Salt Recovery from Wastewater Using Membrane Distillation-Crystallization

Copyright © 2018 American Chemical Society. Osmotic membrane distillation-crystallization is proposed in this study to recover sodium carbonate, potassium nitrate, and sodium sulfate from synthetic industrial solutions leading to valorization of the salts of wastewater coming from gas treatment (flue gases containing CO2, SO2, or NOx) or from brines. The technical viability of the process is discussed in terms of transmembrane fluxes, mass transfer coefficients, and the crystal purity. The effect of concentrations of the feed and osmotic solution, flow rates, and presence of impurities (traces of different salts) was determined as well. The osmotic concentration was the main parameter affecting the transmembrane flux. The concentration of the three salts in the feed had a slight influence, and no effect could be observed by the study of flow rates. Constant mass transfer coefficients were obtained. Two membrane contactors in series were connected to increase the membrane area in order to technically validate one of the main advantages of this kind of technology: the linear and easy scale-up. Super high-purity crystals were produced: Na2CO3·10H2O, Na2SO4·10H2O, and KNO3 free-of-impurity crystals (no Cl- and salt traces trapped), ready to be reused in the industry, if desired. No cocrystallization was observed, which is a remarkable difference with conventional crystallization systems (evaporators), a partial amorphous structure is detected by X-ray diffraction, and fairly pure, large crystals were obtained.

Publication year:2018