Role of carbon sequestration methods in enhancing water holding capacity of dredged Yellow River sediment: biochar and CO2 utilization

Dredged Yellow River sediment (DYRS) is widespread in nature and generally features low water holding capacity due to poor grain grading and lack of clay minerals. Low water holding capacity can impede its application in interdisciplinary engineering and ecological scenarios such as ecological slope substrate and ecological remediation of mining area. This study investigates the role of carbon sequestration methods in the water holding capacity and microscopic mechanism of DYRS. DYRS is improved by two types of carbon sequestration methods, i.e., biochar additive and CO ₂ curing with the agent of reactive MgO (rMgO). The results show that the biochar additive and CO2 curing lead to an increase rate of water holding capacity by 49.5% and 180%, respectively. The biochar-treated DYRS features an optimum water holding capacity of DYRS, corresponding to an optimum particle size fraction of biochar. However, such an optimum water holding capacity of DYRS does not hold for the case of CO ₂ curing. The increasing dose of rMgO and CO ₂ curing duration are both favorable for improving the water holding capacity of DYRS, attributed to the binding products of chemical reaction. The performance of water holding capacity in treated DYRS is closely associated with altered pore structures by carbon sequestration methods. Biochar leads to a change of trimodal pore structure in untreated DYRS to bimodal pore structure in treated DYRS. However, CO ₂ curing reshapes the trimodal pore structure and facilitates the formation of new smaller pore sizes in treated DYRS. The research findings are fundamental for the future application of dredged river soils and carbon sequestration methods in engineering practice.