Ultrafiltration of Divalent Metal Cations from Aqueous Solution Using Polycarboxylic Acid Type Biosurfactant

Abstract

Biosurfactant-based ultrafiltration was used to remove the divalent metal ions, Cu+2, Zn+2, Cd+2, and Ni+2ions from aqueous solution containing either a single metal species or a mixtures of metal ions. Polycarboxylic acid type biosurfactant, sodium salt of 2-(2-carboxyethyl)-3-decyl maleic anhydride (DCMA-3Na) derived from spiculisporic acid was added to trap the metal ions through the binding onto the micelles and/or the formation of metal-biosurfactant precipitates. The present study aimed at investigating the permeating flux and the removal efficiencies of divalent metal cations from aqueous solutions using a batch-type stirred ultrafiltration cell. Concerning the flux decline, the membrane of molecular weight cutoff (MWCO) 1,000 is more vulnerable to the formation of a gel layer and the concentration polarization than that of MWCO 3,000. Formation of metal-biosurfactant precipitates makes the gel concentration of DCMA-3Na relatively low compared with the case of chemically synthesized surfactant such as SDS and CPC. However, biosurfactant-based ultrafiltration is of practical significance because high rejection efficiencies for cupric, zinc, cadmium ions can be achieved only with equimolar ratio of DCMA-3Na to the metal ions. DCMA-3Na exhibits the metal binding affinity on the order of Cd+2> Cu+2≈ Zn+2> Ni+2when one metal species is present. Even under the competitive binding condition when four metal ions are present in the mixture, DCMA-3Na shows the same affinity order toward the metal ions, although small variations in rejection coefficients are observed.