Boron and Silicon Adsorption on an Aluminum Oxide
- Sabine Goldberg and
- R. A. Glaubig
Boron and Si adsorption on the Al oxide, alon (δ-Al2O3), were investigated under changing conditions of pH, total solution anion concentration, reaction time, and order of anion addition. Boron adsorption increased at low pH, exhibited a peak near pH 8, and decreased at high pH. The constant capacitance model was successfully used to describe B adsorption over the pH range 5 to 9 and at initial B concentrations ranging from 0.185 to 1.85 mol m−3 using only one adjustable parameter, the B surface complexation constant. Silicon adsorption was much greater than B adsorption and exhibited a broad maximum extending from pH 6 to 10. Simultaneous B and Si adsorption produced a small, significant reduction in B adsorption but had no effect on Si adsorption, indicating that some of the sorption sites showed anion preference. The magnitudes of the adsorption maxima for B and Si remained essentially constant for total reaction times ranging from 10 min to 24 d. The Al oxide was very soluble, solutions were supersaturated with respect to gibbsite after 10 min at pH 4.6 to 5.7. We therefore recommend short reaction times (<2 h) for the study of adsorption reactions on δ-Al2O3 and amorphous Al oxide.
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