Eco-efficient sodium alginate-enhanced MICP for graphite tailings stabilization: Mechanical performance and weathering resistance

Abstract

With the expansion of mining activities, the long-term open storage of tailings produced in the process of mineral processing has become an important source of dust pollution and environmental risk in mining areas, posing potential threats to the stability of ecosystem and human health. Microbially induced calcium carbonate precipitation (MICP) is a promising green solidification technology; however, its long-term stability and solidification performance remain to be improved. In this study, sodium alginate (SA), a naturally degradable polysaccharide, was introduced as a bioenhancer for MICP. The effects of SA dosage on urease activity, CaCO₃ content, mechanical strength, and resistance to wind and rainfall erosion were systematically investigated. The underlying synergistic solidification mechanisms of the SA–MICP process were elucidated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results demonstrate that SA exhibits a pronounced concentration "window effect", achieving optimal curing performance at a 1.5% dosage. The urease activity reaches 162.5 U/L with 61.8% CaCO3 content. Compared to SA-free samples, the unconfined compressive strength and splitting tensile strength increase by 1.22-fold and 3.95-fold respectively. Meanwhile, the UCS/STS ratio drops significantly from 6.26 to 2.81, indicating that SA primarily enhances interfacial bonding and crack resistance. Additionally, the material shows marked improvements in surface hardness, Young's modulus, wind erosion resistance, and rain erosion resistance. Microstructural analyses indicated that SA facilitated Ca^2 + chelation via its carboxyl groups, promoting oriented CaCO₃ nucleation and the formation of an organic–inorganic composite cementation network, thereby increasing the homogeneity and compactness of the precipitate structure. In contrast, excessive SA (>3%) hindered mass transfer and led to nonuniform precipitation, reducing the solidification efficiency. Overall, this work demonstrates that the SA–MICP synergistic approach can markedly increase the strength and environmental durability of tailings, offering a green and efficient strategy for dust control and ecological restoration in mining areas and providing theoretical and engineering foundations for MICP applications under extreme climatic conditions.