A positively charged PI/PDA/PEI nanofiltration membrane was prepared in this study by crosslinking between polyethyleneimine (PEI) and poly(dopamine) (PDA) on the polyimide (PI) support membrane for separating Mg 2+ and Li + from MgCl 2 /LiCl mixed solution, and its chemical structure, surface properties, and separation performance were investigated.The results indicate that the PI/ PDA/PEI membrane has a thin positively charged layer and shows excellent rejections against many inorganic salts [MgCl 2 (93.1%) > MgSO 4 (86.5%)> Na 2 SO 4 (74.7%)> LiCl (37.6%)].More importantly, the membrane exhibits long-term stability and good separation of Mg 2+ and Li + , and the Mg/Li ratio of the permeate of brine obtained from West Taijnar salt lake can be reduced from 65.3 to 5.0 at pH 6.5 by filtration.
An improved semi-empirical model used to predict the separation performance of salt lake brine by nanofiltration (NF) membrane was obtained.The transmission of the eight single salts is in the order of NaCl > LiCl > KCl > MgCl 2 > Li 2 SO 4 > K 2 SO 4 > Na 2 SO 4 > MgSO 4 .In the double salts permeation experiment, the regulation coefficient was revised by introducing an adjustment equation A in this model, because the calculated values deviated from the experimental data.The modified semi-empirical model and the experimental data under different concentration conditions has a good consistency.It shows that the semi-empirical model can be used to predict the transmission of salt lake brine.
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