A method of boron removal from saline water containing boron and magnesium
or calcium salts including a multi-stage reverse-osmosis (RO) separation
process and comprising the steps of a first stage RO separation at
pH<8.2; a second stage RO separation over at least part of the
first-stage permeate; a third stage RO separation over the second-stage
brine. The method is characterized in that the second stage separation is
carried at pH>9 and the brine concentration is limited to a degree
preventing Mg(OH).sub.2 or CaCO.sub.3 scaling on RO membrane surfaces,
the permeate constitutes product water, and the brine contains boron and
magnesium or calcium ions; the third stage separation is carried at
weak-acid pH, whereby the bulk of the magnesium or calcium ions are
separated with the brine, while the bulk of the boron ions are retained
in the permeate. The method further comprises a fourth stage of
separation over the third-stage permeate, where the bulk of the boron
ions is separated from the third-stage permeate, and the permeate of the
fourth stage constitutes product water with low boron content.