Fabrication of a cost-effective metal oxide-based adsorbent from industrial waste slag for efficient CO2 separation under flue gas conditions

Efficient and affordable adsorbents for CO 2 capture are essential in implementing carbon capture technology to mitigate the negative impact of greenhouse gas emissions. This study focuses on synthesizing new nanoporous adsorbents from industrial waste slag using a simple and cost-effective coprecipitation method. In this method, raw slag was milled for 48 h and used as a benchmark for comparing two newly synthesized adsorbents. Selectivity and pure gas isotherm experiments were conducted for all adsorbents in the 25–65°C temperature range and under harsh industrial conditions of 65°C and 15 % CO 2 . This study utilized the response surface methodology (RSM) to optimize the CO 2 adsorption parameters. Specifically, the optimized adsorption conditions were determined for the 15/85 % CO 2 /N 2 condition, and the optimal values for pressure and temperature were found to be 5 bar and 45°C, resulting in CO 2 /N 2 selectivity of 5.65. The NH 3 -slag adsorbent was identified as the superior choice based on its selectivity and maximum adsorption capacity. The maximum adsorption capacity and cyclic efficiency were determined to be 4.15 mmol/g and 98.1 %, respectively, at a temperature, pressure, and composition of 45°C, 5 bar, and 15 % CO 2 . Isotherm and thermodynamic models were employed to further investigate the adsorption process. The isotherm results indicated that the adsorption of CO 2 by adsorbents occurred heterogeneously in patch-wise sites. Meanwhile, the thermodynamic parameters showed that the process was exothermic and spontaneous, with ΔH° falling below 20 (kJ/mol), showing physisorption phenomena. • Two novel nanoporous adsorbents have been synthesized from industrial waste slag. • The optimal conditions were determined by conducting a coupling of IAST and RSM. • 45°C, 5 bar and 15/85% composition of CO 2 /N 2 were the optimum operational conditions. • NH 3 -slag demonstrated a CO 2 adsorption capacity of 2.95 mmol/g after 10 cycles at optimum conditions. • Isotherm and thermodynamic modelling were done for a better understanding of the adsorption process.