Thickener Product

Overview

A thickener is the workhorse of solid-liquid separation in mineral processing: a wide, shallow tank in which finely ground slurry settles under gravity, splitting into a dense underflow of 45–70 % solids and a clarified overflow that returns to the plant as process water. Concentrators run thickeners on concentrate ahead of filtration and on tailings ahead of disposal; in water-scarce regions the tailings thickener is effectively the mine's water recycling plant, recovering 70–85 % of the water in the feed. The same machine built for clarity rather than density — maximising overflow quality — is called a clarifier.

The continuous thickener dates to John Dorr's 1905 invention at a South Dakota gold mill, and the configuration he set — circular tank, central feed, perimeter overflow, slowly rotating rakes moving solids to a central discharge — is unchanged. What transformed performance was chemistry: synthetic polyacrylamide flocculants, introduced from the 1950s, aggregate fine particles into fast-settling flocs and raised unit throughput by an order of magnitude, enabling the compact "high-rate" thickeners that now dominate.

How it works

Slurry enters the Feedwell at the tank centre through a tangential Feed Pipe that spirals away the feed's momentum. Flocculants work best on dilute pulp, so modern feedwells self-dilute: the incoming jet entrains clarified tank water through Dilution Port, dropping feed density toward 5–15 % solids. Dilute polymer solution from the Flocculant Dosing Plant is injected at the Flocculant Sparge points, where long polyacrylamide chains bridge between particles and bind them into flocs millimetres across that settle hundreds of times faster than the parent particles. The mixing intensity must sit in a narrow band — too little and floc formation is incomplete, too much and the flocs shear apart — which is why feedwell hydraulics, including the Deflector Shelf, get CFD attention from manufacturers.

Flocculated slurry exits the open feedwell bottom and settles through the quiescent volume of the Settling Tank. Three zones develop: clear water on top, a hindered-settling zone, and a compacting bed at the floor where flocs consolidate under their own weight, squeezing trapped water upward. Clear water overflows the levelled V-Notch Weir Plate into the perimeter Overflow Launder at typically under a few hundred ppm suspended solids, watched by the Turbidity Meter.

Rakes and drive

On the floor, the Rake Mechanism turns at 0.1–0.5 rpm. Each angled Rake Blade ploughs settled solids one increment inward per pass along the 1:6–1:12 sloped Tank Floor toward the Discharge Cone. Vertical Dewatering Picket on the arms cut drainage channels through the bed, releasing trapped water and measurably raising underflow density. The Rake Drive Head is a torque machine more than a power machine: through the Final Drive Gear Set and Slewing Ring Bearing, a modest motor delivers torque ratings beyond 3 MN·m on large tanks.

Rake torque from the Rake Torque Sensor is the thickener's vital sign. A rising trend means the bed is growing denser or deeper than the rakes can shift; the Automatic Rake Lift then automatically raises the arms up to ~600 mm to ride over the bed while it is drawn down. Ignoring torque ends in a "bogged" thickener — rakes seized in consolidated mud — which can take days of dredging to recover and is the classic thickener failure.

Underflow and control

The Underflow System pulls dense slurry from the cone with lined slurry pumps, the Cone Scraper keeping the outlet from bridging. A gamma Density Gauge closes the discharge loop: below-target density diverts flow back via the Recirculation Line rather than sending thin slurry to tailings. Plant-level control ties together flocculant dose (via the Flocculant Flowmeter), underflow rate, Bed Level Sensor mud-line and Bed Pressure Sensor inventory readings in the Thickener PLC Cabinet, balancing the standing conflict between underflow density, overflow clarity and rake torque.

Flocculant preparation is its own discipline: dry powder is wetted grain by grain in the Powder Feeder to avoid gel lumps, aged 30–60 minutes in the Make-Up Tank while polymer chains uncoil, and metered by low-shear Flocculant Dosing Pump units because a centrifugal impeller would mechanically destroy the polymer. Doses are small — 5–50 g per tonne of solids — but on a 100,000 t/d tailings stream flocculant is a seven-figure annual line item.