Valorization of grape seed residues post-oil extraction as an adsorbent for hexavalent chromium in water. Kinetics, isotherms, thermodynamics, and techno-economic analysis

The objective of the present research was to valorize grape seed residues post-oil extraction (GSR-POE) obtained by pressing as a potential adsorbent of Cr (VI) from simulated aqueous solutions. For this, we first compared the removal of Cr (VI) by grape seeds (GS) and GSR-POE, obtaining that GSR-POE achieves higher removal efficiency than GS. Subsequently, it was determined that, with a particle size of 75 μm of GSR-POE and pH=2, the adsorption efficiency of Cr (VI) was favored, achieving the removal of 68.76 % of a simulated aqueous solution of Cr (VI) of 100 mg/L with a GSR-POE dosage of 0.8 g/L. The kinetic study showed that the GSR-POE adsorption process best fitted the pseudo-second order model, likewise, the Langmuir isotherm best described the process resulting in a maximum adsorption capacity of 169.48 mg/g. The thermodynamic study showed that the process is endothermic and spontaneous. The mechanisms involved in the adsorption process would be chemisorption and electrostatic attraction as there is a higher adsorption at pH=2 which is lower than the point of zero charge of GSR-POE (pH_PZC= 4.95). Finally, a techno-economic analysis confirmed the economic viability and profitability of implementing a plant for GSR-POE production. In conclusion, under the conditions of this study, GSR-POE is a cost-effective and efficient adsorbent for Cr (VI) adsorption.