Come today we will know about Extractive Metallurgy. Extractive Metallurgy is a branch of metallurgical engineering that studies the process and methods of extracting metals from their natural mineral deposits . The field is a materials science , encompassing all aspects of ore, washing, concentration, separation, chemical processes and extraction of pure metals and their alloys to suit various applications , sometimes for direct use as a finished product. but more often in a form that requires more work to achieve the given properties to suit the applications. [1]
The fields of ferrous and non-ferrous metallurgy are generally grouped into the categories of mineral processing , hydrometallurgy , pyrometallurgy and electrometallurgy , depending on the process adopted to extract the metal . Several processes are used for the extraction of the same metal depending on the occurrence and chemical requirements. (Extractive Metallurgy)
Mineral processing
Mineral processing begins with beneficiation , which initially involves breaking the ore into the required size, which is carried out by crushing, grinding, sieve, etc., depending on the concentration process. Thereafter, the ore is physically separated from any unwanted impurities, depending on the form of the phenomenon and or further processing is involved. Separation processes take advantage of the material’s physical properties. These physical properties can include density, particle size and shape, electrical and magnetic properties, and surface properties. Major physical and chemical methods include magnetic separation, foam flotation, leaching etc., whereby impurities and unwanted substances are removed from the ore and the metal base ore is concentrated, which means that the percentage of the metal in the ore is increased. This concentrate is either processed to remove moisture or used for metal extraction or made into shapes and forms that can undergo further processing, with ease of handling.
Ore bodies often contain more than one valuable metal. The remnants of the previous process can be used as feed in the second process to extract the secondary product from the original ore. Additionally, a concentrate may contain more than one precious metal. That concentrate would then be processed to separate the valuable metals into separate components.
Hydrometallurgy
Hydrometallurgy deals with processes involving aqueous solutions to extract metals from ores . The first step in the hydrometallurgical process is leaching , which involves dissolving valuable metals in an aqueous solution and/or a suitable solvent. After separating the solution from the solids of the ore, the extract is often subjected to various processes of purification and concentration before the valuable metal is recovered either in its metallic state or as a chemical compound. This may include precipitation , distillation , adsorption and solvent extraction . Precipitation, cementation in the final recovery stage, or electrometallurgical procedures may be involved. Sometimes, hydrometallurgical processes can be performed directly on the ore material without any prior treatment. More often, the ore must be treated by various mineral processing steps, and sometimes by pyrometallurgical processes. [2]
Pyrometallurgy
Pyrometallurgy involves high temperature processes where chemical reactions take place between gases, solids and molten substances. Solids containing valuable metals are processed or converted to their elemental or metallic state to form intermediate compounds for further processing. Pyrometallurgical processes that involve gases and solids are typified by calcining and roasting operations. The processes that produce molten products are collectively known as smelting operations. The energy required to maintain high temperature pyrometallurgical processes may derive from the exothermic nature of chemical reactions. Typically, these reactions are oxidized, for example to sulfides.to sulfur dioxide . Often, however, energy must be added to the process by the combustion of the fuel or, in the case of some smelting processes, by the direct application of electrical energy.
The Ellingham diagram is a useful way of analyzing possible reactions and predicting their outcome.
Electro metallurgy
Electrometallurgy involves metallurgical processes that take place in some form of electrolytic cell . The most common types of electrometallurgical processes are electrowinning and electro-refining., Electrowinning is an electrolysis process used to recover metals in aqueous solution, usually an ore, as a result of one or more hydrometallurgical processes. The metal of interest is plated at the cathode, while the anode is an inert conductor. Electro-refining is used to dissolve impure metal anodes (usually from the smelting process) and produce high purity cathodes. Fused salt electrolysis is another electrometallurgical process by which a valuable metal is dissolved in a molten salt that acts as an electrolyte, And the valuable metal collects at the cathode of the cell. The mixed salt electrolysis process is conducted at a temperature high enough to maintain both the electrolyte and the metal in a molten state. The realm of electrometallurgy has significant overlap with the fields of hydrometallurgy and (in the case of fused salt electrolysis) pyrometallurgy. moreover, Electrochemical phenomena play an important role in many mineral processing and hydrometallurgical processes. (Extractive Metallurgy)
Lonometry
Ionometallurgy uses non-aqueous ionic solvents such as ionic liquids (ILs) and deep eutectic solvents (DES). DES are usually liquids composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a lower melting point than each individual component. for. DES are typically liquid at temperatures below 100 °C, and they exhibit physico-chemical properties similar to those of conventionally used ionic liquids, while being much cheaper and more environmentally friendly.
