KR910002385B1 - Production of magnesium hydroxide from sea water - Google Patents

Abstract

A magnesitum hydroxide [Mg(OH)2 is produced from sea water by (1) reacting sea water with slaked lime to give magnesium hydroxide slurry, (2) washing the slurry with sea water, (3) drying the washed slurry, (4) crushing and mixing the dried slurry with industrial water or SiO2-free, refined water in a crusher, and (5) washing the precipitate with industrial water or SiO2- free, refined water one or two times after settling the crushed slurry. The process has an advantage of reducing impurities in magnesium hydroxide with much less amount of water compared with the conventional process.

Description

Manufacturing method of magnesium hydroxide using sea water

The present invention relates to a method for producing magnesium hydroxide (hereinafter referred to as Mg (OH) ₂ ) from seawater, and more particularly, to preparing various Mg (OH) ₂ from seawater including magnesia clinker. It relates to a process for producing purer Mg (OH) ₂ by improving the washing process to reduce impurities.

CaO+Co₂) 및 소화(CaO+H₂O→Ca(OH)₂)시켜 만든 소석회와의 반응으로 이루어 진다.In general, the process for producing Mg (OH) ₂ from seawater calcined seawater and limestone (CaCo ₃

CaO + Co ₂ ) and digestion (CaO + H ₂ O → Ca (OH) ₂ ) to react with slaked lime.

That is, Mg ²⁺ ions contained in about 3-4 g / L in seawater cause ion exchange due to the difference in ionization tendency with Ca ²⁺ contained in slaked lime, resulting in Mg ²⁺ + Ca (OH) ₂ -Ca ²⁺ + the reaction, such as Mg (OH) ₂ are obtained a Mg (OH) _2.

In order to improve the purity of Mg (OH) ₂ during the manufacturing process, 1) Ca ²⁺ ions form CaCO ₃ as impurities by removing carbonate ions contained in seawater and fresh water using H ₂ SO ₄ . 2) washing the reactants with sea water to remove unreacted impurities in the Ca (OH) ₂ state with Mg ²⁺ ions in sea water, and 3) washing the reactants with Mg (OH) ₂ slurry in ionic state. There is a process of washing with fresh water to dissolve and remove impurity ions such as Ca ²⁺ , Na ⁺ , and K ^{+ that} are adsorbed or dissolved.

In the above method, after washing seawater and slaked lime, Mg (OH) ₂ slurry (about 20% of Mg (OH) ₂ solid) generated through seawater washing and precipitation process is washed with 5-10 times fresh water and then precipitated. Then, a slurry of about 20% Mg (OH) _{2 in} solid content is precipitated again and is separated from fresh water in which some impurities are dissolved.

Extracting the double precipitate to repeat the above operation 1-2 times to prepare Mg (OH) ₂ .

However, in the slurry prepared by the above method, Mg (OH) ₂ is distributed very finely and irregularly, thus causing irregular brown motion in the dispersion medium and collision of particles and particles. In this process, particles are agglomerated by van der Waals attraction. This will happen.

In addition, when the particles come into contact with a polar medium such as water, they charge on the surface and the charged particle surface adsorbs counter ions to electrically neutralize from the surrounding medium. In this process, alkaline or alkaline earth ions such as Mg (OH) ₂ -water clad Ca ²⁺ , Na ⁺ , K ⁺ and even water molecules are surrounded, making it difficult to reduce impurities by dissolving the wash water. New water to dissolve them is not easy to access, so a large amount of fresh water is required for cleaning.

In the case of MgO clinker, the higher CaO / SiO ₂ ratio among clinker or impurities is more resistant to erosion of slag. In this case, it is preferable to reduce the amount of SiO ₂ rather than to increase the amount of CaO to increase the overall MgO purity. Since about ₂ to 40 ppm of SiO ₂ is dissolved and 1 to 5 ppm is present as a solid, SiO ₂ is adsorbed to Mg (OH) ₂ in the industrial water washing process to increase the amount of SiO ₂ as impurities in the final MgO.

The present invention, to improve the above problems, to prepare a higher purity Mg (OH) ₂ using less industrial water or purified water from which SiO ₂ is removed by drying the seawater washed Mg (OH) ₂ slurry. If this is described in detail as follows.

That is, according to the present invention, the dried Mg (OH) ₂ slurry, which has been washed by the conventional method, is dried once, and then the dried product is subjected to about 5 times the amount of Mg (OH) ₂ solid in a wet mill such as a ball mill. Mg (OH) ₂ is washed 1-2 times with industrial water or purified water from which SiO ₂ is removed by precipitation by mixing with it and grinding it with industrial water or purified water from which SiO ₂ is removed. It relates to a manufacturing method. After seawater washing, the drying process is followed by evaporation of adhering water during drying. The particles grow and exist in a state where they can be separated into individual particles in water.

However, after drying, these particles are in the form of agglomerated masses with very weak forces, so that the specific surface area in contact with the wash water is small.

Therefore, it is good to facilitate the dissolution and removal of the impurity ions adsorbed in the form of agglomerate to Mg (OH) ₂ by lightly pulverizing during the first fresh water washing.

This separation are particles larger than Mg (OH) particles in the _second slurry finishing the water washing, due to the presence of a discrete state to the individual particles are surrounded capacity for impurity ions and water molecules almost disappeared on Mg (OH) ₂ The rate of dissolving the adsorbed impurities in the unit washing water is not only very high compared to the conventional method, but also the ratio of solids in the precipitate is high, so that the settling ability is improved, thereby greatly reducing the amount of washing water.

In addition, as the amount of washing water is reduced, not only the collection rate of Mg (OH) ₂ is improved but also the amount of SiO ₂ attached to Mg (OH) ₂ and remaining as impurities can be reduced.

As a method of drying the washed slurry, intermittent drying in a dry oven, continuous drying using a rotary kiln, spray dryer, freeze dryer, etc. Although the drying method is effective and effective to remove less adherent moisture, it is more preferable that the adhered moisture is removed so that the amount of Mg (OH) ₂ in the dried product is 70% or more.

In the fresh water washing method according to the present invention, since the precipitate after the first washing with fresh water contains more than 50% of water, it is effective to divide 2-3 times at a time rather than washing a large amount of water at a time, and the fresh water amount is to be hydrated. when magnesium varies with the purity of Mg (OH) _2, but it is preferably about 5 times for Mg (OH) ₂ solids.

Hereinafter, the present invention will be described in detail through examples.

Example 1

In order to investigate the purity of Mg (OH) ₂ according to the amount of industrial water of the present invention and the conventional method, the slaked lime and seawater were reacted at pH11.2, washed twice and washed, and then the Mg (OH) ₂ slurry was dried. Impurity composition was measured, as shown in Table 1 below.

TABLE 1

Drying ratio of 100% [Inventive Example (1)] and 80% [Inventive Example (2)] of Mg (OH) ₂ slurry containing impurities as shown in Table 1 above

1 g of dried Mg (OH) ₂ slurry was added to 5 liters of industrial water, and then ground and mixed in a ball mill for about 5 minutes. The precipitate was placed in a measuring cylinder and dried to conduct chemical analysis.

5 liters of industrial water was further added to the precipitate, and the precipitate was dried by the above operation, and chemical analysis was performed again.

After repeating the above operation once more, their chemical analysis results are shown in Table 2 below (in terms of oxides).

In addition, 5 liters of industrial water was added to 5 liters of Mg (OH) ₂ precipitate (about 1 Kg of Mg (OH) ₂ solid) having an impurity composition as shown in Table 1 above, followed by sufficient mixing, and the precipitate was dried for chemical analysis. Yes). 5 liters of industrial water was added to the precipitate again, and the precipitate was dried for chemical analysis.

The above operation was repeated once more and the results are shown again in Table 2 below.

TABLE 2

As shown in Table 2, when impurities soluble in water, such as Ca ²⁺ , Na ⁺ , K ⁺ , are washed with the same amount of washing water, they are removed at a significantly faster rate than the conventional method when the washing method of the present invention is used. It can be seen.

Example 2

Purified water containing 0.2 ppm or less of SiO ₂ was performed in the same manner as in Example 1, and the results thereof are shown in Table 3 below.

In addition, 30 liters of industrial water was added to 1 liter of Mg (OH) ₂ precipitate (containing about 1 Kg of Mg (OH) ₂ solid) having an impurity composition as shown in Table 1 above, and the precipitate was dried for chemical analysis ( Conventional example).

The above operation was repeated 1-2 times with the above washed precipitates, and the results are shown in Table 3 below.

TABLE 3

As shown in Table 3, the present invention can obtain high purity Mg (OH) ₂ with a small amount of washing water compared to the conventional method, and it can be seen that the SiO ₂ component is hardly increased even when the washing is repeated.

As described above, in the present invention, since the impurity removal effect on the unit washing water amount is larger than that of the conventional method, when the same amount of washing water is used, the amount of impurities can be greatly reduced, and Mg (OH) having an almost equivalent amount of impurity composition is used. ₂ ) In the preparation, the washing method according to the present invention has the effect of removing impurities even with about 1/6 degree of washing water, compared to the conventional method.

Claims (1)

Seawater and slaked reacted to obtain a Mg (OH) ₂ slurry, and then washed with sea water and washed again with fresh water to produce magnesium hydroxide ₍ Mg (OH) ₂₎ , Mg (OH) washed with the sea water ₂ Once the slurry is dried, the dried product is put together with industrial water or purified water without SiO ₂ in a wet mill, and then pulverized and mixed, and the precipitate is precipitated again to remove the industrial water or SiO ₂ with purified water. Magnesium hydroxide production method using sea water, characterized in that for washing 1-2 times.