Brine concentration

A process for separating solvent from a feed solution, said process comprising:

• contacting a feed solution comprising solutes dissolved in a solvent with one side of a nanofiltration membrane,
• applying hydraulic pressure to the feed solution, such that solvent and some of the dissolved salts from the feed solution flow through the nanofiltration membrane to provide a permeate solution on the permeate-side of the nanofiltration membrane and a concentrated solution on the retentate-side of the nanofiltration membrane;
• contacting the permeate solution from the nanofiltration membrane with one side of a reverse osmosis membrane and applying hydraulic pressure to the permeate solution, such that solvent from the permeate solution flows through the reverse osmosis membrane to leave a concentrated solution on the retentate-side of the reverse osmosis membrane,
• using the concentrated solution from the retentate-side of the reverse osmosis membrane as at least part of the feed solution to the nanofiltration membrane;
• withdrawing at least a portion of the concentrated solution from the retentate-side of the nanofiltration membrane;
• and
• wherein, prior to being used as at least a portion of the feed solution to the nanofiltration membrane, the concentrated solution from the retentate-side of the reverse osmosis membrane is passed through an additional semi-permeable membrane to provide a permeate solution on the permeate-side of the additional semi-permeable membrane and a retentate solution on the retentate-side of the additional semi-permeable membrane, which permeate solution is used as at least a portion of the feed to the nanofiltration membrane.