Patent Application
20240360536
The present invention relates to a method for recovering magnesium from sediment generated in an electrolytic chlorine generation system using seawater and/or brackish water,
Magnesium is as strong as steel and 40% lighter than aluminum and is used in a variety of applications due to its high strength-to-weight ratio, durability, impact resistance and structural properties. Magnesium is used as a very important raw material in major domestic industries such as electronics, automobiles, and steel, and the demand for magnesium for producing lightweight, high-quality products is expected to increase significantly in the future. Additionally, the compound has great utility in various industries, including the pharmaceutical industry, agriculture, and construction. Currently, most of the magnesium consumed domestically relies on imports.
The world's terrestrial reserves of magnesium are estimated to be about 3.6 billion tons, and mainly exist as minerals such as magnesite, dolomite, serpentine, and brucite. The concentration of magnesium in seawater is about 1300 mg/L, and considering the entire amount of seawater, the total amount of magnesium present in seawater is 184×1015 tons, which is about 500,000 times that of land resources.
Methods for recovering magnesium can be broadly divided into methods for recovering magnesium from minerals and methods for recovering magnesium from seawater (including salt water and brackish water). When recovering magnesium from minerals, the magnesium is extracted using acid and then an alkaline substance is added to solidify the magnesium through a precipitation reaction. Methods for recovering magnesium from seawater include precipitation using alkaline substances, use of ion exchange resin, and solvent extraction.
To date, much research has been conducted on recovering magnesium from seawater using alkaline precipitants. The mainly used precipitants were lime, dolomite, NaOH, KOH, NH4OH, etc., and in most cases, calcium was removed before precipitating magnesium. The biggest difficulty in recovering magnesium using existing alkaline precipitants was precipitating and filtering the resulting magnesium hydroxide. This is because magnesium hydroxide is not only a fine particle but also exhibits low crystallization characteristics.
The technology to produce magnesia (magnesium oxide) by extracting magnesium from seawater has already been commercialized worldwide, but it is not easy to secure economic feasibility, so the development of highly efficient and economical extraction technology is still required. Economics related to the cost of alkali precipitants such as NaOH and NH4OH can be said to be a major obstacle to commercialization of the technology. Among several ways to solve this problem, discovering an inexpensive precipitant to replace the existing precipitant can be an alternative. For example, alkaline industrial by-products such as paper sludge ash (PSA), cement kiln dust (CKD), slag, and coal ash can be used as precipitants. However, so far, little research has been conducted using industrial by-products as precipitants. Kang et al (2012) only conducted a study to recover magnesium in the form of magnesium hydroxide by adding coal and NaOH to seawater.
The magnesium compounds most commonly used in industry are magnesium chloride (MgCl2), magnesium hydroxide [Mg(OH)2], and magnesium sulfate (MgSO4). Magnesium sulfate is obtained from minerals or artificial synthesis and is mainly manufactured by adding sulfuric acid into magnesium carbonate (MgCO3) or magnesium oxide (MgO). Magnesium sulfate is very soluble in water. For example, 71 g and 91 g of magnesium sulfate are dissolved in 100 mL of water at 20° C. and 40° C., respectively. However, it is virtually insoluble in alcohol and insoluble in acetone. Meanwhile, magnesium sulfate exists in various forms of hydrate depending on temperature (MgSO4·xH2O, x=1˜7), but the heptahydrate salt is the most common form. It is mainly used as paper filler, fire retardant, fertilizer, medicine, etc.
The biggest difficulty in recovering magnesium using existing alkaline precipitants was precipitating and filtering the resulting magnesium hydroxide. This is because magnesium hydroxide is not only a fine particle but also exhibits low crystallization characteristics. The technology to produce magnesia (magnesium oxide) by extracting magnesium from seawater has already been commercialized worldwide, but it is not easy to secure economic feasibility, so the development of highly efficient and economical extraction technology is still required. In particular, economics related to the cost of alkali precipitants such as NaOH and NH4OH can be said to be a major obstacle to commercialization of the technology. In addition, research on separating magnesium from existing seawater mainly consists of recovering magnesium in the form of magnesium hydroxide by adding NaOH to seawater. Research has also been conducted on separating magnesium in the form of magnesium salts by adding acid, but there is an economic problem because the recovery rate is low, and it uses a large amount of acid.
The object of the present invention is to provide a method for recovering magnesium compounds used in industry from sediments generated in an electrolytic chlorine generation system using seawater and brackish water.
Another object of the present invention is to provide magnesium compounds used in industry from sediments generated in an electrolytic chlorine generation system using seawater and brackish water.
To achieve the above object, the present invention relates to a method for recovering magnesium from sediment generated in an electrolytic chlorine generation system using seawater or brackish water, comprising:
In one embodiment of the present invention, the sulfuric acid is preferably waste sulfuric acid or sulfuric acid used in industrial sites but is not limited thereto.
In another embodiment of the present invention, the seawater is preferably seawater concentrate, but is not limited thereto.
In one embodiment of the present invention, in the above method, it is preferable to treat sulfuric acid (H2SO4) with sediment generated from an electrolytic chlorine generation system using seawater and brackish water to extract high concentration of magnesium, and then separate the magnesium sulfate using an organic solvent, and
In one embodiment of the present invention, in this method, it is preferable to comprise eluting magnesium using 0.5 to 1 M sulfuric acid in magnesium hydroxide, a sediment generated in an electrolytic chlorine generation system and mixing the eluent with the sulfuric acid to ethanol or acetone in a ratio of 1:1.5 to 1:2 (v:v) to precipitate magnesium, and
Additionally, the present invention provides a magnesium compound recovered by the method of the present invention.
In one embodiment of the present invention, the magnesium is preferably magnesium sulfate, but is not limited thereto.
The present invention will be described below.
The present invention is a two-step process of extracting high concentration of magnesium using sulfuric acid (H2SO4) and sediment generated in an electrolytic chlorine generation system using seawater and brackish water, and then separating the magnesium sulfate by precipitation using an organic solvent. There is no need for the existing process of generating magnesium hydroxide (Mg(OH)2) to separate magnesium from seawater or seawater concentrate and since there is a high concentration of magnesium in the sediment generated from the electrolytic chlorine generation system using seawater and brackish water, using a method of the present invention using sulfuric acid can ensure high efficiency recovery rate and economic feasibility.
In addition, in general, as the concentration of sulfuric acid increased, the MgSO4 precipitation efficiency increased. In the present invention, the amount of precipitation was highest at the lowest concentration, 0.5M sulfuric acid (1.5 g (ethanol) and 1.7 g (acetone) precipitated per 1 g of sediment) and as a result of EDX and XPS, it has the distinction of being able to obtain high purity MgSO4 by precipitating it in a form free of other inorganic impurities, and the used organic solvent can be reused with a recovery rate (over 99.5%).
According to the present invention, the present invention is a two-step process of extracting high concentration of magnesium using sulfuric acid (H2SO4) and sediment generated in an electrolytic chlorine generation system using seawater and brackish water, and then separating the magnesium sulfate by precipitation using an organic solvent. There is no need for the existing process of generating magnesium hydroxide (Mg(OH)2) to separate magnesium from seawater or seawater concentrate and since there is a high concentration of magnesium in the sediment generated from the electrolytic chlorine generation system using seawater and brackish water, using a method of the present invention using sulfuric acid can ensure high efficiency recovery rate and economic feasibility. In addition, the present invention has the advantage of reducing the amount of industrial waste generated by using sediment and sulfuric acid generated in an electrolytic chlorine generation system using seawater and brackish water and providing magnesium compounds, which are useful resources widely used in industry.
Hereinafter, the present invention will be described in more detail through examples, but these are merely illustrative and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that the embodiments described below can be modified without departing from the essential gist of the invention.
Overview of the Present Invention: MgSO4·xH2O(s) Precipitation Method
The method for recovering magnesium from sediment generated in the electrolytic chlorine generation system using seawater and brackish water of the present invention was carried out in the same order as
This is detailed below.
The sediment generated from the electrolytic chlorine generation system using seawater and brackish water was dried at 105° C. for 24 hours, made into powder, and used in a magnesium elution test. The mass of each powder sample was 1.00 g. 50 mL of different concentrations of sulfuric acid (0.5, 1.0, 1.5, 2.0, 2.5 M) were added into each of the five solid samples, and then stirred at 150 rpm for 20 minutes. The reason for using sulfuric acid is to prevent calcium, which interferes with the recovery of magnesium, from eluting together with magnesium by precipitating it as calcium sulfate (CaSO4). The magnesium eluate using sulfuric acid was filtered using a GF/F filter.
The magnesium eluate using sulfuric acid filtered in Example 1 and one of five organic solvents (99.9% ethanol, 99.9% acetone, 99.9% acetonitrile, 99.9% methanol, 99.9% isopropyl alcohol) were mixed 1:1. (v:v), 1:1.5 (v:v), and 1:2 (v:v) ratios. For example, 50 mL, 100 mL, and 150 mL of ethanol or acetone were added into 50 mL of magnesium eluate using 0.5 M sulfuric acid. Seventy-five solutions with five different sulfuric acid concentrations, different organic solvent types, and mixing ratios were refrigerated at 3° C. for 12 hours. The resulting solid was filtered using a GF/F filter and then dried at 70° C. The mass of the dry solid was measured and analyzed by FE-SEM/EDX and XPS.
After the solid was precipitated in Example 2, the remaining solution (ethanol and acetone) was placed in a round flask and connected to a vacuum fractionation distillation tube and a condenser. When the solution was boiled in water at 40-47° C., some of the liquid vaporized and separated. The solution separated by vaporization was analyzed by GC-MS.
The results of the above examples are as follows.
Table 1 below shows the XRF analysis results of sediment generated in the electrolytic chlorine generation system using seawater and brackish water of the present invention.
Referring to Table 1, the main constituent of the sediment is composed of magnesium (Mg, 69.5 wt %), and additionally calcium (Ca, 5.1 wt %), silicon (Si, 0.6 wt %), sodium (Na, 0.3 wt %), chlorine (Cl, 4.2 wt %) and sulfur (S, 0.5 wt %), indicating that these elements can coprecipitate when producing chlorine using seawater or brackish water.
In addition, Mg comprised in the sediment has a relatively lower solubility constant than calcium hydroxide (Ca(OH)2, solubility constant=5.5×10−6), and exists in the form of magnesium hydroxide (Mg(OH)2, solubility constant=5.61×10−12) (Zheng, L.; Xuehua, C.; Mingshu, T. Hydration and setting time of MgO-type expansive cement. Cem. Concr. Res. 1992, 22, 1-5).
Table 1 shows the results of analysis of the constituent elements of sediment generated in an electrolytic chlorine generation system using seawater and brackish water using XRF.
Referring to
Referring to
The results of precipitation experiments conducted by varying the sulfuric acid concentration of the eluate and the type of organic solvent are summarized in Table 2.
Referring to Table 2 below, when looking at the amount of magnesium sulfate (MgSO4) precipitated according to the change in sulfuric acid concentration (0.5-2.5M) of the eluate obtained by dissolving 1 g of the precipitate in sulfuric acid and the changing conditions of the mixing ratio (1:1; 1:1.5; 1:2) with five types of organic solvents, under 0.5 M sulfuric acid conditions, a 1:1.5 mixing ratio of ethanol and acetone (precipitation efficiency: ethanol=68%; acetone=97%) and a 1:2 mixing ratio (precipitation efficiency: ethanol=150%; acetone=170%) and under 1.0 M sulfuric acid conditions, a 1:2 mixing ratio (precipitation efficiency: ethanol=108%; acetone=127%).
The optimal conditions for precipitating magnesium sulfate from sediment generated in an electrolytic chlorine generation system using seawater and brackish water are as follows. It is preferable to elute the precipitate using 0.5˜1.0 M sulfuric acid and mix the eluate with one of two organic solvents (ethanol and acetone) at a ratio of 1:1.5-1:2 (v:v) to precipitate magnesium sulfate. Most preferably, elution is performed using 0.5M sulfuric acid and mixing with acetone in a ratio of 1:2 (v:v) to precipitate magnesium sulfate.
Table 2 is a table comparing precipitation amount and precipitation efficiency according to sulfuric acid concentration and organic solvent mixing ratio.
XPS Analysis Results after Magnesium Sulfate Precipitation
As a result of XPS analysis after magnesium sulfate precipitation, the qualitative analysis of the precipitate showed that magnesium sulfate (MgSO4) was the main component and was consistent with the SEM-EDX results.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0003864 | Jan 2022 | KR | national |
| 10-2022-0154549 | Nov 2022 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2023/000373 | 1/9/2023 | WO |
