CO2 capture using red mud & mechanically-activated red mud and its kinetics under ambient conditions

Abstract

Greenhouse gas emissions and the growing stockpiles of red mud, an alkaline industrial waste with potential for CO2 sequestration, present significant environmental challenges. This article aims to enhance the CO2 sequestration capacity of red mud by mechanically activating its surface using a high-energy planetary ball mill for extended grinding periods. The novelty of the study lies in investigating the CO2 sequestration capacity and evaluating its kinetics includingadsorption and desorption on feed and mechanically-activated red mud under atmospheric temperature and pressure for the first time via a direct gas-solid carbonation route using a fixed bed column. The effect of ball size (10,8 and 6 mm) used in high-energy planetary ball mills while mechanical activation, CO2 flow rate (20-80 ml/min), and reaction time (1-5 h) on the CO2 capture has been studied. Apart from this, experimental data on CO2 sequestered (1-5 h) and the extent of CO2 desorption (7-35 days) are fitted to various kinetic models, including pseudo-first-order, pseudo-second-order, and Avrami's fractional order models. Results showed that the CO2 sequestration capacity of feed red mud is 3.75 mg/g, while the capacity of mechanically-activated red mud increased to 18.28 mg/g, with an adsorption time of 5 h at ambient temperature and pressure. The most suitable fit is attained with Avrami's fractional order model, suggesting that both physisorption and chemisorption contribute to enhancing the CO2 sequestration capacity of red mud. The mechanism for this process has also been proposed along with the suitable characterizations.