Ions approach an interface differently depending on the forces in play. Ions are non-specifically adsorbed (positively or negatively) when they are subjected in the interphase only to long-range coulombic interactions (attraction or repulsion). They are believed to retain their solvation shell, and in the position of closest approach to the interface they are separated from it by one or more molecular layers.
See also: specific adsorption
PAC, 1986, 58, 437. 'Interphases in systems of conducting phases (Recommendations 1985)' on page 447 (https://doi.org/10.1351/pac198658030437)