Anionic Dye Removal by Polypyrrole-Modified Red Mud and Its Application to a Lab-Scale Column: Adsorption Performance and Phytotoxicity Assessment

Feng Zhang,Mengyan Guo,Yue Yin,Ya-Nan Luan,Chunlei Qiao,Changqing Liu,Hesham Hamad,Yihua Xiao

doi:10.1155/2021/7694783

Abstract

In this study, polypyrrole-modified red mud (PRM) was prepared for the efficient removal of anionic dyes (methyl orange and Congo red) from aqueous solutions. The phytotoxicity (bean sprouts) of the dye solution before and after dye removal was investigated. Adsorption kinetics confirmed that the adsorption of methyl orange (MO) and Congo red (CR) on PRM was controlled by chemical reactions between the functional groups of polypyrrole and dyes. From Langmuir isotherm fitting, we found the theoretical adsorption capacities of MO and CR on PRM were 194.1 and 314.9 mg/g, respectively. The adsorption progress of MO and CR on PRM was found to be spontaneous and endothermic. The column studies demonstrated that, under dynamic flow, the PRM can efficiently remove MO and CR from aqueous solution, with adsorption capacities of 31.08 and 55.04 mg/g, respectively. In the toxicity test, the phytotoxicity of the column effluents (after dye removal) was significantly lowered compared to the initial dye influents. After the removal of MO and CR, the average root length of bean sprouts was increased from 3.30 cm to 5.18 cm and from 3.01 cm to 7.00 cm, respectively. These findings highlighted the efficient removal of dyes by PRM from aqueous solution, demonstrating the possible application of PRM for the removal of dye from dye-contaminated wastewaters.

Highlights

Different types of contaminations in water bodies pose great threat to the environment and society [1, 2]
We report a detailed application of polypyrrole-modified red mud (PRM) as adsorbent for the removal of anionic dyes: methyl orange (MO) and Congo red (CR)
The polypyrrole modification improved the roughness of the adsorbent surface, with increased granular-like morphology occurred on the surface of PRM

Summary

Introduction

Different types of contaminations in water bodies pose great threat to the environment and society [1, 2] Among these contaminations, organic dyes are highly noteworthy because over 40,000 types of organic dyes are fabricated and widely used in a lot of industrial including textile, paper, and leather [3]. The presence of dyes in the aqueous solutions poses a huge threat to the environmental livings because they have been confirmed to be carcinogenicity, genotoxicity, and neurotoxicity [6, 7]. Among these dyes, there are more than 7,000 different synthetic chemical molecules involved which are nonbiodegradable under environmental conditions [7, 8]. The sufficient removal of organic dyes before discharging into water bodies is of great significance to environmental safety

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