Elsevier

Advanced Powder Technology

Volume 32, Issue 12, December 2021, Pages 4509-4521
Advanced Powder Technology

Original Research Paper
Preparation of microbial dust suppressant and its application in coal dust suppression

https://doi.org/10.1016/j.apt.2021.10.001Get rights and content

Highlights

  • MICP is a green and high-efficient dust suppression technology.

  • MICP technology is newly applied to controlling coal dust in coal mines.

  • The bacteria screened are indigenous, can adapt to the coal habitat conditions.

  • Microbe-induced mineralization products can consolidate coal dust into a whole.

Abstract

To promote the application of microbially induced carbonate precipitation (MICP) technology for coal dust suppression, two urease-producing bacteria (SZS1-3 and SZS1-5) in a coal mine soil were screened. 16 s rDNA sequencing of these bacteria indicated sequences similar to those of Acinetobacter guillouiae CIP 63.46 and Staphylococcus caprae ATCC 35538, respectively. Strains SZS1-3 and SZS1-5 had their largest urease activity at the initial urea concentration of 0.5 mol/L, under slightly alkaline (pH = 9) and neutral (pH = 7) initial pH levels, respectively. Their final mineralized products were vaterite-type and calcite-type calcium carbonate. Although dust suppression results indicated that both bacteria can effectively bind coal dust particles, consolidated coal dust treated with SZS1-5 had a stronger resistance to wind and rain. The screening, mineralization and dust suppression potential analysis of these two urease-producing bacteria can provide reference for the application of MICP technology in coal dust suppression.

Introduction

As a basic energy source and an industrial raw material, coal has had an important contribution to China's economic development [1]. Owing to rapid development of the coal industry and the continuous improvement in mechanization, mining scales and coal usage have dramatically increased [2]. However, during coal mining, processing and transport, a large volume of dust is released into the atmosphere which not only pollutes the environment, it also exposes mine workers to high dust concentrations, posing severe effects on their health [3], [4]. To reduce exposure to coal dust and the release of dust into the atmosphere, dust prevention technologies have been developed. However, conventional dust suppression methods, including water spraying, thatch cover and dust-proof nets, have certain drawbacks, such as high costs and limited dust suppression capabilities [5]. Although chemical dust suppressants are relatively efficient, they have a few disadvantages. For example, wetting dust suppressants have a short effective period, being prone to secondary dust [6]. Adhesive dust suppressants have been recorded to cause environmental pollution [7]. Most of the agglomerated dust suppressants are corrosive [8], while composite dust suppressants are difficult to develop, with some components also resulting in environmental pollution [9]. As demand for coal continues to increase, it is therefore important that specific requirements for environment-friendly, low-cost, and efficient dust suppression technology are formulated.

Recently, the microbially induced carbonate precipitation (MICP) method has attracted widespread attention due to it being economic, environment-friendly and being highly efficient in particle aggregation. The MICP process can be achieved through many processes including urea hydrolysis, denitrification, iron reduction, sulfate reduction and other ways [10]. Among them, the urea hydrolysis reaction process is easy to control and can produce a large amount of CO32– in a short time. Therefore, it has been most widely used [11]. The basic principle of MICP through urea hydrolysis is presented in Fig. 1. Under the catalysis of microbial urease, urea undergoes hydrolysis to generate carbonate ions which then react with cations (such as Ca2+) in the system to form carbonate precipitation with a gelling effect. The mineralization process is continuous, and granular matter can be cemented to form a whole with a certain strength and rigidity [12], [13], [14]. This process results in MICP technology being environment-friendly, sustainable and having efficient advantages; MICP has been employed in the fields of soil reinforcement, historical heritage protection and soil dust suppression [15], [16], [17], [18], [19]. For example, DeJong et al. [16] applied MICP technology to improve the engineering performance of sand and found that compared with untreated loose samples, the treated samples have higher initial shear stiffness and ultimate shear capacity. Liu et al. [18] used MICP technology to form an anti-corrosion layer on the surface of ancient clay tiles, and the results proved that the MICP protection layer can effectively alleviate the weathering of ancient clay tiles. Meng et al. [19] found that the MICP method could significantly enhance the bearing capacity and wind erosion resistance of the surficial soil through the formation of soil crusts.

Based on the features of MICP technology and the characteristics of coal dust, its role in coal dust prevention has also been investigated [1], [20], [21], [22]. However, the use of MICP technology for the prevention and control of coal dust is a new research direction which has many problems that are yet to be resolved. First of all, there are only a few strains suitable for coal dust control, especially strains with high urease activity. Although urease-producing bacteria are widely distributed in nature, the unique physical and chemical conditions of coal dust may limit the survival and activity of existing urease bacteria. Therefore, the screening of urease microorganisms in different habitats and the exploration of their mineralization potential in coal dust will be of great significance for the preparation of high-efficiency microbial dust suppressants and the development of MICP technology in the field of coal dust suppression. Secondly, the choice of which strain to prepare for the microbial dust suppressant is also very important for its adaptability and ecological impact on the application site. Indigenous bacteria adapt to original habitat conditions, being able to grow better and play a role during application [23], [24], [25], therefore having less potential safety hazards to the environment. Screening indigenous urease strains for the application habitat is therefore important for the smooth application of MICP technology.

However, there are few studies on the application of MICP technology to coal dust suppression. At the same time, most of the urease bacteria currently used are derived from ordinary soil or water. The selection of indigenous dominant urease-producing strains in coal mines is rarely reported. Based on the above analysis, we aim to screen urease-producing bacteria from soil in a mining area and analyze the effects of different external environmental factors on the growth and urease activity of these strains. The mineralization process of the strains and their characteristics are also explored. Microbial dust suppressants were prepared and their consolidation performance for coal dust was discussed, providing data to support the theoretical basis for the application of microbially induced mineralization technology in the coal dust suppression.

Section snippets

Soil and coal samples

Soil and coal samples used in this experiment were obtained from the Anjialing coal mine (located in Pinglu District, Shuozhou City, Shanxi Province). The physical and chemical properties of soil are shown in Table 1. Industrial analysis of coal samples was undertaken (Table 2). The true relative density of coal is 1.55. Coal samples were pulverized using a crushing instrument (Huangdai 800Y, Zhejiang Yongkang Platinum Metal Products Co., Ltd., China) and the pulverizged coal was screened using

Identification of urease-producing bacteria

Strains SZS1-3 (Genbank number: MW182407) and SZS1-5 (Genbank number: MW186146) are two dominant strains isolated from the soil of the mining area. Fig. 3 shows the two strains on the solid medium for urease-producing screening and their Gram staining results. According to the strain neighboring phylogenetic tree (Fig. 4), SZS1-3 and Acinetobacter guillouiae CIP 63.46, and SZS1-5 and Staphylococcus caprae ATCC 35538 exhibited 100% and 99% confidence in homology, respectively. Therefore, strain

Conclusions

Herein, two urease-producing microorganisms with mineralization potential were screened and identified from the soil of coal mine. The effects of environmental factors on the biomass and urease activity of strains SZS1-3 and SZS1-5 were compared and analyzed. The mineralization products of the two urease-producing bacteria and their effects on consolidating coal dust were characterized through microscopic scanning, elemental analysis, X-ray diffraction, and wind and rain resistance tests, and

Prospect for industrial application of microbial dust suppressant

As shown in Fig. 15, the steps of microbial dust suppressant in the industrial application are as follows. Firstly, the bacteria are freeze-dried into lyophilized powder, so that they are in a dormant state for easy storage and transportation. In industrial application, lyophilized powder is activated and cultivated to obtain the bacterial solution required for the microbial dust suppressant. The solid particles of urea and calcium chloride are dissolved in water and stirred evenly to obtain

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank funding and supporting on the study from the Key Program of the National Natural Science Foundation of China [grant numbers 42077444, 51674038, 51874193, 51934004]; the National Key Technologies R&D Program of China [grant number 2018YFC0807900]; the Shandong Province Natural Science Foundation [grant numbers ZR2020ME101, ZR2018JL019]; the Shandong Province Science and Technology Development Plan [grant number 2017GSF220003]; Shandong Province First Class Subject Funding Project [grant

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