Synthesis of nanometric mg(OH) 2 and mgo nanoparticles with tunable physicochemical properties from magnesite mining waste

Abstract

This invention relates to a method for synthesizing high-purity magnesium hydroxide (Mg(OH)2) and magnesium oxide (MgO) nanoparticles from waste magnesite mines. The method provides a sustainable process that utilizes environmentally friendly chemicals and low energy consumption. By employing ion exchange resins and cellulose derivatives, the morphology and surface properties of the particles can be precisely controlled. Unlike conventional methods, this technique adheres to green chemistry principles and aims to valorize mining waste within the framework of industrial symbiosis. The synthesized nanoparticles have potential applications across a wide range of sectors, including defense, chemical, healthcare, and agriculture.

Description

[0001] A Methode for the Production of Nanometric Mg(OH)zand MgO Nanoparticles with Tunable Physicochemical Properties from Magnesite Mine Wastes

[0002] Background of the invention

[0003] The invention relates to a sustainable method for producing high-purity and nanometric-sized magnesium hydroxide (Mg(OH)2) and magnesium oxide (MgO) nanoparticles from waste magnesite ore. This method develops a process in line with green chemistry principles, using low energy consumption and environmentally friendly chemicals. The morphology and surface properties of the nanoparticles can be controlled through the use of ion exchange resins and cellulose derivatives. The obtained nanoparticles have a wide range of application potential in various sectors such as defense, chemistry, and healthcare due to their high surface area and functionality.

[0004] State of the Art

[0005] The recovery of magnesite mining waste has gained significant importance in recent years due to the resolution of environmental issues and the increasing demand for advanced materials. Magnesite waste primarily consists of magnesium carbonate and impurities such as calcium, iron, silicon, and boron, and is produced in large quantities during mining and processing activities. Traditional disposal methods are insufficient in reducing the environmental impacts of this waste and also overlook the potential of these wastes as valuable raw materials for advanced technology. These issues highlight the need for innovative methods to process magnesite waste into functional materials.

[0006] Various techniques have been developed for the synthesis of magnesium hydroxide (Mg(OH)2) and magnesium oxide (MgO) from magnesite or magnesite waste. Among these methods, the most common is the leaching process. In this method, magnesite waste is treated with acidic solutions to dissolve magnesium ions, which are then precipitated with alkaline substances to produce Mg(OH)2. However, this method has significant limitations, such as typically achieving product purity below 90%, producing micron-sized particles, and requiring large amounts of concentrated chemicals. Additionally, this process is far from environmentally sustainable, as it increases the amount of chemical waste and necessitates additional purification steps.

[0007] Another common method is the calcination and precipitation process. In this method, magnesite is calcined at high temperatures to convert it into MgO, which is then reacted with ammonia or sodium hydroxide to synthesize Mg(OH)z. Although this method yields products of higher purity compared to the leaching method, it incurs high energy costs and a significant carbon footprint due to the requirement for high-temperature calcination. Additionally, the Mg(0H)zand MgO particles produced by this method are typically micron-sized and cannot be reduced to the nanometric dimensions necessary for advanced technological applications.

[0008] Some studies have proposed innovative precipitation processes that incorporate ion exchange resins or stabilizers to reduce impurities and control particle size. For instance, ion exchange resins have been employed to selectively remove calcium impurities; however, their high cost and frequent regeneration requirements limit their practical application. Similarly, stabilizers are used to prevent particle agglomeration, but these chemicals increase costs and leave undesirable residues in the final product.

[0009] The limitations and inadequacies of existing technical solutions, low product purity, inadequate particle size control, high energy requirements and lack of environmental sustainability of the methods for the recovery of magnesite wastes make it necessary to develop the production of Mg(OH)2 and MgO nanoparticles from magnesite wastes.

[0010] Brief Description and Objectives of the Invention

[0011] The invention described in this document presents a method for producing nanometric-sized and high-purity magnesium hydroxide (Mg(0H)z) and magnesium oxide (MgO) particles from waste magnesite ores. The method involves a leaching process with dilute acids for low energy consumption, impurity removal using ion exchange resins, and morphology control with cellulose derivatives. This process ensures environmentally friendly production in line with green chemistry principles.

[0012] One objective of the invention is to develop a production method for Mg(OH)2and MgO nanoparticles utilizing magnesite mining waste. This method transforms waste materials into high-value-added nanomaterials, thereby promoting more efficient use of natural resources and reducing waste.

[0013] Another objective of the invention is to develop a method for producing high-purity Mg(OH)2and MgO nanoparticles. The production method described in the invention overcomes the impurity and micron-size limitations of traditional methods, enabling the production of nanoparticles with 95-99% purity and controlled morphology.

[0014] Additionally, the invention aims to develop an environmentally friendly and sustainable method for producing Mg(OH)2and MgO nanoparticles. The chemical processes adopt an eco- friendly approach in line with green chemistry principles. By using innovative methods such as dilute acids and ion exchange resins, the environmental impact is minimized, and the production process becomes more sustainable.

[0015] Furthermore, the invention aims to develop a sustainable production method for Mg(OH)2and MgO nanoparticles with a broad range of applications. The nanoparticles produced by this method exhibit functional properties such as flame retardancy, antibacterial activity, and anticancer effects, thanks to their high surface areas and controlled morphologies. Consequently, these particles have the potential to be utilized in various industries, including defense, healthcare, chemistry, and agriculture.

[0016] Description of Figures

[0017] Figure 1: TEM images of magnesium oxide (MgO) nanoparticles

[0018] Figure 2: PXRD of MgO nanoparticles

[0019] Figure 3: Thermogravimetric analysis results of magnesium hydroxide (Mg(OH)2) nanoparticles Figure 4: FTIR spectra of magnesium chloride (MgCI2) obtained from mining waste and pure MgCI2(a: Pure MgCI2, b: MH-17_2H, c: MH-18_2H, d: MH-19_2H, e: MH-20_2H) Detailed Description of the Invention

[0020] The invention relates to a method for producing high-value magnesium hydroxide (Mg(OH)2) and magnesium oxide (MgO) nanoparticles from magnesite mining waste. The method includes the following steps: a. Dispersing magnesite waste powder in water at a concentration of 25-50% by weight. b. Subjecting the mixture to ultrasonic bath treatment at room temperature for 30 minutes to ensure homogeneous distribution. c. Reacting the magnesite waste powder-water mixture with dilute hydrochloric acid (HCI) (0.5- 3.0 M) at temperatures of 20-80 °C for 1-6 hours. d. Transferring the resulting turbid liquid to a column containing a filter to separate dissolved magnesium (Mg) and calcium (Ca) elements from impurities such as iron (Fe), silicon (Si), and boron (B). e. Using a membrane containing cross-linked polystyrene-based ion exchange resin to separate dissolved Ca2+ions from the solution. f. Preparing an aqueous solution of cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, or cellulose acetate) in dilute sodium hydroxide (NaOH) solutions at a concentration of 10-40% by weight at room temperature. g. Adding the prepared aqueous solution of cellulose derivatives to the column after the separation of Ca2+ions from the liquid solution. h. Heating the column to 40-80 °C for 30-60 minutes, allowing the hydroxide (OH-) ions in the cellulose derivatives to react with Mg2+ions to form Mg(OH)2. i. Centrifuging and drying the solution exiting the column to obtain Mg(OH)2nanoparticles. j. Calcining the synthesized Mg(OH)2nanoparticles at temperatures ranging from 300-1200 °C and heating rates of 0.5-25.0 °C / min to synthesize MgO nanoparticles. The method described in the invention is a sustainable green production method developed by using magnesite mine wastes of nanometric sized MgO and Mg(0H)2 particles with controllable surface area and morphology to be used in defense industry, electricalelectronics, aerospace, chemistry, textile, health and agriculture sectors with their properties such as flame retardant, heat insulation, anti-bacterial, anti-fungal, anti-cancer, anti-diabetes and high drug carrying capacity. An important feature of this method is that it allows the synthesis of high purity Mg(OH)2 and MgO nanoparticles from waste magnesite ore using a single column.

[0021] The method described in the invention is a sustainable green production process for nanometric-sized MgO and Mg(OH)2particles with controllable surface area and morphology, using magnesite mining waste. These particles exhibit properties such as flame retardancy, thermal insulation, antibacterial, antifungal, anticancer, antidiabetic, and high drug delivery capacity, making them suitable for use in various industries, including defense, electronics, aerospace, chemistry, textiles, healthcare, and agriculture. A significant feature of this method is its ability to synthesize high-purity Mg(OH)2and MgO nanoparticles from magnesite waste using a single column.

[0022] During the step of dispersing magnesite waste powder in water at a concentration of 25-50% by weight, the waste-to-water ratio varies depending on the content and type of the ore. For instance, if the impurity content (components not containing Mg) in the magnesite waste powder is between 5-15%, it is dispersed in water at a concentration of 25-30% by weight. If the impurity content is 15% or higher, it is dispersed in water at a concentration of 30-50% by weight. Similarly, during the reaction of the magnesite waste powder-water mixture with dilute (0.5-3.0 M) HCI, the acid molarity, reaction temperature, and duration vary depending on the content and type of the ore. For example, if the total content of Fe, Si, Ca, and B in the magnesite mining waste is between 5-10%, the reaction is carried out with HCI concentrations of 0.5-1.5 M for 1-2 hours at temperatures of 20-40 °C. If the impurity content is between 10- 20%, the reaction is carried out with HCI concentrations of 1.5-3.0 M for 1-3 hours at temperatures of 30-50 °C. If the impurity content is 20% or higher, the reaction is carried out with HCI concentrations of 2.0-3.0 M for 1-4 hours at temperatures of 30-80 °C. After step 2, to control the reaction yield and impurity levels, a sample is taken from the liquid, dried, and the dissolved solid is analyzed using FTIR. The presence of Mg and Ca elements is checked in the fingerprint region of the FTIR spectrum. Additionally, element analysis is confirmed with XRF analysis. The formation of magnesium chloride is estimated by titration to calculate the reaction yield. The method achieves a reaction yield of 95-99%, which varies depending on the purity of the mining waste. For example, if the impurity content in the mining waste is between 5- 10%, the reaction yield ranges between 98-99%. If the impurity content is 15% or higher, the reaction yield ranges between 95-97%.

[0023] The turbid liquid obtained from the reaction described in step (c) is a mixture containing the chloride salts of Mg and Ca elements. The Fe, Si, and B elements present in the liquid precipitate out.

[0024] In step (e), the membrane containing the cationic ion exchange resin separates elements based on their size. The membrane primarily achieves separation by binding cationic ions to the anionic groups present in its structure. Since the Caz+ion is larger than the Mg2+ion, it binds to the anionic groups in the membrane and is thus separated from the mixture. The cationic ion exchange resin used in the structure is determined by the R / C ratio (R: total capacity measured in equivalent weight of the resin used, C: total equivalent mass of anions in the solution). Depending on the ore content, the R / C ratio should be 1, 1.5, 2.0, 2.5, or 3.0. The ion exchange resin used at this stage is crosslinked polystyrene-based and is commonly used in pure water purification processes, providing a cost advantage to the system.

[0025] After the separation of Ca ions from the liquid solution, aqueous solutions of cellulose derivatives with varying degrees of substitution and polyol structures (carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and cellulose acetate) are introduced into the column. The morphology of the resultant Mg(OH)2nanoparticles is contingent upon the type of polyol employed. This enables the synthesis of nanoparticles with spherical, cubic, layered, or flower-like morphologies. For instance, utilizing hydroxypropyl methyl cellulose yields Mg(OH)2with a flower-like morphology. Hydroxymethyl cellulose or hydroxypropyl cellulose results in cubic Mg(OH)2nanoparticles. When hydroxypropyl cellulose is used, smaller cubic Mg(OH)2nanoparticles (20-30 nm) can be synthesized. Employing cellulose acetate or carboxymethyl cellulose produces flower-like Mg(OH)2nanoparticles. Carboxymethyl cellulose, in particular, yields smaller flower-like Mg(OH)2nanoparticles (25-40 nm). Methyl cellulose facilitates the formation of spherical Mg(OH)2nanoparticles.

[0026] The solution emerging from the column can be either transparent or white. The color of the solution varies depending on the particle size of Mg(OH)2. Specifically, if the synthesized Mg(OH)2nanoparticles have a particle size of 45 nm or less, the resulting solution is transparent. Conversely, if the nanoparticles are 45 nm or larger, the solution appears cloudy or slightly white. The production of nanoparticles within the size range of 21 -96 nm is feasible, contingent upon the ratio of polyol-structured cellulose derivatives used in this method. Due to their structure, cellulose derivatives limit particle growth and stabilize the particle surface through chelation.

[0027] (i.) In this procedural step, the liquid obtained from the column is centrifuged and dried, followed by particle size and morphology analyses of the resulting Mg(OH)2nanoparticles. Molar calculations are performed to determine the reaction yield occurring in the column.

[0028] (j.) The particle size and morphology of the MgO nanoparticles obtained in this step vary depending on both the nano-Mg(OH)2and the calcination heating rate. Essentially, MgO nanoparticles with particle sizes ranging from 21 to 96 nm and exhibiting either flower-like or spherical morphologies can be produced.

[0029] Figure 4 displays the FTIR spectra of magnesium chloride (MgCI2) derived from mining waste and pure MgCI2. The spectra shown here are coded a-e, representing Mg(OH)2nanoparticles synthesized at different HCI acid concentrations. Specifically, MH-17_2H corresponds to nanoparticles synthesized at 1.0 M HCI concentration, MH-18_2H at 1.5 M HCI, MH-19_2H at 2.0 M HCI, and MH-20_2H at 2.5 M HCI, all with a reaction time of 2 hours.

Claims

CLAIMS1. A method for synthesizing high-value magnesium hydroxide (Mg(OH)2) and magnesium oxide (MgO) nanoparticles from magnesite mining waste, characterized by the following steps: a. Dispersing waste magnesite powders in water at a concentration of 25-50% by weight. b. Subjecting the mixture to ultrasonic bath treatment at ambient temperature for 30 minutes to ensure homogeneous distribution. c. Reacting the waste magnesite powder-water mixture with dilute hydrochloric acid (HCI) (0.5-3.0 M) at temperatures ranging from 20-80 °C for 1 -6 hours. d. Transferring the resulting turbid liquid to a column containing a filter to separate dissolved magnesium (Mg) and calcium (Ca) from impurities such as iron (Fe), silicon (Si), and boron (B). e. Utilizing a membrane containing cross-linked polystyrene-based ion exchange resin to isolate dissolved Ca2+ions from the liquid. f. Preparing an aqueous solution of polyol -structured cellulose derivatives by incorporating carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, or cellulose acetate into dilute sodium hydroxide (NaOH) solutions at a concentration of 10-40% by weight at ambient temperature. g. Introducing the prepared aqueous solution of polyol -structured cellulose derivatives to the column after the separation of Ca2+ions from the liquid. h. Heating the column to 40-80 °C for 30-60 minutes during this process, allowing the hydroxide (OH") ions in the polyol -structured cellulose derivatives to react with Mg2+ions to form Mg(OH)2.i. Centrifuging and drying the solution obtained from the column to isolate Mg(OH)2nanoparticles. j. Calcining the synthesized Mg(OH)2nanoparticles at temperatures ranging from 300-1200 °C and heating rates of 0.5-25 °C / min to produce MgO nanoparticles.

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