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Rare earth elements (REEs), comprising seventeen metallic elements, including lanthanides, scandium, and yttrium, are indispensable for modern technological industries due to their unique properties. However, their supply is critically risky for the European Union, with 95% of global production concentrated in China, Brazil, Vietnam, Russia, India, and Australia. This mini-review examines the adsorption of REEs onto pyrolytic carbon-based materials as a sustainable recovery method from secondary raw materials. The review covers different types of carbon-based adsorbents used in several research works, such as activated carbon, chars, and biochar, and discusses their adsorption mechanisms and influencing factors. Comparative analyses of adsorption capacities highlight the significance of surface area and functionalization in enhancing adsorption efficiency. Despite promising results, the variability in adsorption performance due to experimental conditions and the scarcity of real-world application studies are noticed. This review underscores the need for further research using real e-waste leachates to validate the practical applicability of pyrolytic carbon-based adsorbents for REEs' recovery, aiming for an economically and environmentally sustainable solution. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chars from the pyrolysis of mixtures composed by pine, plastics, and scrap tires. [•] Removal of Pb2+ from aqueous medium using chars. [•] Char from mixture of the three raw materials with worst Pb2+ removal performance. [•] Char from mixture composed by tires and plastics more efficient in Pb2+ adsorption. [•] Chemisorption with Ca2+, K+, and Zn2+ exchange on Pb2+ removal by tire derived char. [ABSTRACT FROM AUTHOR]

Pyrolysis chars derived from rice wastes were chemically activated and used in W(VI) oxyanion adsorption assays in synthetic and mining wastewaters. For comparison purposes, a commercial activated carbon (CAC) was also used. Different experimental conditions were tested in the adsorption assays: solid/liquid ratio (S/L), initial pH, contact time, and initial W concentration. The porous carbon P2C+KOH presented the overall best performance in both media, due to its high surface area (2610 m2 g−1), mesopore volume (1.14 cm3 g−1), and neutral pH pzc (6.92). In the synthetic wastewater, the highest uptake capacity of P2C+KOH (854 mg g−1) was found in the assays with an S/L 0.1 g L−1, an initial pH 2, and an initial W concentration of 150 mg L−1, for 24 h. This value was almost 8 times higher than the one obtained for CAC (113 mg g−1). In the mining wastewater, P2C+KOH showed an even higher uptake capacity (1561 mg g−1) in the assay with the same experimental conditions, which was almost 3 times higher than for CAC (561 mg g−1). These results suggest that P2C+KOH seems to be an efficient alternative to CAC in the W(VI) adsorption from liquid effluents. [Display omitted] • Porous carbons derived from rice wastes used in W(VI) adsorption assays. • Higher pH pzc , surface area and mesopore volume promoted the best adsorbents. • Best adsorption performances achieved in acidic aqueous solutions. • Uptake capacities up to 854 mg g−1 attained in a synthetic solution. • Uptake capacities up to 1561 mg g−1 achieved in a mining wastewater. [ABSTRACT FROM AUTHOR]

Chromium is one of the most important raw materials for the European Union. Adsorption has become an important process for the recovery of metals from wastewaters, which has led to a demand for low-cost and eco-friendly adsorbents. The objective of this work was to use new and renewable carbon-based adsorbents from rice wastes in the removal/recovery of Cr(III) from synthetic and real wastewaters. Rice wastes were submitted to co-pyrolysis and the resulting char was optimized through physical and/or chemical activations/treatments. A commercial activated carbon was used for comparison purposes. All adsorbents were characterized (including an ecotoxicity test for the char precursor) and submitted to Cr(III) removal assays from a synthetic solution, in which two solid/liquid ratios (S/L) were tested (5 and 10 g/L). The CO 2 activated carbon at a S/L = 5 g/L was the biomass-derived adsorbent that performed better, obtaining a maximum Cr(III) uptake capacity of 9.23 mg/g comparable to the one obtained by the commercial adsorbent at the same S/L (9.80 mg/g). The good results on this biomass-derived carbon were due to the effective volatile matter removal during the activation (from 22.7 to 4.25% w/w), which increased both surface area (from <5.0 to 325 m2/g) and ash content (from 30.0 to 40.4% w/w), allowing an increase in Cr(III) removal due to ion exchange mechanism and porosity development. The best adsorbent, under optimized conditions, was also applied to a chromium rich industrial wastewater. The results obtained in this real case application demonstrated a competition effect due to the presence of other ions. Image 1 • Pyrolysis rice waste char was optimized through different activations/treatments. • The activated carbons (AC) were characterized and used in Cr(III) removal assays. • Physical activation without washing originated the best pyrolysis AC (P1C+PA). • P1C+PA presented similar Cr(III) uptake capacities than a commercial AC. • P1C+PA performed better in an industrial wastewater than in a synthetic solution. [ABSTRACT FROM AUTHOR]