Calcium Metal Production Methods

Thermite production of Calcium metal (metallic calcium) and the electrolytic method of producing metallic calcium each have their own advantages. The thermite method of producing metallic calcium not only has a short process flow, low energy consumption, high product quality, and environmentally friendly conditions, but is superior to the electrolytic method and is worthy of development. craftsmanship.

calcium metal block pure calcium metal metallic calcium 98.5
calcium metal powder
pure calcium metal granule
calcium metal cored wire

Theoretical basis for producing calcium metal by thermite method

The reduction of calcium oxide with aluminum can be carried out according to the following three reactions under high temperature and high vacuum conditions:

6CaO+2Al=3CaO·Al2O3+3Ca(1)

4CaO+2Al=CaO·Al2O3+3Ca(2)

33CaO+14Al=12CaO·7Al2O3+21Ca(3)

Reduction is carried out under high temperature and high vacuum conditions. Which reaction is used to control production depends on the formation temperature and formation speed of the reaction product under the same vacuum conditions, the stability of the reaction product, and the release of calcium vapor from the reactant. Diffusion speed.

Characteristics of reducing calcined limestone (i.e. lime) with aluminum under vacuum conditions:

1. The reaction between reduced lime and the solid powder agglomerates of reducing agent is carried out between solid-solid and solid-gas phases. The diffusion rate of substances between the two phases will directly affect the reaction speed;

2. The reduction reaction is an endothermic reaction, so the heat transfer of the agglomerate and the heat conduction process of the agglomerate reaction layer, that is, the heat transfer rate, have a greater impact on the overall reaction rate;

3. During the reduction reaction, only calcium vapor diffuses outward;

4. The reduction rate of the outer part of the agglomerate is higher than that of the inner layer of the agglomerate. Therefore, it can be considered that the reduction reaction gradually advances from the surface of the agglomerate inward, so the reaction belongs to a shrinking nucleation reaction process. The reason why the reaction proceeds at the interface is that the speed of calcium vapor diffusing outward from the inside of the agglomerate and the speed of heat transfer from the outside to the inside of the agglomerate are mutually restricted. Based on this principle, the production of metallic calcium by the aluminothermic method is based on the relationship between the heat transfer and heat supply rate of the two-phase material (i.e., the dynamic balance of energy). It is also based on the relationship between the speed of calcium produced by the reaction and the calcium transported by diffusion. In terms of the relationship between speed (that is, the dynamic balance of mass), when the dynamic balance of energy and mass in the reaction zone is solved, the reduction process of reducing CaO with aluminum will have the greatest reduction efficiency.

Control of raw material quality and production conditions

In order to improve reduction efficiency, product quality and labor productivity, the raw materials and production conditions used when producing calcium by the thermite method must meet the following requirements:

1. Chemical composition of raw materials:

① Limestone: CaCO3>98%, R2O3+SiO2<2.0%, Na2O+K2O<0.01%, burning rate 43~44%; Limestone mineral structure: crystalline, fine-grained rock ore, no cleavage plane, resistant Grinding index R1<10%, gray ratio<1.5%;

②Mineralizing agent: using metal fluoride, MeFx>98%, R2O3+SiO2<2%;

③Aluminum powder: Al>99%

2. Process conditions:

① Limestone calcining: Calcining temperature 1150~1200℃, limestone block size: 15~40mm in rotary kiln, 100~250mm in vertical kiln.

②Charge fineness: lime: -0.074mm, aluminum powder: -0.83mm, mineralizer: -0.074mm.

③Pellet pressure: Domestic LYQ double-roller pellet machine, working pressure 140~180Kg-f/cm3.

④Vacuum reduction: reduction temperature: 1180~1250℃, vacuum degree: 3~7Pa, reduction time 12~14h.

3. Reasonable ingredients

In order to reduce the consumption of raw materials, save energy and improve reduction efficiency, the reduced charge must be properly proportioned.

According to the above three reduction reactions, the ingredients formula is:

Taking 100kg of lime as the calculation basis, the lime contains CaO%, the aluminum powder contains Al%, the mineralizing agent contains MeFx%, the Al ratio = M, the amount of mineralizing agent is: 1% of the amount of 100Kg of lime. ~1.5% added.

Calculated according to reaction (1) 6Ca+2Al=3Ca·Al2O3+3Ca:

Theoretical amount of aluminum: =16.0714, Kg

Actual amount of aluminum added: =16.0714×M, Kg

The amount of mineralizer added: =, Kg

In the formula, the aluminum ratio (M) is adjusted according to the market prices of calcium and aluminum.

Calculated according to reaction (2) 4Cao+2Al=Ca·Al2O3+3Ca:

Theoretical amount of aluminum: =24.017, Kg

Actual amount of aluminum added: =24.017×M, Kg

The amount of mineralizer added: =, Kg

Calculated according to reaction (3) 33Cao+14Al=12Ca·7Al2O3+21Ca:

Theoretical amount of aluminum:=20.455, Kg

Actual amount of aluminum added: 20.455×M, Kg

The amount of mineralizer added: =, Kg

The amount of lime, the amount of aluminum and the amount of mineralization (Kg) calculated in the above calculation formula are then converted into percentages, which is the batching ratio of the charge for producing metallic calcium by the thermite method. This batching ratio is based on the chemical composition of the charge and The value calculated from the most reasonable aluminum ratio should be said to be the best and most economical ratio for the furnace charge. Under the best reduction conditions, higher reduction efficiency can be obtained.

4. Improve equipment levels, develop large-scale production lines, increase output, improve quality, and improve labor productivity

For the production of metallic calcium by thermite method, large-scale equipment that is energy-saving, environmentally friendly, highly mechanized, and equipped with automatic detection must be used to increase production, increase labor productivity, and continuously and stably ensure the quality of metallic calcium.

1. Calcination of limestone:

A Ф2.8/Ф3.2×55~60M rotary kiln is used, using gas, coke oven gas or natural gas as the heat source. The lime at the kiln head and the tail gas at the kiln tail are equipped with waste heat utilization devices (waste heat boiler or heat exchanger to preheat limestone). The kiln end is automatically fed with materials, the kiln head lime is automatically put into the warehouse, and the kiln head and kiln end temperature, pressure, and gas flow are automatically recorded.

2. Charge batching and ball pressing

The three kinds of raw materials (lime, aluminum powder, mineralizer) are put into the warehouse respectively. They are batched by microcomputer, finely ground and mixed, put into the warehouse, and then sent to the briquetting machine to form balls.

3. Vacuum thermal reduction of pellets

Using a single-sided, double-row reduction furnace with 48 to 50 tanks, and applying regenerative combustion technology to the calcium reduction furnace can enable the large-scale development of the reduction furnace and greatly reduce the energy consumption of the aluminothermic method for calcium production. The reduction furnace using regenerative combustion technology improves the air flow in the furnace. The burners can be evenly arranged across the entire furnace width, so that the flame fills the furnace, thereby enlarging the furnace size and lengthening it while ensuring uniform heating. The reduction tank increases the calcium production in a single tank, thereby increasing the total calcium production, improving labor productivity, and improving the quality of the crude calcium produced during condensation. The purity of crude calcium can reach about 98%, and the impurities Al, Mn, and Mg are The content is low.

Conclusion

The production of metallic calcium by the thermite method is an emerging industry. The production cost, labor conditions, environmental protection, and investment of calcium metal produced by the thermite method are all superior to those of the electrolytic method. Therefore, the production of metallic calcium by the thermite method can achieve greater economic benefits. benefit. However, the use of thermite method to produce calcium still causes serious energy waste and environmental pollution in the smelting industry. Since the country is gradually increasing its efforts in reducing energy consumption and emissions, thermite smelting must be technically changed.

The backward situation of the calcium industry. Follow the theoretical basis of the aluminothermic calcium smelting method, pay attention to the quality of raw materials, select the most economical and reasonable aluminum ratio according to the market price ratio of aluminum to calcium, and strictly control the production process according to the composition of the raw materials and reasonable ingredients.

The purpose of energy saving, production increase and emission reduction can be achieved by improving the technical conditions, improving equipment level, developing large-scale production lines, especially applying regenerative combustion technology to reduction furnaces. In order to develop the calcium industry, it is imperative to further change the backward situation of the aluminothermic calcium smelting industry.

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