Efficient Recovery of Elemental Mercury from Hg(II)-Contaminated Aqueous Media Using a Redox-Recyclable Ion-Exchange Material

Abstract

The use of lithium-intercalated transition metal dichalcogenides, Li x ES 2 , as redox-recyclable ion-exchange materials for the extraction of the aqueous heavy metal ions Hg 2+ , Pb 2+ , Cd 2+ , and Zn 2+ was investigated (0.25 e x e 1.9; E ) Mo, W, Ti, Ta). For Li x TiS 2 and Li x TaS 2 , hydrolysis produced S 2-(aq) ions, which precipitated Hg(II) as HgS(s). In contrast, the materials Li x MoS 2 and Li x WS 2 did not undergo hydrolysis to form S 2ions. Instead, ionexchanged materials such as Hg 0.50 MoS 2 and Pb 0.15 MoS 2 were isolated. The selectivity of Li x MoS 2 for the heavy metal ions was Hg 2+ > Pb 2+ > Cd 2+ > Zn 2+ . The affinities for the latter three ions but not for Hg 2+ increased when the extractions were performed under anaerobic conditions. When Hg y MoS 2 was heated under vacuum at 425 °C, an entropy-driven internal redox reaction resulted in deactivation of the extractant, producing essentially mercury-free MoS 2 and a near-quantitative amount of mercury vapor (collected in a cold trap). The ratio of the volume of metallic mercury (secondary waste) to the volume of 10.0 mM Hg 2+ (aq) (primary waste) was 1.5 × 10 -4 . Samples of MoS 2 produced by heating Hg y MoS 2 were reactivated to Li x MoS 2 by treatment with n-butyllithium. Some samples were used for three cycles of extraction, deactivation/recovery, and reactivation with a primary waste simulant consisting of 10 mM Hg 2+ (aq) in 0.1 M HNO 3 with no loss in ion-exchange capacity. When the Mo/Hg molar ratio was 5.0 and the initial [Hg 2+ (aq)] ) 1 mM, only 0.033(2) µM mercury (6.5 ppb) was detected in the filtrate after the extraction step. The highest observed capacity of Li x MoS 2 for Hg 2+ (aq) was 580 mg of mercury/g of Li 1.9 MoS 2 .

Sequestration of Heavy Metals from Water with Layered Metal Sulfides

“…Surprisingly, there remain very few reports concerning the soft heavy metal ion-exchange properties of metal chalcogenides. [13][14][15] Herein, we report the heavy metal ion remediation properties of the layered sulfide material K 2x Mn x Sn 3Àx S 6 (x = 0.5-0.95) (KMS-1), which previously was shown to be an excellent sorbent for strontium ions.[16] Very rapidly KMS-1 removes mercury, lead, and cadmium from water with a capacity and selectivity that allows their concentration to be reduced to well below the government allowed safe drinking levels. This property makes KMS-1 promising for decontamination of a wide variety of wastes containing heavy metal ions.…”

“…KMS-1 is more efficient as heavy metal ion scavenger than LiMoS 2 , [14] another example of a layered sulfide. KMS-1 is also stable in atmosphere and water, whereas LiMoS 2 [24,25] and thiol-functionalized sorbents [26] need to be Because KMS-1 is relatively inexpensive and can rapidly reduce the Hg 2 + , Pb 2 + , and Cd 2 + content of aqueous media well below the acceptable limits for water, it is promising for the detoxification of a variety of wastes and drinking water from heavy metal ions.…”

Recovery of Mercury From Contaminated Liquid Wastes

“…A research group at Colorado State University (CSU) has a material that takes advantage of redox and ion-exchange chemistry to effectively remove mercury (II) ions from aqueous systems (Gash, 1998). This material uses a process known as intercalation to insert metal atoms between the layers of the transition metal chalcogenide host.…”

The removal of mercury from water by open chain ligands containing multiple sulfurs

“…Filters of various types can be used to remove mercury [25][26][27][28][29][30][31][32][33][34][35][36]. While many of these are very effective, they all require that the contaminated water be diverted through the filter at a controlled rate.…”