Intelligent leaching rare earth elements from waste fluorescent lamps.

Rare earth elements (REEs), one of the global key strategic resources, are widely applied in electronic information and national defense, etc. The sharply increasing demand for REEs leads to their overexploitation and environmental pollution. Recycling REEs from their second resources such as waste fluorescent lamps (WFLs) is a win-win strategy for REEs resource utilization and environmental production. Pyrometallurgy pretreatment combined with acid leaching is proven as an efficient approach to recycling REEs from WFLs. Unfortunately, due to the uncontrollable components of wastes, many trials were required to obtain the optimal parameters, leading to a high cost of recovery and new environmental risks. This study applied machine learning (ML) to build models for assisting the leaching of six REEs (Tb, Y, Eu, La, and Gd) from WFLs, only needing the measurement of particle size and composition of the waste feed. The feature importance analysis of 40 input features demonstrated that the particle size, Mg, Al, Fe, Sr, Ca, Ba, and Sb content in the waste feed, the pyrometallurgical and leaching parameters have important effects on REEs leaching. Furthermore, their influence rules on different REEs leaching were revealed. Finally, some verification experiments were also conducted to demonstrate the reliability and practicality of the model. This study can quickly get the optimal parameters and leaching efficiency for REEs without extensive optimization experiments, which significantly reduces the recovery cost and environmental risks. Our work carves a path for the intelligent recycling of strategic REEs from waste.

Utilizing E-Waste for Construction of Magnetic and Core-Shell Z-Scheme Photocatalysts: An Effective Approach to E-Waste Recycling.

The increasingly large stream of e-waste is seriously threatening the environment; meanwhile, global energy shortage is on the rise. Based on the principles of energy regeneration and waste utilization, we introduced a win-win approach to utilize waste capacitors for construction of magnetic and core-shell Z-scheme Nb-Pb-codoped BaTiO3/Ni-Pd@graphite-like carbon nitride (g-C3N4) photocatalysts for H2 evolution. Using simple ball-milling, waste capacitors were transformed to Nb-Pb-codoped BaTiO3/Ni-Pd-Ag-Sn nanoparticles and g-C3N4 was coated on the nanoparticles, forming a core-shell structure. The Ni-Pd acted as the electron mediator in the Z-scheme, and Ag-Sn also facilitated the electron transfer. Moreover, Ni made the Z-scheme magnetically separable. The Z-scheme showed a remarkably enhanced photocatalytic H2 evolution rate, which was 22.2 times higher than that of g-C3N4. Such an enhanced photocatalytic performance was attributed to the special Z-scheme and core-shell structure, improving the light adsorption, increasing the Brunauer-Emmett-Teller (BET) surface area, facilitating the efficient separation of electron-hole pairs, and maintaining the strong redox ability of charge carriers. Furthermore, the photoluminescence analysis combined with density functional theory (DFT) calculations provided the basis for the Z-scheme mechanism. This study adequately utilized the composition of e-waste to construct a highly efficient and magnetically separable Z-scheme for H2 generation, which realizes energy regeneration, waste recycling, and environmental protection.

Physicochemical reactions in e-waste recycling.

Electronic waste (e-waste) recycling is becoming a global concern owing to its immense quantity, hazardous character and the potential loss of valuable metals. The many processes involved in e-waste recycling stem from a mixture of physicochemical reactions, and understanding the principles of these reactions can lead to more efficient recycling methods. In this Review, we discuss the principles behind photochemistry, thermochemistry, mechanochemistry, electrochemistry and sonochemistry for metal recovery, polymer decomposition and pollutant elimination from e-waste. We also discuss how these processes induce or improve reaction rates, selectivity and controllability of e-waste recycling based on thermodynamics and kinetics, free radicals, chemical bond energy, electrical potential regulation and more. Lastly, key factors, limitations and suggestions for improvements of these physicochemical reactions for e-waste recycling are highlighted, wherein we also indicate possible research directions for the future.