Abstract
Biochars were produced with magnesium chloride as an additive for the sorption of hexavalent chromium dissolved in water using five types of straw (from taro, corn, cassava, Chinese fir, and banana) and one type of shell (Camellia oleifera) as the raw materials. The removal of hexavalent chromium by the six biochars mainly occurred within 60 min and then gradually stabilized. The kinetics of the adsorption process were second order, the Langmuir model was followed, and the adsorption of Cr(VI) by the six biochars was characterized by Langmuir monolayer chemisorption on a heterogeneous surface. Banana straw biochar (BSB) had the best performance, which perhaps benefitted from its special structure and best adsorption effect on Cr(VI), and the theoretical adsorption capacity was calculated as 125.00 mg/g. For the mechanism analysis, Mg-loaded biochars were characterized before and after adsorption by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS). The adsorption mechanism differed from the adsorption process of conventional magnetic biochar, and biochar interactions with Cr(VI) were controlled mainly by electrostatic attraction, complexation, and functional group bonding. In summary, the six Mg-loaded biochars exhibit great potential advantages in removing Cr(VI) from wastewater and have promising potential for practical use, especially BSB, which shows super-high adsorption performance.
Highlights
Chromium (Cr) waste is mainly generated by electroplating, leather making, chemical, pigment, metallurgy, refractory, and other industries [1], and in the aqueous environment, Cr mainly exists as Cr(VI) and Cr(III) [2]
The mass concentration of hexavalent Cr in wastewater must be strictly controlled and wastewater can only be discharged after reaching a standard
Biochars prepared from the six starting materials were labelled as Banana straw biochar (BSB), CSB, FSB, MSB, TSB, and CFSB
Summary
Chromium (Cr) waste is mainly generated by electroplating, leather making, chemical, pigment, metallurgy, refractory, and other industries [1], and in the aqueous environment, Cr mainly exists as Cr(VI) and Cr(III) [2]. Due to the high solubility, toxicity, mutagenicity, carcinogenicity, and teratogenicity of Cr(VI), it cannot be biodegraded and will accumulate in the food chain, causing damage to the human body [3]. Cr(VI) causes greater biotoxicity and environmental hazards than does Cr(III) [4]. Traditional methods for removing Cr from wastewater mainly include electrolysis [5], chemical methods [6], ion exchange methods [7,8], membrane separation [9], catalytic reduction [10], and adsorption [11,12]. The bioavailability, reactivity, and mobility levels of pollutants can be suitably
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