Cu2+, Cr3+, and Ni2+ in mono- and multi-component aqueous solution adsorbed in passion fruit peels in natura and physicochemically modified: a comparative approach

Among the low-cost adsorbent are agricultural residues, which can be used in natura or modified forms. This work evaluated the adsorption of Ni²⁺, Cu²⁺, and Cr³⁺ in mono- and multi-component aqueous solutions using passion fruit peels in natura (Nat-PF) and physicochemically modified (Mod-PF). The adsorption was investigated by kinetic and isotherm models. A comparative investigation was conducted to analyze the effect of the experimental conditions by statistical test, adsorption capacity ratio, selectivity of adsorbate, and distribution coefficient. In both adsorbents, the process occurs in monolayer by chemosorption. Equilibrium was reached after 30 min, with highest adsorption capacity for Cu²⁺ as 0.495 mg g^-1, for Cr³⁺ as 0.483 mg g^-1, and for Ni²⁺ as 0.464 mg g^-1. The adsorption in Mod-PF was less affected in multi-component solutions, reducing the adsorption capacity by 0.06-0.15 times when compared to monocomponent solutions, while in Nat-PF a reduction of more than half of adsorption capacity was obtained. The modifications imposed on the biomass led to a change in its adsorptive selective, being Cr³⁺  > Cu²⁺  > Ni²⁺ for Nat-PF and Cu²⁺  > Ni²⁺  > Cr³⁺ for Mod-PF.

Activated carbons from passion fruit shells in adsorption of multimetal wastewater

This work aims to use a solid agro-industrial residue (passion fruit shells-PF) to manufacture different activated carbons (ACs) capable to retain Cr³⁺, Cu²⁺, and Ni²⁺ on synthetic wastewater. The PF was carbonized and chemically activated with three precursors, giving rise to three ACs: phosphoric acid ([Formula: see text]), sodium acetate ([Formula: see text]), and potassium hydroxide (AC_KOH). The ACs were characterized by SEM, ASAP, FTIR, and pH-PZC. The adsorption phenomena were studied by kinetic and isotherm models. The efficiency of the process was investigated in mono- and multimetallic solution with two-way ANOVA and Tukey test at 95% confidence interval. The physical-chemical modifications in the solid increased the surface area, the porosity, and the heterogeneity. The phenomena had a better fit to the pseudo-second-order kinetic model and to the Freundlich isotherm model. Analyzing the interaction between the ACs and the composition of the solutions, the selectivity of the solid and the competition for activated sites were verified. Efficiencies higher than 95% were obtained for Ni²⁺, 80% for Cu²⁺, and 70% for Cr³⁺. The viability of the process in mono- and multimetallic solutions opens the possibility of integrated management of metallic wastewater and agro-industrial residues.