Multiform Sulfur Adsorption Centers and Copper-Terminated Active Sites of Nano-CuS for Efficient Elemental Mercury Capture from Coal Combustion Flue Gas

Abstract

Nanostructured copper sulfide synthesized with the assistance of surfactant with nanoscale particle size and high Brunauer-Emmett-Teller surface area was for the first time applied for the capture of elemental mercury (Hg) from coal combustion flue gas. The optimal operation temperature of nano-CuS for Hg adsorption is 75 °C, which indicates that injection of the sorbent between the wet flue gas desulfurization and the wet electrostatic precipitator systems is feasible. This assures that the sorbent is free of the adverse influence of nitrogen oxides. Oxygen (O) and sulfur dioxide exerted a slight influence on Hg adsorption over the nano-CuS. Water vapor was shown to moderately suppress Hg capture efficiency via competitive adsorption. The simulated adsorption capacities of nano-CuS for Hg under pure nitrogen (N), N + 4% O, and simulated flue gas reached 122.40, 112.06, and 89.43 mgHg/g nano-CuS, respectively. Compared to those of traditional commercial activated carbons and metal sulfides, the simulated adsorption capacities of Hg over the nano-CuS are at least an order of magnitude higher. Moreover, with only 5 mg loaded in a fixed-bed reactor, the Hg adsorption rate reached 11.93-13.56 μg/g min over nano-CuS. This extremely speedy rate makes nano-CuS promising for a future sorbent injection technique. The anisotropic growth of nano-CuS was confirmed by X-ray diffraction analysis and provided a fundamental aspect for nano-CuS surface reconstruction and polysulfide formation. Further X-ray photoelectron spectroscopy and Hg temperature-programmed desorption tests showed that the active polysulfide, S-S dimers, and copper-terminated sites contributed primarily to the extremely high Hg adsorption capacity and rate. With these advantages, nano-CuS appears to be a highly promising alternative to traditional sorbents for Hg capture from coal combustion flue gas.

Formation of Polysulfides from Consolidation of Cu Vacancies on CuS (001) Surfaces

“…These deficiencies in basic understanding of covellite created a huge gap between experimental and theoretical studies. For example, the CuS material shows great potential in the removal of elemental mercury according to extensive studies in recent years, − but the removal mechanism is still not well understood yet, especially for its high mercury adsorption capacity.…”

“…Furthermore, it was found that polysulfides can stabilize copper-deficit covellite by DFT + U calculations. Li et al deduced that polysulfides on CuS surfaces may contribute greatly in mercury removal according to the XPS analysis . Poly-sulfur ions S x 2– are regarded as the primary sites of CuS x /layered double hydroxide (LDH) composite for Hg 0 oxidation and immobilization .…”

“…Li greatly in mercury removal according to the XPS analysis. 16 Poly-sulfur ions S x 2− are regarded as the primary sites of CuS x / layered double hydroxide (LDH) composite for Hg 0 oxidation and immobilization. 23 The extraordinary mercury adsorption performance of molybdenum sulfide porous chalcogel (MoS x ) 24 and platinum polysulfide aerogels (K-Pt-S x ) 25 are also attributed to the abundant S−S bond sites.…”

Density Functional Theory Study of Elemental Mercury Immobilization on CuSe(001) Surface: Reaction Pathway and Effect of Typical Flue Gas Components

“…First, the Hg 0 adsorption capabilities of traditional ACs (< 5 mg g –1 ) are largely suppressed due to limited active sites carried by ACs. − Second, the Hg 0 removal efficiency of ACs was also demonstrated to be inhibited by typical industrial flue gas components such as water vapor (H 2 O) and sulfur dioxide (SO 2 ). , Thus, adopting ACs for industrial Hg 0 removal is estimated to be pricey, reaching $14,400/lb of Hg to $38,200/lb of Hg for 99% removal efficiency in a coal combustion scenario . Moreover, the immobilization of Hg 0 on AC surfaces primarily relies on physisorption, which undergoes severe re-emission issues and inevitable secondary pollution when the Hg-laden ACs are dumped and landfilled . From these perspectives, it is of urgent importance to develop novel sorbents that are highly efficient for Hg 0 uptake, insusceptible to typical industrial flue gas components, and capable of permanently sequestrating Hg 0 from polluted sources.…”

CeO2-Decorated α-MnO2 Nanotubes: A Highly Efficient and Regenerable Sorbent for Elemental Mercury Removal from Natural Gas

“…In industries, fixed beds of sulfur-impregnated activated carbons, metal sulfides , as well as silver-impregnated molecular sieves are typically deployed in both regenerative and nonregenerative methods to reduce the mercury concentration of contaminated streams to fewer than 10 ng·m –3 , by means of amalgamation, absorption, chemical, and physical adsorption. However, issues such as the leaching of sulfur and capillary condensation of carbons in wet streams have directed research toward the examination of alternative, highly selective, efficient, reusable, and environmentally friendly sorption materials.…”