Adsorption of Crystal Violet on Used Black Tea Leaves from Acidic Solution: Equilibrium, Thermodynamic and Mechanism Studies

Mohammad Abul Hossain

doi:10.18483/ijsci.849

Abstract

The present study investigates the potential use of used black tea leaves (UBTL) for the removal of Crystal Violet (CV) from acidic solution in batch process. The influences of different adsorption parameters such as contact time, concentration, processing temperatures and ionic strength were investigated. UV-visible spectrophotometer was used to analysis CV at a specific pH (6.0) of solution. Several model isotherms were depicted at different processing temperatures using acidic solution of pH 2.0. Langmuir, Freundlich, Tempkin, Dubinin-Radushkevich (D-R) and Florry-Huggins model equation were subjected to analyze the equilibrium adsorption data. The experimental data reveals Langmuir and D-R models comparatively better fitted than Freundlich, Tempkin and Florry-Huggins models. The equilibrium adsorption capacity (qm) computed from Langmuir equation is 184.1 mg/g at 30oC which is increased with increase of processing temperature. The adsorption energy (E) calculated from D-R model indicates physical adsorption which plays cardinal role in this adsorption process. The value of separation factor informs that the adsorption process is favorable in nature. The effect of electrolytes (NaCl and NaNO3) suggests a possible adsorption mechanism of CV onto UBTL. The values of thermodynamic variables such as Gibbs free energy (∆Gads), enthalpy (∆Hads) and entropy (∆Sads) suggests the adsorption process is non-spontaneous, physisorption with negligible amount of fragmentation of dye molecules.

Highlights

Synthetic dyes are used extensively at this recent period in many industries including dye houses, paper printers and textile dyers
The continuous treatment of black tea leaves by boiling water brings a considerable change in composition while preparing used black tea leaves (UBTL)
The outcome obtained from the present study reveals used black tea leaves (UBTL) is a potential adsorbent

Summary

Introduction

Synthetic dyes are used extensively at this recent period in many industries including dye houses, paper printers and textile dyers. Use of variety of dyes and chemicals in the dyeing processes causes considerable variation in the wastewater characteristics like pH, color and chemical oxygen demand (COD). Due to their strong interaction with many surfaces of synthetic and natural fabrics, reactive dyes are used for dying wool cotton nylon, silk and modified acrylics. Crystal Violet (CV) is one the most useful dye uses in textile and paper dyeing and 15% of such dyes produced worldwide are released to environment in wastewater [3]. Several possible treatment process have been developed to remove CV from wastewater stream include physiochemical, chemical and biological treatment process, such as coagulation and flocculation [4] fungal decolonization [5], ozonation [6], photodegradation [7], adsorption [8], electrochemical techniques [9], chemical bleaching [10] and micellar enhanced ultrafiltration [11].

Methods

Results

Conclusion