Patent ID: 7854847

Claim:
A method of recovering a caustic-borate extraction solution from a hemicaustic effluent stream comprising: providing an aqueous hemicaustic stream comprising a caustic compound, a borate compound, and hemicellulose, wherein the hemicaustic stream has a pH greater than 12; providing a nanofiltration system comprising at least one but no more than three alkali-resistant nanofiltration membranes; passing the aqueous hemicaustic stream through the nanofiltration system to produce a permeate stream comprising the caustic compound, the borate compound, and hemicellulose, wherein less than about 20% by weight of the hemicellulose in the hemicaustic stream passes through the nanofiltration system to the permeate stream, and the borate concentration of the permeate stream is from about 60% to about 95% of the borate concentration of the hemicaustic stream, and greater than about 50% by weight of the caustic in the hemicaustic stream passes through the nanofiltration system to the permeate stream.