Immobilization mechanism of fluorine in aqueous solution with calcium aluminates

Immobilization of fluorine in aqueous solution with 3CaO . Al2O3 (C(3)A) and 12CaO . 7Al(2)O(3) (C(12)A(7)) has been investigated under the shaking and static conditions. The hydration products are identified by XRD and the microscopic observation has been made for the hydrated particles using electron microprobe analysis. It is found that the degree of immobilization of fluorine increases in the order of CA(2)< CA <C(12)A(7)<C(3)A and the immobilization of fluorine occurs through the formation of Ca3Al2(OH)(12-x)F-x and C(3)A . Ca(OH)(2-x)F-x. 18H(2)O. The former which contains a larger amount 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 phase 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 case of C(12)A(7). During this conversion the F- ion is incorporated into (OH-) site in the Ca3Al2(OH)(12) phase.