Interaction between nano-biochar and Pb during migration in saturated porous media: Impact of ionic strength, pH and flow velocity

Biochar is widely applied in improving soil quality and remediating contaminated soil, but its mobility and impacts on other pollutants in porous media are not clear. In this study, column breakthrough experiments were carried out to investigate the co-transport behavior of Nano-biochar (NBC) and Pb, and the HYDRUS-1D was utilized to fit the breakthrough and retention curves in combination with the DLVO theory. Meanwhile, batch adsorption experiments were also conducted to explore the interaction between Pb and NBC. The results showed that the transport of NBC increased with lower ionic strength (IS) and higher pH values, as well as with increased flow velocity. The presence of Pb markedly reduced the transport of NBC, due to an increase in the hydrodynamic particle size of NBC and decrease in electrostatic repulsion between NBC and quartz sand . The mobility of Pb increased with higher IS and flow velocity, but decreased with increasing pH. Conversely, the presence of NBC altered the migration pattern of Pb in quartz sand, which led to higher Pb mobility under conditions of lower IS. Specifically, the migration rate of Pb decreased from 88.45 % to 60.24 % as the IS increased from 1 to 50 mM. However, NBC generally enhanced the mobility of Pb, except under conditions of higher IS (specifically at 10 and 50 mM). These findings elucidate the mechanisms by which NBC enhances Pb mobility in porous media, offering a critical theoretical framework for mitigating Pb contamination in soil and groundwater systems. • NBC impacted Pb(II) migration through sorption with Pb(II). • NBC enhanced and inhibited Pb(II) mobility under lower and higher IS conditions, respectively • Pb(II) inhibited NBC transport due to hydrodynamic particle size of NBC increase • NBC acted as a carrier for Pb(II) transport in porous media