Method of boron removal in presence of magnesium ions

A method of boron removal from saline water containing boron and calcium 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 secondstage brine;
• wherein the entire second stage separation is carried out at a pH>9 with the brine concentration being limited to a degree preventing CaCO3 scaling on RO membrane surfaces, the permeate constituting product water, and the brine containing boron and calcium ions;
• the third stage separation is carried at weak-acid pH, whereby the bulk of said calcium 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 thirdstage permeate, and the permeate of the fourth stage constitutes product water with low boron content.

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 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, said second stage separation taking place within a single vessel;
• 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.