Flocculants for mineral processing: Application and technical progress of polyacrylamide

I. Introduction

In modern mineral processing industry, high efficiency separation and concentration process is of great significance to improve resource utilization, reduce energy consumption and reduce environmental pollution. Polyacrylamide (PAM) is an important synthetic polymer flocculant. Due to its unique molecular structure and controllable properties, it has become an indispensable chemical additive in mineral processing. This paper will comprehensively discuss the application principle, type selection, application process and latest technological progress of PAM in mineral processing.

2. the basic characteristics of polyacrylamide

Polyacrylamide is a polymer polymerized from acrylamide monomer. Its molecular chain contains a large number of amide groups, which can introduce different functional groups through chemical modification. PAM has the following outstanding features:

2-1.Adjustable molecular weight: The molecular weight of industrial PAM can range from millions to tens of millions of daltons to meet the needs of different sedimentation rates;

2-2.Ionic characteristics can be controlled: anionic, cationic or non-ionic products can be obtained through copolymerization or post-modification;

2-3.Bridging adsorption capacity: Long molecular chains can form "bridging" between multiple particles to promote flocs formation;

2-4.Good stability: long-term chemical stability can be maintained under appropriate conditions;

2-5.Low dosage and high efficiency: usually only a few ppm can be added to significantly improve the settling effect.

3. the mechanism of PAM in mineral processing

In mineral processing applications, PAM functions mainly through the following mechanisms:

3-1.Charge neutralization

For charged particle system, PAM with opposite charge can neutralize particle surface charge through electrostatic action, reduce Zeta potential, weaken the repulsion force between particles, and promote particle aggregation. This mechanism is particularly important in the treatment of clay minerals.

3-2.Adsorption bridging

The active groups on the PAM molecular chain can adsorb multiple particles at the same time, and connect multiple particles through the "bridging" effect of the polymer long chain to form a three-dimensional network structure of floc. This is the main mechanism of PAM.

3-3.Net sweep effect

PAM with high molecular weight can form a network structure in the water and trap suspended particles like a filter during sedimentation, which is particularly obvious in concentration operations.

4. the main types and selection of PAM for mineral processing

According to the different needs of mineral processing, PAM can be divided into the following main types:

4-1.Non-ionic polyacrylamide (NPAM)

Features: No charge, adsorption by hydrogen bond and van der Waals force

Application scenario:

Neutral or weakly acidic pulp

Treat minerals that do not have a strong charge on their surface

Separation process sensitive to ionic environment

4-2.Anionic polyacrylamide (APAM)

Features: Containing carboxyl group and other negative electric groups, molecular weight is usually higher

Application scenario:

Handling positively charged minerals (such as iron ore)

Alkaline pulp environment

Concentration operations requiring large flocs

4-3.Cationic Polyacrylamide (CPAM)

Features: Contains positive groups such as quaternary ammonium salt, charge density can be adjusted

Application scenario:

Treatment of negatively charged clay minerals

Fine tailings dewatering

Treatment of organic pulp

4-4.Amphoteric polyacrylamide

Features: Contains positive and negative electric groups at the same time, more adaptable

Application scenario:

Complex composition pulp

A treatment system with large pH fluctuations

Special mineral separation process

Selection principle:

Select the opposite charge type according to the surface electrical properties of the mineral

Select the molecular weight according to the settling speed requirement (the larger the molecular weight, the faster the settling)

Consider the pH value of the pulp to match the applicable pH range of PAM

The best model is determined by laboratory bottle test

5. the main application of PAM in mineral processing

5-1.Solid-liquid separation during mineral selection

After flotation, magnetic separation and other cleaning processes, PAM is used to accelerate the settlement of concentrate and tailings and improve the efficiency of thickener. For example, in iron concentrate treatment, properly selected APAM can increase the sedimentation rate by 3-5 times and the underflow concentration by 10-15%.

5-2.Tailings treatment and dehydration

The application of PAM in tailing dewatering is more and more widely due to the requirement of tailing dry discharge in modern mines. By optimizing PAM type and addition method, the water content of tailings filter cake can be reduced by 2-4 percentage points, and the area of tailings pond can be significantly reduced.

5-3.Slime water treatment

In the process of coal washing, PAM can effectively solve the problem of fine slime settlement. The specially modified CPAM shows excellent flocculation effect on clay-containing slime, and the turbidity of circulating water can be controlled below 50NTU.

5-4.Laterite ore and other special mineral treatment

For refractory minerals such as laterite and bauxite, high temperature resistant and salt-resistant PAM products have been developed, which can maintain good performance under high ionic strength environment.

5-5.Slurry pipeline transportation

Adding proper amount of PAM can reduce the pipe transport resistance of high concentration pulp and realize energy saving and consumption reduction. In some cases, transmission energy consumption has been reduced by 15-20%.

6.PAM use process points

6-1.Dissolve the configuration

A dedicated dispersion dissolving device is recommended

The configuration concentration is usually 0.1-0.5%

The solution water temperature should be controlled at 30-50℃

Mixing speed should be moderate to avoid mechanical degradation

6-2.Add method

The multi-point add policy is adopted

Ensure adequate dilution before adding (0.01-0.05%)

The addition location should be selected in a turbulent region to ensure fast mixing

Automated dosing systems improve stability

6-3.Dosage control

Typical dosage range:

Concentration operation: 5-50g/t solids

Filter agent: 100-500g/t solid

Tailings dehydration: 200-800g/t solid

Testing is required to determine the optimal dose, and excessive use may lead to dispersion effects.

7.Technological progress and development trend

7-1.New PAM product development

Nanocomposite PAM: The introduction of nanomaterials to improve temperature and salt resistance

Environmentally responsive PAM: pH/ temperature responsive intelligent flocculant

Biodegradable PAM: reduces cumulative environmental risk

7-2.Application of technological innovation

Microinterface flocculation technology: improve the utilization rate of chemical agents

Composite flocculation system: PAM and inorganic flocculant used together

Online monitoring and intelligent dosing: closed-loop control based on turbidity and Zeta potential

7-3.Green development

Reduce residual monomer content (<0.05%)

Develop more environmentally friendly production processes

Improve product efficiency to reduce usage

8. Conclusion

Polyacrylamide is a high efficient flocculant in mineral processing, and its scientific application is of great significance to improve beneficiation efficiency, reduce energy consumption and realize cleaner production. With the increasingly thin and refined mineral resources, the performance requirements of PAM products are also increasing. The future development of PAM will pay more attention to specialization, intelligence and green, and provide more efficient and environmentally friendly solutions for the mineral processing industry. In the practical application of plant selection, we should pay attention to the selection test and process optimization, and give full play to the technical and economic advantages of PAM.