Dewatering Processes
Most processing operations have a dewatering stage at the end of the process, and generally, dewatering processes are divided into three stages:
- Sedimentation/settling of solid particles (Thickeners)
- Filtration (Filters)
- Drying using heat (Dryers)
Sedimentation is the most efficient method for separating solid particles from liquids, especially when there is a significant density difference between the solid and water. However, in most mineral processing operations, dewatering typically involves a combination of sedimentation and filtration methods. The primary functions of thickeners include:
- Controlling the concentration/solid percentage of the pulp for downstream flows
- Dewatering (increasing solid content) of the pulp before filtration processes
- Water recovery and reuse as process water in production lines
- Water treatment through the removal of salts and reduction of water hardness (Clarifiers)
The most important factor in selecting thickeners is the required area for particle settling. The size of the thickener depends on factors such as the input material flow rate, pulp solidity, output solidity, and the settling rate of solid particles.
The main components of a thickener include the tank/body (steel or concrete), feed-well, solid discharge rake, drive system, and the bridge connecting the body to the center of the thickener. The diagram below illustrates an overview of the thickener and its distinguishing components.
Two control systems used to maintain the solid particle sedimentation performance within thickeners include the following:
- Maintaining the amount of settled solid particles by adjusting the underflow discharge rate.
- Maintaining the level of settled solid particles by adjusting the flocculant dosing rate.
Operational control system in thickeners leads to achievement of the following optimal conditions:
- Higher average pulp density of solid materials in underflow stream
- Reduced flocculant consumption for settling solid particles
- Consistent density control (ensuring stable and continuous solid particle sedimentation conditions)