Adsorption of selenite and selenate by nanocrystalline aluminum oxide, neat and impregnated in chitosan beads.
Nanocrystalline metal oxide impregnated chitosan beads (MICB) were successfully developed with nanocrystalline aluminum oxide (n-Al2O3) to form n-Al2O3 impregnated chitosan beads (AICB). AICB were able to simultaneously adsorb inorganic aqueous selenite and selenate more effectively than n-Al2O3 or chitosan alone. For completeness, adsorption performance was also compared to n-TiO2, a widely studied adsorbent for selenium, and n-TiO2 impregnated chitosan beads (TICB). For the selenite system, n-Al2O3 was the primary active adsorbent responsible for removal as chitosan has a low affinity for selenite. For selenate, however, chitosan was the primary active adsorbent. The association constants for the adsorbent/adsorbate complexes and the relative amounts in which they are present supported this hypothesis. The association constants for selenate binding on n-Al2O3 and chitosan were 1.215 × 10(-2) and 3.048 × 10(-3), respectively, and the association constants for selenite binding on n-Al2O3 and chitosan were 1.349 × 10(-2) and 1.990 × 10(-4), respectively. For systems with coexisting selenite and selenate, AICB is potentially the most robust option as it maintained the most consistent performance regardless of fractionation of the selenium species. Kinetic studies and equilibrium isotherms were completed and effectively modeled using pseudo-second order kinetics and Langmuir adsorption theory, making it the first comprehensive systematic study of neat n-Al2O3 and AICB for selenium adsorption. pH significantly impacted adsorption due to changes in the adsorbent surface charge; increasing pH corresponded with decreasing adsorbent performance, beginning at approximately pH 6.5-7 for AICB. The trend in performance due to the effect of pH indicated that selenate binds to the amine group in chitosan, as suggested by other studies. In addition, increasing background sulfate concentration was found to negatively impact adsorption efficacy for both selenite, and more significantly, selenate, as sulfate is known to compete with selenium oxyanions due to their similar structures. The results indicate that, in order to maintain consistent removal in more realistic systems, a pre-treatment process to manage sulfate will be necessary as indicated for other adsorbents implemented for selenium adsorption in aqueous systems.
Yale University, Department of Chemical and Environmental Engineering, 9 Hillhouse Ave., Mason Lab 301, New Haven, CT 06511, United States.
Jamila S
JS
Yamani
Yale University, Department of Chemical and Environmental Engineering, 9 Hillhouse Ave., Mason Lab 301, New Haven, CT 06511, United States.
Amanda W
AW
Lounsbury
Yale University, Department of Chemical and Environmental Engineering, 9 Hillhouse Ave., Mason Lab 301, New Haven, CT 06511, United States; Yale University School of Forestry and Environmental Studies, 195 Prospect St., New Haven, CT 06511, United States. Electronic address: julie.zimmerman@yale.edu.
Julie B
JB
Zimmerman
D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry*; D048271:Chitosan / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008863:Microspheres; D053758:Nanoparticles / Q000737:chemistry*; D064586:Selenic Acid / Q000302:isolation & purification*; D020887:Selenious Acid / Q000302:isolation & purification*; D013431:Sulfates / Q000737:chemistry; D013696:Temperature
D013431:Sulfates; D048271:Chitosan; D020887:Selenious Acid; D064586:Selenic Acid; D000537:Aluminum Oxide
Adsorbent; Adsorption; Metal oxide; Selenium; Sulfate; Sustainable; Titanium dioxide