Thickeners: learn about the most common types and the main faults

Thickeners are used for solid-liquid separation by the process of large-scale sedimentation. In general, the asset uses the force of gravity to separate the elements. In other words, the suspension is continuously pumped into the thickener, the mixture at rest provides the separation in which the denser solids precipitate and flow through a pipe (underflow). Meanwhile, the liquid exits through the pipe located at the top of the tank.

Basically, they are concrete tanks equipped with a scraping mechanism to remove the sedimented material and a central chamber that receives the mixture. The purpose of this compartment is to prevent the inlet force from moving the mixture excessively and thus hindering the suspension process.

The thickener also helps to increase the density of the thickener, organize solid particles on top of each other and keep the solid in suspension to prevent the thickener from grounding.

However, there are several factors that influence the sedimentation process, such as the nature (size and shape) of the particles, the pre-treatment (percentage of solids) of the pulp, the surface characteristics and the viscosity of the liquid.

Main faults in thickeners

Structurally, thickeners tend not to have many faults in the tank, rake or pipes. However, it is always important to look out for excessive wear, cracks and leaks, which can be detected during routine inspections.

Other faults are related to components such as pumps, motors and drive systems. To avoid these, it is possible to install a performance monitoring system, which will help detect faults at an early stage and prevent unplanned downtime.

If you’re looking for tools to help increase the reliability, availability and maintainability of your assets, get to know the Dynamox solution!

In addition to these problems, there are those related to the effectiveness of the thickener’s operation. In terms of solid-liquid separation, the implementation project must be based on calculating the area of the sedimentation section and the height of the equipment, thus obtaining the volume of sediment. If sizing is not done properly, the efficiency of the operation may be lower than expected.

A relevant factor (and one that can become a problem) is the rake speed setting. If the speed is too low, it will hinder the movement of the arms. If it’s too fast, it will produce turbulence and decompression of the pulp in the underflow.

Another problem is the presence of a higher proportion of materials in finer particle size ranges. This means a reduction in separation efficiency and greater consumption of aggregating reagents. This situation makes it more difficult to operate industrial filters. Lamellar and acicular particles also tend to reduce filter productivity and blind the filter medium.

Types of thickeners

There are a few main types of thickener, including:

• Conventional continuous: it has a system for feeding and removing the thickened material, as well as devices for discharging the overflow and underflow.

• High capacity: similar to conventional, but with structural modifications to increase the capacity of the asset. These include the insertion of lamella or changes to the positioning of the feed.

• Lamella: a type of high-capacity thickener with a series of inclined plates forming channels. This configuration increases sedimentation capacity.

• Super thickeners: the big difference lies in the half-height feed. Its principle is to flocculate the feed and feed the already flocculated pulp at half height. In this way, the flocs grow by incorporating solid particles and other flocs.

Thickeners X Clarifiers

Both are considered sedimentation assets, but the object of interest is different. In other words, the aim of thickeners is to thicken commercially valuable material or tailings. Clarifiers, on the other hand, have the function of generating a maximally clarified product (overflow). For this to happen, the concentration of solids in the clarification feed has to be less than (5%) and the concentration of solids in the underflow is generally above 40%.

Industrial thickener applications

Thickening produces a thickened product (underflow), which becomes suitable for the next operation: pumping, filtering, conditioning, etc. In some cases, flocculants are applied to aggregate the fine particles, contributing to sedimentation. It is therefore useful for:

• Obtaining pulps with suitable concentrations, for example: raising the percentage of solids in an iron ore pulp from 45 to 70%, to be pumped through a pipeline – concentration thickeners;

• Thickening of tailings with a high concentration of solids for more efficient transportation and disposal – tailings thickeners;

• Recovery of water for industrial recycling in order to recover the supernatant flow as recirculation water for the ore beneficiation process;

• Recovery of solids or solution from leaching operations, used in hydrometallurgical processes.