Low Temperature One-Pot Hydrothermal Carbonization of Corn Straw into Hydrochar for Adsorbing Cadmium (II) in Wastewater

Heng Li,Yue Liu,Yan Shi,Mingshu Chi,Li Bai,Xiuling Xu

doi:10.3390/en14248503

Abstract

Corn straw, a typical agricultural waste, was directly converted into hydrochar with a yield of 77.56% by hydrothermal carbonization at 140–230 °C for 2 h with a solid–liquid ratio of 1:20. The morphology and surface properties were characterized by elemental analysis, specific surface area and pore size analysis and Fourier transform infrared spectroscopy. The results showed that with the increase of hydrothermal reaction temperature, some physical and chemical properties such as the increase of hydrocarbon content, crystallinity, and specific surface area of hydrochar changed significantly. A series of chemical reactions such as dehydration, decarboxylation, and aromatization occurred in the hydrothermal carbonization process so that the prepared hydrochar had rich oxygen-containing functional groups (-HO, C-O-C, C=O) and unique porous structure made the hydrochar prepared at 170 °C had the best removal effect on Cd2+ in solution (5.84 mg/g). These specific conditions could remove Cd2+ and greatly improve the adsorption performance. The pseudo-second-order kinetic model and Freundlich isotherm model could better describe the adsorption behavior of Cd2+. Therefore, corn straw hydrochar as a potential adsorbent for removing Cd2+ from water.

Highlights

In recent years, with the rapid development of industrialization, an increasing number of water bodies and soils have been seriously polluted, especially the heavy metal content severely exceeding the standard, which brings serious damage to the ecological environment, and poses a threat to human life and health [1]
In order to meet certain requirements for water quality, methods such as adsorption, ion exchange, chemical precipitation, reverse osmosis, and membrane treatment technology have been developed in recent years [4]
From the product pictures after hydrothermal carbonization (HTC) of corn straw and the corresponding XRD images, it could be seen that the color change of hydrochar reflects the degree of carbonization of the product, which was consistent with the analysis of SEM and Van Krevelen diagrams discussed later

Summary

Introduction

With the rapid development of industrialization, an increasing number of water bodies and soils have been seriously polluted, especially the heavy metal content severely exceeding the standard, which brings serious damage to the ecological environment, and poses a threat to human life and health [1]. Due to its strong mobility, long persistence, high toxicity, and bioaccumulation, cadmium must be removed before industrial wastewater is discharged into the environment [2]. In order to meet certain requirements for water quality, methods such as adsorption, ion exchange, chemical precipitation, reverse osmosis, and membrane treatment technology have been developed in recent years [4]. The adsorption method has been widely used in the actual treatment process because of its advantages of high efficiency, economy, and simple operation

Methods

Results

Conclusion