When treating magnesium hardness with lime, which compound is precipitated?

When treating magnesium hardness with lime, the process primarily involves the reaction of magnesium ions in the water with calcium hydroxide, which is derived from lime. This reaction results in the formation of magnesium hydroxide, a compound that precipitates out of the water, thereby reducing magnesium hardness.

Magnesium hydroxide has low solubility in water, and when it forms, it can be easily removed from the water supply through sedimentation or filtration. This precipitation is essential for softening water that contains high levels of magnesium, which can contribute to scaling and other issues in water systems.

While calcium carbonate and calcium hydroxide are also related compounds in water treatment processes, in this specific context of treating magnesium hardness with lime, it is magnesium hydroxide that is the target product and the compound that effectively reduces magnesium hardness in water.