Patent ID: 7097769

Claim:
A method of boron removal from saline water containing boron and magnesium salts including a multi-stage reverse-osmosis (RO) separation process yielding product water, each stage of said process being carried out in a pressurized vessel with RO membranes separating entrant saline feed water into permeate with low salt concentration and brine with high salt concentration, said method comprising at least the steps of: a first stage RO separation at a pH<8.2; a second stage RO separation of at least part of the first-stage permeate; a third stage RO separation of the second-stage brine; wherein the entire second stage separation is carried out at a pH>9 with the brine concentration being limited to a degree preventing Mg(OH) 2 scaling on RO membrane surfaces, the permeate constituting product water, and the brine containing boron and magnesium ions; the third stage separation is carried out at a weak-acid pH, whereby the bulk of said magnesium ions are separated with the brine, while the bulk of said boron ions are retained in the permeate, and wherein the method further comprises a fourth stage of separation of the third-stage permeate, where the bulk of said boron ions is separated from said third-stage permeate, and the permeate of the fourth stage constitutes product water with low boron content.