Eco-friendly, renewable Crambe abyssinica Hochst-based adsorbents remove high quantities of Zn²⁺ in water

Although not considered poisonous and with natural occurrence, Zn contamination is mainly related to anthropic actions. This research aim was to develop, from crambe wastes, adsorbents with high adsorption capacity of Zn²⁺. The crambe biomass was modified with H₂O₂, H₂SO₄ and NaOH 0.1 mol L^-1, resulting in four crambe-based adsorbents: C. in natura (unmodified), C. H₂O₂, C. H₂SO₄ and C. NaOH. These were studied by determination of their chemical components, SEM, FTIR, pH_PZC, thermal stability (by TG/DTG curves), SSA, pore volume and pore diameter (by BET and BJH). Adsorption studies were also carried out to evaluate its Zn removal capacity. Evaluations were taken on adsorbent dose and the influence of the pH, as well as studies on adsorption kinetics and equilibrium. These results were evaluated by pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion, Langmuir, Freundlich, Dubinin-Radushkevich and Sips (linear and nonlinear models). Results show that the crambe-based adsorbents may have functional groups such as hydroxyls, amides, carbonyls and carboxylates, which may be responsible for the Zn²⁺adsorption. The materials have heterogeneous structure, allowing the occurrence of mono and multilayer adsorption of Zn. The finest results point out the occurrence of mono and multilayer of Zn²⁺ (evidenced by Sips-nonlinear model), with an increase in Q_sat of 72% (C. H₂O₂), 22% (C. H₂SO₄) and 80% (C. NaOH). The developed crambe adsorbents have low cost of production (since the raw material is until now a solid waste) and have high removal ratio of Zn²⁺ from waters, being a promising technology.