Supported liquid membrane-based simultaneous separation of cadmium and lead from wastewater

Abstract

This work is aimed at the investigation of simultaneous extraction and recovery of heavy metals (cadmium and lead) from aqueous solutions through a coconut oil-based Flat Sheet Supported Liquid Membrane (FS-SLM). Environmentally benign nature of coconut oil is the prime advantage in this technique. N-Methyl-N,N-dioctyloctan-1-ammonium chloride (Aliquat 336) is an ideal carrier agent for the transportation of the said heavy metals. Ethylenediaminetetraacetic acid (EDTA) was selected as stripping agent keeping in view its metal chelating capacity. Initially, the performance of Supported Liquid Membrane (SLM) was investigated only for the transportation of cadmium, or precisely Cd(II). A porous polymeric solid membrane viz., polyvinylidene fluoride (PVDF) was used as a support in order to hold and contain the membrane liquid in the SLM structure. The size of the pores in the support is 0.2μm. The effects of various operating conditions viz. concentration of the carrier in membrane phase, concentration of stripping agent, pH of feed phase etc. were studied. The optimum process conditions for the transportation of Cd(II) were: 0.5% (v/v) Aliquat 336 in coconut oil as membrane phase, 0.015M EDTA as stripping agent, and pH of 6.5 in the feed phase. The initial feed concentration was 5ppm and the total transportation time was 10h. Transportation of another heavy metal viz., lead (Pb) was also carried out with the above optimum process conditions. Finally, simultaneous transportations of both metals (lead and cadmium) were studied with various molar ratios (Cd:Pb) in the feed. The optimum extraction and recovery of cadmium were found as 79% and 67%, respectively, and that of lead were found as 84% and 78%, respectively, in simultaneous transportation. Lead was observed to be preferentially transported through SLM due to its favorable electronic configuration.