Comparative analysis of the adsorption behavior and Freeze–Thaw modification effects of different biomass materials on Cd(II)

• Four biomass materials (Bio, Ftbio, Reed, and Peat) were systematically compared for Cd(II) adsorption and plant uptake. • Freeze–thaw modification enhanced micropore volume and improved adsorption stability of Ftbio. • Structural and chemical mechanisms were clarified (CdCO 3 precipitation vs. amorphous complexation). • Integration of adsorption and plant experiments revealed distinct Cd uptake and translocation patterns. Freeze–thaw phenomena in cold-region soils may increase Cd mobility and plant uptake, yet comparative studies that link amendment microstructure, adsorption mechanisms, and plant responses, especially those including freeze–thaw-modified biochar, remain relatively scarce. Purpose: This study aims to investigate the adsorption properties and freeze–thaw modification effects of various biomass materials on Cd(II). Materials and Methods: Four biomass materials—corn cob biochar (Bio), freeze–thaw–modified corn cob biochar (Ftbio), reed biochar (Reed), and peat (Peat)—were selected and systematically analyzed for their structural properties, adsorption kinetics, and thermodynamic behaviors. The structural characteristics, adsorption kinetics, and thermodynamic behaviors of the four materials were systematically characterized, and their effects on Cd(II) enrichment and transport in Brassica napus were verified through pot experiments. Results and Discussion: Experimental results demonstrated that all materials exhibited mesoporous structural characteristics. The specific surface area and micropore volume of Ftbio were significantly enhanced after freeze–thaw modification, indicating an improvement in structural stability. The adsorption process followed a pseudo–second–order kinetic model and was dominated by chemisorption, with Peat and Reed exhibiting higher adsorption capacities and affinities compared to the other materials. Fourier transform infrared spectrometer (FTIR) and X–ray diffractometer (XRD) analyses revealed differences in the adsorption mechanisms among the materials. Ftbio and Reed facilitated the formation of CdCO 3 crystals, whereas Peat predominantly underwent amorphous complexation. Results from the pot experiments indicated that Peat promoted plant growth and inhibited Cd(II) enrichment, whereas Ftbio maintained high adsorption efficacy while alleviating freeze–thaw stress. Conclusions: This study demonstrated that Peat and freeze–thaw–modified Ftbio have significant potential for the remediation of heavy metal–contaminated soils, making them suitable for plant–friendly phytostabilization (promoting plant growth while suppressing Cd(II) uptake) and freeze–thaw-resilient immobilization (maintaining high adsorption efficacy under freeze–thaw conditions), respectively. Reed reduced enrichment but showed higher translocation and therefore requires caution.