Study of Forward Osmosis Process and its Effects on the Concentration of Salt Lake Brine

Separation and concentration are two indispensable technical components of the gradient-coupling membrane technique for the extraction of valuable resources from salt lake brine. Herein, we systematically studied the forward osmosis (FO) process and its effects on the concentration of salt lake brine. First, the chemical composition, structure, and surface properties of both sides of the FO membrane were characterized and analyzed. We then deeply probed the effect of operating conditions and the properties of the draw solution on the water flux and ion transport, according to the experimental results and mathematical models. Moreover, the hypersaline NaCl solution and the old brine (salt lake brine after potassium precipitation) were applied as the draw solutions to concentrate the separated brine (salt lake brine after nanofiltration membrane separation). It was shown that the surface structure and concentration polarization of the membrane obviously affected the water flux and reverse salt transport, while the high concentration of the draw solution simultaneously caused a large osmotic pressure, resulting in a large water flux and reverse salt transport. In addition, the water fluxes reached 18.28 L·m–2·h–1 (NaCl) and 29.78 L·m–2·h–1 (the old brine), and the enrichment ratios for Li+ were 1.98 and 4.78, respectively. This study further advances the application of FO membranes in the development of salt lake resources and also contributes to the technical support of the brine concentration part of the membrane-coupling process.