Cathode Carbon Block Research Articles

Hydroxyapatite‐spent cathode carbon block modified asphalt and molecular dynamics simulation study

AbstractThe highly toxic substances contained in spent cathode carbon blocks (SCCB) pose a serious threat to human health and the ecological environment, and are difficult to recycle. To address this issue, we utilize H2O2 to oxidize cyanides and grow hydroxyapatite (HAP) on spent cathode carbon blocks to adsorb fluoride ions, achieving controlled removal of cyanides and fluorides. Subsequently, the hydroxyapatite‐spent cathode carbon block composite material (H‐SCCB) is applied to modified asphalt, and simulations of the interaction between hydroxyapatite interfaces and asphalt components are conducted. The results indicate that the total cyanide and fluoride ion concentrations in the experimental wastewater meet the discharge standards for industrial wastewater in China. Hydroxyapatite successfully grows on SCCB, presenting a rich porous structure and significantly increased surface area. Mechanical testing shows that 4% H‐SCCB exhibits optimal performance, with a 23.28% increase in complex modulus (G*) compared to the matrix asphalt. Creep recovery capability (R) increases by 54.32% and 7%, respectively. Additionally, molecular dynamics simulations reveal that the interface adsorption between hydroxyapatite and asphalt binder is primarily influenced by electrostatic forces. Under the influence of hydroxyapatite, the diffusion abilities of asphalt four components are as follows: resin > aromatic > saturate > asphaltene.

Kinetic, gas emission, reaction pathway and interaction mechanism analysis during oxidative pyrolysis of aluminium electrolysis waste with beech wood

The oxidative pyrolysis kinetic, gas emission, reaction pathway and interaction mechanism during oxidative pyrolysis of spent cathode carbon block (SCCB) and beech wood (BW) were investigated via the thermogravimetry combined with Fourier transform infrared spectrometer (TG-FTIR) analysis. The hemicellulose, cellulose, and lignin in BW and the carbon materials and fluoride in SCCB were determined as the main five components based on thermogravimetric experiment. Compared with pure SCCB, the addition of BW increased the comprehensive oxidative pyrolysis index. Furthermore, the total of 44 kinetic parameters were obtained by the Shuffled Complex Evolution (SCE) method, which were used to further forecast the mass loss of the above five main components. The evolved gases were detected by FTIR, and the results indicated that the main gases for BW/SCCB oxidative pyrolysis were CO2, which corresponded to the oxidation of cellulose, lignin and carbon materials. Small amounts of phenols, alcohols, ethers, ketones, aldehydes, carboxylic acids, CO, aromatics, alkene were attributed to the thermal decomposition of hemicellulose and cellulose. Pyrolysis of cellulose and lignin produced small quantities of hydrocarbons. HF was formed by the thermal decomposition of fluoride. Eventually, the reaction pathway was proposed and the possible interaction mechanism was analyzed during the oxidative pyrolysis of BW/SCCB blends.

Numerical Simulation and Test Analysis of Flow Field in an Aluminum Electrolytic Cell with Graphitized Cathode Carbon Block

Numerical Simulation and Test Analysis of Flow Field in an Aluminum Electrolytic Cell with Graphitized Cathode Carbon Block

Waste Treatment by Waste: Study on Iron Recovery from High-Iron Red Mud by Spent Cathode Carbon Block as Reductant and the Behavior of Na/F

Waste Treatment by Waste: Study on Iron Recovery from High-Iron Red Mud by Spent Cathode Carbon Block as Reductant and the Behavior of Na/F

Synthesis of gel crosslinked composite material from spent cathode carbon blocks and its application in modified asphalt binders

The utilization of spent cathode carbon blocks (SCCB) from aluminum electrolysis has become challenging due to their content of highly toxic cyanides and environmentally harmful fluorides. To achieve reliable recovery and utilization of hazardous waste, targeted research has been conducted on the treatment of waste cathode carbon blocks and their potential application in asphalt pavement. Hydrogen peroxide (H2O2) is employed to remove cyanides from the waste cathode carbon blocks, meeting the construction requirements for transportation areas. Anhydrous calcium chloride is used as a calcium source to precipitate soluble fluorides in the solution. Finally, the waste cathode carbon blocks are gel-crosslinked using polyvinyl alcohol-polyvinyl pyrrolidone, addressing the release of fluorides beyond environmental tolerance. This results in the synthesis of a composite material consisting of calcium fluoride deposits and gel-encapsulated waste cathode carbon blocks (PSB), which exhibits good thermal stability in the temperature range of 0–217 °C. Through DSR and MSCR testing, it has been demonstrated that the gel-crosslinked waste cathode carbon block composite material improves the asphalt's sensitivity to temperature and enhances its resistance to rutting at high temperatures. The 1% PSB/SBS modified asphalt shows the best performance, compared to SBS, the complex modulus (G*) of the modified asphalt increased by 117.4% at 46 °C, and the recovery indices for creep at 64 °C improved by 39.28% (at 0.1 kPa) and 55.65% (at 3.2 kPa), and thermal gravimetric analysis of the asphalt confirms that the addition of PSB improves the asphalt's thermal stability. Fluorescence microscopy analysis reveals that the inclusion of PSB does not affect the morphological development of SBS swelling and plays a stabilizing and supporting role in the asphalt mixture.

Study on thermal conversion and detoxification mechanism of fluorine during co-combustion of meager coal and spent cathode carbon block

Fluoride is a toxic and harmful ingredient in the spent cathode carbon blocks (SCCB). Gaseous fluoride pollution is a significant potential pollution source in the process of boiler collaborative disposal of SCCB. In this paper, meager coal and SCCB were used as fuel, the mixing ratio and temperature were variables, the law of thermal conversion of fluorine during the co-combustion process was studied, and the properties of ash residue were discussed. At the same time, CaO was added to the furnace to reveal the influence of temperature on the effect of fluorine fixation in the furnace. The results showed that combustion was the most suitable method for removing soluble fluorine from SCCB, and the thermal conversion rate of soluble fluorine was up to 99.68–99.98%. The higher the combustion temperature, the higher the conversion of gaseous fluoride, and the worse the effect of fluorine fixation in the furnace. It is not suitable for fluorine fixation in the furnace when the furnace temperature exceeded 1100 ℃. The higher the mixing ratio of SCCB, the higher the production of gaseous fluoride, and a proper mixing ratio is vital for co-combustion. Ash residue after mixing 10% SCCB combustion belongs to general industrial solid waste. This study has important theoretical significance for determining the applicable furnace type, the appropriate mixing ratio and effective fluoride treatment measures in the co-combustion process of coal and SCCB.

Resourceful reuse and performance evaluation of modified electrolytic aluminum spent cathode carbon block material as cement admixture

In order to address the environmental hazards and sustainable recycling of spent cathode carbon block (SCCB), this study designed a one-step strategy of “breaking cyanide-sinking fluoride-polydopamine wrapping” and a secondary modification of nanoscale SiO2 grafting. The impact of modified SCCB on cement was also investigated. The results showed that, after harmless treatment, the fluoride and cyanide concentrations of SCCB decreased to 7.3 mg/L (<10 mg/L) and 0.024 mg/L (<1 mg/L), respectively, thereby effectively treating harmful ions. In addition, based on the excellent mechanical properties of highly graphitized carbon blocks in SCCB and the volcanic ash effect of nanoscale SiO2, the dispersibility of SCCB in cement was enhanced, which consequently strengthened mechanical interlocking ability between SCCB and cement. This slightly improved the mechanical properties of cement mortar. These findings concurrently provide a safe and practical approach for the disposal of SCCB and a novel additive material for construction and building materials.

Recovery of fluoride from spent cathode carbon block by combustion combined with water leaching process

Spent cathode carbon blocks (SCCBs) is a kind of hazardous waste that can be harmful to the environment. In this study, a process of high-temperature combustion combined with water leaching was explored to dissociate toxic substances from SCCB and recover valuable components. Combustible components in SCCB can be converted into useable heat energy. The combustion parameters and water leaching process were optimized, and the transformation trend of important components was explained. According to the experimental findings, under optimal conditions, the combustion weight loss rate of SCCB reaches 81.5%, and the defluorination rate reached 88.2%. The toxic leaching concentration of fluoride from the treated residue was reduced to 49 mg L−1, in line with the safe discharge standard. The characterization results showed that the final recovered product was highly similar to its analytical reagent counterpart. This treatment process has the environmental benefits of secondary resource recycling and can effectively reduce the negative impact of SCCB on the environment.

Green synthesis of aluminum hydroxide from alumina–silica based solid hazardous waste

The collaborative detoxification and extraction of valuable resources from various industrial wastes are proposed based on the composition characteristics and toxic properties of different solid/hazardous wastes such as coal gangue, aluminum dross, red mud, spent cathode carbon blocks, and carbide slag. The coupling reaction mechanism of the valuable or toxic components of aluminum, sodium, silicon, calcium, iron, fluorine, and nitrogen in the industrial wastes was studied in order to explore the potential value of waste. The results show that the alumina and sodium components in the industrial wastes are efficiently extracted, and the reaction process is promoted by iron and carbonaceous substances. The hazardous solid waste aluminum dross and the spent cathode carbon block are detoxified during the reaction process. The optimal reaction temperature is 1150 °C, and the residence time is 45–75 min. The extraction rate of Al2O3 is 92.4–93.3%, and the extraction rate of Na2O is 93.5–94.4%. The extracted alumina and sodium components can be used to prepare a series of high quality alumina.

Pilot experimental study on pollutant emission characteristics from co-combustion of coal and spent cathode carbon block

Spent cathode carbon block (SCCB) is a hazardous waste produced by the electrolytic aluminum industry. Collaborative treatment of the SCCB in pulverized coal boilers is a potentially valuable technology. Pilot experiments were carried out on a 240 t/h pulverized coal boiler and its supporting flue gas treatment measures as a function of the mixing ratio of SCCB to verify the feasibility of coal collaborative disposal of SCCB. The thermal conversion characteristics of fluoride after mixing SCCB with coal were studied. A continuous emission monitoring system was used to monitor the impact on SO2, NOx and particulate matter in real time. The effectiveness of existing flue gas control measures was evaluated, and optimization suggestions of the flue gas control measures were postulated. The content of heavy metals (Hg, Cd, Ni, Pb, As, Se) in solid waste from co-combustion and the physical phase of solid waste were investigated. In addition, the transformation of heavy metals such as Hg, Cd, Ni, Pb, Cr, As and fluoride in defluorination wastewater during flue gas treatment were analyzed. The results show that it is feasible to use a pulverized coal boiler to dispose SCCB. The existing flue gas treatment measures proved to be appropriate, and desulfurization wastewater can achieve the discharge standards. Defluorination gypsum, fly ash and slag are not hazardous waste. When the mixing ratio of SCCB is increased, the existing neutralization and flocculation precipitation processes of the desulfurization wastewater are affected. It is suggested to add Al2O3 for the defluorination process before the desulfurization tower.

Study on Slagging Characteristics of Co-Combustion of Meager Coal and Spent Cathode Carbon Block

The harmless disposal of spent cathode carbon blocks (SCCBs) has become an urgent issue in the primary aluminum industry, and the disposal of SCCBs by co-combustion in pulverized coal boilers is expected to be the most effective treatment method. A muffle furnace at 815 °C was used in this study to perform a co-combustion experiment of meager coal and SCCBs. The ash fusion characteristics (AFTs), microscopic morphology, and minerals composition of co-combustion ash were characterized. The interaction mechanism of different mineral components and the change in AFTs and viscosity-temperature characteristics were investigated using FactSage software. Results show that the change in the ash deformation temperature (DT) is correlated linearly with the SCCB addition ratio, whereas other characteristic temperatures exhibit a nonlinear relationship. The contents of SiO2, Al2O3, and Na2O collectively determine the DT in the ash, and the influence degree from high to low is in the order of SiO2, Na2O, and Al2O3. The phase diagram of Na2O–Al2O3–SiO2 is used to accurately predict the changing trend of the melting point of co-combustion ash. The ratio changes between refractory and fusible minerals in the ash, as well as the degree of low-temperature eutectic reaction between sodium- and calcium-containing minerals, are the main factors affecting the melting point of ash. When the blending amount of SCCBs is 5%, mostly complete combustion is achieved, and slagging does not occur easily. The optimal blending ratio of SCCBs is obtained using the co-combustion method from the aspect of AFTs and viscosity-temperature characteristics. This work lays a theoretical foundation for industrial application.

Pyrolysis kinetics, thermodynamics, and interaction analysis of co-pyrolysis of bituminous coal and electrolytic aluminum solid waste

The thermal degradation behavior, kinetics and thermodynamic characteristics were investigated during the co-pyrolysis of Tangkou bituminous coal (TK) and spent cathode carbon block (SCCB) derived from electrolytic aluminum solid waste. In the N2 atmosphere, thermogravimetric analysis was carried out at four heating rates (5, 10, 20 and 40 K/min). The novelty was that the deconvolution technology with bi-Gaussian function was used to separate the complex thermogravimetric curves. The devolatilization of organic matter, the secondary depolymerization of macromolecules, the secondary repolymerization of macromolecules in coal and the thermal decomposition of fluoride in SCCB were found as different components of the whole co-pyrolysis process of TK and SCCB. Kinetic parameters were estimated by the model-free method and model-fitting method. The results showed that the average activation energy for four stages was 211.30, 222.10, 253.31 and 268.12 kJ/mol, and four stages of co-pyrolysis process fit well with chemical reaction model with reaction order n = 2.5, 3.0, 3.0 and 1.5, respectively. The thermodynamic parameters, including enthalpy (ΔH), Gibbs free energy (ΔG) and entropy (ΔS) were calculated to determine the feasibility and reactivity of the co-pyrolysis process. Eventually, the interaction effect was found in the fourth stage of co-pyrolysis of TK/SCCB.

Co-combustion characteristics of electrolytic aluminum waste and coal

The electrolytic aluminum waste, which would inevitably be produced from the electrolytic process in the aluminum industry, is harmful to environment and human body. Sending it to the coal-fired boiler seems to be an eco-friendly scheme to dispose the waste. In this study, the co-combustion characteristics of the electrolytic aluminum waste (cathode carbon blocks (CCB) and hardened material (HM)) and the bituminous coal (BC) are investigated. During the thermogravimetric experiment, the char combustion of CCB shows the similar trend as that of BC before 800 °C. A series of oxidization reactions of carbon in anthracite and graphite (both are the raw materials of CCB) could be observed at relatively high temperature. The mass of HM changes smoothly as the temperature rises. Both CCB and HM could promote the ignitability of the blends efficiently, in which the ignition point comes to 517.33 °C when the mass proportion of HM is 30%. The addition of CCB brings out the second peak in DTG curves of the blends. The burnout performance is weakened as the increase of mass proportion of HM. Remarkable synergy happens during the co-combustion process between BC and CCB/HM, because the pre-exponential factors of the blends increase abruptly compared with that of BC in the early stage of the char combustion. Compared with the activation energy, the pre-exponential factor changes more intensely, which plays a more important role in the co-combustion process.

A milliseconds flash joule heating method for the regeneration of spent cathode carbon

Spent cathode carbon (SCC) blocks of aluminum electrolytic cell were hazardous waste produced in the production of electrolytic aluminum. In this present work, a facile, rapid, and economical strategy was proposed to remove fluoride and other toxic substances in the SCC block by the flash joule heating method. SCC after flash joule heating (F-SCC) were prepared in different flash voltages and number of passes; the chemical composition, microscopic morphology and carbon configuration of the SCC and F-SCC were described in detail. The results show that the purification efficiency depends upon the flash voltages and pass number. In terms of flash voltage, 150 V (5.62 kJ/g) is the optimal voltage to maintain the micro-expansion characteristics of the cathode carbon. Multiple flash joule heating can not only maintain its high-graphitization carbon, but also improve its micro-expansion characteristics. In addition, the electrochemical performance of F-SCC was characterized, and F-SCC displayed excellence capacitance performance. The low-cost, rapid -regeneration method based on the flash joule heating provides an effective method for the clean recycling and high-value utilization of carbonized solid waste.

Performance of TiB2 Wettable Cathode Coating

A TiB2 wettable cathode coating was deposited on a graphite carbon cathode material via atmospheric plasma spraying (APS). The microstructure and phase composition of the TiB2 coating were analyzed via scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The wettability and corrosion resistance of the coating were studied in a molten-aluminum electrolytic system. The results showed that the surface of the TiB2 coating prepared via plasma spraying was flat and that the main phase of the coating was TiB2. The wettability between the TiB2 coating and liquid aluminum was better than that between graphite cathode carbon block and liquid aluminum. The abilities of the TiB2 coating and graphite cathode carbon block to resist sodium (Na) penetration and prevent molten salt corrosion were compared through a corrosion test. The TiB2 coating was found to have better resistance to Na penetration and better refractory cryolite corrosion resistance than graphite cathode carbon block.

Evaluation of cathode quality and damage of aluminium electrolytic cell based on non-destructive technology

To evaluate the quality and damage condition of the electrolyzer, wave velocity detection technology and impact echo technology were used to detect the cathode part of the electrolyzer. The experimental results show that wave velocity is linearly related to the porosity, and there is also a linear relationship betweenwave velocity and the square root of reciprocal density in cathode carbon blocks (CCBs) before installation into electrolyzer. Combined with detection results of wave velocity and voltage drop, the large-size CCBs with relatively good quality can be found. Through the impact echo technology on cathode steel rods (CSRs), the results of the on-site detection show that the damage condition of CSRs can be effectively evaluated, and the damage location of CSRs can be determined. This study proposes a novel and quantifiable method for the evaluation of cathode quality and damage, which provides a reference for prolonging the service life of the electrolyzer.

Co-combustion characteristics and kinetics of meager coal and spent cathode carbon block by TG-MS analysis

As a hazardous waste, the spent cathode carbon block (SCCB) has a high calorific value while it is difficult to fire, its harmless disposal is a major difficulty at present. Herein, a method of mixed combustion of meager coal and SCCB in a pulverized coal furnace for disposal of SCCB is proposed, and thermogravimetric mass spectrometry (TG-MS) is used to characterize the combustion and gas release characteristics. The effects of the heating rate and mixing ratio on combustion are analyzed as well. The result shows that the comprehensive combustibility index and combustion stability index of SCCB-5 at a heating rate of 50 °C/min are both the highest. Abundant oxygen-containing groups in SCCB promote the co-combustion process. The release of hydrogen fluoride is relatively low below 1000 °C so that the use of pulverized coal boilers meets the temperature requirement for disposal of SCCB. The good melting characteristics of ash after mixing sintering also confirm this point. Finally, the kinetic calculation results show that the combustion activation energy is the lowest when the mixing ratio is 5%, which is in good agreement with the experimental results. The highest activation energy values for the combustion of meager coal, SCCB and SCCB-5 are 46.90, 89.39, 59.87 kJ mol−1, respectively.

Recovery of Copper and Cobalt from Converter Slags via Reduction–Sulfurization Smelting Using Spent Pot Lining as the Reductant

Large amounts of solid wastes are produced in copper and aluminum smelting processes, which not only cause losses of valuable resources but also threaten the ecology and environment. In this study, a reduction–sulfurization smelting method was used for recovering Cu and Co from converter slags by using spent pot lining (SPL) as the reductant. CaO was added to fix the fluorine from SPL into the cleaned slag. Thermodynamic analysis and experiments were performed to verify the feasibility and determine the optimal conditions of this smelting process. The optimum reductant addition of spent cathode carbon block (SCCB) and spent SiC side block (SSCB) was 8–12 wt %, and the copper and cobalt recovery reached more than 98 and 96%, respectively. The addition of 10 wt % CaO for SCCB improved slag viscosity and promoted the separation between slag and matte/alloy and fixed fluorine in the cleaned slag in the form of insoluble calcium fluoride. The metallized Cu–Co matte was obtained, in which Cu mainly existed in the form of sulfide and Co mainly existed in the form of an iron cobalt alloy.

Recycling and utilization of spent potlining by different high temperature treatments

Spent potlining (SPL) is generated at the end of the service life of aluminum reduction cells and is a hazardous solid waste that negatively impacts the environment and ecology. Based on the differences in the hazardous and valuable components of SPL, a classified recycling and utilization path is proposed in this work. Three different high-temperature processes of oxygen-controlled treatment, vacuum treatment, and co-processing in a cement kiln were adopted for spent cathode carbon block (SCCB), spent silicon carbide block (SSCB) and spent barrier and insulating refractory materials (SBIM), respectively. After the classified treatments, all the cyanides in SCCB were decomposed, almost all the Si3N4 was decomposed and Na2SiO3 was removed from SSCB, and over 99% of the fluorides was separated from SCCB and SSCB to obtain high graphitization carbon and silicon carbide. The fluorides in SBIM were converted into a mineralizer that lowered the burning temperature of the cement clinker. The performances of prepared cement met the requirements of Portland slag, Portland pozzolana and Portland flash ash cements.

Study on Kinetics of Vacuum Heat Treatment Process of the Spent Cathode Carbon Blocks from Aluminum Smelters

The spent cathode carbon block (SCCB) produced from the overhaul aluminum reduction cell is regarded as hazardous solid waste because it contains a large amount of soluble fluoride and small amount of cyanide. Coupling vacuum-heating method is considered an effective way to address the issues of such hazardous waste. Herein, SCCB is processed under the conditions of 3000 Pa and 1673–1973 K. The correlation between soluble fluoride content and treatment time was analyzed. The apparent activation energy of the detoxification reaction was calculated based on the Arrhenius equation. The rate-determining step of the detoxification process has also been analyzed in detail. The results show that the detoxification process is a first-order reaction. The apparent activation energy was k = 15.08 kJ mol−1, and gas diffusion was the rate-determining step of the detoxification reaction.