A magnetic modification of conventional adsorbent powders to remove them rapidly from water is investigated. In this paper we study the possibility of using a non-magnetic adsorbent powder mixed with magnetite and a coagulant such as ferric chloride added after the adsorption to create magnetic flocs that can be magnetically separated (magnetic seeding). A natural zeolite and Na-activated zeolite mixed with magnetite and ferric chloride are tested. The combination of sedimentation (with coagulant) followed by magnetic filtration is from six to 30 times faster than only sedimentation (with coagulant) in attaining the same final turbidity. Also, a magnetic activated carbon (MAC) powder with and without the addition of ferric chloride is tested. The process conditions that lead to a residual turbidity less than 10% after 5–10 min of magnetic separation are defined for all the powders. The tests on Mn(II) adsorption on Na-activated zeolite–magnetite mixtures show that the adsorption improvement due to activation is not affected by the addition of the coagulant. Moreover, adsorption of the tested cationic surfactants on MAC is up to 30% higher by adding ferric chloride. Negligible concentrations of Fe(III) are found in all treated samples. This technique can potentially be applied to any non-magnetic adsorbent powder and/or to any existing coagulation/flocculation treatment.