Problem 128 - A Complete Resource Book in Chemistry for JEE Main

Question

For which of the following metals may be hydrometallurgical extractive method be employed? (a) copper (b) iron (c) chromium (d) tin

Step-by-Step Solution

Answer

Copper may be extracted using hydrometallurgical methods.

Step 1: Understanding Hydrometallurgy

Hydrometallurgy involves the use of aqueous solutions to extract metals from their ores. It often includes processes like leaching, solution concentration, and metal recovery. It is particularly suited for metals that form soluble complexes in an aqueous solution or when it's beneficial for lower energy costs compared to traditional pyrometallurgy.

Step 2: Evaluate Copper

Copper can be extracted hydrometallurgically using processes like heap leaching with sulfuric acid, which dissolves the copper ions from ore. This makes it a candidate for hydrometallurgical extraction.

Step 3: Evaluate Iron

Iron is typically extracted using pyrometallurgical methods like blast furnaces because its common ores, such as hematite and magnetite, are not easily soluble in water or acidic solutions, making hydrometallurgy inefficient for iron extraction.

Step 4: Evaluate Chromium

Chromium extraction usually involves pyrometallurgical processes because chromium ores do not react well in aqueous conditions suitable for hydrometallurgy, making them difficult to process using this method.

Step 5: Evaluate Tin

Tin ores, like cassiterite, are not particularly soluble in available aqueous solutions used in hydrometallurgy, leading to the predominant use of pyrometallurgical methods for extraction. Thus, it's not commonly extracted hydrometallurgically.

Step 6: Determine the Suitable Metal

Based on the analysis, copper is suitable for hydrometallurgical extractive methods as it can be effectively leached into solution using aqueous media.

Key Concepts

Copper Extraction

Copper extraction through hydrometallurgy is an efficient and widely used method in metal extraction processes. The key advantage of hydrometallurgical processes for copper is their ability to dissolve copper ions from copper-bearing minerals using aqueous solutions, such as dilute sulfuric acid.
This process is often applied in methods like heap leaching, where large piles of copper ore are sprinkled with an acidic solution.
As the solution percolates through the heap, it dissolves copper ions:

• The copper-rich solution, known as 'pregnant leach solution,' collects at the bottom of the heap.
• Subsequent processes then recover the copper from this solution, often involving solvent extraction and electrowinning methods, which are highly effective at extracting and refining copper ions into pure metal form.

Using hydrometallurgy to extract copper provides numerous advantages, including lower energy costs compared to pyrometallurgical methods and the ability to process lower-grade ores economically.

Aqueous Solutions

Aqueous solutions play a crucial role in the hydrometallurgical extraction of metals. These solutions typically involve water as the solvent and are often acidic in nature. They serve multiple functions in metal extraction processes.
For copper extraction, aqueous solutions aid in leaching processes by hosting chemical reactions that dissolve metal ions from ore bodies.
Some key points about aqueous solutions in hydrometallurgy include:

• Aqueous solutions are efficient in transporting dissolved metal ions, which are later subjected to concentration and recovery processes.
• The typical solution for copper leaching is dilute sulfuric acid, which reacts with minerals to form soluble copper sulfate.
• Control of the acidity, temperature, and concentrations in these solutions is vital to maximize metal recovery and process efficiency.

Overall, the ability of aqueous solutions to facilitate these chemical interactions makes them indispensable in hydrometallurgy.

Metal Leaching

Metal leaching is an essential process in hydrometallurgy, allowing for the extraction of metals from ores via chemical reactions. This involves dissolving target metals into a liquid medium, typically an aqueous solution.
Leaching is often conducted in large, open-air setups such as heaps or tanks, where the ore is exposed to leaching agents.
Key factors in effective metal leaching include:

• The nature of the ore and its mineral composition, which dictate the choice of leaching reagents and methods.
• The reactivity of the metals with the leaching solution, where more reactive metals or minerals tend to leach more effectively.
• Temperature, pH, and the duration of leaching processes strongly influence the rate of metal dissolution and recovery.

In the context of copper, sulphuric acid is beneficial as it enhances the leaching of copper ions, allowing the efficient extraction of copper from various ore forms.