Research On Remediation Of Cr(Ⅵ) By Green Tea Extract Synthesized Nanoscale Zero-valent Iron And Copper Bimetallic

In recent years, problems caused by heavy metal pollution have become increasingly severe, hexavalent chromium(Cr( Ⅵ)) is a kind of extremely carcinogenic and teratogenic inorganic contaminants, the health of human have been threated when the Cr( Ⅵ) from slag and wastewater into the soil and groundwater.The nanoscale zero valent iron(nZVI) and its bimetallic material have been widely used to control the environmental contamination which caused by heavy metal. However, the most of nanoscale zero valent iron and bimetallic materials are synthesized by traditional reducing agents, which belong to the toxic substances, be harmful to the organism during the process of preparation and application, and will caused secondary pollution. In addition to the poor stability, the nanomaterials prepared by chemical agents usually lose the activity faster. All of the problems have greatly limited the nanoscale zero valent iron and bimetallic material in practical engineering.Considering these problems, a new method have been choosed to synthesized nanoscale zero valent iron and copper bimetallic(nZVI/Cu), green tea extract(GTE) as reducing agent. The bioactive substances in plant extracts as reducing and masking agent, reacting with copper and iron salts to prepare nZVI/Cu, which could avoid the use of toxic chemicals substance, weakened secondary pollution and enhance the stability of the material. In this study, Cr(Ⅵ) in groundwater repaired by the green tea extract synthesized nanoscale zero valent copper and iron bimetallic(GT-nZVI/Cu), the effect of different environmental condition on the removal of Cr(Ⅵ) were investigated. Through the soil column experiments, the effect of different environmental factors on the migration performance of Cr(Ⅵ) in soil were discussed, which provide scientific reference to situ remediation technology of Cr(Ⅵ) in groundwater and soil.The main conclusions of this article include:(1) GT-nZVI/Cu was spherical structure, the particle size within the range of 60 ~ 100 nm. There is clear oxidation and corrosion in the surface after GTnZVI/Cu react with Cr(Ⅵ) of solution,the particles linked closely and mainly in the form of agglomerated state.(2) GT-nZVI/Cu have a good removal efficiency on Cr(Ⅵ) of solution, when the reaction environment PH was 5, the temperature was 303 K, the original concentration of Cr(Ⅵ) was 5mg·L-1, adding 0.4g·L-1 GT-nZVI/Cu within 60 min the Cr(Ⅵ) removal rate could reach more than 95.06%. It have effect on the removal of Cr(Ⅵ) after change PH, reaction temperature, contaminated solution original concentration and the addition of humic acid, the removal efficiency of Cr(Ⅵ) increased with increasing reaction temperature, but decreased with increasing initial PH value, concentration of contaminated solution and humic acid.(3) On the basis of the kinetic data, the removal Cr(Ⅵ) by GT-nZVI/Cu follows the pseudo first order reduction kinetics model under different factors. The relationship between the reduction rate and the reaction temperature accord with Arrhenius law, the reaction activation energy was 35.018 kJ· mol-1,which lower than the activation energy required for the average reaction, so it is easy for entire reaction process.(4) Chromium contaminated soil as the test soil. Study the effect of different environmental factors, such as the GT-nZVI/Cu suspension concentration and the concentration of pollutants, on the effect of Cr(Ⅵ) migration in contaminated soil and the change of soil exudate through adding GT-nZVI/Cu suspension were investigated, research show that, the migration efficiency of Cr(Ⅵ) increased with increasing GT-nZVI/Cu suspension concentration within a certain range and reducing the concentration of pollutants in soil, but the Cr(Ⅵ) migration rate decreased when GT-nZVI/Cu concentration was 1.5 g·L-1. And the conductivity and oxidation-reduction potential of soil exudates show a decreasing trend, pH value increased slightly but remained neutral during the growth of reaction time.(5) Based on the experimental data, parameters of model could be calculated. Solute transportation model was established to simulate the change of Cr(Ⅵ) by mathematical model transform. The simulation result fits the experimental result well, it could predict the Cr(Ⅵ) change in the soil media to a certain extent. And the experimental results were more in line with the simulation results within reducing the concentration of pollutants in soil.