Comprehensive characterization of viticultural biomass and its derived biochars: insights into copper sorption...

The extensive use of copper (Cu) in viticulture has resulted in its high accumulation in soils, threatening ecosystems and soil health. Biochar, widely recognized for its potential in remediating metal-contaminated environments, offers promising sorption properties that strongly rely on both feedstock composition and the final biochar's characteristics. This study investigates five biochars produced from different vineyard by-products; grape marc (BM), grape seed (BS), exhausted grape seed (BES), pruning (BP1), and pruning subjected to double pyrolysis (BP2). These biochars were comprehensively characterized in terms of physicochemical and structural properties, elemental composition, and potential toxicity. The maximum copper sorption capacities of the biochars ranged from Q_max of 39.35 to 134.36 mg Cu²⁺g^-1, depending on their properties, and followed the Langmuir isotherm and pseudo-second-order (PSO) kinetic models (for BM). Fourier-transform infrared spectroscopy (FT-IR) confirmed the presence of surface functional groups such as -OH, -COOH, and aromatic structures. Zeta potential (ZP) analysis indicated a predominantly negative surface charge across a wide pH range. Copper sorption was primarily attributed to π-cation interaction and precipitation mechanisms, while copper desorption assays revealed limited copper release, suggesting strong retention. Scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDS), was used to analyze the morphology of the biochar and to verify copper incorporation in the Cu-loaded samples. Given the strong influence of feedstock on metal sorption efficiency, vineyard by-products were characterized by thermogravimetric analysis (TGA), FT-IR, and determination of lignocellulosic composition and physicochemical properties. Biochar from vineyard by-products, particularly grape marc (BM), demonstrated the highest potential, highlighting the valorization of vineyard by-products as a sustainable in situ remediation strategy in vineyard soils, in line with circular economy principles.