| Summary: | 碩士 === 淡江大學 === 水資源及環境工程學系碩士班 === 98 === Most adsorbents based on iron oxides are available as fine powders or are generated in-situ in aqueous suspension as hydroxide floc or gel, making separation of these adsorbents from treated liquid very difficult. Recently, several researchers have developed techniques for coating iron oxide onto the surface of substrates to overcome the problem of solid-liquid separation. However, the iron content on the coated substrates is very low. Instead of using coating techniques, in this study iron-rich chitosan-iron oxide composites were formed by mixing chitosan and ferric chloride solution with alkaline solution.
The shape, solubility of adsorbent and ratio of chitosan and iron oxides affect Arsenic (As(V)) removal efficiency. According to literatures, five factors, namely concentration of chitosan, Fe, and NaOH, height of the needle head, and the cross-linking reaction, might affect the formation of chitosan-iron oxide composites and As(V) removal efficiency were tested, and their significance were screened experimentally according to fractional factorial design. Subsequently, the selected influential variables (Fe and chitosan concentrations) were included in the regression models of Aspect ratio (%), Solubility of Fe (%), and As removal efficiency (%) which were determined by CCD and RSM. The formula for making ‘the best’ adsorbent was determined based on Derringer’s desirability function including Aspect ratio, Solubility of Fe, and As Removal efficiency.
Adsorption of arsenic (V) by adsorbent produced using ‘the best’ formula was studied at pH 7.0 under equilibrium and dynamic conditions. The monolayer adsorption capacity obtained from fitting experimental data with Langmuir model was 11.72 mg/g, and the time to reach equilibrium is about 5 hours, indicating a specific adsorption occurring between the arsenic species and the surface of the adsorbent. SEM analysis reveals that the surface of adsorbent was smooth.
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