Phase transformation and its role in stabilizing simulated lead-laden sludge in aluminum-rich ceramics

Abstract

This study investigated the mechanisms of stabilizing lead-laden sludge by blending it into the production process of aluminum-rich ceramics, and quantitatively evaluated the prolonged leachability of the product phases. Sintering experiments were performed using powder mixtures of lead oxide and γ-alumina with different Pb/Al molar ratios within the temperature range of 600–1000 °C. By mixing lead oxide with γ-alumina at a Pb/Al molar ratio of 0.5, the formation of PbAl 2O 4 is initiated at 700 °C, but an effective formation was observed when the temperature was above 750 °C for a 3-h sintering time. The formation and decomposition of the intermediate phase, Pb 9Al 8O 21, was detected in this system within the temperature range of 800–900 °C. When the lead oxide and γ-alumina mixture was sintered with a Pb/Al molar ratio of 1:12, the PbAl 12O 19 phase was found at 950 °C and effectively formed at 1000 °C. In this system, an intermediate phase Pb 3(CO 3) 2(OH) 2 was observed at the temperature range of 700–950 °C. Over longer leaching periods, both PbAl 2O 4 and PbAl 12O 19 were superior to lead oxide in immobilizing lead. Comparing the leaching results of PbAl 2O 4 and PbAl 12O 19 demonstrated the higher intrinsic resistance of PbAl 12O 19 against acid attack. To reduce metal mobility, this study demonstrated a preferred mechanism of stabilizing lead in the aluminate structures by adding metal-bearing waste sludge to the ceramic processing of aluminum-rich products.