Gravity separation separates minerals based on their density differences and must be carried out in a medium. Therefore, the density of the minerals and the density of the medium are the most important factors affecting the gravity separation process. The ease of separation between two minerals through gravity separation can be roughly judged by the following formula:
Where δ₁, δ², and p are the densities of the light mineral, heavy mineral, and medium, respectively.
The E value is called the criterion for judging the selectivity of gravity separation; the larger the E value, the easier the separation. Conventionally, E values are divided into several levels as shown in Table 4-2.
Table 4-2 Judging the ease of separation through gravity separation based on E value
| E Value | E>2.5 | 2.5>E>1.75 | 1.75>E>1.5 | 1.5>E>1.25 | E<1.25 |
| Difficulty of reselection | Extremely easy | easy | Medium | difficulty | Extremely difficult |
Taking the separation of metallic and non-metallic minerals as an example, metallic minerals generally have a density greater than 4.6 g/cm³, while non-metallic minerals generally have a density less than 2.8 g/cm³. When separating them in an aqueous medium (p = 1.0 g/cm³),
it is evident that separation is easy.
From the above formula, it can be seen that for two specific minerals, i.e., with constant δ₁ and δ₂, the larger the density p of the medium, the larger the E value, and the easier the separation becomes. For example, when p = 1.8 g/cm³, separating metallic and non-metallic minerals,
is extremely easy.
Of course, the particle size and shape of mineral particles, as well as the motion state of the medium, are also important influencing factors in the gravity separation process. Therefore, using the E value as a criterion to judge the ease of gravity separation is only preliminary and rough.