IJCT 12(6) 713-718

Indian Journal of Chemical Technology Vol. 12, November 2005, pp. 713-718

Studies on extraction of chromium(VI) from acidic solution by

emulsion liquid membrane

Sekhar Chakraborty, Siddhartha Datta * & Pinaki Bhattacharya

Department of Chemical Engineering, Jadavpur University, Kolkata 700 032, India Received 11 November 2004; revised received 15 July 2005; accepted 2 September 2005

High molecular weight amines, quaternary salts etc. have the potential of removing heavy metal ions including the toxic ones at low concentrations. In the present work an attempt has been made to extract Cr(VI) through emulsion liquid surfactant membrane (or, emulsion liquid membrane-ELM) from it’s acidic solution using alamine-336 and caustic soda as extractant and striping reagents respectively. Around 97% extraction of Cr(VI) from aqueous solutions of potassium dichromate through batch experimentations have been achieved. Being crucial to the overall success of the ELM processes, experiments on emulsion stability have also been performed to arrive at a reasonably stable emulsion composition. Effect of various process parameters such as initial solute concentration, concentration of internal phase etc. as also that of pH on extraction of chromium have been investigated .

Keywords: Emulsion liquid membrane, alamine-336, simultaneous extraction and stripping, equilibrium concentration,

ELM

IPC Code: C22B3/06; C22B34/32

By virtue of its large surface area for mass transfer, short diffusion path, good permeability characteristics, simultaneous extraction and stripping in a single unit etc. liquid surfactant membranes (as distinct from Supported liquid membranes, Liquid membrane droplet columns, Hollow fiber liquid membranes, Liquid membranes in stirred cells etc.) is viewed as a potentially viable technique for separation of organic and inorganic contaminants from waste waters, removal of heavy metal ions from liquid streams etc. ever since Dr. Norman Li 1 invented and used the technique to separate hydrocarbons way back in 1968.

Emulsion liquid membrane (ELM) is made by first making a primary emulsion (oil/water or water/oil) and then dispersing the same into another phase, oil or water (also referred to as the third or external phase containing the extractible species) thereby forming a multiple emulsion of the type O/W/O or W/O/W. The dispersed phase usually has a droplet size range of 0.5-10 μm while that of the emulsion globules (i.e. the continuous phase) are between 0.1-0.2 mm 2. The flux of the diffusing species through the membrane phase as also the capacity of the receiving phase can be enhanced by using appropriate additives. Two types of facilitated transport mechanisms of ELM (viz. type-I and type-II) have been identified by Matulevicius & Li 3.

In type-I the diffusing species, dissolved in the membrane phase reacts with the internal phase reagent to form membrane insoluble products that remains encapsulated within the internal phase viz . removal of weak acids and bases 4-6. Since the solute is immediately removed by reaction with internal reagent, the concentration driving force for mass transfer is maximized. In type II facilitation, an oil soluble carrier/extractant is incorporated in the membrane phase to carry the oil insoluble extractible

species across the membrane by forming complex. The complex reacts with internal phase reagent at the membrane-internal phase interface releasing the carrier which diffuses back to the membrane-external phase interface for further complexation reactions until the internal reagent gets depleted. A high degree of separation can be achieved by using only a small amount of carrier even though the partition coefficients between external and membrane phases may be significantly smaller viz . extraction of copper

ions by ELM technique 7

.

Liquid surfactant membrane technique has been widely applied by researchers in various areas of separation and extraction of which extraction of heavy

metal ions are of particular interest viz. copper 7,9, cobalt 10, zinc 11,12, nickel 13, molybdenum 14 etc. ______________

*For correspondence (E-mail: sdatta_che@)