(177d) Kinetics, Equilibrium and Thermodynamics of the Bio-Removal of Cadmium From Water by Using Lemon Peel and Green Coconut Shell Powder

Rohit Kumar Baranwal , P. Mondal*, P. Singh

¹Department of Chemical Engineering, Indian Institute of Technology Roorkee

Roorkee- 247667, Uttarakhand, India

*Corresponding author: Phone: +91-1332-285181; Fax: +91-1332-276535,

E-mail: mondal2001@gmail.com

ABSTRACT

            Cadmium is a conservative pollutant and can cause several diseases such as renal disturbances, lung insufficiency, bone lesions, cancer and hypertension due to the long term consumption of cadmium contaminated water. It enters into water stream from electroplating, smelting, alloy manufacturing, pigments, plastic, cadmium-nickel batteries, fertilizers, pesticides, mining, textile and refining industries. Amongst various techniques available for cadmium removal from water, adsorption is the most popular process due to its high efficiency, easy handling and economic feasibility. Agro based bio-sorbents are getting special interest in recent years as these are abundantly available and low cost waste materials.

           In the present paper the kinetics, equilibrium and thermodynamics of cadmium removal using lemon peel and green coconut shell powder have been investigated in batch reactor. The optimum conditions have been used to compute the kinetics, equilibrium and thermodynamic parameters.  Characterization of both adsorbents has been carried out using various techniques such as proximate and ultimate analysis, FTIR, TGA, SEM, EDAX and XRD.

          Under the optimum conditions and with 50 mg/l of initial concentration the % removals of Cd using lemon peel and coconut shell were 80.8 % and 93.1 % respectively.  Adsorption of Cd on both the adsorbents has been found to follow pseudo second order kinetic model. Equilibrium data were fitted to Langmuir and Freundlich isotherm models. The Langmuir isotherm has been found to give better prediction on the cadmium removal than Freundlich isotherm for both the bio-adsorbents. The maximum adsorption capacity (q_max) obtained from Langmuir isotherm for cadmium ion removal using lemon peel and green coconut shell powder have been found to be as 11.24 mg/g and 14.5 mg/g respectively.

The change in entropy (DS°) and change in enthalpy (DH°) for cadmium ions adsorption on green coconut shell adsorbent have been estimated as 11.3 J/mol/K and -34.4 kJ/mol respectively. Whereas, these values for lemon peel adsorbent are 6.441 kJ/mol/K and -19.492 kJ/mol respectively. The present adsorbents seem to be highly competitive to many other adsorbents reported recently for cadmium ion removal from water.