Immobilization of Cd(II) by phosphorus-modified bamboo biochar from solution: mechanistic study from qualitative to quantitative analysis

Abstract

Bamboo-derived biochar has shown unique advantages in heavy metals immobilization due to its vascular bundles and high cellulose content. Phosphorus modification has emerged as an effective way to enhance biochar’s performance for heavy metals removal, while their efficacy and mechanisms for Cd(II) immobilization remain unclear. To quantify the relative contribution of various mechanisms on Cd(II) adsorption and assess the application potential, this study comparatively investigated the immobilization of Cd(II) by phytic acid-modified biochar (PABC), sodium phytate-modified biochar (SPBC), and pristine bamboo biochar (BBC) in batch adsorption and soil incubation combined with spectroscopic techniques. The phosphorus modification of biochar significantly increased the adsorption of Cd(II), SPBC achieved the highest adsorption capacity for Cd(II) (71.09 mg/g), followed by PABC (21.37 mg/g) and BBC (19.12 mg/g). The superior performance of SPBC is attributed to its enhanced ion exchange capacity, which accounted for 60.1% of the adsorption mechanism. In contrast, mineral precipitation dominated the adsorption in BBC (40.4%), cation-π interactions (36.69%) and mineral precipitation (34.39%) were significant in PABC. Soil incubation experiments for 180 d also confirmed the best performance of SPBC in Cd immobilization in acidic soil. SPBC also enhanced dissolved organic carbon levels, whereas PABC significantly increased phosphorus concentrations. These results highlight the potential of PABC and SPBC as promising amendments for both Cd immobilization and soil amelioration in heavy metals contaminated soil ecosystems.