A cross-flow microfilter capable of operating at elevated temperatures and pressures was evaluated for its ability to remove inorganic salts from supercritical water (SCW). The separation characteristics of-molten sodium nitrate were investigated. The overall performance of the cross-flow microfilter and the effects of process variables on the separation efficiency were evaluated. Separation efficiencies up to 85% were observed. An empirical model was developed for the prediction of the filtrate salt concentration and the fluidized cake resistance as a function of the salt solubility and salt flux to the filter. Physical principles governing the separation process were defined.