Animated Solution for Chemistry - Metallurgy: The correct statement(s) related to processes involved in the extraction of metals is(are)

The extraction of metals from their ores is one of the most fascinating applications of chemistry. It is a beautiful symphony of thermodynamics, kinetics, and inorganic reactions. In this problem, we are presented with four different metallurgical processes. Our goal is to act as metallurgical detectives and verify the accuracy of each statement. Let's break them down one by one.

We begin with option (A), which discusses the roasting of Malachite. Malachite is a stunning green mineral, chemically known as basic copper carbonate, with the formula $CuC{O}_3\cdot Cu(OH{)}_2$.

When we subject Malachite to roasting—which involves heating it strongly—it undergoes thermal decomposition. The heat breaks down the carbonate and hydroxide components, releasing carbon dioxide and water vapor.

The solid residue left behind is cupric oxide, $CuO$. In the realm of mineralogy, naturally occurring cupric oxide is known as Tenorite. However, the statement claims that roasting produces Cuprite, which is cuprous oxide, $C{u}_{2}O$. Because the oxidation state of copper remains $+2$ during this decomposition, it cannot form the $+1$ oxide without a reducing agent. Therefore, statement (A) is incorrect.

Next, we examine option (B), focusing on Calamine. Calamine is the traditional name for zinc carbonate, $ZnC{O}_3$.

The process mentioned here is calcination. Calcination is a fundamental metallurgical step where an ore is heated strongly in the absence or limited supply of air. The primary goal is to drive off volatile impurities or decompose carbonates.

When $ZnC{O}_3$ is calcined, it readily decomposes into zinc oxide ($ZnO$) and carbon dioxide gas. The resulting zinc oxide is known by its mineral name, Zincite. This perfectly matches the statement provided. Thus, statement (B) is absolutely correct.

Moving on to option (C), we delve into the extraction of copper from Copper pyrites, $CuFe{S}_2$. This ore is the most important source of copper, but it comes with a stubborn companion: iron.

During the smelting process in a reverberatory furnace, the ore is heated strongly. The iron present in the ore oxidizes to form ferrous oxide, $FeO$. Left alone, this basic oxide would be a nuisance. To eliminate it, metallurgists add an acidic flux, specifically silica ($Si{O}_2$).

The basic $FeO$ and the acidic $Si{O}_2$ react beautifully at high temperatures to form molten iron silicate, $FeSi{O}_3$. This product is known as slag. Because slag is lighter than the molten copper matte, it floats on top and can be easily skimmed off. This elegant chemical trick effectively removes the iron impurity. Hence, statement (C) is correct.

Finally, we arrive at option (D), which describes the Macarthur-Forrest cyanide process for extracting silver. This is a classic example of hydrometallurgy, where metals are extracted using aqueous solutions.

The process begins by treating impure silver with a dilute aqueous solution of potassium cyanide ($KCN$). However, silver is a noble metal and won't dissolve easily. This is where oxygen plays a crucial role. By bubbling atmospheric oxygen through the mixture, the silver is oxidized. This allows it to react with the cyanide ions to form a highly soluble complex, potassium dicyanoargentate, $K[Ag(CN{)}_2]$.

Once the silver is safely dissolved in the solution, the impurities are filtered away. To recover the pure silver, we introduce zinc dust. Zinc is significantly more electropositive (more reactive) than silver. It acts as a powerful reducing agent, displacing the silver from the complex to form $K_2[Zn(CN{)}_4]$, while pure silver metal precipitates out.

This statement flawlessly describes the process, making statement (D) correct.

After a thorough chemical investigation of each process, we have our answers. The roasting of Malachite yields Tenorite, not Cuprite. The calcination of Calamine successfully produces Zincite. Silica is indeed the perfect flux to remove iron from Copper pyrites. And the cyanide process brilliantly utilizes oxygen and zinc to extract silver.

Therefore, the correct statements are (B), (C), and (D).