Adsorption of textile dyes on Pine Cone from colored wastewater: Kinetic, equilibrium and thermodynamic studies

Abstract

In this paper, the adsorption of Acid Black 26 (AB26), Acid Green 25 (AG25) and Acid Blue 7 (AB7) onto Pine Cone (PC) was investigated in aqueous solution. Surface study of PC was investigated using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The effect of operational parameters such as adsorbent dosage, dye concentration, inorganic anion (salt), pH and temperature onto dye removal was studied. The intraparticle diffusion model, the pseudo-first order and the pseudo-second order were used to describe the kinetics data. Equilibrium isotherms were analyzed using Langmuir, Freundlich and Tempkin adsorption models. Thermodynamic parameters of dye adsorption were obtained. The experimental data fitted well to the pseudo-second order kinetics model for dyes. The results indicated that isotherm data of AB26 and AG25 followed Langmuir isotherm and isotherm data of AB7 followed Freundlich isotherm models. The thermodynamic data indicated that the adsorption was endothermic process. Dye desorption studies in aqueous solution at pH 12 showed that maximum desorption of 93%, 97% and 94.5% were achieved for AB26, AG25 and AB7, respectively. It can be concluded that PC could be effectively employed as an effective biosorbent for the removal of dyes.

Introduction

Dyes have been used as colorants at different industries such as textile, food, paper, cosmetic, etc. [1]. More than 0.7 million tons of synthetic dyes are produced annually worldwide. In addition, over 10,000 different dyes and pigments have been applied in those industries. Researches indicate that approximately 15% of produced synthetic dyes per year have been lost during processing operations that involve the production and handling with many organic compounds hazardous to human health [2]. Wastewaters of dye production and application industries present an environmental problem because of the aesthetic nature due to the fact that the color is visible even in a low dye concentration.

The textile industry consumes large quantities of water at its different steps of dyeing and finishing, among other processes. The non-biodegradable nature of dyes and their stability toward light and oxidizing agents complicate the selection of a suitable method for their removal [3], [4]. In addition, toxicity bioassays have demonstrated that most of them are toxic.

Several methods such as membrane [5], electrochemical [6], coagulation/flocculation [7], biological [8], [9], [10], etc. have been used for dye removal from wastewater. Among the treatment methods, adsorption is considered to be relatively superior to other techniques because of low cost, simplicity of design, availability and ability to treat dyes in more concentrated form [11], [12]. The research of the recent years mainly focuses on utilizing agricultural natural materials as low cost and available adsorbents [13], [14], [15], [16], [17], [18], [19], [20], [21] (Table 1).

A literature review showed that Pine Cone was not used to remove dyes from colored wastewater. In this study, Pine Cone was used as an agricultural natural adsorbent to remove Acid Black 26 (AB26), Acid Green 25 (AG25) and Acid Blue 7 (AB7) from aqueous solution. Effective parameters such as adsorbent dosage, dye concentration, inorganic anion (salt), pH and temperature were investigated on dye removal. Kinetic, isotherm and thermodynamic studies were conducted to evaluate the adsorption capacity of Pine Cone.