Title

Sol-gel synthesized adsorbents for mercury(II), chromium(III) and cobalt(II) separations

Date of Award

2004

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Lawrence L. Tavlarides

Keywords

Sol-gel, Adsorbents, Mercury(II), Chromium(III), Cobalt(II), Separations

Subject Categories

Chemical Engineering | Civil and Environmental Engineering | Engineering | Environmental Engineering

Abstract

Novel organo-ceramic adsorbents are synthesized and characterized for mercury(II), chromium(III) and cobalt(II) separations from aqueous streams. Mercury(II) adsorption on thiol functional adsorbents (SOL-AD-IV) is studied for two systems: (1) coal-fired utility plant scrubber water, and (2) acidic nuclear wastes. To exemplify the removal of mercury from these systems, simulants are prepared and used. Results show that the mercury adsorption capacity is higher than reported in the literature. In addition, the adsorbent exhibits high adsorption capacity even at 4 M HNO 3 . In column operation, flow rates as high as 1100 BV/h could be employed with effluent concentrations reaching below 0.06 μg/L. This adsorbent is found to exhibit superior mercury adsorption characteristics with a demonstrated long life cycle.

Chromium(III) and cobalt(II) adsorption is evaluated using phosphonic acid (SOL-PHONIC) and phosphinic acid (SOL-PHINIC) functional adsorbents synthesized via sol-gel processing by co-condensation of clusters of functional precursor (FPS) and cross-linking (CA) silanes. Nuclear magnetic resonance (NMR) spectroscopy is used to examine the evolution of oligomeric species with hydrolysis and condensation reaction times. The effects of both the FPS and CA oligomeric species on the physicochemical properties of the resulting adsorbent materials are evaluated and explained in terms of structural and adsorption capacity characteristics. The adsorbents are further characterized by solid-state NMR spectroscopy to elucidate the incorporation of the FPS and the nature of the functional groups in the adsorbent matrix. SOL-PHONIC is employed for the removal of chromium, and both SOL-PHONIC and SOL-PHINIC are employed for the removal of cobalt. Results show that chromium and cobalt adsorptions are solution pH dependent. Cobalt adsorption tests evaluated using the two adsorbents show that SOL-PHONIC exhibits a higher selectivity towards cobalt over nickel. The adsorption capacities observed for both metal ions are higher than those reported in the literature. Column operation results for both metal ions show that the breakthrough curves are sharp at breakthrough and gradually increase thereafter. This phenomenon is attributed to the requirement of more than one adsorption site per metal ion for adsorption to take place. The effluent concentrations of chromium and cobalt operated in a column both reach below 0.02 mg/L.

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