Influence of humic substances on photolysis of divalent mercury in aqeous solution

Mercury (II) solutions were irradiated by a simulated sunlight in the presence of humic acid (HA) or fulvic acid (FA). Results show that, under the experimental conditions and the FA and HA chosen, less than 20% of the Hg in solution was photolysed with a rate of (1.63\ub10.29) 710–2 s–1 (n=23) and the rest of (2.38\ub10.40) 710–4 s–1 (n=23) depending on the substitutes of humic substances to which Hg were bond. The sunlight photolysis lifetimes were estimated to be 4 and 250 sunlight hours respectively under summer conditions at Stockholm latitude

Abstraction of preadsorbed oxygen from CaO(100) by carbon monoxide

The mechanism for abstraction of preadsorbed oxygen from CaO(100) by CO(g) to form CO2(g) is investigated by electronic structure calculations. The reaction mechanism is assumed to be the reverse of the one obtained for the decomposition of N2O(g) at CaO(100) [Surf. Sci 292 (1993) 317]. A 32 kcal/mol barrier for reaction is calculated. Adsorbed oxygen, Oads, to surface vibration frequencies in the range 840–930 cm−1 are calculated. These values are in qualitative agreement with experiment

N2O adsorption and decomposition at a CaO (100) surface studied by means of theory

The adsorption and decomposition of an N2O molecule at different sites on a CaO(s) surface are investigated by means of ab initio quantum chemistry. The calcium, Ca2+, and oxygen, Os2−, sites at a perfect (100) surface and at a corner position, Oc2−, are considered. Adsorption energies at different sites are calculated and the largest value, 6 kcal/mol, is obtained for a corner site. The barrier for dissociation is calculated to 26 and 27 kcal/mol at the Oc2− and Os2− sites, respectively. These values are some 10 kcal/mol lower than the experimental estimate, and the discrepancy is understood from methodological difficulties to describe the free N2O molecule. A mechanism for the dissociation over an O2− site is proposed, whereby the transfer of the O atom goes via a linear N-N … O … O2− transition state

Study of the reduction and reoxidation of a CaO surface

The reduction of NO with CO and H2 is shown to comprise two basic reactions: a surface oxygen abstraction by the reducing agent and a reoxidation of the surface by NO. The former reaction step has been demonstrated by transient CO2 formation during CO exposure of oxidized CaO surfaces, while the latter was demonstrated by N2 and/or N2O transient formation during NO exposure of a prereduced CaO surface. It was shown that at low temperatures (between room temperature and 500 \ub0C) both N2 and N2O were formed, but at temperatures above 500 \ub0C only N2 was observed. The activation energies of the respective steps have been determined using temperature-programmed reaction experiments. The activation energy of the surface oxygen abstraction was determined to be 25 kcal/mol and is similar to the apparent activation energy of the overall reaction. The activation energy of the NO bond breakage was determined to be maximum 10 kcal/mol as measured by N2O formation. The importance of an N2O2- or N2O22- intermediate in the formation of N2O will be discussed, and the importance of N2O decomposition in forming N2 at temperatures above 500 \ub0C will be compared with a N surface diffusion mechanism

Distribution equilibrium of mercury (II) chloride between water and air applied to flue gas cleaning

In the literature, different values of the distribution coef-ficient K H for HgCl 2 between water and air are present in a range that spans more than 3 orders of magnitude. In order to determine if a waste incineration scrubber solu-tion could become saturated with regard to HgCl 2 , an ac-curate experimental determination of the distribution constant of HgCl 2 at elevated temperatures is needed. In this work, the coefficient has been determined at four dif-ferent temperatures between 10 and 50 \ub0C. The Arrhenius expression obtained is 5.5 x 10 5 x exp[-(8060 \ub1 2200)/T] with a corresponding enthalpy for the process HgCl 2 (aq)?I HgCl 2 (g) of 67 \ub1 20 kJ/mole. K H at 293 K was found to be ~5 x 10 -7 atm M -1 , which is in almost perfect agreement with an earlier study. Applying the obtained K H values to waste incineration scrubber conditions shows that no major saturation effect will occur