The absorption rates of (1) NO in aqueous solutions of Fe"-EDTA, (2) NO in aqueous solutions or slurries of MgS03 with added Fe'-EDTA, and (3) NO in the presence of S02 in aqueous slurries of MgS03 with added Fen-EDTA were measured using a stirred vessel with a plane gas-liquid interface at 25 °C and 1 atm. The forward rate constant of the complexing reaction, NO + Fe"-EDTA <=± Fen(EDTA)(NO), at various pH's was derived from the enhancement factor for absorption of NO in aqueous solutions of Fen-EDTA. The reduction of NO coordinated to Fen-EDTA with S032~i s found to be very slow as compared with the above complexing reaction. Coexisting S02 can promote the absorption rate of NO by aqueous slurries of MgS03 with Fen-EDTA. It is believed that coexisting S02 plays a part of releasing S032" from the complex Fe"(EDTA)(S032~)(N0) and that the presence of S02 in the gas phase effectively improves the pH of the solution at the interface toward favorable values for the reaction of NO with Fen-EDTA.

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The absorption of such lean NO, as encountered in flue gases in aqueous mixed solutions of NaCI02 and NaOH was carried out using a stirred vessel with a plane interface at 25 °C and atmospheric pressure. The rate of N02 absorption was analyzed by the chemical absorption theory under the fast-reaction regime. The reaction which prevailed was found to be the parallel reactions involving oxidation and hydrolysis, and to be second order with respect to N02. The second-order rate constant for the hydrolysis was evaluated as 3.09 X 108 L/mol s. The order of reaction relative to CI02' was derived as unity for chlorite concentrations greater than 1.0 M. The third-order rate constant for the oxidation was derived as 7.32 X 10® (L/mol)2/s at [NaOH] = 0.20 M. For the absorption of NO, there appears to be a gradual jump in absorption rate at the interfacial concentration of NO ranging from 5 X 10"7 to 2 X 10"® mol/L. Above this transition region, the order of reaction in NO approaches 2, whereas below the transition region, the order of reaction becomes unity.

The rates of single and simultaneous absorptions of dilute SO2 and NOin aqueous mixed solutions of NaClO2and NaOHwere measured at 25°C using a stirred vessel with a plain gas-liquid interface. In the SO2-NaClO2system, the absorption rate exceeded the gas-film controlled rate, which implies the possibility of gas-phase oxidation of SO2 due to the evolved C1O2. In the SO2-(NaClO2+NaOH) system, the absorption rate agreed with that under gas-film controlled conditions. In the (SO2+NO)-(NaClO2+NaOH)system, the reduction of the NO absorption rate in the presence of SO2 substantially exceeded that evaluated through the decrease in interfacial concentration of NaClO2and NaOHdue to surface reaction with coexisting SO2. The rate of absorption of SO2 exceeded the gas-film controlled rate. The decomposition of NaClO2proceeds to a greater degree during simultaneous absorption than the single absorption of SO2.

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