Separation of Heavy Metals and Dyes from Aqueous Solution by Biopolymer and Surfactant Supported Ultrafiltration

Abstract

Polymer Enhanced Ultrafiltration is a technique that is equally effective for removing both inorganic and organic pollutants from water. In this study, inorganic pollutants such as heavy metals (i.e. Cu, Zn, Pb, Ni, Co) and organic pollutants or dyes like Methylene Blue (MB), Alizarin Red S (ARS) and Reactive Black 5 (RB5) were removed. This is surfactant as well as bio-polymer based technique; surfactants are amphiphilic in nature with polar head and non-polar long organic chain. At a certain concentration namely critical micelle concentration (CMC), solution properties change and aggregation or assemblage of surfactant monomers take place in the interior of solution. This aggregation or micelles in the interior of solution have capacity to entrap pollutants: inorganic pollutants on the micellar surface and organic dyes get accumulated into core of micelles in both a separate or simultaneous fashion. Thereafter a membrane is used to hamper these entrapped pollutants along with surfactants on one side of solution called retentate while the pollutants free stream of water is obtained on other side of membrane called permeate solution. Removing efficiency of pollutants in this permeate solution is assessed by two major physical parameters, rejection co-efficient (R) and permeate flux (J). These parameters are highly dependant on many factors, for example, choice of surfactant, pH, membrane pore size, pressure, concentration of surfactants and target pollutants. This study was divided in two parts: In part (I), heavy metals i.e. lead, cobalt, nickel, copper and zinc were removed with help of bio-polymer namely sericin at Chemical Engineering Department, University of Waterloo, Canada; whereas in part (II), organic dyes for example Reactive Black 5 (RB-5), Methylene Blue (MB) and Alizarin Red S (ARS) were separated by using suitable surfactants i.e. SDS, CTAB, CPC and TX-100 at Chemistry Department Quaid-i-Azam University, Islamabad-Pakistan. Concentration of metals and organic dyes in permeate solution was measured by inductively coupled plasma mass spectrometer (ICP-MS) and UV-Visible spectrophotometer respectively. Mainly two parameters rejection percentage (R%) and permeate flux (J) were studied on account of their importance to measure and control the separating efficiency of surfactants/sericin from water in both part I and part II. Three membranes of different pore size of 5000, 10,000 and 30,000 MWCO (molecular weight cut-off) were used in this study.