Question

Phosphorus is one of the impurities present in pig iron that is removed in the basic-oxygen process. Assuming that phosphorus is present as \(\mathrm{P}\) atoms, write equations for its oxidation and subsequent reaction in the basic slag.

Short answer

The phosphorus oxidation reaction is \text{4P} + \text{5O}_2 \rightarrow \text{2P}_2\text{O}_5 and the reaction with basic slag is \text{P}_2\text{O}_5 + 3\text{CaO} \rightarrow \text{Ca}_3(\text{PO}_4)_2.

Step-by-step solution

Write the Oxidation Reaction

The first step in the removal of phosphorus (\text{P}) in the basic-oxygen process is its oxidation. The oxidation of phosphorus can be represented by the following chemical equation:\[\text{4P} + 5\text{O}_2 \rightarrow 2\text{P}_2\text{O}_5\]This shows that one mole of phosphorus reacts with oxygen to form phosphorous pentoxide \text{P}_2\text{O}_5.

Write the Reaction with Basic Slag

In the basic-oxygen process, the \text{P}_2\text{O}_5} further reacts with basic slag (primarily composed of \text{CaO}, calcium oxide). The reaction can be represented as:\[\text{P}_2\text{O}_5 + 3\text{CaO} \rightarrow \text{Ca}_3(\text{PO}_4)_2\]Here, phosphorous pentoxide reacts with calcium oxide to form calcium phosphate, which is removed in the slag.

Key concepts

Oxidation Reaction

The basic-oxygen process begins with the oxidation of phosphorus present in pig iron. This is crucial because oxidation transforms phosphorus into a form that can be easily removed. The oxidation process can be represented by the chemical equation:

\(\text{4P} + 5\text{O}_2 \rightarrow 2\text{P}_2\text{O}_5\).

Here, four atoms of phosphorus (\text{P}) react with five molecules of oxygen (\text{O}_2) to create phosphorus pentoxide (\text{P}_2\text{O}_5).

During this reaction:

• The phosphorus atoms lose electrons, which means they are oxidized.
• Oxygen molecules gain those electrons to form phosphorus pentoxide.

This oxidation reaction is a redox reaction, meaning it involves both reduction and oxidation processes simultaneously.

Phosphorus Impurities

The presence of phosphorus as an impurity in pig iron affects its quality. Phosphorus is considered a detrimental impurity because it makes steel brittle and less ductile.

Here’s why dealing with phosphorus impurities is essential:

• Phosphorus in small amounts can improve strength, but excessive phosphorus causes brittleness and poor durability in steel.
• Removing phosphorus during steel manufacturing improves the steel's mechanical properties and longevity.

In the basic-oxygen process, steel manufacturers aim to minimize phosphorus content to ensure the steel's quality.

Basic Slag Reaction

Once phosphorus is oxidized to phosphorus pentoxide (\text{P}_2\text{O}_5), it needs to be removed from the melt. This is done by reacting it with basic slag. Basic slag is primarily composed of calcium oxide (\text{CaO}). The reaction forms calcium phosphate, which is part of the slag and can be separated from the steel.

The chemical equation for this reaction is: \(\text{P}_2\text{O}_5 + 3\text{CaO} \rightarrow \text{Ca}_3(\text{PO}_4)_2\).

In simpler terms:

• Phosphorous pentoxide (\text{P}_2\text{O}_5}) reacts with calcium oxide (\text{CaO}) present in the basic slag.
• They form calcium phosphate (\text{Ca}_3(\text{PO}_4)_2).

The calcium phosphate formed is incorporated into the slag, allowing it to be easily removed from the molten iron, thus purifying the steel.

Chemical Equations

Understanding the chemical equations involved in the basic-oxygen process is essential. These equations illustrate the transformation of phosphorus impurities into removable compounds.

Here are the key equations:

• Oxidation of Phosphorus: \(\text{4P} + 5\text{O}_2 \rightarrow 2\text{P}_2\text{O}_5\)
• Formation of Calcium Phosphate: \(\text{P}_2\text{O}_5 + 3\text{CaO} \rightarrow \text{Ca}_3(\text{PO}_4)_2\)

These equations are fundamental to understanding the removal of phosphorus in the basic-oxygen process. Each one details the reactants and products involved:

• The oxidation reaction shows the conversion of phosphorus to phosphorus pentoxide.
• The reaction with basic slag shows how phosphorus pentoxide forms calcium phosphate, which is separable from the molten iron.

Knowing these chemical reactions helps you grasp how impurities are systematically and effectively eliminated from pig iron during steel production.