Problem 133 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following ores is best concentrated by froth floatation method? (a) cassiterite (b) galena (c) malachite (d) magnetite

Step-by-Step Solution

Answer

Galena is best concentrated by froth flotation.

Step 1: Understanding Froth Flotation

Froth flotation is a method used to separate hydrophobic materials from hydrophilic materials. It is most commonly used for sulfide ores, where the ore particles are made to attach to air bubbles and float to the surface.

Step 2: Characteristics of Ores

Consider the properties of each option. Cassiterite (tin oxide) and magnetite (iron oxide) are oxide ores, which are not typically processed using froth flotation. Malachite (copper carbonate hydroxide) is a carbonate ore, also not typically used with this method. Galena is a sulfide ore.

Step 3: Identifying Sulfide Ores

Galena is a lead sulfide ( ext{PbS}) and is known to be effectively concentrated by froth flotation because sulfide ores can be made hydrophobic easily.

Step 4: Conclusion

Since froth flotation is most effective for sulfide ores, and galena is a sulfide ore, it is the best candidate for concentration using this method.

Key Concepts

Sulfide Ores

Sulfide ores are types of mineral deposits that contain sulfide minerals, typically consisting of metal elements combined with sulfur. These ores are a significant source of metals such as lead, zinc, copper, and nickel. The chemical structure of sulfide ores often makes them ideal for certain processing techniques, particularly froth flotation.

Froth flotation is highly effective for sulfide ores because they can be easily made hydrophobic. This means that the ore particles repel water and prefer to attach to air bubbles. This property is crucial in separating the sulfide particles from the surrounding material during the flotation process.

• Sulfide ores often include pyrite (iron sulfide), chalcopyrite (copper iron sulfide), and galena (lead sulfide).
• The extraction of metals from sulfide ores can involve both flotation and smelting techniques.

Understanding how these ores behave and how to extract valuable metals from them is central to efficient mineral processing.

Galena Concentration

Galena is a primary ore of lead and consists mainly of lead sulfide (\( \text{PbS} \)) which is dense and often has a metallic sheen. It is one of the most studied and economically important sulfide minerals. Given its properties, galena is highly suitable for concentration by froth flotation.

During the froth flotation process, galena particles are made hydrophobic. This is done using special reagents that selectively bind to galena surfaces. Once hydrophobic, the galena particles attach to air bubbles that are introduced into the slurry, allowing them to float to the surface while other non-target materials remain in the suspension.

• Galena can also contain trace amounts of silver, which can make the concentration even more valuable.
• Efficient concentration of galena often involves fine grinding to liberate the galena grains from other minerals and gangue.

This method is advantageous due to the high purity of lead achieved and its effectiveness in treating fine particles.

Hydrophobic Materials Separation

Froth flotation capitalizes on the hydrophobic and hydrophilic properties of particles to achieve separation. In mineral processing, hydrophobic materials prefer to avoid water molecules and attach to air bubbles instead, facilitating their separation from the hydrophilic particles that remain in the aqueous phase.

The process begins by mixing the pulverized ore with water and certain chemicals known as flotation reagents. These reagents are crucial as they modify the surface properties of the minerals, making some hydrophobic. When air is bubbled through this slurry, the hydrophobic particles attach to the rising bubbles and form a froth on the surface, which can be collected.

Key aspects of hydrophobic materials separation include:

• Selection of appropriate reagents to ensure only target materials become hydrophobic.
• Control of air bubble size to optimize the attachment of mineral particles.

This separation method is widely used because of its efficiency and the high grade of concentrated ore that it produces.

Lead Sulfide

Lead sulfide, chemically denoted as \( \text{PbS} \), is a significant mineral in mining due to its role as the primary source of lead. It forms in hydrothermal veins, often alongside other minerals like sphalerite and quartz. As a sulfide mineral, lead sulfide readily undergoes froth flotation, making it an excellent candidate for this beneficiation method.

This mineral is crucial for producing lead in various industries, including battery manufacturing, construction, and radiation shielding. Its shiny, metallic luster and cubic crystal structure contribute to its easy identification and processing.

In galena, which is a form of lead sulfide, flotation helps concentrate the lead by exploiting the mineral's natural hydrophobicity. Combined with reagents, this property is enhanced, making \( \text{PbS} \) particles float and separate from other materials.

• Lead extraction from galena involves not only flotation but also subsequent smelting and refining processes to achieve high purity lead.
• Safety measures are critical because lead compounds can be toxic.

Understanding lead sulfide's properties ensures better recovery rates during mineral processing.