261958 Modelling of Electrodialytic Removal of Multiple Ions From Synthetic Solutions

Tuesday, October 30, 2012: 10:42 AM
402 (Convention Center )
Jogi Ganesh Dattatreya Tadimeti1, Shilpi Jain2, Navneet Kumar2, Sujay Chattopadhyay2, Amiya Kumar Ray2 and P.K. Bhattacharya3, (1)Department of Polymer and Process Engineering, Indian Institute of Technology Roorkee, Saharanpur, India, (2)Department of Paper Technology, Indian Institute of Technology Roorkee, Saharanpur, India, (3)Indian Institute of Technology, Kanpur, Kanpur, India

Drinking water is slowly becoming a very precious commodity with rapid urbanization of world. Uncontrolled pollution in every aspect of mother earth (water, soil, environment and air) is posing challenge to flora and fauna. Days are not very far when we will have no ground water available for drinking purposes. Therefore, means to recycle used water through low cost technology needs to be devised. Commercial waste water treatment reduces BOD/COD and provides water that can be drained in channels and rivers. To make this water drinkable we need to critically analyse its contents and pass it through adsorption bed, membrane module and UV treatment. We are looking for application of electrodialysis to purification of water containing metal ions from a synthetic solution of sucrose. Electrodialysis (ED) is claimed to be more energy economic process compared to conventional reverse osmosis and ultrafiltration.

Electrodialysis is a unit operation commonly used   to separate the ions from water through selectively permeable membranes (cationic/anionic) and electric voltage. The feed solution (containing electrolytes) is passed between two membranes (cation exchange & anion exchange). The cathode and anode compartments are isolated from the middle feed chamber and voltage is applied across these membranes. Dissociated salts in the feed move towards their respective anion and cation exchange membranes under the influence of electric potential. Lee et al. [2006] discussed no of isses concerning the performance of ED operation. Factors those govern the process are (i) Membrane, (ii) Ions, (iii) medium and (iv) potential applied. For a given ion, the efficiency of separation depends on the membrane type (surface charge, porocity, resistance etc.). The rate of adsorption, diffusion, desoprtion of ions from one side to other decides the resistance.

Current density was estimated theoretically for a known concentration and flow range and the behaviour was noted for batch recirculation electrodialysis. The cell was operated below limiting current density (lcd). A linear concentration profile (with increase in current density) was assumed between the bulk to membrane surface while the concentration at membrane surface was obtained from ‘limiting current density'. This value approaches zero while the current density approaches limiting value.

Removal of excess calcium ion from sugar solution using ED was conducted. Process parameters (flow, voltage and concentration) influencing removal efficiency of Ca2+ ions were estimated. Limiting current density and current densities of solutions containing multi ions were also estimated using the model. The method of calculating the limiting current density was verified from literature data and found to be quite accurate. The limiting current density of the process was estimated theoretically using Nernst-Planck equation [1&2] and found to decrease with time which supports experimental findings. Diffusivity and mass transfer coefficients were calculated [4&5] and found to match well with literature [3]. The proposed model can be used for estimation and design of an electrodialysis stack to achieve a desired output.

Key words: electrodialysis, limiting current density, current density, mass transfer coefficient.

References

1.     Lee Hong-Joo, Strathmann Heiner, Moon Seung-Hyeon. ‘Determination of the limiting current density in electro-dialysis desalination as an empirical function of linear velocity'. Desalination 190 (2006) 43-50.

2.     Geraldes Vitor, Afonso Maria Dina. ‘Limiting current density in the electrodialysis of multi-ionic solutions'. Journal of Membrane Science 360(2010) 499-508.

3.     Jae-Hwan Choi, Hong-Joo Lee, and Seung-Hyeon Moon. ‘Effects of Electrolytes on the Transport Phenomena in a Cation-Exchange Membrane'. Journal of Colloid and Interface Science 238, 188–195 (2001).

4.     Treybal Robert E. ‘Mass-Transfer Operations'. Third Edition, McGraw-Hill publications.

5.      Bruce E. Poling, John M. Prausnitz, John P. O'Connell. ‘The Properties of Gases and Liquids'. Fifth Edition, McGraw-Hill publications.


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