Environmental dependence of extracting phosphogypsum–microbial induced carbonate precipitation: experimental evidence and insights

Phosphogypsum (PG), a major by-product of the phosphate industry, presents environmental risks because of its residual heavy metals and anionic impurities. Here, we developed a sodium gluconate-activated PG-derived calcium source for microbially induced carbonate precipitation (SGPG-MICP), aiming to couple PG calcium valorization with impurity stabilization. The effects of temperature, pH, bacterial suspension-to-cementation solution ratio (BS:CS), and bacterial concentration (OD₆₀₀) on carbonate precipitation were systematically evaluated. Two-way ANOVA and empirical response surface modeling confirmed the coupled effects of environmental and reaction parameters on CaCO₃ production, identifying an optimal operational window of approximately 30 °C, weakly alkaline pH of 8–9, OD₆₀₀ of 0.8–1.0, and BS of 1:8. SGPG-MICP treatment significantly reduced the concentrations of heavy metal ions and harmful anions in the solution to below the corresponding regulatory limits. The immobilization of heavy metal ions and harmful anions was jointly achieved through bacteria activity and mineralization. The carbonate precipitates consisted predominantly of calcite, with minor vaterite. The changes in the temperature led to modification of the crystal type with some vaterite completely transforming into calcite. Also, while higher pH values transformed calcite crystals from large aggregates into smaller, dumbbell-shaped structures, reducing the bacterial ratio and OD₆₀₀ value resulted in a morphological change in calcite from needle-like to block-like within the dumbbell-shaped structures. These findings demonstrate that SGPG-MICP is a promising method for the sustainable reuse of PG and provide guidance for optimizing process conditions to enhance waste stabilization and resource recovery.

Subjects

Crystal morphology

Heavy metal immobilization

Microbial induced carbonate precipitation

Phosphogypsum

Solid waste treatment

DDC Class

551: Geology, Hydrology Meteorology

004: Computer Sciences

Funding(s)

United Nations University Hub on Engineering to Face Climate Change at Hamburg University of Technology

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Environmental dependence of extracting phosphogypsum–microbial induced carbonate precipitation: experimental evidence and insights