Introduction
In the “gold extraction journey” of gold mining, from mining, crushing, grinding to separation, gold mining wastewater treatment, dewatering, and tailings treatment, solid-liquid separation is a core and challenging step. Suspended fine solid particles in the slurry (such as clay, slime, fine gold inclusions) can interfere with gold recovery and increase the difficulty of tailings management and water treatment.
Polyacrylamide (PAM) , as a highly efficient polymeric flocculant, is the “behind-the-scenes hero” solving these problems. By altering the surface characteristics of solid particles, promoting their aggregation, and accelerating sedimentation, PAM plays an irreplaceable role throughout the gold production process.
I. Three Core Applications of PAM in Gold Mining wastewater treatment
1. Thickening & Extraction: Improving Gold Recovery Efficiency
Gold ore is typically finely ground to the micron level to fully liberate gold minerals. When the ground slurry enters a thickener (or concentrator), adding a suitable amount of PAM solution causes the suspended gold-bearing solids to rapidly aggregate into large flocs and settle quickly to the bottom. The clarified overflow water is returned to the front of the process as circulating water.
- Effect: Prevents loss of fine gold, increases underflow concentration of the thickener, and provides ideal feed for subsequent processes such as cyanidation, carbon-in-pulp (CIP/CIL), or pressure filtration.
2. Tailings Dewatering: Enabling Dry Stacking and Safe Storage
Tailings slurry contains extremely fine solid particles and high clay content, resulting in very slow natural settling. PAM significantly accelerates the settling rate of tailings in thickeners or paste thickeners. Further dewatering using belt filter presses or plate-and-frame filter presses produces “dry tailings” or “paste” that are easy to transport and store.
- Effect:
- Reduces the land footprint and environmental risks of tailings storage facilities (TSFs);
- Enables underground cemented backfill using dewatered tailings to stabilize mined-out areas and control surface subsidence;
- Reduces water consumption, particularly valuable in arid and water-scarce mining regions.
3. Water Recycling & Environmental Compliance
Gold mining requires large volumes of process water, and the suspended solids, heavy metals, and cyanide (if cyanidation is used) in wastewater must be controlled. By efficiently clarifying slurry water with PAM, process water can be closed-loop recycled after simple treatment, reducing fresh water intake. For wastewater that must be discharged, PAM combined with coagulants effectively removes suspended solids to help meet environmental discharge standards.
II. How to Choose the Right Type of PAM?
Gold mines generally use anionic or non-ionic polyacrylamide, and rarely use cationic types (as they may react adversely with negatively charged gold minerals or process reagents).
| Condition | Recommended Type | Reason |
|---|---|---|
| Neutral or alkaline slurry, suspended solids are positively charged metal oxides, silicates, etc. | Anionic (most common) | Strong charge adsorption ability, large flocs, fast settling, cost-effective |
| Acidic slurry or high-salinity/high-organic slurry | Non-ionic | Insensitive to pH fluctuations and ionic interference, produces dense flocs |
| Extremely clear overflow water required | High molecular weight anionic (e.g., 18–24 million) | Strong adsorption bridging, captures ultra-fine particles |
The specific product must be determined through jar tests, evaluating parameters such as settling rate, supernatant turbidity, floc size, and cost per ton of ore.
III. Key Precautions When Using PAM
1. Avoid Inhibiting Gold Leaching/Flotation
During flotation or cyanidation leaching, if PAM is overdosed or has excessive contact time with the slurry, its long chains may adsorb onto the surface of fresh gold particles or gold sulfides, forming a barrier film that hinders the interaction of flotation reagents or cyanide with the gold surface, thereby reducing gold recovery.
- Solution: PAM should preferably be added in solid-liquid separation stages such as thickening and dewatering, not before grinding or flotation/leaching. If addition early in the process is unavoidable, the dosage must be strictly controlled and its impact on recovery verified.
2. Pay Attention to Chemical Addition Order
When using a coagulant (e.g., polyaluminum chloride PAC, aluminum sulfate) together with PAM, always add the coagulant first to destabilize the colloidal system, then add PAM to perform bridging flocculation. Reversing the order will significantly reduce flocculation efficiency.
3. Prepare PAM Solution Correctly
- Use cold or room-temperature clean water (never hot water). Add the powder slowly and evenly to avoid forming “fish eyes” (undissolved gel lumps).
- Use slow mixing (≤200 rpm) for about 40–60 minutes to ensure complete dissolution.
- Prepare a 0.1%–0.3% solution, use it as soon as possible or store for no more than 24 hours (to avoid viscosity degradation).
IV. Typical Application Case Data (Example)
| Application Scenario | PAM Type | Dosage (g/t dry solids) | Effect |
|---|---|---|---|
| Gold concentrate thickening | Anionic, 20 million MW | 10–30 | Underflow concentration increases from 40% to 55%, overflow SS <200 ppm |
| Whole tailings dewatering | Non-ionic, 18 million MW | 15–50 | Settling rate increases 5-fold, filter cake moisture <20% |
| Tailings water clarification | Anionic + low MW | 5–10 | Recycled water SS <50 ppm, meets flotation water quality requirements |
Note: Actual values need to be adjusted based on specific ore characteristics.
V. Future Outlook
As the gold mining industry moves toward “green, safe, and efficient” operations, the application of PAM continues to evolve:
- Novel polymeric flocculants: Modified or composite PAM that maintains excellent performance at higher salinity and lower temperatures.
- Automated dosing systems: Closed-loop control based on turbidity or settling interface sensors to precisely inject PAM, reducing consumption and stabilizing operation.
- Eco-friendly biodegradable flocculants: Reducing residual PAM accumulation in tailings over the long term, lowering potential ecological risks.
Conclusion
Polyacrylamide may appear to be just a “supporting” chemical in gold mining, but it directly impacts key indicators such as gold recovery rate, water utilization efficiency, tailings safety, and environmental compliance. Correctly selecting the PAM type, precisely controlling the addition point and dosage, and implementing scientific preparation and dosing procedures will bring significant economic and environmental benefits to gold mining operations.
For gold mines, PAM is not the “lead actor” in gold extraction, but it is the “gold medal supporting actor” that ensures the entire process line runs smoothly, efficiently, and cleanly.
