Mechanism and kinetics of salt recoveries by seeding membrane distillation crystallization
Sprache des Vortragstitels:
ISIC 2023 International Symposium on Industrial Crystalization
Sprache des Tagungstitel:
Membrane distillation (MD) coupled with crystallization presents a sustainable and continuous process for treating saline and wastewater while simultaneously recovering salt and water using renewable energy sources. However, further analysis is required to better understand critical details such as crystallization mechanisms, salt kinetics, seeding crystal types and sizes, and concentration to provide a physicochemical understanding. Seeding crystallization plays a vital role in preventing membrane surface crystallization and ensuring continuous operation by allowing crystal growth of seeds in the metastable region without requiring supersaturation levels. In this work, a pilot plant membrane distillation column, as well as the single effects of the processes, are studied in detail. At low temperatures and with saline solutions exceeding 10% initial salinity, the process achieves precipitation in the metastable region S = 1.002 ± 0.02 as the first salt reaches its solubility limit. The growing crystals can be continuously separated from the process by sedimentation. The crystal size ranges from 150 to 300 µm and was monitored by on- and offline detection. Varying operating parameters such as temperature, seeding concentration, and crystal growth revealed further insights into the separation of salts based on their solubility products, enabling the fractional crystallization of different salts. The investigations show that MDC is a relevant option for both water and salt recovery in wastewater treatment, as well as for complex solutions.