| Chromium poses a high potential risk to the environment and human health due to its persistence in the environment and its carcinogenicity.Therefore,chromium contamination management has become one of the most urgent environmental problems worldwide.In this paper,we successfully prepared nitrogen-doped iron-based biochar materials(Fe/NBC)and characterized their microstructures by using reed straw,urea and iron trichloride as raw materials and coupled with non-homogeneous atomic doping technology through carbon thermal reduction technique.The effect of Fe/NBC on the removal of Cr(VI)in the aqueous reaction system and the removal mechanism were investigated by controlling the preparation temperature,p H and coexisting anions and cations of the reaction system.The main findings of the study are as follows.(1)The nitrogen atom doping process affects the surface morphology and structure of Fe after the carbon thermal reduction reaction,forming regular round spheres of about 1 μm diameter.The Fe/NBC materials synthesized by nitrogen atom doping not only possess higher specific surface area of microporous pores,but also smaller mesopore pore size with regular pore structure distribution,which is favorable to the distribution of active sites and increases the contact between active sites and substrates.In addition,the nitrogen doping process is found to increase the disorder and defect degree of Fe-based biocarbon materials by Raman spectroscopy analysis.(2)The highest removal efficiency of Cr(VI)in aqueous solution was95.49% when the carbon thermal reduction temperature of Fe/NBC materials was 1000°C and Fe:N(molar ratio)= 1:2.The removal of Cr(VI)by Fe/NBC materials and is almost independent of the coexisting ions and is highly applicable.The analysis of adsorption kinetics,adsorption isotherm and adsorption thermodynamics model shows that the adsorption process of Cr(VI)by Fe/NBC materials is a spontaneous heat-absorbing chemisorption process,and increasing the temperature of the reaction system can improve the adsorption performance of Fe/NBC materials.(3)In the remediation of Cr-contaminated soil,Fe/NBC showed higher remediation efficiency and remediation rate compared with BC and Fe/BC materials.When the Fe/NBC material was added at 3%,the removal efficiency of Cr(VI)from soil was 50.85% at day 14.The simulated groundwater/surface water leaching,simulated acid rain leaching and simulated waste leachate leaching experiments showed that the Cr(VI)in the soil after remediation by Fe/NBC has good stability,and the lowest Cr(VI)concentration in the leachate when the Fe/NBC material was added at 5%,and the remediation efficiency was 77.50%～82.85%,and it was not easily affected by the extreme environment.(4)The modified BCR continuous extraction method and the Tessier continuous extraction method were used to study the chromium fugacity in the soil,and it was found that Fe/NBC materials significantly improved the sequestration capacity of chromium in the soil from the fugacity that is easily absorbed and utilized by organisms to the fugacity that is not easily absorbed and utilized by organisms.As the addition of Fe/NBC materials increased,the proportion of chromium fugitive forms in the soil that were not readily bioavailable increased.In addition,by comparing two continuous extraction methods,the improved BCR continuous extraction method and the Tessier continuous extraction method,it was found that the Tessier continuous extraction method was more suitable for the analysis of chromium fugitive forms in the soil after Fe/NBC remediation. |
