Reverse Osmotic Separation of Sodium Chloride and Cobalt (II) Chloride through Membranes Prepared from Schiff Bases of Polyallylamine

Abstract

Crosslinked membranes from Schiff base derivatives of polyallylamine were prepared with 2-pyridinecarboxaldehyde (P) and with P followed by salicyl-aldehyde, and used for the reverse osmotic separation between sodium chloride (NaC1) and cobalt (II) chloride (CoCl₂). The membranes whose rejection (R) was high against CoCl₂ and low against NaCl at each single feed supply showed a reduced difference in R in the case of a mixed solute feed due to Donnan exclusion by fixed charges in the CoCl₂-complexed membrane. An approximate calculation of the complexed CoCl₂ revealed that a very small portion of Schiff base groups took part in the complexation. Composite membranes on a cellulosic sheet solved the problem of an extreme reduction of the membrane strength after complexation, enabling continuous and repeated use. Some transport parameters were determined. Since they indicated a semipermeable character for CoCl₂, multistage runs of a single membrane or low pressure runs of a more porous composite membrane were suggested for the effective separation of NaCl and CoCl₂.