I. Introduction

Polyacrylamide (PAM for short) is a linear high-molecular polymer with excellent flocculation, thickening and drag reduction properties, and plays an irreplaceable role in the mineral processing industry. As an important chemical agent in modern mineral processing technology, polyacrylamide, through its unique molecular structure and performance characteristics, significantly enhances the efficiency of mineral separation and the effect of wastewater treatment, while reducing energy consumption and costs during the mineral processing. With the increasingly refined and complex mineral resources and the continuous improvement of environmental protection requirements, the research and application technology of polyacrylamide for mineral processing is also constantly innovating, providing strong support for the sustainable development of the mineral processing industry.

Ii. Basic Characteristics of Polyacrylamide

1.Chemical Structure and Classification

Polyacrylamide is a high-molecular compound formed by the free radical polymerization reaction of acrylamide monomers. Its molecular chain contains a large number of amide groups (-CONH₂), and these active groups can introduce functional groups of different properties through hydrolysis or chemical modification. According to the ionic characteristics, polyacrylamide used in mineral processing is mainly classified into three categories:

Anionic polyacrylamide (APAM) : Carboxylic acid groups (-COO⁻) are introduced through hydrolysis or copolymerization, carrying a negative charge, and are suitable for treating mineral particles with a positively charged surface.

Cationic polyacrylamide (CPAM) : By modifying and introducing cationic groups such as quaternary ammonium salts, it carries a positive charge and is mainly used to treat pulp with high organic matter content.

Nonionic polyacrylamide (NPAM) : It does not contain ionic groups in its molecular chain and functions through hydrogen bonds and van der Waals forces, with a wide pH range of adaptability.

2.Physical and chemical properties

Polyacrylamide for mineral processing is usually in the form of white granules or powder, with a density of approximately 1.3g/cm³, and it has excellent water solubility and chemical stability. Its molecular weight range is wide (from several million to tens of millions of Daltons), and it can be customized according to the requirements of different mineral processing processes. Polyacrylamide solution has remarkable viscoelasticity, and its viscosity increases sharply with the increase of concentration and molecular weight. In mineral processing applications, the solubility and solution stability of polyacrylamide are key performance indicators. Generally, it is necessary to control the dissolution time and temperature (the general dissolution temperature should not exceed 60℃) to achieve the best application effect.

Iii. Main Applications of Polyacrylamide in Mineral Processing

1.Mineral particle flocculation and sedimentation

In the mineral processing technology flow, polyacrylamide is widely used as an efficient flocculant in the concentration, sedimentation and filtration processes. Its mechanism of action mainly includes:

Bridging flocculation: Long-chain polymers simultaneously adsorb multiple mineral particles through multiple active sites, forming a "particle-polymer-particle" bridging structure.

Charge neutralization: Charged polyacrylamide molecules can neutralize the surface charges of mineral particles, reduce the repulsive force between particles, and promote aggregation.

Net capture effect: The polymer chains form a three-dimensional network structure, mechanically capturing fine particles.

In the separation of metal ores such as iron ore, copper ore and bauxite, anionic polyacrylamide can significantly increase the sedimentation rate of concentrate, thereby enhancing the processing capacity of the thickener by 30-50%. For instance, after a large iron mine adopted customized high-molecular-weight APAM, the concentration of the underflow during concentration increased from 55% to 68%, while the turbidity of the overflow decreased to below 50NTU.

2.Tailings treatment and dewatering

Modern mineral processing plants are facing severe pressure in tailings treatment. Polyacrylamide plays a key role in tailings concentration and dry stacking technology:

Tailings concentration: By optimizing the type and dosage of polyacrylamide, the solid content of the tailings slurry can be increased from 20-30% to 45-55%, significantly reducing the water storage capacity of the tailings pond.

Pressure filtration dewatering: When used in combination with cationic polyacrylamide, it can reduce the moisture content of tailings filter cakes by 2 to 5 percentage points, creating conditions for dry stacking of tailings.

Preparation of paste: The preparation of high-concentration tailings paste relies on polyacrylamide with a specific structure to achieve a balance between shear thinning and static thickening.

3.Adjustment of pulp viscosity

In the process of complex mineral separation, polyacrylamide can be used as a viscosity regulator to improve the rheological properties of the pulp:

Reducing turbulent resistance: A trace amount of polyacrylamide (50-100 PPM) can reduce pipeline transportation resistance by 30-70% by inhibiting the formation of turbulent vortices.

Suppression of fine sludge interference: Selective flocculants can preferentially flocculate gangue fine sludge, reducing its "covering" effect on useful minerals and improving the separation efficiency.

Foam stability control: In the flotation process, PAM with a specific molecular weight can adjust the stability of the foam layer, optimizing the grade and recovery rate of the concentrate.

Iv. Selection and Process Optimization of Polyacrylamide

1.Selection principles

For different mineral systems and process links, the selection of polyacrylamide needs to take into account multiple factors:

Key points for selecting factors to consider

For mineral surface electrical properties, anionic type is selected for positively charged surfaces, cationic type for negatively charged surfaces, and nonionic type near the isoelectric point

The cationic type of pulp pH value works better under acidic conditions, while the anionic type is more stable under alkaline conditions

The particle size distribution: Fine particle size usually requires a higher molecular weight, while coarse particle size can choose a medium molecular weight

For water with high dissolved salt content and high salinity, salt-resistant or hydrophobic modified products should be selected

For high-temperature environments, cross-linked or heat-resistant modified products with good thermal stability should be selected

2. Use parameter optimization

In practical applications, the optimal process parameters need to be determined through laboratory tests and industrial debugging.

Preparation concentration: Usually 0.1-0.5%. If it is too high, it will lead to incomplete dissolution; if it is too low, it will increase the volume of the reagent added.

Dosing point selection: It should be added in the turbulent area to ensure thorough mixing, but avoid excessive shearing that could damage the molecular structure.

Dosage control: Generally, it should be between 5 and 200g/t of dry ore. Excessive dosage may lead to "colloid protection" and instead inhibit flocculation.

Mixing intensity: Strong mixing is required in the initial stage (velocity gradient G>300s⁻¹), and the stirring intensity should be reduced in the later stage (G<50s⁻¹).

3.Compounding technology

To enhance the processing effect and reduce costs, a compounding usage strategy is often adopted:

When used in combination with inorganic flocculants: First, add aluminum salts/iron salts for charge neutralization, and then add PAM for bridging flocculation, which can reduce the dosage of organic flocculants by 30-40%.

Cationic and anion compounding: The compounding of cationic and anion PAM in a specific proportion can form a network structure, which is particularly suitable for sticky fine particle systems.

In combination with surfactants: In the treatment of flotation tailings, the addition of nonionic surfactants can improve the diffusion adsorption performance of PAM.

V. Technological Progress and Development Trends

1.Development of new polyacrylamide

High-temperature and salt-resistant type: By introducing high-temperature resistant groups such as sulfonic acid groups and hydroxypropyl groups, products suitable for high-temperature and high-salt pulp are developed.

Environmental response type: ph-sensitive, temperature-sensitive, REDOX sensitive and other intelligent PAM, achieving controllable flocculation and flocculation.

Compound functional type: An integrated agent with multiple functions such as flocculation, inhibition and foaming, simplifying the mineral processing process.

Biodegradable type: Develop environmentally friendly flocculants modified based on natural polymers to reduce environmental load.

2.Apply technological innovation

Micro-interface flocculation technology: Utilizing micro-bubbles and micro-oil droplets as "Bridges" to enhance the selective flocculation effect of PAM.

Magnetic flocculation technology: Combining magnetic nanoparticles and PAM to achieve rapid sedimentation and magnetic recovery.

Ultrasonic-assisted technology: By regulating the conformation and dispersion state of PAM molecules through ultrasound, the utilization efficiency is improved.

Digital twin optimization: Based on big data and AI algorithms, a digital twin system for PAM dosing is established to achieve real-time optimization control.

3.Green and sustainable development

With increasingly strict environmental protection regulations, the greening of polyacrylamide used in mineral processing has become an important development direction:

Raw material cleaning: Use bio-based acrylamide monomers to reduce reliance on petroleum-based raw materials.

Low-carbon process: Develop green production processes such as low-temperature synthesis and low-energy consumption drying.

Product harmlessness: Strictly control the content of residual monomers (≤0.05%), and develop a low-toxicity and heavy metal-free catalytic system.

Circular economy model: Research on the recycling and regeneration technology of PAM and explore closed-loop recycling usage schemes.

Vi. Conclusion

Polyacrylamide, as a key chemical agent in modern mineral processing industry, its application technology level directly affects the mineral processing efficiency, resource utilization rate and environmental performance. With the increasing complexity of mineral processing objects and the rising demand for "zero discharge" of mineral processing wastewater, polyacrylamide products are rapidly developing towards specialization, high efficiency and greenness. The future research and development of polyacrylamide for mineral processing should focus on three directions: First, the development of dedicated flocculation systems for emerging minerals such as lithium, rare earths, and strategic metals; The second is to deepen the basic research on the application of intelligent responsive polymers in mineral processing; The third is to establish an environmentally friendly evaluation system covering the entire life cycle. Through collaborative innovation among industry, academia and research, the application value of polyacrylamide in the mineral processing field is continuously enhanced, providing technical support for the efficient and sustainable development of mineral resources.