A Meticulous Study on the Adsorption of Mercury as Tetrachloromercurate(II) Anion with Trioctylamine Modified Sodium Montmorillonite and Its Application to a Coal Fly Ash Sample

Clay materials have hogged the limelight for their effectiveness in environmental remediation. In this paper, we report an effective solid phase extraction method for mercury based on the adsorption of tetrachloromercurate(II) anion with trioctylamine intercalated onto sodium montmorillonite. The adsorption is facile in acidic medium, and the adsorbent was well characterized by diverse physicochemical and spectroscopic techniques. Various isotherm models were employed to correlate the experimental adsorption data. The electrostatic interaction between HgCl 4 2- and the protonated amine is well supported by a Langmuir isotherm model with a maximum adsorption capacity of 140.84 mg g –1 . The ordered transition state that arises due to the proximity of the HgCl 4 2- and the positively charged amine is accompanied by a decrease in the translational entropy of the system. The N 2 adsorption–desorption isotherm study revealed the mesoporous nature of the adsorbent, and the thermodynamically favorable adsorption process resonates well with the ensuing negative free energy and enthalpy changes in accordance with the sorption mechanism. Packed bed column study demonstrated the scale up to 800 mL sample volume at 10 mg L –1 Hg(II) concentration, and the adsorbent could be regenerated and reused for 10 cycles with thiourea as the eluent. The removal of mercury from a coal fly ash sample validated the method.