Efficient bio-cementation between silicate tailings and biogenic calcium carbonate: Nano-scale structure and mechanism of the interface.

Biogenic calcium carbonate (bio-CaCO) cementing tailings is an efficient technology to immobilize heavy metals in waste tailings. However, the underlying mechanism of interface cementation has not yet been clearly established, which limits the technological development. In this study, we used advanced techniques, including atomic force microscopy-based Lorentz contact resonance (AFM-LCR) spectroscopy, AFM-based nanoscale infrared (AFM-IR) spectroscopy, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy, to reveal the structural, mechanical, and chemical properties of the interface on the nanoscale. Ureolytic bacteria produced bio-CaCO to fill in pore space and to bind cement tailings particles, which prevented the formation of leachate containing heavy metals. After cementation, a strong 40-300 nm thin interface was formed between the taillings and bio-CaCO particles. Unlike chemically synthesized CaCO, bio-CaCO is strongly negatively charged, which gives it better adhesion ability. Fourier transform infrared (FTIR), AFM-IR, and Si ssNMR spectra indicated that the Si-OH and Si-O-Si groups on the silicate surface were converted to deprotonated silanol groups (≡Si-O) at a high pH and they formed strong chemical bonds of Si-O-Ca on the interface through a Ca ion bridge. In addition, hydrogen bonding with Si-OH also played a role at the cementation interface. These findings provide the nano-scale interfacial structure and mechanism of bio-CaCO cementing silicate tailings and accelerate the development of tailings disposal technology.