Extraction of Highly Reactive Metals

Metals are found in ores generally in the form of combination with other types of elements or metals. Thus, as a result, once the metal ore has been extracted from the ground, they need to be converted into its pure metal form. This process of extracting metals from their ore is known as metal extraction. There are different techniques of metal extraction, and each of these processes requires a certain number of steps to transform the ore into a free metal. This process takes into account the type of the metal ore, the impurities present in it and their specific nature, and the level of reactivity of the metal that needs to be extracted. We shall be discussing the extraction process of moderately reactive metals further in this article.   

How are Highly Reactive Metals extracted?

If we look right at the first few metals of the reactivity series, we will come across highly reactive metals such as Caesium (Cs) > Potassium (K) > Sodium (Na) > Lithium (Li) > Calcium (Ca) > Magnesium (Mg) > Aluminum (Al) > Zinc (Zn) > Iron (Fe). These metals can react with cold or hot water in order to create steam that contains hydrogen gas and hydroxides. If we go from magnesium to chromium, the next 4 metals are known as active metals since they can react with steam or hot water in order to create hydrogen gas and oxides. The 6 elements from iron to lead can be recycled from hydrogen from sulfuric, nitric, and hydrochloric acids. The oxides of the metals can be lowered by warming them up along with hydrogen gas, carbon, or carbon monoxide.

The process of Electrolytic Reduction turns the concentrated ores into metal oxides. Since carbon is of less reactivity as compared to the listed metals, carbon cannot be used to reduce them.

• Electrolytic reduction: In the electrolytic reduction process, electricity is used to pass through a dissolved or molten ionic substance, which results in the electrodes reacting chemically and the elements succumbing to decomposition. The combined state of these metals’ oxides, hydroxides, and chlorides are usually reduced electrically with the help of this process. The metals are eventually collected in the cathode. Several metals can be obtained using this process, such as Na, K, or Al. As electricity is used to pass through a dissolved solution of sodium chloride or molten sodium chloride, the sodium metal will be collected at the cathode.
  
  

Na + + e − Na

2 Cl − − e − Cl2

2 NaCl 2Na + Cl2 

• The electrolysis process of Aqueous Sodium Chloride: The aqueous solution of sodium chloride is actually dissociated, so it is found as chloride and sodium ions. In this aqueous solution, the process of electrolysis of Aqueous Sodium Chloride is much simpler. However, water can go through reduction as well as oxidation reactions at several different potentials. Thus, the reduced or oxidised element is actually sodium and chloride ions, along with the molecules of water. Two competing reactions can happen at the cathode and the anode.

At the cathode, if a reduction reaction takes place, we will find the pH level at 7. The water can be transformed into hydrogen gas, while the sodium ions can then be turned into sodium metal.

2H2O (l) + 2e – H2 (g) + 2OH –

Na + (l) + e – Na (l)

At the anode, we will find the pH level at 7, which means an oxidation reaction will take place. The water will be oxidised to give out oxygen, or a chloride ion can be oxidised in order to create chlorine molecules.

2H2O O2(g) + 4H +

2Cl – Cl2 + 2e – 

• Electrolysis of Alumina that is fused: The negative electrode is actually a steel container that has a coat of carbon. Keep in mind that aluminium oxide is also a form of the ionic compound. The ions of Al3+ and O2- can shift around freely, and this conducts electric current when melted. The cathode of the alumina or cryolite solution will yield aluminium, whereas the anode will yield oxygen.

If it is a Cathode Reaction, then the formula is  4Al+3 + 12e– 4Al

If it is an Anode Reaction, then the formula is – 6O-2 – 12e– 3O2

Since aluminium is comparatively denser as compared to alumina, it will settle at the cell’s bottom and can be removed as purely liquid metal. If we look at the positive carbon anode, there will be a release of O2. CO2 will also be released at the carbon anode due to the reaction with oxygen to produce carbon dioxide gas.

• Hall-Héroult process: The Hall – Héroult process is used majorly as an industrial process that includes smelting aluminium. It involves the process of absolving aluminium oxide (alumina) that has been obtained mostly from bauxite, which is also the chief ore of aluminium under molten cryolite, thus electrolysing the already melted salt bath, generally within a cell. The aluminium is dissolved at 950 °C (1,750 °F). This process will collect aluminium metal at the cathode and oxygen gas at the anode.

Conclusion

Metals are found in ores generally in the form of combination with other types of elements or metals. Thus, as a result, once the metal ore has been extracted from the ground, they need to be converted into its pure metal form. This process of extracting metals from their ore is known as metal extraction. The process of electrolytic reduction is used to turn the concentrated ores into metal oxide. Since carbon is of less reactivity than these metals, carbon cannot be used to reduce them.