Reduction of mercury emissions from anthropogenic sources including coal combustion

Understanding the sources of mercury release from coal: A combined experimental and molecular simulation study

Understanding the occurrence modes of mercury in coal is important as its release poses long-term adverse effects on the environment and human health during coal production and utilization. However, the matter still remains a subject of controversy due to differing results from direct and indirect analyses, which suggest various possible modes of occurrence for mercury in coal. Additionally, the experimental measurement of Hg concentration presents challenges, further contributing to the complexity of the issue. A comprehensive investigation of experiments and molecular simulations is conducted herein. Electron probe microanalysis and elemental mapping analysis show that elemental Hg is concentrated in framboidal pyrites while absent in organic matter. To understand the occurrence modes of mercury in inorganic and organic materials at the atomic level, molecular simulations are performed for Hg2+ adsorption and retention in MMT, pyrite, and kerogen slit nanopores. It is found that the inorganic MMT and pyrite surfaces have a greater adsorption capacity than the organic kerogen surface (pyrite > MMT > kerogen). The outer-sphere adsorption is mainly observed with at least one monolayer of water molecules exiting between the ion and mineral surfaces. MMT has the highest retention for Hg2+ transport as the self-diffusion coefficient is the smallest among the three slit pores (MMT < pyrite < kerogen). The high adsorption and retention originate from the strong Hg2+-mineral interaction. These results suggest that mercury in coal is most likely associated with inorganic minerals instead of organic matter.

Efficient immobilization and detoxification of gaseous elemental mercury by nanoflower/rod WSe2/halloysite composite: Performance and mechanisms

Gaseous mercury pollution control technologies with low stability and high releasing risks always face with great challenges. Herein, we developed one halloysite nanotubes (HNTs)-supported tungsten diselenide (WSe2) composite (WSe2/HNTs) by one-pot solvothermal approach, curing Hg0 from complicated flue gas (CFG) and reducing second environment risks. WSe2 as a monolayer with nano-flower structure and HNTs with rod shapes in the as-prepared sorbent exhibited outstanding synergy efficiency, resulting in exceptional performance for Hg0 removal with high capture capacity of 30.6 mg·g-1 and rate of 9.09 μg·g-1·min-1, which benefited from the high affinity of selenium and mercury (1 ×1045) and the adequate exposure of Se-terminated. The adsorbent showed beneficial tolerance to high amount of NOx and SOx. An online lab-built thermal decomposition system (TPD-AFS) was employed to explore Hg species on the used-sorbent, finding that the adsorbed-mercury species were principally mercury selenide (HgSe). Density functional theory calculations indicated that the hollow-sites were the major adsorption sites and exhibited excellent selectivity for Hg0, as well as HgSe generation needed to overcome the 0.32 eV energy barrier. The adsorbed mercury displayed high environmental stability after the leaching toxicity test, which significantly decreased its secondary environmental risks. With these advantages, WSe2/HNTs possess enormous potential to achieve the effective and permanent immobilization of gaseous mercury from CFG in the future.

Identification of mercury species in coal combustion by-products from power plants using thermal desorption-atomic fluorescence spectrometry on-line coupling system

Along with the environmental protection policies becoming strict in China, the air pollution control devices (especially selective catalytic reduction (SCR)) are widely equipped in coal-fired power plants. The installation and run of these devices will inevitably affect mercury (Hg) species distribution in coal fired by-products such like fly ash (FA) and gypsum. In this work, a new on-line coupling system based on atomic fluorescence spectrometry (AFS) with a home-made chromatographic workstation was successfully developed to identify Hg species through thermal programmed desorption (TPD). The influences of matrix, furnace temperature, and carrier gas flow on analytical performance were investigated and the parameters were optimized. The FA and gypsum samples from coal-fired power plants equipped with SCR were collected and the mercury species were analyzed by the developed coupling system. HgCl₂ and HgO were the main species in FA, while Hg₂Cl₂ and HgO were the main species in gypsum. All of Hg species in the studied FA and gypsum samples were released below 400 °C. A sequential extraction procedure was applied to further verify the operational Hg species including mobile and non-mobile fractions in FA and gypsum samples. This study demonstrated that AFS coupled with TPD procedure was an effective method to analyze Hg species in coal combustion by-products from power plants.

Multifarious Biological Applications and Toxic Hg2+ Sensing Potentiality of Biogenic Silver Nanoparticles Based on Securidaca inappendiculata Hassk Stem Extract

INTRODUCTION

The use of environmentally benign resources for nanoparticles synthesis is consistently pushed to the front burner in a bid to ensure and enhance environmental protection and beneficiation. In this light, application of different plant parts for the reduction and stabilization of nanoparticles is gaining popularity.

MATERIALS AND METHODS

In this contribution, we have exploited Securidaca inappendiculata stem extract (SISE), as the reducing and stabilizing agent for room temperature synthesis of highly stable and dispersed AgNPs. The major bioactive compounds in SISE were profiled using an ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-MS-QTOF-MS).

RESULTS AND DISCUSSION

SISE could reduce silver salts to its nanoparticles almost instantaneously with a maximum absorption spectrum at 423 nm, under the optimal conditions. The fabricated SISE AgNPs was extensively characterized using FTIR, TEM, SEM, XRD, EDS, Zeta analysis/DLS and TGA/DTG analysis. SISE AgNPs with average particles size between 10-15 nm and a zeta potential value of -19.5 ± 1.8 mV was obtained. It was investigated for in-vitro biological applications by carrying out, antimicrobial, antioxidant, hemolytic, cytotoxicity and antidiabetic assays. It was found that SISE AgNPs exhibited potent antimicrobial capacity against some food borne microbes, good antioxidant property, while also demonstrating high biocompatibility. Moreover, with a view to extending further the applications SISE AgNPs, it was tested as a colorimetric nanoprobe for Hg2+ detection in aqueous environment, where good linearity between 0.10 and 10.0 μM, with a detection limit of 26.5 nM, were obtained. The practicality of the probe was investigated by carrying out Hg2+ detection in water sample, with good accuracy and precision.

DISCUSSION

Overall, this work introduced a new stabilizer for biocompatible AgNPs with far-reaching applications.