ORIGINAL RESEARCH article
Front. Clim.
Sec. Carbon Dioxide Removal
Comparative Study on the Enhancing Effects of CaSO4 and CaCl2 Supplementation on Red Mud Carbonation
Provisionally accepted
- 1Shandong University of Science and Technology, Qingdao, China
- 2Shandong Jiaogong Construction Group Co., Ltd., Rizhao, China
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Red mud (RM), a strongly alkaline solid waste generated during alumina production, can undergo carbonation with CO2 for mineral sequestration. To investigate the promoting effect of external calcium sources on RM carbonation, desulfurization gypsum (CaSO4) and calcium chloride (CaCl2) were selected as supplements, and RM samples with/without these calcium sources were prepared. Experiments were conducted under various CO2 concentrations (100%, 15%, 1%) and atmospheric conditions for both RM suspensions and solid-state RM (simulating open-air piles). The results showed that: (1) With increasing CO2 concentration, the time for RM suspensions to reach pH equilibrium shortened (30 min for 100% CO2 vs. 15 h for 1%), and the equilibrium pH decreased (to 6.8 for 100% CO2 vs. 8.3 for 1%); (2) Under atmospheric conditions, the pH of RM suspensions supplemented with CaSO4 and CaCl2 decreased to 8.6 and 8.0, respectively, with CaCO3 characteristic peak intensity increasing compared to pure RM; (3) For solid RM, the two calcium sources lowered the minimum pH to 8.8 (CaSO4) and 8.4 (CaCl2), ultimately stabilizing around 9.0, whereas pure RM remained at 10.1. The CO2 sequestration capacities reached 45.3 g/kg and 47.2 g/kg, respectively, while forming a porous CaCO3 coating on the RM particles. The calcium sources significantly enhanced the stability and durability of the carbonation reaction, providing a scientific basis for long-term CO2 sequestration.
Keywords: Calcium source, Carbon Dioxide, Carbonates, Mineral Carbonation, Red mud
Received: 03 Nov 2025; Accepted: 28 Jan 2026.
Copyright: © 2026 Cheng, Yan, Jin, Wang, Jia, An and Sun. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Lu Jin
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