Metallurgy & Hydrometallurgy: Electrolytic Reduction & Processes, Lecture notes of Chemistry

Download Metallurgy & Hydrometallurgy: Electrolytic Reduction & Processes and more Lecture notes Chemistry in PDF only on Docsity!

General Principle of Metallurgy

P.S. Sengupta

Second Class

Electrolytic Reduction

It is the method of reducing metals with the help of electrolysis.

Metals that are placed high in the reactivity series are highly

electropositive and they cannot be reduced by carbon as reducing

agent.

The electrolytic reduction is a type of electrolysis. The oxides ,

hydroxide and chlorides of metals in fused state are electrically

reduced by using this method. The metals are extracted at the

cathode.

Certain metals like Na , K, Mg , Ca , Al are obtained by electrolytic

reduction process. This method assures purity of metals obtained.

continued

Hydrometallurg y is the process of extraction and refining that involves the use of water and aqueous solutions. It is carried out at moderate temperatures and is generally carried out in three steps: (a) Leaching: metal ions are extracted from their ore by water/acids/bases/salt solutions. Redox reactions that occur are often essential. (b)Purification and concentration: Impurities are separated either by absorption on the surface of activated charcoal, ion exchange, or water evaporation; leaving behind a more concentrated solution. ( c ) Precipitation: the process of electrolysis is often used to precipitate the desired metal ions in an ionic solid or reduce them to their free metal.

Solvent extraction In the solvent extraction , a mixture of an extranct in a diluent is used to extract a metal from one phase to another. In solvent extraction this mixture is often referred to as the "organic" because the main constituent (diluent) is some type of oil. The PLS (pregnant leach solution) is mixed to emulsification with the stripped organic and allowed to separate. The metal will be exchanged from the PLS to the organic they are modified. The resulting streams will be a loaded organic and a raffinate. When dealing with electrowinning, the loaded organic is then mixed to emulsification with a lean electrolyte and allowed to separate. The metal will be exchanged from the organic to the electrolyte. The resulting streams will be a stripped organic and a rich electrolyte. The organic stream is recycled through the solvent extraction method, while the aqueous streams cycle through leaching and electrowinning processes respectively. Solvrnt extraction known as liquid-liquid extraction is a method to separate compounds based on their relative solublities in two different immiscible liquid , usually water and an organic solvent

Chromatography employs continuous adsorption and desorption on a packed bed of a solid to purify multiple components of a single feed stream. In a laboratory setting, mixture of dissolved materials are typically fed using a solvent into a column packed with an appropriate adsorbent, and due to different affinities for solvent (moving phase) versus adsorbent (stationary phase) the components in the original mixture exit the column in the moving phase at different rates, which thus allows to selectively collect desired materials out of the initial mixture. The eluent or eluant is the "carrier" portion of the mobile phase. It moves the analytes through the chromatograph. In liquid chromatography, the eluent is the liquid solvent; in gas chromatography, it is the carrier gas. Eluate. The eluate is the analyte material that emerges from the chromatograph. It specifically includes both the analytes and solutes passing through the column, while the eluent is only the carrier.

Ion exchange

Chelating agents, natural Zeolite, activated carbon, resins, and liquid organics impregnated with chelating agents are all used to exchange cations or anions with the solution Selectivity and recovery are a function of the reagents used and the contaminants present. **Na

is exchanged by Ca 2 + ion**.

Actual method and surface interaction

1. Negatively charged material dodged
2. Big voume of aqueous solution 3 .Sorption and valuable cation will exchange with H

ion

4. Impurities and H

ion exchange

5. Small volume of elluent will make more concentration than input concentration 6 .The elluent will exchange.

Metal recovery Electrolysis Electrowinning and electrorefining respectively involve the recovery and purification of metals using electrodeposition of metals at the cathode, and either metal dissolution or a competing Oxidation reaction at the anode. Precipitation Precipitation in hydrometallurgy involves the chemical precipitation of either metals and their compounds or of the contaminants from aqueous solutions. Precipitation will proceed when, through reagent addition, evaporation, pH change or temperature manipulation, any given species exceeds its limit of solubility.