Diffusion dialysis for NaCl and NaAc recovery using polyelectrolyte complexes/PVA membranes

Diffusion dialysis (DD) technique is nowadays mainly utilized for recovering acid or alkali solutions, but the recovery of salts such as sodium chloride (NaCl) and sodium acetate (NaAc) is much more difficult due to their low diffusivity. Polyelectrolyte complexes (PECs)/polyvinyl alcohol (PVA) membranes containing functional groups of COH, SiOH, N+(CH3)3 and SO3Na are pioneered for DD process of salts. The membranes have improved stability in water and salt solution. The dialysis coefficients of NaCl (UNaCl) are in the range of 0.00196-0.00290 m/h, which are 6-30 times higher than the values of commercial DF-9010 and CJMCDD-1 membranes. The dialysis coefficients of NaAc (UNaAc) are in the range of 0.00108-0.00503 m/h, which are 30-143 times higher than the value of CJMCDD-1 membrane, whereas DF-9010 membrane has poor stability in NaAc solution. Finally, PECs/PVA membranes are applied to NaCl/threonine (Thr) mixture and NaAc waste residue solution, showing their outstanding advantages for DD process of salts. The membranes show both high permeability and selectivity for NaCl/Thr mixture, with separation factor (SNaCl/Thr) as high as 6.495 (DF-9010: 1.25; CJMCDD-1: 0.224). The UNaAc values for NaAc waste residue solution are 0.000602-0.00120 m/h, higher than that of commercial CJMCDD-1 membrane.