Green grape marc biosorbents preparation for mercury removal in aqueous media

In this study, grape marc waste from Negroamaro (a South of Italy vine variety) winery production, were used for the preparation of biosorbents for Hg(II) removal in aqueous media. A green approach was used to develop a proper biosorbent through two different grape marc washing procedures. In particular, the common chloridric acid and the greener citric acid, were evaluated. Comparing the adsorption results, the biosorbent prepared using citric acid as washing agent (GM-CA) gave similar results to the biosorbent washed with HCl (GM-HCl) with a maximum adsorption capacity of 36.39 mg g-1. Isothermal studies revealed a heterogeneous physical adsorption of Hg(II) on the biosorbents. Moreover, FTIR analysis of the grape marc-based biosorbent without and with Hg(II), confirmed ionic interactions in the biosorbent that fit with a pseudo-second order kinetic model. No significant adsorption on the biosorbent was observed when two other heavy metals, copper(II) and nickel(II), previously studied for similar sorbents, were considered. Finally, reusability of GM-CA biosorbent was also demonstrated over three cycles. Thus, the green preparation approach used in this work can be considered suitable for development of grape marc-based biosorbents.