Enhancing the strength of tailings sand in different particle sizes using a modified enzyme-induced carbonate precipitation method

Tailings sand is, at present, a typical industrial solid waste and is prone to polluting soil and water resources. This study aims at helping solve the difficulty of utilising tailings sand for secondary purposes and proposes a low-cost and environment-adapted modified enzyme-induced calcium carbonate precipitation (EICP) technology to solidify tailings sand and improve its secondary utilisation rate. This study modified EICP by adding xanthan gum (XG) to optimise it and explore the curing effect. The powdered biopolymer can be uniformly mixed with tailings sand through a simple dry-mixing method, significantly improving construction operability. The effects of different temperatures and pH on urease activity were studied using soybean urease, and then the effects of different conditions on calcium carbonate production were analysed. On this basis, tailings-sand samples in three different particle sizes were solidified, and the solidification effect and microscopic cementation mechanism were analysed. The research results indicate that soybean urease activity remains stable within the temperature range of 10–50°C and pH range of 5–10, demonstrating excellent engineering applicability. The modified EICP technique demonstrates exceptional efficacy in solidifying large-grained tailings sand (D 3 ), achieving a 255.97% increase in unconfined compressive strength, significantly outperforming conventional EICP and XG methods. For large particle sizes, mechanism analysis reveals that XG and CaCO 3 synergistically form a ‘rigid–flexible integration’ pore-filling network. This study not only provides an economical and efficient new method for tailings-sand solidification but also establishes a theoretical and technical foundation for the targeted reinforcement of tailings sand in various particle sizes.