KR800000416B1 - Process for producing magnesia clinker - Google Patents

Abstract

Magnesia clinkers with CaO-SiO2 ratio>=2, bulk d.>=3.35, contg. relatively small amts. of B, were prepd. by pptg. Mg(OH)2 with quick lime, calcined dolomite or slaked lime from a seawater or brine soln. at pH<=11.2. Thus, CO2-free seawater and purified dolomite were mixed at pH 11.7, and fed to a thickener, a portion of the ppt. being cycled to the reactor to keep the Mg(OH)2 in the reactor at 12 g/l. The resultant cake was dried, molded and burned at 1600 and 1800≰C to give a product bulk d. 3.41, 3.45 and apparent porosity 2.80, 1.14.

Description

Method for manufacturing magnesia clinker

1 and 2 respectively show process diagrams showing an example of the magnesia klinker-manufacturing process part and an example of the magnesium hydroxide manufacturing process part of the manufacturing process of the present invention.

The present invention relates to a method for producing a magnesia clinker having a high specific gravity and a low boron content. Magnesia clinker adds quicklime or light dolomite to an aqueous solution containing magnesium ions, such as seawater or nectar, and converts the magnesium ions in the solution into Mg ⁺⁺ + Ca (OH) ₂ → A precipitate of magnesium hydroxide is produced by a reaction of Mg (OH) ₂ ↓ + Ca ⁺⁺ , which is prepared by concentration, washing with water, filtration and calcining. Magnesium hydroxide, an intermediate product of magnesia clinker, is very small and has poor sedimentation and filterability. For example, in the case of magnesium hydroxide obtained by adding a slurry of light doromite to seawater, a magnesium hydroxide cake obtained by vacuum filtration usually contains 50 to 55% of unbound water.

This unbound water is removed by drying. Saving the heat required for miniaturization of manufacturing facilities and removal of unbound water by improving the sedimentation properties of magnesium hydroxide and improving the filtration is economically significant. Many studies aim to increase the sedimentation and filterability of magnesium hydroxide. Has been implemented. On the other hand, little research has been conducted on how to improve the manufacturing process of magnesium hydroxide and obtain industrially good magnesia clinker. The sinterability of magnesia clinker produced by aqueous magnesium hydroxide greatly depends on the purity of magnesium hydroxide and the composition of impurities.

For example, magnesia clinker with a MgO content of 96% or more cannot be fired by the paste feed method, as it can directly fire magnesium hydroxide cake onto rotary kilns. ) Is produced by a two-stage firing method.

In addition, even when the two-stage firing method is carried out, the molar ratio (CaO / SiO ₂ ) of calcia and silica contained in the magnesia clinker is less than 1, which is relatively easy to sinter. It is possible to sinter to about (96% of true specific gravity).

However, the molar ratio of calcia and silica contained in the magnesia clinker of 2 or more is very difficult to make the volume specific gravity 3.3 or more (93% of the total ratio) even if the light conditions are selected.

Magnesia particles having a molar ratio of calcia and silica of 2 or more have much stronger properties than those having a molar ratio of 1 or less when the magnesia refractory material is made of magnesia refractory material.

Therefore, when magnesia particles having a molar ratio of calcia, silica and silica of 2 or more and a high volume specific gravity are obtained, these particles are used as raw materials, and the compressive and bending strengths during heating are applied, and the slag erosion resistance This strong refractory can be manufactured.

정도로 줄일수가 있다는 것이다.The present invention relates to a method for producing magnesia clinker with improved properties of magnesium hydroxide, and the magnesia clinker obtained by the method of the present invention can easily obtain a volume ratio of 3.4 or more even when the molar ratio of calcia and silica is two or more. Further, the characteristics of the magnesia clinker obtained by the method of the present invention are characterized by the fact that the content of boron in comparison with the conventional magnesia clinker

It can be reduced to a degree.

Magnesia clinkers having a high boron content are known to deteriorate the properties of the magnesia refractory during heating.

The present invention will be described with reference to the drawings.

1 is an example of the manufacturing method of magnesia clinker of the present invention and shows a typical manufacturing method of magnesia clinker which is already carried out. In the method of adding light rhodiumite (A) or quicklime containing substances to an aqueous solution containing seawater or magnesium ions, two types of light rhodiumite or quicklime are added by extinguishing by adding industrial water (W) in the fire extinguisher (1). There is a method and the present invention can use both methods.

The reaction is carried out by mixing decarburized gas seawater (B) and light rhodiumite (A) or quicklime or respective digests in a reaction tank (2), Mg ⁺⁺ + Ca (OH) ₂ → Mg (OH) ₂ ↓ + Ca ^{++ It} is a process that causes a reaction, and instead of seawater, a solution containing Mg ions such as juice can be used. A feature of the present invention is that the reaction is carried out in the presence of excess Ca (OH) ₂ than the amount necessary to completely carry out the reaction of Mg ⁺⁺ + Ca (OH) ₂ → Mg (OH ₂ ) ↓ in this reaction step. Mg ⁺⁺ + Ca (OH) ₂ → Mg (OH) ₂ reaction is equimolar (等 Mol) reaction, the pH of the solution at the end of the reaction is 10.8 (20 ℃). Therefore, when pH of reaction liquid is higher than 10.8, it will contain unreacted Ca (OH) ₂ . If the pH of this reaction is set to 11.2 or more, the volume of magnesia clinker obtained will start to increase gradually, showing a particularly significant increase in volume ratio above pH 11.7. A method of obtaining magnesium hydroxide having good filterability by making the amount of Ca (OH) ₂ present in the reaction exceed the equivalent reaction amount is described in US Pat. No. 3,080,215. However, the object of US Pat. No. 3,080,215 is to obtain a good filterable magnesium hydroxide, and a very small excess is also desirable in the excess of Ca (OH) ₂ , which is different from the method, object and effect of the present invention.

In general, carrying out this reaction in an excess Ca (OH) ₂ state results in smaller crystals of magnesium hydroxide, which leads to poor filterability, and the same tendency is recognized even when the method of the present invention is used. However, even when excess Ca (OH) ₂ as in the present invention is present, it is possible to obtain magnesium hydroxide which can be industrially filtered by using a method such as increasing various circulations. By taking the multiple reaction method, excess Ca (OH) ₂ can also be used as a raw material for another magnesium hydroxide manufacturing process. However, the method of making the reaction tank [(2-1) to (2-6)] like 2nd degree | times into two or more stages, and making the pH of the reactor solution of the last stage into 10.8 or less is a more excellent method. The obtained magnesium hydroxide is concentrated in a concentrator (3), and washed with a washing tank (4). Water washing improves the volume specific gravity of the magnesia clinker obtained as well as possible. The degree of washing with water is preferably carried out until the ratio of the amount of chloro ions and the amount of Mg (OH) ₂ contained in the magnesium hydroxide cake (obtained by filtration of washed magnesium hydroxide with the filter 5) is not more than 0.6%, It is especially preferable to be 0.3% or less.

The magnesia clinker obtained by the method of the present invention has a sufficiently high specific gravity even when the firing temperature is low, but the predetermined temperature of the magnesia clinker is 1800 ° C. or more in order to reduce the reheat shrinkage rate at the time of sintering. desirable. The volume fraction of the magnesia particles obtained by the method of the present invention is easily obtained that the molar ratio of calcia and silica included in the magnesia particles is close to 3.4 (96% of the true specific gravity), and the two-stage firing process ( That is, when the molding is carried out in the molding machine 7 through the small furnace 6 and fired in the furnace 8, a volume specific volume of 3.5 (98% of the true specific gravity) is also obtained.

In the drawings, A: light road road mite, B: decarburized cutlet seawater, P: magnesia clinker W: industrial water, W ₀ : wastewater 1: fire extinguisher 2: reactor 3: concentrator 4: washing tank 5: filter 6: light furnace 7: Molding machine 8: Min. 2-1 to 2-6: Reactors are respectively indicated. The effects of the present invention will be described below with reference to Examples and Comparative Examples.

Example 1

To the reaction tank equipped with a stirring device and a pH automatic control device, decarbonated seawater and a slurry refined by digesting light dolomite with 14 times water are continuously added.

The flow rate of the slurry is adjusted using a pH automatic control system so that the pH of the reaction solution is 11.7.

The reaction solution is continuously introduced into the concentrator, and magnesium hydroxide is precipitated to discard the supernatant.

The amount of calcium hydroxide in the waste liquid is 0.37 g / l. Most of the precipitated magnesium hydroxide is circulated from the pump to the reaction tank, and most of the concentrated magnesium hydroxide is circulated from the pump to the reaction tank, and various circulation amounts are adjusted so that the amount of magnesium hydroxide in the reaction solution is 12 g / L. The obtained magnesium hydroxide cake was obtained. The amount of chloro ions contained in this cake is 0.3% by the ratio of the amount of chloro ions and the weight of magnesium hydroxide.

The magnesium hydroxide cake is dried until the water content reaches 10%, and then molded at a pressure of 500 kg / cm 2. This molded product is calcined at 1600 ° C and 1800 ° C for 1 hour in a furnace. The volume, weight, and chemical adjustments of the sintered material are as follows.

The dried magnesium hydroxide was further calcined in an electric furnace at 900 ° C. for a small amount of magnesia obtained at a pressure of 500 kg / cm 2. The molded product is calcined at 1800 ° C. for 1 hour in a gas furnace.

The volume specific gravity, external appearance ratio and chemical adjustment of the obtained sintered product are as follows.

Example 2

Six reactors equipped with a stirrer and a pH automatic control system are arranged as shown in FIG. 17% of decarbonated seawater was continuously added to Reactor 1-5 and 15% of Reactor 6, respectively. In each reactor, light doromite was digested with 14 times of water, a purified slurry was added, and the solution of each reactor was adjusted so that the pH of the reactor was adjusted from reactor 1-5 to 11.7 reactor 6 to 10.8. The reaction solution is led to a concentrator to precipitate and concentrate magnesium hydroxide.

The precipitate-concentrated slurry was washed with decarbonated industrial water, filtered, and a cake of magnesium hydroxide having a water content of 49% was obtained. The amount of chloro-ion contained in this cake was 0.3% by weight ratio of magnesium chloro-ion as measured.

The magnesium hydroxide cake is dried until the water content reaches 10%, and then molded at a pressure of 500 kg / cm 2. The apparent porosity and chemical composition in the volume of the sintered product which was calcined for 1 hour at 1800 degrees Celsius in a gas furnace were as follows.

Example 3-6 Reference Example 1

To a reactor equipped with a stirring device and a pH automatic control device, decarbonated seawater and quicklime are digested with 12 times water and purified calcium hydroxide slurry is continuously added. The flow rate of the calcium hydroxide slurry is adjusted using a pH automatic control device so that the pH of the reaction solution becomes the following value.

The reaction solution is continuously introduced into the concentrator, and the supernatant is discarded by precipitating and concentrating magnesium hydroxide. Most of the precipitated concentrated magnesium hydroxide is circulated through a pump to adjust the amount of circulation so that the amount of magnesium hydroxide in the reaction solution is 15 g / l.

The magnesium hydroxide thus produced was washed with water and filtered to obtain a magnesium hydroxide cake having a water content of 48 to 52%. The amount of chloro-ion contained in this cake was measured, and the weight ratio of the amount of chloro-ion and magnesium hydroxide was always 0.3% or less. After drying the cake of magnesium hydroxide until the water content is 10%, the fine powder of silica gel is added and mixed so that the molar ratio of calcia and silica in the concave is 2, and then molded at a pressure of 500 kg / cm 2. The molded product is baked in a furnace at 1800 degrees Celsius for 1 hour. The volume ratio, appearance porosity and chemical composition of the obtained sintered product are as follows.

Reference Example 2

The reaction slurry equipped with the stirring device and the pH automatic control device is continuously added to the purified slurry obtained by digesting the ethanol seawater and the light dolomite with 14 times water. Adjust the flow rate of the slurry using an automatic control device so that the pH of the reaction solution is 10.8. The reaction solution is continuously introduced into the concentrator, and magnesium hydroxide is precipitated and concentrated to remove the supernatant. The amount of unreacted magnesium ions in the waste liquid was 0.0026 g / l. Most of the precipitated magnesium hydroxide is circulated through a pump to adjust the amount of circulation so that the amount of magnesium in the reaction solution is 12 g / l. The precipitated magnesium hydroxide was washed with water and filtered to obtain a cake of magnesium hydroxide having a water content of 50%. The weight ratio of chloro ion and magnesium hydroxide contained in this cake was 0.3%. The tube of magnesium hydroxide is dried until the water content reaches 10%, and then molded at a pressure of 500 kg / cm 2. The volume specific gravity, appearance porosity, and chemical composition of the sintered product obtained by firing the molded product in a gas furnace at 1800 degrees Celsius for 1 hour are as follows.

The dried magnesium hydroxide was calcined at 900 degrees Celsius for 1 hour in an electric furnace to form a small amount of magnesia obtained at a pressure of 500 kg / cm 2. The product is baked in a gas furnace at 1800 degrees Celsius for 1 hour. The volume ratio, appearance porosity and chemical composition of the obtained sintered product are as follows.

As described above, the magnesia clinker obtained by the method of the present invention has a large characteristic of having a large volume and a low content of boron and is excellent as a raw material of magnesia refractory material.

Claims (1)

To the solution containing magnesium ions, alkali containing calcia or calcium hydroxide, such as quicklime, hydrated lime, doromite and its hydrates, is added to the solution containing magnesium ions and alkali containing calcia or calcium hydroxide. Boron content having a CaO / SiO ₂ molar ratio of at least 2 and a volume specific gravity of at least 2.35, characterized by calcination by washing the magnesium hydroxide obtained by reaction while maintaining the pH of the mixed solution at least 11.2 or higher. Process for preparing this low magnesia clinker.

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