Sand modification with a saponite clay suspension as a waste of the diamond mining industry
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-12-15 |
| Journal | Construction and Geotechnics |
| Authors | A. L Nevzorov, Yu. V Saenko, A. M Shiranov |
| Institutions | Northern (Arctic) Federal University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Objective: To modify alluvial fine sand using a saponite clay suspension (a high-volume waste product from the diamond mining industry) to significantly reduce its hydraulic conductivity (permeability) for use in landfill liners and waste containment structures.
- Modification Method: Colmatation (clogging) of sand pores via filtration of the saponite suspension. This method is proposed as an energy-efficient alternative to mechanical mixing.
- Key Requirement: Successful clogging requires the preliminary addition of aggregation agents (chalk or dolomite) to the sand layer to prevent the washout of fine clay particles during filtration.
- Performance with Chalk (CaCO3): The addition of 3% chalk reduced the hydraulic conductivity (K) by 15 to 31 times. Increasing the chalk content to 5% resulted in a reduction of 15 to 39 times.
- Performance with Dolomite (CaCO3¡MgCO3): Dolomite proved less effective, achieving a maximum K reduction of 14.3 times, attributed to its larger particle size and lower activity compared to chalk.
- Optimal Process: To maximize clogging depth, the suspension should be filtered through loose sand at a flow rate greater than 3.5 m/day, followed by subsequent compaction of the modified layer.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sand Particle Density | 2.64-2.66 | g/cm3 | Alluvial fine sand samples |
| Sand Compaction Coefficient (Kcom) | 0.90-1.00 | Dimensionless | Range tested for foundation/liner materials |
| Initial Hydraulic Conductivity (K0) | 1.3-2.05 | m/day | Unmodified sand (depending on Kcom) |
| Saponite Suspension Concentration | 0.58-0.63 | % | Clay particle content in suspension |
| Saponite Particle Size (Solid Phase) | 91.5-94.2 | % less than 0.001 mm | Highly dispersed fraction |
| Confining Pressure (Triaxial Chamber) | 100 | kPa | Applied during permeability testing |
| Chalk Addition (by dry sand mass) | 3 or 5 | % | Aggregation agent (CaCO3) |
| Dolomite Addition (by dry sand mass) | 3 or 5 | % | Aggregation agent (CaCO3¡MgCO3) |
| Max K Reduction (Chalk 5%) | 39 | Times | Achieved with highest chalk content |
| Final Hydraulic Conductivity (km) | 0.03-0.08 | m/day | Sand modified with Chalk (3% or 5%) |
| Critical Flow Rate (Washout Prevention) | >3.5 | m/day | Required flow velocity during suspension filtration |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Preparation: Alluvial fine sand samples (73 mm diameter, 145 mm height) were prepared in triaxial test chambers. Chalk (CaCO3) or Dolomite (CaCO3¡MgCO3) additives (3% or 5% by mass) were sieved to remove particles larger than 0.1 mm and mixed into the middle third of the sand sample.
- Stress Application: A constant confining pressure of 100 kPa was maintained in the triaxial chamber using operating fluid to simulate natural stress conditions and prevent side-wall leakage.
- Initial Saturation and K Measurement: Samples were saturated with distilled water (bottom-up flow) for 12 hours at a hydraulic gradient (I) of 0.25. Initial hydraulic conductivity (K0) was then measured at four gradients (I = 0.25, 0.5, 0.75, and 1.0).
- Suspension Filtration (Clogging): Saponite clay suspension (0.58-0.63% concentration) was filtered through the sample (top-down flow), simulating filtration into a landfill base.
- The initial gradient was I=2, increasing every 10 minutes to maintain a flow rate greater than 3.5 m/day, necessary to prevent clay sedimentation on the upper perforated disk.
- Filtration continued for 60 minutes, or until the gradient reached I=10, or until clay particles were observed exiting the bottom of the sample (washout).
- Perforated Disk Cleaning: After clogging, the upper perforated disk was cleaned by circulating distilled water in the over-stamp space for 12 hours to remove settled saponite particles.
- Final K Measurement: The hydraulic conductivity (km) of the modified sand was measured again using distilled water (bottom-up flow) at four gradients (I = 0.25, 0.5, 0.75, and 1.0). Measurements were repeated until a stable K value was achieved over 12 hours.
Commercial Applications
Section titled âCommercial ApplicationsâThe modification of sand using saponite clay waste is directly applicable to geotechnical engineering and environmental protection sectors, specifically:
- Landfill Liners and Barriers: Creating low-permeability base liners and protective screens for municipal solid waste (MSW) landfills, particularly in regions where high-quality natural clay is scarce or difficult to transport.
- Waste Containment Facilities: Isolating storage areas for various hazardous wastes, including radioactive waste, leveraging the high sorption capacity of saponite clay minerals (montmorillonite group) for heavy metal ions.
- Tailings Storage Facilities (TSF): Utilizing the saponite waste itself to improve the sealing properties of the TSF foundation or surrounding dams, providing a circular economy solution for the diamond mining industry.
- Canal and Reservoir Sealing: Reducing water loss through filtration in irrigation canals, water reservoirs, and other hydraulic structures by applying the saponite suspension via colmatation.
- Ground Improvement: Modifying highly permeable sandy foundations beneath infrastructure to reduce groundwater flow and improve stability.
View Original Abstract
The results of the laboratory water permeability tests of a sand modified by a saponite clay fraction from the diamond mining industry waste are presented. The filtration of clay suspension through a landfill ground bed as a method of the additive enrichment is approved. The experimental apparatus consisted of the triaxial test chambers and semi-automatic devices for water and suspension supplying. The chambers excluded a sidewall leakage in the samples and provided required values of the vertical and horizontal stresses when measuring permeability. The samples of an alluvial fine sand and a sand mixed with 3 and 5 % a chalk and a dolomite were investigated. After preliminary saturation the rate of distilled water flow through the samples were determined at four values of hydraulic gradient. Then the filtration of a suspension containing up to 0.58-0.63 % clay particles was conducted. After that, the pore disks at the top of samples were washed by circulating water flow. At the last step of experiments the velocity of water flow was measured again at four values of hydraulic gradient. The experiments indicated that the modification of the sand by clogging the pores by the saponite clay fraction from a suspension flow is possible if a sand comprises the additives causing the aggregation of clay particles. The hydraulic conductivity of a sand with 3 % chalk decreased by 15-31 times, with 5 % - by 15-39 times at different values of relative compaction. The effect of a dolomite addition was not significant, the hydraulic conductivity decreased by a maximum of 14.3 times. To achieve the maximum depth of clogging, it is recommended to filtrate the suspension through a loose sand at a hydraulic gradient that provides a flow rate more than 3.5 m/day, after that, the sand layer should be compacted.