阅读说明：本技术 一种利用铝电解槽废旧阴极制备铝电解用炭素阴极的方法 (Method for preparing carbon cathode for aluminum electrolysis by using waste cathode of aluminum electrolysis cell ) 是由 赖延清 杨凯 田忠良 肖劲 龚培育 仲奇凡 于 2019-12-05 设计创作，主要内容包括：本发明公开了一种利用铝电解槽废旧阴极制备铝电解用炭素阴极的方法,以铝电解废旧阴极炭块和冶金焦为骨料,采用一次破碎、两次成型、二次浸渍、三次焙烧的方法,充分利用废阴极炭材料结构特点,根据骨料特征合理匹配阴极炭块制备工艺,通过制备工艺与材料之间的相互补充,同时实现了对废阴极炭块、冶金焦杂质的脱除和铝电解槽阴极炭块的制备。本发明通过利用废旧阴极制备铝电解用炭素阴极的过程,实现废旧阴极中杂质的脱除,成功避免现有工艺带来的环境污染,成倍提升废旧阴极的使用量和使用效率,实现制备高效、无污染铝电解用炭素阴极的目标。(The invention discloses a method for preparing a carbon cathode for aluminum electrolysis by using waste cathodes of aluminum electrolysis cells, which takes waste cathode carbon blocks and metallurgical coke for aluminum electrolysis as aggregates, adopts the methods of primary crushing, secondary forming, secondary dipping and tertiary roasting, fully utilizes the structural characteristics of the waste cathode carbon materials, reasonably matches the preparation process of the cathode carbon blocks according to the characteristics of the aggregates, and simultaneously realizes the removal of impurities of the waste cathode carbon blocks and the metallurgical coke and the preparation of the cathode carbon blocks of the aluminum electrolysis cells by the mutual supplement between the preparation process and the materials. According to the invention, through the process of preparing the carbon cathode for aluminum electrolysis by using the waste cathode, the removal of impurities in the waste cathode is realized, the environmental pollution caused by the existing process is successfully avoided, the use amount and the use efficiency of the waste cathode are improved by times, and the aim of preparing the carbon cathode for aluminum electrolysis with high efficiency and no pollution is realized.)

1. A method for preparing a carbon cathode for aluminum electrolysis by using a waste cathode of an aluminum electrolysis cell is characterized by comprising the following steps:

(1) the method comprises the following steps of mixing waste cathode carbon blocks, metallurgical coke, asphalt and an organic carbon source in a mass ratio of 50-85: 0 to 7: 8-18: 0-10, mixing and blending to obtain a mixture; the particle size of the mixture except the organic carbon source is divided into four grades of more than 20mm, 5-20 mm, 0.074 mm-5 mm and less than 0.074mm, and the mass ratio of each grade is 10-25: 10-30: 5-20: 15-35;

(2) kneading the mixture obtained in the step (1) at 120-250 ℃ for 40-150 min, and then forming to obtain a carbon block raw material;

(3) roasting the carbon block raw material obtained in the step (2) for one time in a non-oxidizing atmosphere to obtain a roasted carbon block for one time, wherein the roasting temperature for one time is 1200-1600 ℃, and the roasting time is 300-900 min;

(4) crushing the primary roasted carbon block in the step (3), controlling the crushing granularity to be more than 20mm and accounting for 65-80%, adding asphalt accounting for 5-10% of the mass ratio of the primary roasted carbon block and 2-8% of organic carbon source, performing secondary kneading at 120-250 ℃ for 60-180 min, and then performing secondary molding;

(5) and (3) performing primary dipping treatment on the carbon block subjected to secondary kneading and secondary molding in the step (4) to obtain a primary dipped carbon block, wherein in the primary dipping process, dipping liquid is asphalt and an organic carbon source, and the mass ratio of the dipping liquid to the organic carbon source is 50-80: 15-30 ℃, wherein the primary dipping temperature is 120-250 ℃, and the time is 150-360 min;

(6) carrying out secondary roasting on the primary impregnated carbon block in the step (5) in a non-oxidizing atmosphere to obtain a secondary roasted carbon block, wherein the secondary roasting temperature is 1000-1400 ℃, and the time is 700-1200 min;

(7) and (3) carrying out secondary impregnation treatment on the secondary roasted carbon block obtained in the step (6) to obtain a secondary impregnated carbon block, wherein in the secondary impregnation process, impregnation liquid is asphalt and an organic carbon source, and the mass ratio of the impregnation liquid to the organic carbon source is 50-80: 15-30 ℃, wherein the secondary impregnation temperature is 120-250 ℃, and the time is 150-360 min;

(8) and (3) roasting the secondary impregnated carbon block obtained in the step (7) for three times in a non-oxidizing atmosphere to obtain a carbon cathode, wherein the temperature of the roasting for three times is 1000-3000 ℃, and the time is 500-1000 min.

2. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (1), the mass ratio of the waste cathode carbon blocks, the metallurgical coke, the asphalt and the organic carbon source is 55-80: 0-5: 5-15: 0 to 7; the organic carbon source is selected from at least one of polyhydric alcohols with the carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose.

3. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (2), the kneading temperature is 140-210 ℃, and the kneading time is 60-120 min; the forming mode is extrusion forming.

4. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (3), the primary roasting temperature is 1300-1500 ℃, and the time is 450-750 min.

5. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (4), the crushing granularity is controlled to be more than 20mm and accounts for 70-80%, and then asphalt accounting for 6-8% of the mass ratio of the primary roasted carbon block and an organic carbon source accounting for 3-6% of the mass ratio of the primary roasted carbon block are added for secondary kneading and molding; the organic carbon source is selected from at least one of polyhydric alcohols with the carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose; the secondary kneading temperature is 140-210 ℃, and the time is 100-160 min; the secondary forming mode is extrusion forming.

6. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (5), in the primary impregnation process, the impregnation liquid is pitch and an organic carbon source, and the mass ratio of the pitch to the organic carbon source is 55-75: 20-30 ℃, the primary impregnation temperature is 140-210 ℃, the time is 180-320 min, and the organic carbon source is selected from at least one of polyhydric alcohols with carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose.

7. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (6), the secondary roasting temperature is 1100-1300 ℃ and the time is 800-1100 min.

8. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (7), in the secondary impregnation process, the impregnation liquid is pitch and an organic carbon source, and the mass ratio of the impregnation liquid to the organic carbon source is 55-75: 20-30 ℃, the secondary impregnation temperature is 140-210 ℃, the time is 180-320 min, and the organic carbon source is selected from at least one of polyhydric alcohols with carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose.

9. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (8), the tertiary roasting temperature is 1800-2400 ℃, and a semi-graphitized carbon cathode is obtained, wherein the ash content of the semi-graphitized carbon cathode is less than 1.0%; or the tertiary roasting temperature is 2400-3000 ℃, and the graphitized carbon cathode is obtained, wherein the ash content of the graphitized carbon cathode is less than 0.5%.

10. The method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of the aluminum electrolysis cell according to claim 1, which is characterized in that: in the step (3), the step (6) and the step (8), the non-oxidizing atmosphere is an inert atmosphere or a reducing atmosphere.

Technical Field

The invention belongs to the field of carbon waste recovery, and particularly relates to a method for preparing a carbon cathode for aluminum electrolysis by using a waste cathode of an aluminum electrolysis cell.

Background

In the production process of electrolytic aluminum, a large amount of waste carbon materials are generated, wherein due to the corrosion of electrolyte, about 10kg of waste cathode carbon blocks are generated when 1 ton of electrolytic aluminum is produced, and the waste cathode carbon blocks become main solid pollutants in the aluminum electrolysis industry. Taking 2018 as an example, the electrolytic aluminum yield in China already reaches 3648 ten thousand tons, more than 35 ten thousand tons of waste cathode carbon blocks are produced, and the quantity of the waste cathode carbon blocks is huge and cannot be ignored.

In the waste cathode carbon blocks, the main components are carbon, cryolite, sodium fluoride, alumina, aluminum fluoride, and a small amount of aluminum carbide, sodium carbide and cyanide. But the carbon in the waste cathode carbon blocks accounts for 50-70 percent and is highly graphitized, and the rest of the electrolyte taking fluoride as a main body is available resource, so that the waste cathode carbon blocks have better economic benefit and development prospect for separation and recovery.

The existing method for producing the carbon cathode for aluminum electrolysis by using the waste cathode is based on wet purification of the waste cathode, the process is long, and a large amount of wastewater is generated in the purification process. Meanwhile, the effect of removing impurities in the waste cathode carbon blocks is limited, the waste cathode carbon blocks are only used as additives in the production of carbon cathodes for aluminum electrolysis, and the use efficiency of the waste cathode carbon blocks is reduced.

Disclosure of Invention

In order to solve the problems of long flow, large pollution and low use efficiency in the process of producing the carbon cathode for aluminum electrolysis by using the waste cathode, the invention provides a method for preparing the carbon cathode for aluminum electrolysis by using the waste cathode of an aluminum electrolysis cell, and the aim of preparing the carbon cathode for aluminum electrolysis with high efficiency and no pollution is fulfilled under the condition of purifying the waste cathode.

In order to achieve the technical purpose, the invention adopts the following technical scheme:

a method for preparing a carbon cathode for aluminum electrolysis by using a waste cathode of an aluminum electrolysis cell comprises the following steps:

(1) the method comprises the following steps of mixing waste cathode carbon blocks, metallurgical coke, asphalt and an organic carbon source in a mass ratio of 50-85: 0 to 7: 8-18: 0-10, mixing and blending to obtain a mixture; the particle size of the mixture except the organic carbon source is divided into four grades of more than 20mm, 5-20 mm, 0.074 mm-5 mm and less than 0.074mm, and the mass ratio of each grade is 10-25: 10-30: 5-20: 15-35;

(2) kneading the mixture obtained in the step (1) at 120-250 ℃ for 40-150 min, and then forming to obtain a carbon block raw material;

(3) roasting the carbon block raw material obtained in the step (2) for one time in a non-oxidizing atmosphere to obtain a roasted carbon block for one time, wherein the roasting temperature for one time is 1200-1600 ℃, and the roasting time is 300-900 min;

(4) crushing the primary roasted carbon block in the step (3), controlling the crushing granularity to be more than 20mm and accounting for 65-80%, adding asphalt accounting for 5-10% of the mass ratio of the primary roasted carbon block and 2-8% of organic carbon source, performing secondary kneading at 120-250 ℃ for 60-180 min, and then performing secondary molding;

(5) and (3) performing primary dipping treatment on the carbon block subjected to secondary kneading and secondary molding in the step (4) to obtain a primary dipped carbon block, wherein in the primary dipping process, dipping liquid is asphalt and an organic carbon source, and the mass ratio of the dipping liquid to the organic carbon source is 50-80: 15-30 ℃, wherein the primary dipping temperature is 120-250 ℃, and the time is 150-360 min;

(6) carrying out secondary roasting on the primary impregnated carbon block in the step (5) in a non-oxidizing atmosphere to obtain a secondary roasted carbon block, wherein the secondary roasting temperature is 1000-1400 ℃, and the time is 700-1200 min;

(7) and (3) carrying out secondary impregnation treatment on the secondary roasted carbon block obtained in the step (6) to obtain a secondary impregnated carbon block, wherein in the secondary impregnation process, impregnation liquid is asphalt and an organic carbon source, and the mass ratio of the impregnation liquid to the organic carbon source is 50-80: 15-30 ℃, wherein the secondary impregnation temperature is 120-250 ℃, and the time is 150-360 min;

(8) and (3) roasting the secondary impregnated carbon block obtained in the step (7) for three times in a non-oxidizing atmosphere to obtain a carbon cathode, wherein the temperature of the roasting for three times is 1000-3000 ℃, and the time is 500-1000 min.

As a preferred scheme, in the step (1), the mass ratio of the waste cathode carbon blocks, the metallurgical coke, the asphalt and the organic carbon source is 55-80: 0-5: 5-15: 0 to 7; the organic carbon source is selected from at least one of polyhydric alcohols with the carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose.

According to the invention, by controlling the mass ratio of the raw materials, the tightness degree of the raw materials of the waste cathode in the re-kneading and molding process can be ensured, and the strength and the true density of the molded carbon block are greatly improved; meanwhile, the organic carbon source is used for filling fine pore passages in the waste cathode which cannot be reached by the asphalt, so that the defect that the internal defect of the formed carbon block is rich when the waste cathode is used as aggregate and single asphalt is used as a binder is overcome. The particle sizes of other carbon materials except the organic carbon source are mainly controlled so that the waste cathode and other materials used as aggregates can be uniformly distributed in the formed cathode, and the overall strength of the cathode is improved; the granularity of the carbon material used as the binder is controlled in order to realize a good contact effect between the carbon material and the aggregates, so that the effect of the binder on the interaction of the aggregates can be better exerted in the roasting process, the generation of large pore paths and cracks is effectively reduced, and the quality of the cathode is improved.

Preferably, in the step (2), the kneading temperature is 140-210 ℃, and the kneading time is 60-120 min; the forming mode is extrusion forming.

Preferably, in the step (3), the primary roasting temperature is 1300-1500 ℃, and the time is 450-750 min.

As a preferable scheme, in the step (4), the crushing granularity is controlled to be more than 20mm and accounts for 70-80%, and then asphalt accounting for 6-8% of the mass ratio of the primary roasted carbon block and an organic carbon source accounting for 3-6% of the mass ratio of the primary roasted carbon block are added for secondary kneading and molding; the organic carbon source is selected from at least one of polyhydric alcohols with the carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose; the secondary kneading temperature is 140-210 ℃, and the time is 100-160 min; the secondary forming mode is extrusion forming.

Preferably, in the step (5), in a primary impregnation process, the impregnation liquid is pitch and an organic carbon source, and the mass ratio of the pitch to the organic carbon source is 55-75: 20-30 ℃, the primary impregnation temperature is 140-210 ℃, the time is 180-320 min, and the organic carbon source is selected from at least one of polyhydric alcohols with carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose.

The crushing after the primary baking and sintering can expose a large number of internal holes generated by volatilization of impurities in the waste cathode, and eliminate the structural influence on the formed cathode in the impurity removal process, such as internal cracks; furthermore, through secondary kneading, the exposed cathode defects such as holes, cracks and the like can be effectively repaired and reshaped, and the influence of internal defects on the cathode quality in the subsequent processing process is eliminated; on the basis, the impregnation is carried out again, and by utilizing the characteristics of low viscosity, good fluidity and certain coking rate of the impregnation liquid, impurities can be effectively infiltrated and blocked and removed, and macropores and fine cracks generated in the kneading process can be effectively formed, so that the compactness of the cathode finished product is increased, and the performance of the cathode is improved.

Preferably, in the step (6), the secondary roasting temperature is 1100-1300 ℃ and the time is 800-1100 min.

Preferably, in the step (7), in the secondary impregnation process, the impregnation liquid is pitch and an organic carbon source, and the mass ratio of the pitch to the organic carbon source is 55-75: 20-30 ℃, the secondary impregnation temperature is 140-210 ℃, the time is 180-320 min, and the organic carbon source is selected from at least one of polyhydric alcohols with carbon number less than 7, citric acid, carboxymethyl cellulose, resorcinol, hydroquinone and glucose. The invention carries out secondary impregnation after secondary roasting, and can effectively permeate and block the small holes and micropores generated after volatilization of volatile components in the secondary roasting process by utilizing the characteristics of low viscosity, good fluidity and certain coking rate of the impregnation liquid, thereby reducing the open pores of the cathode, increasing the compactness of the finished cathode product and improving the performance of the cathode.

As a preferred scheme, in the step (8), the tertiary roasting temperature is 1800-2400 ℃, so that a semi-graphitized carbon cathode is obtained, wherein the ash content of the semi-graphitized carbon cathode is less than 1.0%; or the tertiary roasting temperature is 2400-3000 ℃, and the graphitized carbon cathode is obtained, wherein the ash content of the graphitized carbon cathode is less than 0.5%.

The three-time roasting process preferably adopts a high-temperature roasting process at the temperature higher than 1800 ℃ so as to completely remove residual impurities in the waste cathode and reduce the influence of inert impurities on the conductivity of the cathode carbon block; meanwhile, the graphitization degree of the carbonaceous material in the waste cathode is improved. Compared with a carbon material with low graphitization degree, the semi-graphitized and graphitized carbon cathode has obviously improved electron transfer capability; and in the application process, the material has less defects, so that the material has better resistance to scouring and penetration of molten electrolyte and metal liquid.

Preferably, in the step (3), the step (6) and the step (8), the non-oxidizing atmosphere is an inert atmosphere, such as argon, nitrogen, or the like; or a reducing atmosphere such as carbon monoxide, hydrogen, and the like.

The method takes the aluminum electrolysis waste cathode carbon blocks and metallurgical coke as aggregates, adopts the methods of primary crushing, secondary forming, secondary dipping and tertiary roasting, and simultaneously realizes the removal of impurities of the waste cathode carbon blocks and the metallurgical coke and the preparation of the cathode of the aluminum electrolysis cell. The aluminum electrolysis waste cathode carbon block is used as a main body, and the characteristic of high graphitization degree is favorable for reducing the resistivity and sodium permeability of the obtained carbon block; the crushing process is mainly used for effectively eliminating internal defects generated in the impurity removal process through the second kneading molding and dipping process, so that the quality of a cathode product is improved; the impregnation liquid consists of asphalt and an organic carbon source, so that the problem that fine pore passages and cracks generated by impurity removal when the waste cathode is used as aggregate are difficult to solve by using single asphalt is effectively solved, and the improvement of the true density and the strength of the cathode is facilitated; the roasting conditions are reasonably controlled in the roasting process, so that the internal defects of the formed carbon blocks are effectively reduced while impurities in the aggregates are removed. In conclusion, the invention makes full use of the structural characteristics of the waste cathode carbon material, reasonably matches the preparation process of the cathode carbon block according to the aggregate characteristics, and realizes the preparation of the high-performance cathode carbon block through the mutual supplement between the preparation process and the material.

The invention has the following beneficial effects:

(1) according to the invention, in the process of preparing the carbon cathode for aluminum electrolysis by using the waste cathode, the impurities in the waste cathode are removed, the flow of the original process is effectively shortened, the pollution problem caused by a wet process is reduced, and the aim of efficiently preparing the carbon cathode for aluminum electrolysis without pollution is fulfilled.

(2) The method utilizes the pyrogenic process to treat the waste cathode, realizes effective removal of impurities compared with a wet process, increases the proportion of the waste cathode in raw materials, avoids the influence of the impurities on the performance of the carbon cathode for aluminum electrolysis, and effectively improves the use amount and the use efficiency of the waste cathode.

(3) The invention adopts a two-stage roasting method to realize the removal of impurities in the waste cathode of the aluminum electrolysis cell while ensuring the production of the carbon cathode for aluminum electrolysis; on the basis, the problems of high porosity, low volume density, low strength and the like of the carbon cathode for aluminum electrolysis brought in the impurity removal process are solved by adopting a secondary crushing and kneading method, and the quality of the cathode is improved.

Detailed Description

The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.