Dehydration and Dehydroxylation Process

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Questions and Answers

What type of furnace is used for handling materials of mixed particle sizes and lumps which disintegrate during the process?

Sintering furnace

Fluidized bed reactor

Shaft furnace

Rotary kiln (correct)

What is the typical temperature range for roasting sulfide ores?

Above 1200 °C

Below 500 °C

Above 1500 °C

Below 900 to 1000 °C (correct)

What is the primary purpose of roasting in sulfidic sources of metals?

To remove impurities from the ore

To reduce the sulfur content of the ore

To produce metal oxides and sulfur dioxide (correct)

To convert the ore into a more reactive form

What is the process of producing agglomerated fine powders based on atomic diffusion?

Sintering Signup and view all the answers

What type of furnace is commonly used for calcination of materials with small and uniform particle sizes?

Fluidized bed reactor Signup and view all the answers

What is the primary difference between pyrometallurgy and hydrometallurgy in copper extraction?

Type of ore used Signup and view all the answers

What is the purpose of sulfation roasting in metal extraction?

To oxidize metal sulfides to sulfates Signup and view all the answers

What is the final product of dead roasting in metal extraction?

Metal oxides Signup and view all the answers

What is the primary reason for removing water from the material?

To improve the product quality and yield Signup and view all the answers

What is the term used to describe the removal of water of crystallization from a material?

Dehydration Signup and view all the answers

What is the general reaction for calcination?

Solid 1 = Solid 2 + Gas Signup and view all the answers

What is the primary difference between calcination and drying?

Endothermicity Signup and view all the answers

What is the primary function of calcination in process metallurgy?

To decompose carbonates Signup and view all the answers

What is the most suitable type of furnace for calcining coarse limestone?

Shaft furnace Signup and view all the answers

What is the primary factor that governs the rate of calcination?

Heat supply Signup and view all the answers

What is the decomposition of hydroxides also referred to as?

Calcination Signup and view all the answers

What is the primary means of extracting metals from ores or other materials in pyrometallurgy?

Heat Signup and view all the answers

What is the purpose of ore-dressing in pyrometallurgy?

To prepare ore using crushing, grinding, washing, drying, flotation, etc. Signup and view all the answers

What is the result of roasting in pyrometallurgy?

Conversion of metal sulfide to metal oxide or to a free metal Signup and view all the answers

What is the purpose of calcination in pyrometallurgy?

To decompose carbonates and other compounds, causing loss of moisture, reduction or oxidation Signup and view all the answers

What is the primary purpose of smelting in pyrometallurgy?

To isolate an element from its ore using heat and a reduction agent Signup and view all the answers

What is the purpose of refining in pyrometallurgy?

To purify an impure material Signup and view all the answers

What is the purpose of drying in pyrometallurgy?

To remove water from materials, reducing the weight of the material handled Signup and view all the answers

What is a metallurgical reactor defined as?

A piece of equipment designed to carry out a certain type of reaction and/or a certain unit process Signup and view all the answers

Study Notes

Dehydration and Calcination

Water can be present in materials as free water, water of crystallization, or combined water.
Dehydration refers to the removal of water of crystallization, while dehydroxylation is the removal of water, resulting in the breakdown of hydroxyl groups to form water vapor.
Calcination is a thermal decomposition process that can be expressed as Solid 1 → Solid 2 + Gas.
Calcination is often used in process metallurgy, where the compound Solid 1 is usually a carbonate, and Solid 2 is an oxide.
Example: CaCO3 (s) → CaO (s) + CO2 (g)
Calcination is more endothermic than drying, requiring a relatively high temperature.

Objectives of Calcination

Bring about thermal decomposition
Induce phase transition
Remove volatile fractions such as CO2 and H2O

Types of Furnaces for Calcination

Shaft furnace: suited for calcining coarse limestone
Rotary kiln: used for handling materials of mixed particle sizes and lumps
Fluidized bed reactor: used for materials of small and uniform particle size

Pyrometallurgy

A branch of metallurgy that uses heat as the primary means of extracting metals from ores or other materials.
Pyrometallurgic techniques include:
- Ore-dressing
- Sintering
- Roasting
- Calcination
- Smelting
- Refining
Normally, the final product is in the molten form.

Pyrometallurgic Techniques

Ore-dressing: preparation of ore using crushing, grinding, washing, drying, flotation, etc.
Roasting: heating a sulfide ore in air to convert it to a metal oxide or free metal.
Calcination: decomposition of carbonates and other compounds, causing loss of moisture, reduction or oxidation using high temperature.
Sintering: process that produces agglomerated fine powders through atomic diffusion.
Smelting: chemical process to isolate an element from its ore using heat and a reduction agent.
Refining: purification of an impure material.

Reactor Design

A metallurgical reactor is a piece of equipment designed to carry out a certain type of reaction or unit process.

Drying

Removal of water is necessary to reduce the weight of the material handled.
Water removal prevents charge blow off in electric furnaces.

Roasting

Mostly used for sulfidic sources of metals.
Oxidation of metal sulfides to produce metal oxides and sulfur dioxide.
Carried out by heating the sulfides in air or oxygen below the melting points of the sulfides and oxides.

Objectives of Roasting

Partial oxidation causing loss of part of the sulfur content.
Oxidation to sulfates (sulfation roasting).
Complete removal of sulfur, i.e., conversion to oxides (dead roasting).

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Description

Learn about the importance of water removal in materials and the difference between dehydration and dehydroxylation processes. Understand how water presence affects product quality and yield.