Connecting Adsorption Mechanisms with Heavy Metal Immobilization in BiocharAmended Contaminated Soils

MEDINA, ROCIO; PARDO, SHEILA DANIELA; BLANCO, ANDRÉS; BARBERO MEDINA, GONZALO PEDRO; GOÑI-URTIAGA, ASIER; PANETTIERI MARCO; WANNAZ, E.D; SALAZAR, MARIA JULIETA

Pisa

Conferencia; 13th conference of SUITMA (Soils of Urban, Industrial, Traffic, Mining and Military Areas); 2025

Biochar (BC), produced through biomass pyrolysis, shows potential for remediatingheavy metal (HM) contaminated soils via immobilization. This study investigated howsoybean straw derived BCs, pyrolyzed at different temperatures (300, 400, and 500°C),influence HM distribution among chemical fractions in a contaminated urban agriculturalsoil (SAC), correlating results with adsorption mechanisms identified in aqueoussolutions. BCs were characterized for specific surface area, zeta potential (pζ), pH, C and Ncontent, thermal stability (TGA), functional groups (FTIR), and crystalline composition(XRD). Adsorption isotherms for Cd, Cu, Pb, and Zn (present in SAC) were performedto determine maximum adsorption capacity. Metal-loaded BCs were analyzed byFTIR/XRD to identify dominant adsorption mechanisms. The SAC, collected near anindustrial waste dump in an urban area in Córdoba, Argentina, was divided into fourtreatments: SAC, SAC+BC300, SAC+BC400, and SAC+BC500. These were incubatedfor one year (darkness, 65% water-holding capacity), with HM fractionation assessedquarterly via Tessier sequential extraction. BCs showed increased surface area, thermal stability, maximum adsorption capacity, Cand N content and pH with higher pyrolysis temperature. The pζ measurements revealednegative surface charges even at pH 2, favoring cation adsorption, with BC400 exhibitingthe highest colloidal stability. Functional groups (-OH, C=O, C=C, C-O, and CH) werestable across temperatures, though some decreased due to lignocellulosic degradation.Calcite and silicates became more evident at higher temperatures, findings also foundby XRD. Post-adsorption analyses showed complexation of all HMs with C=O groups(decreasing with temperature), Zn complexation with aromatic C–H groups (increasingwith temperature), precipitation mediated by calcite of Cd, Cu, and Pb for BC400 andBC500. BC amendment reduced the available fraction of all HMs in SAC, shifting Cu to organicmatter-bound fraction, attributable to stable complexation; Cd and Zn to carbonateassociatedfraction, attributable to calcite-mediated precipitation or pH-sensitivecomplexation; and Pb to both fractions. Temperature-enhanced effects onimmobilization were observed only for Cd and Zn.