A new concept is introduced for separating and concentrating (predominantly) Mg2+ and SO42- from seawater, along with low monovalent ion concentrations. Seawater is first subjected to cationic ion exchange aimed at balancing the equivalent concentration ratio between divalent cations and anions. This step's effluent undergoes nanofiltration, and the MgSO4-rich retentate of the nanofiltration step undergoes further semi-batch diananofiltration for reducing the monovalent ion concentrations. Regeneration of the ion exchange resin is carried-out by permeate attained from nanofiltrating SWRO desalination retentate. The paper presents detailed results from all process steps followed by cost-analysis amounting to similar to$1.6 kg(-1) of separated Mg2+.