Spent Pot Lining Research Articles

Electrochemical performance of graphene oxide synthesized from graphitic spent potlining for energy storage application

The hazardous nature of spent pot lining (SPL) generated from aluminum smelters poses environmental challenges due to its high fluoride and cyanide content. However, techniques and recent studies have shown that SPL can be converted into valuable carbon-based materials through innovative recycling with potential applications in energy storage devices. This work presents an electrochemical performance evaluation of graphene oxide (GO) electrodes derived from acid-treated SPL for supercapacitor applications. The SPL-derived graphene oxide (SPL-GO) was synthesized via a facile and scalable improved Tour method. SPL-GO electrodes were fabricated by drip-coating SPL-GO/PVDF/DMF suspension on nickel foams. The morphology, structure, and chemical composition of the SPL-GO were characterized using advanced techniques such as energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD). The electrochemical properties of the SPL-GO in 3 M KOH were characterized with a three-electrode system using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The results demonstrate that SPL-GO exhibits a relatively high specific capacitance of 762.90 F/g at 1 A/g with corresponding power and energy densities of 502 W/kg and 106.60 Wh/kg, respectively. Additionally, excellent cycling stability of 85.4 % was achieved after 10,000 cycles with a coulombic efficiency of 95.23 %. These results suggest a superior rate capability of SPL-GO, rendering it a viable candidate for supercapacitor applications. Furthermore, this work sets the foundation for the sustainable use of industrial waste in energy storage devices, suggesting a novel, eco-friendly material for practical supercapacitor applications.

Optimization of process parameters and kinetics of fluoride extraction from spent potlining using response surface methodology

Over the years, spent potlining (SPL) treatment has only focused on the extraction of its hazardous compounds, especially fluorides and cyanides. The literature has not sufficiently addressed the optimization and kinetics of fluoride extraction using statistical modeling to determine relevant factors for efficient, cost-effective, and sustainable SPL treatment. Hence, this study is focused on response surface methodology (RSM) combined with central composite design (CCD) to statistically model fluoride extraction of SPL behaviour in acidic environments. Shrinkage core model (SCM) was used to investigate the kinetics of fluoride extraction. The RSM analyses suggested a second-order quadratic model with outstanding accuracy, statistically supported by R2 and adjusted R2 values of 0.986 and 0.973, respectively. The quadratic model indicates the main factors influencing fluoride extraction, showing the complex interactions of temperature, particle size, acid concentration, and leaching time. These main factors were observed to have significant effects on fluoride extraction, except for particle sizes of the SPL. The optimization process, a key success of this study, achieved fluoride extraction of 87.49% at specific factor levels of 48.43 °C, 0.752 mm, 1.2 M, and 10 min. Subsequently, the SCM investigations suggested that diffusion through a liquid film mechanism best approximates the fluoride extraction kinetic behaviour with R2 > 0.80 across varying temperatures. Investigations into temperature dependence with the Arrhenius plot further validated that the reaction kinetics were principally controlled by diffusion through liquid film, with an activation energy of 36.26 kJ/mol. Integrating these kinetic frameworks provides a novel approach to analyzing and optimizing SPL fluoride extraction. Overall, adopting the present study in the industrial settings with the optimized parameters will ensure efficient, sustainable, and cost-effective treatment of SPL.

Synergistic reutilization of spent pot lining and water quenched blast furnace slag as mold flux

A treatment method that synergistic reusing spent pot lining (SPL) and blast furnace slag (BFS) as mold flux (a functional material used in steel enterprises) was developed to achieve the harmless treatment of hazardous substances and recycling of valuable resources in spent pot lining. Mold flux made of SPL and BFS shows outstanding metallurgical performance. More importantly, toxic fluoride and cyanide in SPL were effectively harmless-treated utilizing industrial waste heat after making mold flux. The fluorine leaching ratio of amorphous mold flux residual after a leach test for 128 h is 1.08 wt%, which is 1/24 of that of raw SPL. The microstructure characterization proved the addition of BFS enhanced the fluorine immobilization effect by optimizing the network structure of amorphous mold flux residue. Compared to the traditional landfill treatment, the estimated additional economic benefits of processing one ton of SPL with this method are approximately 1924 USD.

NOx Reduction in a Cement Kiln with Spent Pot Lining: A Reaction Kinetics Study on HCN–NO and HNC–NO Interactions

NO_<i>x</i> Reduction in a Cement Kiln with Spent Pot Lining: A Reaction Kinetics Study on HCN–NO and HNC–NO Interactions

Insights into the synergistic calcination of spent pot lining and red mud for stabilization of fluorine and recovery of iron

Spent pot-lining (SPL) and red mud (RM) are significant industrial solid wastes generated from the aluminum industry, holding valuable potential as secondary resources. This study addresses the pressing challenges of mitigating fluoride emissions resulting from the pyrometallurgical process of SPL and recovering iron (Fe) components from RM. To achieve these objectives, a synergetic reduction-stabilization process via co-calcination was proposed. During co-calcination, the carbonaceous content of SPL acts as a reducing agent, facilitating the reduction of Fe oxides in RM to magnetite (Fe3O4). The recovered Fe3O4 was efficiently separated through magnetic separation with 66.9% recovery efficiency. Additionally, the co-calcination process synergistically stabilizes fluoride emissions from SPL due to the presence of calcium oxide (CaO) in RM. This results in fluoride emissions reacting with CaO to form insoluble fluorite (CaF2), leading to significantly reduced fluoride leaching concentrations (18.3 mg L−1), well below national recommended standards (100 mg L−1). Mineral transformations revealed that Na3AlF6 from SPL decomposed into NaF, AlF3, and HF, with subsequent reactions with CaO leading to CaF2 formation. The selectivity of element combinations among Ca-Fe-F-O can be attributed to the distinct ionic potentials in the HF-CaO-Fe2O3-C system, where CaF2 arose from a hard acid (Ca(II))-hard base (F-) interaction, and Fe2O3 reduction was influenced by the weaker bonding between soft base O2- and borderline acid Fe(III)/Fe(II) repulsion, according to the Hard-Soft Acid-Base (HSAB) theory. This proposed synergistic utilization approach not only detoxifies harmful fluoride emissions but also offers a sustainable method for Fe recovery, holding significant potential for environmental and economic benefits in the context of aluminum industry waste management practices.

High-efficiency degradation of Fe-CNs in SPL through microwave-activated persulfate

Cyanide in spent potlining (SPL) is primarily present as sodium cyanide (NaCN) and iron (II, III) cyanide complexes (Fe-CNs). NaCN is easy to degrade, while Fe-CNs is extremely difficult to degrade. In this work, a novel microwave-activated persulfate technology (MW-PS) was firstly proposed to degrade Fe-CNs promptly and efficiently. The removal rate of 99.88 % was achieved within 180 s under optimal conditions of pH = 10.15, [oxidant]:[Fe-CNs] molar ratio of 5:1, and microwave power of 300 W. The remaining total cyanide content was less than 0.04 mg·L−1. The degradation mechanism of ferrocyanide (II) and ferricyanide (III) in the MW-PS degradation system was systematically analyzed through electron paramagnetic resonance (EPR) and element identification techniques. The ROS (SO4−, HO, O2−, and 1O2) generated under microwave activation and first attacked the C-Fe complex bond in Fe-CNs, causing the bond to dissociate and release the free CN−, and then CN− was thoroughly oxidized. This work develops a simple and high-efficiency decyanation technology for complex cyanide contained industrial waste disposal.

A Review of Top Submerged Lance (TSL) Processing—Part II: Thermodynamics, Slag Chemistry and Plant Flowsheets

In Part II of this series of review papers, the reaction mechanisms, thermodynamics, slag chemistry and process flowsheets are analyzed concerning cases where the TSL bath smelter has found its application. These include the primary and secondary production routes of five non-ferrous metals (tin, copper, lead, nickel, zinc), ironmaking and two waste-processing applications (spent pot lining and municipal solid waste/related ash treatment). Thereby, chemistry and processing aspects of these processes are concisely reviewed here, allowing for clear and in-depth overview of related aspects. In contrast to Part I, the focus lies on a holistic analysis of the metallurgical processes themselves, especially the particularities induced by carrying them out in a TSL reactor rather than on the respective equipment and auxiliaries. The methodology employed per metal/application is presented briefly. Firstly, the feed type and associated statistical information are introduced, along with relevant process goals, e.g., the secondary metallurgy of copper involves the recovery of platinum group metals (PGMs) from waste from electrical and electronic equipment (WEEE). Subsequently, associated chemistry is discussed, including respective chemical equations, analysis of the reaction mechanisms and phase diagrams (especially of associated slag systems); these are redrawn using FactSage 8.1 (databases used: FactPS, FToxid, FTmisc, FTsalt and FTOxCN) and validated by comparing them with the literature. Then, based on the above understanding of chemistry and thermodynamics, the flowsheets of several industrial TSL plants are introduced and discussed while providing key figures associated with process conditions and input/output streams. Finally, this article culminates by providing a concise overview of the simulation and digitization efforts on TSL technology. In light of the foregoing discourse, this paper encapsulates basic principles and operational details, specifically those pertaining to TSL bath smelting operations within the non-ferrous industry, thereby offering valuable insights intended to benefit both scholarly researchers and industry professionals.

Insights into optimal gas-ash-energy nexus: Oxy-steam combustion of spent pot lining

Altering the atmosphere type may boost the physicochemical drivers of the combustion, thus contributing to the circularity and sustainable management of hazardous wastes. This study aimed to compare the combustions of spent pot lining (SPL) in the oxy-steam and air atmospheres. The SPL combustion with 21% (Oxy21), 30% (Oxy30), and 40% (Oxy40) O2 in the oxy-steam atmosphere improved the performance indices. Weighted mean activation energy (Em) fell from 148.36 kJ/mol in the air atmosphere to 118.04 kJ/mol in Oxy21, with the lowest Em value occurring in Oxy30 (referred to as energy-saving pathway). With the temperature rise, the pattern of fluorine distributions in the air atmosphere (the oxy-steam atmosphere) exhibited 65.60 → 92.27% (65.87 → 9.08%) of fluorine in bottom ash, 7.33 → 31.84% (22.31 → 72.83%) in off-gas, and 0.4 → 2.56% (11.82 → 22.22%) in fly ash. The increased O2 concentration slightly affected the combustion characteristic indices and fluorine distributions. Steam appeared to enhance the pore expansion. The advance decomposition of Na3AlF6, the new emergence of NaAlO2, and the disappearance of CaF2 characterized the oxy-steam combustion of SPL. The gas-ash-energy nexus was jointly optimized via artificial neural network. The oxy-steam combustion destroyed the stability of both soluble and insoluble fluorine, thus greatly releasing fluorine-bearing gas.

Four-stage chemical treatment of spent pot lining carbon for titanium oxide doped high performance supercapacitor electrode material

Obtaining carbon materials in a sustainable way and applying them in energy storage systems is attracting more attention. Spent potlining (SPL) which is a carbon-rich waste produced in electrolytic cells of aluminium smelters can be a potential source of carbon for engineering applications. However, SPL is hazardous in nature and needs to undergo chemical treatment for most engineering applications. In this study, a four-step procedure was adopted to remove sodium fluoride (NaF), cryolite (Na3AlF6), alumina (Al2O3), calcium fluoride (CaF2), sodium aluminate (NaAl11O17) and silica (SiO2) from the SPL. The adopted treatment processes proved effective as Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD) results showed no traces of the major impurities after the treatment. The treated carbon-rich SPL was activated using NaOH to obtain activated SPL (ASPL). The ASPL was doped with TiO2 to form ASPL-TiO2 (1:1), ASPL-TiO2 (3:1) and ASPL-TiO2 (2:1) electrodes. The electrode materials were tested using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The ASPL, ASPL-TiO2 (1:1), ASPL-TiO2 (3:1) and ASPL-TiO2 (2:1) demonstrated specific capacitance of 180.2 F/g, 279.1 F/g, 536.7 F/g, and 203.2 F/g at 10 A/g respectively with high stability over 1000 cycles. The present study was designed to determine the suitability of using chemically treated SPL as an alternative source of carbon for supercapacitor applications and this was achieved as the material exhibited an improved charge storage capacity.

Recycling of spent pot lining (SPL) from aluminum smelters by water leaching

Recycling of spent pot lining (SPL) from aluminum smelters by water leaching

Numerical simulation study on the effects of co-injection of pulverized coal and SPL (Spent Pot-Lining) into the blast furnace

This study investigated the potential use of spent pot-lining (SPL) as a supplementary fuel in blast furnaces (BFs) to replace coke or pulverized coal (PC). A numerical model was established to study the combustion behavior of mixed fuel (MF) containing 80 % PC and 20 % SPL in the raceway of BF. The study focused on the effects of blast velocity, temperature, injection rate, and oxygen content on combustion. Results showed that the burnout rate has a positive relationship with blast velocity and oxygen content, and decreases with the increase of blast temperature and injection volume. To obtain a high temperature zone, it is recommended to increase the oxygen content and air volume of the blast, and the blast temperature (1473 K) and injection volume (169 kg/t) maintain the basic operating conditions. These results can provide insights into the potential use of SPL as a waste resource in iron-making processes, which can promote the substitution of industrial waste SPL for PC in high-energy-consuming industries, contribute to the development of green metallurgical technology, and advance global energy conservation and emission reduction techniques.

Microstructure Characterization of Cement Pastes with Recycled Aluminum Spent Pot Lining

The use of locally available industrial by-products as supplementary cementitious materials and mineral fillers is vital for reducing the embodied carbon of modern concretes. Spent pot lining (SPL), a by-product of the aluminum industry, is massively produced worldwide. SPL treated with the low caustic leaching and liming process (LCLL-ash) is no more hazardous and can be used as cementitious material. This study aims to better understand the microstructure changes of cement paste incorporating aluminum smelter wastes, such as LCLL-ash and synthetic anhydrite. Ground LCLL-ash was used to partially replace cement in cement pastes with a constant water-to-binder ratio of 0.35. A small amount of anhydrite was added to some mixes. This study investigated chemo-micromechanical properties of cement paste systems through multiple techniques, including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, wavelength-dispersive spectroscopy, and microindentation test. The results showed that the reactive alumina from LCLL-ash modified the hydrated phases with the presence of the carbo-aluminate phases. The pastes containing LCLL-ash exhibited a higher CH, and C-S-H contents refer to the reference, suggesting that LCLL-ash has a slight nucleation effect. Moreover, LCLL cement paste showed an increase in the Ca/Si ratio of the C-S-H phase intermix. Finally, microindentation results revealed that adding anhydrite with 10% LCLL-ash enhanced the mechanical property of the cement paste at 28 days.

Effect of fluorite addition on the reactivity of a calcined treated spent pot lining in cementitious materials

Treating SPL by the low caustic leaching and liming process generates an inert nonhazardous residue called LCLL Ash and a fluorite byproduct Calcined LCLL Ash that is ground into a fine powder demonstrates pozzolanic behavior in cement. The effect of the calcination temperature and fluorite byproduct addition on the reactivity of LCLL Ash was studied by the compressive strength activity index, Frattini test and Rilem R3 tests followed by XRD analysis. At 800°C, the formation of nepheline causes alkali uptake, the LCLL Ash showed a slightly lower reactivity with 10% fluorite addition. At 1000°C, calcined LCLL Ash/CF showed a better amorphization of phases and increasing reactivity due to reactions between fluorite and sodium oxide. Unlike LCLL Ash, no delay in hydration or hydro reactivity was observed with calcined LCLL Ash/CF.

Development of sustainable ultra-high performance concrete recycling aluminum production waste

Ultra-high performance concretes (UHPC) are a promising means to foster sustainable and resilient infrastructures as they allow reducing concrete volume, while enhancing structural durability. However, their applications are often limited by the high cost and the availability of raw materials. This study aims to engineer a novel UHPC mix design at a relatively low cement content by recycling treated spent pot lining (SPL) from aluminum smelters, herein called LCLL-ash. First, the UHPC mixtures with different cement content replacement levels by LCLL-ash powders were designed by means of the Compaction-Interaction Packing Model (CIPM). Then, a multi-technique characterization was carried out for measuring the fresh properties, microstructure images and crystalline phases by SEM and XRD analysis, heat transfer by isothermal calorimetry, autogenous shrinkage, compressive strength and microindentation properties. The presented results show that the addition of LCLL-ash delayed the hydration kinetics, while slightly reducing the workability and compressive strength. On the other hand, replacing 12% of cement with LCLL-ash reduced the early-age autogenous shrinkage by 19%. Finally, the environmental impact and the cost of the developed UHPC were assessed, confirming the potentials for producing sustainable LCLL-UHPC with reduced shrinkage.

Measurement and control of containing-fluorine particulate matter emission during spent pot lining combustion detoxification process

The particle size distribution (PSD), composition, morphology, and formation mechanism of particulate matter (PM) released from the combustion of spent pot lining with and without CaSiO3 were investigated. The results showed that NaF and Na3AlF6 were found to be the main compositions of PM, and the particle size distribution of PM shows a bimodal distribution. CaSiO3 substantially inhibited the emission of PM by transforming NaF, Na3AlF6, and CaF2 into stable Ca4Si2O7F2. Moreover, CaSiO3 also limited the formation of high hazardous PM0.2 by providing SiO2, Al2O3, and NaAlSiO4 with high melting points as the core of promoting the growth of PM in particle size.

Response surface methodology approach for optimizing the gasification of spent pot lining (SPL) waste materials.

This paper presents new results on the gasification of spent pot lining (SPL) waste material generated in the primary aluminium smelting industry. The main objective is to test the performance of the gasification process of treated SPL materials and to develop an optimization method to maximize the quality of syngas fuel. The novelty of this study is the development of statistical models to predict the syngas composition and the gasification performance indicators during the SPL waste materials thermal conversion process. Modelling and simulation analysis are performed to convert the SPL solid materials to syngas fuel. The percentage of hydrogen (H2) and carbon monoxide (CO) in the syngas fuel, the cold gasification efficiency (CGE) and the carbon conversion (CC) are determined. The response surface methodology (RSM) is used for the optimization of the performance of the gasification process. The effects of the input factors such as the temperature, the equivalence ratio and the steam to fuel ratio on the output variables (H2 and CO in the syngas, the CGE and the CC) are determined. The optimization results show that the optimized operating parameters to maximize the H2, CO, CGE and CC were T = 1200°C, ER = 0.1 and SFR = 1.29, respectively. The optimum values for the H2, CO, CGE and CC were 37.2%, 22.2%, 79.75% and 97.7%, respectively. New correlations for the variation of the output variables versus the input factors are also presented.

Improvement of treated spent pot lining reactivity in cementitious material by calcination

Treating spent pot lining by the Low Caustic Leaching and Liming (LCLL) process creates an inert non-hazardous residue called LCLL Ash. Ground as a fine powder and calcined, LCLL Ash showed a pozzolanic behavior in cement. The effect of the calcination temperatures on LCLL Ash reactivity was studied by compressive strength activity index, Frattini tests, and RILEM R3 tests, followed by XRD analysis. When calcinating LCLL Ash at temperatures below 800 °C, no differences in reactivity were seen between calcined and non-calcined LCLL Ash. At 800 °C, the formation of nepheline caused an alkalis uptake, showing a slightly lower reactivity of LCLL Ash than cement at 112 days. Beyond 800 °C up to 1200 °C, calcined LCLL Ash manifested better amorphization of phases and increased reactivity, similar to cement at 112 days. Finally, neither delay on hydration nor hydroreactivity was observed with calcined LCLL Ash starting at 800 °C.

Successive selective leaching procedures for valorization of spent pot lining carbon

Spent pot lining (SPL) is a hazardous by-product obtained during the decomposition of carbon cathodes in the electrolytic cells used in aluminium smelting. The carbon cathode lining materials degrade over time thereby affecting the performance of the electrolytic cell. Fluoride contents of up to 20 wt% and cyanides up to 1 wt% have been reported as the main environmental concerns in SPL. This study investigated the effect of successive selective leaching (SSL) of pollutants from the SPL in obtaining suitable carbon for use in energy storage applications. Compositional and microstructural analyses were performed on the leached and as-received SPL samples using X-ray fluorescence spectroscopy (XRF), transmission electronic microscopy – energy dispersive X-ray (TEM-EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. In this study, the XRD analysis revealed that fluoride ions in the SPL exist as sodium fluoride (NaF) and calcium fluoride (CaF2). The results indicated that the SSL of SPL is dependent on pH, temperature, types of lixiviant used for the selective leaching and number of washings. It was established that increasing the number of washings with steady stirring rate reduced electrical conductivity and fluoride concentration in the filtrate. Furthermore, high ion removal was achieved at 100 ℃. The current study therefore demonstrated successful removal of pollutants such as CaF2, SiO2, NaF, Al2O3 and Na3Al11O17 while providing insight into the chemical structure and morphology of the treated and untreated SPL.

Gas-to-ash detoxification feasibility and pathways by co-combustion of spent pot lining and food waste shells

Seeking substitutions for Ca-bearing reagents, this study explored the synergistic co-disposal and co-circularity of spent pot lining (SPL) and food waste shells (oyster, clam, and egg shells) in an eco-friendly way. This study is first to evaluate the feasibility of their co-combustions with or without their mechanochemical activation (MCA) toward the gas-to-ash detoxification of fluorine (F). 50% calcined oyster shell fixed about 97.87% of the F content of SPL in the blend ash and outperformed 50% CaO. MCA weakened the diffraction peaks of graphite carbon by favoring the fixation performance through which collisions between particles and the mixing uniformity were promoted. The combination of 10% SiO2 and 40% calcined clam or egg shells raised the F fixation rate to 98.72 and 99.23%, respectively. F was converted to the complex F–Si–Ca compounds rather than to CaF2. Ca and Si compounds facilitated stabilizing F and Na synchronously and formed NaCa2SiO4F. The leaching F concentration of the ash was less than 100 mg/L, meeting the Chinese criterion (GB 5085.3–2007). The recycling of the food waste shells performed effectively in the cleaner disposal process of SPL by suppressing fluorine emissions.

In-depth purification of spent pot-lining by oxidation-expansion acid leaching – A comparative study

Spent pot lining (SPL) is a hazardous solid waste generated after overhauling the aluminum electrolytic cell. SPL contains carbon resources with high graphitization and toxic impurities, such as NaF, Na3AlF6, and CaF2. These toxic substances are difficult to remove from graphite completely. This study introduces an innovative method of oxidation-expansion acid leaching (OEAL) to eliminate impurities inside the graphitized carbon. For such a purpose, typical purification methods (conventional leaching, flotation-acid leaching) were investigated and compared to OEAL. The experimental outcomes indicated that the process efficiency for removing SPL impurities by various methods had the following sequence from high to low: OEAL > flotation-acid leaching > conventional leaching. The maximum SPL impurities removal rate by conventional leaching and flotation-acid leaching was 89.65 %, while it was 99.36 % with the OEAL method. For understanding fundamental aspects of the SPL impurity removal, their rejection mechanisms in the examined methods were systematically studied by different instrumentals and chemical analysis techniques. As a result of the reaction between H+ and residuals during OEAL process, the distance between graphitized carbon layers expands. This expansion resulted in a qualitative improvement in the SPL impurity removal by OEAL, making SPL one of the graphite or graphene oxide resources.