| As a new separation membrane technology developed in recent years, nanofiltration (NF) membrane is a pressure driven process that forms the transition between ultrafiltration and reverse osmosis with respect to its flux and separation performance, the most appealing field of membrane science and technology compared with those traditional membranes, the advantages of NF membranes are as follows: having hole diameters of nanometers, low operation pressure, economic for it can replace many procedures in traditional process and separation technology , having high selectivity to different irons, and so on. Now NF membrane has been applied to many fields, such as medicine, food industries, biologic engineering, metallurgy, and so on, moreover, nanofiltration membrane can also be used to separate or adjust the ratio of mono- and multi-valent ions.The present work indicates the organic NF membranes and the inorganic NF membranes all have shortages, so develop composite NF membranes that have low cost, mechanically strong and thermally/chemically - resistant, easy to cleanout and good performances is a very important task.As we know, to separate or reject ions, the NF membrane not only needs nano-sized pores structure, but also needs charged on the surface. Driven by commercial interests, the negatively charged nanofiltration membrane receives more attention than positively charged one, because most nanofiltration applications focus retention of low molecular weight molecules and multi-valent anions. Now many negatively charged membranes are available in the market such as Nitto Denko NTR series, Filmtec NF series and osmonics DK series, etc. However, at some occasions, such as for retention of multi-valent cations , membrane and recovery of cathode electrophoresis lacquer, positively charged nanofiltration membrane is actually needed.For preparing a positively charged membrane, in this paper, the preparation of inorganic - organic composite NF membranes were presented, that is by phase conversion methods, polysulfone/Al2O3 composite nanofiltrtion membranes were prepared in advance, of which the average hole diameters were about 40~50A. The influences of the kind and concentration of additive in the casting solutions were discussed, and NMP was the one that can result in better performance. And then the charge modified NF membrane CTCM was prepared by coating process, moreover by using phase-inversion process the charge modified NF membrane SLCM was prepared too. The three membranes were characterized and applied on theenrichment of gold from thiourea leaching solution.the experiments used a dead-end membrane module to determine the pure water flux and solution rejections, Streaming potential was used to indicate the magnitude of electric property of the charge-modified NF membrane. Ftir and SEM are used to analyses the structure and component of membranes. Meanwhile studied the chemical stability, bearing solvent ect. Under the conditions of operation pressure about 0.65MPa and feed temperature 25 ℃, the rejection performance of NaCl respectively is about 30.22%, 18.21% and 21.15% , while the flux respectively is about 8.492Z ·m-2 ·h-1,7.006L·m-2·h-1 and 6.7941 ·m-2· h-1, streaming potential respectively is about 7.4mV and 5.3mV.In the enrichment of gold from thiourea leaching solution, the experiments showed us that charge modified NF membranes have better rejection performance. And the experiments also showed us that those factors which could make impacts on the result of purification included the feed concentration , operating pressure, concentrating time, and so on. Under the conditions of operation pressure about 0.65MPa and feed temperature 20℃, the rejection performance of Au ion is about 88-95%.
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