Metal removal from single and multimetallic equimolar systems by extracellular polymers extracted from activated sludges as evaluated by SMDE polarography

This paper provides information on the use of static mode dropping electrode (SMDE) polarography for the measurement of the metal complexation potential of extracellular (ECP), extracted from activated sludges, from aqueous solution containing Pb, Cu, Cd and Ni in single, bi-, tri- and multimetallic equimolar systems. This technique was useful for the evaluation of different free metal species (Pb, Cu, Cd, Ni) existing in the test solution. First, the ability of ECP to complex each metal, studied at pH 7 was carried out using polarography titration and Chau and Ruzic's models. The ECP exhibited the following order of metal complexation (number of sites): Cu > Pb > Ni > Cd. In an equimolar mixture, results indicated that the metal complexation capabilities of ECP in multimetallic systems are not affected for Cd and Pb, weakly affected for Ni. In a multimetallic equimolar mixture, the quantities of metal removed were in accordance with the number of sites present in ECP. It was not possible to quantify Cu removal by ECP due to the distortion of the peak obtained by polarography in SMDE mode. At the study potential for Cu (0.15 to −0.20 V) the high concentration of organic matter (ECP) may have caused interference with the mercury drop. The IR data, supported by the pKa of ECP revealed that the carboxylic group of ECP may play a major role in metal binding onto ECP at pH 7.