Effect of MICP synergized with magnesium oxide on solidification of Zn²⁺ contaminated red clay

As industrialization accelerates, the pollution problem of Zn²⁺ is becoming increasingly severe, posing a significant threat to the stability of ecosystems and engineering structures. To cope with this challenge, this study examines the solidification effect of MICP (Microbially Induced Carbonate Precipitation) synergized with magnesium oxide on Zn²⁺ contaminated red clay. The variation of unconfined compressive strength (UCS) and shear strength index of solidified soil under different concentrations of cementation solution, magnesium oxide contents and Zn²⁺ concentrations were investigated by UCS tests and direct shear tests. The curing effect of MICP synergized with magnesium oxide technology on Zn²⁺ was analyzed by ion occurrence form test and pH value changes of samples before and after curing. The results show that the incorporation of magnesium oxide significantly improves the UCS and shear strength of Zn²⁺ contaminated red clay. When the content of magnesium oxide is 5%, the utilization rate is the highest. When the concentration of cementation solution is 1.0 mol/L, the UCS and shear strength are the highest. The shear strength index of solidified samples is mainly affected by the content of magnesium oxide. The incorporation of magnesium oxide facilitates calcium carbonate precipitation during MICP by increasing the pH value. This process accelerates the transformation of zinc ions from a weak acid-extractable state to reducible, oxidizable, and residual states.