•Metal ions with different valences in HCl solutions were firstly investigated through DD.•Simple titration methods and mathematic model have been used to calculate PCl-PCl-.•The PCl-PCl- for HCl with different metal chlorides have been compared.The diffusion dialysis (DD) of hydrochloric acids in presence of their different metal salts has been investigated with a two-compartment cell in the following systems: HCl + NaCl, HCl + FeCl2, HCl + NiCl2, HCl + CuCl2, HCl + ZnCl2, and HCl + AlCl3. The corresponding Cl− permeability coefficients (P) from an organic–inorganic hybrid anion exchange membrane are determined by a simple method. That is, the experimental ions concentrations in diffusate are fitted based on the mass transfer and ionic equilibrium equations, combined with an optimized procedure. The fitted P values for Cl− follow the order in the investigated concentration range: PCl-total(CuCl2)(6.1×10-6m/s)>PCl-total(FeCl2)(3.1×10-6m/s)>PCl-total(NiCl2)(2.6×10-6m/s)>PCl-total(AlCl3)(2.0×10-6m/s)>PCl-total(NaCl)(1.6×10-6m/s)>PCl-total(ZnCl2)(3.4×10-7m/s) This changing trend is then correlated with the metal–acid complexes formation as well as the physic-chemical properties of metal ions: Cu, Fe, Ni can promote the transport of chloride ions much more than Al and Na due to their positive or neutral complexes formation with Cl−, whereas, Zn shows apparent hindrance effect to DD at its high concentration because of the dissociation equilibrium of large amount of its negative complexes within the membrane. And compared with Al, Na shows less influence to HCl transport because of its lower valence. The complexes formations between metal ions with Cl− contribute much to DD effect, as reflected well by the P value. Our work here investigates and compares the permeability of Cl− ions in the systems with different metal salts through a simple and easy method. Therefore, the results and findings can provide clues for further DD developments and applications in metal industries.

•SPPO/nano silica hybrid membranes were prepared by casting method.•The membranes show high separation performance in the alkali recovery.•Hydroxyl groups at the surface of nano silica particles play an assistant transport.Hybrid membranes for alkali recovery were prepared by incorporating nano silica particles into sulfonated poly(2,6-dimethyl-1,4-phenyleneoxide) (SPPO). The membranes possess ion exchange capacities (IECs) of 1.48–1.69 mmol/g, water uptake (WR) of 71–74%, swelling degree of 73–78% as well as favorable thermal stability and alkali resistance. They were investigated in NaOH/Na2WO4 feed solution for alkali recovery via diffusion dialysis (DD) at various temperatures. Results show that the as prepared hybrid membranes exhibit better separation capacity with the highest hydroxide flux (UOH) of 0.014 m/h at 55 °C and an acceptable separation factor of 34.5. The pure SPPO (as control) exhibits much lower UOH values at the investigated temperature range. The structure and physico-chemical properties of the hybrid membranes were investigated to better understand the DD results. Hydroxyl groups at the surface of nano silica particles are believed to play an important role in OH− diffusion.

Polyamidoamine (PAMAM) dendronized hollow fiber membranes (HFMs) were synthesized and used in the recovery of heavy metal ions. The dendronized HFMs showed strong binding ability with Cu2+, Pb2+, and Cd2+ ions. Generation 3 (G3) PAMAM dendronized HFM (G3-HFM) retained 72% of its Cu2+ binding capacity after five cycles of use and recovery. Interestingly, Cu2(OH)3Cl, Pb3(CO3)2(OH)2, and CdCO3 crystals were grown on G3-HFM surface when G3-HFMs were immersed in CuCl2, Pb(NO3)2, and CdCl2 solutions, respectively, while no crystal was observed with nonmodified HFMs. The results provide new insights into the applications of membrane-supported dendrimers in the recovery of heavy metal ions.Keywords: dendrimer; dendron; heavy metal ion; hollow fiber membrane; nanocrystal; PAMAM;