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Maximizing Water Recovery with Intelligent Thickening

YPT Thickeners

A thickener is a large, continuous, gravity-settling tank used in mineral processing and bulk materials operations to separate solids from liquids, concentrate the solids and recover clear liquid for re-use.

In a typical thickener installation, a feed slurry is introduced into the centre of a circular or rectangular tank, flocculants may be added, and the slower settling solids drop outwards to form a dense underflow zone while clarified liquid overflows from the top launder for recycling.

Areas of Application

Thickeners are widely used in mineral processing, tailings management and other industries. Key applications include:
  • Concentration of mineral slurries ahead of dewatering steps (e.g., ahead of filters or pressure filters) in mining, metallurgy and chemical plants.
  • Tailings thickening, where large tonnages of fine particles must be separated from process water, enabling recycling of water and reduction of tailings volume.
  • Clarification of process water for reuse, including in heap leach plants, CCD circuits and closed-circuit water systems.
  • Pre-treatment of concentrates or slurries to improve feed solids density to downstream filters or dryers (reducing footprint and improving performance).

Principle of Operation

The operational principle of a thickener involves several steps:

  • Feed entry:

    The feed slurry enters the thickener, often through a feedwell or centre column, to minimise turbulence and distribute flow evenly.

  • Flocculation (optional):

    In some applications, flocculants or coagulants are added to accelerate settling of fine particles and promote formation of a sediment bed.

  • Settling and thickening:

    The tank’s calm conditions allow particles to settle by gravity; as the bed of solids builds, the upward flow of overflow water decreases and solids consolidate, increasing underflow density.

  • Underflow discharge:

    The concentrated solids at the base of the thickener are removed via a rake mechanism or a sliding scraper, flocculated sludge plate, or other mechanism to produce a thickened underflow.

  • Overflow withdrawal:

    The supernatant liquid (overflow) is removed via a peripheral launder, typically containing clear water that can be recycled into the process.

  • Continuous control:

    Modern thickeners monitor bed level, clarity of overflow, underflow density and rake torque, and adjust feed rate, flocculant dosage or rake speed for stable performance.

YPT Thickeners Highlights

High-Capacity Clarification for Every Process Stream

Design Criteria

When designing or specifying a thickener, the following criteria are important:

Feed characteristics:

Particle size distribution, solids concentration, slurry viscosity, flocculant response and specific gravity all impact settling behaviour and thickener sizing.

Throughput and tonnage:

The nominal feed flow rate (m³/h) or solids tonnage determines the diameter, depth and number of units required.

Settling rate and design area

The required clarifier area (m²) is often sized based on an overflow rate (m³/m²/h) derived from settling tests.

Underflow density target:

The desired underflow solids concentration (e.g., % solids by mass) influences bed height, rake torque, underflow exit design and required rake mechanism.

Tank geometry and depth

Deeper tanks can provide longer settling distances and higher capacity, but may require greater structural strength and increased capital cost.

Rake mechanism and torque:

The rake drive must be sized to handle the drag of settled solids, sliding interface and rake friction, especially under heavy solids load.

Flocculants and polymer dosing:

If flocculation is used, polymer selection, dose rate, mixing and tailing load must be considered to ensure reliable performance.

Overflow clarity and water recovery:

The design must clearly separate settlement zone and flocculated solids from overflow to achieve high clarity and water recycle (often 65 % to 95 % or more).

Wear, scale and fouling:

The thickener tank bottoms, rake arms, drives and feedwell must be designed for wear from abrasive slurries, scouring flows and possible scaling from flocculants/chemicals.

Instrumentation and control:

Bed level sensors, rake torque monitors, underflow density measurement, overflow clarity monitoring and automated controls improve stability.

Technical Specifications

Here are some typical specification ranges for mining thickeners (actual values will vary by duty, feed, polymer use and design):

Tank diameter:

~20 to 60 m (large plant)Smaller units may be <10 m

Tank depth (solid + overflow zone):

~5 to 15 mDeeper gives longer settling distance

Overflow rate / surface loading:

~0.3 to 2.0 m³/m²/hDepends on feed conditions

Underflow solids concentration:

~25 % to 60 % by massTarget depends on downstream process

Rake drive torque:

Sized per bed load (~kNm)High drag under heavy loads

Clarified overflow turbidity:

< 50 to < 100 mg/LDepends on requirement

Water recovery (recycled)

~65 % to 95 %+Good for water-limited sites

Polymer/flocculant dosage:

Typically ~10–100 g/t solidsVaries widely

Important Considerations:

  • Feed disturbances and surges:

    Thickeners must tolerate feed tonnage or solids fluctuations; poor feed control causes ragging, short-circuiting or collapse of solids bed.

  • Settling tests are essential:

    Without proper test work (settling curves, flocculation response), thickener sizing can be overly conservative or fail to meet recycle targets.

  • Underflow density vs rake torque trade-off:

    Higher underflow density often means higher rake torque, requiring heavier drives; balance design accordingly.

  • Polymer/flocculant variability:

    Feed change (mineralogy, chemistry, temperature) can alter polymer response; a flexible polymer system or backup scenario is prudent.

  • Wear and maintenance hidden cost:

    Tank bottoms and rake arms in abrasive slurries wear significantly and may constitute major refurbishment cost; materials and access design matter.

  • Water clarity and recycle target:

    Achieving high water recovery (>90 %) often requires careful control of overflow quality, launders, launder launders, and solids-carryover prevention.

  • Climate and freezing risk:

    In colder regions, thickeners may need insulation or heating systems for launders and underflow lines.

  • Tailings management link:

    Underflow solids concentration directly affects tailings dewatering cost, storage facility design and water recycling; thickener performance is a key enabler of sustainable tailings design.