Feedstock-dependent mobility of pyrogenic carbon colloids under naphthalene: dominant role of zeta potential and adsorption behavior.

Understanding the transport behavior of pyrogenic carbon (PyC) colloids derived from different feedstocks in soil and water in the presence of hydrophobic organic contaminants is crucial for optimizing remediation strategies and controlling risks. This study investigated five PyC colloids derived from miscanthus straw pellets (MSP), oil seed rape (OSR), wheat straw pellets (WSP), soft wood pellets (SWP), and sewage sludge (SS) using column experiments with naphthalene (Nap). Nap adsorption reduced the absolute zeta (ζ) potential values of PyC colloids (from -36.4 ∼ -45.6 mV to -33.6 ∼ -42.3 mV). PyC colloids with less negative ζ potentials exhibited higher Nap adsorption capacity (R2 = 0.93), supported by density functional theory calculations confirming that polar functional groups (-COOH/-OH) hindered Nap adsorption. The mobility (Meff) of PyC colloids in the presence of Nap was 52.33 % (MSP), 48.82 % (OSR), 35.02 % (WSP), 34.89 % (SWP) and 21.5 % (SS), showing strong correlation with ζ potential (R2 = 0.88). Two-site kinetic modeling further showed that Nap increased attachment coefficient at reversible sites (katt), while its effect on irreversible sites (kstr) varied depending on feedstock type. The maximum solid particle concentration (Smax) was strongly correlated with ζ potential. These findings demonstrate that Nap adsorption reduces PyC colloid mobility primarily by decreasing ζ potential magnitude and weakening electrostatic repulsion between colloids and quartz sand, thereby enhancing retention. In contrast, hydrodynamic diameter played a negligible role. Our research provides a scientific basis for optimizing the effect of pollution remediation, enhancing environmental safety, and mitigating ecological risks in PyC practical applications.