What compound is formed when calcium oxide reacts with sulfur dioxide during flue gas desulfurisation?

When calcium oxide reacts with sulfur dioxide during flue gas desulfurisation, the primary product formed is calcium sulfite. This reaction typically occurs in processes designed to remove sulfur dioxide emissions from exhaust gases, which are a significant contributor to air pollution and the formation of acid rain.

Calcium oxide, also known as quicklime, acts as a basic oxide that can react with sulfur dioxide, a common pollutant found in flue gases. The reaction can be represented as follows:

[ \text{CaO} + \text{SO}_2 \rightarrow \text{CaSO}_3 ]

In this reaction, calcium oxide combines with sulfur dioxide, resulting in the formation of calcium sulfite. This compound is then often further treated or neutralized, sometimes converted to calcium sulfate, but the immediate product of this reaction during the desulfurisation process is specifically calcium sulfite.

The other compounds listed do not directly result from this reaction or are not the primary focus of flue gas desulfurisation. For example, calcium sulfate could be produced in secondary processes following the initial reaction, while calcium carbonate and sulfuric acid are not products of the reaction between calcium oxide and sulfur dioxide under typical desulfurisation conditions.