The Application of Nanoscale Zero-Valent Iron Slurry: Degradation Pathways and Efficiencies of Aqueous TCE under Different Atmospheres, and Transport Phenomena and Influence on Colony in Soil
In this research, nanoscale zero-valent iron (NZVI) was synthesized using the chemical reduction method. Experimental results have revealed that nanoiron synthesized by the reagent-grade chemicals had a size range of 50-80 nm, as determined by FE SEM. BET specific surface area of thus synthesized nanoparticles was 66.34 m2/g. NZVI prepared by the industrial-grade chemicals had a broader particle size distribution (30-80 nm) and its BET specific surface area was 61.50 m2/g. Results of XRD showed that both types of NZVI were composed of iron with a poor crystallinity. Additional test results further showed that both types of NZVI had similar characteristics.
NZVI prepared by the chemical reduction method tends to aggregate resulting in a significant loss in reactivity. To overcome this disadvantage, four water-soluble dispersants were used in different stages of the NZVI preparation process. Of these, Dispersant A (an anionic surfactant) has shown its superior stabilizing capability to others. An addition of 0.5 vol % Dispersant A during the nanoiron preparation process would result in a good stability of NZVI slurry (NZVIS).
Degradation of trichloroethylene (TCE) by NZVIS under different atmospheres was carried out in batch experiments. Experimental results have shown that the TCE dechlorination rate increased markedly when the reaction proceeded under hydrogen gas atmosphere as compared with that of air. Methane was the primary end product with a trace amount of ethane and ethylene when the reaction was conducted under the atmosphere of H2. It was suggested that an addition of H2 to the reaction system could promote the hydrogenolysis reaction for better degradation. On the other hand, ethane was the main product when the reaction system consisted of nanoscale palladized iron and H2 atmosphere. It demonstrated that Pd-catalyzed TCE dechlorination has resulted in a direct conversion of TCE to ethane in the study. The greatest dechlorination rate was obtained when 2 g/L nanoscale palladized iron and 50 mL H2 was employed in the reaction system. Under the circumstances, the TCE (10 mg/L) removal efficiency was up to 99 % in 3 minutes. Experimental results have demonstrated that the reaction system with both nanoscale palladized iron and H2 atmosphere would promote TCE degradation rate.
The culture of microorganism in soil showed minor changes to microbial community structures between the pre- and post-injection conditions. The number of microorganism colony was found to be increased after adding 1 mL NZVIS to 1 g soil. Experimental results revealed that NZVIS would not cause the inhibition or reduction of microorganism activity.
Surface modification of NZVI slurry by Dispersant A could enhance its transport in saturated porous media. Sticking coefficients were determined to be 0.56 and 0.11, respectively, for bare and Dispersant A-modified NZVIS transporting in quartz sand columns. The sticking coefficient for modified NZVIS transport in soil (loamy sand) column was determined to be 0.0061. Apparently, NZVIS modified by Dispersant A would enhance the transport of NZVI in saturated porous media.
The results of combining electrokinetic technology and NZVIS injection tests in horizontal soil column illustrated that the sticking coefficient was 0.00034 and the total content of iron reduced 10 wt. %. Experimental results revealed that the transport distance of NZVIS in saturated horizontal soil column would be greatly increased under electronkinetic conditions.
Advisor:Hsing-Lung Lien; Gordon C. C. Yang; Chun-Hsiung Kuei; Dong-Hwang Chen
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:transport phenomena reaction pathway trichloroethylene slurry nanoscale zero valent iron
Date of Publication:02/15/2007