Biosorption of Cr(III) from solutions using vineyard pruning waste

The kinetics and biosorption mechanism of Cr(III) ions on vineyard pruning waste (VPW) have been studied using different parameters such as initial concentration, biosorbent dosage, temperature, contact time and solution pH. The results indicated that adsorption was pH-dependent and temperature-dependent. VPW exhibited the highest Cr(III) uptake capacity of 12.453 mg g−1 at 303 K and at an initial pH value of 4.2. The kinetic data for the VPW samples support the pseudo-second-order model (R2 > 0.99), but the first-order kinetic model (R2 < 0.89) and intra-particle model (R2 < 0.88) did not adequately correspond to the experimental values. The equilibrium adsorption data were interpreted using Langmuir and Freundlich models, and the adsorption of Cr(III) on VPW was better represented by the Langmuir equation (R2 > 0.990) than Freundlich (R2 < 0.980). In addition, thermodynamic parameters such as ΔG*, ΔH* and ΔS* were found out to be 72.71, −18.77 kJ/mol and −301.93 J/mol K, respectively. The negative value of ΔH* (−18.77 kJ/mol) showed that the biosorption of Cr(III) on VPW is exothermic. VPW has been characterized by FT-IR, scanning electron microscopy (SEM), BET surface area and energy dispersive X-rays (EDXs). The results have confirmed the applicability of this the VPW as an efficient biosorbent for Cr(III) ions.