Interactive influence of Fe–Mn and organic matter on pentachlorophenol sorption under oxic and anoxic conditions

• Adsorption of PCP is highly dependent on pH control.
• Weakened PCP sorption under anoxic experiment.
• PCP dynamics were linked to redox-driven cycling of Fe, Mn and DOM.
• Organic matter removal resulted in ∼90% reduction of the Kd values.
• Mn oxide removal may encourage transitory PCP sinks in reductomorphic environments.
• Seasonally flooded soils may have higher levels of non-labile PCP.

This study examined the adsorption of pentachlorophenol (PCP) on geosorbents (original bulk soil and soils treated to significantly remove organic carbon and oxides of Fe and Mn) under oxic and anoxic experimental conditions. pH effects on adsorption capacities were maximal at pH < pKa of PCP (4.7). Decrease in redox potential and an increase in dissolve organic carbon inhibited PCP sorption. While contribution of Mn oxide to PCP sorption was negative due to decreasing charge interference, the study equally implied negligible role of surface area compared to organic matter contents and oxides of Fe with R2 ≤ 0.825. The rate of Fe2+ and Mn2+ release under anoxic condition reduced interactions of phenolate with iron oxides and consequently, the distribution coefficients coupled with increased dissolve organic carbon. Pseudo second order and Langmuir isotherm provided the best kinetic and isotherm models respectively, although adsorption processes appeared to involve more than one kinetic stage based on intra-particle diffusion model (R2 ≤ 0.982). The study suggests that soil treatment to remove Mn oxide may encourage transitory PCP sinks in some reductomorphic environments.