In Situ Remediation of Phosphogypsum with Water-Washing Pre-Treatment Using Cemented Paste Backfill: Rheology Behavior and Damage Evolution

The accumulation of original phosphogypsum (OPG) has occupied considerable land resources, which have induced significant environmental problems worldwide. The OPG-based cemented paste backfill (OCPB) has been introduced as a promising solution. In this study, a water-washing pre-treatment was used to purify OPG, aiming to optimize the transport performance and mechanical properties of backfills. The overall results proved that in treated phosphogypsum-based cemented paste backfill (TCPB), the altered particle size distribution can alleviate the shear-thinning characteristic. The mechanical properties were significantly optimized, of which a maximum increase of 183% of stress value was observed. With more pronounced AE signals, the TCPB samples demonstrated better residual structures after the ultimate strength values but with more unstable cracks with high amplitude generated during loading. Principal component analysis confirmed the adverse effects of fluorine and phosphorus on the damage fractal dimensions. The most voluminous hydration products observed were amorphous CSH and ettringite. The interlocked stellate clusters may be associated with the residual structure and the after-peak AE events evident in TCPB, indicate that more significant stress should be applied to break the closely interlocked stitches. Ultimately, the essential findings in this experimental work can provide a scientific reference for efficient OPG recycling.

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Utilisation of Water-Washing Pre-Treated Phosphogypsum for Cemented Paste Backfill

Minerals ◽

10.3390/min9030175 ◽

2019 ◽

Vol 9 (3) ◽

pp. 175 ◽

Cited By ~ 17

Author(s):

Yikai Liu ◽

Qinli Zhang ◽

Qiusong Chen ◽

Chongchong Qi ◽

Zhu Su ◽

...

Keyword(s):

Setting Time ◽

Microstructural Analysis ◽

Engineering Application ◽

Cemented Paste Backfill ◽

Water Washing ◽

Paste Backfill ◽

Pre Treatment ◽

Chinese Standard ◽

Better Than

Recycling phosphogypsum (PG) for cemented paste backfill (CPB) has been widely used at phosphate mines in China. However, the impurities in PG prolong the setting time and reduce the uniaxial compressive strength (UCS), limiting the engineering application of PG. This paper aims to investigate the feasibility of treated PG (TPG) washed repeatedly using deionised water (DW) for CPB. A water-washing pre-experiment was first conducted to find the proportion with the least DW demand and the effects of water-washing on ordinary PG (OPG). Then, based on the PG:DW ratio obtained from the pre-experiment, the properties of the OPG-based CPB (OCPB) and TPG-based CPB (TCPB) were tested using slump tests, UCS tests, and microstructural analysis. The results show that (1) after 11 water-washings at the PG:DW ratio of 1:1.75, the pH of the supernatant (pH = 6.328) meets the requirements of Chinese standard GB 8978-1996. (2) Water-washing improves the particle gradation quality of PG and removes the soluble impurities adsorbed at the surface of PG crystals. (3) The initial slump values of TCPB are 0.19–1.15 cm higher than that of OCPB, furthermore, the diffusivity values of TCPB are better than the performance of OCPB, with 0.61–1.68 cm of superiority. (4) The UCS values of TCPB are up to 0.838 MPa, 1.953 MPa, and 2.531 MPa, after curing for 7, 14, and 28 days. These are 0.283 MPa, 0.823 MPa, and 0.881 MPa higher than that of OCPB, respectively. It can be concluded that water-washing pre-treatment greatly improves the workability and mechanical property of PG-based CPB. These results are of great value for creating a reliable and environmentally superior alternative for the recycling of PG and for safer mining production.

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Effect of wetting-drying cycle on hydraulic and mechanical properties of cemented paste backfill of the recycled solid wastes

Chemosphere ◽

10.1016/j.chemosphere.2021.131163 ◽

2021 ◽

pp. 131163

Author(s):

Dan Ma ◽

Saibo Kong ◽

Zhenhua Li ◽

Qiang Zhang ◽

Zihe Wang ◽

...

Keyword(s):

Mechanical Properties ◽

Solid Wastes ◽

Cemented Paste Backfill ◽

Paste Backfill

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Experimental Investigation on Mechanical Properties of In Situ Cemented Paste Backfill Containing Coal Gangue and Fly Ash

Advances in Civil Engineering ◽

10.1155/2020/7964267 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Xinguo Zhang ◽

Shichuan Zhang

Keyword(s):

Mechanical Properties ◽

Tensile Strength ◽

Fly Ash ◽

Young’S Modulus ◽

Young's Modulus ◽

Friction Angle ◽

Coal Gangue ◽

Cemented Paste Backfill ◽

Paste Backfill

Cemented paste backfill containing coal gangue and fly ash (CGFACPB) is an emerging backfill technique for coal mines that allows environmentally hazardous coal gangue and fly ash to be reused in the underground goaf. Meanwhile, CGFACPB can provide an efficient ground support and reduce the surface subsidence. Due to the difference of consolidation environment between the laboratory and the field, the mechanical properties of the cemented paste backfill vary significantly. In this paper, the core specimens were collected from an underground coal mine where the CGFACPB was used for coal mining, and the mechanical properties of the collected specimens were investigated. The cores were obtained from the underground coal mine, and then the standard cylinders or discs were prepared in laboratory. The uniaxial compressive strength (UCS), Young’s modulus, and Poisson’s ratio were determined by the compression tests, and the tensile strength was achieved by the Brazilian test. Then the internal friction angle and cohesion were calculated using the improved Mohr–Coulomb strength criterion. The results showed the development of UCS can be divided into four stages, and the final long-term stable value was about 5.1 MPa. The development of Young’s modulus had similar trend. Young’s modulus had a range from 550 MPa to 750 MPa and the mean value of 675 MPa. Poisson’s ratio gradually increased with the underground curing duration and eventually approached the stable value of 0.18. The failure type of compression samples was mainly single-sided shear failure. The development of tensile strength can be divided into two stages, and the stable value of the tensile strength was about 1.05 MPa. The development of cohesion can be divided into four stages, and the stable value was about 1.75 MPa. The stable value of the internal friction angle was about 25°. This study can provide significant references for not only the long-term stability evaluation of CGFACPB in the field but also the design of optimal recipe of the cemented paste backfill (CPB).

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Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

Geotechnical and Geological Engineering ◽

10.1007/s10706-018-0455-5 ◽

2018 ◽

Vol 36 (4) ◽

pp. 2171-2187 ◽

Cited By ~ 10

Author(s):

Naguleswaran Niroshan ◽

Ling Yin ◽

Nagaratnam Sivakugan ◽

Ryan Llewellyn Veenstra

Keyword(s):

Mechanical Properties ◽

Cemented Paste Backfill ◽

Paste Backfill

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Experimental Investigation on Mechanical Properties of Cemented Paste Backfill under Different Gradations of Aggregate Particles and Types and Contents of Cementing Materials

Advances in Materials Science and Engineering ◽

10.1155/2019/9456861 ◽

2019 ◽

Vol 2019 ◽

pp. 1-11

Author(s):

Jiangyu Wu ◽

Meimei Feng ◽

Guansheng Han ◽

Xiaoyan Ni ◽

Zhanqing Chen

Keyword(s):

Mechanical Properties ◽

Cemented Paste Backfill ◽

Compression Tests ◽

Deformation Properties ◽

Paste Backfill ◽

Strength And Deformation ◽

Cementing Material ◽

Optimal Strength ◽

Ae Signals ◽

Aggregate Particles

Obtaining the optimal gradation of aggregate particles is beneficial for improving the strength of cemented paste backfill (CPB). Consequently, the uniaxial compression tests with acoustic emission (AE) monitoring were performed on CPB, for which the aggregate particles satisfied the Talbot grading theory. The effects of the Talbot indices of aggregate particles and types and contents of cementing materials on the mechanical properties of CPB were analyzed. The AE characteristics and stress-strain behaviors of CPB were discussed. The results show that the specific Talbot index reflected the optimal strength and deformation properties of CPB is 0.45, and the maximum UCS is 7.6 MPa. The mechanical properties of CPB also can be optimized by changing the type of cementing material and increasing the content of cementing material. The effects of the Talbot indices of aggregate particles and types and contents of cementing materials on the crack damages reflected by the AE signals of CPB are mainly observed in the oa stage and ab stage during the loading process.

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Influence of new hydrophobic agent on the mechanical properties of modified cemented paste backfill

Journal of Materials Research and Technology ◽

10.1016/j.jmrt.2019.09.039 ◽

2019 ◽

Vol 8 (6) ◽

pp. 5716-5727 ◽

Cited By ~ 2

Author(s):

Bingqian Yan ◽

Fenhua Ren ◽

Meifeng Cai ◽

Chen Qiao

Keyword(s):

Mechanical Properties ◽

Cemented Paste Backfill ◽

Hydrophobic Agent ◽

Paste Backfill

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An Experimental Study on the Microstructures of Cemented Paste Backfill during Its Developing Process

Advances in Civil Engineering ◽

10.1155/2018/9783046 ◽

2018 ◽

Vol 2018 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Bo Zhang ◽

Jie Xin ◽

Lang Liu ◽

Lijie Guo ◽

Ki-Il Song

Keyword(s):

Mechanical Properties ◽

Pore Size ◽

Physical And Mechanical Properties ◽

Pore Distribution ◽

Early Age ◽

Pore Shape ◽

Cemented Paste Backfill ◽

Sem Images ◽

Paste Backfill ◽

Analysis System

The aim of this study was to examine the microstructure of cemented paste backfill (CPB) during its development and relate the characteristics of the microstructure to the physical and mechanical properties of CPB. The geometry and morphology of the microstructures of CPB were observed by the scanning electron microscopy (SEM). The characteristics including pore size, pore shape, and orientation of the microstructures of CPB at different curing times were analyzed based on the SEM images. The porosity, fractal dimension, and probability entropy were characterized using the Particles and Pore Recognition and Analysis System (PPRAS). It was found that the pore size, pore shape, and orientation of the microstructure of CPB significantly change as the curing time increases, resulting in the increase of UCS. Meanwhile, the arrangement of the pores affects the mechanical properties of CPB. At the early age of CPB development, the probability entropy is above 0.96, indicating a chaotic pore distribution and no obvious orientation. At the late age of CPB development, the probability entropy becomes smaller and the order and orientation of the pore distribution are enhanced, leading to an increase in USC. The UCS of CPB is also greatly affected by the characteristics of the pore morphology. During the development of CPB, the pore shape becomes smoother. The UCS of CPB approximately linearly improves with an increase in the average roundness of pores.

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Mechanical properties and microstructure of layered cemented paste backfill under triaxial cyclic loading and unloading

Construction and Building Materials ◽

10.1016/j.conbuildmat.2020.119540 ◽

2020 ◽

Vol 257 ◽

pp. 119540 ◽

Cited By ~ 1

Author(s):

Jie Wang ◽

Jianxin Fu ◽

Weidong Song

Keyword(s):

Mechanical Properties ◽

Cyclic Loading ◽

Cemented Paste Backfill ◽

Cyclic Loading And Unloading ◽

Paste Backfill ◽

Loading And Unloading

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Experimental Study on Mechanical Properties of Cemented Paste Backfill under Temperature-Chemical Coupling Conditions

Advances in Materials Science and Engineering ◽

10.1155/2019/9754790 ◽

2019 ◽

Vol 2019 ◽

pp. 1-10

Author(s):

Yin Liu ◽

Hao Li ◽

Haifeng Wu

Keyword(s):

Mechanical Properties ◽

Structural Model ◽

Sulfate Solution ◽

Sodium Sulphate ◽

Effect Of Temperature ◽

Cemented Paste Backfill ◽

Chemical Coupling ◽

Deterioration Mechanism ◽

Paste Backfill ◽

Physical And Chemical

To investigate the effect of temperature-chemical coupling on the mechanical properties of cemented paste backfill, three temperatures (20°C, 35°C, and 50°C) and sodium sulfate solution mass concentrations (3%, 5%, and 7%) are applied to simulate the complex environment in a mine. Uniaxial compressive strength and the CPB stress-strain relationship are investigated by applying stress, and the deterioration mechanism was analyzed theoretically according to physical and chemical reactions. At the same time, a structural model of the CPB deterioration mechanism under TC coupling is constructed. Combined with analysis through X-ray diffraction and scanning electron microscopy, it is shown that ettringite and gypsum are the main erosive substances that destroy the structure of CPB and that increased temperatures accelerate the chemical reaction. The concentration change consumes calcium hydroxide, changing the relationship between ettringite and gypsum. Sodium sulphate crystallization is the main form of physical deterioration. The continuous load accelerates the inelastic deformation time of CPB, resulting in a large yield deformation process.

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