| Arsenic（As）is a contaminant commonly detected in aquatic and soil environment.It is highly toxic and carcinogenic and has been identified by the World Health Organization（WHO）as the primary toxic substance which is extremely hazardous to the ecosystem and human health.The role of biochar（BC）as an environmentally friendly adsorbent in the remediation of As contaminated-water and soil is attracting much attention.However,the ability of pristine BC to remediate As contamination is limited.Towards this issue,BC/micro-nanosizedα-Mn O2 composites（BM）with different mass ratios were synthesized using wheat straw as the raw material of BC in this study.BM samples were characterized by multiple techniques（e.g.,scanning electron microscopy-energy dispersive X-ray spectroscopy（SEM-EDX）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,zeta potential,specific surface area,etc.）to reveal surface physicochemical properties.The remediation effect of BM on As contamination was investigated,and the oxidation and adsorption mechanism of As removal by BM in water was explored.Based on soil incubation,the effect of BM addition on As species in soil was investigated and the passivation mechanism of BM on As in soil was probed.The main results are summarized as follows:（1）The characterization results reflected that the micro-nanosizedα-Mn O2 was successfully loaded on the BC surface and distributed uniformly in the voids on BC surface.After compositing with micro-nanosizedα-Mn O2,the specific surface area of BC was increased by about 7.5～13.6 times.The fourier infrared spectroscopy and X-ray photoelectron spectroscopy analyses showed that the surface functionality of BC was significantly improved,and the Mn ions of the BM were mainly present in the tetravalent form.（2）The adsorption thermodynamic of As（III,V）in water by BM was well fitted with the pseudo-second-order kinetic model and Langmuir model,indicating that the adsorption process was mainly driven by single-molecule layer chemisorption.The adsorption performance of BM for As（III,V）was much higher than that of BC,and its theoretical maximum adsorption capacity was as high as 49.8 mg/g and 38.7 mg/g,respectively,which was related to the loading of micro-nanosizedα-Mn O2.In addition,the adsorption-desorption cycle experiments showed that BM had good reproducibility as an adsorption material for As（III,V）.Based on the analysis of FTIR,XPS and SEM-EDX results of BM before and after the reaction,the main removal mechanism of As（III,V）by BM was found to be the surface complexation of As with the functional groups of BM（Mn-OH,BC-COOH and BC-OH,etc.）and the oxidation of As（III）by Mn（IV）.（3）The soil incubation experiments showed that the application of BM promoted the conversion of soil As from the chemically labile species（exchange state As,calcium-bound As,aluminum-bound As and iron-bound As fraction）to stable species（residual As fraction）.This demonstrated that BM had a good passivation effect on As in soil and could greatly reduce the biological effectiveness of As in soil.Also,BM application changed soil p H,organic matter content and iron form,which could directly affect the soil arsenic presence patterns.The main remediation mechanisms are the following:the mobility and bioavailability of As decreased significantly through stabilization.In addition,BM effectively increased the contents of organic carbon,total nitrogen,available phosphorus and available potassium in soil,thereby showing ability to improve soil quality. |
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