Reference glass materials with increased lithium content for direct elemental analyses and method of their preparation

Abstract

Reference materials with increased lithium content for direct elemental analyses, wherein the glass contains 55 to 75 wt.% SiO2, 7 to 15 wt.% Na2O, 6 to 15 wt.% CaO, up to 3.5 wt.% AI2O3, up to 3.5 wt.% K2O, and up to 12 wt.% Li2O, and the value of the relative standard deviation (RSD) of homogeneous element distribution in the glass, determined by inductively coupled plasma mass spectrometry combined with laser ablation (LA-ICP-MS), is less than or equal to 5%.

Description

DescriptionReference glass materials with increased lithium content for direct elemental analyses and method of their preparationTechnical Field

[0001] The invention relates to reference glass materials with increased lithium content for direct elemental analyses and the method of their preparation.Background Art

[0002] High-tech technologies and industrial applications focused on "smart" electronic devices are transitioning to environmentally friendly production, i.e. , those leaving a low carbon footprint. The identification of strategic raw materials containing non-ferrous metals and metalloids, as well as their deposits, is crucial. The development of lithium batteries is accelerating due to growing demand for electronic devices, stationary energy storage systems (batteries), and electric vehicles. In addition to lithium, batteries also contain various metals such as nickel, cobalt, aluminium, and manganese. Other raw materials containing borates, gallium, indium, rare earth elements, cobalt, niobium, silicon, and titanium have also been designated as "critical" deposit sources. A thorough and precise characterization of deposits of critical minerals and raw materials is essential for assessing their overall profitability. Determining chemical composition with high accuracy or detecting impurities is thus an integral part of mineral exploration, and industrial utilization of these raw materials. Selecting a suitable analytical method and its correct application is important for chemical analysis and the determination of minor and trace amounts of elements of interest in the demanded mineral raw materials. Common analytical methods include, for example, electron microprobe analysis (EMPA) or inductively coupled plasma mass spectrometry combined with laser ablation, known as "LA-ICP-MS."

[0003] Compared to optical emission spectrometry, LA-ICP-MS allows direct analysis of the overall composition of solid material without prior decomposition and conversion into liquid form. This analytical method is also used to characterize geological materials in terms of microstructure of individual mineral grains, zoning, element migration, etc. The irreplaceability of LA-ICP-MS in quantifying target components in a sample lies in its ability to measure light elements such as Li, or volatile elements (e.g., Be, B, P, S...). A major and current issue concerning available laboratory standards (NIST SRM - National Institute of Standards and Technology Standard Reference Materials) for analytical measurement of real geological samples is the underestimation of concentrations of these elements, which naturally leads to significant inaccuracies in analysis. Real geological samples, i.e., lithium-rich silicates (zinnwaldite, lepidolite, spodumene), which represent the mainsource of lithium, contain on average 1.2-2.8 wt.% of Li (http: / / georem.mpch- mainz.gwdg.de; Martin, G., Schneider, A., Voigt, W., Bertau, M. 2017. Lithium extraction from the mineral zinnwaldite: Part II: Lithium carbonate recovery by direct carbonation of sintered zinnwaldite concentrate. Minerals Engineering 110, 75-81 ), thus typically reaching concentrations several orders of magnitude higher than commercially available analytical standards with significantly lower lithium concentrations (NIST-SRM - 610 max. 470 ppm, i.e. , approx. 0.05 wt.%), which are used for direct analysis.

[0004] Commercially available certified materials are mostly in the form of homogeneous powder obtained by grinding the respective minerals, and their precise composition is determined based on inter-laboratory comparisons. However, such powdered standards are more suitable for monitoring and controlling the accuracy of laboratory methods dealing with analysis of the overall composition of solid samples after decomposition (conversion of the solid sample into a liquid solution). Therefore, they are not suitable for lateral analyses (e.g., determining the composition of individual grains or crystalline phases in minerals), as they are not homogeneous throughout their volume. Examples include: Lepidolite ((https: / / shop.nist.gov / ccrz _ ProductDetails?sku=183&cclcl=en_US) , Petalite(https: / / shop.nist.gov / ccrz ProductDetails?sku=182&cclcl=en_US)). Geological sample standards (mostly based on spodumene or pegmatite minerals) are also available on the market in powdered form, containing lithium in the range of 480 ppm-28000 ppm, i.e., 0.05 to 2.8 wt.%.

[0005] The market for commercially available standards in "bulk" form covering the required concentration range is limited. Identifying a suitable standard that meets the key requirement for the LA-ICP-MS method, i.e., a standard whose composition and analyte content closely resemble the analyzed sample often remains an open and unattainable task for the analyst.

[0006] The object of this invention is to design and prepare homogeneous glasses that would cover the lithium concentration range determined in strategic raw materials and could potentially be used as reference materials (standards) for direct elemental analyses such as laser ablation, EPMA, pXRF.Summary of Invention

[0007] Said object is achieved through reference glass materials with increased lithium content for direct elemental analyses. The core of the invention lies in the fact that the glass contains 55 to 75 wt.% SiO2, 7 to 15 wt.% Na2O, 6 to 15 wt.% CaO, up to 3.5 wt.% AI2O3, up to 3.5 wt.% K2O, and up to 12 wt.% Li2O, whereby the value of the relative standard deviation(RSD) of homogeneous element distribution in the glass, determined by the LA-ICP-MS method, is less than or equal to 5%.

[0008] The glass may further contain minor elements present in oxides selected from the group consisting of B2O3, Fe2O3, P2O5, TiO2, Y2O3, ZrO2, CuO or their combinations up to 5 wt.%, and Rb2O, Sc2O3, Ga2O3, Ge2O3, Nb2O5, Ta2O5, Cs2O, SnO, WO3or their combinations up to 3.5 wt.%.

[0009] Said object is also achieved by a method for preparing glass for reference glass materials with increased lithium content according to this invention, involving a glass melting process. The core of the process is that the glass is melted for at least 5 hours, with the melting temperature gradually increased up to 1550 °C. Once the melt is formed, it is repeatedly stirred until the relative standard deviation (RSD) of homogeneous element distribution in the glass, determined by the LA-ICP-MS method, is less than or equal to 5%. Preferably, the melt is stirred at least four times per hour at the melting temperature of 1550 °C.

[0010] Said object is likewise achieved through reference glass materials with increased lithium content for direct elemental analyses, whereby the glass contains 55 to 75 wt.% SiO2, 7 to 15 wt.% Na2O, 6 to 15 wt.% CaO, up to 3.5 wt.% AI2O3, up to 3.5 wt.% K2O, and up to 12 wt.% Li2O, obtained by melting the glass, while the melting process is carried out for at least 5 hours, with the temperature increased up to 1550 °C, once the melt is formed, it is repeatedly stirred until the relative standard deviation (RSD) of homogeneous element distribution in the glass, determined by inductively coupled plasma mass spectrometry combined with laser ablation (LA-ICP-MS), is less than or equal to 5%. Preferably, the melt is stirred at least four times per hour at the melting temperature of 1550 °C. The glass may further contain minor elements present in oxides selected from the group consisting of B2O3, Fe2O3, P2O5, TiO2, Y2O3, ZrO2, CuO or their combinations up to 5 wt.%, and Rb2O, Sc2O3, Ga2O3, Ge2O3, Nb2O5, Ta2O5, Cs2O, SnO, WO3or their combinations up to 3.5 wt.%.Brief Description of Drawings

[0011] Fig. 1 shows an elemental map of calcium (A) and silicon (B) distribution, demonstrating the homogeneity of the prepared reference materials - standards, according to the invention, with a lithium content of 2 wt.% for the example of model glass labelled FG910LiT in Table 1.

[0012] Fig. 2 shows an elemental map of titanium (A) and copper (B) distribution, demonstrating the homogeneity of the prepared reference materials - standards, according to the invention, with a lithium content of 2 wt.% for the example of model glass labelled FG910LiT in Table 1.Description of Embodiments

[0013] The present invention was carried out through conventional glass melting, using elemental composition and concentration ranges as specified in Table 1 , which also includes examples of model glasses with specific compositions within the stated concentration range. As the lithium content and other minor and trace elements were increased, the contents of all major elements were proportionally adjusted. Conventional glass melting refers to the traditional process of melting a prepared glass batch in a high-temperature furnace while regularly stirring the molten glass, also known as the "melt."

[0014]

[0015] The glasses were prepared using conventional melting with an optimised stirring process at temperatures up to 1550 °C for a minimum duration of five hours. The composition of the resulting glasses was experimentally verified using X-ray fluorescence spectroscopy (XRF), and,following microwave digestion, by inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0016] In an illustrative embodiment of the invention carried out under laboratory conditions, approximately 250 g of glass batch was processed, mixed according to the targeted composition of the molten glass to produce around 200 g of glass. The batch was placed into a melting vessel, such as a platinum crucible. The heating rate of the furnace was set to 10 °C / min up to a temperature of 1550 °C. At approximately 1300 °C, the melt reached sufficient viscosity for initial stirring. As the temperature increased to 1550 °C, the melt was stirred again at least once, preferably twice. Upon reaching 1550 °C, the melt was stirred again and subsequently stirred at regular intervals - optimally every 15 minutes - for the required melting duration of at least five hours.

[0017] This repeated stirring every 15 minutes was deemed optimal in this example, as it ensured sufficient frequency to achieve the desired homogeneity without causing an undesirable drop in melt temperature. This was necessary because stirring had to be performed outside the furnace, which did not allow in-situ stirring.

[0018] If stirring could be performed directly within the furnace - i.e. , without removing the crucible - it would be possible to increase the stirring frequency. However, under such conditions, the stirring frequency at 1550 °C should be at least four times per hour.

[0019] The melting duration includes the entire process, starting from the moment the sample is placed into the furnace at ambient temperature, which in this example was 25 °C.

[0020] Stirring optimisation during conventional glass melting was carried out by gradually increasing the melting temperature to 1550 °C and repeatedly stirring the melt - ten times over five hours, and sixteen times over seven hours.

[0021] From the beginning of the melting process, i.e., from approximately 25 °C, portions of the melt were sampled at 4, 5, 6, and 7 hours, at 1550 °C and with the required number of stirrings, to obtain representative samples of the prepared glass. These samples were then analysed to determine the homogeneity / distribution of selected major and minor elements.

[0022] Homogeneity analysis confirmed that a melting duration of five hours was sufficient to ensure uniform element distribution, with an RSD value < 5%, as determined by the LA-ICP-MS method.

[0023] After the required melting time, the melt was poured onto a substrate or into a specialised mould to achieve the desired shape. In this embodiment,the glass was cooled gradually in a muffle furnace using a temperature programme of 1 °C / min, from 530 °C down to ambient laboratory temperature.

[0024] The above-described method of preparing glass for reference materials according to the invention under laboratory conditions is illustrative only. The glass may also be prepared using the claimed method under industrial conditions, employing equipment commonly used in the glass industry.

[0025] The prepared glass, intended for use as a reference material with increased lithium content for direct elemental analyses, is cut into blocks of suitable size (typically 1 x 1 x 1 cm), which are then further processed according to the requirements of the selected analytical method.

[0026] Model glasses FG910, FG91 OLi, and FG911 Li, along with trace element sets FG91 OLiT and FG911 LiT, were subjected to spatial homogeneity studies using LA-ICP-MS. Other glasses listed in Table 1 may also be tested with similar results. For each sample, 20 points were measured and evaluated using a laser beam diameter of 50 pm. The points were randomly distributed across the sample surface. Relative standard deviations (%RSD) of isotopes were calculated from the measured intensity values and compared with RSD values obtained for the NIST 610 reference standard. A material is considered homogeneous if the RSD of measured isotopes is <5%. The NIST 610 standard meets this criterion. RSD values for individual isotopes in the model glasses ranged from 0.8 to 5%, indicating that the prepared samples meet the homogeneity requirement for standards intended for laser ablation ICP-MS.

[0027] Fig. 1 and 2 show elemental maps for calcium and silicon (as major elements), and for trace elements titanium and copper, obtained by measuring glasses with 2 wt.% Li content using electron microprobe analysis (EPMA). The overall composition of these standards, determined by ICP- OES, is provided in Table 2.

[0028] Table 2

[0029] The use of glass calibration standards as reference materials containing elements of interest namely lithium at concentrations comparable to those found in the analysed materials (strategic raw materials) enablesmore accurate elemental determination. This, in turn, contributes to improved data for the exploration and assessment of deposits of these raw materials for industrial applications.

[0030] The reference glass materials developed according to this invention for analytical methods employing laser ablation cover a lithium concentration range that is not available on the market among commonly commercially available reference and certified reference materials. The element distribution within these glasses is comparable to that found in commercial standards such as NIST 610 and NIST 612.Industrial Applicability

[0031] Reference glass materials with compositions as described in this invention may be used as standards for thorough and precise chemical characterisation of raw materials and other materials using analytical methods that require highly homogeneous spatial and depth distribution of elements, while maintaining the physical and chemical properties of the glass material. This includes, for example, the determination of the composition of strategic mineral resources that underpin emerging technologies and the utilisation of alternative energy sources, as well as the detection of impurities in these raw materials using analytical techniques such as laser ablation, electron microprobe analysis (EMPA), or micro X-ray fluorescence (pXRF).

Claims

Claims1. Reference glass materials with increased lithium content for direct elemental analyses, characterised in that the glass contains 55 to 75 wt.% SiO2, 7 to 15 wt.% Na2O, 6 to 15 wt.% CaO, up to 3.5 wt.% AI2O3, up to 3.5 wt.% K20, and up to 12 wt.% Li20, wherein the value of the relative standard deviation (RSD) of homogeneous element distribution in the glass, determined by inductively coupled plasma mass spectrometry combined with laser ablation (LA-ICP-MS), is less than or equal to 5%.

2. Reference glass materials according to claim 1 , characterised in that the glass further contains minor elements present in oxides selected from the group consisting of B2O3, Fe2O3, P2O5, TiO2, Y2O3, ZrO2, CuO or combinations thereof up to 5 wt.%, and Rb2O, Sc2O3, Ga2O3, Ge2O3, Nb2O5, Ta2O5, Cs20, SnO, W03or combinations thereof up to 3.5 wt.%.

3. A method for preparing glass for reference glass materials according to claim1 or 2, comprising a glass melting process, characterised in that the glass is melted for a duration of at least 5 hours, with the melting temperature increased up to 1550 °C, and once the melt is formed, it is repeatedly stirred until the relative standard deviation (RSD) of homogeneous element distribution in the glass, determined by inductively coupled plasma mass spectrometry combined with laser ablation (LA-ICP-MS), is less than or equal to 5%.

4. The method according to claim 3, characterised in that the melt is stirred at least four times per hour at the melting temperature of 1550 °C.

5. Reference glass materials with increased lithium content for direct elemental analyses, wherein the glass contains 55 to 75 wt.% SiO2, 7 to 15 wt.% Na20, 6 to 15 wt.% CaO, up to 3.5 wt.% AI2O3, up to 3.5 wt.% K2O, and up to 12 wt.% Li2O, obtained by melting the glass, wherein the glass is melted for a duration of at least 5 hours, with the melting temperature increased up to 1550 °C, and once the melt is formed, it is repeatedly stirred until the relative standard deviation (RSD) of homogeneous element distribution in the glass, determined by inductively coupled plasma mass spectrometry combined with laser ablation (LA-ICP-MS), is less than or equal to 5%.

6. Reference glass materials according to claim 5, wherein the melt is stirred at least four times per hour at the melting temperature of 1550 °C.

7. Reference glass materials according to claim 5 or 6, wherein the glass further contains minor elements present in oxides selected from the group consisting of B2O3, Fe2O3, P2O5, TiO2, Y2O3, ZrO2, CuO or combinations thereof up to 5 wt.%, and Rb2O, Sc2O3, Ga2O3, Ge2O3, Nb2O5, Ta2O5, Cs2O, SnO, WO3or combinations thereof up to 3.5 wt.%.

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