Abstract: Enzyme-induced calcite precipitation (EICP) is an emerging technology used to enhance the mechanical properties of soils and control heavy metal contaminants. However, the differences in the permeability characteristics of graphite tailings with varying particle sizes result in significant variations in mineralization stability and remediation effectiveness. In this study, biopolymer-synergized EICP technology was used to solidify/stabilize graphite tailings. The application potential of chitosan (CTS) in bioremediation of tailings with different particle sizes was explored from both mechanical strength and environmental perspectives. Scanning electron microscopy, infrared spectroscopy, and X-ray diffraction were employed to reveal the underlying mechanisms of tailings solidification/stabilization. The results indicate that CTS-EICP treatment effectively overcomes the limitations of traditional EICP in tailings solidification/stabilization, where treatment effects significantly decrease with decreasing particle size. When the CTS content is 1.5%, the compressive strength and CaCO3 precipitation rate of tailings with particle sizes smaller than 75 μm increase by 210.29% and 150.1%, respectively. After treatment, the pH of the tailings leachate stabilizes at 7.81−8.36, and the reduction in heavy metal ion concentrations ranges from 89.59% to 100%. CTS promotes the formation of carbonate crystals through a urease-stabilized mechanism, with crystals embedding in the three-dimensional network crosslinked by CTS molecules, thereby constructing a composite barrier structure of “tailings-CTS-carbonate-CTS-tailings.” The findings of this study provide valuable insights for the application of EICP in the solidification/stabilization of graphite tailings with different particle sizes.

Key words: enzyme-induced calcite precipitation (EICP), chitosan (CTS), graphite tailings, particle size, mechanical strength, environmental effects