Metallurgy Flashcards
What is a 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.
How is the metal of interest typically found in minerals?
The metal of interest is present only in small amounts in most minerals.
What are ores?
Minerals that contain a high percentage of metal, from which it can be extracted conveniently and economically.
Is it true that all ores are minerals?
True.
Is it true that all minerals are ores?
False.
What is an example of a mineral that is an ore of aluminium?
Bauxite.
What is an example of a mineral that is not a profitable source of aluminium?
China clay.
What is the extraction process of a metal from its ore?
The extraction consists of the following metallurgical processes:
* concentration of the ore
* extraction of crude metal
* refining of crude metal.
Fill in the blank: Hematite and magnetite are examples of minerals containing a high percentage of _______.
iron
What percentage of iron is present in around 800 minerals?
Iron is present in around 800 minerals.
What is the chemical formula of china clay?
Al2O3.2SiO2.2H2O.
What are the nonmetallic impurities and rocky materials in ores collectively known as?
Gangue
Gangue includes siliceous matter and other impurities that need to be removed during ore processing.
What is the preliminary step in metallurgical processes?
Removal of impurities
This step is crucial for increasing the concentration of the desired metal.
What is the process called that increases the concentration of the metal of interest in the ore?
Concentration of ore
This process involves the removal of gangue and impurities.
Name one factor that affects the choice of method for ore concentration.
Nature of the ore
Other factors include the type of impurity and environmental considerations.
What is gravity separation or hydraulic wash used for?
To separate ore with high specific gravity from low specific gravity gangue
This method utilizes running water to wash away lighter gangue particles.
What type of ores is the gravity separation method generally applied to?
Native ores and oxide ores
Examples include gold and haematite (Fe2O3).
Fill in the blank: The process of washing crushed ore with running water to remove lighter gangue particles is called _______.
Gravity separation
This method relies on the difference in specific gravities between the ore and the gangue.
True or False: The concentration of ore is the final step in metallurgical processes.
False
Concentration of ore is a preliminary step before further metallurgical processes.
What is leaching?
A method based on the solubility of the ore in a suitable solvent and the reactions in aqueous solution.
What happens to the crushed ore during leaching?
It dissolves in a suitable solvent, converting the metal present into a soluble salt or complex while the gangue remains insoluble.
What is cyanide leaching?
A process where crushed gold ore is leached with an aerated dilute solution of sodium cyanide.
What is produced when gold is leached with sodium cyanide?
A soluble cyanide complex of gold.
What remains insoluble during the cyanide leaching of gold?
The gangue, which is aluminosilicate.
Fill in the blank: 4Au (s) + 8CN- (aq) + O2 (g) + 2H2O (l) → 4[Au(CN)2]^- (aq) + 4OH^- (aq). This equation represents the _______ of gold.
[cyanide leaching]
What process is used to recover gold from a deoxygenated leached solution?
Cementation
Gold is reduced to its elemental state by reacting with zinc.
What is the chemical reaction for the recovery of gold using zinc?
Zn (s) + 2[Au(CN)2]⁻(aq) → [Zn(CN)4]²⁻(aq) + 2Au (s)
This reaction illustrates the reduction of gold to its elemental form.
What metals can be selectively leached from crushed ore using ammonia?
- Nickel
- Copper
- Cobalt
These metals form soluble complexes with ammonia.
What are the soluble complexes formed when nickel, copper, and cobalt are leached with ammonia?
- [Ni(NH3)6]²⁺
- [Cu(NH3)4]²⁺
- [Co(NH3)5H2O]³⁺
These complexes are formed from the respective metals during leaching.
What is the purpose of alkali leaching?
To form a soluble complex from the ore
This method separates the ore from impurities.
What ore is treated with sodium hydroxide or sodium carbonate in alkali leaching?
Bauxite
Bauxite is an important ore of aluminum.
What is the temperature and pressure range for the alkali leaching of bauxite?
470 - 520 K at 35 atm
Conditions are critical for effective leaching.
What is the reaction for the alkali leaching of bauxite?
Al2O3(s) + 2NaOH(aq) + 3H2O(l) → 2NaAl(OH)4
This reaction produces soluble sodium meta-aluminate.
What happens to the hot solution after alkali leaching?
It is decanted, cooled, and diluted
This process prepares the solution for neutralization.
What is formed when the solution from alkali leaching is neutralized with CO2?
Hydrated Al2O3 precipitate
This precipitate can be further processed to obtain pure alumina.
What is the reaction that forms hydrated Al2O3 during neutralization?
2NaAl(OH)4 + 2CO2(g) → Al2O3.3H2O(s) + 2NaHCO3(aq)
This reaction produces Al2O3 and sodium bicarbonate.
What is the final step to obtain pure alumina from the precipitate?
Heating around 1670 K
This step removes water to yield Al2O3.
What type of ores can be leached with hot aqueous sulfuric acid?
Sulphide ores such as ZnS and PbS
This method effectively converts insoluble sulphides into soluble sulphates.
What is the chemical reaction for the leaching of ZnS with sulfuric acid?
2ZnS(s) + 2H2SO4(aq) + O2(g) → 2ZnSO4(aq) + 2S(s) + 2H2O
This reaction demonstrates the conversion of sulphide to sulphate.
What is magnetic separation?
A method applicable to ferromagnetic ores based on the difference in magnetic properties of the ore and impurities.
It separates magnetic ores from non-magnetic impurities.
Which types of ores can be separated using magnetic separation?
Ferromagnetic ores such as tin stone from wolframite and chromite, pyrolusite from siliceous impurities.
This method relies on the magnetic properties of certain ores.
How does an electromagnetic separator function?
The crushed ore is poured onto a belt moving over two rollers, one of which is magnetic.
The magnetic part of the ore is attracted to the magnet while non-magnetic parts fall away.
What are the two steps in the extraction of crude metals from concentrated ores?
- Conversion of the ore into oxides of the metal
- Reduction of the metal oxides to elemental metals.
Why is the reduction of oxides easier than other metal compounds?
According to thermodynamics, reduction of oxide is easier compared to reduction of other compounds of metal.
What is the first step in the extraction process of metals?
Conversion of the concentrated ore into the oxides of the metal of interest.
What is roasting in the context of metal extraction?
A method for converting sulphide ores into their oxides by heating with excess oxygen in a suitable furnace.
This process occurs below the melting point of the metal.
Fill in the blank: The method usually applied for the conversion of sulphide ores into their oxides is called _______.
roasting
What is the chemical reaction for lead sulfide roasting?
2PbS + 3O2 → 2PbO + 2SO2
This reaction describes the conversion of lead sulfide into lead oxide and sulfur dioxide.
What is the chemical reaction for zinc sulfide roasting?
2ZnS + 3O2 → 2ZnO + 2SO2
This reaction illustrates the transformation of zinc sulfide into zinc oxide and sulfur dioxide.
What is the chemical reaction for copper(I) sulfide roasting?
2Cu2S + 3O2 → 2Cu2O + 2SO2
This reaction represents the conversion of copper(I) sulfide into copper(I) oxide and sulfur dioxide.
What is the purpose of roasting in metal extraction?
To remove impurities such as arsenic, sulphur, and phosphorous by converting them into their volatile oxides
Roasting is a crucial step in the extraction process to purify metals.
