Graphitization Cathode Technology and Market Development Trends [SMM Aluminum Industry Conference]

On April 16, at the AICE 2025 SMM (20th) Aluminum Industry Conference and Aluminum Industry Expo—Alumina and Aluminum Raw Materials Forum, hosted by SMM Information & Technology Co., Ltd., SMM Metal Trading Center, and Shandong Aisi Information Technology Co., Ltd., and co-organized by Zhongyifeng Jinyi (Suzhou) Technology Co., Ltd. and Lezhi Qianrun Investment Service Co., Ltd., Wang Zhaoyang, General Manager of Luoyang Wanji Carbon Co., Ltd., analyzed the technology and market development trends of graphitized cathodes. **Applications, Processes, and Standards of Aluminum Cathodes** Aluminum cathodes: high-graphite cathode carbon blocks, fully graphitized cathode carbon blocks. Classification of aluminum cathode carbon blocks: Semi-graphite cathodes: Using high-temperature electrically calcined anthracite as the aggregate and medium or high-temperature pitch as the adhesive, this product has poor conductivity, weak corrosion resistance, and a short cell life (around 1,000 days). It no longer meets current industrial policies and market demands and has been phased out. High-graphite cathodes: Using high-temperature electrically calcined anthracite and graphite scraps as the aggregate and medium or high-temperature pitch as the adhesive, this product has average conductivity, slightly better corrosion resistance, and a moderate cell life (around 1,800 days). It remains a good choice for aluminum companies focused on price but is expected to be phased out in the near future. Graphitized cathodes: Using calcined petroleum coke as the aggregate and medium or high-temperature pitch as the adhesive, with high-temperature graphitization heat treatment at 3,000°C, this product offers excellent conductivity, significant power savings, and a cell life exceeding 3,500 days. It is gradually becoming the mainstream in the market. **KHD Cathode Vibration Molding Machine (Germany)** Key features: 1. Continuous vacuum extraction; 2. Low porosity of products; 3. Uniform texture of products; 4. High bulk density of products. **Ring-Type Covered Roasting Furnace** Key features: 1. Excellent insulation, uniform heating of products; 2. Stable internal structure; 3. High coking value of products, 2-3% higher than open furnaces. **Internal Heat Series Graphitization Furnace** Key features: 1. High power efficiency; 2. Uniform graphitization; 3. Stable product quality. **U-Type Internal Series Graphitization Furnace** Graphitization process: By combining cathode roasted products into a circuit as conductors, using electric energy to heat the cathode to around 3,000°C, and utilizing thermal activation to transform thermodynamically unstable carbon atoms from a disordered layered structure to an ordered graphite crystal structure, while removing impurities such as sulfur, vanadium, iron, and silicon, high-quality graphite is produced. **Processing Unit** Key features: 1. High processing precision; 2. Exquisite product appearance; 3. High automation and capacity; 4. Effective dust collection. He also introduced the standards for aluminum cathode carbon blocks. **The Important Role of Cathodes in Aluminum Electrolysis Cells** Applications of cathode carbon blocks: 1. Cathode carbon blocks are an essential component of the lining in aluminum electrolysis cells. 2. The performance of cathode carbon blocks significantly impacts the power consumption and cell life of electrolysis cells. 3. As a container, cathode carbon blocks must withstand corrosion from molten aluminum and electrolyte while ensuring uniform current distribution in the aluminum and electrolyte. Cathode carbon blocks play a crucial role in electrolysis cells, often referred to as the "kidneys" of the cell. The quality of the cathode directly affects the cell's lifespan and economic efficiency and is critical for cell maintenance. ►Container function: Cathodes, paste, and side carbon blocks together form a container where molten aluminum and electrolyte are held, undergoing processes such as heating, electrolysis, and aluminum tapping. ►Thermal conductivity and high-temperature resistance: Aluminum electrolysis cells operate at temperatures above 930°C, requiring heat-resistant materials to withstand the heat and good thermal conductivity to distribute heat evenly across the cathode, preventing significant thermal stress and deformation. ►Conductivity: Current enters the cell through the steel rod at the cathode bottom, distributing relatively evenly across the cell base. After passing through the molten aluminum and electrolyte, it forms a circuit with the anode, enabling electrochemical reactions and completing the electrolysis process. Cathode voltage drop is a key parameter for cell operation. ►Corrosion resistance: Cathodes must withstand sodium salt erosion in molten salts and prevent the formation of Al₄C₃, requiring high stability in the carbon atom structure of the cathode lining. **Reasons for the Rise of Graphitized Cathodes** Why use graphite to make aluminum cathodes? Graphite is an excellent conductor of heat and electricity, with thermal and electrical conductivity comparable to most metals but with unique characteristics. While the thermal conductivity of most metals increases with temperature, graphite's thermal conductivity decreases. At extremely high temperatures, graphite becomes thermally insulating, making it a reliable thermal insulation material under ultra-high temperatures. **Properties of Graphite** ►High-temperature resistance: Graphite has a melting point of 3,850°C and a boiling point of 4,250°C, with strength increasing with temperature. It is commonly used in missile and rocket burner throat materials and is an important material in aerospace and military industries. ►High electrical and thermal conductivity: Graphite's electrical conductivity is 100 times higher than that of most non-metallic ores. Its thermal conductivity exceeds that of steel, iron, and lead. Thermal conductivity decreases with temperature, and at extremely high temperatures, graphite becomes an insulator. ►Lubricity: Graphite's lubricating properties depend on the size of its flakes. Larger flakes result in a lower friction coefficient and better lubrication. It is often used in high-temperature bearings without the need for additional lubricants. ►Chemical stability and plasticity: Graphite has excellent chemical stability at room temperature, resisting acid, alkali, and organic solvent corrosion. It is also highly malleable and can be processed into thin sheets and various shapes. ►Thermal shock resistance: Graphite can withstand drastic temperature changes without damage. Its volume changes minimally during sudden temperature shifts, preventing cracks. **Advantages of Graphite Materials in Cathode Production** Extended cell life: The first series of graphitized cathode electrolysis cells in China (Wanji Aluminum) started operation on January 18, 2006, with an average cell life exceeding 3,730 days. The longest cell life was 5,696 days, ending on October 31, 2021. In contrast, companies using high-graphite cathodes have mostly undergone one or two major overhauls, with some even requiring three overhauls, each costing around 2 million yuan. Superior power savings: After adopting graphitized cathodes and casting technology, the cell bottom voltage drop reached a minimum of 175 mV, more than 90 mV lower than that of high-graphite cathodes. The stable nature of graphite also results in a relatively small increase in cell bottom voltage drop during use, saving 300 kWh per ton of aluminum produced. The additional investment can be recouped in a short time. Stable operation: Due to the low sodium absorption of graphitized cathodes, their sodium expansion coefficient is very low, resulting in minimal horizontal expansion and corresponding cell shell deformation after cell startup, reducing early cell damage. Additionally, the excellent thermal conductivity of graphite helps form a good furnace wall, effectively protecting the sides and reducing horizontal current consumption, ensuring stable cell operation. Enhanced current to increase capacity: Due to strict government policies against illegal aluminum production, China's aluminum market is expected to face a supply gap, leading to strong profitability. Therefore, increasing capacity will become a priority for aluminum plants. Both international and domestic examples show that adopting graphitized cathodes can enhance capacity by strengthening current. Environmental benefits: Lining materials generated after cell overhauls contain large amounts of hazardous elements, causing severe environmental damage. They have been classified as hazardous waste, requiring costly disposal by aluminum enterprises. Graphitized cathodes, with their longer lifespan, produce less hazardous waste, attracting attention from environmental authorities and aluminum plants, potentially becoming a necessity due to environmental demands. Three balances: Graphitized cathodes better maintain the thermal income and expenditure balance of electrolysis cells, ensure the material balance of electrolyte and alumina concentration, and achieve a balance between the anode (the heart of the cell) and the cathode (the kidneys of the cell). **Current Status, Opportunities, and Challenges in the Aluminum Cathode Industry** Current status of the aluminum cathode industry: 1. Graphitized cathode capacity increased to 850,000 mt/year. In recent years, cathode capacity has remained around 700,000 mt. In 2021, capacity was 740,000 mt/year, increasing to 850,000 mt/year in 2022, up 14.8% YoY, with the increase coming from graphitized cathode products. In addition to traditional cathode companies, some electrode producers have also adjusted their product structures to enter the graphitized cathode business. 2. Graphitized cathode production has grown significantly, accounting for over 70% of total cathode production. In 2023, China's aluminum cathode production approached 400,000 mt, with less than 1% YoY growth. Graphitized cathode production was 270,000 mt, up 30% YoY, accounting for 70% of total cathode production. Cathode market price trends over the past five years: 3. Graphitized cathode prices have been highly volatile, with cut-throat competition intensifying. Over the past five years, cathode prices have fluctuated dramatically, from nearly 20,000 yuan/mt in 2019 to around 14,000 yuan/mt in 2021, then sharply rising to around 36,000 yuan/mt, before gradually pulling back in 2023, triggering a series of price collapses. Cathode companies have been competing to lower prices, with the current lowest price falling below 15,000 yuan/mt, leaving most cathode companies facing losses. The extreme price volatility has discouraged some companies from investing in cathodes. Over time, as losses expand, the industry is expected to return to rationality and shift toward healthy competition. **Supply and Demand in the Aluminum Cathode Market** China's total aluminum capacity is approximately 45 million mt. If all aluminum production adopts graphitized cathodes, with a consumption of 6-8 kg of cathode per ton of aluminum, the annual national consumption would be 250,000-340,000 mt. With all new domestic projects coming online, domestic demand is unlikely to change significantly. China's cathode market is mainly concentrated in Shanxi Jinzhong, Henan, and Ningxia, with total capacity reaching 800,000 mt. Since last year, some graphite electrode companies have entered the cathode industry, further expanding total capacity. Overall, the market remains severely oversupplied, with intense cut-throat competition. He also introduced the situation of Chinese companies building aluminum projects overseas. **Current Status of the Low-Sulphur Petroleum Coke Market for Graphitized Cathodes** Limited growth in low-sulphur coke production: 1. Domestic low-sulphur petroleum coke production has been declining. In recent years, China's imports of heavy crude oil have increased significantly, with the proportion of high-sulphur crude oil rising, leading to a clear trend of increased production of high-sulphur and low-quality petroleum coke. 2. Overseas low-sulphur petroleum coke resources are limited. Import data in recent years shows annual imports of around 4 million mt, with little room for growth.

③ Due to the limited resources of low-sulphur petroleum coke, China has imported a large amount of high-sulphur sponge coke. Through desulphurization and precise blending technology, the issue of declining raw material quality has been addressed.

Application of New Technologies in Aluminum Cathodes

New Technology Applications in Aluminum Cathodes

1. Wide Steel Bar + Phosphorus Pig Iron Casting Technology

By altering the connection method and assembly form between the cathode steel bar and the cathode carbon block, the cathode conductive structure has been optimized. This helps to reduce the horizontal current in the aluminum liquid, increase the vertical current, expand the conductive cross-sectional area, lower the resistance of the steel bar, enhance conductivity, reduce the direct current (DC) consumption in the electrolytic cell, and achieve a significant reduction in both the horizontal current in the aluminum liquid and the cathode voltage drop. The cathode current distribution becomes more uniform and stable, extending the service life of the electrolytic cell.

2. Copper-Inlaid Steel Bar Casting

Still using graphitized cathodes as the carrier, the goal is to optimize the cathode conductive structure and reduce the horizontal current and cathode voltage drop. This technology is currently in the exploratory stage, with various design institutes involved, and small-scale test cells are being conducted in an orderly manner.

3. High-Strength, High-Conductivity, High-Volume Density Cathodes Are Also Being Applied

Currently, some aluminum enterprises have implemented graded procurement for cathode carbon blocks, with the first grade being the best and the second grade meeting national standards. Incentive measures have been provided for the first grade, which to some extent promotes the healthy development of the cathode industry. Meanwhile, some users have expressed market demand for impregnated cathodes, which will also occupy a place in the future.

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