Tailings are the leftover materials from mining operations, often containing water and fine particles. Managing them safely and efficiently is crucial. How do mines transform these wet, messy slurries into stable, reusable materials? The answer lies in thickening and dewatering.
The tailings thickening and dewatering process separates water from mineral solids, reducing volume and improving stability. Thickeners concentrate tailings by settling solids, while dewatering removes additional water through filters or centrifuges. This process minimizes environmental impact, recovers water for reuse, and reduces storage costs. Choosing the right equipment and methods is key for efficiency.
Thickening and dewatering may sound straightforward, but the technology behind it is complex. Let’s break it down step by step to understand how mining operations handle tailings effectively.
What is The Purpose and Working Principle of Tailings Thickening?
1. Purpose of Tailings Thickening
The primary objectives of tailings thickening and dewatering are:
- Increasing tailings concentration: Removing excess water from the tailings slurry.
- Facilitating storage: High-concentration tailings are suitable for dry stacking or paste backfilling.
- Water recovery: Reclaiming water for reuse in the mineral processing circuit, thereby conserving water resources.
- Reducing land footprint: Minimizing the land area required for wet tailings disposal and lowering the risk of seepage.
- Enhancing stability: Dry-stacked tailings offer greater stability and safety.
2. Principles of Tailings Thickening
Thickening relies on the principle of gravitational sedimentation:
- Tailings particles settle due to gravity, with solids accumulating at the bottom.
- The clear liquid at the top overflows and is recovered.
- The thickened slurry (underflow) is discharged from the bottom.
- The addition of flocculants can accelerate particle settling and improve thickening efficiency.
3. Tailings Concentration
The concentration (solids content) of the tailings slurry determines the subsequent handling method:
- Low-concentration tailings: Dilute slurry, typically disposed of via wet discharge into a tailings storage facility.
- Medium-concentration tailings: Transported after undergoing a thickening process.
- High-concentration/paste tailings: Dewatered and thickened, making them suitable for dry stacking or backfilling.
What Types of Equipment are Used for Tailings Thickening?
Selecting the right thickening equipment makes or breaks tailings management. With varying slurry properties and production demands, mines need tailored solutions that balance performance and cost.
Three main types of thickeners dominate tailings operations: conventional, high-efficiency, and deep-cone (paste) thickeners. Each serves distinct purposes based on particle size, throughput needs, and desired underflow density. Proper selection impacts water recovery rates, storage requirements, and long-term operational costs.
1. Conventional Thickeners
Design: Circular tanks (15- 100 m diameter) with rotating rakes
Feed System: Central feed well distributes slurry evenly
Discharge Options:
- Peripheral overflow for clarified water
- Central underflow pumps for thickened slurry
Performance:
- Solids concentration: 40-50%
- Typical settling rate: 0.5-2.0 m/hour
Best For:
- Large-volume operations
- Coarse particle slurries (> 45 μm)
- Basic water recovery needs
At a Chilean copper mine, conventional thickeners process 50,000 TPD of tailings with 75% water recovery.
2. High-Efficiency Thickeners
Key Features:
- Optimized feedwell designs
- Automated flocculant dosing systems
- Steeper floor slopes (45-60° vs 15° in conventional)
Performance Boosters:
- Polyacrylamide flocculants increase settling 5-10x
- Lamella plates enhance clarification
Output Specifications:
- Underflow density: 50-65% solids
- Processing capacity: 2-3x conventional units
Installation Cases:
- Ideal for fine particle treatment (< 20 μm)
- Common in iron ore and bauxite operations
3. Deep-Cone (Paste) Thickeners
Structural Distinctions:
- Height-to-diameter ratio >1:1 (vs 0.3:1 conventional)
- 60° cone angles enable paste formation
Operational Benefits:
- Produces non-segregating pastes (65-75% solids)
- Enables direct paste backfill or dry stacking
- Eliminates conventional tailings dams
Application Notes:
- Requires robust underflow pumping systems
- Optimal for mines with backfill requirements
- 30-40% higher capital cost than conventional
Equipment Selection Matrix
Consider these factors when choosing thickeners:
Feed Characteristics
- Particle size distribution (PSD)
- Specific gravity
- Initial solids concentration
Process Requirements
- Target underflow density
- Water recovery rate
- Continuous vs batch operation
Economic Factors
- Capital expenditure
- Operating costs (power, chemicals)
- Maintenance requirements
How Do Flocculants and Sedimentation Aids Improve Tailings Thickening?
Tailings slurries often contain ultrafine particles that resist settling. How do miners overcome this challenge?
Flocculants clump fine particles together, speeding up sedimentation. The right chemical dosage dramatically improves water clarity and thickening efficiency. Polyacrylamide-based flocculants are widely used but need proper mixing and pH control.
Types of Flocculants
- Anionic (- charge): Good for positively charged slurries (e.g., iron ore).
- Cationic (+ charge): Effective on clays and silts.
- Non-ionic: Works in varied pH conditions.
Optimal Use Tips:
- Test slurry first in a lab to determine the best chemical.
- Use automated dosing for consistency.
- Overdosing can create floating slime (poor settling).
| Factor | Effect on Thickening |
| Low dosage | Weak flocs, slow settling |
| Correct dosage | Fast, clear separation |
| Too much | Gel-like sludge, poor water release |
What Are The Common Methods for Tailings Dewatering?
Getting tailings to the right dryness level can mean the difference between safe storage and environmental risks. While thickening removes some water, many operations need advanced dewatering to meet modern standards.
The three primary tailings dewatering methods are filtration (vacuum/pressure), mechanical compression (filter presses), and thermal drying. Filter presses dominate dry stacking applications by achieving 70-85% solids, while thermal drying remains rare due to high energy costs. Selection depends on target moisture content, particle size, and disposal method.
1. Filtration Dewatering
- If further dewatering is required after the tailings slurry has been thickened, filtration dewatering may be employed.
- Filtration equipment includes vacuum filters and pressure filters (such as plate-and-frame filter presses).
- Pressure filtration can achieve a high solids content in the tailings, facilitating dry stacking.
- Filtration dewatering is suitable for applications that require drier tailings.
2. Pressure Filter
- A plate-and-frame filter press can compress tailings filter cake to a high concentration (e.g., over 70%).
- The resulting tailings filter cake has a low moisture content and is suitable for direct dry stacking.
- It serves as a key piece of dewatering equipment for the dry stacking of tailings.
3. Thermal Drying
- In some cases, thermal drying is used for further dewatering.
- Thermal drying is energy-intensive and is only employed when specifically required.
- For most tailings, a combination of thickening and pressure filtration is used to achieve a "dry" state; thermal drying is rarely utilized.
Selection of Dewatering Method
- The dewatering method should be selected based on the final intended use of the tailings (e.g., wet disposal, dry stacking, or backfilling).
- Dry stacking requires dewatering to a high solids content.
- For wet disposal, tailings can be transported directly after moderate thickening.
How Can Reclaimed Water From Tailings be Reused Dfficiently?
Mining operations consume massive amounts of water. Did you know up to 80% of process water can be recovered from tailings? Smart water reuse cuts costs and protects local supplies.
1. Importance of Water Recovery
Water recovered from the thickening and dewatering of tailings (such as overflow and filtrate) should be reclaimed and reused:
- Returned to the mineral processing circuit to conserve water resources.
- Minimize discharge of wastewater, which benefits environmental protection.
- Improved overall water resource utilization efficiency.
2. Water Recovery System
- Tailings thickening systems should be equipped with facilities for the collection and transport of recovered water.
- Recovered water should ideally be returned to the mineral processing plant for recycling.
- The quality of the recovered water must meet the requirements of the mineral processing operations.
3. Water Recovery Rate
High-efficiency thickening and dewatering can significantly increase the water recovery rate.
This reduces the amount of water carried by the tailings slurry, thereby easing the burden on the tailings storage facility.
How Does Thickening Influence Tailings Storage Methods?
Traditional tailings dams are risky and space-intensive. How does thickening change the game? Thicker slurries enable safer, more sustainable storage options.
Thickened tailings (with 50-70% solids) allow for:
- Dry stacking (no dam needed)
- Reduced footprint
- Lower risk of dam failures; paste and filtered tailings can even be used for backfill or construction materials in some cases.
Storage Method Comparison
| Method | Solids % | Water Recovery | Stability |
| Conventional Slurry | 30-40% | Low | High risk |
| Thickened Tailings | 50-60% | Medium | Moderate |
| Paste Tailings | 60-70% | High | Very stable |
| Filtered (Dry Stack) | 75-85% | Max | Safest |
Key Considerations:
Geotechnical Stability:
- Thicker tailings don't liquefy during earthquakes
- Reduced seepage means less groundwater contamination
Closure Costs:
- Dry stacks require less long-term monitoring
- Could be revegetated 5-10 years sooner
Climate Factors:
- Paste works well in arid regions
- Wet climates may need filtered tailings
Conclusion
The tailings thickening and dewatering process is a critical component of modern mining operations, transforming unstable slurries into manageable, reusable materials while recovering valuable water resources. By selecting the right thickening
equipment, optimizing flocculant use, and applying appropriate dewatering methods, mines can significantly reduce environmental risks, lower storage costs, and enhance operational efficiency. Whether through conventional thickeners, high-efficiency systems, or advanced filtration, these technologies empower sustainable tailings management—enabling dry stacking, safer storage, and even material reuse. As water scarcity and environmental regulations tighten, investing in robust thickening and dewatering processes isn’t just best practice—it’s essential for the future of responsible mining.