The Use of Aminated Yerba Mate Biomass for the Removal of Anionic Dyes from Aqueous Solutions

In line with circular economy principles, raw spent yerba mate (Ilex paraguariensis) waste (YMs) was transformed into a high-value aminated adsorbent (AYMs) for the removal of anionic dyes, namely Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84). The modification involved a two-step process using epichlorohydrin and aqueous ammonia, and the adsorbents were characterized via FTIR, BET, C/N elemental analysis, and pH_PZC. Batch experiments evaluated pH effects, kinetics (PFO, PSO, and intraparticle diffusion), and equilibrium isotherm analysis (single- and dual-site Langmuir models and Freundlich models). The results confirmed successful functionalization of the biomass with amino groups, shifting the point of zero charge (pH_PZC) from 4.74 (YMs) to 8.73 (AYMs). The optimal adsorption pH was 2.0 for YMs and 3.0 for AYMs. Kinetic data were best described by the pseudo-second-order model, while equilibrium data followed the dual-site Langmuir model, indicating energetic heterogeneity of the AYMs surface. The maximum adsorption capacity of AYMs reached 62.81 mg·g^-1 for RB5 and 61.78 mg·g^-1 for RY84, representing a fivefold and threefold increase over the YMs, respectively. These findings demonstrate that AYMs is a high-performance, sustainable alternative to commercial activated carbons, providing a scalable waste-to-value solution for industrial effluent treatment.