Dilute SO₂ Absorption Equilibria in Aqueous HCl and NaCl Solutions at 298.15 K

The solubility of dilute SO 2 in aqueous HCl and NaCl solutions was determined at 298.15 K as a function of ionic strength up to 3 mol·L -1, in the partial pressure range between (0.075 and 1.8) kPa. Measurements were carried out by a saturation method using a laboratory batch reactor. Equations to correlate the apparent Henry's law constant, H m, and the apparent first dissociation constant, K m1, were obtained as a function of ionic strength. Comparisons between experimental results and theoretical predictions were also made. A model based on the classical Sechenov equation was tested, and a new value for the SO 2 gas-specific parameter was obtained to calculate H m . Two different models were considered for calculating the activity coefficients to determine K m1 . An extended version of the Debye−Hückel theory described the experimental results for ionic strengths below 0.1 mol·L -1 . The Pitzer model was in good agreement with the experimental data in the ionic strength range between (0 and 3) mol·L -1 . The close fit between measured and calculated data showed that the selected models can be successfully used for estimating the solubility of SO 2 in salt solutions at low partial pressures.