Skip to content 
This case study describes a polymer program optimization conducted at a mineral processing facility experiencing declining thickener performance and increasing polymer consumption. The facility processed a mixed oxide ore with significant clay content — a combination that creates demanding and variable polymer requirements. The optimization identified a combination of grade mismatch, preparation quality problems, and dosing point issues that, when addressed together, produced a 31% reduction in polymer consumption alongside improved thickener performance.
Note: Facility details have been generalized to protect client confidentiality. Performance data reflects actual measured results.
Facility Background
Facility type: Mineral processing — mixed oxide ore with clay-rich overburden Processing rate: 2,800 tonnes ore per day Water circuit: Closed-loop recycling, target recycling rate 85% Treatment equipment: Two 35-meter diameter high-rate thickeners in parallel PAM application: Thickener feed well dosing (anionic PAM) Process water TDS: 1,800–2,400 mg/L (variable, elevated due to recycling) Key performance indicators: Thickener overflow turbidity (<100 NTU target), underflow solids content (>58% target), water recycling rate
The Problem
Declining Thickener Performance
Over a 14-month period following a change in ore source within the same deposit, thickener performance had progressively deteriorated. Overflow turbidity had increased from an average of 65 NTU to 148 NTU — well above the 100 NTU target required for direct recycling to the processing circuit. Underflow solids content had declined from 61% to 54%, increasing the volume of solids reporting to the tailings storage facility and reducing water recovery.
The ore change had introduced a higher clay fraction — approximately 22% clay content compared to 12% in the previous ore zone. This change had not been accompanied by any polymer program review.
Increasing Polymer Consumption
The operations team had responded to declining performance by progressively increasing dosage. PAM consumption had increased from 145 g/tonne of ore processed to 228 g/tonne — a 57% increase that translated to an additional $186,000 in annual polymer spend without restoring target performance.
Water Recycling Rate Below Target
With thickener overflow above 100 NTU, the recycled water was carrying fine clay particles back into the grinding circuit. This was causing product quality variation and required periodic fresh water dilution to maintain acceptable process water quality — increasing fresh water consumption above the facility’s water allocation target.
Investigation and Diagnosis
Finding 1: PAM Grade Not Matched to Higher Clay Content
The anionic PAM in use — molecular weight 14 million Daltons, 20% charge density — had been selected for the original lower-clay ore. With the new ore zone’s 22% clay content, the combination of lower molecular weight and lower charge density was insufficient for effective clay particle bridging.
Jar testing with current ore slurry using five alternative grades demonstrated that a 17 million Dalton, 30% charge density anionic grade produced significantly better flocculation — achieving overflow turbidity below 80 NTU at 160 g/tonne, compared to the best result of 185 NTU at 228 g/tonne with the current grade.
The higher charge density improved clay particle adsorption; the higher molecular weight provided greater bridging reach across the larger clay particle aggregates.
Finding 2: Preparation Quality Degrading Solution Activity
Inspection of the polymer preparation system revealed two problems. First, the preparation water temperature was averaging 14°C during winter months — significantly below the 20°C minimum for consistent dissolution. Second, the mixing time of 25 minutes was below the recommended 30–45 minutes even at optimal temperature.
Visual inspection of the preparation tank identified a significant buildup of gel accumulation on the agitator blades and tank walls — evidence of persistent fish eye formation that had been depositing partially dissolved polymer rather than delivering it to the thickener.
Comparative testing of fresh solution prepared at 25°C with 40-minute mixing time versus the current preparation conditions showed a 23% difference in effective solution viscosity — indicating significantly higher active polymer content in the correctly prepared solution.
Contact our technical team today for a systematic PAM program assessment at your mineral processing facility. → Contact our technical team today
Finding 3: Dosing Point Location Suboptimal
The PAM dosing point was located 2.3 meters upstream of the feed well inlet, in a section of feed pipe with a 90-degree elbow immediately downstream of the injection point. Flow modeling and G value calculation confirmed that PAM was passing through the elbow — G estimated at 380 s⁻¹ — immediately after injection, before adequate contact time with slurry particles had occurred.
At G = 380 s⁻¹, polymer chains were being subjected to significant shear before bridging could occur, reducing effective molecular weight and flocculation capacity. Relocating the dosing point to the feed well itself — where G was estimated at 85 s⁻¹ — would provide appropriate mixing without excessive shear.
Solution Implementation
Phase 1: Preparation System Correction (Weeks 1–2)
Immediate measures implemented before any product change:
- Installed a heat exchanger on the preparation water supply, maintaining temperature above 22°C year-round
- Extended mixing time protocol to 45 minutes minimum
- Cleaned preparation tanks and agitator blades thoroughly to remove gel accumulation
- Implemented weekly tank inspection and cleaning schedule
Effect measured within one week: effective solution viscosity increased by 21%, confirming that preparation quality improvement delivered more active polymer per kilogram consumed. Polymer dosage was reduced by 15% while monitoring performance — achieving equivalent overflow turbidity to the pre-optimization condition despite the reduction.
Phase 2: Dosing Point Relocation (Week 2–3)
The PAM injection point was relocated from the feed pipe to the feed well, using a new injection manifold that distributed polymer across the feed well inlet width. Capital cost: approximately $4,200 for pipe modification and injection manifold fabrication.
Following relocation, overflow turbidity improved by 22 NTU at the same dosage — confirming that shear damage at the pipe elbow had been reducing effective polymer performance.
Phase 3: Grade Transition (Weeks 3–8)
Trial stock of the 17 million Dalton, 30% charge density grade was procured. A phased transition was implemented:
- Weeks 3–4: 50/50 blend of current and new grade at reduced total dosage
- Weeks 5–6: 100% new grade at 160 g/tonne
- Weeks 7–8: Optimization of new grade dosage through step reductions to 148 g/tonne confirmed optimum
The blended transition approach allowed operators to observe progressive performance improvement and build confidence in the new grade before full commitment.
Results After 120 Days
| Metric | Before Optimization | After Optimization | Improvement |
|---|---|---|---|
| PAM dosage | 228 g/tonne ore | 148 g/tonne ore | −35% |
| Annual polymer consumption | 233 tonnes/year | 152 tonnes/year | −81 tonnes |
| Annual polymer cost | $651,000 | $449,000 | −$202,000 (−31%) |
| Thickener overflow turbidity | 148 NTU average | 72 NTU average | −51% |
| Underflow solids content | 54% | 63% | +9 percentage points |
| Water recycling rate | 79% | 87% | +8 percentage points |
| Fresh water consumption | 168 m³/day makeup | 94 m³/day makeup | −44% |
| Total annual saving | >$220,000 |
The total annual saving exceeded $220,000 — combining the $202,000 polymer cost reduction with fresh water savings and reduced tailings management costs from improved underflow density.
Key Lessons
Ore characteristic changes require polymer program reviews. The 14-month delay between the ore zone change and the polymer program review allowed $260,000 in excess polymer spend to accumulate. Any significant change in ore source, mineralogy, or clay content should trigger an immediate jar test review with representative current feed samples.
Preparation quality problems are invisible without systematic inspection. The gel accumulation in the preparation tanks — a clear indicator of persistent fish eye formation — had gone unnoticed for months because no routine inspection protocol existed. Weekly tank inspection, implemented as part of the optimization, is a low-cost operational change with high performance value.
Dosing point location can be as impactful as grade selection. The $4,200 capital cost of relocating the injection point delivered a 22 NTU overflow turbidity improvement — equivalent in value to a significant polymer grade upgrade. Infrastructure optimization should be evaluated alongside chemistry optimization in any systematic review.
For guidance on dosing point optimization, see: Integrating PAM in Clarifier Systems Effectively
Frequently Asked Questions
How representative are these results for other mineral processing facilities?
The specific numbers — 31% cost reduction, 9-point underflow improvement — reflect this facility’s specific starting conditions. The types of problems identified (grade mismatch after ore change, preparation quality, dosing point shear) are among the most commonly encountered in mineral processing polymer programs globally. The magnitude of improvement varies but the pattern of multiple compounding issues is very typical.
Our thickener performance varies significantly between shifts — could preparation quality be a factor?
Yes, this is one of the most common causes of shift-to-shift performance variation. If preparation procedure is not standardized and enforced across all shifts — mixing time, water temperature, powder addition rate — solution quality varies between batches, producing variable thickener performance that is often attributed to influent variation rather than polymer quality. Implementing and auditing a standardized preparation procedure often resolves apparent influent-related performance variation.
How much capital investment is typically required for a mineral processing PAM optimization?
In this case, $4,200 for dosing point relocation was the only capital cost. Most PAM optimizations require no capital investment — the improvements come from grade selection, preparation procedure, and dosage management. Where capital is required (preparation heating, tank upgrades, dosing point modification), it is typically in the range of $5,000–$30,000 and is recovered within 1–3 months of improved operation.
Conclusion
This case study demonstrates that significant performance and cost improvements are achievable in mineral processing thickener applications through systematic identification and correction of compounding polymer program problems. The 31% polymer cost reduction and $220,000+ annual saving were achieved through the combination of preparation quality improvement, dosing point relocation, and grade optimization — each contributing independently to the overall result.
The case also illustrates a broader principle: polymer program problems in industrial settings are rarely single-cause. The most impactful optimizations identify and address multiple contributing factors simultaneously, producing improvements that exceed what any single intervention could achieve alone.
If your mineral processing operation is experiencing thickener performance problems or polymer consumption above industry benchmarks, contact us today for a free initial assessment. → Get in touch today
