![TYPES OF LEACHING
CYANIDE LEACHING
4Au(s)+8CN-(aq)+O2(g)+2H2O(l)4[Au(CN)2]-(aq)+4OH-(aq)
Zn (s) + 2Au(CN)2]- (aq) [Zn(CN)4]2-(aq) + 2Au (s)
AMMONIA LEACHING
Ammonia selectively leaches these metals by forming
their soluble complexes viz. [Ni(NH3)6]2+, [Cu(NH3)4]2+, and
[Co(NH3)5H2O]3+
6/9/2020Metallurgy sakthibalaji
12](https://image.slidesharecdn.com/metallurgy-200609102937/85/introduction-to-metallurgy-for-chemist-12-320.jpg)
2Na[Al(OH)4](aq)+CO2(g)Al2O3.xH2O(s)+2NaHCO3(aq)
ACID LEACHING
2ZnS(s) +2H2SO4(aq)+O2(g) 2ZnSO4 (aq)+2S(s) + H2O(l)
6/9/2020Metallurgy sakthibalaji
13](https://image.slidesharecdn.com/metallurgy-200609102937/85/introduction-to-metallurgy-for-chemist-13-320.jpg)
introduction to metallurgy for chemist
- 2. METALLURGY AND BASIC EXTRACTION TECHNIQUES BY SAKTHIBALAJI C S 6/9/2020Metallurgy sakthibalaji 2
- 3. WHAT IS METALLURGY? 6/9/2020Metallurgy sakthibalaji 3 • Metallurgy relate to the science and technology of metals. The branch of science and technology concerned with the properties of metals and their production and purification. • Metallurgy comprises of 3 steps: i. Concentration of Ore ii. Isolation of metal from the concentrated Ore iii. Purification of the metal
- 4. BASIC TERMINOLOGIES • Mineral: A naturally occurring substance obtained by mining which contains the metal in free state or in the form of compounds like oxides, sulphides etc... is called a mineral • Ore: Minerals that contains a high percentage of metal, from which it can be extracted conveniently andeconomically are called ores • Flux: a chemical substance that forms an easily fusible slag with gangue. 6/9/2020Metallurgy sakthibalaji 4
- 5. BASIC TERMINOLOGIES (contd…) 6/9/2020Metallurgy sakthibalaji 5 • Slag: Waste matter separated from metals during the extraction of ores. • Gangue: In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. • The separation of mineral from gangue is known as mineral processing.
- 7. EXTRACTIVE TECHNIQUES 6/9/2020Metallurgy sakthibalaji 7 • It is the process of removing impurities or undesired materials from the ore leaving behind the required metal. • Different process followed are i. Hydraulic washing OR Gravity seperation ii. Magnetic separation iii. Froth floatation iv. Leaching
- 11. LEACHING 6/9/2020Metallurgy sakthibalaji 11 • It involves the use of aqueous solutions to extract metal from metal bearing materials which is brought into contact with a material containing a valuable metal. aqueousThe vary in termssolution conditions oxidation-reduction of pH, potential, presence of chelating agents and temperature.
- 12. TYPES OF LEACHING CYANIDE LEACHING 4Au(s)+8CN-(aq)+O2(g)+2H2O(l)4[Au(CN)2]-(aq)+4OH-(aq) Zn (s) + 2Au(CN)2]- (aq) [Zn(CN)4]2-(aq) + 2Au (s) AMMONIA LEACHING Ammonia selectively leaches these metals by forming their soluble complexes viz. [Ni(NH3)6]2+, [Cu(NH3)4]2+, and [Co(NH3)5H2O]3+ 6/9/2020Metallurgy sakthibalaji 12
- 13. TYPES OF LEACHING( conti…) ALKALI LEACHING Al2O3(s)+2NaOH(aq)+3H2O(l)2Na[Al(OH)4](aq) 2Na[Al(OH)4](aq)+CO2(g)Al2O3.xH2O(s)+2NaHCO3(aq) ACID LEACHING 2ZnS(s) +2H2SO4(aq)+O2(g) 2ZnSO4 (aq)+2S(s) + H2O(l) 6/9/2020Metallurgy sakthibalaji 13
- 14. METALS AND ITS EXTRACTING 6/9/2020Metallurgy sakthibalaji 14 TECHNIQUES Metals - in decreasing order of reactivity Reactivity Potassium Sodium Calcium Magnesium Aluminium extract by electrolysis Carbon Zinc Iron Tin Lead extract by reaction with carbon or carbon monoxide Hydrogen Copper Silver Gold Platinum extracted by various chemical reactions
- 15. CLASSIFICATION 6/9/2020Metallurgy sakthibalaji 15 Metallurgy categories: • Roasting • Calcination • Smelting • Refining is classified into following
- 16. ROASTING 6/9/2020Metallurgy sakthibalaji 16 • The processing of strong heating of the ore in presence of excess amount of air below its melting point. • Purpose of roasting: i. ii. To convert the sulphide into oxide and sulphate To remove impurities like S, As, Sb. iii. To remove moisture iv. To Oxidise easily oxidisable substances
- 17. ROASTING • It is mainly used for sulphide ores • it converts the sulphides into oxides • 2ZnS+3O2 2ZnO+SO2 • 2Cu2S + 3O2 2Cu2O + 2SO2 • Roasting also removes impurities such as As,S,P by converting them into their volatile oxides. 4As + 3O2 2As2O3 • S8 + 8O2 8SO2 P4 + 5O2 P4O10 6/9/2020Metallurgy sakthibalaji 17
- 18. CALCINATION 6/9/2020 Metallurgy sakthibalaji 18 • Calcination is heating to high temperatures in the absence of air or oxygen. • The main purpose of calcination of ores are to convert carbonates and hydroxides ores into oxides. • ZnCO3 → ZnO + CO2 • CaCO3 → CaO + CO2 • Al2O3.3H2O Al2O3 + 3H2O
- 19. i. Remove the volatile impurities ii. To remove moisture iii. Make the mass porous Purpose of calcination 6/9/2020 Metallurgy sakthibalaji 19
- 20. CALCINATIONVS ROASTING 6/9/2020 Metallurgy sakthibalaji 20 CALCINATION ROASTING It is the process of heating in absence of air It is the process of heating in presence of air to oxidise the impurities It is employed for carbonate ores It is employed for sulphide ores Calcination produces carbon dioxide along with metal oxide Roasting produces sulphur dioxide along with metal oxide
- 21. SIMILARITIES •Both are processes of heating the ore below its melting point. •Both aim at removal of impurities in the ore. 6/9/2020Metallurgy sakthibalaji 21
- 22. SMELTING 6/9/2020Metallurgy sakthibalaji 22 • Smelting is a form of extractive metallurgy; its main use is to produce a base metal from its ore. • Smelting makes use of heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving only the metal base behind. • The reducing agent is commonly a source of carbon such as coke, or in earlier times charcoal.
- 23. PROCESS 6/9/2020Metallurgy sakthibalaji 23 • 2𝐶 + 𝑂2 → 2𝐶𝑂(Burning of fuel to CO) • 𝐹𝑒2 𝑂3+ 3𝐶𝑂→ 2𝐹𝑒+ 3𝐶𝑂2( CO reduces hematite to iron) • 𝐶𝑎𝐶𝑜3 → 𝐶𝑎𝑂+ 𝐶𝑂2 (Decomposition) • 𝐶𝑎𝑂+ 𝑆𝑖 𝑂2 → 𝐶 𝑎𝑆𝑖 𝑂3(Impuritiesareremoved)
- 24. REDUCTION OF METALS • AUTO REDUCTION • CARBON REDUCTION • METAL REDUCTION • REDUCTION BY HYDROGEN 6/9/2020Metallurgy sakthibalaji 24
- 25. REDUCTION BY METALS • Metallic oxides such as Cr2O3 can be reduced by an aluminothermite process. In this process, the metal oxide is mixed with aluminium powder and placed in a fire clay crucible. An ignition mixture (usually magneisium and barium peroxide) is used. • Cr2O3 + 2Al 2Cr + Al2O3 • B2O3 + 6Na 2B + 3Na2O • Rb2O3 + 3Mg 2Rb + 3MgO 6/9/2020Metallurgy sakthibalaji 25
- 26. REDUCTION BY HYDROGEN • This method can be applied to the oxides of the metals (Fe, Pb, Cu) having less electropositive character than hydrogen. • Ag2O (s)+ H2 (g) 2Ag (s) + H2O (l) • 2NiO(s)+CO(g) + H2(g) 2Ni (s)+CO2(g)+H2O (l) 6/9/2020Metallurgy sakthibalaji 26
- 27. AUTO REDUCTION • Simple roasting of some of the ores give the crude metal. In such cases, the use of reducing agents is not necessary. For example, mercury is obtained by roasting of its ore cinnabar (HgS) • HgS (s) + O2 (g) Hg (l) + SO2(g) 6/9/2020Metallurgy sakthibalaji 27
- 28. METAL RECOVERY BY PURIFICATION 6/9/2020Metallurgy sakthibalaji 28 • Sometimes, however, further refining is required if ultra-high purity metals are to be produced. • The primary types of metal recovery processes are • i) electrolysis • ii) gas phase reduction. • iii) zone refining
- 29. Thermodynamics of metallurgy Harold Ellingham used the above relationship to calculate the ΔG⁰ values at various temperatures for the reduction of metal oxides by treating the reduction as an equilibrium process. ΔG= Δ H-T Δ S ΔG= -RT ln Kp 6/9/2020Metallurgy sakthibalaji 29
- 31. OBSERVATIONS For most of the metal oxide formation, the slope is positive The graph for the formation of carbon monoxide is a straight line with negative slope. It indicates that CO is more stable at higher temperature As the temperature increases, generally ΔG value for the formation of the metal oxide become less negative and becomes zero at a particular temperature. Below this temperature, ΔG is negative and the oxide is stable and above this temperature ΔG is positive 31
- 32. Applications Ellingham diagram for the formation of Ag2O and HgO is at upper part of the diagram -decompose on heating even in the absence of a reducing agent. Any metal can reduce the oxides of other metals that are located above it in the diagram. Formation of chromium oxide lies above that of the aluminium, meaning that Al2O3 is more stable than Cr2O3 The carbon line cuts across the lines of many metal oxides and hence it can reduce all those metal oxides at sufficiently high temperature. 32
- 33. LIMITATIONS 1. It gives information about the thermodynamic feasibility of a reaction. It does not tell anything about the rate of the reaction. 2. The interpretation of ΔG is based on the assumption that the reactants are in equilibrium with the product which is not always true. 33
- 34. EXTRACTION OF ALUMINIUM - HALL-HEROLD PROCESS • carbon attached with tank - cathode. • The carbon blocks immersed in the electrolyte – anode • 10% CaCl2 helps to lower the M.P of the mixture • 4Al3+ (melt) + 6O2- (melt)+ 3C(s) 4Al(l) + 3CO2(g) 6/9/2020 Metallurgy sakthibalaji 34
- 35. REFINING PROCESS OF METALS • Distillation low boiling volatile metals like zinc (boiling point 1180 K) and mercury (630 K) • • Liquation The crude metal is heated to form fusible liquid and allowed to flow on a sloping surface 6/9/2020 Metallurgy sakthibalaji 35
- 36. ELECTROLYTIC REFINING • Anode - impure metal (silver) • 2Ag(s) 2Ag+ (aq)+ 2e- • Cathode - pure metal (silver) • 1Ag+ (aq)+ 1e- Ag (s) • Electrolyte - Acidified salt solution of metal ( AgNO3) 6/9/2020 Metallurgy sakthibalaji 36
- 38. ZONE REFINING • ELEMENTS SUCH AS GERMANIUM (GE), SILICON (SI) AND GALIUM (GA) THAT ARE USED AS SEMICONDUCTOR ARE REFINED USING THIS PROCESS. • METAL IS TAKEN IN THE FORM OF A ROD. ONE END OF THE ROD IS HEATED USING A MOBILE INDUCTION HEATER WHICH RESULTS IN MELTING OF THE METAL ON THAT PORTION OF THE ROD. • WHEN THE HEATER IS SLOWLY MOVED TO THE OTHER END THE PURE METAL CRYSTALLISES WHILE THE IMPURITIES WILL MOVE ON TO THE ADJACENT MOLTEN ZONE FORMED DUE TO THE MOVEMENT OF THE HEATER. • AS THE HEATER MOVES FURTHER AWAY, THE MOLTEN ZONE CONTAINING IMPURITIES ALSO MOVES ALONG WITH IT 6/9/2020Metallurgy sakthibalaji 38
- 40. VAPOUR PHASE METHOD •MOND PROCESS - NICKEL: IMPURE NICKEL WITH CO AT 350 K TO GIVE NICKEL TETRACARBONYL. THE SOLID IMPURITIES ARE LEFT BEHIND. NI (S) + 4 CO (G) NI(CO)4 (G) • NICKEL TETRACARBONYL AROUND 460 K, THE COMPLEX DECOMPOSES TO GIVE PURE METAL. NI(CO)4 (G) NI (S) + 4 CO (G) 6/9/2020Metallurgy sakthibalaji 40
- 41. VAN-ARKEL METHOD - ZR/TI • THE IMPURE TITANIUM METAL WITH IODINE AT 550 K TO FORM VOLATILE TITANIUM TETRA-IODIDE.(TII4) • TI (S) + 2I2 (S) TII4 (G) • TITANIUM TETRAIODIDE IS PASSED OVER A TUNGSTEN FILAMENT AT 1800 K GIVES PURE TITANIUM WHICH IS DEPOSITED ON THE FILAMENT • TII4 (G) TI (S) + 2I2 (S) • THE IODINE IS REUSED 6/9/2020Metallurgy sakthibalaji 41