Research On Remediation Of Cr(Ⅵ) Contamination Soil By Nano-Zero Valent Composite Particles

In recent years, heavy metal contaminated soil has been a global environmental problems, and Chromium(Cr) is one of the toxic heavy metals to soil and water, so the remediation of Cr(Ⅵ) contaminated soil is a very hard and necessary work now. In this study, nano-Fe-Ni and nano-Fe-Cu bimetallic composite particles are used to remediate the Cr (Ⅵ) contaminated soil in the steel plant. Different factors are carried out to study the effect on the reduction-immobilization of Cr (Ⅵ) in the steel plant soil, such as the pH value of soil solution, the remediation time, dosages of nano-bimetallic composite particles, ionic strength, coexisting anions and humic acid. Then three factors (pH value, time and dosages) and three levels is designed according to the Box-Beknhen central composite experimental design principles, and there are15groups of experiments in the later, and the response surface methodology on the reduction-immobilization of Cr(Ⅵ) in soil by nano-bimetallic composite particles is carried out to reveal the future effect on the reduction-immobilization of Cr(VI) in steel plant soil.In this study, the main conclusions are as follows:(1) In the impact factor experiment of effect on the reduction-immobilization of Cr(VI) by nano-bimetallic composite particles showed that the maximum reduction rate is99.91%when0.3g nano-Fe-Ni bimetallic composite particles were added into soil; the maximum reduction rate is94.97%when0.6g Fe-Cu bimetallic composite particles were added into soil;(2) When the soil pollution pH value was4, the maximum reduction rate of Cr(VI) by nano-Fe-Ni bimetallic composite particles is98.93%; when the soil pollution pH was3, the maximum reduction rate of Cr(VI) by nano-Fe-Cu bimetallic composite particles are97.66%;(3) The maximum reduction rate of Cr(VI) by nano-Fe-Ni and nano-Fe-Cu bimetallic composite particles are99.69%and91.58%when the remediation time was12h.(4) The reduction rate of Cr(Ⅵ) by nano-Fe-Cu and nano-Fe-Ni bimetallic composite particles is promoted with the low ionic strength, high ionic strength can inhibite the reduction of Cr(VI);(5) NO3-can enhance the reduction of Cr(Ⅵ) by nano-Fe-Cu and nano-Fe-Ni bimetallic composite particles, the other four anions can inbihite the reduction of Cr(VI), and the concentration of anions were higher, the inhibition effect was more significantly. (6) The effect on the reduction of Cr(Ⅵ) is not significant with the humic acid when the soil solution pH<6; the high concentration humic acid can promote the reduction of Cr(Ⅵ) when the soil solution pH≥6.(7) The study on reduction kinetics of Cr(Ⅵ) by nano-Fe-Ni and nano-Fe-Cu bimetallic composite particles were showed that the good linear relationship was exist between the In(c/co) and time t, and this linear relationship was according with the pseudo-first-order kinetic reaction within the time range of this study. The rule of apparent rate constant is consistent with the law of reduction rate curve.(8) The analyze of three-dimensional response surface image and the contours indicated that the three environmental factors is influent to the reduction rate of Cr(Ⅵ) significantly(p<0.05), and the order of effect on reduction rate is remediation time>the dosages of nano-bimetallic composite particles>pH value of soil solution;...