Recycling of Waste Iron Tailings by Biomineralization for Cemented Paste Backfill Production

Numerous waste iron tailings worldwide require eco-friendly treatment methods, with biotechnology being a promising option. However, bacteria survival in cemented paste backfill has been a persistent challenge. This study presents a method that adjusts the cementing solution composition (e.g. urea and calcium ions) to enhance Bacillus licheniformis biomass in backfill. This approach, free from additives, aims to determine the optimal cementing solution concentration for bacterial growth in backfill. The results indicate that a solution with 1.0 mol/L urea and 1.2 mol/L calcium ions has the highest strength, surpassing the control group by 4.56%. Quantitative analysis reveals that this solution enhances the production of calcium carbonate while reducing the content of calcium hydroxide (CH), the hydration product. The interplay between biomineralization and hydration reactions is explained by the fact that CH in hydration reactions contributes calcium ions to the biomineralization process, establishing a complementary relationship between hydration and mineralization products. This discovery opens up a novel path to integrate MICP with waste iron tailings recycling for cemented paste backfill.