Direct mineral carbonation of fly ash under high pressure using acid mine drainage: effects of solid-to-liquid ratio, stirring speed and CO2 pressure

Abstract

CO2 emissions contributing to global warming and waste related to energy genera-tion using coal pose an issue in developing countries. Mineral carbonation (MC) offly ash (FA) using acid mine drainage (AMD) can reduce CO 2 and the negative envi-ronmental impact of FA including AMD from coal mining activity. The present studyexamined the direct carbonation (DC) of FA using pure water and AMD in a 600 mLautoclave pressure reactor. A preliminary study was conducted to observe theleaching behavior of FA in water and AMD. DC was conducted to determine theeffect of solid-to-liquid ratio (0.2 and 0.5 g mL 1 ), stirring speed (100 and 400 rpm)and CO 2 pressure (1–4 MPa) on the carbonation performance. The maximum cal-cium carbonate content in the carbonated FA was 4.33 wt% with a 60% conversionof calcium to CaCO 3 for DC with pure water. The electricity required by the pro-cess was 18.9 kWh t 1 -CO 2 , corresponding to 0.019 t-CO 2 emitted t 1 -CO 2 fixedin FA. DC using AMD was effective and the maximum CaCO 3 content in FA was6.68 wt%. This was due to the additional calcium content and enhanced calciumextraction provided by AMD. The actual CO 2 uptake capacity was 29.4 g-CO 2 kg 1fly ash. Studies on AMD as a reaction solvent for MC are few but can improve thecarbonation performance of FA. Hence, the method can be viable for mining indus-tries to mitigate negative environmental impacts and generate additional revenuethrough carbon credits.