Immobilization mechanism of fluorine in aqueous solution with calcium aluminates

Immobilization of fluorine in aqueous solution with 3CaO . Al2O3 (C(3)A) an d 12CaO . 7Al(2)O(3) (C(12)A(7)) has been investigated under the shaking an d static conditions. The hydration products are identified by XRD and the m icroscopic observation has been made for the hydrated particles using elect ron microprobe analysis. It is found that the degree of immobilization of f luorine increases in the order of CA(2)< CA <C(12)A(7)<C(3)A and the immobi lization of fluorine occurs through the formation of Ca3Al2(OH)(12-x)F-x an d C(3)A . Ca(OH)(2-x)F-x. 18H(2)O. The former which contains a larger amoun t of F (x=0-1.2) is the major hydration product for hydrated C(3)A, and the latter which contains a smaller amount of F (x=0-0.12) is the dominant pha se for hydrated C(12)A(7). The conversion of the hexagonal hydrates of C(2) A . 8H(2)O and C(3)A . Ca(OH)(2). 18H(2)O to the cubic hydrate of Ca3Al2(OH )(12) occurs rapidly in the case of C(3)A, while it occurs slowly in the ca se of C(12)A(7). During this conversion the F- ion is incorporated into (OH -) site in the Ca3Al2(OH)(12) phase.