Materiais adsorventes obtidos da biomassa de Ingá-cipó (Inga edulis): remoção de metais pesados e avaliação ecotoxicológica

Abstract

Water contamination by toxic metals, especially hexavalent chromium Cr(VI) and divalent lead Pb(II), represents a significant environmental challenge due to their persistence and harmful effects on aquatic organisms. In this study, two adsorbent materials derived from the biomass of Inga edulis bark were developed and evaluated: raw biomass (BMIG) and sulfuric acid–activated biomass (BMIGA). The materials were characterized using physicochemical techniques, which confirmed structural modifications and the presence of functional groups capable of interacting with the studied metals. Batch adsorption experiments enabled the identification of favorable operational conditions and showed that BMIGA exhibited maximum adsorption capacities of 356.6 and 222.1 mg g-1 for Cr(VI) and Pb(II) ions, respectively, compared to BMIG, which presented an adsorption capacity of 46.0 mg g-1 for Cr(VI) and showed no removal of Pb(II) ions. Chemical activation resulted in an increase in surface area and the introduction of oxygenated functional groups, which enhanced the adsorption of both metal ions. Kinetic models indicated that Cr(VI) adsorption by BMIG and BMIGA followed the Elovich model, characterizing a chemisorption process on a heterogeneous surface. For BMIGA and Pb(II), the best fit was obtained with the pseudo-second-order model, suggesting interaction with oxygenated functional groups. In isotherm studies, Cr(VI) adsorption fitted both the Langmuir and Freundlich models, whereas Pb(II) showed a better fit to the Freundlich model. Thermodynamic analyses demonstrated that Cr(VI) adsorption by BMIG was non-spontaneous, while BMIGA promoted spontaneous adsorption for both metals. Under continuous-flow conditions, fixed-bed columns exhibited stable performance, with breakthrough times of 200.0 min and 281.7 min for Cr(VI) adsorption and 554.8 min for Pb(II) adsorption at low concentrations, which were compatible with practical applications and showed good agreement with the Thomas, Yoon–Nelson, and Clark models. The ecotoxicological assessment performed with Daphnia similis confirmed the high toxicity of solutions containing Cr(VI) and Pb(II) ions prior to treatment. After adsorption, no acute effects were observed on the organisms, demonstrating that the materials were able to significantly reduce toxicity. Finally, the saturated adsorbents were applied in electrochemical tests for green hydrogen and oxygen production, revealing potential for reuse and value addition after environmental application. Overall, the results demonstrate that Inga edulis bark is a promising biomass for the production of sustainable and efficient adsorbents with multifunctional potential, contributing to pollution mitigation strategies and technologies associated with the circular economy.