Crystal phase and nanoscale size regulation utilizing the in-situ catalytic pyrolysis of bamboo sawdust in the recycling of spent lithium batteries

Current Li-ion battery (LIB) recycling methods exhibit the disadvantages of low metal recovery efficiencies and high levels of pollution and energy consumption. Here, products generated via the in-situ catalytic pyrolysis of bamboo sawdust (BS) were utilized to regulate the crystal phase and nanoscale size of the NCM cathode to enhance the selective Li extraction and leaching efficiencies of other valuable metals from spent LIBs. The catalytic effect of the NCM cathode significantly promoted the release of gases from BS pyrolysis. These gases (H2, CO, and CH4) finally transformed the crystal phase of the NCM cathode from LiNixCoyMnzO2 into (Ni-Co/MnO/Li2CO3)/C. The size of the spent NCM cathode material was reduced approximately 31.7-fold (from 4.1 μm to 129.2 nm) after roasting. This could be ascribed to the in-situ catalytic decomposition of aromatic compounds generated via the primary pyrolysis of BS into C and H2 on the surface of the cathode material, resulting in the formation of the nanoscale composite (Ni-Co/MnO/Li2CO3)/C. This process enabled the targeted control of the crystal phase and nanoscale size of the material. Water leaching studies revealed a remarkable selective Li extraction efficiency of 99.27 %, and sulfuric acid leaching experiments with a concentration of 2 M revealed high extraction efficiencies of 99.15 % (Ni), 93.87 % (Co), and 99.46 % (Mn). Finally, a novel mechanism involving synergistic thermo-reduction and carbon modification for crystal phase regulation and nanoscale control was proposed. This study provides a novel concept for use in enhancing the recycling of valuable metals from spent LIBs utilizing biomass waste and practices the concept of "treating waste with waste".

Deep resource utilization of hazardous arsenic-alkali slag: Thermodynamic analysis, mechanism investigation and process optimization

The best solution to address environmental pollution caused by arsenic-containing hazardous waste is to prepare high-purity elemental arsenic from such waste. The key to this approach lies in the efficient separation of arsenic from various impurities. This paper presents a viable solution for producing high-purity elemental arsenic from arsenic-alkali slag, and the keylies in utilizing the selective precipitation of magnesium ammonium arsenate (MgNH4AsO4) to achieve efficient separation of arsenic from alkali, antimony, and other impurities. Thermodynamic analysis and hydrometallurgical condition experiments indicate that in complex alkaline arsenic-containing solutions, over 90% of arsenic components can selectively precipitate in the form of MgNH4AsO4. The content of arsenic in the resulting precipitate reaches approximately 30%, while the content of antimony is below 0.1%. This achieves efficient enrichment of arsenic and preliminary separation of impurities in complex arsenic-alkali slag. Thermodynamic analysis and pyrometallurgical condition experiments demonstrate that the precipitate of MgNH4AsO4 can be reduced to elemental arsenic with an arsenic content reaching 99.85%, and an antimony content as low as 0.05%. This achieves a profound separation of arsenic from impurities. Based on the research presented in this paper, a production line was established that enables the deep resource utilization of arsenic-alkali slag.

Repurposing of spent lithium-ion battery separator as a green reductant for efficiently refining the cathode metals

Developing green and high-efficient pyrometallurgy processes to recycle precious metals from spent lithium-ion batteries (LIBs) is of great importance for resource sustainability and environmental protection. Herein, a novel reduction roasting approach relying on spent LIB separator to refine the spent cathode is proposed. The efficiency of repurposing separator as a reductant for roasting the spent LiCoO₂ cathode and the underlying mechanisms were investigated. After the separator-mediated roasting at 500 °C for 2 h, Li⁺ leaching efficiency of the cathode reached 93.2 %, >2.6 times higher than those after roasting without reductant (25.2 %) or with benchmark reductant graphite (26.1 %). Under the separator-added roasting condition, the cathode was converted to the desired products, CoO and Li₂CO₃. Based on the analysis of in-situ reaction using thermogravimetric/differential scanning calorimetry and pyrolysis gas species identification, the separator-mediated reduction roasting of cathode was composed of two stages, i.e., reducing gas generation due to separator pyrolysis, followed by the reducing gas mediated LiCoO₂ reduction. During the process, the generated C₂H₄ and CO dominated the reduction. The use of co-existing separator to recover precious metals from spent LIBs is an effective and sustainable strategy to maximize the utilization of spent LIBs.

Recovery of valuable metals from spent lithium-ion batteries by complexation-assisted ammonia leaching from reductive roasting residue

Recycling valuable metals in spent LIBs is not only in line with the purpose of resource recycling but also an important measure for environmental protection. In this article, a process using biomass reduction roasting followed by a unique complexation-assisted ammonia leaching is proposed. Using waste areca powder (WAP) as a biomass reducing agent, the roasted residue is leached in an aqueous solution for the carbonate. The leaching efficiencies of Ni, Co, and Mn reach over 99% under ammonia leaching conditions of 1.5 M ammonium citrate (AC), 3 M ethylenediamine (EDA). The kinetics of ammonia leaching indicates the activation energies of Ni, Co, and Mn are 51.8 kJ mol^-1, 47.7 kJ mol^-1, and 40.8 kJ mol^-1, respectively, which shows the whole duration is controlled by chemical reactions. Most importantly, this study systematically explores the mechanism of ammonia leaching and provided a useful recommendation for selecting the right ammonium salt.

A promising selective recovery process of valuable metals from spent lithium ion batteries via reduction roasting and ammonia leaching

In this study, a promising process has been developed for selective recovery of valuable metals from spent lithium ion batteries (LIBs). First, reduction roasting which used spent anode powder as reduction agent and water immersion are applied to preferentially recover lithium. Subsequently, an ammonia leaching method is adopted to eff ;ectively separate nickel and cobalt from water immersion residue. Results indicate that Li₂CO₃, (NiO)_m·(MnO)_n, Ni, Co are the ultimate reduction products at 650 °C for 1 h with 5% anode powder. 82.2 % Li is preferentially leached via water immersion after reduction roasting and Li₂CO₃ products are obtained by evaporation crystallization. Thermodynamics shows that reducing ammonia leaching is feasible for water immersion residue. Amounts of 97.7 % Ni and 99.1 % Co can be selectively leached by NH_3·H₂O and (NH₄)₂SO₃ while Mn remain in the residue as (NH₄)₂Mn(SO₃)_2·H₂O, (NH₄)₂Mn(SO₄)_2·6H₂O and (NH₄)₂Mn₂(SO₃)₃ under the optimized conditions. Ammonia leaching kinetic show the activation energy of Ni and Co is 84.44 kJ/mol and 91.73 kJ/mol, which indicate the controlling steps are the chemical reaction. Summarily, the whole process achieves the maximum degree of selective recovery and reduces the environmental pollution caused by the multistep purification.

Microwave-absorbing properties of cathode material during reduction roasting for spent lithium-ion battery recycling

As a hazardous material to the environment and human health, spent lithium-ion batteries need to be recycled in a reasonable way. To explore the effect of microwave heating on spent lithium-ion batteries (LIBs) recycling, the microwave-absorbing properties of a spent cathode powder (LiNi_xCo_yMn_zO₂) were studied by measuring its dielectric properties from 25-900 °C at 2450 MHz under different conditions (temperature, carbon dose and apparent density). X-ray diffraction and thermogravimetric analysis (TGA) were used to study decomposition and reduction reactions in the heating process. The results indicated that the cathode material has good microwave-absorbing properties over the entire temperature range (25-900 °C), especially when mixed with carbon. As the reduction reactions proceed, the dielectric properties of the material increase rapidly from 600 °C, which means that microwave heating can promote a carbothermal reduction reaction. The effect of the carbon dose on the dielectric properties indicates that the carbothermal reduction reaction can fully occur when the carbon dose reaches 18%. Furthermore, the best microwave-absorbing performance can be achieved when the apparent density of the material is 1.41 g/cm³. These studies have established a basis for research towards the direct recovery of lithium from LIBs by microwave reduction roasting.

Improved recovery of valuable metals from spent lithium-ion batteries by efficient reduction roasting and facile acid leaching

A combined process was investigated to recover valuable metals from LiNi_xCo_yMnzO₂ cathode materials of spent lithium-ion batteries. In this approach, the cathode materials were first roasted with graphite which recycled from anode materials, and then conducted to a reductant-free sulfuric acid leaching for efficient recovery of valuable metals. The reduction roasting was meticulously investigated to control the composition of roasted products, and the physicochemical changes of the cathode materials in the reduction thermal treatment was studied by XRD, TGA, XPS, SEM and EDS analyses. The experimental results show that under the optimum processing conditions of 600 °C, 3 h, and mass ratio of cathode materials to anode graphite of 6:1, the mixed electrode materials can be transformed into the desired phase of CoO, NiO, MnO and Li₂CO₃ primarily. Being different from obtaining Co and Ni metallic phase in reduction roasting, producing CoO and NiO benefit to a lower energy consumption, no H₂ emission in the leaching process, and more facile conditions for complete leaching. More than 99% of Ni, Co and Li were extracted, and more than 97% of Mn was leached without adding reductant under the optimum conditions: 1.05 times of theoretical H₂SO₄ consumption, and L/S = 6 ml·g^-1 at 85 °C for 1 h. This promising process can not only make efficient use of waste anode graphite, save energy consumption, but also avoid generation of massive H₂ in the subsequent facile leaching of valuable metals.

Efficient separation of silica and alumina in simulated CFB slag by reduction roasting-alkaline leaching process

Although circulating fluidized bed (CFB) combustion technology is regarded as an efficient technology to use abundant coal gangue as fuel, large amounts of CFB slag has to be stockpiled and raises the environmental stress. This work focused on the comprehensive utilization of silica and alumina in CFB slag. The combustion process of coal gangue and the subsequent separation of alumina and silica by alkaline leaching of the simulated CFB slag were investigated. The results show that, in the combustion process, kaolinite in coal gangue firstly converts into meta-kaolinite at 600-900 °C due to dehydroxylation, and then the meta-kaolinite splits into mullite and amorphous silica at ≥1000 °C. Whereas by reduction roasting with hematite, the CFB slag simulated at 800-1100 °C can be completely converted into hercynite and free silica in forms of quartz solid solution and cristobalite solid solution. However, the conversion reaction rate for the CFB slag simulated at 1200 °C decreases significantly due to the formation of well crystallized mullite prior to the reduction roasting. Additionally, either quartz solid solution or cristobalite solid solution is readily soluble and hercynite is insoluble in alkaline solution. Under optimal conditions, more than 95% of silica in the reduction roasted product can be dissolved in alkaline solution and the mass ratio of alumina to silica in the leached residue can increase from 0.85 to above 20. This study lays a foundation for developing a novel technique to efficiently recycle the carbon, silica and alumina in coal gangue and thus to alleviate the environmental stress.