Effectiveness and mechanism of cyanide tailings cementation by steel slag coupled with non-ureolytic microbially induced carbonate precipitation

Ammonia production by ureolytic bacteria limited the practical application of microbial induced carbonate precipitation (MICP). In this work, a coupled technique of steel slag (SS) combined with non-ureolytic bacterial mineralization is proposed to investigate the effects and mechanisms of enhanced cyanide tailings (CT) solidification. The results showed that SS promoted the growth, carbonic anhydrase (CA) activity and mineralized precipitation production in Bacillus mucilaginosus. The addition of 3 % SS increased the unconfined compressive strength (UCS) by 27.35 % to 1.35 MPa; the permeability coefficient was 6.01x10(- 7)cm & sdot;s(-1), which was reduced by 56.13 %. The coupled technique degraded 95.3 % of the cyanide in the CT; the addition of SS reduced the exchangeable states Cu (1.79 %), Pb (2.48 %), Zn (6.95 %) and Cr (11.83 %) in the bio-cured CT and converted them to the carbonate-bound states Cu (1.24 %), Pb (2.7 %), Zn (0.28 %) and Cr (4 %). Scanning electron microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric Analysis (TG), Fourier Infrared Spectroscopy (FTIR), and Computed tomography analyses showed that SS and Bacillus mucilaginosus interactions facilitated the hydration reaction, resulting in hydrated calcium silicate (C-S-H) and more carbonate minerals with different crystalline shapes; the C-S-H and the carbonate minerals filled up the pore spaces of the CT, which contributed to the stabilization of heavy metals. This study provided new ideas for the resourceful utilizations of industrial solid waste SS and the harmless treatment of CT.