Properties and Extraction of Non-Ferrous Metals
Non-Ferrous Metals: Properties and Uses
There are also other non-ferrous metals.
1. Chrome
Chrome has a steely gray color, is very hard, and possesses great sharpness. It resists oxidation and corrosion very well. It is used as polished chrome for decorative objects, as hard chrome for the manufacture of stainless steels and tool steels.
- Density: 6.8 kg/dm³
- Melting point: 1900 °C
- Resistivity: 1.1 ohm ⋅ mm²/m
2. Nickel
Nickel has a bright silver color and can be polished very easily. It is magnetic (like a ferrous product) and is very resistant to oxidation and corrosion. It is used to produce stainless steels (alloyed with steel and chrome), in chemical industry equipment, and for coating metals (by electrolysis).
- Density: 8.85 kg/dm³
- Melting point: 1450 °C
- Resistivity: 0.11 ohm ⋅ mm²/m
3. Tungsten
Tungsten has a very high melting point, so it is used for incandescent light bulb filaments and the manufacture of cutting tools for machines.
- Density: 19 kg/dm³
- Melting point: 3370 °C
- Resistivity: 0.056 ohm ⋅ mm²/m
4. Cobalt
Cobalt has properties similar to nickel but is not magnetic. It is used for hardening tool steels (HSS) and as an element in the manufacture of hard metal (sintering) used in cutting tools.
- Density: 8.6 kg/dm³
- Melting point: 1490 °C
- Resistivity: 0.063 ohm ⋅ mm²/m
Environmental Impact of Metal Extraction
a) During the extraction of minerals: If this extraction is carried out in the open, the impact may be greater, as it can affect certain habitats.
b) During the collection of the different metals: We have different types of impacts.
c) During the recycling process: The environmental impact is much smaller but still significant.
1. Emissions
- Heavy metals (metal oxides and volatile metal vapors), which are carcinogenic.
- Gases, dust, and hydrogen gas, which are very corrosive (dangerous to health and the environment).
- Solutions: Avoid releasing emissions from the factory, select the location carefully, and use masks.
2. Wastewater
- Water from washing and stripping of metals (alkaline and acid solutions) and sludge.
- Solutions: Neutralize with chemicals and use landfills (to prevent leaks that may contaminate groundwater).
3. Noise Pollution
- Caused by facilities and equipment.
- Solutions: External insulation. If the noise level exceeds 80 decibels, use hearing protection.
Extraction Processes for Various Metals
Tin Extraction
- The cassiterite is crushed and ground in appropriate mills. Then, it is introduced into a vat with water and stirred. By decantation, tin ore sinks to the bottom and is separated from the gangue.
- Subsequently, it is introduced into a furnace, where sulfides in the tin mineral are oxidized and transformed into oxides.
- Tin ore, in oxide form, is introduced into a reverberatory furnace where reduction occurs (transformation of tin oxide to tin). Tin is deposited on the bottom, and the scum is at the top.
- Finally, to obtain 99% pure tin, it is subjected to an electrolytic process.
Copper Production Methods
Dry Process: Used when copper content exceeds 10%. It is the most widely used process.
A) The copper ore is introduced into a shredder or crusher and then passed through a ball mill to pulverize it. This mill consists of a cylinder with very fine holes, where the pulverized ore and steel balls rotate freely when the cylinder rotates.
B) To separate the ore from the gangue, the powdered ore is introduced into a tank filled with water and stirred. The mineral, being heavier, will sink to the bottom, while the gangue will float and be removed.
C) The mineral concentrate is placed in an oven, where it is partially oxidized. The aim is to oxidize the iron but not the copper. Nowadays, it is usually placed on a metal conveyor belt that moves slowly while the ore is heated. This separates the iron from the copper.
D) Everything is then introduced into a reverberatory furnace where it melts. Flux (silica and lime) is added to react with sulfur, forming iron oxide and slag. The copper obtained here has a purity of approximately 40% and is known as raw copper or blister copper. If copper with a purity over 99.9% is desired, electrolytic refining in a vat is needed.
Wet Process: It is used when the copper ore content is less than 10%. The procedure involves crushing all the ore and treating it with sulfuric acid. Then, through electrolysis, copper is obtained.
Zinc Procurement Procedures
Dry process (for ore content over 10%) and wet process (for ore content below 10%).
Dry Process
Wet Process
Lead Extraction
Obtaining lead consists of four phases:
1. Enrichment: Galena is crushed and milled. Then, the ore is separated from the gangue by flotation.
2. Oxidation of sulfides: All Pb sulfides are roasted (about 700 °C) to transform them into oxides. By adding silica and lime, lead monoxide (PbO) is obtained.
3. Pb monoxide reduction: This is done in a muffle furnace (a kind of small blast furnace). Coking coal and lime are used. The lead obtained contains many impurities and is called work lead.
4. Refining of lead: There are two phases: 1st, separation of other metals (copper, zinc, silver, etc.), and 2nd, refining.
Aluminum Extraction
The Bayer method is the most economical process for obtaining aluminum and is therefore the most widely used.
1. The bauxite is transported from the mine to the processing location (near ports, since most are imported).
2. It is crushed and ground until it is pulverized.
3. It is stored in silos until ready to be processed.
4. In a mixer, bauxite powder, caustic soda, lime, and hot water are introduced. This causes the bauxite to dissolve in the soda.
5. In the decanter, waste (oxides that are in a solid state and were not attacked by soda) is separated.
6. In the heat exchanger, the solution is cooled, and water is added.
7. In the precipitation vat, alumina precipitates at the bottom.
8. A filter separates the soda from the alumina.
9. The alumina is heated to about 1200 °C in an oven to completely remove moisture.
10. In the refrigerator, the alumina is cooled to room temperature.
11. To obtain aluminum from alumina, it is dissolved in molten cryolite (which protects the bath from oxidation) at a temperature of about 1000 °C and subjected to an electrolysis process that breaks down the material into aluminum and oxygen.
Titanium Production Process
Currently, the Kroll method is used almost exclusively.
Chlorination: Heat the titanium mineral. Then add carbon, and chlorine is circulated throughout the mass. Titanium tetrachloride (TiCl4) is obtained.
Transformation: The compound is introduced into an oven at 800 °C. After introducing an inert gas (helium or argon) and magnesium, a titanium sponge is formed.
Collection: The titanium sponge is introduced into an oven, and fluxes are added. The result is pure titanium.
Magnesium Extraction Methods
Electrolysis and Reduction.
Magnesium rises to the surface because it has a lower density than the molten salt mixture. The vat has to be metallic and acts as a cathode. It consists of introducing the ore into an electric furnace, and flux is added to cause the removal of oxygen.