Scaling of nanofiltration membranes used for chromium(III) ions recovery from salt solutions.

The effect of membranes' structure on the efficiency of chromium(III) ions recovery from salt solution at low pH and the efficiency of chemical cleaning of these membranes were analyzed in this work. The nanofiltration membranes (DL and HL) used in this study were provided by GE Osmonics. The DL membrane had an irregular, dense support layer structure, while the HL membrane had a loose one. In the case of the DL membrane, it was found that, under tested solutions, the layer of mineral scale formed on the surface gradually decreases the membrane permeability coefficient. In the case of the DL membrane, the scaling was observed only on the surface. On the other hand, a small roughness (118Å) and low density charge (zeta potential at level -4) of the HL membrane causes an uneven growth in deposits and, consequently, irregular nature of the surface structure which hinders the removal of accumulated sediment from the tested membranes' surface. Additionally, the loose structure of the support layer of HL membrane contributes to its internal scaling. Consequently, the permanently loose structure of the HL membrane permeability coefficient was observed.

Effect of interaction between anionic surfactants and poly(piperazine-amide) nanofiltration membranes used for chromium(III) recovery from saline solution.

The effect of the anionic surfactant on the permeation properties of the nanofiltration (NF) membranes used for chromium(III) recovery from saline solution at low pH have been presented in this paper. The membrane surface layer performance periodically modified by sodium dodecyl sulphate (SDS) solution has been studied with measurements of zeta potential, atomic force microscopy (AFM) and permeability coefficient of tested membranes. It was found that the membrane surface layer modification by SDS caused a substantial reduction in the possibility of separation of loose NF membrane characterized by a high density of positively charged groups activating under the effect of the low pH of the saline solutions (HL membrane). On the other hand, in the case of dense NF membranes characterized by a strong negatively charged surface (DL membrane) constituting used the SDS improves the separation of chloride and chromium(III) ions. In this case, the surfactant solution also provides a high membrane permeability coefficient behavior over a long period of use. DL membrane modification by SDS allowed both to retain the stable membrane working for a long period and to limit the frequency of the chemical cleaning of this membrane.