Mineral scaling behavior in typical salt-resistant solar interfacial desalination: Edge-preferential crystallization vs. enhanced convection

Abstract

The burgeoning solar interfacial evaporation (SIE) technology reveals enormous prospect to address the global freshwater crisis, but its application might be limited by a grossly neglected problem of inorganic salt scaling. Herein, based on the carbon nanotubes (CNTs)@carbon black (CB)/polyvinyl alcohol (PVA) evaporators, the scaling behavior and its influence on the SIE performance were investigated systematically in the two typical anti-salt modes, including the edge-preferential crystallization (T-type mode) and the enhanced convection with vertically aligned vessels (EC-type mode). The results revealed that the scaling occurred easily in both modes when only Ca2+ and SO42− co-existed in the feed water. Meanwhile, in the T-type mode, the scaling aggravated the NaCl crystallization, resulting in a coverage of NaCl crystals on the whole evaporator surface. For a high salt concentration (10.0 wt% NaCl) with SI(Ca2++SO42−) = −0.13, the evaporation rate seriously decreased to ∼ 12.6% of its initial value after 12 h. On the contrary, the scaling behavior was significantly suppressed in the presence of Na+ and Cl− ions in the EC-type mode. Furthermore, the slight scaling presented a negligible effect on the NaCl accumulation, which ensured a stable evaporation rate of 2.58 ± 0.10 kg m−2h−1 under the same condition (10.0 wt% NaCl and SI of −0.13) for even 12 h irradiation under 2.0 sun. Therefore, it can be emphasized that developing novel evaporators not only requires a good anti-salt ability, but also possesses an excellent resistance to scaling for the practical application of SIE in the future.