Sorption kinetics and stability of conventional adsorbents for mercury remediation

In-situ remediation of mercury at numerous contaminated sites worldwide is a challenging and costly endeavor due to the persistency of this contaminant. In this study, we evaluated eight commercially available sorbent media ranging from carbon-, clays- and silica-based materials (PBC- Biochar, eSorb - Sorbster, nsPAC - Powdered Activated Carbon, fsPAC - Powdered Activated Carbon with Mackinawite, F300 - Filtrasorb 300, Si-SH - Silica Thiol, eBind - RemBind, Q-Clay - Organoclay PM-199), for their effectiveness in sorbing mercury (Hg2+) and mercury complexed with dissolved organic matter (Hg-DOM). Under the chosen experimental conditions of this study, results showed that in the absence of DOM, the kinetic rates of Hg2+ sorption onto the evaluated sorbents were in the order of 0.31 min(-1) (Si-SH) to 2.98 min(-1) (nsPAC), whereas in the presence of DOM, the rates varied from 0.16 min(-1) (F300) to 0.95 min(-1) (nsPAC). The measured sorption capacity for Hg2+ in the absence of DOM varied from 3.02 mg/g (Q-Clay) to 35.15 mg/g (Si-SH), whereas in the presence of DOM, calculated partition coefficient (KD) ranged from 69.7 mL/g (Q-Clay) to 41,510 mL/g (Si-SH). Furthermore, kinetic data suggest liquid film diffusion was the rate-limiting steps governing mercury sorption onto the studied media. Overall, the obtained study parameters (kinetics/isotherm) are particularly important in informing robust engineering designs for deployment of the vast majority of evaluated sorbents. Thus, sorbent-based strategies offer viable solutions for cost-effective cleanup of mercury at industrially contaminated sites.