Author(s): Rong Xiao
Linked Author(s):
Keywords: Biochar; Heavy metal; Saline soil; Wetland plants; Yellow River Estuary
Abstract: The purpose of this study was to investigate the ability of different local salt marsh plants pyrolyzed biochars to adsorb and immobilize heavy metal Cd/Pb since soil Cd pollution in Yellow River Estuary had been reported to approach serious level. The biochars were produced from withered stem of Phragmites australis (PB), Suaeda salsa (SB) and fresh twigs of Tamarix chinensis (TB) under different pyrolysis temperature and time. Pyrolysis products detecting showed that the ash, pH, electrical conductivity and carbon content of the biochars increased significantly while production rate decreased with the rise of pyrolysis temperature and time. The results of the adsorption experiments indicated that biochar addition could effectively reduce the concentration of Cd and/or Pb in Cd /Pb single or mixture solution. And the increasing pyrolysis temperature and time of biochars enhanced the adsorption effect significantly. The highest adsorption rates of Cd by three biochars were 98.46% for SB, 96.18% for TB, and 84.93% for PB, while the highest adsorption rates of Pb were 97.11% for SB, 82.14% for PB, and 61.73% for TB, respectively. However, both decreased adsorption capacity of the two heavy metal ions and relatively higher adsorption efficiency for Pb than Cd in the Pb and Cd mixture solution suggested a competitive adsorption. A 30 days incubation experiment was conducted using salt marsh soil amended with biochars by different application rates (0.5%, 1% and 2%), to investigate the short-term effects of biochar addition on Cd and Pb immobilization in saline soil. The PB and SB addition efficaciously immobilized Pb within the first 15 days after incubation, but Pb remobilized within the next 15 days period, while the TB addition did not significantly fix Pb. Differently, biochars addition promoted conversion of Cd from the residue to the less immobile fractions. This study confirms that SB could be a vital biochar to produce Pb and Cd in water environment. PB and SB biochars immobilized soil Pb during the early period of incubation, while three wetland plants produced biochars were not found to be effective in the immobilization of Cd in this study. Further study is needed to elucidate the underlying mechanisms. Field studies would be necessary to confirm the effectiveness of biochar application on heavy metals’retention, prior to large scale application.
Year: 2018