Qualitative and relative distribution of Pb2+ adsorption mechanisms was investigated using corn stalk biochars (CSBs) and rice husk biochars (RHBs) produced from a pilot-scale fluidized bed pyrolysis system under mild air oxidization conditions (oxygen content 0–6%) at low temperature (450 °C). Boehm titration, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM-EDS) were used to analyze the characteristics of biochars, and adsorption isotherms and kinetics analysis were studied. The Pb2+ adsorption capacities of CSBs (about 40 mg/g) presented about twice the amount of RHBs (about 22 mg/g), which were mainly caused by cation exchange and precipitation mechanisms, with the contribution content to the total sorption up to 90%. With oxygen content increasing from 0% to 6%, the absorbed lead capacity due to cation exchange of CSBs increased from 19.10 to 30.40 mg/g, and the corresponding contributions to total Pb2+ sorption increased from 49.00% to 73.80%. When the oxygen content of pyrolysis atmosphere increased, the contribution of cation exchange in Pb2+ adsorption exhibited extremely different tendencies in CSBs and RHBs under the combined action of metallic accumulation in ash and non-active silica embedding in the retract process, which plays a dominant role in Pb2+ adsorption. This study suggests that CSBs produced by fluidized bed under mild air oxidation improved cation exchange capacity, and were promising, low-cost biochar for Pb2+ remediation in the aqueous environment.
Bibliographical noteFunding Information:
The authors are grateful for the financial supports from National Key Research and Development Program of China (No. 2018YFB0605102 ), National Natural Science Foundation of China (No. 51676040 ), Natural Science Foundation of Jiangsu Province (No. BK20181281 ), Scientific Innovation Research of College Graduate in Jiangsu Province (No. KYCX19_0075 ), the Scientific Research Foundation of the Graduate School of Southeast University (No. YBJJ1809 ), as well as the financial support from the Program of China Scholarship Council (No. 201806090030 ).
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- Adsorption mechanisms
- Fluidized bed pyrolysis
- Lead adsorption
- Mild air oxidization
- Relative contribution