Extraction of Alkali Metals

Extraction is a process of separation of an element / compound from a mixture. Some examples of extraction are liquid-liquid extraction, solid phase extraction etc. 

Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs) and Francium (Fr) are Alkali metals. These elements along with Hydrogen form Group 1 that lies in the S-Block  of the periodic Table. Extraction of Alkali metals means separation of alkali metals from their ores, which is a complicated process as they cannot be extracted through the usual method of extraction of metals.

Why is Extraction of Alkali metal complicated?

Some properties of Alkali metals make it difficult for them to be extracted from their ores. 

We cannot extract Alkali metals by reduction of their chlorides and oxides, as they are strong reducing agents. They cannot be displaced by other metals from aqueous solution of their salt, as they are highly electropositive in nature. The standard electrode potential of alkali metals is much lower as compared to water, making hydrogen release at cathode. So, alkali metals cannot also be extracted by the process of electrolysis. Even when we use mercury at the cathode, the alkali method deposited at the cathode will combine with mercury to form an amalgam whose extraction is once again complicated.

Hence, all elements of alkali metals are extracted through a different process. Let’s have a look at that. 

Extraction of Lithium (Li) 

Lithium is an alkali metal that has a good amount of heat and electrical conductivity.Hence lithium is used in the manufacturing of glass , pharmaceuticals, batteries, lithium oils, high temperature lubricants etc. 

Due to its high reactivity, pure elemental lithium is not found in nature. Lithium always exists as a constituent of salt and other compounds. Lithium is extracted by the process of electrolysis of dry lithium chloride and potassium chloride. The electrode cell is operated at 723K temperature and current of 8-9 V. 

The following reaction takes place during electrolysis: 

LiCl = Li+  + Cl- 

At Cathode:  Li+  +  e-  —> Li 

At Anode: 2Cl-  – 2e-   ——-> Cl2

Lithium obtained through this process is 99% pure and is stored in paraffin wax. 

Extraction of Sodium (Na)

Sodium is the sixth most abundant metal in the earth crust. Sodium with chlorine forms Sodium Chloride (NaCl) which is a very important compound for us. In its metallic forms , sodium is used to make easters and many other organic compounds. It is also used as a reducing agent for the extraction of boron and silicon. 

The extraction of Sodium takes place by Down’s Process in which sodium is obtained by the electrolytic process of fused sodium Chloride. In this process a fused mixture of sodium chloride and calcium chloride is kept in Down’s cell at temperature 873 K using graphite anode and Iron cathode. Sodium is released at cathode and Cl2 gas is released at anode.

NaCl —-> Na+ + Cl – 

At cathode: Na+ + e– —-> Na 

At anode: Cl– ——–> Cl + e–

Cl + Cl ——-> Cl2

Pure sodium is obtained at cathode while Chlorine gas is released at anode. 

Extraction of Potassium

Potassium is a light, white and a soft metal. It is a highly reactive metal especially with water and air. It is the 7th most abundant metal on the earth crust. It is used for the manufacturing of glass, soaps, baking powder, tanning creams etc. 

Potassium is obtained from Potassium Chloride. It can only be obtained through the process of thermochemical technique where sodium acts as a reductant. In this cycle, molten potassium chloride is consistently taken care of to a stuffed refining segment where it is again heated.. The liquid chloride then undergoes sodium fumes that are streaming up through the segment delivered by a gas-terminated reboiler . The subsequent results of this cooperation are sodium chloride and potassium metal at equilibrium

Na + KCl = NaCl + K 

Extraction of Rubidium (Rb)

Rubidium is a soft, ductile, malleable metal with a low melting point. It is used in telecommunications, biomedical, space technology, opticals, laser technology etc. Rubidium is generally produced in minor quantities from lithium or cesium rich minerals. One can also extract rubidium from mine tailings but this process is quite difficult and expensive as they require a series of physical and chemical treatments for the extraction of rubidium metal. 

Extraction of Cesium (Cs) 

Caesium is the most reactive alkali metal with a melting point of 28.5 °C. The physical and chemical properties of cesium is very similar to that of potassium and rubidium. Cesium is a very soft, ductile and pale metal , with silvery-golden colour. There are around 30 isotopes of cesium. Among them, 133Cs is the most steady one, while 134Cs and 137Cs are the most ordinarily noticed splitting results of uranium.

The extraction of cesium can be done through several processes such as precipitation, solvent extraction, adsorption ,membrane separation etc. These are some ways to extract cesium from aqueous solutions.

Extraction of Francium (Fr)

Francium is one of the rarest alkali metals on the earth. Almost twenty isotopes of francium have been found. The most steady is francium-223. Isotopes are at least two types of a component. Isotopes vary from one another as per their mass number. The mass number addresses the quantity of protons in addition to neutrons in the core of an iota of the component. The quantity of protons decides the component, however the quantity of neutrons in the molecule of any one component can change. Every variety is an isotope.

Francium is not extracted from earth’s crust. IT has barely any use because of its rarity. 

Conclusion

Majority of the alkali metals can be obtained through the process of electrolysis. Since some metals are highly reactive, they even react with air. The extraction of Alkali metals from their ores is a difficult process but somehow we have managed to find a way to extract the metals but there are still many complications. Francium for example is very difficult to extract as it is one of the rarest elements on earth. Caesium is usually extracted from aqueous solution whereas Na , Li and K can be extracted through electrolysis of some compounds.