A Study On Remediation Of Cr(Ⅵ) And TCE In Water By CMC Stabilized Nano Zero-valent Iron

Groundwater is an important fresh water resources for human being. With thegrowth of population and economy, groundwater pollution becomes serious. Theheavay metal Cr(VI) and organic pollutant trichloroethylene TCE in groundwaterhave greatly been concerned by people. In recent years,scientists have proposed thatnanozero-valent iron (nZVI) could be a reductant for in-situ groundwaterremediation. However, nZVI is easy to oxidation and aggregation in application,and it cannot degrade pollutants effectively. It is very crucial to modify nZVI toenhance the stability and mobility.. In this paper, carboxymethyl cellulose (CMC),an environmentally friendly material, was used as coating agent for nZVI(CNZVI)and was characterized by transmission electron microscope (TEM) andscanning electron microscope (SEM). Contrast experiment and column experimentwere performed for different nano iron in water to study their dispersion andmobility. The reactivity of CNZVI was evaluated for removal of Cr(VI) and TCE inwater by batch experiments This study could provid theoretical and experimentalbasis for CNZVI application in groundwater remediation. The main results are asfollows.(1) TEM characterization showed that the single CNZVI is round ball withobvious shell film-inner core structure, the core is composed of Fe0.Particle size is100~170nm and single Fe0particle size about20nm. SEM images showed that withthe increasement of CMC coating ratio the Fe0particle size is smaller. Fe0isdistributed in the grid structure of CMC. To compare with common nano zero-valentiron (nZVI) and commercial zero-valent iron nanoparticles (RNIP), the dispersionstablity and mobilityof CNZVI in water is much better.(2) CNZVI can effectivly reduct Cr (VI) in water. Under the same content of Fe0,CNZVI can reduct Cr (VI) all completelyas100%, which is1.35times for nZVI and 2.5times for RNIP. By improving the CMC coating proportion and CNZVI dosage,CNZVI can increase the removal efficiency of Cr(VI). The initial concentration of Cr(VI) does not affect the reaction between CNZVI and Cr(VI). Humic acid (HA) couldcompete with pollutants for Fe0surface activity point andmitigate the reaction.(3) CNZVI can degrade TCE in water. After14days, CNZVI (Fe0content1g/L)can degrade54%of TCE (initial concentration10mg/L). Under the same content ofFe0,TCE degradation rate by CNZVI is87%of nZVI and54%of RNIP., Thedegradation rate of TCE is reduced with the increase of Na+, Ca2+and HA in thewater,. High concentration of metal ions can decrease CMC solubility and result inFe0rapid oxidation and aggregation. HA can also inhibit the reaction and competewith TCE for Fe0surface active position to generate Fe complex.(4) The presence of Cr (VI) can enhance TCE dechlorination reaction by CNZVI.The result indicates that CNZVI is better for combined pollution in groundwater.