Reaction mechanism in fluoride adsorption to aluminum oxide

Despite a fair amount of research (excluding non-open access journals, to which I have not got access), I cannot seem to find an explanation of the process that takes place when $\ce{F^-}$ adsorbs to activated alumina ($\ce{Al_2O_3}$).

I do know that the process involves both chemisorption (monolayer formation) and physisorption, but since the latter is explained solely by van der Waals forces, I am primarily looking for an explanation of the former.

EDIT: Does adsorption take place only at the aluminium ions? If not, does that mean that all aluminium compounds with oxidation state +3 will be equally good adsorbents?

EDIT: I have found an article (https://link.springer.com/article/10.1023/A:1012929900113) which proposes a mechanism that involves aluminium-fluoride complex formation. If this is the case - why is this even classed as an adsorption reaction at all, and not just a normal chemical reaction? And what role do the $\ce{OH^-}$ ions play? Do they keep the aluminum in the ionic lattice of the alumina?

• My impression was that NaOH was used as part of a regeneration process so the alumina can be reused. Maybe because, as it says in the abstract you site, that absorption best occurs under slightly acidic conditions so under basic conditions the process is reversed? Just an idea, not an answer ;) – airhuff Feb 4 '17 at 3:59
• This may be of interest. – airhuff Feb 4 '17 at 4:01