What is required for the regeneration of virgin greensand?

The regeneration of virgin greensand specifically requires soaking in potassium permanganate. This process is essential because greensand is primarily used for the removal of iron and manganese from water. Over time, the iron and manganese particles become saturated and less effective at filtration, necessitating a regeneration process.

Potassium permanganate acts as an oxidizing agent and rejuvenates the greensand by oxidizing the trapped iron and manganese, allowing them to be flushed away. This helps to restore the greensand's filtration properties and enhances its ability to treat water effectively.

In contrast, the other substances mentioned serve different purposes not related to the regeneration of greensand. Sodium chloride is commonly used for the regeneration of ion-exchange resins. Hydrochloric acid is often utilized for cleaning various materials, but it does not facilitate the specific regeneration that greensand requires. Lime water could be applied for other water treatment processes but does not contribute to regenerating the filtration capabilities of greensand.