| It is well known for its abundant reserves of non-ferrous metals ores in Hunan Province of China, and soils in the vicinity of mining and smelting areas are seriously polluted by heavy metals such as As, Cd, Pb and so on. In this study, the research was finished using giant reed(Arundo donax L.) as a restoration target plant to cleanup abandoned paddy soils contaminated by As, Cd, Pb, Zn near a smelter in Hunan Province through long-term field experiment, and the comprehensive utilization of harvested plant was also studied. In the paper, changes of pH, dissolved organic carbon (DOC) contents and As, Cd, Pb, Zn concentration in different soil layer leachants as well as soils and giant reed were determined in order to explore the migration and transformation characteristics of As, Cd, Pb, Zn in soil-plant-water system. The effect of liquefaction reagents, time, temperature, liquid ratio, catalyst quantity to the liquefaction rate of giant reed was studied. Meanwhile, the characteristics of polyurethane synthesized from liquefied products of giant reed were determined. The results are shown as followed:Under giant reed phytoremediation system, dissolved organic carbon (DOC) concentration in soil leachants increased significantly and was 1.7 times of the control system(P<0.05). As and Pb concentrations in soil leachants were significantly reduced (P<0.05). In leachants of the control system, the concentrations of DOC and As, Cd and Pb, Zn, Pb and Zn were significantly correlated (P<0.01), but only the concentrations of Pb and Zn were significantly correlated (P<0.01) in giant reed phytoremediation system. Accumulation of As, Cd, Pb and Zn in giant reed mainly hindered in the roots while of those elements in stems and leaves were slight. Large biomass of giant reed accumulated enough heavy metals and had a certain role in stabilization and removal of As, Cd, Pb and Zn from the soil.Under the condition of liquid ratio 5:1, temperature 160℃, liquefaction time 60min and catalyst (sulfuric acid) content 3%, the liquefaction percentage of giant reed in ethylene glycol system arrived 81.6%. Composition of cellulose and lignin in giant reed were extensively decomposed afer liquefacion and a mass of alcoholic hydroxyl groups after liquefaction were determined based on the FI-IR spectra analysis. The hydroxyl value of liquefied giant reed in ethylene glycol was 481 mg KOH g-1. Polyurethane was synthesized using 15g ethylene glycol liquefaction products of giant reed,25g of methyl diphenyl diisocyanate,0.45g water,0.5g tween-80 and 0.3g combined catalyst and the density of synthesized polyurethane was 213kg m-3. Liebermann-Storch-Morawski color reaction experienced the changes of black-lemon yellow-brown-green fluorescence; The main characteristic FT-IR peaks of the synthesized products were N-H stretching vibration in 3339 cm-1, saturated CH stretching vibration in 2872-2972 cm-1, C=O stretching vibration in 1713 cm-1, C=C stretching vibration of benzene ring in 1453-1619 cm-1, C-C stretching vibration in 1241 cm-1. These results showed the main composition of the synthesized products was polyurethane.Overall, giant reed can be regarded as the potential remediation plant for metal-contaminated soil and can achieve the comprehensive utilization through synthesized polyurethane using the ethylene glycol liquefaction techniques... |
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