Effect of Cr2O3 addition on corrosion mechanism of refractory castables for waste melting furnaces and concurrent formation of hexavalent chromium

Abstract

Cr2O3 containing refractories are used as the linings of various waste melting furnaces. Formation of hexavalent chromium (Cr(VI)) has been a major concern despite its admirable corrosion resistance properties. Al2O3-CaO-Cr2O3 refractory castables (0, 4%, 8%, and 12wt% Cr2O3) were fabricated in reducing condition to inhibit Cr(VI) formation while subsequent corrosion tests using waste slag was performed in air atmosphere to simulate the operating conditions. The corrosion mechanism between Cr2O3-containing corundum castables and synthetic waste slag were investigated by XRD and SEM-EDS, whereas concurrent formations of Cr(VI) were assessed effectively by leaching tests. Corrosion of castables (0wt% Cr2O3) occurs via dissolution of Al2O3 and CA6 phases, and formation of Ca2(Al,Mg)(Al,Si)2O7 and (Ca,Na)(Al,Si)2Si2O8, which were significantly restricted by the formation of Al2O3-Cr2O3 (III) solid solution (4%, 8%, and 12wt% Cr2O3). Most of the specimens exhibited less than 5mg/L (EPA limit) of Cr(VI). Only specimen M3 (12wt% Cr2O3) from slag-refractory interface (stage C) leached out 5.41mg/L of Cr(VI) which is above the EPA limit. Specimen M2 (8wt% Cr2O3) exhibits optimum properties in terms of corrosion and Cr(VI) formation.