Optimizing Biebrich Scarlet removal from water by magnetic zeolite 13X using response surface method

Abstract

The aim of this work was to study the removal of anionic Biebrich Scarlet (BS) dyes from aqueous solution by using magnetic Fe₃O₄ zeolite 13X (Fe₃O₄/13X). The composite adsorbent, synthesized by co-precipitation method, was characterized by X-ray Powder Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Vibrating Sample Magnetometry (VSM), as well as Inductively Coupled Plasma (ICP) and Zeta Potential (ZP) measurements. The three-factor Central Composite Design (CCD) combined with Response Surface Modeling (RSM) was used for maximizing the BS dye removal from aqueous solution. The three independent variables, namely the solution pH (in the 3–9 range), initial dye concentration (30–100 mg/L) and adsorbent mass (90–350 mg/L) served as inputs to the quadratic model of adsorption capacity. The findings yielded by analysis of variance (ANOVA) confirmed the high significance of the regression model. The predicted values of the BS adsorption capacity were in good agreement with the corresponding experimental values. Optimized conditions for maximum BS dye removal by Fe₃O₄/13X were pH 3.10, 98.05 mg/L initial dye concentration, and 288.82 mg/L adsorbent mass. The validity of the quadratic model was examined by conducting experiments in which the optimum values of process variables were employed, and good agreement was found between the experimental and predicted values. The present study shows that magnetic zeolite can be used as an adsorbent for highly efficient BS dye removal.

Introduction

Dye elimination from the manufacturing industry, such as textile, food, leather and printing, is a significant environmental concern. The azo dyes, including Biebrich Scarlet (BS), are particularly problematic, due to their high prevalence. BS is one of common anionic azo dyes with the sodium 6-(2-hydroxynaphthylazo)-3,4´-azodibenzenesulfonate chemical formula, shown in Scheme 1. The BS dye comprises two NN groups, along with two sulfonate groups and two sodium atoms. This dye is non-biodegradable and its byproducts are highly toxic, thus posing risk to human health and aquatic flora and fauna.

Extant research has focused on BS dye removal from wastewater for which biological, chemical and physicochemical processes, such as photocatalytic decolorization [1,2], microbial degradation [3], adsorption [4] and biosorbent [5,6] methods have been proposed.

Wastewater containing azo dye effluents is very difficult to treat by the conventional methods due to its complex structure, as azo dyes are stable under the effect of an oxidizing agent and light, and resist aerobic digestion [7]. Nonetheless, adsorption process has been shown effective in azo dye removal from wastewater, with activated carbon as the most commonly used adsorbent [8].

Magnetic adsorbents have been extensively studied for their suitability in environmental applications, such as removal of organic pollutants [9,10], metals [11,12] and dyes [13,14]. These adsorbents combine adsorption process and magnetic separation ability, eliminating the need for a separation process, such as centrifuge, typically employed to separate the solid phase from the solution [15]. This adsorbent can also be utilized to process large wastewater volumes in a short time, without generating contaminants such as flocculants [16]. In extant studies, researchers have used magnetized zeolite [17], activated carbon [18] and graphene [19] for removal of different effluents.

Zeolite 13X is commonly used as adsorbent for separation of oxygen from air, as well as in drying processes. Although removal of various dyes has been the subject of extensive research, to the best of the authors’ knowledge, effectiveness of using magnetic 13X zeolite for the removal of BS dye from wastewater remains insufficiently explored. In this research, Fe₃O₄ was dispersed over zeolite 13X in a simple one-step process, referred to as co-precipitation method. Composite magnetic zeolite was chosen because presence of Fe₃O₄ in the zeolites can improve BR dye removal efficiency. The Fe₃O₄/13X synthesis was characterized by X-Ray Powder Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Vibrating Sample Magnetometry (VSM), as well as Inductively Coupled Plasma (ICP) and Zeta Potential (ZP) measurements. For the first time, this magnetic adsorbent was used for removing BS from its aqueous solution. The influence of the solution pH, initial dye concentration and adsorbent mass on the removal capacity was investigated.

The goal of this work was to explore the application of magnetic zeolite in the BS removal from its aqueous solutions. To achieve this objective, Central Composite Design (CCD) combined with Response Surface Modeling (RSM) was used to maximize the adsorption capacity of the synthesized Fe₃O₄/13X for BS removal from aqueous solution. In particular, the individual effects of initial dye concentration, solution pH and adsorbent dosage as the three independent variables, as well as their joint effect on the adsorption capacity of the synthesized Fe₃O₄/13X for BS dye removal were examined, while seeking to validate the proposed model.