of lithium ions at the mg / L level was achieved.

[0059] Example 3: Compatibility verification of different functionalized materials The preparation method of the functionalized modified membrane in this embodiment is basically the same as that provided in Example 1, except that the raw materials for preparing the functionalized modified membrane are shown in Table 2. The quantitative analysis method for Li in this embodiment is basically the same as that in Example 2, except that the standard brine is prepared in this embodiment: the concentration of MgCl2 is 400 mg / L, and LiCl is added to prepare Li. + The functionalized modified membrane was prepared using the raw materials shown in Table 2, with a standard solution of 50 mg / L as the mass concentration.

[0060] Table 2 Raw materials for preparing functionalized modified membranes

[0061] The results in Table 2 show that the functionalized modified membrane prepared by DTPA and cyclodextrin (a hydroxyl-containing natural polymer substitute) can still maintain high signal intensity and excellent precision in Li precipitation enrichment and LIBS detection, which proves the scalability and versatility of the materials in the technical solution of this invention.

[0062] Comparative Example 1: Comparison between existing technology and direct LIBS detection of pure water samples Table 3 Comparison of existing technologies and direct LIBS detection of pure water samples

[0063] LiCl was directly added to a high-salinity water sample (MgCl2 concentration of 400 mg / L) to prepare Li + LIBS detection was performed on a standard solution with a mass concentration of 50 mg / L. Due to the instability of the gas-liquid interface, the plasma became unstable (droplet splashing) when the laser penetrated from the gas phase into the liquid phase, and the matrix effect was severe, resulting in low signal intensity and large fluctuations in the LIBS spectrometer. The LOD was extremely high, which could not meet the requirements for stable and rapid detection at the mg / L level.

[0064] Comparative Example 2: Unmodified nylon membrane (purely physical trapping) Compared to Example 3, a commercially available nylon membrane was used without modification to directly perform membrane solid-phase extraction on the precipitated lithium carbonate in the sample. The preparation of the standard brine in this comparative example was the same as in Example 3: the concentration of MgCl2 was 400 mg / L, and LiCl was added to prepare Li... + A standard solution with a mass concentration of 50 mg / L was used, and then LIBS spectroscopy was performed directly on the membrane surface for method comparison to explore the solid-phase extraction efficiency of membrane modification technology for lithium carbonate precipitation.

[0065] Table 4 Test results of the unmodified nylon film in Comparative Example 2

[0066] The results in Table 4 show that although the pure nylon membrane can enrich most of the precipitate through physical interception, it has low capture efficiency for small particles due to the lack of a chemical synergistic adsorption mechanism and poor uniformity of precipitate distribution, resulting in significantly lower Li signal intensity and stability (RSD) than the functionalized modified membrane of the present invention.

[0067] Comparative Example 3: Membranes modified with a single functional material (chitosan only) Using the same preparation conditions, except that no EDTA complexing material was added and only chitosan material was used to modify the membrane surface, lithium carbonate was then enriched and detected using the same experiments.

[0068] Table 5. Test results of Comparative Example 3

[0069] Results Analysis: Although chitosan modification alone introduces amino groups (electrostatic adsorption), the lack of the polydentate carboxylic acid complex structure of EDTA prevents the formation of more stable chelate capture. Therefore, the Li signal intensity remains lower than that of the membrane material synergistically modified with EDTA / chitosan. This demonstrates that the synergistic effect of EDTA and chitosan is key to achieving efficient enrichment.

[0070] Based on the experimental results of the above embodiments and comparative examples, this invention creatively combines three technologies—chemical precipitation enrichment, functionalized membrane solid-phase extraction (MSPE), and solid-phase laser-induced breakdown spectroscopy (LIBS)—in a highly efficient manner.

[0071] Functional Synergistic Modification: This invention utilizes the synergistic effect of complexing agents such as EDTA and natural polymers such as chitosan to rapidly functionalize nylon and other base films. Comparative Example 3 demonstrates that the Li signal intensity of films modified using only chitosan or EDTA is lower than that of films modified with synergistic modification. This synergistic effect, based on physical retention, introduces amino, carboxyl, and hydroxyl functional groups, achieving enhanced capture of Li precipitate particles through electrostatic adsorption and multidentate complexation, ensuring efficient enrichment of the target element.

[0072] The conversion from "liquid LIBS" to "solid LIBS": Comparative Example 1 clearly shows that when high-salinity brine is directly subjected to LIBS detection, the signal is unstable (RSD reaches 20%~40%) and the limit of detection (LOD) is extremely high (approximately 50 mg / L), making trace analysis difficult. This invention significantly alleviates the fatal defects of traditional liquid LIBS, such as droplet splashing, plasma instability, and high-salt matrix effects, by efficiently converting Li in the liquid sample into a highly stable solid target (enriched on the membrane surface).

[0073] This invention exhibits high sensitivity and high precision: the results of Example 2 show that this invention can achieve an excellent linear relationship between net Li intensity and concentration, and reduce the limit of detection (LOD) to the mg / L level. Simultaneously, the RSD after enrichment with the modified membrane is extremely low (approximately 2.0%), far superior to the direct LIBS detection in Comparative Example 1 (20%~40%), indicating that the method has good quantitative accuracy and reproducibility.

[0074] This invention features rapid, on-site monitoring capabilities: the method replaces traditional, complex laboratory pretreatment processes (such as digestion, dilution, and ionization) with a simple precipitation-membrane filtration operation, followed by rapid solid-phase LIBS analysis. This allows the entire analytical process to be completed within minutes, meeting the needs of the brine lithium extraction industry for rapid on-site online or real-time monitoring, and helping to improve lithium extraction efficiency and reduce production costs.

[0075] Example 3 demonstrates that the present invention is not limited to the combination of EDTA / chitosan / nylon membrane, but is also compatible with alternative functionalized materials such as DTPA and cyclodextrin, as well as various base membranes. This broad compatibility ensures the versatility and scalability of the method under different brine compositions and LIBS instrument configurations.

[0076] In summary, this invention is suitable for the precipitation, enrichment, and detection of lithium and other metal ions in salt lake brines. This membrane solid-phase extraction + laser-induced breakdown spectroscopy detection technology achieves a synergistic strategy combining multiple methods, providing a simple and efficient solution for the rapid and sensitive detection of analytes in aquatic environments.

[0077] As demonstrated by the above embodiments, this invention combines chemical enrichment, functionalized solid-phase capture, and rapid solid-state LIBS analysis. By modifying the base membrane with functionalized materials such as EDTA and chitosan, the capture capacity for precipitated particles is significantly enhanced, enabling rapid and highly sensitive quantitative analysis of lithium ions at the mg / L level in salt lake brine. This invention utilizes the complexing ability of EDTA and the amino functional groups of chitosan to achieve synergistic enrichment of lithium carbonate precipitates through physical retention and chemical adsorption / complexation capture, ensuring efficient capture of the target element. This effectively concentrates mg / L-level lithium ions dispersed in the liquid under the laser focus of the LIBS. This invention improves the detection sensitivity of lithium to the mg / L level while maintaining the rapid and portable characteristics of LIBS, allowing it to be directly applied in salt lake environments for real-time, high-precision quality control and efficiency evaluation of lithium extraction processes (such as precipitation, filtration, adsorption, and elution).

[0078] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a solid target for laser-induced breakdown spectroscopy, characterized in that, Includes the following steps: Salt lake brine samples were mixed with sodium carbonate and reacted under conditions of pH > 10 to obtain a carbonate precipitate suspension. The carbonate precipitate suspension is filtered using a functionalized modified membrane to obtain a laser-induced breakdown spectroscopy solid target. The functionalized modified membrane includes a base membrane and a natural polymer material and a complexing agent loaded on the base membrane. The complexing agent has a multidentate carboxylic acid complex structure. The base membrane is a microporous filter membrane. The laser-induced breakdown spectroscopy solid target is enriched with carbonate precipitate.

2. The preparation method according to claim 1, characterized in that, The natural polymeric material includes one or more of chitosan, chitosan derivatives, cyclodextrin, lignin, chitin, and chitin derivatives.

3. The preparation method according to claim 1, characterized in that, The complexing agent comprises one or more of ethylenediaminetetraacetic acid (EDTA), disodium EDTA, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, sodium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, and diethylenetriaminepentaacetic acid; the mass percentage of the complexing agent is 10-20% of the mass of the natural polymer material.

4. The preparation method according to claim 1, characterized in that, The base membrane includes a nylon membrane, a mixed cellulose ester microporous filter membrane, a cellulose acetate membrane, a polyamide membrane, a polyvinylidene fluoride membrane, or a polytetrafluoroethylene membrane; the diameter of the base membrane is 13~50 mm, and the pore size of the base membrane is 0.22~0.45 μm.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The preparation method of the functionalized modified membrane includes the following steps: The surface of the base film is coated with a functionalized solution, and then subjected to alkali neutralization, water washing and drying in sequence to obtain the functionalized modified film. The functionalized solution includes natural polymer materials, complexing agents and solvents, and the content of natural polymer materials in the functionalized solution is 1~4% (w / v).

6. The preparation method according to claim 5, characterized in that, The alkaline reagent used for alkali neutralization includes a sodium hydroxide solution, wherein the molar concentration of NaOH in the sodium hydroxide solution is 1~6 mol / L.

7. The preparation method according to claim 1, characterized in that, The pH value of the reaction is 10.6~11; the molar ratio of carbonate ions in the sodium carbonate to lithium ions in the brine sample is 10~30:1; the reaction includes sequential stirring and settling, the stirring time is 5~15 min, and the settling time is 5~10 min.

8. A rapid solid-phase laser-induced breakdown spectroscopy method for detecting salt lake brine, characterized in that, Includes the following steps: The laser-induced breakdown spectroscopy solid target prepared according to claims 1 to 7 is fixed on the laser-induced breakdown spectroscopy sample stage, and laser ablation and spectral acquisition are performed on the laser-induced breakdown spectroscopy solid target to obtain the intensity of the laser-induced breakdown spectral characteristic lines of lithium in the salt lake brine sample. The intensity of the characteristic spectral lines of the laser-induced breakdown spectrum of lithium is substituted into a linear fitting curve or a linear fitting equation to obtain the concentration of lithium ions in the brine sample of the salt lake; the linear fitting curve or linear fitting equation is a linear fitting relationship between the intensity of the characteristic spectral lines of the laser-induced breakdown spectrum of lithium and the concentration of lithium ions.

9. The rapid detection method for solid-phase laser-induced breakdown spectroscopy of salt lake brine according to claim 8, characterized in that, The linear fitting equation between the intensity of the characteristic spectral line of the laser-induced breakdown spectrum of lithium and the lithium ion concentration is: Y = kX + b, where X is the lithium ion concentration in mg / L and Y is the intensity of the characteristic spectral line of the laser-induced breakdown spectrum.

10. The rapid detection method for solid-phase laser-induced breakdown spectroscopy of salt lake brine according to claim 8 or 9, characterized in that, The detection wavelength for the intensity of the characteristic laser-induced breakdown spectral lines of lithium in the brine sample from the salt lake was 670.78 nm.

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