Abstract:

As a typical high concentration saline wastewater, Na⁺,Mg²⁺//Cl^--H₂O solution system was treated via membrane distillation and crystallization to recycle the pure water and high NaCl crystal products with high property, simultaneously. The performance of membrane distillation and the properties NaCl product were explored under the different operation temperature and the various concentration of salts. The results indicate that, the permeate flux obviously increased with the increasing of the operation temperature, due to the increasing of the different vapour pressure with the temperature. Moreover, the permeate flux slightly decreased with the adding content of MgCl₂ to the solution, it was mainly due to the decrease of the mass fraction of water and the increase of solution viscosity. The surface crystal particle deposition was also evaluated via lunching the comparison experiments. In addition, the hollow fiber membrane used in the experiments presents favorable reusability with 20 cycles during the membrane distillation. The NaCl crystal products obtained under the operation temperature of 65℃ exhibited the narrow size distribution, the smooth crystal surface, the perfect cube structure and without agglomeration, and the average size was 91.04, 91.38 and 122.56 μm, and the coefficient of variation (C.V.) was 28.78, 30.63 and 36.77, respectively. Meanwhile, the conductivity recycled water was 5 μS?m^-1, and the purity of crystal products were higher than 98.15% after washing with the selective solution (ethanol). Therefore, by regulate the membrane permeate flux and interface function, the membrane distillation crystallization is a feasible technology to process the high concentration saline wastewater (Na⁺,Mg²⁺//Cl^--H₂O) to recycle the pure water and NaCl product with high purity, smooth surface and uniform size under the appropriate operation temperature and the lower Mg²⁺ concentration. This research can explore the potential approach for the ‘near zero discharge’ treatment of multiple ions high saline wastewater and the reuse of the inorganic salt resource.

Key words: membrane distillation, crystallization, high saline wastewater, permeate flux, crystal morphology

摘要：

利用真空膜蒸馏-结晶耦合技术处理多元高盐废水(Na⁺、Mg²⁺//Cl^--H₂O)，回收纯水和高品质NaCl晶体产品，考察不同操作温度和不同无机盐离子浓度对膜蒸馏性能和NaCl晶体产品性质调控作用。结果表明随着温度升高导致饱和蒸气压增大，增大了跨膜压差，膜的渗透通量逐渐升高；随着溶液中Mg²⁺浓度的逐渐升高，膜的渗透通量呈下降的趋势，主要是由于水的质量分数下降和溶液黏度增加；膜蒸馏过程中，通过对比实验，分析了疏水微孔膜表面在膜蒸馏操作条件下表面晶体颗粒沉积的程度，证实了使用的中空纤维膜性能稳定，重复使用20次后仍能保持稳定通量；操作温度为65℃时，不同离子浓度的饱和原料液(MgCl₂质量占NaCl和MgCl₂总质量的0%、5.0%和10.0%)得到NaCl晶体产品平均粒径分别为91.04、91.38和122.56 μm，粒度分布的变异系数C.V.值分别为28.78、30.63和36.77，粒径分布集中，表面相貌平整，呈完美的立方体形态，没有团聚现象；同时，膜蒸馏得到的水纯度较高，电导率均小于5 μS?m^-1，采用选择性溶剂乙醇洗涤后的NaCl晶体产品纯度均大于98.15%。综上，通过膜蒸馏过程中渗透通量和膜界面的有效调控，在适宜的操作温度和较低的Mg²⁺含量下，膜蒸馏结晶过程从多元高盐废水(Na⁺、Mg²⁺//Cl^--H₂O)控制分离获得纯度较高、表面形貌完好、粒度均一的NaCl晶体产品。这一研究将为综合治理多元无机高盐废水，实现废水的近零排放和无机盐资源回用开拓新的思路。

关键词: 膜蒸馏, 结晶, 高盐废水, 渗透通量, 晶体形貌