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Coal bottom ash (CBA) was modified on the basis of the engineering problems of low resource utilization of CBA and difficulty in treating HMS through alkali activation to synthesize geopolymers and solidify heavy metal-contaminated soil (HMS).

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How to effectively recycle Ni–Co ore mining mullock (OMM) is a key means to address both local environmental pollution and resource waste. In this study, OMM and bottom ash (BA) were prepared into cementitious materials (OBM) by mechanochemical means with gentle conditions. It is mainly realized by grinding the mixture and pressing it into columnar blocks. The results show that the maximum compressive strength of OBM is 4.803 MPa in 28 day meet the standard of China mine backfilling for mine repair, and the stability efficiency of Ni2+ and Co2+ is above 90%. The mechanism studies show that the amorphous materials recombine to form silicon-aluminum polymers, while a small portion of Ni2+ and Co2+ binds to the polymer during consolidation to form massive structure. Most of the heavy metal ions are encased in the hard structure, which is relatively stable and without pollution risk. The chemical behavior of metals in the system is fitted by geochemical model. This study not only solved the problem of heavy metal contamination in OMM, but also transformed it into a cementitious material that can be used for backfilling of local pits.