The Research On Removal Of Heavy Metal And Trichloroethylene From Aqueous Solution By Coated Nano-zero Valent Iron

With the rapid development of society, science and technology has made great breakthrough. People’s life,production and exploitation of natural resource, such as stacking of garbage, factory "three wastes" emission,the use of chemical fertilizers and pesticides, have caused water, soil and air pollution. Water is the most important resource, soil is the basis for the survival of the crop, and the cleanliness of atmosphere is closely related to health of people. Entire environmental pollution problems will directly endanger human body and mind, China has valued the control of various types of pollution as a top priority.Nanoscale zero-valent iron (NZVI) particles used to repair a variety of environmental pollutants,it has been widespread concerned. However, nano zero-valent iron is liable to spontaneous combustion when exposed to air, even in contact with air will be slowly oxidized to iron oxide or hydroxide forming on the surface and thus lose some activity, these problems affect the practical application of nano zero-valent iron. To solve problems, this study used environmentally friendly material such as agar (Agar), sodium carboxymethyl cellulose (CMC) and starch (Starch) as parcel agent to prepare coated nano zero-valent iron materials using rheological phase reaction method, characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), investigated its removal and reduction capacity towards heavy metal Cu2+, trichlorethylene (TCE) and Ni2+-TCE mixed waste. The main conclusions of this work were made as follows:1. The coated nanoscale zero-valent iron were synthesized with cheap and environmentally friendly Agar, CMC and Starch as coating agent. Characterization results showed that:agar-coated nano zero-valent iron (Agar-NZVI) particles were uniformly dispersed,the size ranged from 60nm to 120nm; sodium carboxymethyl cellulose coated nanoscale zero-valent iron (CMC-NZVI) particle size was about 50-1 OOnm,spaced apart from each other, with good dispersion; starch-coated nano zero-valent iron (Starch-NZVI) particle size was about 8-20nm, showing core-shell structure, particles were round or oval shape, and had a better dispersion.2. Results of Cu2+removal by coated nano zero-valent iron showed that:the main factors that impact on the removal of Cu2+were dosage of coated nano zero-valent iron, initial Cu2+ concentration and pH.In condition of weak acidity, low initial Cu2+ concentration and large amount of coated nano zero-valent iron, it were in favor for the removal.In wastewater that containing Cu2+ concentration of 5mg/L, Agar-NZVI, CMC-NZVI, Starch-NZVI and NZVI dosage of 0.3g/L, pH of 7.0, temperature of 25℃ and reaction time of 3h,it reached the best removal rates of 99.68%,99.39%, 95.88%,90.87%,respectively.3. The main factors affected degradation of TCE by coated nano zero-valent iron were:coated nano zero-valent iron dosage, initial concentration of TCE and the initial solution pH. Experimental results showed that the optimum reaction pH value of 5, in addition, a high dosage of coated nano zero-valent iron and low initial TCE concentration were conducive for the dechlorination.The reduction degradation system was in line with pseudo-first-order kinetic model,the reaction rate increased with the initial concentration of TCE decreased and coated nano zero-valent iron dosage increased.When TCE concentration was 10mg/L in the wastewater, pH was 5.0, Agar-NZVI, CMC-NZVI, Starch-NZVI dosage was 1.5g/L, temperature was 30℃, reaction time was 330min, the removal rates were 59.62%,68.22%, 75.19%, respectively.4. Coated nano zero-valent iron removal of Ni2+-TCE results showed: coated nano zero-valent iron can be used to simultaneously remove compound contaminants.The removal of nickel ions and TCE were better with higher dosage of nano zero-valent iron and lower initial concentration.Capacity of four zero-valent iron material handling wastewater was:NZVI<Agar-NZVI <CMC-NZVI<Starch-NZVI,effect of wrapped agent act on pollutants could be-ignored.When Ni2+ and TCE concentrations were 5mg/L in the mixed wastewater, amount of Starch-NZVI was 1.5g/L, temperature was 30℃, reaction time was 2.5h, Ni2+and TCE had best treatment effect,with Ni2+ removal rate 99.38%, TCE degradation rate 49.36%.