Aggregation of Na2SO4 Nanocrystals in Supercritical Water

Supercritical water oxidation processes (SCWO) have been developed as an alternative technology to treat toxic and/or complex chemical wastes with very good efficiency. However, one main limitation of SCWO processes comes from the precipitation of inorganic compounds which can lead to clogging and interruption of the continuous process. Unfortunately little information is available in the literature regarding the precipitation mechanism and the salt particle properties in supercritical water (T >= 374 degrees C, P >= 22.1 MPa). This work intends to study the formation of salt aggregates from one common salt: disodium sulfate (Na2SO4). A specific and dedicated experimental setup is presented and succeeded in recovering salt powders from supercritical precipitation. Several analyses are performed on the salt samples to obtain aggregate sizes, morphologies, and size distributions. On the basis of the experimental results and a previous work, a numerical modeling of the salt precipitation and aggregation is reported to acquire information on the possible aggregation mechanism.