Selective separation of divalent ions from seawater using an integrated ion-exchange/nanofiltration approach

• Published in: Chemical engineering and processing 2018-04, Vol.126, p.8-15
• Main Authors: Tang, Samuel C.N., Birnhack, Liat, Cohen, Yehuda, Lahav, Ori
• Format: Article
• Language: English
• Subjects: Desalinated water; Ion exchange; Mg2; Nanofiltration; Post treatment
• ISSN: 0255-2701; 1873-3204
• DOI: 10.1016/j.cep.2018.02.015

[Display omitted] •We introduce a new process for selective separation of Mg2+ from seawater.•Process relies on sequential ion exchange, nanofiltration and diananofiltration.•Ion exchange serves to reduce hardness to result in equal TH:SO42− equivalent ratio.•Resin is regenerated with nanofiltration permeate of 1st SWRO step retentate.•Product solution is a selective MgSO4 rich-solution obtained at ∼$1.6 (kg Mg)−1. 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 ∼$1.6 kg−1 of separated Mg2+.