Abstract The object of this study was to investigate the synthesis of a nanoscale zero-valent iron slurry (NZVIS) for use in Fenton-like reactions, and to evaluate its efficiency for As(III) oxidation to As(V) in spiked deionized water and simulated groundwater containing humic acid. Furthermore, this study used injection of the nanoiron slurry combined with electrokinetic processes to remediate As(III) in soil. NZVI was prepared by a chemical reduction process. The efficiency of using 3 wt% soluble starch (SS) to stabilize NZVI was also studied. It was found that the SS could keep the nanoparticles dispersed for over one day. The NZVI was characterized by XRD, FE-SEM, ESEM-EDS, and EDS-mapping, to observe its morphology and crystal structure. In this research the iron species observed took non-crystalline forms. In water batch tests, studies in deionized water were compared with those in simulated groundwater with humic acid, and dissolved oxygen content was adjusted. Injection of NZVIS oxidized As(III) to As(V) in all cases. In both deionized water and simulated groundwater, it was found that when the dissolved oxygen(DO) content was not increased, the NZVIS generated non-selective oxidant OH¡E, thus reducing the As(V) production rate. When dissolved oxygen content was increased, the DO oxidized organic matter present in the simulated groundwater, allowing the OH¡E to react further with As(III) and increasing the As(V) production rate. Finally, a test was performed in actual groundwater under optimal reaction conditions, without increasing the dissolved oxygen content, for comparison of As(V) yield. The concentration of As(V) was found to be higher in this test (As(V) Conc. = 17.55 £gg/L) than when using simulated groundwater (As(V) Conc. = 4.63 £gg/L). This study further examined NZVIS injection combined with electrokinetic (EK) technology for the remediation of soil columns containing a low concentration (initial conc. = 100 mg/kg) and a high concentration (initial conc. = 500 mg/kg) of As(III). EK alone without injection of NZVIS (Test E-1) resulted in a residual soil As(V) concentration of 24 mg/kg in the low-concentration test group. In Test E-2, where NZVIS was injected into the anode reservoir, and Test E-3, where NZVIS was injected into the cathode reservoir, residual soil As(V) concentrations were 2.3 mg/kg and 3.4 mg/kg, respectively. The high-concentration test group was comprised of Test E-4 (EK alone without injection of NZVIS), Test E-5 (NZVIS injected into anode reservoir), and Test E-6 (NZVIS injected into cathode reservoir). In these tests, only soil sections 0.2 and 0.4 (normalized distance from anode reservoir) met soil regulation standards. Residual As(V) concentrations in soil sections 0.6, 0.8, and 1.0 are much higher than the regulatory standard. In soil section 1.0, the residual As(V) concentration was less in Test E-6 than in Test E-5 (116.6 mg/kg and 183.5 mg/kg, respectively). This may be because at high pH values, the iron surface does not corrode, instead arsenic adsorption prevails. Only a fraction of negatively charged As(V) species will migrate towards the anode resulting in a relatively low soil As(V) concentration near the cathode.

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Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.

Thesis (Th.M.)--Dallas Theological Seminary, 2007. / Description based on print version record. Includes bibliographical references (leaves [62]-73). Issued also in microform.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Oscar Biblarz, Garth Hobson. Includes bibliographical references (p. 45-47). Also available online.

<p> Collocations, two or more words that co-occur (e.g., <i>extensive research, conduct a study),</i> are linked with native-like lexical accuracy and fluency. Yet even advanced-level second language (L2) learners frequently have difficulty producing appropriate collocations. To help them achieve accurate and fluent collocation production, researchers believe that L2 writers should take advantage of learner friendly collocation tools. To explore whether L2 writers benefit from collocation tools, the current study examined the effect of three collocation tools (two online and one paper) on accurate production of collocations in L2 writing. The collocation tools included (a) the <i> Longman Dictionary of Contemporary English</i> (LDOCE) (online), (b) <i> Macmillan Collocation Dictionary</i> (MCD) (online), and (c) <i> wordandphrase.info</i> (WPI) (paper).</p><p> L2 writers of English (<i>N</i> = 45) in an intensive English program (IEP) in the southwestern part of the USA were divided into three groups. Each group was provided with collocation training for a different collocation tool. After training, each group used the collocation tool to correct 16 miscollocations (8 verb + noun; 8 adjective + noun) embedded in an essay-format collocation test. After each test, the participants completed a quality review checklist. The procedure was repeated three times so that each group used each tool but in a different order; thus, the study employed a Latin Square Design.</p><p> This study used quantitative data to examine the effect of these three collocation tools on L2 learners&rsquo; ability to self-correct collocations in their own writing. Qualitative data were used to further understand L2 writers&rsquo; use of and perception of the collocation tools.</p><p> The results indicated that online collocation tools (LDOCE and WPI) contributed more than a book collocation dictionary (MCD) to accurate collocation production in L2 writers&rsquo; essays. L2 writers favored WPI because it was easier to navigate and it helped them locate the correct collocations. Furthermore, both online tools, namely, LDOCE and WPI, helped the participants correct more collocations than MCD. Focusing on the type of collocations, the participants made more accurate collocation corrections to adjective + noun collocations than to verb + noun collocations.</p><p> The study has several implications. First, English language teachers need to introduce collocation tools to L2 writers because without such introductions, L2 writers will remain unaware of the availability of useful collocation tools. Second, L2 writers will benefit from explicit collocation introduction to and practice with strategies for using collocation tools effectively. Such training will help L2 writers improve their collocation accuracy and fluency. Third, learners should be able to differentiate verbs, adjectives, and nouns. These parts of speech are important to assist learners in producing appropriate verb + noun and adjective + noun collocations.</p>

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