Insights to the transport of heavy metals from an industrial effluent through functionalized bentonite incorporated mixed matrix membrane: Process modeling and analysis of the interplay of various parameters

Abstract

Ethylene diamine tetraacetic acid (EDTA) was immobilized on bentonite clay particles by single step synthesis process and the prepared functionalized bentonite (FB) particles were incorporated in polysulfone membrane. The FB particles made the membrane surface negative (zeta potential of M-2 membrane having 2 wt% FB was –22 mV at pH 7) facilitating adsorption of heavy metals. They imparted hydrophilic properties to the mixed matrix membrane (MMM) indicated by the reduction of contact angle which in turn reduced membrane fouling. M-2 membrane exhibited the highest permeability 7.4 × 10^-11 m/Pa.s and metal ion removal in the range of 92–98 % for Ni (II), Cu (II), Zn (II) and Pb (II). Among the heavy metals studied, lead showed the maximum retention. FT-IR study precisely indicated the presence of chemical interaction among FB particles and polymer matrix thus, restricting the leaching of additives from the membranes. The mechanism of heavy metal removal by MMM was identified as adsorption promoted by ion-exchange. The MMM exhibited about 98% lead rejection and breakthrough time of 9 h for a battery effluent. A first principle-based modified convection-adsorption model was utilized to predict both the permeate flux and concentration profiles for a long term filtration experiment. The same model was used to generate a performance curve for scaling up of a real industrial wastewater to identify the suitable operating conditions and the membrane area. An in-depth analysis of the parameter space was carried out to establish the inter-relation between various parameters, like, membrane resistance and membrane-solute interaction variables (adsorption capacity, adsorption kinetic constant and adsorption resistance parameter). This analysis would be helpful in making a MMM with desirable properties for an optimal performance.