Transformation of WTP sludge into adequate ceramic mass for
bricks requires a few changes in its chemical composition and
plastic properties. The calcium oxide content of the WTP sludge
was 0.2%, which is the lowest value among all the residues
considered in this study. One of the requirements for a good finish
of a structural ceramic material is the presence of mineral phases
that are typical of ternary systems such as CaOeSiO2eAl2O3
(Newman, 1979). Examples of these phases are anorthite (CaAl2-
Si2O8) and gehlenite (Ca2Al2Si2O7); these require about 10% and
20%, respectively, of CaO (Brownell, 1976).