Extracting potassium from seawater has great economic potential, although conventional methods offer low separation capacity and selectivity. In this study, a series of novel potassium ionic sieves (PISs) were synthesized using ocean manganese nodules (OMN) as raw materials. The PISs were characterized by XRD, SEM, and nitrogen adsorption-desorption. The potassium adsorption capacities and separation factors of PISs and OMN in KCl solution and sea brine showed that KMnO4 treatment will result in the highest adsorption and separation performance. The resulted sample OMN-C exhibit major composition of birnessite-type potassium manganese oxides and high micropore volumes. The adsorption capacities of OMN-C to K+ in KCl solution and sea brine were 35.2 mg g(-1) and 22.1 mg g(-1), respectively. The separation factor of OMN-C was alpha(K+/Na+) = 108.6 and the sieve did not adsorb Mg2+, indicating its relatively high separation selectivity to K+. Therefore, OMN-C can selectively extract potassium from sea brine effectively. This study not only utilized the abundant OMN resources, but also prepared effective PISs, which showed great potential in the utilization of seawater. (C) 2013 Elsevier Ltd. All rights reserved.