Sherry wine industry by-product as potential biosorbent for the removal of Cr(VI) from aqueous medium

Abstract

A low-cost biosorbent obtained from the Palomino Fino grape seed, a Sherry wine industry by-product, has been proposed as a way of valorising this material. The biomass was characterised obtaining values of 0.68 +/- 0.05 g mL(-1) for bulk density, 1.02 +/- 0.09 g mL(-1) for apparent density and 33.3% for porosity. The pH(pzc) was 5.2 and the surface negative charge value was 2.4 +/- 0.2 mmol g(-1). The analysis of surface morphology showed differences due to the sorption. The results showed a promising potential for chromium(VI) removal from aqueous solutions. The studies were carried out in batch scale and a 2(3) factorial design was applied for the optimisation of the process. A percentage of 91.7 +/- 0.6% was achieved for the biosorption of Cr(VI) under optimal conditions using pH 5.5, 15 g/L of biosorbent and 8 h of contact time. The biosorption capacity showed a remarkable linearity from 0 to 2 mmol L-1 Cr(VI) and a precision of 0.64% for the removal of 1 mmol L-1 of metal. Langmuir, Freundlich and Temkin isotherm equations and the parameters of six kinetic models were used in the equilibrium modelling and identifying the mechanism of the biosorption. The combination of physical and chemical sorption mechanisms was proposed for the chromium removal with a high maximum sorption capacity (q(max) = 208.3 mg g(-1)). Thermodynamic parameters indicated the spontaneous and endothermic nature of the chromium removal. The successful biosorption was based on the special grape seed components with a relevant content in antioxidant and lignocellulosic compounds.