  Supercritical water desalination (SCWD) is an alternative zero-liquid
discharge desalination technique that can overcome many technical and
environmental challenges in common desalination processes. Our recent
techno-economic analyses on the process integration and intensification of an
SCWD process suggest that SCWD can be an economically competitive zero-liquid
discharge desalination technique for highly concentrated brines. In addition to
these attractive features, this work explores the possibility of utilizing the
SCWD process for the selective recovery of industrially essential materials as
co-products. Model brines containing sodium chloride, neodymium chloride, and
other sodium-containing salts, are examined as model feeds from 25 to 450 C at
25 MPa. The sodium contents in the effluent were not sensitive to the presence
other salts, but that of neodymium was. When sodium acetate was added,
water-insoluble precipitates were obtained. The characterization of these
deposits using gas pycnometer, FT-IR, SEM/EDS, and XRD indicates that the
precipitates mainly contain neodymium hydroxide and some low-concentration
impurities. These results suggest that an SCWD process has the potential to
recover critical materials while producing freshwater.
