Journal Article
Investigation of Adsorption Mechanisms in Competitive and Non-Competitive Systems: Cadmium Immobilization in Contaminated Calcareous Soil Amended with Bone-Derived Biochar
Sobhan Mohamadi; Ghasem Rahimi; Abolfazl Khademi-Jolgeh Nezhad; M. Mirari Antxustegi; María Gonzalez-Alriols
Water, Air, & Soil Pollution · Vol. 237, Issue 18 · 2026
Abstract
Biochar (BC) has emerged as a promising soil amendment for reducing the bioavailability and toxicity of heavy metals such as cadmium (Cd) in contaminated soils. This study investigates the effectiveness of cow bone-derived biochar (CBBC), produced by pyrolysis at 550 °C, and ZnCl₂-activated biochar (A-CBBC) for Cd immobilisation in calcareous soils. Comprehensive characterisation of CBBC and raw bone powder (BP) was performed using elemental analysis, X-ray fluorescence (XRF), Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. Cadmium mobility was assessed through sequential fractionation and adsorption isotherm experiments under both competitive and non-competitive conditions. The results showed a reduction of approximately 10% in the exchangeable Cd fraction and the mobility factor (MF) in soils amended with 5–7% CBBC after six months of incubation. Adsorption isotherms indicated that soluble Cd concentrations were approximately twice as high under competitive conditions than under non-competitive conditions. Cadmium concentrations in untreated soils were 2.7-fold higher than those in soils amended with CBBC and BP. Relative to the control, CBBC and BP increased Cd adsorption by approximately 300 and 140 µmol kg⁻1, respectively. The observed reductions in Cd mobility are consistent with enhanced sorption associated with cation exchange and surface complexation, although these mechanisms are inferred from adsorption behaviour and fractionation data, not directly verified by spectroscopic analysis. Overall, the findings highlight the potential of CBBC and BP as effective amendments for reducing Cd mobility in calcareous soils and support their application as sustainable remediation strategies for heavy-metal-contaminated alkaline environments.