# Evaluation of Viscosity, Strength and Microstructural Properties of Cemented Tailings Backfill

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Materials Characterization

#### 2.1.1. Processing Tailings

^{2}/g respectively. PSD is directly related to the flow properties, permeability, and pumpability of CTB samples. Accordingly, the higher the fines content (<20 μm in size), the lower the permeability coefficient becomes [10]. The fine-grained particles, with their relatively high specific surface, have a higher water-holding capacity and are delivered with coarse-grained particles in a pipeline. CTB frequently produces a plug flow when transported via a pipeline. Note that plug flow is a simple model of the velocity profile of a fluid flowing in a pipe. In plug flow, the velocity of the fluid is assumed to be constant across any cross-section of the pipe perpendicular to the axis of the pipe. The plug flow model assumes there is no boundary layer adjacent to the inner wall of the pipe.

_{2}and Al

_{2}O

_{3}were the main minerals within the tailings (65.7% and 14.3% by weight). The main compositions of the tailings sample (e.g., SiO

_{2}, Al

_{2}O

_{3}, and CaO) exerted a relatively positive effect on coagulation and strength development [35]. One can comment from chemical analyses that the studied tailings contain too much silica minerals. It should be kept in mind that minerals such as micas and clay can reduce the ultimate strength and stability of CTB samples, mainly because of their water absorbent mineral layers. Note that sulfide minerals raise the specific gravity, while the strength of abrasiveness of silica minerals causes serious pipeline wear.

#### 2.1.2. Binder and Mixing Water

_{3}S, 7% for C

_{2}S, 9% for C

_{3}A and 7.5% for C

_{4}AF. The hydraulic modulus [CaO/(SiO

_{2}+ Al

_{2}O

_{3}+ Fe

_{2}O

_{3})], which quantifies the hydraulic activity or the self-cementing characteristics of binders, calculated for OPC is 2.11. The higher the hydraulic modulus, the higher the overall self-cementing ability of the binder becomes. As mixing water, tap water was only used to homogenously mix both tailings and binder. Mixing water strongly affects the mechanical strength properties of CTB samples in terms of the water-to-cement ratio and cement hydration mechanisms. The effects of municipal, lake, and process waters on the strength performance of CTB samples manufactured using different binders were assessed in detail by Benzaazoua et al. [53].

#### 2.2. CTB Sample Preparation

#### 2.3. Viscosity Testing

#### 2.4. Uniaxial Compressive Testing

#### 2.5. Microstructural Analysis

## 3. Results and Discussion

#### 3.1. Viscosity Results of CTB Samples

#### 3.1.1. Effect of Cement-to-Tailings Ratio

^{2}).

^{2}) are 0.9608, 0.9696, and 0.9645, respectively. Among them, the exponential correlation provided the highest correlation coefficient. Moreover, it was also found that the viscosity of the CTB slurry increases with the cement-to-tailings ratio increases significantly due to particle rearrangement and cement hydration products over time. As a result, the relation between c/t and viscosity of CTB samples can be expressed as an exponential equation, and the relevant expression can be defined in Equation (1).

_{1}and B

_{1}are the fitting parameters related to the influence of solid content and c/t factors.

#### 3.1.2. Effect of Solid Content

^{2}was listed in Table 6.

^{2}) of the exponential fitting are obviously higher than the linear and logarithmic fitting results. The R

^{2}for the linear and logarithmic fits were only 0.7943 and 0.7729, while the exponential fit was 0.9723. In summary, the relation between solid content and viscosity of CTB samples can be expressed as an exponential equation, and the relevant expression can be defined in Equation (2).

_{2}and B

_{2}are the fitting parameters related to the influence of solid content and viscosity factors.

#### 3.2. Uniaxial Compressive Strength Results of CTB Samples

#### 3.2.1. Effect of Solid Content

^{2}) obtained was listed in Table 8.

^{2}) for the exponential fit were 0.9630, 0.9603, 0.9502, and 0.9455, respectively. Both linear and logarithmic fitting degrees are significantly less than the exponential fit alone. The effect of solid content on the UCS behavior of CTB samples is in good agreement with the exponential function.

_{3}and B

_{3}are the fitting parameters related to the influence of solid content and UCS factors.

#### 3.2.2. Effect of Cement-to-Tailings Ratio

^{2}) was listed in Table 9.

^{2}are larger than 0.94. Among them, the exponential correlation has the highest R

^{2}. When the solid content was 65%, 68%, 70%, and 72%, the corresponding R

^{2}for the exponential fit were 0.9746, 0.9876, 0.9715, and 0.9739, respectively. Moreover, it was also found experimentally that the UCS performance of CTBs increases with increasing cement-to-tailings ratio. The relationship between c/t and UCS of CTB samples could be well expressed as the exponential equation, and the relevant expression can be defined in Equation (4).

_{4}and B

_{4}are the fitting parameters related to the influence of c/t and UCS factors.

#### 3.2.3. Effect of Curing Time

#### 3.3. Microstructural Characteristics

_{)2}liberated during the cement hydration, producing secondary C-S-H gels with bonding properties. This will develop inevitably the microstructure of CTB matrix with a denser packing density having a reduction in the porosity. In this view, a visible densification in the backfill tailings particles was observed to occur due to the formation of cement hydrates, such as C-S-H gels.

## 4. Conclusions

^{2}of the exponential fitting is obviously higher than the linear and logarithmic fitting results. Hence, the relation between SD and viscosity of CTB can be expressed as an exponential equation.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Fundamental characteristics of the studied tailings: (

**a**) particle size distribution curve; (

**b**) X-ray diffraction curve.

**Figure 8.**Relations between SD and UCS of CTB: (

**a**) c/t: 1:04; (

**b**) c/t: 1:06; (

**c**) c/t: 1:08; (

**d**) c/t: 1:10.

**Figure 10.**Relations between curing time and UCS of CTB: (

**a**) SD: 65%; (

**b**) SD: 68%; (

**c**) SD: 70%; (

**d**) SD: 72%.

**Figure 11.**SEM micrographs of 28-day cured polished CTB surface: (

**a**) SD: 65%; (

**b**) SD: 68%; (

**c**) SD: 70%; (

**d**) SD: 72%.

Varieties/% | SiO_{2} | Al_{2}O_{3} | CaO | MgO | P | Fe | S | Au |
---|---|---|---|---|---|---|---|---|

Tailings | 65.7 | 14.3 | 1.88 | 0.49 | 0.08 | 3.05 | 0.13 | <0.01 |

Varieties/% | SiO_{2} | Fe_{2}O_{3} | Al_{2}O_{3} | MgO | CaO | SO_{3} |
---|---|---|---|---|---|---|

OPC 32.5 R | 21.36 | 3.21 | 4.92 | 3.41 | 62.33 | 1.92 |

Cement: Tailings Ratio | 1:04 | 1:06 | 1:08 | 1:10 | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Mass fraction of solid, % | 65 | 68 | 70 | 72 | 65 | 68 | 70 | 72 | 65 | 68 | 70 | 72 | 65 | 68 | 70 | 72 | |

Mass fraction (%) | Cement | 13 | 13.6 | 14 | 14.4 | 9.3 | 9.7 | 10 | 10.3 | 7.2 | 7.6 | 7.8 | 8 | 5.9 | 6.2 | 6.4 | 6.5 |

Tailings | 52 | 54.4 | 56 | 57.6 | 55.7 | 58.3 | 60 | 61.7 | 57.8 | 60.4 | 62.2 | 64 | 59.1 | 61.8 | 63.6 | 65.5 | |

Water | 35 | 32 | 30 | 28 | 35 | 32 | 30 | 28 | 35 | 32 | 30 | 28 | 35 | 32 | 30 | 28 |

c/t | Viscosity/Pa·s | ||||
---|---|---|---|---|---|

60% | 65% | 68% | 70% | 72% | |

1:04 | 14.87 | 26.68 | 45.19 | 75.39 | 116.44 |

1:06 | 12.50 | 23.32 | 38.36 | 65.75 | 108.79 |

1:08 | 10.31 | 20.05 | 35.95 | 62.16 | 106.54 |

1:10 | 8.26 | 18.01 | 31.81 | 58.51 | 103.37 |

Fitting Type | Solid Content, SD (wt %) | |||||
---|---|---|---|---|---|---|

60% | 65% | 68% | 70% | 72% | Average | |

linear | 0.9989 | 0.9885 | 0.9607 | 0.9314 | 0.9245 | 0.9608 |

exponential | 0.9970 | 0.9959 | 0.9742 | 0.9483 | 0.9328 | 0.9696 |

logarithmic | 0.9996 | 0.9909 | 0.9642 | 0.9374 | 0.9304 | 0.9645 |

Fitting Type | Cement-to-Tailings Ratio, c/t | ||||
---|---|---|---|---|---|

1:04 | 1:06 | 1:08 | 1:10 | Average | |

linear | 0.8223 | 0.7946 | 0.7867 | 0.7736 | 0.7943 |

exponential | 0.9728 | 0.9687 | 0.9719 | 0.9758 | 0.9723 |

logarithmic | 0.8017 | 0.7733 | 0.7651 | 0.7518 | 0.7729 |

Cement-to-Tailings Ratio, c/t | Solid Content, SD (wt %) | Curing Time, Days | ||
---|---|---|---|---|

3-Day (MPa) | 7-Day (MPa) | 28-Day (MPa) | ||

1:04 | 65% | 0.50 | 1.45 | 5.32 |

68% | 0.65 | 1.61 | 5.73 | |

70% | 0.73 | 1.86 | 6.14 | |

72% | 0.88 | 2.47 | 6.52 | |

1:06 | 65% | 0.44 | 1.15 | 3.14 |

68% | 0.52 | 1.29 | 3.52 | |

70% | 0.60 | 1.43 | 3.91 | |

72% | 0.82 | 1.70 | 4.42 | |

1:08 | 65% | 0.36 | 0.75 | 1.96 |

68% | 0.43 | 0.87 | 2.13 | |

70% | 0.55 | 0.96 | 2.48 | |

72% | 0.68 | 1.25 | 2.89 | |

1:10 | 65% | 0.25 | 0.61 | 1.33 |

68% | 0.30 | 0.70 | 1.41 | |

70% | 0.37 | 0.75 | 1.53 | |

72% | 0.50 | 0.90 | 1.75 |

Cement-to-Tailings Ratio, c/t | Fitting Type | Curing Time, Days | |||
---|---|---|---|---|---|

3-Day | 7-Day | 28-Day | Average | ||

1:04 | linear | 0.9857 | 0.8535 | 0.9910 | 0.9434 |

exponential | 0.9943 | 0.8995 | 0.9951 | 0.9630 | |

logarithmic | 0.9828 | 0.8426 | 0.9881 | 0.9378 | |

1:06 | linear | 0.8802 | 0.9344 | 0.9726 | 0.9291 |

exponential | 0.9331 | 0.9609 | 0.9868 | 0.9603 | |

logarithmic | 0.8704 | 0.9267 | 0.9673 | 0.9215 | |

1:08 | linear | 0.9460 | 0.8863 | 0.9246 | 0.9189 |

exponential | 0.9744 | 0.9302 | 0.9459 | 0.9502 | |

logarithmic | 0.9389 | 0.8771 | 0.9163 | 0.9108 | |

1:10 | linear | 0.9061 | 0.9325 | 0.9012 | 0.9133 |

exponential | 0.9554 | 0.9588 | 0.9223 | 0.9455 | |

logarithmic | 0.8969 | 0.9256 | 0.8918 | 0.9048 |

Solid Content | Fitting Type | Curing Time, Days | |||
---|---|---|---|---|---|

3-Day | 7-Day | 28-Day | Average | ||

65% | linear | 0.9820 | 0.9707 | 0.9340 | 0.9622 |

exponential | 0.9474 | 0.9811 | 0.9954 | 0.9746 | |

logarithmic | 0.8945 | 0.9698 | 0.9962 | 0.9535 | |

68% | linear | 0.9951 | 0.9769 | 0.9488 | 0.9736 |

exponential | 0.9790 | 0.9857 | 0.9982 | 0.9876 | |

logarithmic | 0.9611 | 0.9707 | 0.9983 | 0.9767 | |

70% | linear | 0.9576 | 0.9775 | 0.9656 | 0.9669 |

exponential | 0.9232 | 0.9915 | 0.9997 | 0.9715 | |

logarithmic | 0.8967 | 0.9824 | 0.9996 | 0.9596 | |

72% | linear | 0.9570 | 0.9662 | 0.9818 | 0.9683 |

exponential | 0.9267 | 0.9984 | 0.9966 | 0.9739 | |

logarithmic | 0.8424 | 0.9997 | 0.9956 | 0.9459 |

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**MDPI and ACS Style**

Cao, S.; Yilmaz, E.; Song, W.
Evaluation of Viscosity, Strength and Microstructural Properties of Cemented Tailings Backfill. *Minerals* **2018**, *8*, 352.
https://doi.org/10.3390/min8080352

**AMA Style**

Cao S, Yilmaz E, Song W.
Evaluation of Viscosity, Strength and Microstructural Properties of Cemented Tailings Backfill. *Minerals*. 2018; 8(8):352.
https://doi.org/10.3390/min8080352

**Chicago/Turabian Style**

Cao, Shuai, Erol Yilmaz, and Weidong Song.
2018. "Evaluation of Viscosity, Strength and Microstructural Properties of Cemented Tailings Backfill" *Minerals* 8, no. 8: 352.
https://doi.org/10.3390/min8080352