2002 Volume 42 Issue 7 Pages 794-799
The immobilization of fluorine by calcium aluminum ferrites has been studied using 20 mass ppm F-containing aqueous solution. It is found that the rate of the F immobilization by Ca2(Al, Fe)2O5 is initially slower than that by 3CaO · Al2O3 at the solid/liquid ratio of 1/200, but a similiar immobilization degree is obtained at later stage. The hydration product contributed to the F immobilization is the Ca3(Al, Fe)2(OH, F)12 phase, which is confirmed by the combination of XRD and electron microprobe analysis. For a ferrite phase of Ca2(Al0.68Fe0.32)2O5´ the hydration product has a chemical composition of Ca3Al1.54Fe0.46[(OH)1-xFx]12 (x=0-0.13). The F immobilization by 2CaO · Fe2O3 does not occur to a significant extent, but the F immobilization by 12CaO· 7Al2O3 is accelerated with the addition of 2CaO · Fe2O3 due to the formation of the Ca3(Al, Fe)2(OH, F)12 phase. It is also observed that F can be immobilized by the formation of ettringite (3CaO · Al2O3 · 3CaSO4 · 32H2O, 3CaO · Fe2O3 · 3CaSO4 · 32H2O) through the substitution of F ion for the SO42− site.