Thickener Selection: Differences Among Several Mainstream Types

In mineral processing flowsheets, tailings management, and hydrometallurgical production, thickeners play a crucial role. Through gravity sedimentation, they concentrate low-density slurries into high-density underflow while recovering clarified overflow water for process recycling.

However, during the actual selection process, one should not excessively focus only on equipment diameter and capacity indicators. It is also essential to understand the fundamental differences in technical principles, mechanical structures, and applicable working conditions among various thickener types. These differences can often lead to substandard efficiency after commissioning, frequent overflow “turbidity,” or even serious failures such as rake stoppages due to excessive torque.

This article will delve into the core differences among several mainstream thickeners from three dimensions—working principle, structural form, and supporting systems—to provide clear technical guidance for selection decisions.

I. Differences in Working Principles: Conventional, High-Efficiency, and Paste Thickeners

Differences in working principles often lead to variations in the basic performance and application scope of thickeners.

1. Differences Between Conventional Thickeners and High-Efficiency Thickeners
The key distinction lies in: whether flocculants are used to enhance the sedimentation process.

• Conventional Thickener:

  • Technical Principle: Relies entirely on the gravity sedimentation of solid particles themselves. The smaller the particle size, the slower the sedimentation rate. Fine materials require a long retention time to achieve solid-liquid separation.

  • Performance Characteristics: The unit area processing capacity is relatively low. To achieve the same throughput, a larger footprint is often required. Although the equipment investment is not high, civil construction costs may increase due to the large area needed.

  • Applicable Scenarios: Suitable for materials with relatively coarse particles and good natural sedimentation properties (e.g., some gravity separation concentrates), or for projects with ample space and undemanding thickening targets.

• High-Efficiency Thickener:

  • Technical Principle: Flocculants are added during the feeding process, causing fine particles to aggregate into larger flocs, significantly increasing the sedimentation rate. Simultaneously, its unique feed well design directs the slurry below the settled bed level, preventing already settled particles from re-suspending due to hydraulic turbulence.

  • Performance Characteristics: The unit area processing capacity can be 3-5 times that of conventional equipment, significantly reducing the footprint. The underflow concentration is more stable and controllable. The disadvantages are the added cost of flocculant consumption and higher requirements for reagent type selection and addition control.

  • Applicable Scenarios: Suitable for materials with a high content of fine fractions that are difficult to settle naturally (e.g., non-ferrous metal tailings, flotation concentrates), and for modern concentrators with space constraints.

2.Differences Between High-Efficiency Thickeners and Paste Thickeners
The key distinction lies in: the magnitude of the underflow concentration achieved and the means to achieve it.

• High-Efficiency Thickener:

  • Output State: Produces a relatively high-density underflow, typically in a fluid slurry form. In terms of weight concentration, it generally ranges between 40%-55% (depending on material characteristics).

  • Technical Features: The material still falls within the category of Newtonian or near-Newtonian fluids and can be transported using conventional slurry pumps. The thickening process mainly relies on flocculation sedimentation and the action of a limited compression zone.

• Paste Thickener:

  • Technical Principle: Based on the high-efficiency thickener, it significantly increases the tank depth (using a deep cone structure) and the height of the compression zone, utilizing the substantial pressure generated by the material’s own weight to further expel inter-particle water. It is also equipped with a higher torque rake system to handle the agitation demands of high-viscosity materials.

  • Output State: Produces a paste-like underflow exhibiting non-Newtonian fluid characteristics (similar to toothpaste), with extremely poor flowability. The concentration can typically reach over 65%-70%, and it barely releases water after standing.

  • Applicable Scenarios: Suitable for dry-stack tailings disposal (significantly reducing tailings storage facility capacity pressure), underground mine backfilling (requiring underflow with structural stability and no bleeding), etc. The investment and operating costs of paste thickeners are significantly higher than those of conventional high-efficiency equipment.

II. Differences in Structural Forms: Center Drive vs. Peripheral Drive

After determining the type based on the working principle, the next step is to select the drive method. This choice is closely related to the equipment diameter and load magnitude, and also affects the ease of later installation and maintenance.

1. Center Drive Structure

• Structural Features: The rake mechanism is driven by a drive unit located at the center of the tank. Core components such as the motor and gearbox are centrally arranged at this location.

• Applicable Range: Mostly used for small to medium diameter equipment, typically under 30 meters, handling relatively smaller loads. Some small-diameter models can also be used for paste materials.

• Advantages Analysis:

  • A) Compact overall layout, better space utilization.

  • B) Concentrated drive components facilitate sealing and protection, suitable for indoor installation or cold regions (easier to build enclosures and insulation).

  • C) Higher installation precision leads to good operational stability.

• Limitations Analysis:

  • A) Limited torque transmission capability, unsuitable for very large diameters or extremely high-viscosity materials.

  • B) Maintenance usually requires a shutdown, with personnel needing to enter the tank, resulting in confined space operations.

2. Peripheral Drive Structure

• Structural Features: One end of the rake mechanism is fixed to a central pier, while the other end is supported by a drive carriage that travels on a rail along the top of the tank wall, rotating the entire rake around the center.

• Applicable Range: Primarily used for large-diameter equipment, typically over 30 meters, and can reach up to 100 meters. Suitable for heavy-duty conditions, such as tailings thickening in large concentrators.

• Advantages Analysis:

  • A) Capable of transmitting high torque, simple and reliable structure, able to handle large diameters and heavy loads.

  • B) The drive unit is located at the tank periphery, making inspection and maintenance more convenient without needing to enter the tank center.

• Limitations Analysis:

  • A) The rail and drive wheels are exposed to outdoor conditions, susceptible to weather elements like wind, rain, and snow. Winter considerations like anti-skid and de-icing measures for the rail may be necessary.

  • B) Requires high standards for long-term uniform settlement of the rail foundation; otherwise, operational binding or uneven wear may occur.

3. High Torque / Paste-Specific Structure

• Structural Features: Typically features a deep cone design, equipped with a hydraulic drive system, and possesses a powerful automatic or manual rake lifting mechanism. Its drive capacity far exceeds that of conventional models of the same diameter.

• Applicable Range: Specifically designed for materials with extremely high viscosity and high compression ratio, used in paste thickening scenarios. This type is considered regardless of equipment diameter whenever the material is difficult to process.

• Core Capability: Capable of stable long-term operation under extremely high torque conditions. When the rake resistance exceeds a set value, the lifting mechanism can raise the rake to a certain height, reducing operational resistance and preventing equipment damage.

III. Differences in Key Support Systems

The configuration level of support systems often determines whether a thickener is “barely usable” or “truly efficient.” These details directly impact the equipment’s operational stability, automation level, and operational convenience.

1. Flocculant Dosing System

• Preparation Method Differences: Small, simple equipment might use manual dosing, but concentration and flow rate are difficult to control accurately. In contrast, high-efficiency and paste thickeners must be equipped with automated preparation and dosing systems to ensure stable reagent concentration and addition rate; otherwise, flocculation effectiveness is significantly compromised.

• Addition Point Differences:

  • Single-point addition: Simple process, lower investment, but reagent-slurry mixing uniformity may be insufficient.

  • Multi-point addition: Multiple injection points along the feed pipe or dilution system. Mixing is more thorough, floc formation is more uniform, and reagent utilization is higher.

2. Underflow Discharge and Control System

• Conveying Equipment Differences:

  • Conventional Slurry Pump: Suitable for medium-density underflow from high-efficiency thickeners.

  • Diaphragm Pump or Piston Pump: Suitable for paste thickeners, capable of providing high-pressure output and smoothly conveying high-viscosity, high-density media, but with higher equipment investment.

• Density Control Differences: Whether an online densimeter is configured is key to achieving “unattended operation” and stable underflow control.

  • Nuclear Density Meter: Non-contact measurement, good stability, suitable for high-wear underflow pipelines.

  • Coriolis Mass Flow Meter: High measurement accuracy, can simultaneously obtain flow and density data, suitable for precise metering and control. These have become common configurations in automated thickeners. Simpler equipment often relies on manual timed sampling, which introduces significant control lag.

3. Tank Material

• Concrete Structure: Commonly used in large peripheral drive thickeners, constructed on-site via civil works. Can be economical for large volumes, but the construction period is long, it is immobile once built, and requires high standards for foundation treatment.

• Steel Structure: Common in small to medium-sized or high-efficiency thickeners, using prefabricated sections manufactured in a factory and assembled on-site by welding. The installation period is short, and it is easy to relocate or modify. However, proper anti-corrosion treatment (internal and external) is required (especially when handling acidic or corrosive slurries), and the overall cost can be relatively higher.

IV. Selection Suggestions for Different Application Scenarios

Based on the above analysis of differences, the following selection tendencies can be suggested for common application scenarios:

1. Concentrate Thickening Scenario: The throughput is usually not large, but high stability of underflow concentration is required (directly impacting subsequent filtration). Space within the concentrate building is often limited. It is recommended to prioritize center drive high-efficiency thickeners, which are compact and easy to automate.

2. Tailings Dry Disposal Scenario: If the goal is to reduce tailings storage facility pressure through dry-stack disposal or to meet backfill process requirements, a paste thickener (deep cone structure, high torque configuration, hydraulic drive) should be chosen. If only conventional thickening before discharge into a tailings storage facility is needed, with large throughput and less stringent underflow concentration requirements, then a peripheral drive large-diameter thickener is more economical.

3. Difficult-to-Settle Fine Materials: Whether for concentrate or tailings, if the material has a high content of -400 mesh (or -38 μm) fractions or contains significant clay minerals, high-efficiency thickeners should be prioritized, accompanied by flocculant selection tests. Conventional equipment will almost inevitably face “turbid overflow” problems with such materials.

4. Outdoor Installation in Severe Cold Regions: If the equipment must be installed outdoors in regions with low winter temperatures, carefully evaluate the applicability of the peripheral drive structure (rail icing issues). Alternatively, choose center drive and build simple insulation facilities for the drive unit.

The core of thickener selection lies in achieving a precise match between process requirements and equipment characteristics. No single equipment is suitable for all scenarios; only the option most adapted to the specific working conditions exists.

A standardized selection process is recommended as follows:
First, clarify the basic material characteristics (particle size distribution, density, settling performance), target underflow concentration, and design throughput.
Then, preliminarily determine the equipment range based on the working principle type (Conventional, High-Efficiency, Paste).
Next, combine site conditions and investment budget to finalize the appropriate drive structure (Center, Peripheral) and tank material (Concrete, Steel).
Finally, refine the support system configuration (dosing, discharge, online density monitoring) based on automation requirements.

It is particularly important to emphasize that for critical projects or difficult-to-treat materials, the reliability of design data should be verified through formal settling tests (including flocculant selection tests). Only selection based on thorough testing and a clear understanding ensures that the chosen equipment can meet current production needs and adapt to potential future changes in working conditions.

ZJH Company can customize a thickener tailored to your specific requirements.