Amilton Barbosa Botelho Junior

Integrating sustainable development into higher education is agreed to be urgent; however, the means to do so remains an open question. While projects focused on social-environmental problems allow students to engage in local challenges, inquiry-based learning leads students to investigate technically feasible solutions. This paper describes the BananaGas Project, an inquiry-based learning project in which Chemical Engineering students addressed waste management and energy limitations in Iquitos, Peru. The goal of the project was to apply physicochemical concepts in a local scenario by designing and operating chemical bioreactors for organic waste valorization. Banana peels were used as biomass because they represent a significant local waste stream with potential for biogas production. Comparative analysis of a diagnostic test and formative assessment through technical reports showed students’ learning progression during the project. The students also successfully connected the project development and results with Sustainable Development Goals (SDGs). Detection of higher AI use to prepare reports (>35%) was associated with generic discussions and low integration with experimental data. Overall, the BananaGas Project demonstrated how locally relevant engineering problems can be used to develop technical and investigative skills toward an environmental and social sense of sustainability in undergraduate chemistry education.

Global energy transition is driving the search for alternative, sustainable methods for producing critical minerals. This study evaluates thermal treatments of columbite, followed by organic acid leaching to recover Nb and Ta. Hydrometallurgical processes currently use HF combined with other inorganic acids for columbite leaching, and here, the use of oxalic acid after sulfation. Our analysis considers KHSO₄ a better technical alternative than H₂SO₄, achieving 90% leaching efficiency. Leaching of Nb and Ta by oxalic acid (H₂C₂O₄) after thermal treatment is possible due to the formation of stable metal-oxalate complexes, avoiding risks (operational and occupational health) of handling HF leaching. Leaching efficiencies reached 92.8% for Nb (3.48g/L) and 88.4% for Ta (0.45g/L) at a L/S ratio of 3 (columbite/KHSO₄) at 650 °C for 3 h, followed by leaching with 1.0 mol/L H₂C₂O₄ at a L/S ratio of 10 at 90 °C for 8 h. However, a preliminary economic analysis indicated that the proposed process is currently not economically feasible, mostly due to the cost of organic acid.

The demand for critical raw materials is increasing for energy transition

Rare earth elements (REEs) hold great importance in the transition to a low-carbon economy. However, their increased exploitation, supply risks, low recyclability, and limited substitution by other elements have led to their classification as critical and strategic materials. The extraction of REEs from primary mining sources generates several negative environmental impacts, with greenhouse gas emissions being among the most significant. These emissions are quantified through Life Cycle Assessment (LCA) under the Global Warming Potential (GWP) category. Recycling REEs from secondary sources has emerged as a promising alternative to reduce mining dependence and environmental impacts. Nickel–metal hydride (NiMH) batteries contain approximately 5–10% REEs and represent a potential secondary source through urban mining. Our literature review presents a comparative analysis of the carbon footprint associated with the extraction of REEs from primary sources (bastnäsite and monazite), expressed per tonne of rare earth oxides (REO) produced, and with industrial-scale recycling processes of NiMH batteries, expressed per tonne of recovered REE mixture. The analysis indicates that CO₂ emissions associated with recycling processes (85–179 kg CO₂-eq per tonne of REO) are approximately 4 to 9 times higher than those reported for primary extraction routes; however, this comparison should be interpreted with cautiously, as recycling systems are multifunctional and involve the simultaneous recovery of additional metals such as Ni and Co, whereas primary mining operations are typically focused exclusively on REEs. Furthermore, differences in functional units, energy mixes, and geographical contexts limit the strict comparability of the results. Accordingly, a direct comparison based solely on REEs may overestimate the environmental burden of recycling. Consequently, the reported emission ranges provide an indicative perspective on relative magnitudes under current technological and regional conditions rather than a definitive comparative assessment. Despite the higher reported emissions, recycling should not be regarded as environmentally detrimental; it also plays a vital role in mitigating supply risks and reducing dependence on primary extraction. By diversifying supply sources, recycling enhances resource security and resilience.

Batteries with LiFePO₄ as active material stand out due to the absence of critical materials, such as nickel and cobalt, thermal stability, and security. In the next years, high volumes of LFP batteries will reach their end of life, and overall material recovery will contribute to meeting the Li demand and reducing the CO₂ footprint. Recovery of 97% of plastics and 85.3% graphite prevented materials from burning in furnaces and reduced the CO₂ footprint from recycling. Leaching cathode active material using H₂SO₄ without H₂O₂ resulted in active material leaching with reduced metallic foil solubilization and less reagent consumption. Redirecting H₂O₂ consumption to Fe removal by precipitation, combined with ion exchange columns at 25 °C, successfully deepened Fe purification from solution. Precipitation of Al recovered 15.3% as an Al­(OH)₃ coproduct. After evaporation in a real solution, 72.2% of Li was precipitated as Li₂CO₃, contributing to increasing the recycling share in the Li supply.

The increasing demand for rare earth elements has driven the search for efficient and sustainable recovery methods. Obsolete fluorescent lamps represent a significant secondary source of Y that can greatly contribute to the circular economy and the preservation of natural resources. With the gradual depletion of primary Y reserves and the rise in e-waste generation, the development of eco-friendly and economically feasible recovery techniques has become crucial. Additionally, strict legislation regarding the disposal of e-waste strengthens the need to improve recycling processes. This study aims to investigate the leaching of Y from obsolete fluorescent lamps by organic (C₆H₈O₇, C₂H₄O₂, and C₂H₅NO₂) and inorganic acids (HNO₃). We also seek to assess the environmental impact of this process through life cycle assessment (LCA). Leaching steps were performed with different acid concentrations, followed by selective precipitation with C₂H₂O₄ for Y recovery. LCA was applied to evaluate the environmental impacts and identify critical points in the process. A high Y recovery rate (78.8% for C₂H₅NO₂, 86.7% for C₆H₈O₇, 100% for C₂H₄O₂, and 95% for HNO₃) was obtained with precipitation (C₂H₅NO₂ and C₆H₈O₇ liquor). Our environmental assessment revealed that leaching with organic acids presents a higher environmental impact due to production and disposal methods. The study demonstrated that it is possible to leach Y efficiently from fluorescent lamps using organic acids. The process may be a feasible alternative for large-scale Y recovery, improving organic acid production, and contributing to the sustainable recycling of e-waste and promoting the circular economy.