Na+/Mg2+ interactions on membrane distillation permeation flux and crystallization performance during high saline solution treatment

Abstract

Membrane distillation crystallization (MDC) was an effective method for saline solution treatment to simultaneously recovery pure water and salt products. In MDC process, an important topic was the influence of ionic interactions produced by complex salt solution on MDC performance. We processed a typical ternary saturated solution (Na+/Mg2+//Cl-–H2O) with MDC to investigate the influence of different Na+/Mg2+ ratios on membrane distillation permeation flux and crystal morphology from the perspective of experiment and molecular dynamics simulation. From the simulation results, it was demonstrated that increasing magnesium ions could modify the hydration structure of the cations and influence the diffusion coefficient of the hydrated ions in the solution. The reduced free water and diffusion ability led to the changes in permeation flux and crystal morphology. The crystals with different morphologies could be produced by adjusting the ratio of Na+/Mg2+ and MDC temperature. In addition, selective solvent (ethanol) wash approach was developed to further improve the separation performance and reveal the effect of Mg2+ on NaCl crystal growth.