Question

What do you mean by mineral salt absorption?

Answer 1

Previously, it was considered that mineral salt absorption from the soil occurred simultaneously with water absorption, but it is now well recognised that mineral salt absorption and water absorption are two separate processes.

Complete answer:
Mineral salts are absorbed in the form of ions from the soil solution. They're mostly absorbed through the roots' meristematic areas near the tips. However, depending on the high availability of such minerals around them and/or strong tissue demand at such areas, some mineral salts may be absorbed at different regions on the root surface or over the entire root surface, including the zone of elongation and root hairs.
Ions adsorbed on the surface of root cell walls or membranes can be exchanged with ions of the same sign from an external solution. The cation $K^+$ in the external soil solution, for example, may be exchanged with the H+ ion adsorbed on the root cell surface. An anion can also be swapped for an $OH^-$ ion.
Mineral salts are absorbed according to the concentration gradient via simple diffusion when the concentration of mineral salts in the outside solution is higher than in the cell sap of the root cells. Because it does not necessitate the expenditure of metabolic energy, this is referred to as passive absorption.
Because active mineral absorption is a dynamic process, it necessitates the expenditure of metabolic energy (ATP). By osmosis or through specific carrier proteins in the plasma membrane, active mineral absorption can occur both along and against the concentration gradient.

Note:
Plant cell sap accumulates significant amounts of mineral salts ions against a concentration gradient, as has been observed several times. This cannot be described by simple diffusion or Donnan's Equilibrium, leading some to assume that mineral salt absorption and buildup against a concentration gradient is an active process involving metabolic energy expenditure through respiration.