Salt separation from supercritical water has been identified as a key issue in the deployment of supercrifical -water technologies, particularly in the supercritical-water gasification of biomass. In order to better understand salt separation, neutron radiography has been employed to allow visualization of the transport phenomena associated with the separation of salt from supercritical D2O in a reverse-flow vessel. D2O was used as a surrogate for H2O because of its low neutron-attenuation coefficient and similar physical properties. Salts that formed a brine as a second phase, such as Na2B4O7 and K3PO4, performed well in the separator. Na2SO4, which forms a solid precipitate, created more issues and caused blockage of the separator under certain conditions. (C) 2007 Elsevier B.V. All rights reserved.