Vacuum carbothermal reduction Principle of aluminum chloride

Abstract: The aluminum is bauxite in the form of aluminum oxide, obtained by direct reduction of metal aluminum and other impurities can not be separated without reducing agent can restore it directly out. This paper studies the carbon heat under vacuum conditions restore the low chloride directly decomposition of aluminum from bauxite principle, provide a reference for related engineering practice.

Keywords:: aluminum vacuum technology, carbon thermal reduction method
Introduction
Aluminum is a light metal, is rich in nature reserves. The density of steel is 1 / 3, has a large strength / weight ratio and good electrical conductivity, thermal conductivity, a layer of aluminum oxide film on the surface is not protected rust, while the high recycling rate of aluminum, so aluminum is widely used in automobile manufacturing industry, construction industry and the aerospace industry is an important economic and strategic metals. Therefore, some countries lack of resources are bauxite Research use of these raw materials to produce alumina method, in which the most studied is the acid, chemical and high pressure water limestone sintering. alunite, but an integrated approach has been used in many ways, only to restore industrial production roasting method, in addition to sintered Comprehensive treatment nepheline has been large-scale industrial production. Based on the analysis of several common methods of this study based on the carbon-thermal reduction of the vacuum principle of aluminum chloride.

A common method of aluminum smelting
1.1 acid
Common feature of non-bauxite raw material is high in silica, acid treatment of these materials is reasonable in principle. Depending on the different types of inorganic acid, acid alumina production a variety of different options, but They have common features, similar production process, including the ore pretreatment (roasting and grinding), with the acid in (alumina into aluminum salts soluble inorganic acid), leaching liquid iron, aluminum salts decomposition and calcination of aluminum hydroxide and the acid recycling. many countries with high silicon aluminum-containing raw materials, including hydrochloric acid, sulfuric acid, nitric acid processes, and other Research. It was also used for some countries to deal with different kinds of raw materials by acid raw materials and energy consumption when the unit cost of the product and investments were estimated, and the future industrial application of acid to make an optimistic estimate. but the acid is still in the experimental stage, to be improved and perfected.

1.2 The high-pressure water chemical
This method is the fifties of last century scholars invented the former Soviet Union, it is a wet process using aluminum-containing raw materials to produce high silica alumina new method, namely, the high concentration of lime or alkali treatment, and then by evaporation and crystallization get products. of this method and process of physical chemistry Island line has been a long, extensive Research has made significant progress.

High-pressure water compared to chemical and sintering method has many advantages: to avoid the high investment, high energy consumption sintering process, stripping in the right conditions, availability of high dissolution rate of Al2O3 and Na2O, do not consume high quality coal for the environment protection. According to semi-industrial test results of the technical and economic comparison showed that: power consumption, investment and product cost than with a significant reduction sintering. But there are still many shortcomings of this approach, still need to study and improvement.

1.3 Reduction Roasting
This method is the integrated treatment of alunite industry the only way. Alum stone by dehydration and reduction of SO3 prolapse after roasting, and then deal with Bayer, the product of alumina, potassium sulfate and sulfuric acid.

As part of the vast majority of high alumina bauxite, a high silicon insoluble diaspore type, Al-Si characteristics than the medium-low and can not economically using conventional Bayer alumina production abroad, and most only by soda lime and hybrid sintering alumina production technology, production methods and the two foreign conventional treatment of high grade bauxite Bayer comparison, there is the following disadvantages: the high overall energy consumption per unit of product, long process, construction of large investment. For large and medium-sized alumina plant construction project, the hybrid method of construction per unit of product is much higher than the conventional Bayer process, with the gradual decline in quality of bauxite and energy prices continue to rise, existing law works a mixed technical and economic indicators will gradually deteriorate, manufacturing costs will be increased accordingly. of mixed alumina plant in recent years are associated with a large number of high-grade mining people, leading to abandoned mining the rich and poor, and serious waste of resources. With the continuous development of production, high-grade ore will soon run out, is expected to maintain only a few years time. the use of a low grade ore will now significant decline in aluminum production capacity, rising costs, economic deterioration. The disadvantages our country less competitive in the international aluminum industry and thus its survival and development challenges. and with the rising energy prices and declining grade bauxite, the challenge will become increasingly serious. Links to Research Papers Download http://www.hi138.com 2 vacuum carbothermal chlorination aluminum principle
With low-cost aluminum compounds in high temperature stability, low temperature decomposition of aluminum and aluminum compounds, the characteristics of trivalent, bauxite and coke in the reaction system leads to aluminum chloride gas, then bauxite, coke , and the reaction of aluminum chloride, aluminum chloride to get a (AlCl), aluminum chloride by a reaction system in the lower part of the decomposition temperature of aluminum and aluminum chloride, aluminum chloride can be recycled through collection use, that is the reaction of aluminum chloride system, only three played in the bauxite alumina media direct role in carbon reduction, but because its presence significantly decreased the reduction temperature, and can be relatively pure aluminum metal , so that production from bauxite aluminum direct carbon reduction process as possible. As this principle in the formation of low-cost high temperature reaction of aluminum chloride is a gas volume increased response, so you can choose under vacuum, so easily make the step response. also choose aluminum in a vacuum under study, some of the main reasons there are the following:
(1 of the Act is the first step in the mechanism of aluminum to increase the gas volume of the reaction (Al2O3 + AlC13 gas +3 C ... ... 3AlCl gas +3 CO gas), the volume of gas from 1 to 6 volume changes, thus reducing the pressure of reaction system (under vacuum) will greatly benefit the reaction, the low-cost aluminum compounds are decomposed by carbothermal reduction reaction of bauxite into alumina or two steps, the first step for the high temperature alumina and aluminum compounds of carbon and high-aluminum reaction cheap compounds, the second step is the resulting low-cost aluminum compounds at low temperature decomposition of the metal aluminum.

(2 because it is under vacuum, and the whole process of emissions generated by the direction of control is easy, so will be easy to control pollution, and ultimately can become a low-pollution process,
(3 As the response system is constantly under the conditions of vacuum, so the system is very large gas flow rate, a decomposition of liquid aluminum chloride, aluminum present in the system can be quickly and the gas (carbon monoxide, chloride Al) separately, to avoid aluminum react with these gases, causing the loss and purity aluminum reduction.

(4 by carbothermal chlorination of aluminum required for the calculation of theoretical power consumption may know, carbon thermal reduction method aluminum chloride aluminum other than the current methods have a greater power advantage.

(5 other ingredients such as bauxite iron oxide, Chin, silica, etc., as the reaction gas generated does not occur, it can only remain in the slag, and in the vacuum so that the reaction temperature can be under more pressure state is low, and the direction of flow of gas must AlCl, AlCl so easy to control the condensation point of decomposition, in order to achieve the metal from bauxite aluminum step possible, and because the other components remain in the slag, so get there are aluminum high purity.

Conclusion
With the gradual decline in quality of bauxite and energy prices continue to rise, a corresponding increase in manufacturing costs, while high-grade ore will soon run out, the use of a low grade ore will now significant decline in aluminum production capacity , higher costs and economic benefits to deteriorate. mentioned in this article ways to change the traditional aluminum aluminum production process, is a great reform, it is useful to the law of value and application prospect of the development . Links http://www.hi138.com Research Papers Download