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 and tin can be extracted using hydrometallurgical methods.

Step 1: Understanding Hydrometallurgy

Hydrometallurgy is a method for extracting metals from their ores using aqueous solutions. It's typically used for metals that can easily be dissolved in water or other solvents, often at low temperatures.

Step 2: Examining Copper for Hydrometallurgy

Copper is commonly extracted using hydrometallurgical processes like leaching. An example is the leaching of copper from oxide ores using acidic solutions, making copper suitable for hydrometallurgical extraction.

Step 3: Examining Iron for Hydrometallurgy

Iron is typically extracted by pyrometallurgical methods, such as blast furnace processing. It's less commonly processed hydrometallurgically due to its resistance to aqueous dissolution at practical temperatures and conditions.

Step 4: Examining Chromium for Hydrometallurgy

Chromium is usually not extracted using hydrometallurgical methods. Instead, pyrometallurgical processes are favored for its extraction, as chromium ores are not easily amenable to dissolution in aqueous solutions.

Step 5: Examining Tin for Hydrometallurgy

Tin can be extracted using hydrometallurgical methods. Tin ores, such as cassiterite, can be converted using leaching processes. This method is sometimes used to recover tin efficiently from waste and low-grade ores.

Step 6: Conclusion and Answer

Based on the examination of each metal, copper and tin may be extracted using hydrometallurgical methods. Iron and chromium do not typically employ these methods.

Key Concepts

Copper Extraction

Copper extraction involves obtaining copper from its ores through various methods, including hydrometallurgy. This process often begins with the mining of copper ores, followed by crushing and grinding to produce a fine powder. The powder is treated with a solvent in a process known as leaching.
During leaching, an acidic solution is used to dissolve the copper out of the ore, resulting in a copper-rich solution called a "pregnant leach solution" (PLS). The solution undergoes further processing, typically through solvent extraction and electrowinning, to produce pure copper metal.
One key advantage of hydrometallurgy for copper is its ability to process low-grade ores that would be unsuitable for traditional smelting techniques. It is also considered more environmentally friendly due to lower energy requirements and reduced air pollution.

Tin Extraction

Tin extraction can also be accomplished through hydrometallurgical methods, particularly for ores such as cassiterite, which is tin(IV) oxide. This process is ideal for tin because it allows for the recovery of metal from lower grade ores and even from waste materials.
In the leaching process for tin, an acidic or alkaline solution is often employed to dissolve the tin oxides. After leaching, impurities are removed, and the tin is extracted from the solution through techniques like precipitation or electrolysis.
Hydrometallurgical methods for tin offer a pathway to reclaim metal from discarded products or from impurities in other mining operations, providing an efficient recycling strategy.

Leaching Process

Leaching is a core part of many hydrometallurgical processes. It involves using a liquid solvent to dissolve and separate metal ions from their ores. The solvent can be acidic, alkaline, or even water, depending on the metal being extracted.
Key steps in the leaching process include:

• Crushing and grinding the ore to increase the surface area for better solvent contact.
• Contacting the ore with the solvent to dissolve the desired metal ions, resulting in a solution rich in metal.
• Separating the leach solution from the remaining solid residues.
• Further processing the solution to extract pure metal, using methods like precipitation, solvent extraction, or electrowinning.

Leaching can be applied at relatively low temperatures and pressures, making it an energy-efficient method for metal extraction, particularly in hydrometallurgy.

Metal Extraction Methods

Metal extraction methods involve various techniques to harvest metals from ores, each suitable for different kinds of metals and ore types. Two primary methods are hydrometallurgy and pyrometallurgy.
Hydrometallurgy, as discussed, uses aqueous solutions to extract metals and is preferred for metals like copper and tin that dissolve easily in solvents. Its benefits include lower energy consumption and environmental impact.
On the other hand, pyrometallurgy involves high-temperature processes to extract metals. Commonly used for metals like iron and chromium, this method includes smelting and refining techniques. It requires high energy input but is well-suited for metals that are resistant to dissolution, like those processed in a blast furnace or electric arc furnace.
Each method has its own advantages and limitations, and the choice between them often depends on the specific characteristics of the ore and economic considerations.