A process for the preparation of a granulated or pelletized sorption medium from a partially decomposed organic material like peat, followed by low-temperature thermal activation of the sorption medium to produce a high degree of granule or pellet hardness balanced against an efficacious level of ion-exchange and adsorption capacity, followed by chemical treatment of the sorption material via a preselected solution of soluble salts (called “APTsorb II*M”) for use in a wastewater treatment process where competing toxic metal cations are present in the wastewater is provided by this invention. Depending upon the M+ cations contributed to the peat granule sorption activity sites by the preselected salt used in the salt solution treatment step, the granules exhibit a selectivity α of a first type of more-toxic metal cations (such as cadmium, lead, copper, or other metals at high concentrations) over a second type of less-toxic metal cations of (such as zinc, aluminum, or iron) in the wastewater; greater adsorption activity for the first type of more-toxic metal cations; and greater breakthrough capacity for the first type of more-toxic metal cations. This allows the end user to target the more-toxic metals for adsorption by the sorption medium containing the cations contributed by the preselected solution of soluble salts.