Pilot-scale feasibility study for the stabilization of coal tailings via microbially induced calcite precipitation

Weathering and cementation of historic kimberlite residues from South Africa: Implications for residue stabilization and CO2 sequestration

Enhanced weathering and carbon dioxide (CO2) mineralization of ultramafic mine wastes, including kimberlite residues from diamond mining, provides secure storage of this greenhouse gas and may physically stabilize mine impoundments. Yet, the outcomes of these processes over extensive periods (i.e., decades) remain relatively unknown. This study examined coarse residues from historic impoundments at the Cullinan and Voorspoed diamond mines in South Africa that have weathered over 50 to more than 100 years to investigate weathering and cementation pathways. Cemented residues (n = 7) were mainly composed of lizardite (9.6-43.2 wt.%), saponite (10.2-34.7 wt.%), and augite (6.6-27.8 wt.%), and had minor abundances of calcite (1.7-8.8 wt.%). Electron microscopy and Raman spectroscopy revealed that three plausible pathways contributed to cementing residues: (1) secondary clay precipitation, (2) carbonate precipitation and recycling, and (3) particle entrainment and infilling. Quantitative mineralogical analyses of the cement (<63 μm) and clast (>63 μm) fractions showed that the abundances of most minerals were similar between fractions, indicating that infilling of pore spaces with fine-grained particles contributed substantially to residue cementation. Stable and radiogenic carbon isotope (13C, 14C) analyses of carbonates indicated limited incorporation of organic matter and atmospheric CO2, an indication of surface weathering. Residue cementation led to some strength development (unconfined compressive strengths = 0.1-0.2 MPa), demonstrating the potential for mineral weathering to stabilize mine residues without chemical additives. Modifying residue management practices during the operational, closure, and reclamation phases at Cullinan, Voorspoed, and other mines, such as through residue co-disposal or implementing enhanced weathering practices, may improve residue stabilization and CO2 sequestration..

Critical steps in the restoration of coal mine soils: Microbial-accelerated soil reconstruction

Soil reconstruction is a critical step in the restoration of environments affected by mining activities. This paper provides a comprehensive review of the significant role that microbial processes play in expediting soil structure formation, particularly within the context of mining environment restoration. Coal gangue and flotation tailings, despite their low carbon content and large production volumes, present potential substrates for soil reclamation. These coal-based solid waste materials can be utilized as substrates to produce high-quality soil and serve as an essential carbon source to enhance poor soil conditions. However, extracting active organic carbon components from coal-based solid waste presents a significant challenge due to its complex mineral composition. This article offers a thorough review of the soilization process of coal-based solid waste under the influence of microorganisms. It begins by briefly introducing the primary role of in situ microbial remediation technology in the soilization process. It then elaborates on various improvements to soil structure under the influence of microorganisms, including the enhancement of soil aggregate structure and soil nutrients. The article concludes with future recommendations aimed at improving the efficiency of soil reconstruction and restoration, reducing environmental risks, and promoting its application in complex environments. This will provide both theoretical and practical support for more effective environmental restoration strategies.

Enrichment, characterization, and sand consolidation application of urease active calcite-producing bacteria

Minerals such as calcium carbonate, which is prevalent in marble and limestone, are present naturally in rocks. Both physicochemical processes and microbial processes can result in the creation of calcium carbonate in nature, as is well documented. In this study, microbiologically induced calcite precipitation potential of three different Travertine-type water sources (Pamukkale Travertine Spring (PTS), Pamukkale Travertine Terraces (PTT), and Red Travertine of Karahayit (RTK)) using three different incubation media (NB, NB3, and ATCC1832) were investigated. After enrichment with ATCC1832 media, urease assays were positive for all of the microbial sources. The PTS and PTT were cultured with ATCC1832 medium for 48 h, which showed the best results for urease activity and microbial growth among other samples. Metagenome analyses indicated that PTT enriched with ATCC1832 media contains > 99% Firmicutes, while PTS enriched with ATCC1832 contains > 99% Proteobacteria at the Phylum level. Results from SEM-EDX and XRD analysis revealed that calcite and/or vaterite were the minerals that emerged from the mineralization of the PTS and PTT during incubation. The type of calcium carbonate crystals tended to change from one form to another when the incubation period extends from 72 to 120 h. Both the PTS and the PTT were able to precipitate calcite within the sand column. However, the bacteria from the PTT (26% CaCO3) outperformed those from the PTS (18% CaCO3) in terms of calcium carbonate deposition on the 21st day of incubation.