Nanofiltration of seawater: fractionation of mono- and multi-valent cations

First the capabilities of six nanofiltration membranes (cut-offs of between 100 to 1000 daltons) to selectively ;demineralize salt water containing th e same cations as seawater (monovalent: Ne, K; divalent: Ca2+, Mg2+) were a ssessed and compared. The AFC-30 membrane displaying monovalent cation reje ction rates of about 50% and divalent cations rejection rates higher than 9 0% was chosen for the second part of the study dealing with seawater. The s econd part shows that water with the desired overall cation content and des ired monovalent over divalent cation ratio can be obtained from raw seawate r, without using foreign water, through a series of processes: (1) diafiltr ation, using osmosed seawater as washing solution, with a diavolumes number of 3; (2) concentration, with a volume reduction factor of 1.5; and (3) li ght final dilution of the aforementioned osmosed water. Potential applicati ons of the selectively demineralized. water are in the field of health (pre paration of nasal sprays, medical dietetics, etc.).