Valorization of Hazardous Battery Sludge as a Supplementary Cementitious Material: Influence of Calcination on Reactivity and Lead Stabilization

This study presents a novel approach for the valorization of hazardous industrial sludge generated from lead-acid battery manufacturing, by converting it into a supplementary cementitious material (SCM) through calcination. Three sludge samples were investigated: Sludge sample 1 (SS1), rich in calcium oxide; Sludge sample 2 (SS2), containing high proportions of silica, alumina, and iron oxide (SiO2+Al2O3+Fe2O3>70%); and a blended sample (SS3) composed of 70% SS1 and 30% SS2. The reactivity of the samples calcined at varying temperatures (800°C–900°C) was evaluated using modified R3 calorimetry and bound water analysis, and the amorphous content was assessed via quantitative X-ray diffraction. Results revealed that the cocalcined SS3 exhibited a synergistic enhancement in reactivity compared with SS1 and SS2, attributed to its balanced composition and improved burnability due to the presence of flux elements. A strong correlation was observed between R3 test results and amorphous content in the calcined sludge. Lead emission during calcination was investigated using thermogravimetric analysis and inductively coupled plasma mass spectrometry. High lead volatilization was observed in SS2, whereas SS1 and SS3 showed negligible emissions due to the formation of stable calcium plumbate phases facilitated by high CaO content. Finally, incorporation of the most reactive sample (SS3 calcined at 900°C) as a replacement for portland cement in mortar enhanced compressive strength, demonstrating its performance potential. This study establishes the safety and feasibility of using lead acid battery manufacturing industry sludge to produce SCMs, thus promoting waste valorization, industrial symbiosis, and low-carbon alternatives in the cement industry.