The Processing Steps toExtract Light Metal from Ore
Titanium Extraction• The production of titanium beginning with a report in 1887 by Milsen and Pettersen using sodium ,which was optimised into commercial Hunter process.• Kroll process is invented by William J.Kroll in Luxemburg around the mid 1930s.• Extracted by Kroll process to obtain commercially pure titanium metal.• Rutile (TiO2) are the major ores of titanium.
• Process: i)Conversion of titanium (IV) oxide,TiO2 into titanium (IV) chloride,TiCl4 -The ore rutile(impure TiO2 ) is heated with chlorine and coke at a temperature of about 900◦C. TiO2 + 2Cl2 +2C TiCl4 + 2CO -Titanium tetrachoride, TiCl4 and other metal chlorides are formed because of other metal compounds in the ore. -Very pure liquid titanium (IV) chloride can be separated from other chlorides by fractional distillation under an argon or nitrogen atmosphere and it is stored in totally dry tanks. -As titanium is very reactive, oxygen must be kept out of the reaction vessel so the reaction is done in an atmosphere of argon. -Besides that,titanium chloride is a typical covalent chloride which fumes in moist air due to reaction with water to give titanium (IV) oxide and fumes of hydrogen chloride.
ii)Reduction of Titanium (IV)chlorideA. Reduction by Sodium Used by UK. Titanium (IV) chloride is added to the reactor in which pure sodium has been heated to about 550◦C. The temperature increased to about 1000 ◦C during the reaction. TiCl4 + 4Na Ti + 4 NaCl After the reaction is complete and everything has cooled(several day in total) the mixture is crushed and washed with dilute hydrochloric acid to remove the sodium chloride.
B. Reduction by Magnesium Used in the rest of the world except UK. In a separator reactor,TiCl4 is reduced by liquid Magnesium (15-20% excess) at 800-850 ◦C in a stainless steel retort to ensure complete reduction. TiCl4 + 2Mg (l) Ti(s) + 2 MgCl2(l) MgCl is removed from titanium by distillation under low pressure at high temperature.
MgCl2 can be further refined back to Mg by electrolysis. The resulting porous metallic titanium sponge is purified by leaching or heated vacuum distillation. The sponge is jackhammered out ,crushed and processed before it is melted in a consumable electrode vacuum arc furnace. The melted ingot is allowed to solidify under vacuum. It is often remelted to remove inclusions and ensure uniformity. This melting steps add to the cost of product.
Disadvantages Titanium is about 6 times as expensive as stainless steel. Titanium is expensive because it cannot extracted by reducing the ore using carbon as a cheap reducing agent. Titanium form a carbide ,TiC , if heated with carbon, so pure titanium cannot be obtain. Carbide also makes the titanium brittle. The reducing agents such as sodium and magnesium have to be extracted from their ores by expensive process.
Other technologies are competing with the Kroll process: Electrolysis of a molten salt• Problems with this process include "redox recycling," the failure of the diaphragm, and dendritic deposition in the electrolyte solution. Pyrometallurgical• route that involves the reduction of an intermediate form of titanium with aluminium has combines the advantages of pyrometallurgy and a cheap reductant.
Aluminium Aluminium is the most widely used metal after iron. it is mostly used in an alloy with another metal . Eg: stainless steel. The primary ore of aluminum is bauxite, which forms when high volumes of rain water move through soils. Typically the water dissolves and removes elements such as sodium, potassium, and calcium, leaving altered soils called laterites that contain significant amounts of highly insoluble metals such as aluminum. Bauxite varies greatly in physical appearance, depending on its composition and impurities. It ranges in colour from yellowish white to gray or from pink to dark red or brown if high in iron oxides.
Extraction of Aluminium Aluminum is extracted from its oxide ore "Bauxite". Bauxite contains aluminium oxide, water, iron oxide and other impurities. The purified dry ore, called alumina, is aluminium oxide ,Al2O3. The extraction of aluminum involves the following steps.a) Purification of Bauxiteb) Electrolysis of Alumina (Aluminium Oxide)c) Refining
Purifying the aluminium oxide - theBayer Process Bauxite contains two main impurities Fe2O3 and SiO2. These impurities must be removed in order to get good quality aluminum. These impurities make the aluminum brittle and liable to corrosion. The process occurs in two main steps. Firstly the aluminum ore is mixed with the sodium hydroxide in which the oxides of aluminum and silicon will dissolve, but other impurities will not. These impurities can then be removed by filtration.
Carbon dioxide gas is then bubbled through the remaining solution, which forms weak carbonic acid neutralising the solution and causing the aluminum oxide to precipitate, but leaving the silicon impurities in solution. After filtration, and boiling to remove water, purified aluminum oxide can be obtained.
Formation of pure aluminium oxide-Electrolytic) Cell
The aluminum oxide is mixed with cryolite (made of sodium fluoride and aluminum fluoride) and then heated to about 980 °C to melt the solids.At the Cathode:• The molten mixture is then electrolyzed with a very large current and the aluminum ions are reduced to form aluminum metal which sinks to the bottom of the cell. Al3+ + 3e- ® AlAt the Anode:• Oxygen gas is formed, where it reacts with the carbon the anode is made from to give carbon dioxide gas. 2O2- ® O2 + 4e- More oxide is added as it is used up, and molten aluminum is tapped off the bottom of the cell from time to time.
Diagram showing cell for Aluminium extraction:
Summary• Aluminium is extracted from the ground in compounds, it is the purified to alumina (aluminium oxide) in the Bayer process• The metal is finally obtained after electrolysis in a cryolite solution.
Drawback of Aluminium Extraction: Aluminium extraction is expensive because the process is so long and needs a lot of electrical energy. It generates large quantities of greenhouse gases. Emissions come from extracting aluminum from bauxite and then smelting the ore to get the aluminum. Life cycle assessment shows that aluminium production produces more greenhouse gases than steel production. However when used in vehicles, aluminium’s lighter weight leads to better fuel efficiency, and reduces greenhouse gas emissions from transport.
Environmental problems Loss of landscape due to mining, processing and transporting the bauxite. Noise and air pollution (greenhouse effect, acid rain) involved in these operations. Atmospheric pollution from the various stages of extraction. For example: carbon dioxide from the burning of the anodes (greenhouse effect); carbon monoxide (poisonous); fluorine (and fluorine compounds) lost from the cryolite during the electrolysis process (poisonous). Pollution caused by power generation (varying depending on how the electricity is generated.)
Advantages of Aluminium: It is high strength to weight properties. Does not corrode in the same way as steel, because of the strong thin layer of aluminium oxide on its surface. This layer can be strengthened further by anodising the aluminium. Light, and has high electrical conductivity. Can be recycled in a more efficient manner that is less detrimental to the environment.
Recycling Saving of raw materials and particularly electrical energy by not having to extract the aluminium from the bauxite. Recycling preserves limited resources and requires less energy, so it causes less damage to the environment. Recycling aluminum also helps to decrease greenhouse gas emissions, which pollute the air. Recycling aluminum conserves natural resources by preventing the steady depletion of bauxite and other metal ores.
Aluminium• Indirect carbothermic reduction• can be carried out using carbon and Al2O3,• which forms an intermediate Al4C3 and this can further yield aluminium metal at a temperature of 1900–2000 °C.• it requires less energy and yields less CO2 than the Hall-Héroult process.
Cont..• The aluminum trichlorid precipitate is purifi ed by dissolution and re-precipitation. The final product is calcined to form alumina• the alumina so produced has a higher purity than alumina produced from bauxite by the Bayer process.
• Sulphate extraction method.• Acidic method for decomposing the ore.• Based on the reactivity of beryll enhance by the heat treatment.• The resulting granular is readily to separated.• Subsequently dewatered to 15wt% free water.• The overall extraction are approximately 85wt%.
Lithium• Fusion method• powdered silicate mineral is fused with CaCO3 and the fused mass is extracted with HCl and filtered.• The filtrate contains chlorides Li, Al, Ca, Na and K whereas silicon is removed as insoluble residue.• The filtrate is evaporated to dryness and the residue is extracted with pyridine in which only LiCl dissolves.