Why should salt water be added to the extracted vegetable oil?

Because Nacl can react chemically with P and water to produce double salts Na2P5O (sodium phosphate) and H2 (hydrogen), and the cost of brine is low, which is harmless to human body, so we use brine to remove phosphorus from primary oil. In addition, adding salt water can make the water absorbed by fine particles heavier, so that the filtered oil will be clearer.