Chemical metallurgy material chloridizing roasting method

Abstract

The invention discloses a chemical metallurgy material chloridizing roasting method, and belongs to the technical field of chemical metallurgy. According to the method, ammonium chloride serves as a chloridizing roasting additive, a carbonaceous material serves as a microwave-assisted absorbent, the alkaline chemical metallurgical material, the chloridizing roasting additive and the microwave-assisted absorbent are evenly mixed and ground, then microwave heating is conducted, and chloridizing roasting of the alkaline chemical metallurgical material is completed. The method can effectively improve the chloridizing roasting efficiency of the alkaline chemical metallurgy material, improve the utilization rate of ammonium chloride and reduce the recovery cost of the alkaline chemical metallurgy material, has the advantages of being clean, environmentally friendly, economical, efficient and the like, and is suitable for large-scale industrial production of roasting of the chemical metallurgy material ammonium chloride.

Description

Technical Field

[0001] This invention relates to a chlorination roasting method, specifically a method for chlorination roasting of chemical and metallurgical materials, belonging to the field of chemical and metallurgical technology. Background Technology

[0002] Ammonium chloride is an inexpensive chlorinating agent used in the chlorination roasting of chemical and metallurgical materials. During the roasting process, ammonium chloride can convert oxides, hydroxides, and carbonates of alkali metals, alkaline earth metals, and rare earths into soluble chlorides, while SiO2, Al2O3, and Fe2O3 in the material do not react with ammonium chloride. Therefore, after roasting with ammonium chloride, the material can easily obtain a chloride solution with low Si, Al, and Fe content by water leaching. However, during the roasting process, ammonium chloride easily sublimates and escapes from the surface of the material after heating, leading to a reduction in the effective utilization of ammonium chloride. For example, when calcium carbonate is chlorinated and roasted with ammonium chloride, if calcium carbonate powder and ammonium chloride crystals are mixed according to the stoichiometric ratio of the roasting reaction and roasted at 450°C for 2 hours, the conversion rate of calcium carbonate is less than 25%. To ensure the conversion rate of calcium carbonate, the amount of ammonium chloride added during mixing must be 2 to 3 times in excess. During the roasting process, excess ammonium chloride sublimates upon heating and re-condenses in the flue gas pipeline, clogging the pipeline and causing the roasting equipment to malfunction.

[0003] In recent years, microwave heating has been widely used in metallurgical and chemical processes. However, most chemical and metallurgical materials cannot be heated by microwaves, such as quartz, ammonium chloride, calcium carbonate, magnesium carbonate, calcium oxide, and magnesium oxide. Therefore, existing ammonium chloride roasting processes for chemical and metallurgical materials almost always use external heat sources, which makes it difficult to effectively solve the technical problem of low ammonium chloride utilization in conventional chlorination roasting processes. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for chlorination roasting of chemical and metallurgical materials. This method can effectively improve the chlorination roasting efficiency of alkaline chemical and metallurgical materials, increase the utilization rate of ammonium chloride, and reduce the recycling cost of alkaline chemical and metallurgical materials.

[0005] To achieve the above-mentioned technical objectives, this invention provides a method for chlorination roasting of chemical and metallurgical materials. This method uses ammonium chloride as a chlorination roasting additive and carbonaceous materials as a microwave-assisted absorbent. First, the alkaline chemical and metallurgical materials are mixed and ground with the chlorination roasting additive and the microwave-assisted absorbent. Then, the mixture is heated by microwave to complete the chlorination roasting of the alkaline chemical and metallurgical materials. The alkaline chemical and metallurgical materials are at least one of oxides of M, hydroxides of M, carbonates of M, and basic carbonates of M. M is selected from at least one alkaline earth metal and rare earth element. The roasting conditions are: microwave heating until the surface temperature of the roasted material reaches 250~550℃, and holding at this temperature for 0.1~1 hours. The amount of ammonium chloride added is 0.9~1.1 times the theoretical molar amount of ammonium chloride required for all alkaline compounds in the alkaline chemical and metallurgical materials to be converted into chlorides.

[0006] This invention introduces carbonaceous materials as microwave-assisted absorbers into the roasted material, and then combines microwave heating with chlorination roasting. This enables the roasted material to be rapidly heated from the inside, causing ammonium chloride to decompose and release HCl gas. The HCl gas diffuses inside the high-temperature alkaline chemical and metallurgical material and is rapidly absorbed and converted into anhydrous chloride by alkaline compounds, thereby greatly improving the reaction efficiency of alkaline chemical and metallurgical materials and the effective utilization rate of ammonium chloride in the roasting process.

[0007] The key to the technical solution of this invention lies in introducing carbonaceous materials into the roasting material as microwave-assisted absorbents and combining them with microwave heating to achieve rapid and efficient chlorination roasting of alkaline chemical and metallurgical materials, while significantly improving the utilization rate of ammonium chloride. Microwave heating offers advantages such as speed and uniformity. However, it also exhibits selectivity. Most alkaline materials, including ammonium chloride, oxides, hydroxides, and carbonates of alkaline earth metals and rare earths, have weak microwave energy absorption capabilities and cannot be effectively heated by microwaves. This invention addresses this by introducing carbonaceous materials as microwave-assisted absorbers to achieve rapid heating and chlorination of the roasted material. Firstly, carbonaceous materials possess excellent microwave absorption capabilities, allowing them to rapidly heat up under microwave influence. For example, the heating rate of amorphous carbon via microwave heating is 700 times that of ammonium chloride. Secondly, carbonaceous materials exhibit good thermal conductivity, enabling rapid heat transfer to the roasted material, facilitating rapid heating and chlorination roasting. Thirdly, carbonaceous materials demonstrate good stability, exhibiting minimal chemical reaction with alkaline chemical and metallurgical materials and roasted materials like ammonium chloride during microwave heating. Furthermore, the carbonaceous microwave-assisted absorber is easily separated, recycled, and reused after roasting. Simultaneously, the introduction of carbonaceous materials into the roasting material during microwave heating fundamentally alters the traditional external heating process, achieving internal, non-contact heating. The carbonaceous materials are uniformly dispersed within the roasting material, and under the selective heating effect of microwaves, they act as an internal heater, rapidly raising the temperature. Since ammonium chloride begins to vaporize and absorb a large amount of heat above 100°C, the heating rate of the alkaline chemical metallurgical material is significantly higher than that of ammonium chloride, ensuring the orderly decomposition and release of HCl gas during roasting. By the time ammonium chloride vaporizes and produces a large amount of HCl gas, the temperature of the alkaline chemical metallurgical material has already reached the roasting temperature (above 250°C). Higher temperatures facilitate the absorption of HCl gas from the flue gas, converting it into anhydrous chloride. The rate at which the alkaline chemical metallurgical material absorbs HCl gas is much faster than the rate at which ammonium chloride decomposes and releases HCl gas, effectively preventing the sublimation and escape of ammonium chloride. In addition, since the roasted material is heated from the inside, the internal temperature of the roasted material is significantly higher than its surface temperature during the chlorination roasting process, which can effectively avoid accidents such as material sticking to the wall and forming in the kiln during the roasting process.

[0008] The alkaline chemical and metallurgical materials of this invention include, for example, calcium carbonate, magnesium carbonate, rare earth minerals, magnesium hydroxide, calcium hydroxide, etc.

[0009] As a preferred embodiment, the carbonaceous material is selected from at least one of graphite, carbon black, activated carbon, fly ash, and boiler flue ash. The most preferred carbonaceous material is one with an amorphous structure, as amorphous carbon has strong wave absorption capabilities, which is more conducive to the rapid heating of the calcined material, such as carbon black and boiler flue ash.

[0010] As a preferred embodiment, the amount of carbonaceous material added is 0.01% to 10% of the total mass of the alkaline chemical metallurgical material and the ammonium chloride. If the amount of carbonaceous material added is too low, the heating rate of the roasted material will be low; if the amount of carbonaceous material added is too high, the overall heating rate of the roasted material will be too fast, causing the ammonium chloride to decompose too quickly and escape. Therefore, the amount of carbonaceous material added is further 1% to 5% of the total mass of the alkaline chemical metallurgical material and the ammonium chloride.

[0011] Based on the method of "carbonaceous materials" combined with "microwave heating and roasting" adopted in this invention, the utilization rate of ammonium chloride can be greatly improved, so that the amount of ammonium chloride used can be close to the theoretical amount. Further preferred, the ammonium chloride is added at 1 times the theoretical molar amount of ammonium chloride required for all alkaline compounds in alkaline chemical and metallurgical materials to be converted into chlorides.

[0012] As a preferred embodiment, the grinding process controls the material particle size to meet -250 mesh. Grinding the material not only ensures uniform mixing of the roasted material and the carbonaceous material, but also refines the particle size of the roasted material, thereby improving roasting efficiency.

[0013] In the roasting process of the present invention, the surface temperature of the roasted material is preferably above 250°C, which can ensure the complete decomposition of ammonium chloride in the roasted material and improve the chlorination roasting efficiency.

[0014] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0015] This invention cleverly introduces carbonaceous materials as microwave-assisted absorbers into the ammonium chloride roasting process of alkaline chemical and metallurgical materials. Combined with microwave heating, this significantly increases the heating rate of the roasting material, promoting chlorination roasting. This allows even alkaline chemical and metallurgical materials with weak microwave absorption to undergo microwave-heated chlorination roasting. Furthermore, traditional heating is external, leading to the easy decomposition and escape of ammonium chloride. By introducing carbonaceous materials and using microwave heating, internal heating of the roasting material is achieved, enabling the alkaline chemical and metallurgical materials and ammonium chloride to undergo chlorination roasting at a lower temperature. The alkaline compounds in the material absorb HCl gas much faster than the rate at which ammonium chloride decomposes and releases HCl gas, thus effectively preventing the sublimation and escape of ammonium chloride during roasting and significantly improving the effective utilization rate of ammonium chloride.

[0016] The carbonaceous microwave-assisted absorber of the present invention has good chemical stability. It does not react chemically with the roasting material and ammonium chloride during the roasting process, and can be separated, recycled and reused after roasting. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are intended to illustrate the present invention and not to further limit the scope of protection of the claims of the present invention.

[0018] Example 1

[0019] Weigh out 50g of -500 mesh calcium carbonate powder and 53.5g of ammonium chloride crystals, and add 2.5g of activated carbon as a microwave-assisted absorbent. Mix well, grind finely, load into a feeding boat, and microwave heat for 8.5 minutes until the surface temperature of the material reaches 500℃. Then, calcine at 500℃ for 0.25 hours to obtain calcined slag. Almost no white smoke is visible during the calcination process. Cool the calcined slag to room temperature, dissolve it in water, filter to obtain filtrate and filter residue, and take samples for analysis. The effective utilization rate of ammonium chloride during the calcination process is 98.51%. The filter residue is washed, dried, and returned for continued use as a microwave-assisted absorbent.

[0020] Example 2

[0021] 1000g of -600 mesh dolomite powder was weighed. 1113.8g of ammonium chloride crystals were added, equal to one times the theoretical amount of ammonium chloride required for the complete conversion of calcium carbonate and magnesium carbonate into calcium chloride and magnesium chloride. Simultaneously, 50g of fly ash from a coal-fired boiler was added as a microwave-assisted absorbent. The mixture was thoroughly mixed and ground to a fine powder. Microwave heating was used to raise the surface temperature of the material to 450℃, and the mixture was roasted at this constant temperature for 0.75 hours to obtain roasted ore. The flue gas generated during roasting was condensed with dry ice to obtain ammonium bicarbonate crystals. The resulting roasted ore was cooled to room temperature, dissolved in water, and filtered to obtain filtrate and filter residue. The filter residue was washed, dried, and sampled for analysis. The effective utilization rate of ammonium chloride during the roasting process was calculated to be 97.62%. Magnesium is first precipitated by ammonia through the filtrate. After filtration, calcium chloride alkaline filtrate and Mg(OH)2 filter residue are obtained. Then, CO2 is passed into the calcium chloride alkaline filtrate to precipitate calcium. The calcium precipitation slurry is heated and filtered to obtain precipitated calcium carbonate filter residue and its post-precipitation liquid. The post-precipitation liquid is cooled and crystallized, and filtered to obtain ammonium chloride crystals and its crystallization mother liquor. The crystallization mother liquor is returned as a solution for calcining sand, and the ammonium chloride crystals are returned to the calcination process for recycling.

[0022] Example 3

[0023] Weigh 50g of mixed rare earth oxides with a REO content of 92.3% and 65g of ammonium chloride, add 1.5g of carbon black microwave-assisted absorbent, mix and grind finely, load into a material boat, and heat in a microwave oven until the surface temperature of the material reaches 400℃. Keep warm and roast for 1 hour to obtain calcined sand. Cool the calcined sand to room temperature, dissolve it in water, filter to obtain filtrate and filter residue, take samples for analysis, the effective utilization rate of ammonium chloride in the roasting process is 96.91%, and wash and dry the obtained filter residue, return it to be used as microwave-assisted absorbent in the roasting process.

[0024] Comparative Example 1

[0025] 50g of -500 mesh calcium carbonate powder and 53.5g of ammonium chloride crystals were weighed, mixed and ground finely, and then placed into a metal boat. The mixture was heated in a microwave oven. During the heating process, the temperature of the boat was significantly higher than that of the material (the boat's microwave absorption performance is much better than that of the material being roasted). This is equivalent to an external heating roasting process. After 95.6 minutes, the surface temperature of the material reached 500℃. The material was then roasted at 500℃ for 0.5 hours to obtain calcined slag. White smoke was emitted during the roasting process. The calcined slag was cooled to room temperature, dissolved in water, filtered, and the resulting filtrate and residue were analyzed. The effective utilization rate of ammonium chloride during the roasting process was 81.75%.

[0026] Comparative Example 2

[0027] Weigh out 50g of -500 mesh calcium carbonate powder and 53.5g of ammonium chloride crystals, add 2.5g of activated carbon, mix well and grind finely, load into a material boat, and place in a muffle furnace for heating and calcination. After 1 hour, the surface temperature of the material rises to 600℃, and a large amount of white smoke is emitted from the furnace during the calcination process. After calcination at 600℃ for 2 hours, calcined sand is obtained. The calcined sand is cooled to room temperature, dissolved in water, filtered, and the filtrate and residue are obtained. Samples are taken for analysis, and the effective utilization rate of ammonium chloride during the calcination process is 72.63%.

[0028] Comparative Example 3 Weigh out 50g of -500 mesh calcium carbonate powder and 53.5g of ammonium chloride crystals, and add 2.5g of activated carbon as a microwave-assisted absorbent. Mix and grind the mixture, load it into a material boat, and microwave it for 15 minutes. The surface temperature of the material rises to 650℃. After maintaining the temperature at 650℃ for 0.25 hours, the material almost completely melts into liquid, indicating that the chlorination roasting temperature is too high and cannot complete the normal chlorination roasting.

[0029] Examples 1-3 show that introducing carbonaceous materials as microwave-assisted absorbers into alkaline metallurgical materials such as calcium carbonate, dolomite, and rare earth oxides, combined with microwave heating, can effectively prevent the sublimation and escape of ammonium chloride during roasting, significantly improving the effective utilization rate of ammonium chloride to approximately 98%. Comparative Example 1 shows that without introducing carbonaceous materials into the alkaline metallurgical materials, heating primarily occurs from the outside, causing hydrogen chloride, a decomposition product of ammonium chloride, to escape before it can be absorbed, thus reducing the utilization rate of ammonium chloride. Comparative Example 2 shows that simply introducing carbonaceous materials into the alkaline metallurgical materials without microwave heating also results in a slow internal heating rate and a rapid external heating rate, leading to severe escape of hydrogen chloride, a decomposition product of ammonium chloride. Comparative Example 3 shows that if the chlorination roasting temperature is too high, normal chlorination roasting cannot be completed.

Claims

1. A method for chlorination roasting of chemical and metallurgical materials, characterized in that: Using ammonium chloride as a chlorination roasting additive and carbonaceous materials as microwave-assisted absorbents, alkaline chemical and metallurgical materials are first mixed and ground with the chlorination roasting additive and microwave-assisted absorbents, and then heated by microwaves to complete the chlorination roasting of alkaline chemical and metallurgical materials. The alkaline chemical and metallurgical material is at least one of the following: oxide of M, hydroxide of M, carbonate of M, and basic carbonate of M; wherein M is selected from at least one of alkaline earth metals and rare earth elements. The roasting conditions are as follows: microwave heating until the surface temperature of the roasted material reaches 250~550℃, and holding at that temperature for 0.1~1h; The amount of ammonium chloride added is 0.9 to 1.1 times the theoretical molar amount of ammonium chloride required for all alkaline compounds in alkaline chemical and metallurgical materials to be converted into chlorides.

2. The method for chlorination roasting of chemical and metallurgical materials according to claim 1, characterized in that: The carbonaceous material is selected from at least one of graphite, carbon black, activated carbon, fly ash, and boiler flue ash.

3. The method for chlorination roasting of chemical and metallurgical materials according to claim 1 or 2, characterized in that: The amount of carbonaceous material added is 0.01% to 10% of the total mass of the alkaline chemical and metallurgical material and the ammonium chloride.

4. The method for chlorination roasting of chemical and metallurgical materials according to claim 1, characterized in that: The grinding process is performed to control the material particle size to meet -250 mesh.