| Abstract
| - The use of lithium-intercalated transition metal dichalcogenides, LixES2, asredox-recyclable ion-exchangematerials for the extraction of the aqueous heavy metalions Hg2+, Pb2+, Cd2+, andZn2+ was investigated (0.25 ≤ x≤ 1.9; E = Mo, W, Ti, Ta). ForLixTiS2 andLixTaS2,hydrolysisproduced S2-(aq) ions, whichprecipitated Hg(II) asHgS(s). In contrast, the materialsLixMoS2 andLixWS2 didnot undergo hydrolysis to form S2- ions.Instead, ion-exchanged materials such as Hg0.50MoS2 andPb0.15MoS2were isolated. The selectivity ofLixMoS2 for theheavymetal ions was Hg2+> Pb2+>Cd2+> Zn2+. Theaffinitiesfor the latter three ions but not for Hg2+ increasedwhenthe extractions were performed under anaerobicconditions. When HgyMoS2was heated under vacuum at425 °C, an entropy-driven internal redox reactionresultedin deactivation of the extractant, producing essentiallymercury-free MoS2 and a near-quantitative amountofmercury vapor (collected in a cold trap). The ratio ofthevolume of metallic mercury (secondary waste) to thevolume of 10.0 mM Hg2+(aq) (primary waste) was 1.5×10-4. Samples of MoS2produced by heating HgyMoS2werereactivated to LixMoS2 bytreatment with n-butyllithium.Some samples were used for three cycles ofextraction,deactivation/recovery, and reactivation with a primarywaste simulant consisting of 10 mM Hg2+(aq) in 0.1 MHNO3with no loss in ion-exchange capacity. When theMo/Hg molar ratio was 5.0 and the initial[Hg2+(aq)] = 1mM, only 0.033(2) μM mercury (6.5 ppb) was detectedin the filtrate after the extraction step. The highestobservedcapacity of LixMoS2 forHg2+(aq) was 580 mg of mercury/gof Li1.9MoS2.
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