Description:FIELD OF THE INVENTION
[0001] The present disclosure relates to a technical field of inorganic chemical synthesis. More particularly, the present disclosure relates to a process for the preparation of sodium silicofluoride (Na₂SiF₆) and associated byproducts.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] CN1234596C discloses a manufacturing method for producing fluorine compounds and silicon dioxide using sodium fluorosilicate as a raw material. The process involves ammonification with ammonium fluoride, followed by gravitational and filtration separation to obtain high-purity sodium fluoride, precipitated silicon dioxide (white carbon black with a specific surface area over 100 m²/g), and a concentrated ammonium fluoride solution (35-45%). The resulting fluorine compounds include ammonium fluoride, sodium fluoride, potassium fluoride, and cryolite. This method efficiently utilizes all elements in sodium fluorosilicate, ensuring high economic benefits while effectively producing valuable fluorine compounds and high-surface-area silicon dioxide.
[0004] CN1131124A discloses a novel method for producing sodium fluorosilicate using fluorite, eliminating the need for HF and SiF₄ gas-state processes. Instead, a soluble fluorosilicate solution is obtained in the presence of a catalyst and then converted into sodium fluorosilicate. The process is simple, energy-efficient, and environmentally friendly. Additionally, the byproduct gypsum is directly marketable, and the sulfuric acid generated in the final solution can be reused, enhancing sustainability. This innovative approach streamlines production, reduces costs, and improves resource utilization, making it a more efficient and commercially viable alternative to conventional methods.
[0005] CN1104377C discloses a manufacturing method for producing sodium fluorosilicate using hexafluorosilicic acid, a by-product of anhydrous hydrogen fluoride production from fluorite and sulfuric acid. Sodium chloride, sourced from a nearby metal anode diaphragm electrolysis process, is also utilized. The process involves chemical reaction, thickening, and centrifugal drying to efficiently convert waste into a valuable by-product. The resulting sodium fluorosilicate is suitable as an auxiliary raw material for glass mosaic production. By implementing this method, the invention transforms waste hexafluorosilicic acid into a useful industrial product, enhancing resource utilization and sustainability in the inorganic chemical industry.
Technical problems associated with the prior arts:
[0006] Impurity and Low Yield in Existing Methods: Traditional methods for producing sodium fluorosilicate often result in impurities and low yields, which compromise the quality of the final product. These limitations hinder its use in industrial applications.
[0007] Environmental Pollution: Byproducts such as sodium fluosilicate are heavily overstocked, leading to environmental pollution due to improper disposal. This is a significant issue in industries like phosphate fertilizer production.
[0008] Inefficient Byproduct Utilization: Current processes fail to efficiently utilize byproducts such as calcium sulfate and sodium chloride, leading to waste and economic losses.
[0009] Complexity and Cost of Waste Treatment: Existing systems require costly waste treatment facilities for acidic fluoride-containing wastewater, resulting in resource loss and high operational costs.
[0010] Thus, there is a need to develop a novel, environment friendly and simple method for preparation of sodium silicofluoride and byproducts with high purity and yield.

OBJECTIVES OF THE INVENTION
[0011] An object of the present disclosure is to provide a process for the preparation of sodium silicofluoride (Na₂SiF₆) and associated byproducts with high yield and purity.
[0012] Another objective of the present disclosure is to promote environmental sustainability by transforming waste into valuable products, thereby reducing pollution, conserving resources, and minimizing reliance on extensive waste treatment infrastructure.
[0013] Still another objective of the present disclosure is to achieve efficient byproduct utilization by enabling the direct commercialization of calcium sulfate and the internal reuse of sodium chloride, thereby minimizing waste generation and maximizing overall resource efficiency.
[0014] Yet another objective of the present disclosure is to provide an enhanced economic efficiency by integrating byproduct recovery and commercialization, such as calcium sulfate, streamlining the production process, and reducing operational costs without compromising product quality.

SUMMARY OF THE INVENTION
[0015] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0016] The present disclosure relates to a process for the preparation of sodium silicofluoride (Na₂SiF₆) and associated byproducts. The process comprises: a) preparing a sodium chloride solution with a concentration ranging from 10-20 % w/w and a specific gravity ranging from 1 to 1.5; b) preparing a hexafluorosilicic acid solution with a concentration ranging from 5-15 % w/w and a similar specific gravity range of 1 to 1.5; c) mixing equal amount of the sodium chloride and hexafluorosilicic acid solutions under controlled and equal flow conditions to facilitate the precipitation of sodium silicofluoride in the mixture; d) filtering the resulting mixture to obtain a solid pellets and a supernatant solution; e) washing the pellets sequentially with a solvent, followed by a base, and again with the solvent to ensure purity; f) drying the washed pellets to yield a final dry product of sodium silicofluoride; and g) adjusting the pH of the supernatant solution with calcium hydroxide (1:10 w/v), leading to the formation of calcium sulfate and enabling the recovery of dissolved sodium chloride for reuse. The key byproducts identified from the process include hydrochloric acid and calcium chloride.
[0017] Other aspects of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learnt by the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0019] Figure 1 illustrates a flowchart of experimental scheme for the present process.
[0020] Figure 2 illustrates XRD image of prepared sample.
[0021] Figure 3 illustrates SEM-EDAX image of the developed material.

DETAILED DESCRIPTION OF THE INVENTION
[0022] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0023] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0024] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0025] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0026] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0027] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range.
[0028] Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0029] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0030] Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
[0031] The following description provides different examples and embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0032] All percentages, ratios, and proportions used herein are based on a weight basis unless otherwise specified.
[0033] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0034] The present disclosure is on the premise of an unique control of solution specific gravities, flow rates during mixing, sequential washing steps, and pH adjustment to optimize purity and yield. The process also incorporates reuse of by-products like sodium chloride and calcium sulfate, which distinguishes it from prior art methods. Thus, the present disclosure introduces a novel process optimizations and parameter controls that enhance efficiency and product quality over the existing prior arts.
[0035] The present disclosure relates to a process for the preparation of sodium silicofluoride (Na₂SiF₆) and associated byproducts. The process comprises: a) preparing a sodium chloride solution with a concentration ranging from 10-20 % w/w and a specific gravity ranging from 1 to 1.5; b) preparing a hexafluorosilicic acid solution with a concentration ranging from 5-15 % w/w and a similar specific gravity range of 1 to 1.5; c) mixing equal amount of the sodium chloride and hexafluorosilicic acid solutions under controlled and equal flow conditions to facilitate the precipitation of sodium silicofluoride in the mixture; d) filtering the resulting mixture to obtain a solid pellets and a supernatant solution; e) washing the pellets sequentially with a solvent, followed by a base, and again with the solvent to ensure purity; f) drying the washed pellets to yield a final dry product of sodium silicofluoride; and g) adjusting the pH of the supernatant solution with calcium hydroxide (1:10 w/v), leading to the formation of calcium sulfate and enabling the recovery of dissolved sodium chloride for reuse. The key byproducts identified from the process include hydrochloric acid and calcium chloride.
[0036] In some embodiment, the sodium chloride solution in step a) is prepared by the steps comprising: i) dissolving 30 to 40 % w/v of sodium chloride in water to obtain a sodium chloride solution; and ii) diluting the sodium chloride solution with water in a ratio of 3:2 to obtain a sodium chloride solution having specific gravity ranging from 1 to 1.5. Preferably, the sodium chloride has an amount ranging from 31 to 39 % w/v or 32 to 38 % w/v or 33 to 37 % w/v or 34 to 36 % w/v or 35 to 36% w/v in the sodium chloride solution. Preferably, the sodium chloride solution having a specific gravity ranging from 1 to 1.45 or 1 to 1.40 or 1 to 1.35 or 1 to 1.30 or 1 to 1.25 or 1 to 1.20 or 1 to 1.15. After the dilution, the final sodium chloride solution obtained has a concentration ranging from 10-20 % w/w, preferably, 11-19 % w/w or 12-18 % w/w or 13-17 % w/w or 14-16 % w/w.
[0037] In some embodiment, the hexafluorosilicic acid solution in step b) is prepared by the steps comprising: i) taking a 15 to 20 % w/w of hexafluorosilicic acid solution; and ii) diluting the hexafluorosilicic acid solution with water in a ratio of 1:1 to obtain a first hexafluorosilicic acid solution having specific gravity ranging from 1 to 1.5. Preferably, the hexafluorosilicic acid has an amount ranging from 16 to 19 % w/w or 17 to 18 % w/w or 18 % w/w in the hexafluorosilicic acid solution. Preferably, the hexafluorosilicic acid solution having a specific gravity ranging from 1 to 1.45 or 1 to 1.40 or 1 to 1.35 or 1 to 1.30 or 1 to 1.25 or 1 to 1.20 or 1 to 1.15. After the dilution, the final hexafluorosilicic acid solution has a concentration ranging from 5-15 % w/w, preferably, 6-14 % w/w or 7-13 % w/w or 8-12 % w/w or 9-11 % w/w.
[0038] In some embodiment, the condition in step c) includes continuous agitation at a speed ranging from 100 to 200 RPM for a time period ranging from 10 to 60 minutes. Preferably, the agitation speed ranging from 100 to 150 RPM for a time period ranging from 20 to 40 minutes. More preferably, the agitation speed is 140 RPM for a time period of 30 minutes.
[0039] In some embodiment, the filteration in step d) is carried out at a pressure ranging from 30 to 40 Kpa. Preferably, the pressure is 34 Kpa.
[0040] In some embodiment, the solvent in step e) is selected from a group comprising of water, ethyl alcohol (70%) and combination thereof. Preferably, the solvent is water.
[0041] In some embodiment, the base in step e) is selected from a group comprising of sodium carbonate, calcium carbonate, potassium carbonate and combination thereof. Preferably, the base is sodium carbonate.
[0042] In some embodiment, the drying in step f) includes temperature ranging from 80 to 140 °C for a time period ranging from 10 to 14 hours. Preferably, the drying temperature ranging from 100 to 120 °C for a time period ranging from 11 to 13 hours. More preferably, the drying temperature is 110 °C for a time period of 12 hours.
[0043] In some embodiment, the pH is adjusted in between 5.5 to 6.5. Preferably, the pH is 5.6 to 6.4 or 5.7 to 6.3 or 5.8 to 6.2 or 5.9 to 6.1 or 6.
[0044] In some embodiment, the process provides a high-purity sodium fluorosilicate powder suitable for industrial applications along with valuable calcium sulfate as byproducts and reusable sodium chloride.
[0045] The present disclosure effectively overcomes the limitations of existing technologies by implementing several key optimizations. Optimized process parameters are crucial, as the invention employs precise control over solution specific gravities, flow rates during mixing, stirring speeds, and sequential washing steps. These optimizations significantly enhance the purity, yield, and properties of the sodium fluorosilicate powder produced. Additionally, selective precipitation is achieved through controlled pH adjustment of the supernatant solution, allowing for the efficient separation of specific components and reducing waste. The invention also ensures byproduct utilization by selling calcium sulfate directly to the market and reusing sodium chloride within the process, thereby minimizing waste and maximizing resource utilization. This approach offers Environmental Benefits by transforming waste into valuable products, reducing pollution, and eliminating the need for extensive waste treatment facilities. Furthermore, the invention achieves Economic Efficiency by integrating the production and sale of byproducts like calcium sulfate, eliminating unnecessary steps, and reducing production costs while maintaining high-quality output.
[0046] A flowchart of the process of the present disclosure is shown in Figure 1. The process begins with preparing two solutions: a sodium chloride (NaCl) solution using 1 kg NaCl and 2.8 L water, aiming for a specific gravity between 1 and 1.5, and a hexafluorosilicic acid (H2SiF6) solution, maintaining its specific gravity between 1 and 1.5. These solutions are mixed in a bowl at a controlled flow rate and stirred at 140 RPM for 30 minutes, resulting in a white precipitate. This precipitate is separated by suction filtration, yielding a pellet and a supernatant solution. The pellet undergoes a washing process with water and sodium carbonate solution, followed by drying at 110°C to obtain sodium fluorosilicate powder. The pH of the supernatant solution is adjusted to 6 using a 1:10 (w/v) solution of calcium hydroxide (Ca(OH)2), leading to the formation of a milky white precipitate. The novelty of this method lies in the specific control of solution specific gravities, flow rates during mixing, and sequential washing steps with water and sodium carbonate. These parameters optimize the purity, yield, and properties of the final sodium fluorosilicate powder. Additionally, the controlled pH adjustment of the supernatant selectively precipitates specific components. The process also results in the formation of byproducts such as calcium sulfate, which is sold to the market directly, and NaCl, which is reused. Overall, the study demonstrates a novel facile methodology for preparing sodium fluorosilicate powder and byproduct formation, highlighting key process optimizations.
[0047] There are several key factors that distinguish the present invention from conventional methods. First, the invention requires precise control over multiple process parameters, including the specific gravities of solutions, flow rates during mixing, and stirring speeds. These variables are crucial in optimizing the purity, yield, and properties of the final sodium fluorosilicate powder. Such meticulous adjustments are not typically intuitive or obvious to individuals without specialized expertise. Second, the method incorporates a unique sequence of washing steps using water and sodium carbonate solution, followed by drying at carefully controlled temperatures. Additionally, the pH adjustment of the supernatant solution to selectively precipitate specific components represents a novel approach that demands a deep understanding of chemical reactions and process engineering principles. Another distinguishing aspect of the invention is its effective integration of byproduct utilization. The process optimizes the reuse of byproducts, such as sodium chloride, and facilitates the commercial sale of calcium sulfate. This level of resource efficiency and process refinement goes beyond standard industry practices and reflects advanced design thinking. Finally, while existing methods for producing sodium fluorosilicate, such as those using hexafluorosilicic acid and sodium chloride, are known, this invention introduces novel reaction control, filtration, and drying techniques. These enhancements significantly improve process efficiency and product quality, making them non-obvious advancements beyond the scope of publicly available knowledge.
Key Innovations
[0048] Controlled Parameters: Specific gravities of solutions, flow rates during mixing, and stirring speeds are meticulously controlled to optimize yield and purity.
[0049] Sequential Washing: Washing with water followed by sodium carbonate ensures removal of impurities while improving the quality of the final product.
[0050] Selective Precipitation: Adjusting the pH of the supernatant selectively precipitates components like calcium sulfate, enhancing process efficiency.
[0051] Economic Benefits: Byproduct utilization (e.g., calcium sulfate) adds economic value while minimizing waste.
[0052] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0053] The present disclosure is further explained in the form of the following examples. However, it is to be understood that the examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope and spirit of the present invention.
Example 1
[0054] The present disclosure outlines a novel process for preparing sodium fluorosilicate powder and associated byproducts, focusing on controlled solution preparation, optimized reaction parameters, and efficient separation techniques. Below is a step-by-step of the preparation of sodium fluorosilicate powder and associated byproducts:
(i) Preparation of Solutions
[0055] Sodium Chloride Solution: 1 kg of sodium chloride (NaCl) was dissolved in 2.8 L of water to achieve a specific gravity between 1 and 1.5. For further dilution, 600 mL of this solution was mixed with 400 mL of water, ensuring the final specific gravity is between 1 and 1.15.
[0056] Hexafluorosilicic Acid Solution: An 18% (w/w) hexafluorosilicic acid (H₂SiF₆) solution was prepared. 500 mL of this solution was diluted with 500 mL of water to maintain a specific gravity between 1 and 1.15.
(ii) Reaction Process
[0057] Mixing: 1 liter each of the prepared sodium chloride and hexafluorosilicic acid solutions were introduced into separate reaction columns. Continuous agitation at 140 RPM ensures thorough mixing and reaction over 30 minutes.
[0058] Precipitation: A white precipitate was formed at the bottom of the reactor during the reaction. This precipitate consists primarily of sodium fluorosilicate.
(iii) Separation and Washing
[0059] Filtration: The white precipitate was separated using suction filtration, yielding a pellet and a supernatant solution.
[0060] Washing: The pellet undergoes sequential washing steps. First with water to remove soluble impurities. Followed by washing with a sodium carbonate solution to enhance purity.
[0061] Drying: The washed pellet was dried in a hot-air oven at 110°C for 12 hours to obtain high-purity sodium fluorosilicate powder.
(iv) Supernatant Treatment
[0062] The pH of the supernatant solution was adjusted to approximately 6 using a calcium hydroxide (Ca(OH)₂) solution (1:10 w/v). This adjustment results in the formation of a milky white precipitate, primarily calcium sulfate.
(v) Byproduct Formation
[0063] Calcium Sulfate: The milky white precipitate formed during pH adjustment was separated and marketed directly as calcium sulfate.
[0064] Reuse of Sodium Chloride: Sodium chloride dissolved in water after separation can be reused in subsequent processes.
[0065] The key byproducts identified from the process include hydrochloric acid and calcium chloride.
(vi) Final Product
[0066] The present method yields high-purity sodium fluorosilicate powder (98.9%) suitable for industrial applications, along with valuable byproducts such as calcium sulfate and reusable sodium chloride.
(vii) Characterization
[0067] Figure 2 represents an X-ray diffraction (XRD) pattern of a sample. The X-axis, which is currently labeled as "Axis Title," likely represents the 2θ angle (diffraction angle in degrees), while the Y-axis indicates the intensity of the diffracted X-rays. The presence of multiple sharp peaks suggests that the sample is highly crystalline.
[0068] Figure 3 shows a Scanning Electron Microscopy (SEM) image on the left and an Energy Dispersive X-ray Spectroscopy (EDX or EDAX) spectrum on the right, which corresponds to a sample of sodium fluorosilicate (Na₂SiF₆). The SEM image reveals the surface morphology of the material, showing a granular or crystalline structure with closely packed particles, suggesting a well-defined crystalline phase. The scale bar at the bottom left provides a reference for particle size and distribution, which is crucial in understanding the microstructural characteristics of the sample.
[0069] The EDX spectrum on the right confirms the elemental composition of the sample, indicating the presence of fluorine (F), sodium (Na), and silicon (Si), which are the primary constituents of sodium fluorosilicate. The intensity of the peaks corresponds to the relative abundance of these elements. The presence of strong F, Na, and Si peaks further supports the identification of Na₂SiF₆, as these elements are key components of its chemical structure. The absence of significant impurities in the spectrum suggests a high-purity sample. This combination of SEM and EDX analysis is useful for characterizing the morphology and elemental composition of sodium fluorosilicate, which is commonly used in water fluoridation, ceramics, and glass manufacturing.
Example 2: Comparative analysis
[0070] A comparison between the existing methods and method of the present disclosure is given in Table 1. Table 1 indicates that the method of the present disclosure provides selective precipitation and purification of Na₂SiF₆ with resource recovery and byproduct management for circular processing. The Percentage yield of Na₂SiF₆ is 98.9%.
Table 1: Comparison between the existing methods and present disclosure.
Key points CN1234596C CN1131124A CN1286217A Batiha et al., Polish J Chem Tech 2011, 13, 23-28 Present disclosure
Starting Material Sodium fluorosilicate (Na₂SiF₆) Fluorite (no HF or SiF₄) Fluosilicic acid (by-product of HF production) and saturated brine. Hexafluorosilicic acid (H₂SiF₆), sodium chloride or sodium hydroxide Hexafluorosilicic acid (H₂SiF₆) and sodium chloride (NaCl)
Main Product Fluorine compounds (e.g., NaF, KF, NH₄F, cryolite) and precipitated silica (SiO₂) Catalytic conversion of soluble fluorosilicate into sodium fluorosilicate, bypassing gas-phase steps ≥95% purity sodium fluorosilicate (Na₂SiF₆), ≤1% free acid, ≤15% moisture Sodium hexafluorosilicate (Na₂SiF₆) Sodium silicofluoride (Na₂SiF₆) as pure pellet
Process Highlights Ammonification with NH₄F, followed by gravity and filtration separation Energy-efficient, avoids HF, and promotes resource recovery Simpler but less detailed purification. Optimized molar ratio, temperature (40°C), contact time (40 min), and seeding Controlled mixing of H₂SiF₆ and NaCl solutions, followed by filtration, washing, drying, and pH adjustment
Yield Not specified Not specified Not specified Max yield of Na₂SiF₆: 94.26% (in case of NaCl) and 97.3% (in case of NaOH) 116 g of Na₂SiF₆ obtained from 1 L each of H₂SiF₆ and NaCl solution; Percentage yield = 98.9%
Byproduct Utilization Precipitated SiO₂ (white carbon black with >100 m²/g surface area), ammonium fluoride (35–45%) Gypsum is obtained and directly marketable; sulfuric acid in the final solution is reused Not specified clearly Use of NaOH
for Na2SiF6 leads to contamination of the precipitate with
iron, while when using NaCl the iron remains soluble and is washed out.
Use of sodium chloride leads to the formation of
coarser sodium hexafluorosilicate crystals Calcium sulfate (from pH adjustment) and sodium chloride (recovered and reused)
Focus Complete utilization of sodium fluorosilicate to generate multiple valuable products General conversion to sodium fluorosilicate with emphasis on process simplicity Simpler but less detailed purification. Focuses on yield and optimization only Selective precipitation and purification of Na₂SiF₆ with resource recovery and byproduct management for circular processing

[0071] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

ADVANTAGES OF THE INVENTION
[0072] The present methodology demonstrates an efficient, environmentally friendly approach to producing sodium fluorosilicate while optimizing resource utilization.
[0073] The process provides a high-purity sodium fluorosilicate powder suitable for industrial applications along with valuable calcium sulfate as byproducts and reusable sodium chloride that minimizes waste.
[0074] Byproduct utilization (e.g., calcium sulfate) adds economic value and offers a cost-effective alternative for producing sodium fluorosilicate.
, Claims:1. A process for the preparation of sodium silicofluoride (Na₂SiF₆) and associated byproducts comprising:
a) preparing a sodium chloride solution with a concentration ranging from 10-20 % w/w and a specific gravity ranging from 1 to 1.5;
b) preparing a hexafluorosilicic acid solution with a concentration ranging from 5-15 % w/w and a similar specific gravity range of 1 to 1.5;
c) mixing equal amount of the sodium chloride and hexafluorosilicic acid solutions under controlled and equal flow conditions to facilitate the precipitation of sodium silicofluoride in the mixture;
d) filtering the resulting mixture to obtain a solid pellets and a supernatant solution;
e) washing the pellets sequentially with a solvent, followed by a base, and again with the solvent to ensure purity;
f) drying the washed pellets to yield a final dry product of sodium silicofluoride; and
g) adjusting the pH of the supernatant solution with calcium hydroxide (1:10 w/v), leading to the formation of calcium sulfate and enabling the recovery of dissolved sodium chloride for reuse.
2. The process as claimed in claim 1, wherein the sodium chloride solution in step a) is prepared by the steps comprising:
i) dissolving 30 to 40 % w/v of sodium chloride in water to obtain a sodium chloride solution; and
ii) diluting the sodium chloride solution with water in a ratio of 3:2 to obtain a sodium chloride solution having specific gravity ranging from 1 to 1.5.
3. The process as claimed in claim 1, wherein the hexafluorosilicic acid solution in step b) is prepared by the steps comprising:
i) taking a 15 to 20 % w/w of hexafluorosilicic acid solution; and
ii) diluting the hexafluorosilicic acid solution with water in a ratio of 1:1 to obtain a first hexafluorosilicic acid solution having specific gravity ranging from 1 to 1.5.
4. The process as claimed in claim 1, wherein the condition in step c) includes continuous agitation at a speed ranging from 100 to 200 RPM for a time period ranging from 10 to 60 minutes.
5. The process as claimed in claim 1, wherein the filteration in step d) is carried out at a pressure ranging from 30 to 40 Kpa.
6. The process as claimed in claim 1, wherein the solvent in step e) is selected from a group comprising of water, ethyl alcohol (70%) and combination thereof.
7. The process as claimed in claim 1, wherein the base in step e) is selected from a group comprising of sodium carbonate, calcium carbonate, potassium carbonate and combination thereof.
8. The process as claimed in claim 1, wherein the drying in step f) includes temperature ranging from 80 to 140 °C for a time period ranging from 10 to 14 hours.
9. The process as claimed in claim 1, wherein the pH is adjusted in between 5.5 to 6.5.
10. The process as claimed in claim 1, wherein the process provides a high-purity sodium fluorosilicate powder suitable for industrial applications along with valuable calcium sulfate as byproducts and reusable sodium chloride.