Influence of humic acid on ionisation constants of sulphurous acid: Calcium sulphite precipitation during clarification of cane juice

Abstract

The presence of humic acid seems to decrease the rate of CaSO₃ precipitation during clarification of cane juice in the sugar manufacturing. The first and second ionisation constants of H₂SO₃ were found to decrease by 8 and 13% at RT in presence of humic acid in solution, respectively. However, t h e first and second ionisation constants of the acid were affected in the range 19-16% respectively across the temperature range 50-90°C. In the presence of humic acid the activation energy was found to increase. The nature of positive slope of Arrhenius plot indicates the diffusion controlled reaction in the precipitation reaction which is consistent with low value of activation energy of ionisation of sulphurous acid.