Chemical Aging Changed Aggregation Kinetics and Transport of Biochar Colloids

作者：Yang Wang, Wei Zhang, Jianying Shang, Chongyang Shen, Stephen Joseph · 发表于：Environmental Science & Technology · 年份：2019 · DOI：10.1021/acs.est.9b00583 · 被引用次数：158 · 研究领域：Fecal contamination and water quality、Groundwater flow and contamination studies、Urban Stormwater Management Solutions

Little is known about aggregation and transport behaviors of aged biochar colloids in the terrestrial environment. This study investigated aggregation kinetics and transport of biochar colloids from aged (HNO 3 treatment) and pristine pinewood biochars pyrolyzed at 300 and 600 °C (PB300 and PB600) in NaCl and CaCl 2 solutions. In NaCl solutions, critical coagulation concentrations (CCCs) of aged PB300 and PB600 colloids (540 mM and 327 mM) were much greater than the CCCs of pristine biochar colloids (300 mM and 182 mM). This is likely due to substantial increase of negatively charged oxygen-containing functional groups (primarily carboxyl) on aged biochar surfaces. Intriguingly, in CaCl 2 solutions the CCCs of the aged PB300 and PB600 colloids decreased to 25.2 mM and 32.1 mM from 58.6 mM and 41.7 mM for the pristine colloids, respectively. This probably resulted from greater surface charge neutralization and Ca 2+ bridging for the aged biochar colloids. In salt solutions (e.g., 10 and 50 mM NaCl and 1 and 10 mM CaCl 2 ), the aged biochar colloids showed higher mobility in porous media than the pristine biochar colloids. This study demonstrated that pristine and aged biochar colloids were stable in the solutions with environmentally relevant ionic strength, and the aging process might substantially increase their mobility in the subsurface.