The Release of Pollutants through the Bleeding of Cemented Phosphogypsum Backfill: Link to Protocols for Slurry Preparation
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Methods
2.2.1. Preparation of Backfill Slurry
2.2.2. Toxic Leaching Test
2.2.3. Bleeding Rate
2.2.4. Sampling and Chemical Analyses of Bleeding Water
2.2.5. Quantities of Pollutants Released Per Ton of Solid in Backfill
3. Results
3.1. Chemical Properties of PG
3.2. Binder/PG Ratio
- (1)
- pH and bleeding rate of backfill slurry
- (2)
- Pollutants in bleeding water
3.3. Solid Concentration
- (1)
- pH and bleeding rate of backfill slurry
- (2)
- Pollutants in bleeding water
3.4. Binder Type
- (1)
- pH and bleeding rate of backfill slurry
- (2)
- Pollutants in bleeding water
3.5. Mixing Procedure
- (1)
- pH and bleeding rate of backfill slurry
- (2)
- Pollutants in bleeding water
4. Discussion
4.1. Release of Pollutants from Backfill Slurry into the Bleeding Water
4.2. Effect of Preparation Protocols on Chemical Properties of Bleeding Water
4.3. Effect of Preparation Protocols on Bleeding Rate of Backfill Slurry
5. Conclusions
- (1)
- The bleeding water from cemented PG backfill contained PO43−, F− and SO42−, which pose a risk of damage to the surrounding environment. The high pollutant concentrations and the high bleeding rate resulted in higher quantities of pollutants being released from the backfill slurry;
- (2)
- The pollutant concentrations in the bleeding water could be minimized via proper protocols for slurry preparation, such as increasing the binder/PG ratio. A greater amount of more binder efficiently transformed PO43−, F− and SO42− into undissolved forms. The dilution effect induced by the low solid concentration also helped to reduce the pollutant concentrations;
- (3)
- The poor water retention and high initial water content of the backfill slurry increased the bleeding rate. Introducing more fine raw materials into the backfill slurry, such as binder and GGBFS, could bond more surface layer water and increase the water retention. The pH of the backfill slurry is also negatively related to water retention;
- (4)
- Cemented PG backfill could solidify/stabilize PO43− in the bleeding water well when the pH value was higher than 11. However, the concentration of F− in the bleeding water always exceeded the limit value of the national standard (10 mg/L); therefore, further studies are needed for the S/S of F−.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Sample | D10 (μm) | D30 (μm) | D60 (μm) | Cu | Cc |
---|---|---|---|---|---|
PG (pH = 1.68) | 10.53 | 27.40 | 62.91 | 6.08 | 1.13 |
PG (pH = 4.15) | 13.65 | 29.02 | 56.38 | 4.13 | 1.09 |
PG (pH = 6.75) | 13.56 | 33.15 | 62.76 | 4.63 | 1.29 |
CCA | 6.12 | 13.26 | 27.74 | 4.53 | 1.04 |
CPC | 3.33 | 8.14 | 22.60 | 6.79 | 0.88 |
GGBFS | 2.00 | 5.55 | 11.94 | 5.97 | 1.29 |
Chemical Component | PG (pH = 1.68) (%) | PG (pH = 4.15) (%) | PG (pH = 6.75) (%) |
---|---|---|---|
SO3 | 44.76 | 42.19 | 42.05 |
CaO | 34.93 | 34.04 | 34.01 |
SiO2 | 3.23 | 2.73 | 2.31 |
P2O5 | 2.61 | 0.80 | 0.65 |
F | 0.81 | 0.43 | 0.35 |
Fe2O3 | 0.28 | 0.25 | 0.27 |
Ba | 0.17 | 0.17 | 0.09 |
MgO | 0.14 | 0.04 | 0.05 |
Na2O | 0.13 | 0.03 | - |
K2O | 0.10 | 0.08 | 0.05 |
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Min, C.; Shi, Y.; Zhou, Y.; Liu, Z. The Release of Pollutants through the Bleeding of Cemented Phosphogypsum Backfill: Link to Protocols for Slurry Preparation. Materials 2022, 15, 7126. https://doi.org/10.3390/ma15207126
Min C, Shi Y, Zhou Y, Liu Z. The Release of Pollutants through the Bleeding of Cemented Phosphogypsum Backfill: Link to Protocols for Slurry Preparation. Materials. 2022; 15(20):7126. https://doi.org/10.3390/ma15207126
Chicago/Turabian StyleMin, Chendi, Ying Shi, Yanan Zhou, and Zhixiang Liu. 2022. "The Release of Pollutants through the Bleeding of Cemented Phosphogypsum Backfill: Link to Protocols for Slurry Preparation" Materials 15, no. 20: 7126. https://doi.org/10.3390/ma15207126