Fouling on aluminum-brass and titanium tube surface in environment of low-temperature multi-effect distillation for desalination

Fouling on aluminum- brass tube and titanium tube in concentrated salt solutions are investigated with various calcium ion concentration and magnesium-to-calcium ion concentration ratio. The test tubes were placed in an environment with constant-temperature of 70 degrees C and then the fouling depositions at different time points were accurately quantified throughout the 63-h process. Besides, the morphology and composition of the surface fouling were detected by scanning electron microscopy and energy-dispersive X-ray spectrometer to identify the fouling crystal type. The results show that the titanium tube surface has a better anti-fouling performance compared with aluminum-brass tube. The mass increment of fouling deposition does not show a positive correlation with calcium ion concentration, rather it is influenced by the presence of magnesium ions and the type of surface material. We also found that the magnesium-to-calcium ion concentration ratio largely affects the fouling deposition, therefore, adding a certain proportion of magnesium ions to the solution can effectively reduce the fouling.