Preparation of a Novel Activated Carbon from Cassava Sludge for the High-Efficiency Adsorption of Hexavalent Chromium in Potable Water: Adsorption Performance and Mechanism Insight

Ling Li,Hongwei Lian,Yan Li,Yiqi Liu,Lei Ding,Jun Zheng,Xiaopeng Jin

doi:10.3390/w13243602

Abstract

Particularly, because of the leakage risk of metal elements from sludge carbon, little attention has been focused on using sludge activated carbon as an adsorbent for the removal of Cr (VI) from contaminated water sources. Herein, a novel sludge carbon derived from dewatered cassava sludge was synthesized by pyrolysis using ZnCl2 as an activator at the optimal conditions. The prepared sludge activated carbon possessed a large BET surface (509.03 m2/g), demonstrating an efficient removal for Cr (VI). Although the time to reach equilibrium was extended by increasing the initial Cr (VI) concentration, the adsorption process was completed within 3 h. The kinetics of adsorption agreed with the Elovich model. The whole adsorption rate was controlled by both film and intra-particle diffusion. The Cr (VI) removal efficiency increased with elevating temperature, and the adsorption equilibrium process followed the Freundlich isotherm model. The adsorption occurred spontaneously with endothermic nature. The removal mechanism of Cr (VI) on the prepared sludge activated carbon depended highly on solution pH, involving pore filling, electrostatic attraction, reduction, and ion exchange. The trace leakage of metal elements after use was confirmed. Therefore, the prepared sludge activated carbon was considered to be a highly potential adsorbent for Cr (VI) removal from contaminated raw water.

Highlights

Hexavalent chromium (Cr (VI)) has been widely applied in petroleum, oil refining, electroplating, tanning, metallurgy, fertilizer, and other industrial processes [1,2]
The trace metal leakage indicated that the prepared ACDCSoptimal was a potential adsorbent for the removal of Cr (VI) from the contaminated raw water
The specific surface areas and iodine value for the prepared sludge activated carbon at the optimal process parameters added to 509.03 m2/g and 557.10 mg/g, respectively

Summary

Introduction

Hexavalent chromium (Cr (VI)) has been widely applied in petroleum, oil refining, electroplating, tanning, metallurgy, fertilizer, and other industrial processes [1,2]. Over the past two decades in many developing countries, raw water sources have been frequently contaminated by wastewater and solid waste containing Cr (VI) due to abnormal discharge [3]. The total Cr (VI) in potable water has been limited within the range of 0.05 mg/L by WHO due to its carcinogenicity, teratogenicity, and mutagenicity [4]. For raw water contaminated by Cr (VI) due to sudden pollution accidents, traditional drinking water treatment processes, comprising coagulation, sedimentation, filtration, and disinfection, are poorly effective for Cr (VI) removal. Local potable water treatment plants were closed for nearly ten days due to water pollution caused by Cr (VI) in Qujing city, China [3]. It is essential to search for a high-efficiency treatment technology to remove Cr (VI) from contaminated raw water sources

Methods

Results

Conclusion