Monte Carlo simulation of the static properties of Hg solution in (O 2 ,N 2 ) gassed water Mohammad Hadi Ghatee ⁎, Hedayat Karimi Department of chemistry, Shiraz University, Shiraz, 71454, Iran abstract article info Article history: Received 19 October 2012 Received in revised form 24 January 2013 Accepted 31 January 2013 Available online 20 February 2013 Keywords: Metal mercury solution in water Nitrogen oxygen gassed water Structural correlation Interaction with mercury Monte Carlo simulation Radial distribution function Potential of mean force Canonical Monte Carlo (CMC) simulations were carried out to investigate the influence of O 2 and N 2 gases on elemental mercury (Hg) solution in water. Particle–particle interactions were all modeled using Lennard– Jones potential function. To provide insight into the interaction of O 2 and N 2 gases with Hg atom in water, two independent mixtures Hg/(O 2 ,H 2 O) and Hg/(N 2 ,H 2 O) with the same bulk mole fraction of component (0.9956, 0.0023, 0.0023, 0.0021 for H 2 O, O 2 ,N 2 and Hg, respectively) were simulated at T =298 K. The results show that Hg in water interacts favorably with O 2 more than with N 2 . This is consistent with the hypothesis that stronger interaction of O 2 gas with the mercury atom leads to a higher adsorption and lower dynamic structure compared with N 2 gas. Independent simulation of Hg/(O 2 ,H 2 O) and Hg/(N 2 ,H 2 O) mixtures indicates that N 2 gas molecules stay off the distance at which O 2 interacts with Hg as the nearest neighboring distance. This procedure enables us to describe the structural properties of Hg ⋯ O 2 and Hg ⋯ N 2 in water at molecular scale which hints exploring techniques of the toxicity level of mercury contaminated water. Alternatively, comparison of potential of mean force indicated that Hg ⋯ O 2 interaction exposes the free energy of −2.93 kJ mol −1 which is more stable pair interaction relative to Hg ⋯ H 2 O(−2.50 kJ mol −1 ) and Hg ⋯ N 2 (−1.79 kJ mol −1 ). © 2013 Elsevier B.V. All rights reserved. 1. Introduction Mercury is one of the most toxic heavy metals which enter the aquatic environments from a variety of natural and anthropogenic sources. Natural sources include volcanoes, crust degassing and by forest fires, whereas anthropogenic sources are mainly solid waste in- cineration, fuel combustion activities and industrial processes [1,2]. Even though mercury levels tend to be low in seawater than in fresh water, but mercury in the ocean has a significant risk to human health. It has been found that a form of the toxic element, called meth- ylmercury, CH 3 Hg, breaks down more slowly in seawater than in fresh water and fishes will ingest the toxic which is to be the main sources of human exposure to methylmercury [3]. There is a possibility that exposure to low doses of methylmercury can damage to the central nervous system [4]. In addition, all the mer- cury species are highly toxic on human physiology. The metal is accu- mulated in the living tissue, particularly in the brain and high concentration of Hg(II) cation causes impairment of pulmonary func- tion and kidney, chest pain and dyspnea [5]. According to the standards, World Health Organization (WHO) has set the limit of mercury (II) in drinking water as 0.001 mg/L [6]. Thus, the removal of this toxic metal from wastewater is a crucial issue from the environment and health point of view. Several techniques com- monly employed for the treatment of mercury-contaminated waters are chemical precipitation, membrane separation, filtration, biological treatment, electrochemical treatment, chemical oxidation or reduc- tion, solvent extraction, coagulation and adsorption [6–9]. Among these treatment methods, the mercury adsorption process was found to be a promising and powerful technique with several ad- vantages such as high efficiency, easiness, low cost, less maintenance and the availability of a broad range of adsorbents [6,7]. Some recent studies have investigated the adsorption of mercuric ions from contaminated water based on nanoparticles supported on activated alumina [6] silica, polyacrylamide and hybrid silica–polyacrylamide [7] carbon nanotubes and activated carbons [5,10]. Since mercury is found to be in two forms, elemental mercury (Hg o ) and oxidized mercury (Hg + , Hg 2+ ), removal of Hg o with cur- rent technologies is much harder than the removal of others because of its high vapor pressure, low solubility in water, and weak adsorp- tion on particles [11,12] Therefore, it is essential to understand the ad- sorption treatment of elemental mercury and its structural analysis in order to help the effective development strategies to reduce its level of contamination and molecular simulations can be a valuable tool to gain both qualitative and quantitative information about such sys- tems, giving a molecular level picture of interactions. Molecular dynamics simulation has been used for structural prop- erties of Hg 2+ ion in aqueous solution [13] the liquid mercury/water interface [14] and hydrated ion near liquids mercury surface [15,16]. Journal of Molecular Liquids 181 (2013) 14–19 ⁎ Corresponding author. Tel.: +98 711 613 7353; fax: +98 711 228 6008. E-mail address: ghatee@susc.ac.ir (M.H. Ghatee). 0167-7322/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molliq.2013.01.025 Contents lists available at SciVerse ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq