CN1202005C - Process for preparing calcium metaborate from borax and lime - Google Patents

Abstract

The present invention relates to a method for preparing calcium metaborate CaO. B2O3. nH2O (wherein n=2, 4 or 6) from borax and calcium oxide and a technical process for comprehensively utilizing byproducts. The method is composed of the steps of calcification, press filtration, drying, product generation, evaporation, carbonation, crystallization by cooling, centrifugal separation and processing in a borax workshop. Borax and calcium oxide are directly calcified under the pH larger than or equal to 11 and at the temperature lower than 45 DEG C for 3 to 16 hours, and products are filtered and dried. Filter liquor is evaporated, carbonated, crystallized by cooling and centrifugally separated to recover borax, and washing water and mother liquor containing a large amount of sodium carbonate and a small amount of disodium borate are used as raw material for preparing borax from boron and magnesium mineral. The present invention has the advantages of sufficiently and effectively utilizing sodium salt and borate and reducing the production cost and satisfies market requirements.

Description

Method for producing calcium metaborate from borax and lime

Technical Field The present invention relates to a comprehensive utilization process for producing calcium metaborate CaO·B ₂ O ₃ ·nH ₂ O (wherein: n=2, 4 or 6) and by-products from borax and lime.

Background Art Calcium metaborate does not exist in nature. Previous research results show: "The complexity of synthesizing calcium metaborate is that it must be generated when the pH value is higher than 11; and at such a high pH value, the excess calcium will be precipitated as calcium hydroxide, which usually causes Reduce the purity of calcium metaborate crystals.” Therefore, the laboratory synthesis method recommended in the literature is to use B ₂ O ₃ /Na ₂ O=0.93-0.50 (i.e. the mixture of borax and sodium hydroxide) solution to precipitate calcium chloride solution, and the former must be greatly excess (three times) than calcium chloride.

The method of directly producing calcium metaborate with borax as raw material in industry has only the method of carrying out metathesis reaction with borax, calcium salt and milk of lime, wherein calcium salt can be calcium chloride, calcium sulfate or calcium nitrate, also can be calcium oxide and corresponding acid mixtures. Strictly controlling the ratio of raw materials can produce industrially applicable calcium metaborate. The common disadvantage of this type of method is that in order to obtain the desired product, in addition to the sodium salt, there is a certain amount of borate in the mother liquor, and the two salts are difficult to separate completely, which limits the application field and market price of recovering the sodium salt. Reduced economic efficiency of production.

Summary of the invention The technical process of the present invention to manufacture calcium metaborate CaO · B ₂ O ₃ · nH ₂ O (wherein: n=2, 4 or 6) by borax and lime is that raw material borax and lime (lime powder, slaked lime powder or milk of lime), according to their molar ratio Na ₂ B ₄ O ₇ ·10H _{2 O :} CaO 1:0.8-1.1 for calcification reaction, pH value ≥ 11, temperature lower than 45°C, liquid-solid ratio 2-8: 1. React for 3-16 hours under stirring. The product is filtered and dried to obtain dihydrate or tetrahydrate products of calcium metaborate; the filtrate is evaporated, carbonated, cooled and crystallized, and centrifuged to recover borax; it contains a large amount of sodium carbonate And the mother liquor of disodium tetraborate and washing water are used as raw materials for making borax from boron magnesium ore, thereby realizing the full and effective comprehensive utilization of sodium and boron.

Characteristic of the present invention is to realize according to following reaction, and calcification reaction is:

The reaction uses NaBO ₂ to maintain the medium pH ≥ 11 alkaline conditions and remove the sodium brought in by borax, and the by-product NaBO ₂ aqueous solution undergoes carbonation reaction:

The converted Na ₂ B ₄ O ₇ crystallized in the form of Na ₂ B ₄ O ₇ ·10H ₂ O after cooling. After centrifugation, the borax is returned to make calcium metaborate; the mother liquor contains a large amount of Na ₂ CO ₃ and a small amount of Na ₂ B ₄ O ₇ and is sent to the workshop for making borax with boron magnesium ore as raw material.

Therefore, the process is essentially to produce calcium metaborate with boron magnesium ore and limestone as raw materials, and borax is only an intermediate product.

Description of drawings The production process of calcium metaborate of the present invention can be seen in accompanying drawing 1 of the description:

Among them: 1-calcification, 2-press filtration, 3-drying, 4-product (calcium metaborate), 5-evaporation, 6-carbonation, 7-cooling crystallization, 8-centrifugal separation, 9-borax workshop, 10- Clear water, 11-lime, 12-borax.

The lime raw material (11) used in the present invention can be lime powder (CaO) or slaked lime powder Ca(OH) ₂ whose quality is suitable for chemical industry. The powder can be used directly, or the powder material can be mixed with boron-calcium washing water in the mixing tank to form a slurry, and then pumped into the calcification tank with compressed air or a pump. If the quality of lime is not ideal, a lime machine can be installed to remove impurities in the ash, undecomposed limestone and burnt lime lumps, and make lime milk for use.

The calcification reaction tank (1) can generally be an open type or a tank with a head, but all should have a stirring device. In the calcification reaction tank, according to the liquid-solid ratio 2-8:1 required by the process, the washing water and clear water of the calcium production process are loaded, and then, according to the molar ratio of the calcification reaction materials, depending on the quality of the lime used, use Cao:Na ₂ O ₄ O ₇ ·1OH ₂ O is 0.8-1.1:1, add the required lime powder (11) (slaked lime powder or lime milk) and borax (12) under stirring, the reaction temperature is lower than 45 ° C, and the reaction is 3-16 hours . Subsequently, the slurry in the calcification tank is sent to filter with a plate and frame filter press (2), and the filter cake is washed with water to remove sodium metaborate and then sent to dry, and the washing water is returned to the calcification ingredients. Drying (3) Use a rotary flash dryer or a fluidized bed dryer or a hollow paddle agitating dryer. When preparing calcium metaborate tetrahydrate, the drying temperature should be ≥ 105°C. When preparing calcium metaborate dihydrate, the temperature should be ≥120°C. Specifically, the drying temperature and time can be controlled according to user requirements, and calcium metaborate tetrahydrate containing 34-35% of B ₂ O ₃ can be produced, and calcium metaborate dihydrate containing 40-42% of B ₂ O ₃ can also be produced The calcification mother liquor that filters out is sent to evaporator (5), removes water evaporation and concentrates to specific gravity 1.25-1.32, promptly sends to carbonation reactor (6), uses the carbonization tail gas of borax workshop (9) to make sodium metaborate solution Carbonation, the temperature is 55-72°C, the carbonation gas pressure is 0.2-0.7Mpa, when the pH value of the solution drops to 9.0-10.2, the reaction will end. Subsequently feed liquid is discharged to cooling crystallizer (7), is cooled to 25-35 ℃. Borax is crystallized in the form of Na ₂ O ₄ O ₇ 10H ₂ O. After centrifugation (8), the mother liquor entrained in the borax is washed away with clear water, and the obtained borax is returned to the calcification tank as a raw material, and the filtrate is sent to the borax workshop (9 ) are used as raw materials. (Each ton of calcium metaborate dihydrate product can recover 280-300 kg of sodium carbonate and about 25 kg of Na ₂ O ₄ O ₇ ). The borax workshop uses boron magnesium ore, soda ash and limestone as raw materials, and adopts the traditional carbon-soda process to manufacture borax.

The concentrated sodium metaborate solution can be carbonated with _CO2 in the exhaust gas from the carbonization tank of the borax plant, provided that the pressure is 0.2-0.7Mpa and the _CO2 concentration in the gas is >5%. The carbonation reactor can be a bubble column, a bubble column or a combination of both.

After the borax is removed, the mother liquor and washing water are sent to the borax workshop (9) for use as raw materials. The borax plant is equipped with many carbonization tanks with stirring and steam jacket heating, in which the roasted boronite is housed. Mineral powder and the added sodium carbonate solution are passed through the kiln gas of the lime kiln (gas containing 30-36% CO ₂ ), and the boron-containing minerals are decomposed at 125-135°C at a pressure of 0.5Mpa to generate soluble boric acid. Sodium salt and insoluble basic magnesium carbonate and magnesium carbonate are filtered through pressure, and the carbon solution is cooled, and borax is crystallized. The tail gas discharged from the carbonization tank contains 5-20% CO ₂ and the pressure is above 0.4Mpa, which can be used to carbonate the sodium metaborate solution.

The process realizes full and effective comprehensive utilization of sodium salt and borate, reduces production cost and adapts to market price.

Detailed ways

Example 1

In an open calcification reaction tank with a mixer, add ^1.5m3 of boron-calcium washing water and ^{1.7m3 of} clean water, start the mixer, add 158kg of lime powder for chemical industry, add 1000kg of borax (including 456kg of recovered borax) and react at room temperature 8 hours. After the reaction is over, use a slurry pump to pump the boron-calcium material to a plate-and-frame filter press for filtration, the feed pressure is 0.4Mpa, and the filtered mother liquor flows into the calcium mother liquor, and then the mother liquor is added to the double-effect evaporator with a feeding pump , control the specific gravity of the final effect feed liquid, and when it reaches 1.28, the solution is discharged to the concentrated liquid tank. Use the concentrated liquid pump to add the concentrated liquid to the carbonization tower, adjust the cooling water to keep the temperature of the liquid at the bottom of the tower at 65°C, feed the carbonization tail gas from the borax workshop, keep the inlet pressure at 0.4Mpa, and send the carbonized tail gas into the tail gas tank. Used as compressed air source for the whole plant. When the pH value of the liquid at the bottom of the carbonization tower drops below 9.8, the tower feed liquid can be discharged into the borax cooling crystallization tank, the mixer is started, cooling water is fed into the feed liquid to cool the feed liquid, and the borax crystallizes out, and the temperature of the feed liquid drops. It can be discharged at 30°C. The crystallized slurry containing borax is separated by a centrifuge, and after the mother liquor entrained in the borax is washed away with a small amount of clear water, 456kg of recovered borax is obtained, which is returned to the calcification tank as a raw material for making calcium metaborate, and the borax mother liquor separated by the centrifuge and washed A total of 736kg of water, (wherein containing Na ₂ CO ₃ 129kg, Na ₂ B ₄ O ₇ 26kg) is sent to the borax workshop for batching, then add boron ore powder and a small amount of soda ash, and feed lime kiln gas for pressurized carbonization to make boron The boron in the ore is transformed into soluble Na ₂ B ₄ O ₇ , which is crystallized by cooling to produce borax Na ₂ B ₄ O ₇ ·10H ₂ O.

The calcium metaborate filter cake on the filter press is washed with clean water to remove the entrained sodium metaborate solution until the pH of the washing water is <9, and then the material can be unloaded. All the washing water returns to the ingredients. The wet filter cake is sent to the rotary flash dryer and dried with hot air at a temperature higher than 280°C. The dried product is calcium metaborate dihydrate, and the finished product contains B ₂ O ₃ 41.5%, CaO 35.1%, and Na ₂ O%. <0.5%, weight 411.5kg.

Example 2

In an open reaction tank with a mixer, add 1.5m ^{3 of} boron-calcium washing water and 1.7m ³ of clean water, start the mixer, add 213kg of hydrated lime powder containing 71% CaO, and then add 1000kg of borax (including 451kg of recovered borax) , reacted at room temperature for 9 hours, and the reaction ended. Pump the slurry to the filter press. Press filtration, filter cake washing, mother liquor thickening, sodium metaborate solution carbonation, cooling borax crystallization and centrifugation borax and other operating processes are the same as example one, obtain the borax 451kg that reclaims, send the carbon lye (borax mother liquor and wash) of borax workshop water) 715kg, including 129kg Na ₂ CO ₃ and 22kg Na ₂ B ₄ O ₇ .

The washed calcium metaborate filter cake unloaded from the filter press is sent to a spin flash dryer, and dried with hot air at a temperature higher than 300°C to obtain 427kg of finished product, which contains B ₂ O ₃ 41%, CaO 35.4% and Na ₂ O < 0.5%.

Example 3

In an open reaction tank with a mixer, add 1.5m ³ of boron-calcium washing water, 0.8m ³ of clean water, start the mixer, add 0.94m ³ of milk of lime containing 150g/L of CaO, and then add 1000kg of borax (including recovered borax 450kg), it will end in 6 hours instead. Pump the slurry to the filter press. Press filtration, filter cake washing, mother liquor thickening, sodium metaborate solution carbonation, cooling borax crystallization and centrifugation borax and other operating processes are the same as example one, obtain the borax 450kg that reclaims, send the carbon lye (borax mother liquor and wash) of borax workshop water) 710kg, including 128kg Na ₂ CO ₃ and 21.5kg Na ₂ B ₄ O ₇ .

The washed calcium metaborate filter cake unloaded from the filter press is sent to the hollow paddle type agitating dryer, heated and dried with 0.5Mpa steam, the material residence time is 1 hour, and the discharge temperature is 120°C to obtain 422kg of finished products. Containing B ₂ O ₃ 41.6%, CaO 33.4% and Na ₂ O<0.5%.

Claims (6)

1. A method for preparing calcium metaborate with borax and lime, characterized in that the method is directly using raw material borax and lime, according to their molar ratio Na ₂ B ₄ O ₇ 10H ₂ O: CaO is 1: 0.8 -1.1, the pH value of the calcification reaction is ≥11, the temperature is lower than 45°C, the liquid-solid ratio is 2-8:1, the reaction is stirred for 3-16 hours, the product is filtered and dried to obtain the dihydrate of calcium metaborate Products; the filtrate is evaporated, carbonated, cooled and crystallized, and centrifuged to recover borax; the mother liquor and washing water containing a large amount of sodium carbonate and disodium tetraborate are used as raw materials for making borax from boron magnesium ore. 2. According to the preparation method of calcium metaborate according to claim 1, it is characterized in that the raw material lime used is lime powder or slaked lime powder or lime milk prepared by removing impurities; the powder material can be directly added or added to the Reactor. 3. The method for preparing calcium metaborate according to claim 1, characterized in that the slurry separation of the calcification reaction is filtered by a plate and frame filter press, the filter cake is washed with clear water, and the washing water is returned to the calcification ingredients. 4. According to the preparation method of calcium metaborate according to claim 1, it is characterized in that the drying process of calcium metaborate is to adopt spin flash dryer or fluidized bed dryer or hollow paddle stirring dryer to produce dihydrate For calcium metaborate, the drying temperature is 120-300°C. 5. According to the preparation method of calcium metaborate according to claim 1, it is characterized in that after the filtrate is evaporated to remove water, when the specific gravity of the concentrated solution is 1.25-1.30, carbon dioxide gas is used to carbonate the feed liquid, and the metaboric acid is Sodium is converted into sodium tetraborate Na ₂ B ₄ O ₇ and sodium carbonate is recycled; the conditions for carbonation are: the carbonation gas pressure is 0.2-0.7Mpa, the carbon dioxide concentration is higher than 5%, the temperature is 55-70°C, and the end point is The pH value of the feed liquid is 9.0-10.2. 6. According to the preparation method of calcium metaborate described in claim 1, it is characterized in that the separation of sodium tetraborate and sodium carbonate is through cooling and cooling, and sodium tetraborate crystallizes out in the form of borax Na ₂ B ₄ O ₇ ·10H ₂ O, The end point temperature of cooling and crystallization is 25-35°C, the borax crystals and the mother liquor are separated by a centrifuge, the sodium carbonate in the borax is washed with clean water, and the borax is recycled as a raw material.

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