Cleaner separation and recovery of valuable metals from spent ternary cathode via carbon dioxide synergetic thermite reduction strategy.

The low-carbon recycling of spent lithium-ion batteries has become crucial due to the increasing need to address resource shortages and environmental concerns. Herein, a low-carbon, facile, and efficient method was developed to separate and recover Li, Al, and transition metals from spent ternary cathodes. Initially, the cathode materials post-discharge and disassembly do not require pre-sorting. Instead of using carbonaceous materials, the Al foil in the cathode serves as the reducing agent during reduction roasting. The impact of different roasting atmospheres (air, N2, CO2) on phase transitions and the extraction of valuable metals was examined. The findings revealed that after synergistic thermite reduction in a carbon dioxide atmosphere, the cathode material is completely dissociated. Li is selectively converted to Li2CO3 rather than LiAlO2, and the reduced reactivity of the Al foil encourages the formation of lower-valence oxides of Ni and Co, rather than their metallic forms. Under optimal roasting conditions at 650 °C for 1.0 h, 91.4% of Li can be preferentially and selectively extracted through carbonation water leaching, with less than 0.1% of Al and transition metals dissolving. Subsequently, ∼98% of Al and ∼99% of Ni, Co, and Mn can be leached using alkaline and acidic solutions, respectively. Compared to the traditional carbon thermal reduction process, this process offers several advantages including the elimination of pre-sorting and additional reducing agents, lower carbon emissions, and higher recovery rates of valuable metals. Thus, this process makes the recovery of metals from spent lithium-ion batteries more environmentally sustainable, simple, cost-effective, and adaptable.

Improved recovery of lithium from spent lithium-ion batteries by reduction roasting and NaHCO3 leaching.

Lithium supply risk is increasing and driving rapid progress in lithium recovery schemes from spent lithium-ion batteries (LIBs). In this study, a facile recycling process consisting mainly of reduction roasting and NaHCO3 leaching was adopted to improve lithium recovery. The Li of spent LiNixCoyMn1-x-yO2 powder were converted to Li2CO3 and LiAlO2 with the reduction effect of C and residual Al in the roasting process. NaHCO3 leaching was utilized to selectively dissolve lithium from Li2CO3 and water-insoluble LiAlO2. The activation energy of NaHCO3 leaching was 9.31 kJ∙mol-1 and the leaching of lithium was a diffusion control reaction. More than 95.19 % lithium was leached and recovered as a Li2CO3 product with a purity of 99.80 %. Thus, this approach provides a green path to selective recovery of lithium with good economics.

Pre-separation combined with reduction roasting for high-quality recovery of graphite and lithium from spent lithium ion batteries.

The recycling of spent lithium ion batteries is of great significance because it contains large amounts of valuable metals. But current recovery methods exhibit limited efficiency in selectively extracting lithium from spent electrode materials and spent graphite becomes metallurgical residues. In this study, we propose a novel recycling flowchart that combines flotation with multi-stage water-leaching to enhance the recovery of graphite and lithium from black mass derived from spent lithium ion batteries. Removal of organics can be conducted by pyrolysis, at the same time, the spent ternary cathode material was decomposed into CoO, NiO, and MnO at a temperature of 600 °C for 60 min using pyrolysis product-derived reductant. The sub-microlevel migration behavior of lithium ions in electrode materials was also examined. The electrode material aggregates were broken up by water crushing, and 38.67 % lithium dissolves into water for recycling. Bubble flotation was used to recycle the excess graphite from the black mass while the residual graphite was used as reductant for the carbothermal reduction. Using the developed scheme, we were able to recover 95.51 % of lithium after carbothermal reduction with 12.31 % carbon residue. Based on basic research, a novel recycling flowchart of spent lithium-ion batteries has been proposed.

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.

Innovative methodology for comprehensive utilization of arsenic-bearing neutralization sludge.

Arsenic-bearing neutralization (ABN) sludge is a classical hazardous waste commonly found in nonferrous metallurgy. However, the current storage of these hazardous wastes not only has to pay costly hazardous waste taxes but also poses significant risks to both the environment and human health. To address these issues and achieve the comprehensive utilization and minimization of ABN sludge, this study proposes a new combined process. The process involves selective reduction roasting, leaching, and carbonation, through which, the arsenate and gypsum in the ABN sludge were recovered in the form of As(s), high-purity CaCO3, and H2S. The selective reduction behaviors of arsenate and gypsum were investigated through thermodynamic analysis and roasting experiments. The results indicated that the 95.35 % arsenate and 96.55 % gypsum in the sludge were selectively reduced to As4(g) and CaS at 950 °C by carbothermic reduction. The As4(g) was condensed to As(s) and enriched in the dust (As, 96.78 wt %). In the leaching process, H2S gas was adopted to promote the leaching of CaS, and resulted in 97.41 % of CaS in the roasted product was selectively leached in the form of Ca(HS)2, leading to a 74.11 % reduction in the weight of the ABN sludge. Then, the Ca(HS)2 was subjected to capture CO2 for the separation of Ca2+ and S2-. The result depicted that 99.69 % of Ca2+ and 99.12 % of S2- were separated as high-purity (99.12 wt %) CaCO3 and H2S (24.89 vol %) by controlling the terminal carbonation pH to below 6.55. The generated H2S can be economically converted to sulfur by the Clause process. The whole process realized the comprehensive resource recovery and the minimization of the sludge, which provides an alternative solution for the clean treatment of hazardous ABN waste.

High-efficiency selective leaching of valuable metals from spent lithium-ion batteries: Effects of Na2S2O8 on the leaching of metals.

A new method was presented for the high-efficiency selective leaching of Li and the efficient recovery of transition metals (TMs) from the cathode materials of spent lithium-ion batteries (spent LIBs). Selective leaching of Li was achieved by carbothermic reduction roasting and leaching with Na2S2O8. After reduction roasting, high-valence TMs were reduced to low-valence metals or metal oxides, and Li was converted to Li2CO3. Then Na2S2O8 solution selectively extracted 94.15% of Li from roasted product with leaching selectivity of more than 99%. At last, TMs were leached with H2SO4 without adding reductant with the leaching efficiency of metals all exceeding 99%. Na2S2O8 added during the leaching process destroyed the agglomerated structure of the roasted product to open the way Li entered the solution. Under the oxidative environment of Na2S2O8 solution, TMs would not be extracted. At the same time, it helped to regulate the phase of TMs and improved the extraction of TMs. Furthermore, the phase transformation mechanism of roasting and leaching was discussed through thermodynamic analysis, XRD, XPS, and SEM-EDS. This process not only realized the selectively comprehensive recycling of valuable metals in spent LIBs cathode materials; but also followed the principle of green chemistry.

Recovery of zinc and extraction of calcium and sulfur from zinc-rich gypsum residue by selective reduction roasting combined with hydrolysis.

A novel process that includes selective reduction roasting followed by hydrolysis was proposed in this work to recover zinc, and efficiently extract calcium and sulfur from hazardous zinc-rich gypsum residue (ZGR) waste for high-purity of CaCO3 and sulfur production. The selective reduction behaviors of ZGR during the reduction roasting were investigated in detail based on thermodynamic analysis and roasting experiments. The effect of roasting temperature, carbon dosage and time on the selective reduction of ZGR was comprehensively investigated, and the results indicated that ZnO and CaSO4 in the ZGR can be selectively reduced to Zn(g) and CaS, respectively. The volatile Zn(g) was oxidized to ZnO and enriched in the dust, which can be used as a secondary zinc resource. Moreover, the hydrolysis behaviors and leaching kinetic of CaS during hydrolysis were studied intensively. Results depicted that in the H2S-H2O system, the CaS in the roasted product can be selectively and efficiently dissolved into the leachate. Furthermore, the kinetic analysis revealed that the hydrolysis of CaS conformed to the internal diffusion reaction control model in the shrinking core model and the apparent activation energy Ea = -12.02 kJ/mol. The obtained hydrolysate with low impurities could be used to capture CO2 for the production of high-purity sulfur and CaCO3. Iron and other impurities in the roasted product were concentrated into the leaching slag in the form of metallic iron and akermanite. The whole process realized the recovery of zinc, and the selective and effective extraction of calcium and sulfur, which could provide an alternative process for the large-scale treatment of these hazardous wastes.

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 NH3·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 (LiNixCoyMnzO2) 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 LiNixCoyMnzO2 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.