How to Choose the Right Thickener

Xinhai on-site indoor installation of concentrator

In modern chemical, mining, and environmental protection fields, efficient separation technology and resource recycling have become core issues for sustainable development. As an indispensable solid-liquid separation device in industrial production, the thickener, through the principle of gravity sedimentation, not only achieves material concentration and purification and water resource recovery, but also plays a key role in reducing energy consumption and emissions. This article will systematically introduce the working principle, main types, and selection guidelines of thickeners, and look forward to their intelligent and efficient future development trend, providing comprehensive technical reference for engineering technicians.

1. Core Applications

(1) Increasing Concentration (Concentration)

①Dewatering thin concentrate slurry or tailings slurry from mineral processing (such as flotation and magnetic separation) to increase its solid content, preparing for subsequent filtration, drying, and other deep dewatering operations.

②Recovering Water Resources (Clarification)

Separating solid particles from the slurry through sedimentation to obtain clear overflow water. This water can be recycled in the production process, greatly saving the consumption of new water and achieving zero wastewater discharge, meeting environmental protection requirements.

③Storage and Transportation The concentrated underflow sludge has a smaller volume, making it easier to temporarily store in a large thickener (often called a "thickening machine"), and reducing the cost and difficulty of subsequent transportation (such as pumping or vehicle transport).

2. Working Principle

The thickener operates based on the principle of gravity settling. Its basic working process is as follows:

(1) Feeding: The thin sludge enters the thickener tank through the central feed well.

(2) Settling: The sludge slowly diffuses outwards in the tank, and solid particles begin to settle freely under gravity, gradually forming a compression zone at the bottom of the tank.

(3) Clarification: A clear water layer gradually forms at the top, called the clarification zone. The clarified water flows out from the overflow weir along the top of the tank, which is called "overflow water".

(4) Collection and Discharge: The concentrated sludge (underflow) settled to the bottom of the tank is gradually collected by a slowly rotating rake at the bottom of the tank to the discharge port in the center of the tank, and then discharged by pumping, which is called "underflow sludge".

3. Main Application Areas

(1) Mineral Processing Plants (The Core Application)

• Concentrate Concentration: Dewatering concentrates obtained from flotation, gravity separation, and magnetic separation.

• Tailings Treatment: Concentrating waste tailings generated after mineral processing; high-concentration underflow is used for mine backfilling or dry stockpiling, while clarified overflow is recycled.

(2) Metallurgical Industry

• Used for red mud separation in alumina production and for concentrating various leachates and precipitates in hydrometallurgical processes.

(3) Coal Industry

• Used for concentrating and clarifying clean coal and coal slurry water in coal washing plants, achieving closed-loop recycling of wash water.

(4) Chemical Industry

• Used for separating various chemical precipitates, catalyst particles, etc.

(5) Environmental Protection and Water Treatment

• Wastewater Treatment Plants: Used for concentrating primary sludge and residual activated sludge.

• Industrial Wastewater Treatment: Treating industrial wastewater containing heavy metals and suspended solids to ensure it meets discharge standards or is reused. River/lake dredging: Dewatering and reducing the volume of dredged sludge.

1. Classification by Transmission Method (Most Common Classification)

This is the most basic and universal classification method, mainly based on the driving method of the rake frame.

(1) Center-Driven Thickener

①Working Principle: 

• The drive unit is located on the central support of the thickener tank. The motor drives the central vertical shaft to rotate through the reducer. The rake frame at the bottom of the vertical shaft rotates accordingly, scraping the settled sludge towards the discharge port in the center of the tank.

②Structural Features:

• Compact transmission structure with reasonable force distribution.

• Usually equipped with a lifting device. When the rake frame torque is too high (e.g., the bottom sludge is too thick or foreign objects are stuck), the rake frame can be automatically or manually lifted to prevent equipment damage.

③Applicable Scenarios:

• Medium-diameter thickeners (usually between 12m and 40m in diameter).

• Medium processing capacity, good material settling performance.

• Widely used in metallurgy, mineral processing, chemical and other industries.

(2) Peripheral Drive Thickener

① Working Principle: 

• The drive unit is located around the periphery of the thickening tank. The motor drives the rollers through a reducer, causing one end of the truss structure to rotate around the center of the tank. The rake at the bottom of the truss scrapes the sludge towards the center.

② Structural Features: 

• One end of the truss is connected to the bearing of the central support column, and the other end is supported by the drive rollers and runs on the track at the top of the tank wall. It is also equipped with safety devices, such as overload alarms and roller slippage detection.

③ Applicable Scenarios: 

• Large and super-large thickening tanks (diameter can reach over 100m).

• It has a very large processing capacity, such as tailings treatment in large mineral processing plants and coal slurry thickening in the coal industry.

• Due to its structural characteristics, it is more suitable for processing fine-grained materials with slow settling velocity and good compressibility.

2. Classification by Working Method

(1) Ordinary (Continuous) Thickener

• This is the most common type, with continuous feeding, continuous discharge of underflow, and continuous overflow of clean water.

• Suitable for modern large-scale continuous production processes.

(2) Intermittent Thickener (Clarifying Tank)

① Working Principle: Batch operation. The slurry is injected into a large tank and allowed to settle for a sufficient time to allow the solids to completely settle. The supernatant is then discharged first, followed by cleaning the concentrate at the bottom.

② Characteristics: Simple structure, no transmission components required, but low efficiency, small processing capacity, and discontinuous operation.

③ Applicable Scenarios: Small factories, mines, laboratories, or special chemical processes with very small processing volumes.

3. Classification by Structural Form

(1) High-Efficiency Thickener

① Working Principle: 

This is not an independent classification, but a technological upgrade. It optimizes the structure of the traditional thickener, with the core being the addition of a flocculant mixing feed well. Before entering the settling zone, the slurry is thoroughly mixed with the flocculant in the feed well, forming large flocs, thus greatly accelerating the settling speed.

② Characteristics:

Extremely high settling efficiency, with a processing capacity per unit area several times or even tens of times that of a traditional thickener.

Higher underflow concentration and clearer overflow water.

More compact structure and smaller footprint.

③ Applicable Scenarios: 

Suitable for extremely fine particles (e.g., -20 microns), difficult-to-settle sludge (e.g., activated sludge in industrial wastewater), or occasions with strict requirements on efficiency and space.

(2) Deep Cone Thickener

① Working Principle: The tank is designed as a tall cone with a deep compression zone. Flocculants are also required. The material is subjected to strong compression by its own static pressure within the deep cone, resulting in a very high underflow concentration.

② Features: It can produce a high-concentration underflow similar to a paste, which can sometimes be directly used for downhole filling or belt conveyor transport.

It has a relatively high height and a relatively small footprint.

③ Applicable Scenarios: Particularly suitable for occasions requiring the preparation of high-concentration slurry, such as tailings filling and paste storage.

(3) Special Types of Thickeners

① Inclined Plate Thickener

• Working Principle: A set of densely packed inclined plates is placed in the settling zone, greatly increasing the effective settling area. Solid particles only need to settle a very short distance (the vertical distance between the two plates) to hit the inclined plate and slide into the sludge collection area, thus significantly improving processing capacity.

• Features: High processing capacity per unit area, compact structure, but relatively complex cleaning and maintenance.

• Applicable Scenarios: Commonly used in situations with large processing volumes but limited space, such as water treatment plants and certain mineral processing steps.

② Multi-layer Thickener

• Working Principle: Within a tall pool, a multi-layer conical structure divides it into 2-4 independent thickening layers, essentially stacking multiple thickeners vertically together.

• Features: Extremely small footprint, large processing capacity. However, complex structure, high cost, and difficult maintenance.

• Applicable Scenarios: Special operating conditions with extremely limited space but high processing capacity requirements.

Three Key Steps in Selection:

Step 1: Determine the properties of the material to be processed (basic premise)

This is the most important basis for selection and requires data acquisition through experiments (sedimentation tests).

1. Solid Properties:

• Particle Size Distribution: Higher content of fine particles (e.g., -20μm) makes sedimentation more difficult, typically requiring a high-efficiency thickener.

• Density: The greater the density difference between the solid and liquid, the easier it is for the solid to settle.

• Sedimentation Characteristics: Initial sedimentation rate and concentration in the compression zone are obtained through static sedimentation tests. These are core parameters for calculating the required thickening area.

2. Chemical Properties:

• Zeta Potential: Affects particle cohesion, determining whether and which type of flocculant is needed.

• pH Value, Corrosivity: Affects the selection of thickener material (e.g., carbon steel, stainless steel, or anti-corrosion coating).

3. Slurry Properties:

Feed concentration and feed rate (dry ore quantity or volumetric flow rate).

Temperature, viscosity, etc.

Step 2: Determining Process Requirements (Target Setting)

1. Underflow Target Concentration:

① How concentrated is the underflow? Is it to reduce the subsequent filtration load, or to meet the requirements for paste storage or filling?

② Higher requirements necessitate a larger concentration area, or the selection of a deep cone or high-efficiency thickener.

2. Overflow Water Quality Requirements:

① What are the requirements for suspended solids (SS) in the reclaimed water?

② Higher requirements may require longer settling times or the addition of flocculants.

3. Processing Capacity:

The required dry ore volume (t/d) and total slurry flow rate (m³/h).

Step 3: Selecting the Thickener Type (Technical Decision)

1. Peripheral Drive Type:

• Scenario: Large throughput, general concentration requirements (e.g., traditional tailings)

• Reason: Can be built with ultra-large diameter, huge processing capacity, economical and reliable.

2. Center Drive Type:

• Scenario: Medium throughput, conventional site requirements

• Reason: Compact structure, stable operation, convenient maintenance, high cost-effectiveness.

3. High-Efficiency Thickener:

• Scenario: Fine-grained, difficult-to-settle materials (e.g., clay, activated sludge)

• Reason: Adding flocculants results in extremely fast settling speed and high processing capacity per unit area.

4. Deep Cone Thickener:

• Scenario: Requires extremely high underflow concentration (paste-like)

• Reason: Special deep cone structure combined with flocculation produces toothpaste-like underflow.

5. High-Efficiency Thickener or Multi-Layer Thickener:

• Scenario: Severely limited site space

• Reason: High processing capacity per unit area, or expansion into newer areas.

6. Intermittent Thickener:

• Scenario: Small batch, intermittent production

• Reason: Simple structure, low investment, flexible operation.

As a core device for solid-liquid separation, the thickener achieves material concentration and water reuse through gravity settling. Its selection requires comprehensive consideration of material characteristics and process requirements. Looking to the future, thickening technology will develop towards greater intelligence and efficiency: intelligent sensors and AI algorithms can achieve real-time operating condition optimization and predictive maintenance; low-energy design and the development of high-efficiency flocculants will significantly reduce operating costs; modular and compact structures facilitate rapid deployment and upgrades of older equipment. These innovations will drive the concentrators to achieve more efficient and energy-saving sustainable development in fields such as environmental protection, mining, and chemicals.