(654c) High-Salinity Solution Treatment for Salt Crystal Morphology Regulation Via Membrane Distillation Crystallization

High saline water is one of the most major targets for wastewater treatment with the serious damage to the environment and the large discharge amount with the booming growth in coal chemical industry, petroleum industry, agricultural chemical industry, etc. Herein, membrane distillation crystallization (MDC) was introduced and modified for improving the controlling salt crystal morphology. High saline ternary solution (Na⁺、Mg²⁺//Cl^--H₂O, saturated solution) was investigated. Impact of Na/Mg ions ratio on crystal morphology were revealed. The crystal particle formation and detachment procedure on the membrane surface were investigated to illustrate the separation feature of MDC (Fig. 1). Moreover, the proper operation condition region of MDC for ternary solution system was investigated, and hybrid control mechanisms Mg/Na ions ratio and operation temperature had significant influence on the nucleation, size distribution, surface morphology (Fig. 2). Benefited from the unfolded crystallization control mechanism and improved separation procedure, MDC is a flexible and promising technology to simultaneously recycle pure water and manufacture salt products from multicomponent high saline solution.

Acknowledgment

We acknowledge the financial contribution from National Natural Science Foundation of China (Grant No. 21527812, 21676043, U1663223, 21978037), MOST innovation team in key area (No. 2016RA4053) and Fundamental Research Funds for the Central Universities (DUT19TD33).

Figure 1. Schematic of surface particle distribution during MDC operation and sample preparation (a), on line detected crystal particle detachment procedure (b) and schematic of the membrane submerged experiment as comparison (c).

Figure 2. SEM images of NaCl crystals with different feed compositions and operation temperatures T_f.