PURPOSE: To improve the metal cation selective separability of a separating agent by embedding a nonionic and non-polymeric metal cation complexing agent into a hydrophilic gel or dispersing the agent into a continuous aq. phase enveloping a water-insoluble ion-permeable film.

CONSTITUTION: An oxidant is dispersed into a crosslinking agent or the aq. phase contg. the precursor of the hydrophilic gel crosslinkable by the crosslinking agent or a thermally crosslinkable precursor material of the hydrophilic gel. This crosslinking agent-contg. dispersion is introduced into a soln. contg. the water-insoluble and ion-permeable film material crosslinkable by the crosslinking agent in order to encapsulate the crosslinking agent-contg. dispersion with the substantially water-insoluble and ion-permeable film material. Next, the formed particles are coated with the water-insoluble and ion-permeable film material or the film consisting of the covalently bonded amino group-contg. film material enclosing the particles is reinforced by additive covalent bonding and crosslinking, by which the objective granular separating agent for separating metal cations from the aq. soln. is produced.