Mercury(II) exchange by highly charged swelling micas, sodium engelhard titanosilicate-4, and sodium titanosilicate

Selective Hg ²⁺-exchange properties of highly charged sodium swelling micas (Na-2-, Na-3-, and Na-4-micas), sodium Engelhard titanosilicate-4 (Na-ETS-4), and sodium titanosilicate were determined by use of distribution coefficients (K _d), ion-exchange isotherms, and Kielland plots for their potential use of Hg decontamination from groundwater and soils. X-ray diffraction (XRD) patterns after 2Na ⁺ → Hg ²⁺ exchange were collected to check for change in (001) spacings of differently charged sodium micas. The isotherms and Kielland plots suggested that Na-ETS-4 was highly selective for Hg ²⁺. Also, the K _d value of Na-ETS-4 was the highest among the tested exchangers, supporting its high selectivity. Hg releases from Hg-exchanged Na-4-mica and Na-ETS-4 were found to be lower compared to other samples tested with simulated groundwater. The (001) spacings of sodium micas after Hg ²⁺ exchange changed from ∼12 to ∼14 Å or/and 12 Å depending on their layer charge density and the uptake amount of Hg. Our results suggest that Na-ETS-4 is a good candidate for mercury(II) decontamination from groundwater and soils.