Study on MICP dust suppression technology in open pit coal mine: Preparation and mechanism of microbial dust suppression material

A hydrogel microparticle based on alginate encapsulation for microbial dust suppression: Enhancing control of dust-suppressing bacteria and coal dust consolidation

This study addresses the issue of unsuitable storage and application of liquid microbial dust suppressants in open-pit coal mines by employing microbial encapsulation technology. Sodium alginate-encapsulated dust suppression hydrogel microparticles with a diameter of ~2.57 mm were prepared, which solidify the dust suppressant, enhancing storage, transport, and application. These hydrogel microparticles demonstrate resistance to fracture force (up to 0.724 N) and springiness (0.516 mm). X-ray Diffraction analysis shows that the microparticles promote calcite-type CaCO3 nucleation and growth, exhibiting greater thermal stability and higher residual mass compared to liquid cultures. Dust suppression experiments reveal that hydrogel microparticles significantly improve coal dust consolidation, reducing dust dispersion. X-ray Photoelectron Spectroscopy and quantum chemical analysis show weak van der Waals interactions between the hydrogel and oxygen atoms on coal dust, with hydroxyl groups forming hydrogen bonds with urea molecules to promote urea aggregation. The carboxylate groups in sodium alginate facilitate calcium ion adsorption, serving as nucleation sites for calcium carbonate. This continuous calcium carbonate growth consolidates the hydrogel microparticles with coal dust, forming a mineralized layer that effectively suppresses dust.

Plant-derived urease-induced calcium carbonate precipitation for solidifying limestone dust: Preparation, performance, and mechanism

Dust pollution from open-pit limestone mines poses a significant challenge to ecological systems and human health, hindering the advancement of green mining and sustainable practices. In contrast to conventional dust-suppression techniques-such as water spraying and the use of chemical or microbial suppressants-enzyme-induced carbonate precipitation (EICP) technology leverages plant-derived urease to produce biological dust suppressants, reducing potential environmental harm. This study evaluates the solidification performance of biological dust suppressants prepared with different calcium sources-calcium chloride (CaCl2), calcium nitrate (Ca(NO3)2), and calcium acetate (Ca(CH3COO)2)-through both macroscopic and microscopic analyses. The findings demonstrate significant advantages of EICP technology in terms of dust-suppression efficiency, environmental impact, and cost-effectiveness. All three biological dust suppressants maintain mildly alkaline pH values, with their calcium-source reactivity in aqueous solutions following the order: Ca(NO3)2 > CaCl2 > Ca(CH₃COO)₂. Each suppressant significantly promotes calcium carbonate (CaCO3) precipitation, with dust suppression efficiency ranked as follows: Ca(NO3)2 > Ca(CH3COO)2 > CaCl2. The Ca(NO3)2-based suppressant demonstrates maximum dust-suppression efficiencies of 94.28 % and 57.18 % at the lowest and highest wind speeds, respectively. The mineralized product mainly consists of uniformly distributed calcite-type CaCO₃, which improves structural stability by filling voids, bonding particles, and forming interconnections. Compared to traditional water and chemical suppressants, these biological dust suppressants offer cost reductions of 42.30-50.80 % and 3.30-12.40 %, respectively. Furthermore, the Ca(CH3COO)2-based suppressant exhibits the lowest corrosiveness, with a 96-h corrosion rate of 0.020 mm/a. Overall, this study highlights the economic viability, environmental compatibility, and sustainability of plant-derived urease-induced CaCO₃ precipitation technology as a promising approach to mitigating limestone dust pollution.

Effectiveness of microbial-induced carbonate precipitation for mitigating the hydraulic erosion of the riverbank

Soil erosion and riverbank degradation pose major threats to ecosystem health and sustainable development of human society. The seemingly effective hard revetment structures have often overlooked the self-purification capacity of rivers. This study experimentally explored the effectiveness of microbial-induced carbonate precipitation (MICP) for mitigating the hydraulic erosion of riverbanks and permeability characteristics of bio-revetment. Erosion tests of MICP-treated sandy soil using the premixing-infiltration technique were conducted with a modified Erosion Function Apparatus (EFA). The erosion resistance of microbially premixed sandy soil did not exhibit the anticipated enhancement due to the limited quantity and ineffective cementation of CaCO3 from the single-time premixed treatment. The erosion rate of the MICP-treated natural sand increased exponentially with the escalation of the flow shear stress. The critical shear stress for the sand treated with premixing and four rounds of infiltration increased by 105.9 times, and the erodibility coefficient decreased by 99.9% compared to the untreated group. This notable enhancement was attributed to the accumulation of effectively cemented CaCO3 from repeated infiltrative consolidation treatments. A generalized power functional model was established to describe the relationship between the critical shear stress and CaCO3 content. The permeability of the revetment was characterized to delineate the connectivity between the aquatic and terrestrial environments. The scanning electron microscopy (SEM) analysis revealed that sand particles and effectively cemented CaCO3 at their contact points formed a skeleton-like structure, creating a novel sand-based material with both water permeability and erosion resistant. This bio-cementation method offers an innovative perspective for mitigating riverbank degradation.

Properties and Behavior of Sandy Soils by a New Interpretation of MICP

Research on MICP technology for ground improvement began in the early 2000s, and since then, it has been considered as innovative research. The field of applications is showing signs of expanding from sandy soil stabilization to remediation. However, the research has not always progressed, because it is extremely difficult to evaluate the ability (viability rate) related to microorganisms and how to handle them quantitatively. In fact, this problem hinders the consensus of research results in terms of quantitative evaluation of microorganisms and the cross-comparison (evaluation) and use of MICP technology research. The crucial disadvantage of using bacteria is that their properties are not constant due to changes over time and in the surrounding environment. Therefore, for engineering purposes, we used the carbonate formation rate (CPR), instead of urease activity, as a function of the microbial mass (OD) with viable bacteria. Thus, the standard OD-CPR relationship was defined experimentally, and the estimation method of viability was established. The required amount of microorganisms for testing was given by OD*, and the relationship "OD = Rcv OD*" was defined to convert from OD* to OD. Rcv was defined as the viable bacterial rate. It was found that the Ca2+/OD ratio controls the inhibition behavior in MICP. At a Ca2+/OD ratio of >8.46 M, then inhibition occurs, while at Ca2+/OD = 8.46 M, CPR = 8.46 OD and the CPR is proportional to the viable OD, Rcv, and OD*. We show that it is possible to perform an experiment using OD* with aged bacteria, obtain Rcv from the standard OD-CPR and OD*-CPR relationships, convert OD* to OD and to perform a unified evaluation without actually determining the viability rate.

Strategies for cost-optimized biocement production: a comprehensive review

Biocement is a promising alternative to conventional cement, offering advantages in sustainability and reducing carbon footprints. However, its widespread adoption has been hindered by the relatively high production costs. This review aims to explore various strategies and advancements in biocement production that can contribute to cost reduction. Specifically, we discuss the selection of low-cost microbial growth media for microbially induced carbonate precipitation (MICP), the utilization of plant extractives as enzyme substitutes in enzyme-induced carbonate precipitation (EICP), the substitution of urea with urine as a low-cost source of nitrogen, the exploration of affordable alternatives to calcium ions, and the valorization of ammonia/ammonium byproducts, and other pathways. The adoption of these strategies could significantly enhance biocement's scalability and sustainability, paving the way for more eco-friendly and cost-effective construction practices.

Enhanced MICP for Soil Improvement and Heavy Metal Remediation: Insights from Landfill Leachate-Derived Ureolytic Bacterial Consortium

This study investigates the potential of microbial-induced calcium carbonate precipitation (MICP) for soil stabilization and heavy metal immobilization, utilizing landfill leachate-derived ureolytic consortium. Experimental conditions identified yeast extract-based media as most effective for bacterial growth, urease activity, and calcite formation compared to nutrient broth and brown sugar media. Optimal MICP conditions, at pH 8-9 and 30 °C, supported the most efficient biomineralization. The process facilitated the removal of Cd2+ (99.10%) and Ni2+ (78.33%) while producing stable calcite crystals that enhanced soil strength. Thermal analyses (thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)) confirmed the successful production of CaCO3 and its role in improving soil stability. DSC analysis revealed endothermic and exothermic peaks, including a significant exothermic peak at 444 °C, corresponding to the thermal decomposition of CaCO3 into CO2 and CaO, confirming calcite formation. TGA results showed steady weight loss, consistent with the breakdown of CaCO3, supporting the formation of stable carbonates. The MICP treatment significantly increased soil strength, with the highest surface strength observed at 440 psi, correlating with the highest CaCO3 content (18.83%). These findings underscore the effectiveness of MICP in soil stabilization, pollutant removal, and improving geotechnical properties.

Preparation and performance evaluation of an efficient microbial dust suppressant for dust control in disturbed areas of blast piles in open-pit coal mines

Open-pit coal mining creates large rock piles as a result of removing overlying strata. When disturbed by loading operations and wind, these rock piles release considerable dust, leading to significant environmental pollution. This study aims to develop an environmentally friendly and cost-effective method for dust control in disturbed areas of open-pit coal mines, using Sporosarcina pasteurii as a microbial dust suppressant to explore its potential application and development. Laboratory experiments were conducted to simulate the growth characteristics of Sporosarcina pasteurii in the microenvironment of blast pile dust. The effectiveness of the microbial dust suppressant was evaluated under conditions of impact disturbance and rainfall erosion through wind and rain erosion tests. Results showed that under optimal conditions, the wind erosion resistance of treated samples improved significantly, with an increase of 98.24%, 86.99%, 64.08%, and 40.98% after 1, 2, 3, and 4 impact disturbances, respectively. Additionally, rain erosion resistance improved by 75.55% after 35 min of simulated rainfall. The growth conditions of Sporosarcina pasteurii in blast pile dust leachate were similar to those in sterile water, demonstrating robust growth and consistent urease activity of 7.78 mmol L⁻1 min⁻1 after 24 h. The mineralization product was calcite-type CaCO3 with uneven particle sizes. This work confirms the feasibility of microbial dust suppressants for managing dust in disturbed areas of open-pit coal mine blast piles, offering a promising approach for dust control in such environments.

Cross-sectional analysis of dyslipidemia risk in coal mine workers: from epidemiology to animal models

OBJECTIVE

To investigate the association between coal dust exposure and the occurrence of dyslipidemia in coal mine workers, and identify relevant risk factors. Methods: We selected a population who underwent occupational health examinations at Huainan Yangguang Xinkang Hospital from March 2020 to July 2022. Participants were divided into two groups based on the presence or absence of dyslipidemia, and their baseline information was collected, including records of coal dust exposure. We employed single-factor analysis to identify risk factors for dyslipidemia and adjusted for confounding factors in the adjusted models. Additionally, we explored the effects in different populations using stratified analysis, smooth curve fitting, and propensity score matching. Finally, we confirmed the causal relationship between coal dust exposure and dyslipidemia by examining tissue sections and lipid-related indicators in a mouse model of coal dust exposure. Results A total of 5,657 workers were included in the study, among whom 924 individuals had dyslipidemia and 4,743 individuals did not have dyslipidemia. The results of the single-factor analysis revealed that dust exposure, age, BMI, blood pressure, and smoking were statistically significant risk factors for dyslipidemia (p < 0.05). Additionally, the three multivariate models, adjusted for different confounders, consistently showed a significant increase in the risk of dyslipidemia associated with coal dust exposure (Model 1: OR, 1.869; Model 2: OR, 1.863; Model 3: OR, 2.033). After conducting stratified analysis, this positive correlation remained significant. Furthermore, propensity score matching analysis revealed that with increasing years of work, the risk of dyslipidemia gradually increased, reaching 50% at 11 years. In the mouse model of coal dust exposure, significant coal dust deposition was observed in the lungs and livers of the mice, accompanied by elevated levels of total cholesterol (TC), alanine transaminase (ALT), aspartate transaminase (AST), and low-density lipoprotein cholesterol (LDL-C). Conclusion Exposure to coal dust significantly increases the risk of developing dyslipidemia, and this positive correlation exists in different populations, particularly with increasing years of work, resulting in a higher risk.

Effects of structural parameters of pressure-swirl nozzle on atomization and dust removal characteristics

To further improve the dust removal efficiency of water spray, the influence of key structure parameters of nozzle on atomization characteristic (droplet size, atomization angle, flow rate, effective spray distance, wind disturbance resistance) was studied. The results showed that the nozzle had good atomization performance when the outlet diameter was 1.5 mm. The internal structure of the nozzle had an obvious influence on the atomization characteristics. The shrinkage angle had a prominent effect on the droplet size and atomization angle. When the shrinkage angle was increased from 60 to 120°, the droplet size and atomization angle were improved by 29.2% and 45.5%, respectively, while the increased shrinkage angle from 120 to 150° only improved by 9.1% and 4.2%, respectively. In addition, the diameter of the center hole had a strong correlation with the effective spray distance. When the diameter of the center hole increased from 1 to 2 mm, the effective spray distance increased by 60.9% (to 7.4 m) at the pressure of 4 MPa, while the effective spray distance without change increased when the diameter of the center hole increased from 2 to 2.5 mm. It was determined that the nozzle with the outlet aperture of 1.5 mm, the shrinkage angle of 120°, and the diameter of the center hole of 2 mm had good atomization and dust control characteristics. Additionally, it was verified that the optimized nozzle had a substantial improvement in controlling respirable dust, and the dust removal efficiencies for PM2.5 and PM5 were increased by 14.29% and 16.52%, respectively, compared to the original nozzle. This study provided guidance for choosing the nozzle of hydraulic support to form the effective dust control spray.

Efficient remediation of cadmium and lead contaminated soil in coal mining areas by MICP application in hydrothermal carbon-based bacterial agents: Nucleation pathways and mineralization mechanisms

The development of industrial mining has resulted in a large amount of Cd and Pb polluting the soil in mining areas, and leads to adverse health effects on the life of both plants and animals. Here, a soft template method was conducted to prepare hydrothermal carbon (HC) with regular morphology, which assisted with Bacillus pasteurii to induce calcite precipitation for decontamination of mining soil. Soil remediation experiments over 30 days of remediation with an HC microbial agent (HCMA) resulted in 89.4% and 87.8% decrease in the amount of leached Cd and Pb, respectively. The content of exchangeable Cd and Pb decreased by 76.1% and 81.0%, respectively. At the same time, soil fertility significantly improved. The electrostatic potential and surface charge distribution of extracellular polymeric substances (EPS) and sodium citrate (NaCit) were analyzed using DFT simulations, their nucleophilic and electrophilic regions were determined, and the nucleation mechanism was determined. The DFT results indicated that the oxygen-containing groups of EPS and NaCit had strong negative electrostatic potential and electronegativity, which could cause Cd2+, Pb2+, and Ca2+ to aggregate on their surfaces. They also combined with CO32- produced by urease during the decomposition of urea, resulting in Cd2+ and Pb2+ being encapsulated by calcium carbonate to form a coprecipitate. X-ray diffraction analyses revealed that the precipitate was mainly calcite calcium carbonate, which is more stable and less prone to secondary leaching of HMs. The gathered data prove the significant role of HCMA in remediation of mining soil contaminated with Cd and Pb.

Preparation of an environment-friendly microbial limestone dust suppressant and its dust suppression mechanism

The development of an efficient and environmentally friendly dust suppressant is crucial to address the issue of dust pollution in limestone mines. Leveraging the synergistic microbial-induced calcium carbonate precipitation (MICP) technology involving NaHCO3 and dodecyl glucoside (APG), the optimal ratio of the dust suppressant was determined through single-factor and response surface tests. The dust suppression efficacy and mechanisms were analyzed through performance testing and microscopic imaging techniques, indicating that the optimal ratio of the new microbial dust suppressant was 20% mineralized bacteria cultured for 72 h, 0.647 mol L-1 cementing solution, 3.142% NaHCO3, and 0.149% APG. Under these conditions, the yield of calcium carbonate increased by 24.89% as compared to when no NaHCO3 was added. The dust suppressant demonstrated excellent wind, moisture, and rain resistance, as well as curing ability. More calcite was formed in the dust samples after treatment, and the stable form of the dust suppressant contributed to consolidating the limestone dust into a cohesive mass. These findings indicate that the synergistic effect of NaHCO3 and APG significantly enhanced the dust suppression capabilities of the designed microbial dust suppressant.

Microbially induced carbonate precipitation with Arthrobacter creatinolyticus: An eco-friendly strategy for mitigation of chromium contamination

Chromium contamination from abandoned industrial sites and inadequately managed waste disposal areas poses substantial environmental threat. Microbially induced carbonate precipitation (MICP) has shown promising, eco-friendly solution to remediate Cr(VI) and divalent heavy metals. In this study, MICP was carried out for chromium immobilization by an ureolytic bacterium Arthrobacter creatinolyticus which is capable of reducing Cr(VI) to less toxic Cr(III) via extracellular polymeric substances (EPS) production. The efficacy of EPS driven reduction was confirmed by cellular fraction analysis. MICP carried out in aqueous solution with 100 ppm of Cr(VI) co-precipitated 82.21% of chromium with CaCO3 and the co-precipitation is positively correlated with reduction of Cr(VI). The organism was utilized to remediate chromium spiked sand and found that MICP treatment decreased the exchangeable fraction of chromium to 0.54 ± 0.11% and increased the carbonate bound fraction to 26.1 ± 1.15% compared to control. XRD and SEM analysis revealed that Cr(III) produced during reduction, influenced the polymorph selection of vaterite during precipitation. Evaluation of MICP to remediate Cr polluted soil sample collected from Ranipet, Tamil Nadu also showed effective immobilization of chromium. Thus, A. creatinolyticus proves to be viable option for encapsulating chromium contaminated soil via MICP process, and effectively mitigating the infiltration of Cr(VI) into groundwater and adjacent water bodies.

Microbial-induced calcium precipitation: Bibliometric analysis, reaction mechanisms, mineralization types, and perspectives

Microbial-induced calcium precipitation (MICP) refers to the formation of calcium precipitates induced by mineralization during microbial metabolism. MICP has been widely used as an ecologically sustainable method in environmental, geotechnical, and construction fields. This article reviews the removal mechanisms of MICP for different contaminants in the field of water treatment. The nucleation pathway is explained at both extracellular and intracellular levels, with a focus on evaluating the contribution of extracellular polymers to MICP. The types of mineralization and the regulatory role of enzyme genes in the MICP process are innovatively summarized. Based on this, the environmental significance of MICP is illustrated, and the application prospects of calcium precipitation products are discussed. The research hotspots and development trends of MICP are analyzed by bibliometric methods, and the challenges and future directions of MICP technology are identified. This review aims to provide a theoretical basis for further understanding of the MICP phenomenon in water treatment and the effective removal of multiple pollutants, which will help researchers to find the breakthroughs and innovations in the existing technologies, with a view to making significant progress in MICP technology.

Microscopic deposition-property relationships in microbial-induced consolidation of coal dusts

In recent years, the preparation of new microbial dust suppressants based on microbial induced carbonate precipitation (MICP) technology through enriched urease-producing microbial communities has become a new topic in the field of coal dust control. The deposition of CaCO3 was the key to suppress coal dust. However, deposition characteristics in the field is not sufficient and the relationship between deposition characteristics and erosion resistance is not clear, which hinders the development of engineering application of new microbial dust suppressant. Therefore, based on X-CT technology, this paper observed and quantified micro-deposition of bio-consolidated coal dust with different calcium sources. Furthermore, a conceptual framework for deposition was proposed and its correlation with erosion resistance was revealed. The results showed that CaCO3 induced by calcium chloride and calcium lactate was aggregate deposited. Aggregate deposited CaCO3 was small in volume, showed the distribution of aggregation in the central area and loose outside, and mosaiced pores. CaCO3 induced by calcium nitrate was surface deposition due to attached biomass. Surface deposition was mostly large volume CaCO3 expanding from the inside out, which could cover coal dust to a high degree and completely cemented pores. In addition, the threshold detachment velocity of coal dust cemented by surface deposition was increased by 17.6-19.1% compared to aggregate deposition. This depended on the abundance and strength of CaCO3 bonding between coal dust particles under different deposition. The two-factor model based on porosity and CaCO3 coverage can well express relationship between erosion resistance and depositional characteristics. Those results will help the engineering application of MICP technology in coal dust suppression.

Influence of Recirculation Flow on the Dispersion Pattern of Blasting Dust in Deep Open-Pit Mines

The recirculation within a deep open-pit mine is a significant factor contributing to the deterioration of the atmospheric environment. However, the underlying mechanisms of how recirculation influences the dispersion pattern of dust clouds within the deep open-pit mine have not been clearly elucidated. In this research, the dispersion patterns of blast dust clouds were investigated in a deep open-pit mine located in northern China. This research initially conducted a similar experiment to verify the existence of recirculation flow in the experimental mine, which can cause dust particles to aggregate toward the upwind slope. In response to the dust pollution issue in deep open-pit mine blasting operations, this study conducted a numerical simulation analysis based on on-site measurement data to investigate the effects of varying natural wind velocity, natural wind direction, and blast location on the diffusion pattern of blasting dust. The results indicate that natural wind velocity (v), natural wind direction (α), and blast location (d) affect the distance between the blast location and the recirculation center point (Drecir), subsequently influencing the diffusion pattern of blasting dust. The recirculation flow effect influences the diffusion of dust toward the upwind slope under smaller Drecir values, leading to widespread and long-term pollution within the mine. Under larger Drecir values, dust diffuses toward the downwind slope with the straight flow of wind, resulting in less pollution within the mine. Through orthogonal experiments, the equation Drecir = -120.61v2 + 237.27v + 0.82d - 0.07α2+ 6.75α + 151.08 was established in this deep open-pit mine, which provides a basis for predicting the diffusion pattern of blasting dust and control strategy in this deep open-pit mine.