As a key piece of equipment for solid-liquid separation, the thickener plays a vital role in mineral processing. Utilizing the principle of gravity sedimentation, it concentrates low-density slurries into high-density underflow while recovering clarified overflow water. Throughout this entire process, there is a large component often regarded as a “supporting role” that is, in fact, the physical foundation and core site for all functions: the thickener tank.
The tank is not merely a container for the slurry; it is the “reactor” where sedimentation occurs, the “warehouse” for underflow storage, and the “skeleton” connecting various mechanisms. The rationality of its design, the stability of its structure, and the completeness of its functions directly determine the overall working efficiency, separation performance, and service life of the thickener.
I. Main Types and Characteristics of Tanks
Depending on the equipment specifications, feed material properties, operational requirements for underflow discharge, and site terrain conditions, thickener tanks can be constructed from steel, concrete, wood, or lined with stone in earthen excavations. The tank wall and bottom can be made from the same or different materials. To prevent corrosion, the inner wall can be coated with paint or lined with synthetic rubber or plastic. In areas with good soil conditions, the tank bottom can be constructed using stone masonry or compacted clay without the need for reinforced concrete.
1. Classification by Installation Method
(1) Tank Installed at Grade, Bottom Embedded Below Ground Level:
The tank is positioned on the ground surface, but its bottom is recessed below grade. An underground corridor is provided for underflow discharge. This structure facilitates tank support and has lower civil construction costs. However, the underflow conveying equipment is located several meters below ground, resulting in poorer operational and maintenance conditions. This configuration is commonly adopted for large and medium-sized thickeners.
(2) Tank Installed Above Ground Level:
The tank is elevated above ground, supported by reinforced concrete beams and columns. The underflow can be transported to the next process step by gravity or via slurry pumps at ground level. The construction cost for this type of structure is higher, but it offers better operating conditions, and the space beneath the tank can be utilized for other purposes. This configuration is sometimes used for small to medium-sized thickeners or those installed indoors.
2. Classification by Shape
(1) Flat Bottom Tank:
The bottom is a flat plate structure. Its characteristics include a simple structure, low construction difficulty, and relatively low build cost. Due to the flat bottom, it relies on the rake mechanism to scrape the settled solids towards the central discharge outlet. Suitable for thickening most conventional materials. The disadvantages are that the underflow concentration is limited by the raking efficiency, and the rake mechanism experiences higher operational resistance.
(2) Cone Bottom Tank:
The bottom is conical, sloping towards the center. This design facilitates the natural flow of underflow towards the discharge point, reducing the load on the rakes for moving settled solids. The conical shape also exerts a certain consolidating pressure on the material at the bottom, which is beneficial for achieving higher underflow concentrations. Commonly used in applications requiring higher discharge densities or for materials with good settling characteristics. However, the fabrication difficulty and cost for a cone bottom are slightly higher than for a flat bottom.
3. Classification by Material
(1) Steel Structure Tank:
Fabricated by welding steel plates. Characteristics include high strength, short construction period, and relatively flexible foundation requirements. Suitable for various scales and mildly to moderately corrosive environments. Steel plates can be welded and assembled on-site, facilitating transport and installation. This is the mainstream choice for current small, medium, and even some large thickeners. The disadvantage is that the steel requires anti-corrosion treatment, and maintenance costs can be high in severely corrosive environments.
(2) Concrete Structure Tank:
Constructed by casting reinforced concrete on-site. Characteristics include excellent overall rigidity, strong seismic resistance, outstanding corrosion resistance, long service life, and typically lower material costs compared to steel for very large tanks. Mainly applied in ultra-large thickeners (several tens of meters in diameter or more) or for handling highly corrosive materials. The disadvantages are a long construction period, a fixed footprint, and difficulty in modification or relocation after completion.
II. Key Design Considerations and Optimizations for Tanks
Increasing demands for thickening efficiency in modern industry have driven continuous optimization in tank design, primarily reflected in the following aspects:
Determination of Geometric Dimensions: Based on the settling characteristics of the material and the required throughput, reasonable tank diameter and depth are determined through settling tests and comparison with similar applications. This ensures sufficient sedimentation area and retention time.
Wear and Corrosion Protection: For highly abrasive materials (e.g., ore slurries), wear-resistant liners (such as ceramic or rubber) are installed in high-wear areas on the inner wall of the tank. For highly corrosive materials, heavy-duty anti-corrosion coatings like glass flake coatings or resin-based systems are applied to extend the equipment’s service life.
Large-Scale and Modular Fabrication: As single-line processing capacities increase, tank diameters continue to grow. To facilitate transport and on-site installation, large tanks are commonly designed using modular approaches, where the tank wall is divided into prefabricated sections that are assembled and welded on-site. Alternatively, bolted structures are used for on-site assembly without welding.
III. Conclusion
As the “body” of the thickener, tank technology forms the engineering foundation ensuring the stability of the thickening operation. The choice of tank type depends on various factors, including material properties, processing scale, and economics. With the advancement of industrial technology, tank design will increasingly focus on alignment with the process flowsheet. Through optimizing geometric shapes, improving internal structures, and utilizing more durable materials, the overall efficiency of solid-liquid separation will continue to be enhanced.
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