Application of Low-Cost Non-Conventional Materials for Effective Decolorization

Research Article

Austin Environ Sci. 2018; 3(1): 1028.

Application of Low-Cost Non-Conventional Materials for Effective Decolorization

Lavanya K1, Deepa M1* and Zakir H2

1Department of Chemical Engineering, Andhra University College of Engineering, India

2Department of Chemical Engineering, Rajiv Gandhi Institute of Petroleum Technology, India

*Corresponding author: Deepa M, Department of Chemical Engineering, Andhra University College of Engineering, Visakhapatnam - 530 003, India

Received: January 03, 2018; Accepted: February 05, 2018; Published: February 12, 2018

Abstract

In the present study “groundnut shell powder” was used to adsorb methylene blue dye from its modeled aqueous solution. The parameters affecting the adsorption process like contact time (1-35 minutes), pH (2-10), initial dye concentration (20-100 ppm),temperature (303-333K), adsorbent particle size (0.75-300μm) and adsorbent dosage (0.02-0.1g) were studied. The obtained equilibrium data was mathematically modeled using the Langmuir, Freundlich, and Temkin isotherm models. Further, the adsorption kinetics was determined using pseudo-first & second order kinetic models. The important thermodynamic parameters like free energy change (?G), change in enthalpy (?H) and change in entropy (?S) are estimated to predict the nature of the adsorption process. Experimental results show that the adsorption is more favored with an increase in contact time, pH, temperature, & adsorbent dosage. It was found that a contact time of just 8 minutes is enough to attain adsorption equilibrium. The Freundlich equation was found to best represent the equilibrium data with a high correlation coefficient (R2=0.999) followed by Langmuir (R2=0.993) & Temkin (R2=0.979) isotherm models. The kinetics of the adsorption was found to be followed by pseudo-second-order model with rate constant KII=1.76 g/mg.min. The ΔH and ΔS of adsorption were found to be 6.98 kJ/mol & 0.1kJ/mol. K, respectively. Moreover, the ΔG of the adsorption was found to be negative in all the temperatures and confirms the feasibility and spontaneity of the adsorption process. Thus, the positive value of ΔH confirms that the adsorption is endothermic together with the positive values of ΔS reflect the affinity of the groundnut shell powder for methylene blue uptake. Moreover, it also shows theincreased randomness at the solid-liquid interface with some structural changes on the adsorbent. Therefore, the adsorption was found to be spontaneous only at high temperatures subject to the limitation T?S>?H.

Keywords: Adsorption; Groundnut shell powder; Methylene blue, Isotherms, Kinetics, Thermodynamics. 

Abbreviations

Co & Ct: Initial Concentration & Concentration of solute in the solution at any Time t, mg/l; Ceq: Concentration of Adsorbate in Equilibrium, mg/l; qeq: Dye uptake, mg/g (amount of dye adsorbed per unit weight of adsorbent at equilibrium); W: Weight of adsorbent; V: Volume of solution, ml; dp: Particle size of the adsorbent, μm; R2: Correlation coefficient; qmax: Maximum sorption capacity, mg/g (qeq for a complete monolayer); b: Langmuir isotherm constant, L/mg; KF: Freundlich isotherm coefficient; m: Measure of adsorption intensity; AT& BT: Temkin isotherm constants, L/mg; KI: Pseudo-First order rate constant, (min-1); KII: Pseudo-Second order rate constant, (g/mg min); R: Universal gas constant, (8.314 J/mol.K); Ka: Equilibrium constant, L/mol; ?G &?H: Change in Gibb’s free energy & enthalpy of adsorption (J/mol); ?S: Change in entropy (J/mol K)

Introduction

Among all the dyes, azo dyes represent one of the most versatile and largest classes of dyes used in the textile industry and are characterized by having an azo group (comprised of Nitrogen double bonds (N=N)) and associated chromophores [1]. During dyeing process, unfortunately, due to the lower adhesion capacity of dye to the cellulosic fibers, nearly 50% of the dyes are lost in to the effluents [2,3]. These effluents containing dyes undergo reductive cleavage of N=N linkage and produce toxic amines causing severe health effects on living organisms during metabolism [4]. In particular, the major effect on humans include carcinogenic effects, cause severe mutagenic, and damage to vital organs such as kidneys, brain, central nervous system etc [5]. In light of the adverse effect on health, the dye removal from wastewater has received enormous attention over the past few decades.