Accumulation of GdCl₃ in the feed of a reverse osmosis system during desalination as determined by neutron absorption

This article deals with the application of in-situ small-angle neutron scattering to investigate wastewater desalination by reverse osmosis. In a first series of experiments we take advantage of the strong neutron absorption of gadolinium (Gd) and use 0.50 g/L GdCl₃ in the feed as an indicator for concentration polarization and scaling at the membrane surface. The continuous decline of scattering during the process of desalination indicates an increase of GdCl₃ salt concentration which after 15 hours has achieved nearly 100% enhancement with respect to its initial concentration.