(700d) Environmentally Benign Vegetable Oil (coconut oil) - Based Supported Liquid Membrane for Simultaneous Extraction and Recovery of Heavy Metals (Cd & Pb) From Its Aqueous Solutions

The growing environmental concern all over the world obligates the chemical industries to minimize the discharge of effluents (wastewater) that may contain various pollutants, especially heavy metals (Hg, Cd, Pb, Ni, As and Cr etc.), that are hazardous to environment and living organisms [1-3]. Heavy metals are dangerous and not biodegradable contaminants that tend to be accumulated in living organisms, causing various diseases and disorders as it leads to illness such as brain damage, memory loss, chromosome breakage, dysfunction of liver, kidney and central nervous system, blindness, deafness and hence it is important that they be removed before effluent disposal. The major sources of effluent containing heavy metals (viz.Cd and Pb) are industries like Chloro-alkali, pulp & paper, battery, fertilizer, mining & combustion and rubber processing [4-7]. Major bottleneck of the separation of heavy metals from industrial effluent is the fact that they are found in trace quantities. The separation and purification of trace amount of solute from their dilute solutions has been an interesting problem for the scientists and engineers for decades.

Some established [8] techniques of heavy metal removal from wastewater include chromatography, adsorption and ion-exchange, crystallization, precipitation and coagulation, solvent extraction, etc. However the applications of such processes are having their own merits and demerits. Hence, it is necessary to develop some cost effective yet environment friendly alternatives for recovery of trace elements from their dilute solutions. In recent times, membrane based technology has emerged as an efficient process for concentration and purification of pollutants in aqueous solutions. Liquid membrane based separation technique is one such extraction/recovery process where transport of solute (metal component) occurs through two extraction processes in series – from solute rich source phase to solvent phase and thereby from solvent phase to strip phase. The liquid membrane based separation can be implemented through various configurations such as Bulk Liquid Membrane (BLM), Supported Liquid Membrane (SLM) and Emulsion Liquid Membrane (ELM) [2].

This work is aimed at investigation of simultaneous extraction and recovery of heavy bi-metals (cadmium and lead) from aqueous solutions through a coconut oil-based supported liquid membrane (SLM). The selection of extractant (carrier) and diluent were carried out by two phase equilibrium studies from various environmentally benign solvents, extractants and their combinations. Aliquat 336 (carrier agent) in coconut oil was found as the best combination for the extraction purpose. Ethylenediaminetetraacetate (EDTA) was selected as stripping agent keeping in view of its chelating capacity to metal ions.  The performance of LM based separation process was investigated by studying the effect of various operating conditions viz. carrier concentration in membrane phase, stripping agent concentration, feed phase pH and molar feed ratio of Cd (II) and Pb(II). The optimum process conditions for the heavy metals transportation was found as follows: feed phase pH of  6.5, membrane phase as 0.5 % (v/v) aliquat 336 in coconut oil, polymeric PVDF  membrane of pore size 0.2µm as solid support and 0.015 M EDTA as stripping agent. The initial feed concentration was 5 mg L^-1  and total operating time was 10 h. The optimum extraction and recovery of cadmium were found as 79% and 67% respectively and that for lead were found as76% and 66% respectively.

Literature Cited

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