Improving Thickener Performance Using Mineral Processing Flocculants

Flocculants can improve thickener performance by 15-40% in underflow density and reduce settling time by 30-60% when properly selected and dosed. The right flocculant polymer type, molecular weight, and charge density directly impact particle aggregation, settling velocity, and clarification efficiency in mineral processing operations.

Thickeners are critical unit operations in mineral processing plants, consuming significant capital and operating costs. Poor thickener performance leads to reduced throughput, excessive water consumption, and downstream processing issues. Flocculants serve as the primary chemical tool to optimize these systems by bridging fine particles into larger, faster-settling aggregates.

Flocculant Selection Criteria for Thickener Applications

Selecting the appropriate flocculant requires understanding the ore mineralogy, particle size distribution, slurry chemistry, and desired performance outcomes. Different mineral systems respond differently to flocculant characteristics.

Anionic Flocculants for General Applications

Anionic polyacrylamides represent 70-80% of flocculants used in mineral thickening. These polymers work effectively on most oxide ores, coal, and base metal concentrates. High molecular weight anionic flocculants (12-20 million Daltons) with medium charge density (20-40%) typically deliver optimal performance for copper and gold tailings thickening.

A copper mine in Chile increased underflow density from 58% to 68% solids by switching from a 15 million Dalton flocculant to an 18 million Dalton product, while simultaneously reducing dosage from 45 g/t to 38 g/t.

Cationic and Non-Ionic Alternatives

Cationic flocculants excel in clay-rich systems where particle surfaces carry negative charges. Phosphate, potash, and oil sands operations frequently employ cationic polymers with molecular weights between 5-12 million Daltons. Non-ionic flocculants find application in high-salinity environments or where water chemistry fluctuates significantly.

Optimizing Flocculant Dosage and Addition Methods

Dosage optimization balances performance improvements against chemical costs. Excessive dosage waste money and can actually impair performance by causing overdosing effects such as restabilization or increased supernatant turbidity.

Dilution and Mixing Requirements

Proper flocculant preparation significantly affects performance. Standard practice involves preparing solutions at 0.05-0.2% active polymer concentration. Two-stage dilution systems with aging tanks provide better polymer activation than single-stage systems. Aging time should be 30-60 minutes for complete polymer hydration.

Addition point location critically influences flocculation efficiency. Installing the flocculant addition point 3-5 meters before the feedwell, with gentle in-line mixing, allows adequate contact time without excessive shear that damages flocs. A nickel operation in Western Australia achieved 22% improvement in overflow clarity by relocating their addition point and installing a static mixer.

Measuring and Monitoring Thickener Performance

Systematic performance monitoring enables data-driven optimization and early problem detection. Key performance indicators should be tracked continuously or at regular intervals.

Critical Performance Metrics

• Underflow density: The primary indicator of thickener performance, measured continuously with nuclear density gauges or manually with Marcy scales
• Overflow clarity: Measured as nephelometric turbidity units (NTU) or suspended solids concentration, target values typically below 200 NTU
• Settling velocity: Determined through settling tests, indicating flocculant effectiveness with typical rates of 15-40 m/h for well-flocculated slurries
• Bed level: Maintained at 30-50% of thickener depth for optimal operation
• Torque: Rake torque increases indicate bed compaction issues or inadequate flocculation

Laboratory Testing Protocols

Regular jar testing or cylinder settling tests validate plant performance and screen alternative flocculants. A standard test protocol involves:

1. Collect representative feed samples at plant feed density
2. Test dosage range from 50-150% of current plant dosage in 25% increments
3. Measure initial settling rate (first 30 seconds) and ultimate settling after 30 minutes
4. Analyze supernatant clarity and settled bed density
5. Document observations on floc size, strength, and formation speed

Troubleshooting Common Thickener Performance Issues

Performance problems stem from various causes including feed variability, water chemistry changes, equipment issues, or suboptimal flocculant application. Systematic diagnosis prevents incorrect remedial actions.

Poor Underflow Density

When underflow density drops below target, investigate these factors in sequence:

• Increased clay content in feed ore reducing permeability (requires higher molecular weight flocculant)
• Flocculant underdosing or poor mixing resulting in incomplete flocculation
• Excessive hydraulic loading exceeding thickener capacity
• Rake speed too high preventing bed consolidation (reduce to 10-15 m/h tip speed)

An Australian gold operation experiencing declining underflow density from 52% to 46% solids discovered through ore characterization that clay content had increased from 8% to 18%. Switching to an ultra-high molecular weight flocculant (22 million Daltons) restored underflow density to 54% solids.

High Overflow Turbidity

Turbid overflow indicates incomplete particle capture or floc breakage. This problem commonly results from:

• Flocculant overdosing causing charge reversal and particle restabilization
• Excessive mixing intensity breaking formed flocs (reduce impeller speed or use gentle static mixers)
• Ultrafine particle generation from grinding circuit changes (add secondary flocculant dosing)
• Water chemistry shifts affecting surface charge (pH, ionic strength, organic content)

Advanced Flocculant Technologies and Strategies

Recent developments in flocculant chemistry and application methods offer opportunities for substantial performance improvements beyond conventional single-polymer approaches.

Dual-Polymer Systems

Sequential addition of two different flocculants can outperform single polymers in challenging applications. A typical system uses a low molecular weight, high charge density polymer as a conditioner, followed by a high molecular weight bridging flocculant. This approach achieved 35% improvement in settling rate and 28% reduction in chemical costs at a Brazilian iron ore operation processing 15 million tonnes annually.

The conditioning polymer neutralizes surface charges and forms microflocs, while the bridging polymer aggregates these into large, fast-settling flocs. Critical success factors include proper dosage ratio (typically 1:3 to 1:5 conditioner to bridging polymer) and adequate mixing between addition points.

Emulsion and Dispersion Polymers

Emulsion flocculants deliver higher active content (30-40%) compared to standard solutions, reducing shipping and storage costs. Dispersion polymers offer rapid activation (under 10 minutes) versus 30-60 minutes for conventional products, enabling smaller aging tanks and more responsive process control.

A zinc-lead operation in Canada switching to emulsion polymers realized annual savings of $180,000 through reduced freight costs and smaller makeup facilities, with equivalent or slightly improved thickener performance.

Automated Dosage Control

Advanced control systems optimize flocculant dosage in real-time based on feed characteristics and thickener response. Systems using feedforward control (adjusting dosage based on feed tonnage, density, and particle size) combined with feedback control (responding to underflow density and overflow clarity) achieve 10-15% reduction in flocculant consumption while maintaining stable performance through feed variations.

Streaming current detectors provide real-time measurement of surface charge conditions, enabling precise dosage adjustments. Implementation costs of $50,000-150,000 typically pay back within 6-18 months through chemical savings and improved water recovery.

Economic Considerations and Cost Optimization

Flocculant costs typically represent $0.10-0.50 per tonne of ore processed, making them a significant operating expense. However, the value delivered through improved thickener performance far exceeds the chemical cost in most operations.

Value Analysis Framework

Comprehensive value assessment considers multiple factors beyond raw chemical cost:

• Water recovery: Each 1% improvement in underflow density recovers approximately 1.5-2.0% more process water, reducing makeup requirements
• Throughput: Improved settling enables 10-25% capacity increases without capital expansion
• Downstream impact: Better overflow clarity reduces recirculating solids loads on process circuits
• Reliability: Consistent performance reduces operational variability and emergency interventions

A copper concentrator processing 40,000 tonnes per day calculated that improving underflow density from 60% to 65% solids delivered annual value of $2.8 million through reduced fresh water consumption and increased processing capacity, versus additional flocculant costs of $400,000 annually.

Competitive Evaluation Process

Regular flocculant trials comparing multiple suppliers ensure optimal product selection and competitive pricing. Structured evaluation protocols should include:

1. Laboratory screening of 4-6 candidate products from 2-3 suppliers
2. Plant trials of top 2-3 performers over minimum 2-week periods
3. Economic analysis including chemical cost, performance improvements, and operational benefits
4. Supply security assessment including manufacturing locations and logistics reliability

Conducting such evaluations annually or when ore characteristics change substantially maintains optimal performance and cost efficiency.