【作者】 黄瑞华；

【导师】 陈国华；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2007， 博士

【摘要】 通过季铵化与接枝共聚两种不同的方式对壳聚糖进行改性,获得了两种不同的壳聚糖季铵盐,分别为2-羟基-3-三甲铵基-丙基壳聚糖（HAPC）和壳聚糖-三甲基烯丙基氯化铵接枝共聚物（GCTACC）。以HAPC和GCTACC为活性层的成膜材料,以亲水性不一的聚砜（PSF）超滤膜、聚丙烯腈（PAN）超滤膜为支撑层,以环氧类、二异氰酸酯类等不同类型的有机试剂为交联剂,采用涂敷和交联的方法,制备了11种新型荷正电复合纳滤膜。利用扫描电境（SEM）、原子力显微镜（AFM）对其结构形貌进行观察;利用红外光谱对膜表面交联情况进行分析;此外,还调查了复合膜的渗透特征和一些其它特征。以高氯酸为催化剂和反应介质,使壳聚糖在均相条件下与缩水甘油醚三甲基氯化铵发生季铵化反应,制备2-羟基-3-三甲铵基-丙基壳聚糖（HAPC）。以HAPC为活性层材料,以PAN为支撑层,以具有不同链长结构的环氧氯丙烷（ECH）和丙三醇三缩水甘油醚（GCGCE）环氧类为交联剂制备了两种HAPC/PAN复合纳滤膜。ECH交联的复合膜在室温下纯水渗透系数为9.25 L·.h^-1·m-2·MPa^-1;在室温和操作压力为1.0MPa下,其截留分子量为560,膜孔径约为0.74nm,均方粗糙度（RMS）为8.50±1.5（103nm）;电压渗系数为12.0 mv·MPa^-1;在操作压力为1.0MPa下,对1000 mg·L^-1 MgCl₂、CaCl₂、KCl、NaCl和Na2SO4溶液的截留率分别为96.6、96.6、56.1、57.5和26.6%,通量分别为7.00、7.30、16.3、15.9、9.86 L·m-2·h^-1。GCGCE交联HAPC/PAN复合纳滤膜。该复合膜在室温下纯水渗透系数为16.6 L·h^-1·m-2.·MPa^-1;在室温和操作压力为1.0MPa下,其截留分子量为800,膜孔径约为0.84nm;均方粗糙度（RMS）为22.3±0.30（103nm）;电压渗系数为4.43mv·MPa^-1;在操作压力为1.0MPa,对1000 mg·L^-1 MgCl₂、CaCl₂、MgSO4、KCl和K2SO4溶液的截留率分别为87.9、72.4、25.4、19.1和11.3%,通量分别为12.2、22.9、28.9、29.6和31.8 L·m-2·h^-1。发现具有长链结构GCGCE交联HAPC/PAN的复合纳滤膜的截留分子量、纯水渗透系数均要大于具有短链结构ECH交联HAPC/PAN的复合纳滤膜。以HAPC为活性层材料,以PAN为支撑层,以具有不同刚软结构的二异氰酸酯如六亚甲基二异氰酸酯（HDI）、甲苯二异氰酸酯（TDI）为交联剂,分别制备了两种HAPC/ PAN复合纳滤膜。HDI交联的复合膜在室温下纯水渗透系数为17.2 L·. h^-1·m-2·MPa^-1;在室温和操作压力为1.0MPa下,截留分子量为520,膜孔径约为0.72nm,电压渗系数为6.31 mv·MPa^-1;均方粗糙度（RMS）为15.6±0.24（103nm）;在操作压力为1.0MPa下,对1000 mg·L^-1 MgCl₂、CaCl₂、KCl、NaCl和Na2SO4溶液的截留率分别为92.9、93.4、50.3、67.3和19.6%,通量分别为12.3、32.8、31.3、10.4和32.3 L·m-2·h^-1;HDI和TDI交联的复合膜在室温下纯水渗透系数为10.6 L·h^-1·.m-2.·MPa^-1;在室温和操作压力为1.0 MPa下,截留分子量为560,膜孔径约为0.74nm;电压渗系数为7.73 mv·MPa^-1;均方粗糙度（RMS）为12.3±0.52 （103nm）;在操作压力为1.0MPa下,对1000mg·L^-1 MgCl₂、CaCl₂、MgSO4、KCl、NaCl和Na2SO4溶液的截留率分别为96.6、95.6、50.4、61.5、61.5和24.7%,通量分别为12.9、14.7、15.3、14.1、13.2和12.6 L·m-2·h^-1。发现以单一具有软性结构的HDI为交联剂制备的纳滤膜具有较强的截留能力和透水能力。以单一具有刚性结构的TDI为交联剂所制备的复合膜较脆、易裂;且制备条件苛刻。以TDI与HDI混合为交联剂所制备的复合膜,有较强的截留能力和适中的透水能力。以HAPC为活性层材料,以PAN超滤膜为支撑层,以己二酸和乙酸酐的混合酸酐为交联剂,制备了另一种HAPC/PAN复合纳滤膜。该膜在室温下纯水渗透系数为6.99 L·.h^-1·m-2·MPa^-1;在室温和操作压力为1.0 MPa下,截留分子量为560,膜孔径约为0.74nm;电压渗系数为7.73 mv·MPa^-1;均方粗糙度（RMS）为7.50±0.31 （103nm）;在操作压力为1.0MPa下,对1000 mg·L^-1 MgCl₂、NaCl、KCl、MgSO4、K2SO4、Na2SO4和CaCl₂溶液的截留率分别为95.8、69.7、65.7、38.1、21.9、27.5和97.2%,通量分别为4.81、7.96、8.88、7.96、8.19、8.27和7.65 L·m-2·h^-1。由于交联时引进酯基,复合膜的疏水性增强,该复合膜截留能力较强,但透水性降低。以HAPC为表面活性层,以PSF为支撑层,分别以HDI和ECH为交联剂,制备了两种HAPC/PSF复合纳滤膜。HDI交联HAPC/PSF的复合膜在室温下纯水渗透系数为13.6 L·. h^-1·m-2·MPa^-1;在室温和操作压力为1.0MPa下,该膜截留分子量为500,膜孔径约为0.71nm;电压渗系数为10.8 mv·MPa^-1;均方粗糙度（RMS）为9.63±0.18 （103nm）;在操作压力为1.0MPa下,对1000 mg·L^-1 MgCl₂、MgSO4、Na2SO4、K2SO4、KCl和NaCl溶液的截留率分别为96.9、58.5、36.5、33.1、76.0和80.9%,通量分别为12.9、11.9、11.6、11.6、13.8和13.9 L·m-2·h^-1;ECH交联的复合膜在室温下纯水渗透系数为12.6 L·.h^-1·m-2·MPa^-1;在室温和操作压力为1.0MPa下,该膜截留分子量为720,膜孔径约为0.82nm;电压渗系数为34.2 mv·MPa^-1;均方粗糙度（RMS）为8.45±0.38 （103nm）,在操作压力为1.0MPa下,对1000 mg·L^-1 MgCl₂、MgSO4、Na2SO4、K2SO4、KCl和NaCl溶液的截留率分别为96.5、45.0、31.8、22.5、67.1和70.8%,通量分别为15.6、14.1、14.4、13.9、15.5和14.1L·m-2·h^-1。以PSF为支撑层, HDI为交联剂所制备的HAPC/PSF复合纳滤膜相对以PAN为支撑层所制备的HAPC/PAN复合纳滤膜,膜的截留性能提高,但透水能力下降;以PSF为支撑层,ECH为交联剂所制备的HAPC/PSF复合纳滤膜相对以PAN为支撑层所制备的HAPC/PAN复合纳滤膜,膜的透水能力增强,但截留性能几乎保持不变。将壳聚糖与三甲基烯丙基氯化铵进行接枝共聚,制备壳聚糖-三甲基烯丙基氯化铵接枝共聚物（GCTACC）。以GCTACC为表面活性层材料,以PAN为支撑层,以ECH为交联剂所制备的GCTACC/PAN复合纳滤膜。该膜在室温下纯水渗透系数为6.30 L·.h^-1·m-2·MPa^-1;在室温和操作压力为1.0MPa下,其截留分子量仅为490左右,膜孔径约为0.70nm;电压渗系数为11.7mv·MPa^-1;均方粗糙度（RMS）为10.2±0.13（103nm）;在操作压力为1.2MPa时,对质量浓度为1000 mg·L^-1的MgCl₂、CaCl₂、MgSO4、、NaCl、Na2SO4溶液的截留率分别为97.6、97.2、89.7、65.0和40.7%;通量分别为6.80、6.12、6.12、5.57和5.51 L·h^-1·m-2。由于以具有短链结构的ECH为交联剂,形成交联网络孔径较小,该膜的透水能力较弱,截留分子量小。以GCTACC为表面活性层材料,以PAN为支撑层,以具有刚软结构不同的二异氰酸酯类（HDI和TDI）为交联剂,制备了二异氰酸酯类交联的GCTACC /PAN复合纳滤膜。HDI交联的复合膜在室温下纯水渗透系数为6.42 L·.h^-1·m-2·MPa^-1;截留分子量为900左右,膜孔径约为0.87nm;电压渗系数为6.80 mv·MPa^-1;均方粗糙度为8.76±0.23（103nm）;在操作压力为1.2MPa下,对2000 mg·L^-1 MgCl₂、CaCl₂、MgSO4、KCl、NaCl和Na2SO4溶液的截留率分别为95.6、95.4、80.8、53.7、66.4和30.7%,通量分别为6.73、6.73、6.12、6.43、7.35和6.73 L·m-2·h^-1。TDI交联的复合膜在室温下纯水渗透系数为14.1 L·.h^-1·m-2·MPa^-1;截留分子量为930左右,膜孔径约为0.89nm;电压渗系数为6.80 mv·MPa^-1;均方粗糙度为7.28±0.07（103nm）;在操作压力为1.2MPa下,对2000mg·L^-1 MgCl₂、CaCl₂、MgSO4、KCl、NaCl和Na2SO4溶液的截留率分别为94.0、91.7、61.9、41.9、57.0和20.1%,通量分别为9.48、10.1、11.3、8.57、8.57和8.57 L·m-2·h^-1。具有刚性结构的GCTACC与具有软性分子链结构的HDI交联时相容性较好,交联网络相对致密,膜的孔径较小。复合纳虑膜透水能力较差,截留分子量较小。以GCTACC为表面活性层材料,以PAN为支撑层,己二酸和乙酸酐混合酸酐为交联剂,制备了另一种GCTACC/PAN复合纳滤膜。该膜在室温下纯水渗透系数为7.13 L·.h^-1·m-2·MPa^-1;截留分子量为900左右,膜孔径约为0.87nm;均方粗糙度为7.70±0.76 （103nm）;在操作压力为1.0MPa下,对1000mg·L^-1的MgCl₂、MgSO4、Na2SO4、K2SO4、KCl和NaCl溶液截留率分别为90.0、56.0、26.4、14.0、41.3和37.4%,通量分别为6.12、5.90、5.42、5.72、6.12和5.67 L·h^-1·m-2。由于交联引进酯基,复合膜的疏水性增强,该复合膜表现出较弱的透水能力。SEM观察显示出该复合膜截面呈层状叠加结构或呈指状分布支撑层上复合了一层较薄的活性层,表面呈现出少量凝胶颗粒或叠加的片状凝胶层。与其它纳滤膜类同,随着料液浓度的增大,膜的截留率下降。随着操作压力的增大,通量呈线性增加;截留率先增大,当操作压力超过某一值时,便趋于稳定或呈现下降的趋势。料液流速对膜性能影响较小。对不同盐溶液的截留顺序为:MgCl₂> MgSO₄> NaCl >Na₂SO₄或MgCl₂ > NaCl > MgSO₄> Na₂SO₄,复合膜的电压渗系数β为正值,均呈现荷正电纳滤膜的特征。首次提出荷正电纳滤膜去除卤水中钙、镁离子后,加入水氯镁石制备光卤石的新方法,具有节能、操作简单、高效等优点。借助XRD对光卤石样品进行了表征。以废水回用为目的,采用自制的荷正电复合纳滤膜处理褐藻酸钠废水。.结果表明,废水经纳滤处理后,出水的CODcr为21.4mg/L,去除率为93.0%;对Ca2+的去除率为89.0% ,对硬度的去除率为88.3%,能很好实现废水的软化和有机物的去除,出水水质完全可回用于生产工艺。更多还原

【Abstract】 Two different quaternized chitosans are prepared by two different methods, 2-hydroxy-3-trimethyl ammonium propyl chitosan （HAPC） and graft copolymer of trimethylallyl ammonium chloride onto chitosan （GCTACC）, respectively. Eleven kinds of positively charged NF membranes are prepared by method of coating and cross-linking using HAPC and GCTACC as surface active layer; PSF UF membrane and PAN UF membrane with different hydrophilicity as support layer and different organic reagents such as epoxide, diisocyanate, etc as cross-linking reagents. Their structure images are characterized by scanning electron microscope （SEM） and atomatic force microscopy （AFM）, and their cross-linking on the surface is analyzed by infrared spectrum （IR）. Besides, the permeation characteristic is investigated as well as other ones.HAPC is prepared using HClO4 as catalyst and reaction medium,which makes chitosan and diglycidyl ether trimethyl ammonium react under mild conditionsTwo kinds of HAPC/PAN composite NF membranes are prepared using HAPC as surface active layer; PAN as support layer and epoxide such as epichlorohydrin （ECH） with short chain; glycerol tridiglycidyl ether （GCGCE） with long chain as cross-linking reagents. At room temperature, the water permeability through the membrane from ECH cross-linking is 9.25 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 560, with a pore diameter of 0.74nm or so, and the root-mean square roughness is 8.50±1.5（103nm）, and its pressure osmotic coefficient of 12.0 mv·MPa^-1. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1MgCl₂, CaCl₂, KCl, NaCl and Na2SO4 is 96.6, 96.6, 56.1, 57.5 and 26.6%, respectively, with a flux of 7.00, 7.30, 16.3, 15.9 and 9.86 L·m-2·h^-1, respectively. At room temperature, the water permeability through the membrane from GCGCE cross-linking is 16.6 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 800, with a pore diameter of 0.84nm or so, and the root-mean square roughness is 22.3±0.30 （103nm）, and its pressure osmotic coefficient of 4.43 mv·MPa^-1. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1 MgCl₂, CaCl₂, MgSO4, KCl and K2SO4 is 87.9, 72.4, 25.4, 19.1 and 11.3%, respectively, with a flux of 12.2, 22.9, 28.9, 29.6 and 31.8 L·m-2·h^-1, respectively.It is found that NF membrane from GCGCE cross-linking shows stronger permeability and bigger cut-off molecular weight （MWCO） than the one from ECH cross-linking, which results from the relatively longer chain in GCGCE.Two kinds of HAPC/PAN composite NF membrane are prepared using HAPC as surface active layer; PAN membrane as support layer and diisocyanate such as hexamethylene diisocyanate （HDI） with clinical structure; toluene diisocynate （TDI） with rigid structure as cross-linking reagents. The performance and characterization about them are listed as follows. At room temperature, the water permeability through the membrane from HDI cross-linking is 17.2L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 520, with a pore diameter of 0.72nm or so, and its pressure osmotic coefficient of 6.31 mv·MPa^-1, and the root-mean square roughness is 15.6±0.24（103nm）. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1 MgCl₂, CaCl₂, MgSO4, NaCl and Na2SO4 is 92.9, 93.4, 50.3, 67.3 and 19.6%, respectively, with a flux of 12.3, 32.8, 31.3, 10.4 and 32.3 L·m-2·h^-1, respectively. At room temperature, the water permeability through the membrane from mixed diisocyanate cross-linking is 10.6 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 560, with a pore diameter of 0.74nm or so, and its pressure osmotic coefficient of 7.73 mv·MPa^-1, and the root-mean square roughness is 15.6±0.24（103nm）. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1 MgCl₂, CaCl₂, MgSO4, KCl, NaCl and Na2SO4 is 96.6, 95.6, 50.4, 61.5, 61.5 and 24.7%, respectively, with a flux of 12.9, 14.7, 15.3, 14.1, 13.2 and 12.6 L·m-2·h^-1, respectively.The composite NF membrane from HDI cross-linking has stronger permeability and allows higher rejection. And the one from HDI cross-ling shows some disadvantages, i.e. this membrane is fragile and easily crackle, and its conditions of preparation are comparatively severe. However, the composite NF membrane from mixed diisocynate containing TDI and HDI has higher rejection, and it allows moderate permeability.Another HAPC/PAN composite NF membrane is prepared using HAPC as surface active layer; PAN as support layer and mixed anhydride of acetic anhydride \and hexane diacid as cross-linking reagent. At room temperature, the water permeability through this membrane is 6.99L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 565, with a pore diameter of 0.74nm or so, and the root-mean square roughness is 7.50±0.31（103nm）. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1 MgCl₂,NaCl,KCl,MgSO₄,K₂SO₄,Na₂SO₄ andCaCl₂ is 95.8,69.7, 65.7, 38.1, 21.9, 27.5and 97.2%, respectively, with a flux of 4.81, 7.96, 8.88, 7.96,8.19,8.27and 7.65 L·m-2·h^-1, respectively. The resultant membrane has higher rejection, but it shows weaker permeability, which results from the stronger hydrophobicity due to cross-linking.Two kinds of HAPC/PAN composite NF membranes are prepared using HAPC as surface active layer; PSF membrane as support layer; both HDI and ECH as cross-linking reagent. At room temperature, the water permeability through the membrane from HDI cross-linking is 13.6 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 500, with a pore diameter of 0.71nm or so, and its pressure osmotic coefficient of 10.8 mv·MPa^-1, and the root-mean square roughness is 9.63±0.18（103nm）. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1 MgCl₂, MgSO4, Na2SO4, K2SO4, KCl and NaCl is 96.9, 58.5, 36.5, 33.1, 76.0 and 80.9%, respectively, with a flux of 12.9, 11.9, 11.6, 11.6, 13.8 and 13.9 L·m-2·h^-1, respectively. At room temperature, the water permeability through the membrane from ECH cross-linking is12.6 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 720, with a pore diameter of 0.82 nm or so, and its pressure osmotic coefficient of 34.2 mv·MPa^-1, and the root-mean square roughness is 15.6±0.24（103nm）. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1 MgCl₂, MgSO4, Na2SO4, K2SO4, KCl and NaCl is 96.5, 45.0, 31.8, 22.5, 67.1 and 70.8%, respectively, with a flux of 15.6, 14.1, 14.4, 13.9, 15.5 and 14.1L·m-2·h^-1, respectively.Compared with the HAPC/PAN composite NF membrane from HDI cross-linking, the HAPC/PSF composite one from HDI cross-linking has higher rejection, but shows weaker permeability. Compared with the HAPC/PAN composite NF membrane from ECH cross-linking, the HAPC/PSF composite one from ECH cross-linking has better performance with stronger permeability and almost unchanging rejection.Graft copolymer of trimethylallyl ammonium chloride onto chitosan （GCTACC） is obtained by grafting trimethylallyl ammonium chloride on chitosan. GCTACC/PAN composite NF membrane is prepared using GCTACC as surface active layer; PAN membrane as support layer and ECH as cross-linking reagent. At room temperature, the water permeability through this membrane is 6.30 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 490, with a pore diameter of 0.70nm or so, and the root-mean square roughness is 10.2±0.13（103nm）. Addtionally, at a pressure of 1.2MPa, the rejection for 1000 mg·L^-1 MgCl₂, CaCl₂, MgSO4, NaCl and Na2SO4 is 97.6, 97.2, 89.7, 65.0 and 40.7%, respectively, with a flux of 6.80, 6.12, 6.12, 5.57 and 5.51 L·h^-1·m-2, respectively. This membrane has weaker permeability due to the introduction of hydrophilicity groups from cross–linking, in good agreement with small MWCO.GCTACC/PAN composite NF membranes are prepared using GCTACC as surface active layer; PAN membrane as support layer; both HDI and TDI as cross-linking reagents. At room temperature, the water permeability through the membrane from HDI cross-linking is 6.42 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 900, with a pore diameter of 0.87nm or so, and its pressure osmotic coefficient of 6.80 mv·MPa^-1, and the root-mean square roughness is 8.76±0.23（103nm）. Addtionally, at a pressure of 1.2MPa, the rejection for 2000 mg·L^-1 MgCl₂, CaCl₂, MgSO4, KCl, NaCl and Na2SO4 is 95.6, 95.4, 80.8, 53.7, 66.4 and 30.7%, respectively, with a flux of 6.73, 6.73, 6.12, 6.43, 7.35 and 6.73 L·m-2·h^-1 L·h^-1·m-2, respectively. At room temperature, the water permeability through the membrane from HDI cross-linking is 14.1L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 930, with a pore diameter of 0.89 nm or so, and its pressure osmotic coefficient of 6.80 mv·MPa^-1, and the root-mean square roughness is 7.28±0.07（103nm）. Addtionally, at a pressure of 1.2MPa, the rejection for 2000 mg·L^-1 MgCl₂, CaCl₂, MgSO4, KCl, NaCl and Na2SO4 is 94.0, 91.7, 61.9, 41.9, 57.0 and 20.1%, respectively, with a flux of 9.48, 10.1, 11.3, 8.57, 8.57 and 8.57 L·h^-1·m-2, respectively.GCTACC/PAN composite NF membrane from HDI cross-linking shows weaker permeability and has low molecular weight cut-off, which can results from the reason that GCTACC is polymer with rigid structure, while HDI has clinical structure, thus the compatibility between GCTACC and HDI is better and the cross-linking reaction is carried on easily, resulting in the compact cross-linked network and smaller pore diameter of membrane.Another GCTACC/PAN composite NF membrane is prepared using GCTACC as surface active layer; PAN membrane as support layer and mixed anhydride of acetic anhydride and hexane diacid as cross-linking reagent. At room temperature, the water permeability through this membrane fis 7.13 L·.h^-1·m-2·MPa^-1, and its molecular weight cut-off is 900, with a pore diameter of 0.87 nm or so, and the root-mean square roughness is 7.70±0.76 （103nm）. Addtionally, at a pressure of 1.0MPa, the rejection for 1000 mg·L^-1 MgCl2, MgSO4, Na2SO4, K2SO4, KCl and NaCl is 90.0, 56.0, 26.4, 14.0, 41.3 and 37.4%, respectively, with a flux of 6.12、5.90、5.42、5.72、6.12 and 5.67 L·h^-1·m-2, respectively. It is found that the resultant membrane shows weaker permeability,as a result of stronger hydrophobicity due to cross-linking.Thus it is not difficult to find that the characteristic and performance of composite membranes are related to the physicochemical characteristic of film-forming material; the type of cross-linking reagent and the compatibility between surface active layer and support layer and roughness, etc.The structure images of composite NF membrane are observed by SEM. The results suggest the cross-section of membrane is consist of adding-layer or a thin active layer on finger-like support layer, and the surface of membrane has a contribution of some gel particle or adding gel-layer. Similar to other nanofiltration membrane, the rejection decreases with an increasing in feed concentration; with an increase of operating pressure, the flux almost increases linearly; and the rejection increases slowly, then approaches a constant value or shows the trend to decrease when operating pressure exceeds a certain value. And the feed cross-flow rate has little influence on membrane performance. Besides, the rejection of composite NF membranes is related to the existent form of ions. The rejection order for different salts is MgCl2 > MgSO4 > NaCl > Na2SO4 or MgCl2 > NaCl > MgSO4 > Na2SO4, and the pressure osmotic coefficients are positive, suggesting the characteristic of positively charged NF membrane.It is reported first that a positively charged NF membrane is adopted to carry on the preparation of carnallite by rejection of Ca2+ and Mg2+brackish water through NF and addition of MgCl2·6H2O. The method has some advantages including high efficiency, conveninent operation, etc. And carnallite is characterized by XRD.Additionally, the positively charged composite membrane prepared is applied to treat wastewater that drained from the production of sodium alginate.The results suggest that after the treatment of nanoflitration , the desalted solution might be reused as technological water , with a rejection of 93.0% for CODcr （21.4mg/L）, a rejection of 89.0 % for Ca2+ and a rejection of 88.3% for rigidity.更多还原