K. S. Gupta

The role of free fall atmospheric dust in catalysing autoxidation of aqueous sulphur dioxide

Abstract The results of atmospheric free fall dust catalysed S(IV) autoxidation in acetate buffered suspensions are in conformity with the rate law: − d[S(IV)] dt = k 6 [S(IV)] [H + ] 1.30 + k 7 [dust] 0.42 [S(IV)] 2 [H + ] 1.36 All available evidence favours the catalytic activity of dust suspensions being due to leached metal ions. Fe(III) is the main suspect, which is in agreemnt with the chemical analysis of dust.

Iron, manganese and copper concentrations in wet precipitations and kinetics of the oxidation of SO2 in rain water at two urban sites, Jaipur and Kota, in Western India

Abstract Rain-water samples were collected from Jaipur and Kota in Western India during the monsoon seasons of 1996–1999. In all cases, the pH of rain-water samples exceeded 7.0 and fell in the range (7.1–8.5). In view of the fact that the trace metals particularly iron, manganese and copper have been held responsible for the catalytic activity of rain-water, the chemical analysis of the collected samples was done with regard to the concentrations of these metals. The kinetics of autoxidation of SO 2 has been studied using rain-water samples as medium.

Kinetics of surface-catalyzed oxidation of sulphur(IV) by dioxygen in aqueous suspensions of cobalt(II) oxide

Abstract A comparative rate analysis of autoxidation of sulphur(IV) in CoO suspension, leachate solution and blank reaction suggests the reaction to be surface catalyzed. In acetate buffers, the experimental rate law is: Robs=Run + (k3 + k 4 [H + ] )[CoO][S(IV)][O2] where Run is the rate of uncatalyzed reaction. The suggested mechanism requires the adsorption of both S(IV) and O2 on the particle surface. Subsequently, the adsorbed species are activated resulting in the oxidation of sulphur( IV), probably through intervention of multiple oxidation states of cobalt.

Role of surface and leached metal ion catalysis in autoxidation of sulphur(IV) in power plant flyash suspensions

Abstract The kinetics of the autoxidation of sulphur(IV) in acetate buffered and unbuffered aqueous suspensions of flyash have been studied. Sulphate is the only autoxidation product. The results in buffered suspensions, at a given pH, are in agreement with the rate law (A) Robs = k1 [S(IV)] + k3 [flyash]0.3 [S(IV)]2. In buffered suspensions, the rate profiles are autocatalytic and a different rate law (B) is observed Robs = kA [ash]0.5 [S(IV))]. In buffered suspensions, in the presence of EDTA (which suppresses the trace metal ion catalysis), the kinetics are in agreement with the rate law (C) Robs = kS [ash] [S(IV)]. A comparative rate analysis in buffered suspensions and in corresponding leachates has shown the trace leached metal ions to be the main cause of catalysis.

The influence of diesel—truck exhaust particles on the kinetics of the atmospheric oxidation of dissolved sulfur dioxide by oxygen

The automobile exhausts are one of the major sources of particulate matter in urban areas and these particles are known to influence the atmospheric chemistry in a variety of ways. Because of this, the oxidation of dissolved sulfur dioxide by oxygen was studied in aqueous suspensions of particulates, obtained by scraping the particles deposited inside a diesel truck exhaust pipe (DEP). A variation in pH showed the rate to increase with increase in pH from 5.22 to about ∼6.3 and to decrease thereafter becoming very slow at pH = 8.2. In acetate-buffered medium, the reaction rate was higher than the rate in unbuffered medium at the same pH. Further, the rate was found to be higher in suspension than in the leachate under otherwise identical conditions. And, the reaction rate in the blank reaction was the slowest. This appears to be due to catalysis by leached metal ions in leachate and due to catalysis by leached metal ions and particulate surface both in suspensions. The kinetics of dissolved SO2 oxidation in acetate-buffered medium as well as in unbuffered medium at pH = 5.22 were defined by rate law: kobs = k0 + kcat[DEP], where kobs and k0 are observed rate constants in the presence and the absence of DEP and kcat is the rate constant for DEP-catalyzed pathway. At pH = 8.2, the reaction rate was strongly inhibited by DEP in buffered and unbuffered media. Results suggest that the DEP would have an inhibiting effect in those areas where rainwater pH is 7 or more. These results at high pH are of particular significance to the Indian subcontinent, because of high rainwater pH. Conversely, it indicates the DEP to retard the oxidation of dissolved SO2 and control rainwater acidification.

Autoxidation of sulphur dioxide in aqueous flyash suspensions

Abstract The fact that the thermal power and other plants continuously belch SO2 and flyash concurrently made us to look into the chemistry of autoxidation of aqueous sulphur dioxide in aqueous suspensions of four different flyash samples obtained from three different thermal power and a fertilizer plants. The particle sizes and metal contents of each flyash sample were determined. Detailed kinetics investiaation showed the major catalysis to be due to leached trace metal ions, and in agreement with the general rate law. where, a = ≤ 0.5; b = 1.5–2; c = 0.4–1.5 The atmospheric calculations indicated the conversion rates of around 0.34 to 1. “59% due to wetted flyash aerosols.

Kinetics and mechanism of the oxidation of 2-furancarbox-aldehyde by thallium(III) in perchloric acid solutions

AbstractThe kinetics of the oxidation of 2-furancarboxaldehyde by thallic perchlorate at 50°C obeys the rate law(1)

Kinetics and mechanism of the reaction between thallium(III) and thiocyanate ion in aqueous perchloric acid solutions

- \frac{{d[T1 (III)]}}{{dt}} = k[T1 (III)] [Substrate]