Reaction of Solid Sodium Aluminate with Sulfur Dioxide

Abstract

The reaction between solid sodium aluminate, one of the binary metal oxides, and SO₂ was studied by using a gas flow reactor. - The sodium aluminates were obtained by evaporating sodium aluminate solutions with Na₂0/Al2O^2- ratios (mole) between O.5 and 3.0, which were prepared by dissolving various amounts of metallic aluminum in sodium hydroxide solution. The reaction behavior and mechanism of sodium aluminate with SO₂ were examined at 330°C and 130°C.
In the case of reaction of sodium aluminate containing excess sodium, it was found that the rate of initial stage was fast, and the reaction in this initial stage occured between SO₂ and NaOH involved in the sample. An approximately linear relationship existed between the amount of initial reaction and the amount of NaOH in the sample. On the other hand, the rate of later stage was slow, and in this region the reaction between Na₂Al2O^2-, involved in the sample, and SO₂ occured. 'The rate of the reaction increased with an increase of the reaction temperature.
The results of X-ray diffraction and IR analysis of the samples before and after the reaction suggested that the reaction was expressed by the following four equations,
2 NaOH SO₂ -4- Na₂SO^2- + H₂0
Na₂Al2O^2- + SO₂ Na₂SO^2- + Al2O^2-
2 Na5A1O^2- + 5 SO₂ 5 Na₂SO^2- + Al2O^2-
2 Na₂SO₃ + O^2- -3.2 Na₂SO₄
For Na₂SO₄ formation, it was recognized that Al2O^2-, which was formed from the reaction between Na₂Al2O^2- and SO₂, promoted the oxidation of Na₂SO^2-.