CN1296278C - Production of acqueous talc from brine - Google Patents

Abstract

The invention discloses a method for preparing hydrotalcite by using salt bittern as a raw material. It is to mix bittern with bauxite acid-dissolved or alkali-dissolved pulp, or waste red mud from Bayer's alumina factory, crystallize under appropriate conditions, wash with water and dry to obtain hydrotalcite. The method has a simple process flow, less investment in equipment, and uses natural resources and industrial waste as raw materials. On the one hand, the cost and consumption are greatly reduced, and at the same time, the problem of a large amount of red mud stacking and its environmental hazards is solved. The obtained product hydrotalcite can be used as catalyst and catalyst carrier in chemical and chemical fields; it can be used as infrared and ultraviolet absorbing and blocking materials in the field of functional materials; it can be used as flame retardant and PVC stabilizer in plastic industry; it can be used as flame retardant and PVC stabilizer in the field of environmental protection , they have a strong adsorption effect on many toxic and harmful anions, so they can be used in sewage treatment, pollution prevention and environmental remediation.

Description

Method for preparing hydrotalcite from salt-making bittern as raw material

technical field

The invention relates to a method for preparing hydrotalcite from salt-making bittern.

Background technique

Salt-making bittern is the solution left after seawater, salt lake water, and underground salt brine are evaporated and concentrated to produce table salt (NaCl) or Glauber's salt (Na ₂ SO ₄ ·10H ₂ O). The dissolved components it contains are mainly MgCl ₂ , followed by MgSO ₄ , NaCl and KCl, in addition to trace components such as MgBr ₂ , see references [1-3] for details. After seawater or brine from other sources is evaporated by sunlight to obtain NaCl, it is difficult to further concentrate by evaporation due to the high viscosity and strong hygroscopicity of the solution. Although there are many technical solutions for comprehensive utilization [1-4], due to factors such as cost and benefit, there are still a considerable amount of bittern that has not been rationally utilized.

Hydrotalcite, also known as layered double hydroxide, English Layered Double Hydroxides, abbreviated as LDH. It has a layered structure, the structural layers are composed of divalent and trivalent metal hydroxides, and the structural layers are filled with carbonate or other anions, so it is also called anionic clay. Hydrotalcite transforms into a double metal oxide after being dehydrated by heating and losing hydroxide, English Layered Double Oxides, abbreviated as LDO. It partially retains the original layered structure, and can restore and reconstruct the crystal structure of hydrotalcite by absorbing water molecules, anions and hydroxides in aqueous solution.

LDH and LDO are artificially synthesized layered mineral materials that have emerged in recent years. They can be used as catalysts and catalyst carriers in the fields of chemistry and chemical industry; they can be used as infrared and ultraviolet absorption and barrier materials in the field of functional materials; in the plastic industry , can be used as flame retardant and PVC stabilizer; in the field of environmental protection, they have a strong adsorption effect on many toxic and harmful anions, so they have broad application prospects in sewage treatment, pollution prevention and environmental restoration.

references

[1] Liu Yifan, Fu Xun, Liang Yuhua, Tang Wenxia, Zhang Changxin, Chen Xinqing, Research on comprehensive utilization of bittern in salt production. Sea Lake Salt and Chemical Industry, 1993, 22(2): 4-7.

[2] Cheng Jiahao, Extraction of potassium and magnesium salts from bittern in Gaotai Salt Lake. Gansu Chemical Industry, 1997, fourth issue, 14-17.

[3] Kang Zheng, Yang Changyuan, Cui Yingde, comprehensive utilization technology of bittern. Fujian Chemical Industry, 1992, first issue, 42-45.

[4] He Chunbao, Zhang Lixiang, Tantian's research on the production of magnesium sulfate by solarization. Sea Lake Salt and Chemical Industry, 1994, 23(3): 18-19.

[5] Yang Shaowen, Cao Yaohua, Current status and progress of comprehensive utilization of red mud from alumina production. Mineral Protection and Utilization, 1999(6): 46-49.

[6] Song Kuiyuan, Song Yulin, Yang Yongzhen, Chen Hongwei, Study on the removal of sulfur (SO ₄ ^2- ) from brine by calcium chloride method. Shenyang Chemical Industry, 1989(1): 4-9.

Contents of the invention

The purpose of the present invention is to provide a kind of method that takes bittern for making salt as raw material to prepare hydrotalcite.

The chemical composition of salt-making bittern is: MgCl ₂ =11.0-45.0%, MgSO ₄ =4.0-8.5%, NaCl=2.0-8.5%, KCl=0.2-2.0%, MgBr ₂ =0.2-0.8%, (see References [1-3]).

One step of the method for preparing hydrotalcite proposed by the present invention is as follows:

1) Mix salt-making bittern with laterite-type bauxite acid-dissolved ore slurry so that the molar ratio of Mg/(Al+Fe ³⁺ ) in the solution is 1:1 to 5:1, dilute with water, and make the Mg in the solution The concentration of ²⁺ ions does not exceed 0.3mol/L, and this solution is recorded as solution A;

2) prepare the mixed solution of NaOH and carbonate or bicarbonate, wherein the mol of carbonate or bicarbonate should be 35% to 50% of the mol of magnesium element in solution A, the mol of NaOH It is 60% to 100% of the molar number of magnesium element, and the total concentration of the solution is not more than 1mol/L, which is recorded as solution B.

3) While vigorously stirring, quickly mix solution A and solution B, and continue stirring for 5-10 minutes;

4) Constant temperature crystallization of the mixed solution at a temperature of 50-80°C for 6-48 hours, dehydration of the mixed solution, filtering and cleaning, drying at a temperature lower than 90°C, grinding to a mesh size of less than 200 and bagging. The obtained product is hydrotalcite, and its general chemical structure is: [Mg _1-x (Al, Fe ³⁺ ) _x (OH) ₂ ] ^x+ [(CO ₃ ) _x/2 ·nH ₂ O], where X=0.5 ~0.17; Mg/(Al+Fe ³⁺ )=1~5.

The so-called lateritic bauxite refers to bauxite whose main mineral composition is gibbsite, and its representative chemical composition is: Al ₂ O ₃ =40-50%, Fe ₂ O ₃ =10-20% , SiO ₂ = 3-10%, TiO ₂ = 2-5%, crystal water = 22-28%; the so-called acid-soluble slurry of laterite-type bauxite refers to the concentration of this ore at 1-5N The solution obtained by dissolving in hydrochloric acid or nitric acid and removing the residue; said carbonate or bicarbonate is one or more of sodium carbonate, ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, or hydrates thereof.

The method two steps of the method for preparing hydrotalcite proposed by the present invention are as follows:

1) Mix salt-making bittern with bauxite alkali-dissolved ore slurry, so that the molar ratio of Mg/Al in the solution is 1:1 to 5:1, and dilute with water if necessary, so that the concentration of Mg ²⁺ ions in the solution is not More than 0.3mol/L;

2) Add the carbonate or bicarbonate solution prepared in advance with a concentration of 0.5-2 mole/L to the above mixed solution, so that the weight ratio of carbonate or bicarbonate to (Mg+Al) in the mixed solution is 1: 1～1∶1.5;

3) Constant temperature crystallization of the mixed solution at a temperature of 50-80°C for 6-48 hours, dehydration of the mixed solution, filtration and cleaning, drying at a temperature lower than 90°C, grinding to a mesh size of less than 200 and bagging. The obtained product is hydrotalcite, and its general chemical structure formula is: [Mg _1-x Al _x (OH) ₂ ] ^x+ [(CO ₃ ) _x/2 ·nH ₂ O], where X=0.5～0.17; Mg/Al =1~5.

The so-called bauxite refers to the general designation of ores that can be used in industry, with gibbsite, boehmite, diaspore or their mixtures as the main minerals; the said aluminum Soil ore alkali-dissolved pulp is a mixed solution of caustic soda (commonly expressed as Na ₂ O ), sodium aluminate (commonly expressed as Al ₂ O ₃ ) and soda ash (Na ₂ CO ₃ ). The representative composition is: Na ₂ O=250 ～300g/L, Al ₂ O ₃ ＝280～350g/L, Na ₂ CO ₃ ＝10～50g/L; the carbonate or bicarbonate is sodium carbonate, ammonium carbonate, sodium bicarbonate, bicarbonate Ammonium, or one or more of its hydrates.

The three steps of the method for preparing hydrotalcite that the present invention proposes are as follows:

1) Mix the salt-making bittern from which sulfate radicals have been removed with the Bayer red mud from the alumina plant, and add them together to the mixer, so that the molar ratio of Mg/(Al+Fe ³⁺ ) in the mixture is 1:1～ 5:1, dilute with water if necessary, so that the solid-liquid ratio of the pulp does not exceed 1:10, stir evenly, make a suspension, and age for 6 to 48 hours;

2) Dehydrate the suspension, dry it in the air or dry it at a temperature lower than 90°C, then calcinate it at 450°C-750°C for 2-5 hours, and grind it to less than 200 mesh for use; the obtained product is a double metal oxide The general chemical structure formula is Mg _m ·(Al, Fe ³⁺ ) _n ·O _x , where x=m+3n/2;

3) Prepare the soluble carbonate or bicarbonate into a solution with a concentration of 0.5 to 2 mole/L, and add 200 to 300 grams of bimetallic oxide per gram of carbonate or bicarbonate, and convert step 2) Add the resultant to the above solution, mix well, and keep stirring for 5-10 minutes, crystallize at a constant temperature at 50-90°C for 6-48 hours, filter or centrifugally dehydrate, wash 2-3 times with water, dehydrate, and dry in the air After drying or drying at a temperature below 90°C, grind to less than 200 mesh for use, and the product obtained is hydrotalcite, and its general chemical structure is: [Mg _1-x (Al, Fe ³⁺ ) _x (OH) ₂ ] ^x+ [(CO ₃ ) _x/2 ·nH ₂ O], where X=0.5-0.17; Mg/(Al+Fe ³⁺ )=1-5.

The so-called Bayer red mud is the industrial waste formed when the Bayer process is used to prepare alumina and aluminum hydroxide. Its particle size is micron to submicron, and its representative chemical composition is: Fe ₂ O ₃ =30-60% , Al ₂ O ₃ =10-25%, SiO ₂ =3-50%, Na ₂ O=2-15%, CaO=0-8%, TiO ₂ =0-10%, (see reference [5 ]); said soluble carbonate or bicarbonate is sodium carbonate, ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, or one or more of their hydrates.

The invention has the advantages of simple technological process, less equipment investment, wide sources of main raw materials and low price. If salt-making bittern and Bayer red mud are used as raw materials to synthesize hydrotalcite, the problems of red mud stacking and environmental hazards can be solved at the same time. The obtained product hydrotalcite can be used as catalyst and catalyst carrier in the chemical and chemical fields; it can be used as infrared and ultraviolet absorbing and blocking materials in the field of functional materials; it can be used as antibacterial additives, flame retardants and PVC stabilizers in the plastic industry; In the field of environmental protection, they have a strong adsorption effect on many toxic and harmful anions, so they can be used in water purification, sewage treatment, pollution prevention and environmental restoration.

Detailed ways

The first method for preparing hydrotalcite proposed by the present invention is to use salt-making bittern as the source of divalent metal elements, i.e. magnesium, and use laterite-type bauxite acid-dissolved ore pulp as the source of trivalent metal elements aluminum and iron. Reaction and crystallization to synthesize hydrotalcite. The main mineral composition of lateritic bauxite is gibbsite, followed by goethite and hematite. This type of bauxite has a loose structure and strong chemical activity, and is easily dissolved by inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid. Considering environmental and cost factors, hydrochloric acid is recommended. Due to the presence of ferric iron, the hydrotalcite synthesized from laterite-type bauxite is reddish. The ratio of divalent metal elements and trivalent metal elements in the additive has a certain influence on the performance of the final product. Generally speaking, when the amount of the former is higher, the crystalline structure of the product is more stable; and when the amount of the latter is higher, the adsorption performance of the product is better. Preferably, the molar ratio of the divalent and trivalent metal elements is within the range of 1:1 to 5:1. The amount of bittern used in actual application can be calculated according to the amount of bauxite, and the content of magnesium in the added bittern should be 0.5 to 2.5 times of the dry weight of bauxite.

When configuring solution B with caustic soda and sodium carbonate or sodium bicarbonate, the molar concentration of the two in the solution is 2:1. The mol of sodium carbonate or sodium bicarbonate in solution B should be 35% to 50% of the mol of magnesium element in solution A, the mol of NaOH is 60% to 100% of the mol of magnesium element, and the total solution The concentration should not exceed 3mol/L. Bittern and laterite-type bauxite acid-dissolved slurry mixture (solution A) needs to be vigorously stirred before mixing with solution B, and the two solutions are quickly mixed while stirring. After that, continue to stir for 5-10 minutes to ensure uniform mixing. The optimum conditions for crystallization are 60-70°C, 10-16 hours.

The crystallized suspension can be dehydrated by filtration, pressure filtration or centrifugation, and natural drying should be adopted as much as possible, or dried at a temperature not exceeding 90°C, or spray drying can also be used.

The second method for preparing hydrotalcite proposed by the present invention is to use salt-making bittern as the source of divalent metal element magnesium, and use bauxite alkali-dissolved ore pulp as the source of trivalent metal element aluminum to synthesize hydrotalcite through hydrothermal reaction . Alkali-dissolved ore pulp is an intermediate product of alumina and aluminum hydroxide prepared by the Bayer process, which can be obtained from an alumina plant. It is caustic soda (commonly expressed as Na ₂ O), sodium aluminate (commonly expressed as Al ₂ O ₃ ) and soda ash (Na ₂ CO ₃ ) mixed solution, the representative components are: Na ₂ O = 250-300g/L, Al ₂ O ₃ = 280-350g/L, Na ₂ CO ₃ = 10-50g/L. Since the raw material does not contain iron, the hydrotalcite product is pure white.

The amount of bittern should be such that the molar ratio of divalent and trivalent metal elements in the mixed solution is within the range of 1:1 to 5:1. After adding sodium carbonate or sodium bicarbonate to the solution, crystallization, dehydration, and drying conditions are the same as the previous method.

The third method for preparing hydrotalcite proposed by the present invention is to use salt-making bittern as the source of the divalent metal element magnesium, and use the Bayer red mud from the alumina factory as the source of the trivalent metal element aluminum, through chemical reaction and crystallization , synthetic hydrotalcite. Due to the high impurity components contained in the Bayer red mud, the product obtained by this method is only suitable for applications that do not require high purity and color, such as waste water treatment, flame retardant additives for dark plastic products, and the like.

When using this method to prepare hydrotalcite, it is necessary to remove the sulfate radicals in the bittern. This is because the red mud contains varying amounts of calcium, and the sulfate radicals in the bittern are easy to react with calcium to form gypsum, which makes the hydrotalcite in the reactant Relative content decreased. The removal of sulfate from bittern is a well-known technique [6]. Adding an appropriate amount of CaCl ₂ to bittern will have the following reaction:

           

The gypsum precipitate that forms is easily separated from the bittern. After the sulfur-free bittern is mixed with red mud, the following reactions will occur between the calcium in the red mud and the magnesium chloride in the bittern:

           

That is, the calcium in the raw material is conducive to the precipitation of Mg(OH) ₂ , and the formed CaCl ₂ will be removed during dehydration and washing. A large amount of NaOH in red mud will also promote the precipitation of magnesium ions in bittern:

            

As a result of the reaction, magnesium is transferred to the solid phase, while sodium and calcium enter the solution and will be removed in the next step.

The ratio of the divalent metal elements in the additives to the trivalent metal elements in the red mud has a certain influence on the performance of the final product. Generally speaking, when the amount of the former is higher, the crystalline structure of the product is more stable; and when the amount of the latter is higher, the adsorption performance of the product is better. The amount of bittern used in actual application can be calculated according to the amount of red mud, and the content of magnesium in the added bittern should be 0.5 to 3 times of the dry weight of red mud.

The amount of water added can be adjusted according to the degree of dryness of the red mud, so that the product after stirring is a viscous and fluid suspension. If the water consumption is too low, it is difficult to mix the raw materials evenly; if the water consumption is too high, the energy consumption and equipment wear of the subsequent process will be greatly increased.

The stirred suspension can be dehydrated by filtration, pressure filtration or centrifugation, and should be dried naturally or at a temperature not exceeding 90°C for further aging during the drying process.

The purpose of calcining the intermediate product is to convert the divalent and trivalent element oxides (hydroxides) in the mixture into solid solutions. The calcined product is a double metal oxide, which can be directly put on the market as a product, and can also be used as a raw material for further synthesizing hydrotalcite.

Hydrotalcite can be obtained by hydrolyzing the bimetallic oxide in a carbonate solution. A representative chemical reaction in solution is:

In the reaction, the molar ratio of LDO to carbonate and bicarbonate is 1: 1, and the molar number of carbonate and bicarbonate should be controlled at 1.1 to 1.5 times that of LDO to ensure that the reaction is complete. The type of carbonate and bicarbonate had little effect on the hydrolysis reaction. Considering the cost factor, sodium carbonate (NaCO ₃ ) is preferably used. The hydrolyzate should be washed 2 to 3 times after dehydration to remove excess carbonate and other soluble impurities.

Below in conjunction with embodiment further illustrate the present invention.

Example 1: Preparation of hydrotalcite from salt lake bittern and bauxite acid-dissolved pulp.

Raw material 1: bittern from a certain salt lake, chemical composition: MgSO ₄ =70g/L, MgCl ₂ =165g/L, NaCl=90g/L, KCl=20g/L. Raw material 2: laterite-type bauxite in a certain place, ore chemical composition: Al ₂ O ₃ = 48%; Fe ₂ O ₃ = 16; SiO ₂ = 7%, TiO ₂ = 3%, crystal water = 24%, others Impurities = 2%.

1) Weigh 175 grams of laterite-type bauxite, grind it into powder, add 6.5 liters of 1N hydrochloric acid, stir until the mineral powder is basically dissolved, filter out the residue, add 1.3 liters of bittern, stir evenly, and record it as solution A;

2) Dissolve 90 grams of NaOH and 120 grams of Na ₂ CO ₃ in 2 liters of water, stir until the solute is completely dissolved, and record it as solution B;

3) Stir solution A vigorously, quickly pour solution B into solution A while stirring, and continue stirring for 5 minutes;

4) The mixed solution was crystallized at a constant temperature of 60°C for 12 hours, the mixed solution was filtered and dehydrated, washed, dried at 80°C, ground to less than 200 mesh and bagged. The resulting product is hydrotalcite.

Example 2: Preparation of hydrotalcite from sea salt bittern and bauxite acid-dissolved pulp.

Raw material 1: sea salt bittern from a certain place, chemical composition: MgSO ₄ =116g/L, MgCl ₂ =311g/L, NaCl=52g/L, KCl=5g/L. Raw material 2: laterite-type bauxite in a certain place, the chemical composition of the ore is the same as in Example 1.

1) Weigh 175 grams of laterite-type bauxite, grind it into powder, add 1.5 liters of hydrochloric acid with a concentration of 4N, stir until the ore powder is basically dissolved, filter out the residue, add 0.7 liters of bittern, then add 15 liters of water, stir evenly, Recorded as solution A;

2) Weigh 100 grams of NaOH and 100 grams of _NaHCO Dissolve in 4 liters of water, stir until the solute is completely dissolved, and record it as solution B;

3) Stir solution A vigorously, quickly pour solution B into solution A while stirring, and continue stirring for 5 minutes;

4) The mixed solution was crystallized at a constant temperature of 80°C for 10 hours, the mixed solution was filtered and dehydrated, washed, dried at 60°C, ground to less than 200 mesh and bagged. The resulting product is hydrotalcite.

Example 3: Preparation of hydrotalcite from sea salt bittern and bauxite alkali-dissolved slurry.

Raw material 1: sea salt bittern from a certain place, chemical composition: MgSO ₄ =72g/L, MgCl ₂ =570g/L, NaCl=3.5g/L, KCl=2.0g/L. Raw material 2: Alkali-dissolved ore pulp from an alumina plant in a certain place, the composition is: Na ₂ O = 260g/L, Al ₂ O ₃ = 310g/L, Na ₂ CO ₃ = 30g/L.

1) Mix 1 liter of bauxite alkali-dissolved slurry with 2 liters of bittern, then add 20 liters of water, and stir evenly;

2) Take 25 liters of pre-prepared sodium carbonate solution with a concentration of 1 mole/L and add it to the above mixture, and stir evenly;

3) The mixed solution was crystallized at a constant temperature of 60°C for 12 hours, the mixed solution was dehydrated, filtered and washed, dried at a temperature of 70°C, ground to a mesh size of less than 200 and packed into bags. The resulting product is hydrotalcite.

Example 4: Preparation of hydrotalcite from bittern sea salt and alkali-dissolved bauxite slurry.

The raw material used is identical with embodiment 3.

1) Mix 1 liter of bauxite alkali-dissolved slurry with 2 liters of bittern, then add 20 liters of water, and stir evenly;

2) Take 28 liters of pre-prepared sodium bicarbonate solution with a concentration of 1 mole/L and add it to the above mixture, and stir evenly;

3) The mixed solution was crystallized at a constant temperature of 70°C for 10 hours, the mixed solution was dehydrated, filtered and washed, dried at 80°C, ground to a mesh size of less than 200 and packed into bags. The resulting product is hydrotalcite.

Example 5: Preparation of hydrotalcite from sea salt bittern and Bayer red mud.

Raw material 1: sea salt bittern from a certain place, chemical composition: MgSO ₄ =80g/L, MgCl ₂ =430g/L, NaCl=16.0g/L, KCl=5.0g/L, according to the method of literature [6] before use Sulphate removal. Raw material 2: Bayer red mud discharged from an alumina plant, its chemical composition is: Al ₂ O ₃ =24.6%; Fe ₂ O ₃ =34.2%; SiO ₂ =16.5%, CaO =3.7%, Na ₂ O = 9.8%, TiO ₂ = 6.8%.

1) Take 1.5 liters of bittern from which sulfate radicals have been removed, weigh 0.5 kg of dry red mud and mix, then add 5 liters of water, stir evenly, make a suspension, and age for 12 hours;

2) Dehydrating the suspension, drying it at 80°C, calcining at 500°C for 3 hours, and grinding it to less than 200 mesh for use;

3) Take 2 liters of sodium carbonate solution with a concentration of 1 mole/L, add the result of step 2) to the above solution, mix well, and continue stirring for 5 minutes, crystallize at a constant temperature at 60°C for 12 hours, filter and dehydrate, Wash it with water for 2-3 times, dry it at 80°C after dehydration, and grind it to less than 200 mesh for use. The product obtained is hydrotalcite.

Example 6: Preparation of hydrotalcite from sea salt bittern and Bayer red mud.

The raw material is the same as in Example 5, and the sulfate group is removed by the method of document [6] before use.

1) Take 2 liters of bittern from which sulfate radicals have been removed, weigh 0.8 kg of dried red mud and mix, then add 6 liters of water, stir evenly to make a suspension, and age for 8 hours;

2) Dehydrating the suspension, drying it at 70°C, calcining at 600°C for 2 hours, and grinding it to less than 200 mesh for use;

3) Take 4 liters of sodium bicarbonate solution with a concentration of 1 mole/L, add the product obtained in step 2) to the above solution, mix well, and keep stirring for 10 minutes, crystallize at a constant temperature at 80°C for 8 hours, filter and dehydrate , and washed 2 to 3 times with water, dried at 80°C after dehydration, and ground to less than 200 mesh for use, and the obtained product is hydrotalcite.

Claims (10)

1. a method for preparing hydrotalcite as a raw material with salt-making bittern, is characterized in that its steps are as follows: 1) Mix salt-making bittern with laterite-type bauxite acid-dissolved ore slurry, so that the molar ratio of Mg/(Al+Fe ³⁺ ) in the solution is 1:1 to 5:1, dilute with water, and make the Mg in the solution The concentration of ²⁺ ions does not exceed 0.3mol/L, and this solution is recorded as solution A; 2) prepare the mixed solution of NaOH and carbonate or NaOH and bicarbonate, wherein the mol of carbonate or bicarbonate is 35% to 50% of the mol of magnesium element in solution A, the mol of NaOH The number is 60% to 100% of the molar number of magnesium element, and the total concentration of the solution is not more than 1mol/L, which is recorded as solution B; 3) While stirring, mix solution A and solution B, and continue to stir for 5 to 10 minutes; 4) Constant temperature crystallization of the mixed solution at a temperature of 50-80°C for 6-48 hours, dehydration of the mixed solution, filtering and cleaning, drying at a temperature lower than 90°C, grinding to less than 200 mesh and bagging, the obtained product is Hydrotalcite, its general chemical structure formula is: [Mg _1-x (Al, Fe ³⁺ ) _x (OH) ₂ ] ^x+ [(CO ₃ ) _x/2 ·nH ₂ O], where X=0.5～0.17; Mg/(Al+Fe ³⁺ )=1-5. 2. a kind of according to claim 1 is the method for raw material preparation hydrotalcite with salt-making bittern, it is characterized in that, said salt-making bittern is that seawater, saline lake water, ground salt brine are through evaporation and concentration, produce The solution remaining after table salt (NaCl) or Glauber's salt (Na ₂ SO ₄ ·10H ₂ O), the dissolved components it contains are: MgCl ₂ =11.0~45.0%, MgSO ₄ =4.0~8.5%, NaCl=2.0~ 8.5%, KCl=0.2-2.0%, MgBr ₂ =0.2-0.8%. 3. a kind of method according to claim 1 is that raw material prepares hydrotalcite with salt-making bittern, it is characterized in that, said laterite type bauxite refers to the bauxite whose main mineral composition is gibbsite Mine, its representative chemical composition is: Al ₂ O ₃ = 40-50%, Fe ₂ O ₃ = 10-20%, SiO ₂ = 3-10%, TiO ₂ = 2-5%, crystal water = 22-20% 28%; acid-soluble pulp of laterite-type bauxite refers to the solution obtained by dissolving the ore in hydrochloric acid or nitric acid with a concentration of 1-5N and removing the residue. 4. a kind of method according to claim 1 is that raw material prepares hydrotalcite with salt bittern, it is characterized in that, said carbonate or bicarbonate is sodium carbonate, ammonium carbonate, sodium bicarbonate, carbonic acid One or more of ammonium hydrogen or its hydrates. 5. A method for preparing hydrotalcite as a raw material with salt-making bittern, is characterized in that its steps are as follows: 1) Mix salt-making bittern with bauxite alkali-dissolved ore slurry so that the molar ratio of Mg/Al in the solution is 1:1 to 5:1, and dilute with water so that the concentration of Mg ²⁺ ions in the solution does not exceed 0.3 mol/L,; 2) Add the carbonate or bicarbonate solution prepared in advance with a concentration of 0.5-2 mole/L to the above mixed solution, so that the weight ratio of carbonate or bicarbonate to (Mg+Al) in the mixed solution is 1: 1 to 1:1.5; 3) Constant temperature crystallization of the mixed solution at a temperature of 50-80°C for 6-48 hours, dehydration of the mixed solution, filtering and cleaning, drying at a temperature lower than 90°C, grinding to a size of less than 200 mesh and bagging, the obtained product is Hydrotalcite, its general chemical structure formula is: [Mg _1-x Al _x (OH) ₂ ] ^x+ [(CO ₃ ) _x/2 nH ₂ O], where X=0.5～0.17; Mg/Al=1～ 5. 6. a kind of according to claim 5 is the method for raw material preparation hydrotalcite with bittern for making salt, it is characterized in that, said bauxite refers to industrially available, with gibbsite, a Boehmite, diaspore or their mixtures are collectively referred to as ores composed of main minerals; bauxite alkali-dissolved ore slurry is a mixed solution of caustic soda, sodium aluminate and soda ash, with Na ₂ O, Al ₂ O ₃ and Na ₂ CO ₃ represent caustic soda, sodium aluminate and soda ash respectively, and the representative components are: Na ₂ O = 250-300g/L, Al ₂ O ₃ = 280-3S0g/L, Na ₂ CO ₃ = 10～50g/L. 7. A method for preparing hydrotalcite with salt-making bittern as raw material, is characterized in that its steps are as follows: 1) Mix the bittern from which sulfate radicals have been removed with the Bayer red mud from the alumina plant, and add them to the mixer together so that the molar ratio of Mg/(Al+Fe ³⁺ ) in the mixture is 1:1 to 5: 1. Dilute with water so that the solid-to-liquid ratio of the pulp does not exceed 1:10, stir evenly to make a suspension, and age for 6 to 48 hours; 2) Dehydrate the suspension, dry it in the air or dry it at a temperature lower than 90°C, then calcinate it at 450°C-750°C for 2-5 hours, and grind it to less than 200 mesh for use; the obtained product is a double metal oxide The general chemical structure formula is Mg _m ·(Al, Fe ³⁺ ) _n ·O _x , where x=m+3n/2; 3) Carbonate or bicarbonate is formulated into a solution with a concentration of 0.5 to 2 mole/L, and the ratio of 200 to 300 grams of double metal oxide per gram of carbonate or bicarbonate is added to the obtained solution in step 2). Add the substance to the above solution, mix well, and keep stirring for 5-10 minutes, crystallize at a constant temperature at 50-90°C for 6-48 hours, filter or centrifugally dehydrate, wash 2-3 times with water, dehydrate and dry in the air Or after drying at a temperature lower than 90°C, grind it to less than 200 mesh for use, and the product obtained is hydrotalcite, and its general chemical structure is: [Mg _1-x (Al, Fe ³⁺ ) _x (OH) ₂ ] ^x+ [(CO ₃ ) _x/2 ·nH ₂ O], where X=0.5-0.17; Mg/(Al+Fe ³⁺ )=1-5. 8. according to claim 5 or 7, a kind of bittern for making salt is the method for raw material to prepare hydrotalcite, it is characterized in that, said bittern for making salt is that seawater, salt lake water, underground brine are concentrated through evaporation, The solution remaining after preparing table salt (NaCl) or Glauber's salt (Na ₂ SO ₄ ·10H ₂ O) contains dissolved components: MgCl ₂ =11.0-45.0%, MgSO ₄ =4.0-8.5%, NaCl= 2.0-8.5%, KCl=0.2-2.0%, MgBr ₂ =0.2-0.8%. 9. a kind of method according to claim 7 is that raw material prepares hydrotalcite with salt-making bittern, it is characterized in that, said Bayer red mud is formed when using Bayer method to prepare alumina, aluminum hydroxide Industrial waste, the particle size is micron to submicron, the representative chemical composition is: Fe ₂ O ₃ =30-60%, Al ₂ O ₃ =10-25%, SiO ₂ =3-50%, Na ₂ O = 2 to 15%, CaO = 0 to 8%, TiO ₂ = 0 to 10%. 10. a kind of according to claim 5 or 7 described a kind of method that takes bittern for making salt as raw material to prepare hydrotalcite, is characterized in that, said carbonate or bicarbonate is sodium carbonate, ammonium carbonate, sodium bicarbonate , ammonium bicarbonate or one or more of its hydrates.