Single and Binary Adsorption Behaviour and Mechanisms of Cd2+, Cu2+ and Ni2+ onto Modified Biochar in Aqueous Solutions

Liwen Zheng,Yujie Huang,Ravi Naidu,Xiangliang Pan,Yanju Liu,Luchun Duan,Wen Zhang,Jianhua Du,Qingqing Zhao,Yongchao Gao

doi:10.3390/pr9101829

Abstract

The chitosan–EDTA modified magnetic biochar (E–CMBC) was successfully used as a novel adsorbent to remove heavy metals. The adsorption behaviour and mechanisms of E–CMBC to Cd2+, Cu2+ and Ni2+ were performed in single and binary system in aqueous solutions. In single–metal system, the adsorption process of Cd2+, Cu2+ and Ni2+ on E–CMBC fitted well with the Avrami fractional–order kinetics model and the Langmuir isotherm model. The measured maximum adsorption capacities were 61.08 mg g−1, 48.36 mg g−1 and 41.17 mg g−1 for Cd2+, Cu2+ and Ni2+, respectively. In binary–metal system, coexisting ions have obvious competitive adsorption behaviour on E–CMBC when the concentration of heavy meal beyond 20 mg L−1. The maximum adsorption capacities of the heavy metals were found to be lower than that in single–metal system. The order of the competitive adsorption ability was Cu2+ > Ni2+ > Cd2+. Interestingly, in Cd2+–Cu2+ system the earlier adsorbed Cd2+ could be completely replaced by Cu2+ from the solution. Different competitive adsorption ability of those heavy metal were due to the characteristics of heavy metal and resultant affinity of the adsorption sites on E–CMBC. The adsorption mechanism indicated that chemical adsorption played a dominating role. Therefore, E–CMBC could be a potential adsorbent for wastewater treatment.

Highlights

With the rapid development of industry, various organic and inorganic industrial pollutants are discharged into the environment, leading to a series of environmental and ecological problems [1,2,3]
The adsorption capacities of E–CMBC to Cd2+ and Cu2+ were 39.75 mg g−1, 30.72 mg g−1 at pH 2, and the adsorption capacity increased with the raise of the pH, increased to 60.35 mg g−1, 48.05 mg g−1 at pH 6
The adsorption capacity to Ni2+ exhibited a slight increase from 37.75 mg g−1 to 40.7 mg g−1 when the pH increased from 2 to 6. It suggested that the adsorption of E–CMBC to Ni2+ is less affected by pH, and the electrostatic interactions is not the key role in the process of Ni2+ adsorption, we found the similar adsorption behaviour of E–CMBC to Pb2+ in single–metal system [28]

Summary

Introduction

With the rapid development of industry, various organic and inorganic industrial pollutants are discharged into the environment, leading to a series of environmental and ecological problems [1,2,3]. Heavy metal ions (such as Cu2+, Cd2+, Ni2+) can accumulate in human organisms, which will have serious impact on human health when its levels exceed the permissible limits [5]. Numerous treatment technologies, such as chemical precipitation [6], membrane filtration [7], electrochemical treatment [8], ion exchange [9], biological treatment [10], have been applied to remove the heavy metal ions from wastewater. There still exists many defects in each technology, such as low adsorption efficiency, low selectivity, high cost, and secondary pollution, which restrain its large–scale application [11,12]. It is important to develop a cheap, efficient and widely available adsorbent

Methods

Results

Conclusion