Browsing by Subject "remediation"
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Item Perchlorate reduction using electrochemically induced pitting corrosion of zero-valent titanium(2009-05-15) Lee, Chun WooPerchlorate is a threat to public health through water but also food. However, there is no effective chemical treatment process which can destroy perchlorate found in groundwater and surface water. Thus, there is growing interest in developing effective technologies, especially chemical treatments, to completely destroy trace levels of perchlorate present in drinking and groundwater. The research on perchlorate reduction by zero-valent titanium (Ti(0)) showed that perchlorate was effectively reduced to chloride using electrochemically developed pitting corrosion on Ti(0). Perchlorate reduction was believed to be caused by an active reductant (dissolved Ti(II)) during the pitting corrosion of Ti(0). The rate of perchlorate reduction was independent on the imposed potential as long as the potential was maintained above the pitting potential of Ti(0), but it was proportional to the applied current. The perchlorate reduction on the pitting developed Ti(0) was inhibited by the presence of chloride and bromide. Inhibition mechanism of perchlorate reduction inhibition was believed to be caused either by competitive adsorption of aggressive anions on bare Ti(0) surface or Ti(II) consumption by electrochemically produced chlorine. Kinetic models were developed based surface coverage of aggressive anions on bare Ti(0) and Ti(II) oxidation by chlorine. These kinetic models supported the perchlorate concentration change in the solution, but Ti(II) consumption model was not able to predict chloride concentration due to insufficient information describing complex nature of pitting on Ti(0). These results shown in this research demonstrate that pitting corrosion developed Ti(0) has the capability to chemically reduce perchlorate present in natural water and engineered systems as well as possible problems associated with electric input. This research may be a starting point for development of a new treatment process that applies titanium or titanium metal ions as a chemical reductant to abate contaminants present in natural and engineering systems. Further developments can be achieved by alloying titanium metal with other metals such as iron and aluminum, and finding a methodology producing stable Ti(II) in ambient conditions.Item Remediation of chromium(VI) in the vadose zone: stoichiometry and kinetics of chromium(VI) reduction by sulfur dioxide(Texas A&M University, 2004-11-15) Ahn, MinImmobilization and detoxification of chromium in the vadose zone is made possible by the existence of an effective reductant, SO2, that exists in a gaseous form at room temperature. Experimental studies were designed to characterize stoichiometry and kinetics of chromium reduction both in aqueous solutions at pH values near neutrality and in soil. First, batch experiments and elemental analyses were conducted to characterize the stoichiometry and kinetics of Cr(VI) reduction in water. The stoichiometric ratio of S(IV) removed to Cr(VI) removed ranged between 1.6 and 1.8. The overall reaction is believed to be the result of a linear combination of two reactions in which dithionate is an intermediate and sulfate is the stable oxidized product. The reaction was also rapid, with the half-time of about 45 minutes at pH 6 and about 16 hours at pH 7. A two-step kinetic model was developed to describe changes in concentrations of Cr(VI), S(IV), and S(V). Nonlinear regression was applied to obtain the kinetic parameters. The rate of reaction was assumed to be second-order with respect to [Cr(VI)] and first-order with respect to [S(IV)], and [S(V)]. The values for the rate coefficient for the first reaction (k1) were found to be 4.5 (?10%), 0.25 (?9.4%) (mM-2h-1) at pH 6 and 7, respectively. The values of the rate coefficient for the second reaction (k2) were 25 (?29%), 1.1 (? 30%) (mM-2h-1) at pH 6 and 7, respectively. The reaction rate decreased as pH increased. Experiments showed that the rate at pH 7 was lower than that at pH 6 by one order of magnitude. Second, batch experiments and elemental analyses were conducted to characterize the stoichiometry and kinetics of Cr(VI) reduction in soil. The stoichiometric ratio of S(IV) removed to Cr(VI) removed was almost 2, which is slightly higher than that for the reaction in water. This higher value may be due to S(IV) oxidation by soil-derived Fe(III). The reaction was rapid, with the half-time less than 2 minutes, which is faster than in water. The rate coefficients, k1 and k2, were 22 (?41%) and 13 (?77%) (M-2h-1), respectively.Item The effects of a computerized-algebra program on mathematics achievement of college and university freshmen enrolled in a developmental mathematics course(Texas A&M University, 2007-04-25) Taylor, Judy M.We face a world in which a college degree increasingly dictates the likelihood of life success. At the same time, there has been an ever-increasing population of students who have not been prepared adequately through their high school education to meet the rigors of college/university-level content. This problem can be seen in the number of students needing Intermediate Algebra. Students who complete remedial courses with a grade of C or better are more likely to pass their first college-level mathematics course and continue their education until they have completed all coursework needed for a degree. Students entering colleges and universities underprepared for collegiate mathematics, reading, and writing have reached epidemic proportions, with 30% of the students needing remediation in one of these areas. A portion of this problem has been identified as mathematics anxiety. Because students have habituated mathematics failure, they are aware of their deficiencies, but still desire a college education. They bring with them years of negative emotions from repeated mathematics failures. These years of negative feelings about mathematics precipitated by repeated failures are often manifested as mathematics anxiety that must be addressed in order to improve students?????? content knowledge. The purpose of this study is to investigate the effects of a web-based technology centric course, Assessment and Learning in Knowledge Spaces (ALEKS), on the remediation of college freshmen enrolled in an Intermediate Algebra class as compared to college freshmen enrolled in an Intermediate Algebra class taught using a traditional lecture method. Mathematics anxiety and attitude toward mathematics will also be investigated to determine if ALEKS can lower the anxiety associated with mathematics, as well as improve attitudes. An algebra test, mathematics anxiety rating scale, and mathematics attitude test was given to both groups of students at the beginning of the semester and at the end of the semester. The overall findings of this research suggested that ALEKS Intermediate Algebra students performed as well as the Control group taking a class in Intermediate Algebra taught by lecture. The anxiety of the Experimental group decreased more than the Control group, and the Experimental group??????s attitude toward mathematics increased at a greater rate than did the Control group.