Naked oats biochar-supported nanoscale zero-valent iron composite: effects on Cd immobilization and enzyme activities in Ulansuhai River sediments of China

Abstract

This investigation aimed to synthesize biochar-supported nanoscale zero-valent iron (BC-nZVI) to immobilize cadmium (Cd) in contaminated sediments of shallow grass-type rivers in typical cold and arid regions in northern China and reduce the bioavailability of Cd. Besides, the influence of multiple factors on the immobilization effect was discussed. In particular, the effects of the addition of humic acid (HA) on the fraction of Cd and enzyme activities were investigated. In this study, BC-nZVI was synthesized and all materials were characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), x-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The remediation effect of BC-nZVI on Cd-contaminated sediments was evaluated through sequential extraction experiments. Batch tests such as experiments of iron-to-carbon ratio, dosage, and incubation time were examined; the effect of HA concentration on Cd immobilization was highlighted, and corresponding enzyme activities (catalase, urease, and alkaline phosphatase) were tested for further illustration. BC-nZVI could immobilize Cd efficiently, with the maximum residual percentage of Cd increasing by 19.57 to 81.98% after 35 days of incubation, at 1:3 iron-to-carbon ratio and 0.05 g dosage. Sequential extraction experiments indicated that most labile fractions of Cd were transformed into stable fraction. When 10 and 20 mg kg−1 HA were added, immobilization was enhanced, and residual fraction increased to 89.43% and 88.70%, respectively. Meanwhile, exclusive of catalase, the activities of urease and alkaline phosphatase were enhanced with increased incubation time. This study proved that BC-nZVI has a significant effect on Cd immobilization. The addition of HA greatly promoted the immobilization of Cd and enzyme activities in sediments. In conclusion, BC-nZVI is an effective substance that can be used to remediate sediments contaminated with heavy metals.