Thickening Process in Slurry Management

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Questions and Answers

What is the primary purpose of monitoring the bed level in a thickener?

To maximize the feed mass flow rate

To assess the efficiency of the thickener (correct)

To control the flocculant dosage

To determine the clarity of the overflow water

Which factor is critical in controlling the clarity of the overflow water from a thickener?

Controlling the feed mass flow rate (correct)

Cake formation stage

Monitoring the bed level

Flocculant dosage rate

What is the recommended approach when there is no sample available for thickener sizing?

Experience-based sizing (correct)

Batch settling tests

Pilot plant testwork

Cylinder settling tests

Which thickener type is specifically designed to save space and is used for quickly settling slurries?

Tray thickener Signup and view all the answers

What is considered the most reliable method for thickener sizing?

Pilot plant testwork Signup and view all the answers

How does centrifugal separation enhance the settling rates of particles?

By applying centrifugal force Signup and view all the answers

What is the role of cake washing in the filtration process?

To remove impurities from the cake Signup and view all the answers

Which type of filter is commonly used in mineral processing and can operate in batch or continuous modes?

Vacuum filter Signup and view all the answers

What is the main function of a thickener in mineral processing?

To produce a clarified liquid while concentrating solids Signup and view all the answers

How is the clarified liquid produced in a thickener?

By maintaining the upward velocity of liquid lower than settling velocity Signup and view all the answers

What does the thickened underflow in a thickener represent?

The collected solid particles at the bottom of the tank Signup and view all the answers

What role does controlling residence time play in thickener operation?

It determines the thickened underflow concentration Signup and view all the answers

Which of the following factors does NOT affect thickener operation?

Color of the slurry Signup and view all the answers

What type of thickener is optimized for high throughput?

High-rate thickener Signup and view all the answers

What is the significance of the settling velocity of particles in a thickener?

It must be higher than the upward velocity of the liquid for effective thickening Signup and view all the answers

Which of the following statements is true regarding thickener design?

Conventional thickeners typically have a diameter from 2 to 200 m Signup and view all the answers

Study Notes

Thickening

Thickening is the process of removing water from a slurry to increase solid content.
Slurry is fed into a thickener tank through a central feedwell.
Solid particles settle at the bottom forming a thickened underflow.
Clarified liquid overflows a peripheral launder.
Thickened underflow is withdrawn from the tank at the bottom.

Factors Affecting Thickener Operation

Particle size and density: Larger, denser particles settle faster.
Feed solids concentration: Higher concentration leads to faster settling.
Flocculant dosage: Chemicals enhance particle aggregation, increasing settling rate.
Tank diameter and depth: Larger tanks allow for longer settling distances.
Rake speed: Slow rake speeds promote settling, while fast speeds help prevent underflow clogging.
Underflow discharge rate: Controlled discharge maintains a stable bed level.
Temperature: Higher temperatures can decrease viscosity, promoting settling.
Slurry viscosity: Low viscosity promotes faster settling rates.

Thickener Types

Conventional thickeners have an open tank design and are the most common.
High-rate thickeners are optimized for flocculation and handle high volumes.
High-density thickeners handle high concentrations of solids.
Paste thickeners are designed for extremely high solid concentration.

Thickener Operation and Control

The two primary functions of a thickener are to produce a clarified overflow and a thickened underflow.
Clarified overflow is achieved by keeping the upward liquid velocity lower than the settling velocity of the slowest particle.
Thickened underflow is achieved by controlling the residence time of the particles in the thickener.
Monitoring the bed level helps assess the efficiency of the thickener.
Controlling the feed mass flow rate determines the clarity of the overflow water.
Maintaining the flocculant dosage rate is important for optimal performance.

Thickener Sizing

Experience: Used as a rough estimate when there is no sample data.
Cylinder (or jar) settling tests: Used for a basic estimate for budget purposes.
Pilot plant testwork: The most reliable method using small-scale thickeners.
Batch settling tests are the most common method for thickener design.

Other Gravity Sedimentation Devices

Tray thickeners save space and are used for slurries that settle quickly.
Lamella thickeners minimize the distance for particle sedimentation.
Hydrocyclones utilize centrifugal force for faster separation.

Centrifugal Sedimentation

Centrifuges increase settling rates by applying centrifugal force.
Hydrocyclones are simpler and cheaper than centrifuges but have limitations on solid concentration and particle size.
Centrifuges are more expensive and complex but offer higher clarifying power.

Filtration

Filtration separates solids from liquids by passing a slurry through a porous medium.
Cake formation occurs as solids build up on the filter medium.
Moisture reduction removes water from the cake.
Cake washing removes impurities (optional).
Cake discharge removes the cake from the filter.
Medium washing cleans the filter medium.

Filter Types

Vacuum filters are common in mineral processing and can be batch or continuous.

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Description

This quiz covers the thickening process in slurry management, focusing on factors that affect thickener operation. It discusses the mechanisms of solid settlement and the importance of parameters such as particle size, feed concentration, and chemical additives. Test your understanding of these key concepts involved in increasing solid content in slurries.