Antagonistic Effects of Humic Acid and Iron Oxyhydroxide Grain-Coating on Biochar Nanoparticle Transport in Saturated Sand

Abstract

Biochar land application may result in multiple agronomic and environmental benefits (e.g., carbon sequestration, improving soil quality, and immobilizing environmental contaminants). However, our understanding of biochar particle transport is largely unknown in natural environments with significant heterogeneity in solid (e.g., patches of iron oxyhydroxide coating) and solution chemistry (e.g., the presence of natural organic matter), which represents a critical knowledge gap in assessing the environmental impact of biochar land application. Transport and retention kinetics of nanoparticles (NPs) from wheat straw biochars produced at two pyrolysis temperatures (i.e., 350 and 550 °C) were investigated in water-saturated sand columns at environmentally relevant concentrations of dissolved humic acid (HA, 0, 1, 5, and 10 mg L(-1)) and fractional surface coverage of iron oxyhydroxide coatings on sand grains (ω, 0.16, 0.28, and 0.40). Transport of biochar NPs increased with increasing HA concentration, largely because of enhanced repulsive interaction energy between biochar NPs and sand grains. Conversely, transport of biochar NPs decreased significantly with increasing ω due to enhanced electrostatic attraction between negatively charged biochar NPs and positively charged iron oxyhydroxides. At a given ω of 0.28, biochar NPs were less retained with increasing HA concentration due to increased electrosteric repulsion between biochar NPs and sand grains. Experimental breakthrough curves and retention profiles were well described using a two-site kinetic retention model that accounted for Langmuirian blocking or random sequential adsorption at one site. Consistent with the blocking effect, the often observed flat retention profiles stemmed from decreased retention rate and/or maximum retention capacity at a higher HA concentration or smaller ω. The antagonistic effects of HA and iron oxyhydroxide grain-coating imparted on the mobility of biochar NPs suggest that biochar colloid transport potential will be dependent on competitive influences exerted by a number of environmental factors (e.g., natural organic matter and metal oxides).

Stability and Transport of Graphene Oxide Nanoparticles in Groundwater and Surface Water

“…The removal efficiencies and relative recovery values obtained in this study correlate well with the stability characterization results as well as observations of nanoparticle transport reported in the literature in the presence of NOM (Godinez et al, 2013;Wang et al, 2013). In this study, as the concentration of NOM increased, a decrease in removal efficiency and an increase in relative recovery were observed, suggesting that the presence of NOM enhances steric hindrance and subsequently particle stability during transport.…”

Do Goethite Surfaces Really Control the Transport and Retention of Multi-Walled Carbon Nanotubes in Chemically Heterogeneous Porous Media?

“…This result is expected because the electrostatic interaction between the negatively charged MWCNTs (i.e., carboxylate groups, −COO − ) and the positively charged GQS (Fe−OH 2+ ) is attractive, whereas it is repulsive for the negatively charged QS. 60,61 Figure S2 also confirms that statement and demonstrates that the significant amounts of roughness shown in Figure S1 will decrease and increase the MWCNT adhesive interaction between GQS and QS, respectively. The value of K D also dramatically increased with a decrease in the grain size of the GQS because of a corresponding increase in the specific surface area (Table S1).…”

Blocking effect of colloids on arsenate adsorption during co-transport through saturated sand columns

“…Due to the difficulty in distinguishing soil colloid from sand chipping, soil colloid retention in the sand columns was not measured in this study. However, the values of model fitting was employed to describe soil colloid retention in all columns (Sun et al, 2015b;Wang et al, 2012;Wang et al, 2013). The amount of retained soil colloids sharply decreased with increasing pH.…”