Which of the following refers to the process that removes hardness-causing minerals like calcium and magnesium?

The correct answer is softening, which specifically refers to the process designed to remove hardness-causing minerals such as calcium and magnesium from water. Hard water, which contains elevated levels of these minerals, can create issues in boiler operations, including scale formation on internal surfaces, reduced efficiency, and increased maintenance costs.

During the softening process, various methods can be employed, such as ion exchange, where calcium and magnesium ions are replaced with sodium ions. This effectively reduces the hardness of the water, making it more suitable for use in boilers and other equipment where high-quality water is essential.

In contrast, the other processes mentioned serve different functions. Coagulation is typically involved in water treatment processes where fine particles are clumped together for easier removal, rather than specifically targeting hardness minerals. Demineralization refers to the removal of all dissolved minerals from water, which goes beyond just addressing hardness and can include the elimination of salts as well. Precipitation is a chemical process where dissolved substances form solid particles, which may contribute indirectly to hardness removal but is not the dedicated method for softening water. Therefore, softening is the most accurate term for the process specifically aimed at addressing water hardness due to calcium and magnesium.