In the lime-soda process, what is the role of lime?

In the lime-soda process, lime primarily serves to reduce the carbonate hardness of water. Carbonate hardness is associated with the presence of calcium and magnesium bicarbonates, which can precipitate out and create scale. When lime is added to water, it reacts with the bicarbonates, converting them into insoluble carbonate forms, which can then be removed through sedimentation or filtration.

This process is crucial in water treatment, as reducing carbonate hardness helps prevent scale buildup in plumbing and reduces the potential for problems in water heating systems. Because carbonate hardness is linked to the bicarbonate ions in water, the addition of lime leads to a precipitation reaction that effectively lowers the concentration of these hardness constituents in the water, thereby softening it. This reaction not only addresses the hardness but also improves the overall quality of the water treated.