Conditions for Al13 Polymer Formation in Partially Neutralized Aluminum Solutions
- Paul M. Bertsch
The influence of synthesis methodology on the formation of the Al13([AlO4Al12(OH)24(H2O)12]7+) polymer was investigated to better establish boundary conditions for its formation. The amount of Al13 polymer formed in solutions ranging in Al concentration from 3.34 × 10−4 to 3.34 × 10−2 mol L−1 was found to be highly dependent on OH/Al ratio (ñ), neutralization rate, mixing conditions, and initial Al concentration. For the 3.34 × 10−3 mol Al L−1 solution synthesized at 1.2 cm3 min−1, the Al13 polymer formed only when ñ exceeded 1.5, whereas this polymer predominated in a solution 3.34 × 10−2 mol L−1 with respect to Al at ñ ≥0.4. There was no evidence for Al13 polymer formation in solutions ≤3.34 × 10−4 mol Al L−1 with ñ = 2.5 synthesized at the 1.2 cm3 min−1 base injection rate; however, the formation of this species could be induced in the 3.34 × 10−4 mol Al L−1 solution by increasing the base injection rate to 100 cm3 min−1. Utilizing an Erlenmeyer flask instead of a beaker for the neutralization reaction resulted in different amounts of Al13 formation, and this was believed to result from differential mixing conditions. The data suggest that the formation of the Al13 polymer in partially neutralized Al solutions is an artifact of synthesis conditions requiring inhomogeneous pH conditions at the point of base injection resulting in the formation of the Al(OH)-4 ion. It would appear that this polymer is of little general significance to secondary Al mineral formation in acidic weathering environments.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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