What is an example of a process used for chemical precipitation of hardness?

Lime softening is a widely used process for the chemical precipitation of hardness in water. The process involves adding lime (calcium hydroxide) to the water, which raises the pH. Increased pH facilitates the conversion of soluble calcium and magnesium ions, which are responsible for water hardness, into insoluble precipitates. As a result, these precipitates can easily be removed from the water through sedimentation or filtration.

This method is particularly effective because it targets the specific ions causing hardness, allowing for a significant reduction in water hardness levels. Lime softening can also reduce other contaminants, making it a valuable treatment method in drinking water processing.

The other options do not specifically focus on the precipitation of hardness. Chlorination is primarily used for disinfection by adding chlorine to kill pathogens. Filtration is a physical process used to remove particulate matter but does not chemically alter the hardness components in the water. Submittering, a term not commonly used in the context of water treatment, does not relate to hardness removal. Therefore, lime softening stands out as the most relevant process for chemically precipitating hardness.