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Extractive metallurgy- to obtain nearly pure elements starting from compounds present in nature.
Pretreatmnet Operations
Oxides are more conveniently reduced to metal than the sulfides, or the metal might be more readily leached from the ore, if it were present as a sulfate.
Pretreatment Process:
Drying Calcination Roasting Agglameration
Drying
Removel of mechanically held water or moisture from the concentrate, or other solid materials by evaporation.
ΔH>0 (endothermic)
Moisture Determination: Representive sample ↓ Weigh the sample ↓ Put it into drying oven
H 2 O ( l ) = H 2 O ( g )
Dry at 105°C (for several hours) ↓ Weigh again ↓ Determine loss in weight
%Moisture: [( Wet weight - Dry weight ) / Wet weight] * 100
Calcination By contrast with drying, calcination involves the removal of H20, CO2. Which are chemically bound as e.g. hydrates or carbonates.
Lost Lost ↑ ↑ Material→Free water→Chemicall bound H2O,CO2→Compeletly dehyrdrated and calcined material ↑ ↑ Drying Calcination
Tcalcination>> Tdrying ΔH>0 (endothermic) T>900°C (The calcination reaction is more endothermic than drying)
- Oxidizing roasting: Burn out sulfur from sulfides and replace them with oxides. SO2+½O2 → SO3 (Formation of SO3) e.g. 2ZnS +3O2 → 2ZnO+ 2SO
- Volatilizing roasting: To eliminate other element with volatile oxider like AS2O3,Sb2O3 which can be recovered as fume. e.g. Sb2S3+9/2O2 → Sb2O3+3SO This is an oxidizing as well as as votalizing. This process is called as FUMING OF ANTIMONY.
Gold ore containing arsenic→Volatilizing roasting→Calcine(without
alsenic)→Further processing ↓ (As2O3(g) removed)
- Chloridizing Roast Conversion certain metals to chlorides. e.g. MO+CaCl2 → MCl2+CaO ↓ is sent to the main process
As a general flowsheet: Non-ferrous metal→Chloridizing Roast→ Volastile Chlorides ↗ T~1000°C -1250°C Chloridizing agent (CaCl2,Cl2)
Alternatively, chlorodizing roasting may be performed at low T o obtain a solid MCl Metals having stable xides such as, Tp,Mg,Al can be roasted form metal chlorides MO+Cl2+C→MCl2+CO (krall process) ↑ metals with stable oxide
- Sulfating Roast Conversion of certain metals from sulfates prior to leaching e.g. MS+2O2→MSO
- Magnetizing Roast Type of roasting prior to smelting
Low grade hematite ore (Fe2O3) 30% Fe ↓ Magnetizing roast T~700°C ↓ Magnetite (Fe3O4) ↓ Magnetic Separation ↓ ↓ Fe3O4 Tailing
- Carburizing Roasting:(Choloridizng Roasting) To prepare a calciner for choloridizing
Boundaries: p: M+SO2 →MS+O r: 2MS+3O2→2MO s: 2MS+3O2→2MO+2SO t: 2MO+O2+2SO2→2MSO u: MS+2O2→MSO
Kp: slope 1 Kr: slope ∞ Ks: slope 3/ Kt: slope -½ Ku: slope ∞
Kinetics of Roasting:
In order to increase the rate of reaction, we have to increase the temperature of roasting (not indefinitly, undesireable products and risk of melting at high temperature.) In roasting, we have to work with small particles to obtain large specific surface area. Large specific surface area increases the reaction rate.
The Possibility of Reducing a Compund MaXb by an Agent R
C, CO, H2 have comparable costs. Metals are generally more expensive then C, CO, H Cheapest to expensive; Si>Al>Mg>Ca
- Separation of the product metal, M, from the compound RcXd C, CO,H2 are good in this respect sine their oxides are gases. H2 is good in the reduction of chlorides since HCl is a gas With condensed oxide reducing seperation is generally affected by and formation of a slag. (The meltin point of the oxide od the reducing agent is desired to be low “ slag-metal seperation”.)
- Contamination of the product metal, M, with the reducing agent R. Reducing agent’s solubility in the product metal is important.
a) using a reducing agent R for which ΔG is a large negative number. b) operating at the lowest possible T c)
at above 1000°C ~ nearly all CO below 400°C ~nearly all CO So, CO is more stable at hight T If a mixture of CO and CO2 (with presence of C ) having composition different from indicated by Boudavard reaction, system will react until equilibrium is established.
Reduction of Metal Oxides with H2 and CO
Value element: M
Reducing agent: R
Look at O(-2) provided by basic oxides Look at O(-2) requirement of acidic oxiddes form the simplest anions If after oxide ion requirement of acidic oxides for simplest anion formation is satisfied, the remains free oxygen anions, then the slag called as BASIC
Pure Ti- Pure TiO TiO2 is very stable. (can reduce by a few reducing agents at high T) Ti element has high O solublity. It is impossible to produce O-free titanium. N, H and C solubility is also high
Production of Titanium (Kroll proces)
Ti Atomic number 22 Atomic weight 47.867 g/mole One of the lightweight elements. Important in aircraft Lighter Faster Fuel efficient In Earth’s crust → we have two forms
- TiO2 (rutile) containing ores.
- FeTiO3 (ilmenite) containing ores AIM: to produce metallic Ti. KROLL PROCESS
- TiO2 is converted into TiCl
- TiCl4 is then reduced by Mg → Sponge Ti
