Research Enhancing Acidic Mine Wastewater Purification: Innovations in Red Mud–Loess
Abstract
:1. Introduction
2. Materials and Methods
2.1. Test Materials
2.2. Flexible Wall Penetration Test
- (1)
- Sample Preparation: A cylindrical mold, 5 cm tall and 5 cm wide, was cleaned, dried, and coated with Vaseline.
- (2)
- Saturation: Using a peristaltic pump, distilled water was progressively transferred into the soil column in a bottom-up arrangement until the liquid level exceeded the sample by 3 cm. This process indicates specimen saturation.
- (3)
- Measurement: The GeotestTK2000 flexible wall permeameter was employed following ASTM D5084-10 standards [42]. Osmotic pressure was 100 kPa, confining pressure was 110 kPa, and the hydraulic gradient was set to 200 for efficiency due to the sample’s firm strength and low permeability. The test involved vacuuming for 8 h at −100 kPa, introducing degassed water into the vacuum saturation cylinder, removing the saturated sample, placing it in the pressure chamber, injecting water, sealing it, and applying confining and osmotic pressure. After a three-day penetration test with hourly water production measurements, the instrument was turned off, and the sample was removed. The permeability coefficient is mathematically represented by Equation (1) based on test results.
2.3. Shear Test
2.4. Microscopic Testing and Characterization
2.4.1. X-ray Diffraction Analysis (XRD)
2.4.2. Fourier Transform Infrared Spectroscopy (FTIR)
2.4.3. Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDS)
2.5. Methods
2.5.1. Penetration Test
2.5.2. Shear Test
2.5.3. Microscopic Testing and Characterization
3. Results and Discussion
3.1. Permeability Characteristics of Red Mud–Loess Engineered Barrier
3.1.1. Effect of Quartz Sand Content
3.1.2. Particle Size Impact
- (1)
- Optimal Mass Ratio for Coarse-Grained Red Mud–Loess Mixtures
- (2)
- Permeability Characteristics of Coarse-Grained Red Mud–Loess Mixed Materials
3.2. Shear Strength Properties of Red Mud–Loess Engineered Barrier
3.2.1. Shear Stress Behavior of Red Mud–Loess (7:3) in Different Pore Conditions
- (1)
- The Theoretical Adsorption Capacity of Coarse-Grained Red Mud–Loess Mixed Material (7:3):
- (2)
- Shear stress–shear displacement curve of red mud–loess mixed material (7:3)
3.2.2. Changes in Shear Strength Parameters
3.3. Research on the Environmental Safety Characteristics of Solidified Soil
3.3.1. Acidity and Alkalinity Study in Cement-Solidification Cadmium-Contaminated Soil with Solid Waste
3.3.2. Cadmium Leaching Toxicity and Speciation in Cement-Solidified Soil with Solid Waste
3.4. Microscopic Analysis of Stabilization and Solidification (S/S) of High-Concentration Heavy Metal-Contaminated Soil
3.4.1. Comparison of Microscopic Morphology in Unsolidified and Solidified Cd-Contaminated Soil
3.4.2. Functional Group Comparison in Unsolidified and CRML-Solidified Cadmium-Contaminated Soil
3.4.3. Mineral Composition Analysis of Solidified Cadmium-Contaminated Soil over Time
4. Conclusions
- (1)
- Quartz sand amount influences fine-grained red mud–loess mixed material (7:3) permeability. A quartz sand content of less than 80% meets the permeability standards for red mud–loess barriers. The durability of the planned barrier diminishes when the composition of the red mud–loess mixture (7:3) deteriorates. Red mud and loess with particle sizes from 0.50 to 0.85 mm in a 7:3 mass ratio generate a 28% moisture-rich mixed material. With a dry density of 1.04 g/cm3, the red mud–loess mixture (7:3) satisfies the permeability standards for a barrier active medium, with a permeability coefficient of 3.39 × 10−4 cm/s.
- (2)
- Loess has a strong ability to neutralize acidic solutions, which is particularly effective in removing heavy metals from wastewater. A mass ratio of 7:3 (red mud to loess) is found to be efficient in the removal of Cd, while also elevating the acidity of acidic wastewater to comply with groundwater guidelines. The mixture controls the high alkalinity of red mud, enhancing its utility in engineering applications such as barriers for acidic wastewater treatment. This study suggests that the quartz sand content significantly affects the permeability of the fine-grained red mud–loess mixtures, with an optimal particle size range identified for maintaining effective permeability in engineered barriers.
- (3)
- Red mud–loess mixed materials (7:3) were tested in four pore solutions: distilled water, acidic solution, Cd-containing acidic solution, and high Cd-containing acidic solution. These materials initially exhibited an increase in behavior followed by gradual stabilization. Moreover, using a mass ratio of 7:3 for red mud to loess proved effective in removing Cd. The observed trend indicated strain hardening. Cd-loaded red mud–loess mixed material (7:3) demonstrated increased cohesiveness and a lower friction angle with higher target ion loading. However, as pollution increased, the cohesiveness of the Cd-loaded red mud–loess mixed materials decreased, despite an increase in the internal friction angle. Interestingly, after loading Cd, the red mud–loess mixed material (7:3) exhibited somewhat greater shear strength than uncontaminated samples.
- (4)
- The red mud–loess mixed material includes Cd acidic solutions (7:3) and the pore solution is acidic. With distilled water as the pore solution and red mud–loess mixed material (7:3), H+ and target ions disrupt particle aggregation. The clay component in the red mud–loess mixed material (7:3) lacks cement because carbonates degrade. The red mud–loess mixed material (7:3) becomes more irregular and rough owing to H+ corrosion in the acidic solution and Cd adsorption products adhering.
- (5)
- SEM analysis of the CRML-solidified soil at 7 and 60 days reveals irregular blocks and granules with needle-rod-shaped crystals, which enhance soil structure and strength over time. CRML-solidified cadmium-contaminated soil undergoes significant alterations in functional groups (-OH and Si-O), indicating the presence of adsorbed water, crystallization water, and mineral formations. The curing agent triggers reactions that enhance soil reactivity, leading to the formation of amorphous silica, calcium carbonate, and cadmium carbonate. XRD analysis of CRML-treated cadmium-contaminated soil demonstrates consistent phase composition between 7 and 28 days. Additionally, the curing agent facilitates the liberation of active groups, thereby boosting soil reactivity. These findings contribute to the understanding of soil remediation and the efficient utilization of solid waste resources in environmental protection. This study’s innovative approach using red mud and loess as PRB active media demonstrates its potential for cleansing acidic wastewater in mining areas.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Composition | SiO2 | Al2O3 | Fe2O3 | CaO | K2O | MgO | TiO2 | Na2O | MnO | SO3 |
---|---|---|---|---|---|---|---|---|---|---|
Red mud | 20.17 | 24.34 | 9.40 | 18.26 | 0.64 | 1.26 | 3.56 | 9.61 | 0.03 | 0.47 |
Loess | 58.88 | 11.75 | 4.54 | 7.98 | 2.18 | 2.05 | 0.60 | 1.70 | 0.07 | 0.03 |
Red Mud–Loess Mass Ratio | Particle Size (mm) | pH0 | Dosage (g/L) | Contact Time (min) | Initial Concentration (mg/L) | Temperature (°C) |
---|---|---|---|---|---|---|
0:10 | <0.075 | 3.0 | 8 (Cd) | 600 | 100 | 25 |
3:7 | 0.075–0.15 | |||||
5:5 | 0.15–0.25 | |||||
7:3 | 0.25–0.50 | |||||
10:0 | 0.50–0.85 |
Sample Size (cm) | Quartz Sand Content (%) | Particle Size (mm) | Initial Moisture Content (%) |
---|---|---|---|
5 × 10 | 0 | <0.075 | 30 |
70 | <0.075 | 8 | |
80 | <0.075 | 5 | |
0 | 0.25–0.50 | 29 | |
0 | 0.50–0.85 | 28 |
Red Mud–Loess Mass Ratio | Particle Size (mm) | pH0 | Dosage (g/L) Cd | Contact Time (min) | Initial Concentration (mg/L) | Temperature (°C) |
---|---|---|---|---|---|---|
7:3 | 0.50–0.85 | 3.0 | 6 | 600 | 100 | 25 |
7 | ||||||
8 | ||||||
9 | ||||||
10 |
Sample No | Sample Size (mm) | Vertical Pressure (kPa) | Pore Water Category |
---|---|---|---|
1 | 61.8 × 20 | 100 | Distilled water (H2O) |
2 | 200 | Acidic solution (pH0 = 3.0) | |
3 | 300 | Acidic solution containing Cd C(Cd) = 100 mg/L, pH0 = 3.0 | |
4 | 400 | Acidic solution with high Cd content m(Cd) = 6 mg/g, pH0 = 3.0 |
Pore Solution | c (kPa) | φ (°) | tan φ | R2 |
---|---|---|---|---|
Distilled water (H2O) | 37.80 | 25.42 | 0.4752 | 0.9719 |
Acidic solution (pH0 = 3.0) | 34.75 | 25.65 | 0.4803 | 0.9989 |
Acidic solution containing Cd C(Cd) = 100 mg/L, pH0 = 3.0 | 28.05 | 27.37 | 0.5176 | 0.9735 |
Acidic solution with high Cd content m(Cd) = 6 mg/g, pH0 = 3.0 | 20.55 | 28.59 | 0.5451 | 0.9885 |
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Salih, W.T.; Xiao, Z.; Dong, X. Research Enhancing Acidic Mine Wastewater Purification: Innovations in Red Mud–Loess. Materials 2024, 17, 2050. https://doi.org/10.3390/ma17092050
Salih WT, Xiao Z, Dong X. Research Enhancing Acidic Mine Wastewater Purification: Innovations in Red Mud–Loess. Materials. 2024; 17(9):2050. https://doi.org/10.3390/ma17092050
Chicago/Turabian StyleSalih, Wdah. T., Zean Xiao, and Xiaoqiang Dong. 2024. "Research Enhancing Acidic Mine Wastewater Purification: Innovations in Red Mud–Loess" Materials 17, no. 9: 2050. https://doi.org/10.3390/ma17092050