Electrometallurgy
Production of metals by electrolysis
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Through Metallurgy, Hall–Héroult process and Electrolysis
Processes
Electrometallurgy is the field concerned with the processes of metal electrodeposition. There are seven categories of these processes:
- Electrolysis
- Electrowinning, the extraction of metal from ores
- Electrorefining, the purification of metals. Metal powder production by electrodeposition is included in this category, or sometimes electrowinning, or a separate category depending on application.
- Electroplating, the deposition of a layer of one metal on another
- Electroforming, the manufacture of, usually thin, metal parts through electroplating
- Electropolishing, the removal of material from a metallic workpiece
- Etching, industrially known to Wikipedia as chemical milling
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Research trends
Molten oxide electrolysis
Molten Oxide Electrolysis in steelmaking is utilizing electrons as the reducing agent instead of coke as in conventional blast furnace. For steel production, this method uses an inert anode (Carbon, Platinum, Iridium or Chromium-based alloy) and places iron ore in the cathode. The electrochemical reaction in this Molten Oxide cell can reach up to 1600 °C, a temperature that melts iron ore and electrolyte oxide. Then the molten iron ore decompose following this reaction:
- Fe2O3(l) + e− → Fe(l) + O2(g)
The electrolysis reaction will produce molten pure iron as a main product and oxygen as its by-product. Because this process does not add coke in the process, no CO2 gas is produced. So no direct greenhouse gas emission. Moreover, if the electricity to run such cells comes from renewable sources, this process may have zero emissions. This technology also can be implemented for producing Nickel, Chromium, and Ferrochromium.
Currently the Massachusetts-based Boston Metal company is in a process to scale up this technology to an industrial level.
Direct decarburization electrorefining
The purpose of this method is to reduce carbon content from steel. This process is suitable for secondary steelmaking industry which recycling steel scrap that has variety of carbon content in their feedstock. This method aim to replace current conventional method that utilizing Basic Oxygen Furnace (BOF) to reduce carbon content of iron by blowing oxygen to make it react with carbon and forming CO2.
In electrorefining, decarburization process happened in electrochemical cell that composed of inert electrode, slag and steel. During the process, current passing through the cell and made slag and steel melted. Oxygen ion from slag decompose and oxidize carbon on steel and to form CO. That decarburizing reaction occurs in three steps as follows:
- O−2 + C ⇌ C(O−(ads)) + e−
- C(O−(ads)) ⇌ C(O(ads)) + e−
- C(O(ads)) ⇌ CO(g)
- (ads) = adsorbed intermediate
The total reaction from this cell is:
- C + ½ SiO2 ⇌ CO(g) + ½ Si(l)
The SiO2 comes from the slag, based on the reaction above, besides producing CO gas. This method also produces pure silicon (depending on the slag). The benefit of this direct decarburization process is that it does not produce CO2, but rather CO, which is not considered as greenhouse gas.