| Compound contaminants are popular in water pollution in real environment,heavy metals and chlorinated organic compounds which are a typical compound contaminant,widely exist in the wastewaters discharged from pesticide,wood preservation and electronic wastes industries.Compound pollution is more complex than single pollution,and is more difficult to handle.So it is urgent and necessary to search a feasible technology to remediate compound pollution.Nanoscale zero valent iron(NZVI)is frequently used for remediation of wastewater polluted by single contaminant,such as removal of heavy metals and reduction of organic pollutants.However,the disadvantages of easy oxidation,easy aggregation and low stability restrain further application of NZVI in remediation of single and compound pollution.In this study,we chose low-cost and available biochar(BC)and sodium bentonite(Na-bent)that are good and eco-friendly sorbents,as ideal carriers to support NZVI to simultaneously remediate wastewater polluted by compound contaminants of a heavy metal and chlorinated organic compound.Through investigation on the removal process and efficiency of compound contaminants by NZVI and supported NZVI,and analysis of some active components produced during the process with XPS,XRD,TEM and HPLC,we aimed to study the mechanism for the enhanced effect of BC and Na-bent on the reactivity and stability of NZVI,and clarify the action mechanism in the compound contaminants remediation by supported NZVI.The main results are as follows:(1)In the system of simultaneous removal of copper ions(200ppm)and 2,4-dichlorophenol(2,4-DCP,20ppm)by BC supported NZVI(BC/NZVI),copper ions are completely removed by BC/NZVI in a short 5min,while NZVI removed copper ions after 45 min,the removal rate was improved notably.After 240 min,85.4% of 2,4-DCP was removed by BC/NZVI,this efficiency was higher than that removed by NZVI(69.5%).95.0% or higher of 2,4-DCP was removed by BC/NZVI after 4 successive recycles,while the removal efficiency of 2,4-DCP by NZVI was close to zero only after 3 successive recycles.(2)The mechanism study revealed copper ions was firstly reduced into Cu(0)to form bimetallic Fe/Cu,which subsequently removed 2,4-DCP by reductive dechlorination.BC as a carrier supported NZVI can improve the dispersion of Fe particles and its anti-oxidation,to enhance the reactivity of NZVI.This improved the reduction rate and efficiency of Cu(Ⅱ),and produced more content of bimetallic Fe/Cu,finally improved the removal rate and efficiency of 2,4-DCP.Furthermore,BC/NZVI showed high efficiency to remove compound contaminants within a wider pH range.(3)In the simultaneous removal of Ni(Ⅱ)(50ppm)and 2,4-DCP(70ppm)by sodium bentonite supported NZVI(Na-bent/NZVI),Ni(Ⅱ)was completely removed by Na-bent/NZVI in 30 min,while NZVI removed Ni(Ⅱ)with the efficiency of 87.9% in a longer time of 120 min.After 120 min,the removal efficiency of 2,4-DCP by NZVI was only 85.8%,and both residual intermediates of 2-CP and 4-CP at different contents weren’t be degraded.By contrast,2,4-DCP was completely removed and dechlorination efficiency was 100% by Na-bent/NZVI in a shorter time of 30 min,showing an obvious improvement in reactivity.(4)The mechanism study revealed the dispersion and anti-oxidation of Fe particles were improved by Na-bent support,this effect improved the reactivity of NZVI to promote the reduction of Ni(Ⅱ)and subsequent formation of bimetallic Fe/Ni,facilitating the complete dechlorination of 2,4-DCP into phenol.Different from the sequence of first removal of Cu(Ⅱ)and subsequent reduction of 2,4-DCP by BC/NZVI,Na-bent/NZVI reductively removed Ni(Ⅱ)and 2,4-DCP simultaneously.(5)Fe/Cu reductively removed 2,4-DCP mainly by two pathways,such as simultaneous dechlorination of ortho and para position,and firstly ortho position then para postion dechlorination;in addition to these two pathways,Fe/Ni dechlorinated 2,4-DCP at para position first,then dechlorinated it at ortho position. |
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