Adsorption Equilibrium and Mechanism and of Water Molecule on the Surfaces of Molybdenite (MoS2) Based on Kinetic Monte-Carlo Method.

The oxidation/weathering of molybdenite (MoS2) is too slow to be monitored, even under pure oxygen and high temperatures, while it proceeds rapidly through humid air. The adsorption of water molecules on molybdenite is necessary for the wet oxidation/weathering of molybdenite. Therefore, we employ kinetic Monte Carlo modeling to clarify the adsorption isotherm, site preferences and kinetics of water on different surfaces of molybdenite. Our results indicate that (1) the adsorption capacity and adsorption rate coefficient of H2O on the (110) surface are significantly larger than those on the (001) surface at a temperature of 0~100 °C and a relative humidity of 0~100%, suggesting that the (110) surface is the predominant surface controlling the reactivity and solubility of molybdenite in its interaction with water; (2) the kinetic Monte Carlo modeling considering the adsorption/desorption rate of H2O, dissociation/formation rate of H2O and adsorption/desorption of dissociated H indicates that the adsorption and dissociation of H2O on the (110) surface can be completed in one microsecond (ms) at 298 K and in wet conditions; (3) the adsorption and dissociation of H2O on molybdenite are not the rate-limiting steps in the wet oxidation/weathering of molybdenite; and (4) kinetic Monte Carlo modeling explains the experimental SIMS observation that H2O and OH (rather than H+/H- or H2O) occupy the surface of MoS2 in a short time. This study provides new molecular-scale insights to aid in our understanding of the oxidation/weathering mechanism of molybdenite as the predominant mineral containing molybdenum in the Earth's crust.

Assessment of toxic elements in road dust from Hutou Village, China: implications for the highest incidence of lung cancer.

We attempt to understand the pollution characteristics and carcinogenic risk of toxic elements around Hutou Village, Xuanwei City, Yunnan Province, China. For this propose, 48 road dust samples were collected systematically, and the concentrations of Cr, Ni, Cu, Zn, As, Cd, Pb, Co, and Cr(IV) were analyzed and compared; the spatial distribution was obtained. The Igeo and EF indices and multivariate statistical analysis (CA, PCA, HACA) were carried out for source investigation, and human health risk assessment was also adopted to evaluate local non-carcinogenic and carcinogenic risks. The result showed that Cr, Ni, Cu, Cd and Co contaminations were quite serious; Zn, As, Cd, and Pb had similar distribution pattern, and Cr and Ni also shared similar distribution characteristics; Cd, Pb, Zn, and As ascribed to anthropogenic sources, while Cr and Ni originated from either anthropogenic activity or natural sources; Co and Cu originated from natural sources; the non-carcinogenic risk of Co cannot be ignored. The carcinogenic risk of Ni was considered unacceptable. Finally, an indoor coal-burning pattern was established that the high Cd and Ni inhalation and ingestion model was associated with lung cancer.

Source apportionment and health risk assessment of air pollution particles in eastern district of Chengdu.

This paper systematically studied the mass concentration levels of PM2.5 and PM10 and obtained the morphological characteristics and components of the particles through scanning electron microscopy (SEM-EDX) and discussed the sources of the particles. Meanwhile, the health risk was evaluated according to the mass concentration of particulate matter. The results showed that the average annual PM2.5 and PM10 in the eastern part of Chengdu were 101.99 µg/m3 and 168.89 µg/m3, respectively, exceeding the national second-level average annual air quality standard (GB3095-2012). Both of them were the highest in winter and the lowest in summer and had a significant positive correlation. The atmospheric particles in the study area were mainly composed of fly ash particles, soot aggregates, mineral particles (sulfate mineral particles, carbonate mineral particles, etc.), which mainly came from coal burning, dust, automobile exhaust and secondary products. The results of the health risk assessment showed that the mass concentration of PM2.5 and PM10 in the atmosphere of the eastern part of Chengdu exceeded the IT-1 target. The average annual air quality index was 185.84, and the air quality index was level 4, classified as medium pollution. PM10 and PM2.5 were both excessive pollutants, and PM10 was the primary pollutant. Relevant measures should be taken to control particulate matter sources to some extent.

Characteristics, Sources and Health Risk Assessment of Trace Metals in PM10 in Panzhihua, China.

Ambient PM10 air samples were collected at two industrial sites and one urban residential site in the mining city of Panzhihua, China, from April, 2014, to January, 2015. Mass concentrations of ten trace metals (As, Cd, Cr, Ni, Co, V, Mn, Cu, Pb, and Zn) in PM10 were determined by inductively coupled plasma-mass spectrometry. The results showed Zn, Pb, Cu, Mn and V were the most abundant elements from the industrial sites. Concentrations for Cd, Cr, Co, Ni, Mn and Cu at industrial sites greatly exceeded the air quality standards of the World Health Organization and the Chinese Ministry of Environmental Protection. Principal component analysis indicated that the main sources of the trace metals were steel smelting, fuel combustion, geological and mineral dust. Four different clusters of particles (i.e., mineral, calcium-containing, soot and aluminosilicate) were identified by scanning electron microscopy coupled with energy dispersive X-ray spectrometry. Chromium (Cr) was found to present the highest excess cancer risk, implying the potential for carcinogenic health effects in local inhabitants. Manganese (Mn) presented a non-carcinogenic health risk to children and adults, while the other metals were within acceptable limits.