Method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride

Abstract

The invention discloses a method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride, and belongs to the technical field of chemical metallurgy. The method comprises the following steps: taking a solution containing calcium chloride as a reaction base solution for decomposing calcium carbonate by ammonium chloride, adding ammonium chloride and calcium carbonate into the base solution, stirring and heating to quickly react in the solution with the temperature of 105-175 DEG C, and regularly or continuously discharging slurry generated by the reaction to maintain the balance of calcium chloride in a reaction system; and carrying out liquid-solid separation on the discharged slurry to obtain a calcium chloride solution, and collecting the gas generated by the reaction for comprehensive utilization. The method has the advantages of high solution reaction temperature, high calcium carbonate decomposition speed, thorough decomposition, easy recycling of gas generated by decomposition, simple process, convenient operation, low production cost and the like, and is suitable for large-scale industrial production of ammonium chloride wet decomposition of calcium carbonate.

Description

Technical Field

[0001] The invention relates to a method for producing calcium chloride by transforming calcium carbonate, and in particular to a method for preparing calcium chloride by decomposing calcium carbonate by using ammonium chloride, and belongs to the technical field of chemical metallurgy. Background Art

[0002] As we all know, calcium chloride is a typical soluble calcium salt. Using calcium chloride solution as raw material, high value-added calcium compound products such as industrial precipitated calcium carbonate, precipitated calcium sulfate, calcium carbonate whiskers and calcium sulfate whiskers can be produced. The raw materials for the production of such high value-added calcium compounds are usually limestone or industrial gypsum. When industrial gypsum is used as raw material, the calcium sulfate in it must first be converted into calcium carbonate, and then the obtained calcium carbonate is converted into calcium chloride. There are two reagents that can convert calcium carbonate into calcium chloride: one is hydrochloric acid and the other is ammonium chloride. In order to reduce the production cost of converting calcium carbonate into calcium chloride, people have conducted a lot of research on the decomposition of calcium carbonate with ammonium chloride.

[0003] There are two processes for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride: pyrolysis and wet process. In the pyrolysis process, calcium carbonate powder is mixed with ammonium chloride crystals and heated and roasted to obtain anhydrous calcium chloride, while flue gas containing NH3 and CO2 is produced. However, NH4Cl is easily sublimated by heat and recondenses into NH4Cl after cooling. When calcium carbonate powder is mixed with ammonium chloride crystals and heated and roasted to prepare calcium chloride, most of the ammonium chloride will sublime directly before it has time to react during the roasting process, so ammonium chloride must be used in excess during the batching process. However, the excess ammonium chloride will recondense in the flue after sublimation, making it difficult for industrial production equipment to operate normally. In the wet process, although the decomposition of calcium carbonate with ammonium chloride solution can reduce production costs, the decomposition efficiency of calcium carbonate is usually too low and has no industrial application value. When calcium carbonate powder is added to the ammonium chloride solution, the reaction rate is very slow even if it is heated to boiling, and a combination of heating and blowing is usually used to promote the reaction. Using air as a carrier gas can remove the NH3 and CO2 produced by the reaction from the solution, but even so, the conversion rate of adding calcium carbonate powder to an ammonium chloride solution at a temperature of 70-80°C and blowing it continuously for 5 hours is only ~90%. Blowing air into a hot solution not only causes serious heat loss, but also consumes a lot of power and is costly. In addition, the concentration of NH3 and CO2 brought out by the blowing air is dilute, making it difficult to recycle. Summary of the invention

[0004] In order to overcome the defects of the prior art in the preparation of calcium chloride by wet decomposing calcium carbonate with ammonium chloride, the present invention aims to provide a method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride, which method has the characteristics of high reaction solution temperature, fast calcium carbonate decomposition speed and high conversion rate, easy recycling of NH3 and CO2 produced by decomposition, simple process, convenient operation, etc., and is suitable for large-scale industrial production.

[0005] In order to achieve the above technical purpose, the present invention provides a method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride. The method comprises reacting an ammonium chloride raw material and a calcium carbonate raw material in a calcium chloride-containing solution with a calcium chloride concentration of ≥20wt.% at a temperature of 105-175°C to generate a calcium chloride slurry and a mixed gas containing NH3 and CO2.

[0006] The key to the technical solution of the present invention is to use a high-concentration calcium chloride solution as a reaction base liquid for wet decomposition of calcium carbonate by ammonium chloride. The base liquid can increase the temperature of the reaction liquid to a temperature above 105°C, promote the rapid and efficient decomposition of calcium carbonate by ammonium chloride, form a calcium chloride slurry, and at the same time smoothly discharge a mixed gas containing NH3 and CO2.

[0007] The main reaction of preparing calcium chloride by wet decomposing calcium carbonate with ammonium chloride in the present invention is as follows:

[0008] NH4Cl = NH4 + + Cl — (1)

[0009] NH4 + =Δ= H + + NH3↑ (2)

[0010] 2H + + CaCO3 =Δ= Ca 2+ + H2O + CO2↑ (3)

[0011] Among them, reaction (2) is the rate-determining step of the whole reaction. This reaction can only proceed smoothly in a solution system with a relatively high temperature. The present invention ingeniously uses a high-concentration calcium chloride solution as the reaction base liquid, which can raise the temperature to above 105°C. At this temperature, reaction (2) can proceed rapidly, and the H generated by reaction (2) + It can promote the rapid progress of reaction (3). The CaCO3 in reaction (3) decomposes, and the CO2 produced by the decomposition is a very effective carrier gas that can promote the rapid volatilization of NH3 in the aqueous solution. Therefore, reaction (2) and reaction (3) have a mutually promoting and reciprocal relationship in the high-temperature calcium chloride solution.

[0012] The overall reaction of reactions (1) to (3) is:

[0013] 2NH4Cl + CaCO3 =Δ= CaCl2 + H2O + CO2↑+ NH3↑ (4)

[0014] In summary, the present invention must use a high concentration of calcium chloride solution as the base liquid to increase the reaction temperature to ≥105°C so that reaction (4) can proceed quickly and efficiently.

[0015] An appropriate amount of NH4Cl may be selectively added to the calcium chloride-containing solution of the present invention, and the mass concentration thereof is 0-15%. A small amount of NH4Cl may play a role in inducing and promoting the reaction.

[0016] The present invention selects the solution containing calcium chloride as the reaction base liquid, mainly because the reaction of ammonium chloride decomposing calcium carbonate in an aqueous solution belongs to an endothermic reaction type. The purpose of selecting the solution containing calcium chloride as the reaction base liquid is to utilize the characteristic that the boiling point of the CaCl2 solution increases with the increase of its concentration. When the concentration of the calcium chloride solution reaches 20%, the boiling point temperature of the CaCl2 solution can be increased to ≥105°C, which can meet the process temperature required for the ammonium chloride to quickly decompose calcium carbonate in the solution, and the product obtained by the reaction is also CaCl2, which is convenient for its recovery and utilization.

[0017] As a preferred solution, the ammonium chloride raw material and the calcium carbonate raw material are added according to the chemical reaction stoichiometric ratio. Compared with the pyrometallurgical process, the wet process can significantly reduce the amount of ammonium chloride used.

[0018] As a preferred solution, the ammonium chloride raw material includes at least one of ammonium chloride solid, ammonium chloride solution and ammonium chloride slurry.

[0019] As a preferred solution, the calcium carbonate raw material includes calcium carbonate powder with a particle size of <60 μm and / or calcium carbonate slurry with a particle size of <60 μm.

[0020] As a preferred solution, the ammonium chloride raw material and the calcium carbonate raw material are added in the following manner: both are added separately, or both are preheated and added separately, or both are mixed well and then added, or both are mixed well and then preheated and then added.

[0021] As a preferred solution, the reaction time is 1 to 3 hours.

[0022] As a preferred solution, the calcium chloride slurry is deaminated with lime and then separated into solid and liquid, and the liquid phase is directly used as a liquid calcium chloride product or further processed into a solid calcium chloride product; or, the calcium chloride slurry is diluted with water, cooled to precipitate ammonium chloride crystals, and solid-liquid separation is performed to obtain a calcium chloride solution and ammonium chloride solids, the ammonium chloride solids are recycled as raw materials, and the calcium chloride solution is used as a raw material for the production of other calcium-containing compounds. More specifically, the calcium chloride slurry is deaminated by adding lime while hot, and then filtered, and the resulting filtrate is directly sold as a liquid calcium chloride product, or further processed into a solid calcium chloride product, or, the calcium chloride slurry is diluted with water to reduce its viscosity, cooled, and the Cl generated by calcium chloride is used. - The common ion effect of ions forces the residual ammonium chloride to crystallize and precipitate, and the calcium chloride solution and ammonium chloride filter cake are filtered out. The ammonium chloride filter cake is directly returned to the decomposition process for ingredients, or the ammonium chloride is first separated from it and then returned to the decomposition process for ingredients, and the obtained calcium chloride solution is used as a raw material for the production of other calcium-containing compounds.

[0023] As a more preferred solution, the other calcium-containing compounds include at least one of precipitated calcium carbonate, precipitated calcium sulfate, calcium carbonate whiskers, and calcium sulfate whiskers. The calcium chloride solution can be further converted into calcium carbonate or calcium sulfate crystals or whiskers with higher added value.

[0024] As a preferred solution, the mixed gas containing NH3 and CO2 is directly used as an industrial production raw material, or is cooled and absorbed to produce ammonium carbonate or ammonium bicarbonate.

[0025] The calcium chloride concentration in the calcium chloride-containing solution of the present invention is further preferably 12 wt.% to 45 wt.%.

[0026] Compared with the prior art, the technical solution of the present invention has the following technical advantages and effects:

[0027] The present invention ingeniously uses calcium chloride solution as the reaction base liquid for ammonium chloride wet decomposition of calcium carbonate, and utilizes the characteristic that the boiling point of CaCl2 solution increases with the increase of its concentration, and heats the temperature of the reaction base liquid to 105-175°C to meet the process temperature required for ammonium chloride to quickly decompose calcium carbonate in the solution, and at this temperature, NH3 and CO2 generated by the reaction can be volatilized immediately. At this time, the slurry generated by the reaction only needs to be discharged regularly or continuously to maintain the balance of the slurry volume in the reaction system, and the solution temperature will not fluctuate greatly, which greatly improves the production efficiency of preparing calcium chloride solution by ammonium chloride wet decomposition of calcium carbonate. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with embodiments. The following embodiments are intended to illustrate the present invention rather than to further limit the scope of protection of the claims of the present invention.

[0029] Example 1

[0030] First, stir 200g of anhydrous calcium chloride into a three-necked flask containing 500mL of water to prepare a base liquid, heat it, then add 107g of ammonium chloride crystals, and add 100g of light calcium carbonate powder (particle size <60μm) to make a slurry. When the base liquid temperature rises to above 115℃, slowly drip the slurry made of calcium carbonate powder, maintain the temperature of the reaction slurry between 115~155℃, and add the calcium carbonate slurry after about 25 minutes. Continue to heat and stir for 1h to allow the residual calcium carbonate in the solution to further decompose, then add 1.3g of calcium oxide to adjust the solution pH to 11, forcing the residual ammonium chloride to decompose completely, stop heating after 15 minutes, filter while hot, and obtain liquid calcium chloride with a specific gravity of 1.36g / mL and a concentration of 36.4%. The gas containing NH3 and CO2 produced by the slurry reaction is absorbed by cooling with dry ice to obtain ammonium bicarbonate crystals.

[0031] Example 2

[0032] A three-stage overflow reactor in series was modified from a 1000mL three-necked flask. Each three-necked flask has an overflow connection port at the upper 2 / 3 of the side. The first stage is used as a receiver for the reaction materials, the second stage is used as a buffer for the reaction system, and the third stage is used as a cooler for the reaction slurry. Take 650mL of calcium chloride solution with a specific gravity of 1.38g / mL as the base liquid, add it to the first-stage reactor, heat and stir, then mix ammonium chloride crystals and -360 mesh limestone powder with a purity of 97.2% with water in a mass ratio of 104:100:85 to form a slurry, and preheat it to 108°C. When the base liquid temperature rises to above 125°C, add the preheated mixed slurry drop by drop, stir and heat to boiling, and after 10 minutes, the first stage of the reactor begins to overflow with a bubble solution to the second stage, and then the slurry in the second reactor is also heated to boiling, and the third stage reactor begins to overflow in less than 2 hours. The reaction slurry overflowing from the third-stage reactor was clarified and filtered, and sampled for analysis. The conversion rate of calcium carbonate in the reaction process reached 98.7%. The calcium chloride solution obtained by filtration was used as an absorption liquid for the mixed gas containing NH3 and CO2 produced by the material reaction, and multi-stage countercurrent absorption was performed. The slurry formed in the first-stage absorption liquid was filtered, washed, and dried while hot to obtain a calcium carbonate product with a purity of 99.8% that met the quality requirements of food additives specified in GB 1886.214-2016. The filtrate was cooled and crystallized to precipitate ammonium chloride, and the obtained ammonium chloride crystals were returned for recycling.

[0033] Comparative Example 1

[0034] Add 72g of ammonium chloride and 40g of light calcium carbonate powder into a three-necked flask containing 400mL of water, heat and stir until boiling, the solution temperature is 102.5℃, react at constant temperature and stir for 3h, cool and filter, take samples for analysis, the conversion rate of calcium carbonate is only 21.3%.

Claims

1. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride, characterized in that: The ammonium chloride raw material and the calcium carbonate raw material react in a calcium chloride solution with a calcium chloride concentration of ≥20wt.% at a temperature of 105-175°C to generate a calcium chloride slurry and a mixed gas containing NH3 and CO2.

2. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to claim 1, characterized in that: The ammonium chloride raw material and the calcium carbonate raw material are added according to the chemical reaction stoichiometric ratio.

3. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to claim 2, characterized in that: The ammonium chloride raw material includes at least one of ammonium chloride solid, ammonium chloride solution and ammonium chloride slurry.

4. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to claim 2, characterized in that: The calcium carbonate raw material comprises calcium carbonate powder with a particle size of less than 60 μm and / or calcium carbonate slurry with a particle size of less than 60 μm.

5. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to any one of claims 1 to 4, characterized in that: The ammonium chloride raw material and the calcium carbonate raw material are added in the following manners: adding them separately, preheating them separately and adding them, mixing them well and then adding them, or mixing them well and then preheating and then adding them.

6. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to claim 1, characterized in that: The reaction time is 1 to 3 hours.

7. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to any one of claims 1 to 4, characterized in that: The calcium chloride slurry is deammonified with lime and then separated into solid and liquid, and the liquid phase is directly used as a liquid calcium chloride product or further processed into a solid calcium chloride product; or, the calcium chloride slurry is diluted with water, cooled to precipitate ammonium chloride crystals, and solid-liquid separation is performed to obtain a calcium chloride solution and ammonium chloride solid, the ammonium chloride solid is recycled as a raw material, and the calcium chloride solution is used as a raw material for the production of other calcium-containing compounds.

8. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to claim 7, characterized in that: The other calcium-containing compounds include at least one of precipitated calcium carbonate, precipitated calcium sulfate, calcium carbonate whiskers, and calcium sulfate whiskers.

9. A method for preparing calcium chloride by decomposing calcium carbonate with ammonium chloride according to claim 1, characterized in that: The mixed gas containing NH3 and CO2 is directly used as an industrial production raw material, or is cooled and absorbed to produce ammonium carbonate or ammonium bicarbonate.