Metals vs. Non-Metals

Differences Between Metals and Non-Metals

• Metals are typically solids at room temperature, with mercury as an exception.
• Metals generally have high densities, but alkali metals are an exception.
• Metals are good conductors of heat and electricity, while lead is a poor conductor.
• Metals usually have high melting and boiling points; alkali metals are the exception.
• Metals are lustrous, possessing a metallic sheen
• Metals are malleable, capable of being beaten into thin sheets, and ductile, able to be stretched into long wires
• Metals produce a metallic sound (sonorous) when struck or experience a collision.
• Metals have low ionization energy, electron affinity, and electronegativity values.
• Metals generally form ionic bonds.
• Metals usually form basic oxides, with zinc oxide (ZnO) and aluminum oxide (Al2O3) being amphoteric, and chromium oxide (Cr2O3) acidic.
• Metals above hydrogen react with non-oxidizing acids like hydrochloric acid (HCl) and sulfuric acid (H2SO4) to produce hydrogen gas (H2).
• Metal halides are generally ionic and soluble in water.
• Metals act as reducing agents.
• Non-metals exist in all three states of matter
• Non-metals have low densities.
• Non-metals are generally non-conductors of heat and electricity, except for graphite.
• Non-metals have low melting and boiling points, except for diamond.
• Non-metals do not possess lustre, though iodine and graphite are exceptions.
• Non-metals are brittle
• Non-metals do not produce metallic sound on collision (non-sonorous)
• Non-metals have high ionization energy, electronegativity, and electron affinity values.
• Non-metals usually form covalent bonds.
• Non-metal oxides are acidic or neutral, such as water (H2O), nitric oxide (NO), carbon monoxide (CO), and nitrous oxide (N2O).
• Non-metals do not evolve H2 gas from acids.
• Most non-metal halides are covalent and insoluble in water.
• Non-metals act as oxidizing agents.

Metalloids

• Metalloids are elements that exhibit properties intermediate between metals and nonmetals.
• Common examples include silicon, germanium, arsenic, antimony, and selenium.

Occurrence of Metals

• Metals can occur in a native or free state.
  • They are unaffected by atmospheric components like oxygen, moisture, and carbon dioxide.
  • Examples include silver, gold, platinum, and copper.
• Metals can occur in a combined or compound state.
  • They are reactive towards atmospheric components like oxygen, water, and carbon dioxide.
  • They exist as oxides, carbonates, halides, sulphides, and sulphates.
  • Examples of oxides include Bauxite (Al2O3.2H2O), Haematite (Fe2O3), and Tin stone (SnO2).
  • Carbonates include Limestone (CaCO3), Magnesite (MgCO3), and Calamine (ZnCO3).
  • Halides include Rock salt (NaCl), Horn silver (AgCl), and Sylvine (KCl).
  • Sulphides include Zinc blende (ZnS), Copper pyrite (CuFeS2), and Cinnabar (HgS).
  • Sulphates include Epsom salt (MgSO4.7H2O) and Gypsum (CaSO4.2H2O).

Ores and Minerals

• Minerals are substances found in nature that contain metals.
  • Examples include Cuprite (Cu2O), Copper glance (Cu2S), Copper pyrite (CuFeS2), and Malachite (CuCO3.Cu(OH)2), all of which are minerals of copper.
• Ore is a mineral from which metal can be extracted commercially or profitably.
• Major criteria for a mineral to be considered an ore:
  • Large deposits must exist in nature.
  • High metal content or percentage.
  • Easy extraction of the pure metal.
• All ores are minerals, but not all minerals are ores.

Metallurgy and its Types

• Metallurgy is the process of extracting metals from their ores and applying them for useful purposes.
• Types of metallurgy depend on the conditions maintained during ore reduction and the reducing agent used:
  • Pyrometallurgy: Extracts metal by chemical reduction of ore at high temperature; the metal is obtained in liquid state; used for Fe, Cu, Zn, Sn, Cr, Ni, Co, etc.
  • Electrometallurgy: Extracts metal by electrolysis of its ore in molten state using suitable electrodes; reactive metals like Na, K, Mg, Ca, etc., are extracted this way.
  • Hydrometallurgy: Extracts metal by dissolving the ore in water using a suitable reagent and precipitating the metal by adding more electropositive metals; silver and gold are extracted this way.

Alloys and Amalgams

• An alloy is a homogeneous mixture of metal with other metals or non-metals, altering the properties of the constituent metal.
• Types of alloys:
  • Ferrous alloys: Alloys of iron with other metals or nonmetals, such as steel (Fe + C) and stainless steel (Fe + Ni + Cr + C).
  • Non-ferrous alloys: Alloys of metals other than iron, such as Brass (Cu + Zn), Bronze (Cu + Sn), and German silver (Cu + Zn + Ni).
• Amalgams are alloys of mercury with other metals, like sodium amalgam (Na-Hg) and zinc amalgam (Zn-Hg).

Significances of Alloy Formation

• Alloys increase the hardness and strength of metals.
• Alloys improve color.
• Alloys lower the melting point of metals.
• Alloys change reactivity.
• Alloys prevent metals from corrosion, as seen with stainless steel resisting rust in moist air.

Steps in Metallurgical Operation

• The process involves several steps to extract metals from their ores:
  • Crushing and grinding involves crushing ore in jaw crushers and pulverizing/grinding in ball mills or stamp mills to reduce the ore into smaller pieces

Ore Dressing or Ore Concentration

• Gangue or matrices are removed from the ore to increase its concentration.
• Methods are applied depending on the nature of the ore and gangue particles:
  • Gravity separation or hydraulic classifier: This method separates minerals based on their relative densities
  • Powdered ore is washed by an upward stream of water
  • Soluble and lighter impurities are washed away, leaving behind the heavier ore.
  • Oxide ores such as haematite (Fe2O3) and bauxite (Al2O3.2H2O) are concentrated using this method.

Froth Floatation Process

• Preferential wetting of ore and impurities by two immiscible liquids (water and oil, such as pine or eucalyptus oil).
• Powdered ore is mixed with water and a little pine or eucalyptus oil, then agitated by air in a drum.
• Ore particles are wetted by oil and rise to the surface along with froth, which is skimmed off and dried.
• Gangue particles are wetted by water and settle at the bottom.
• Sulfide ores like ZnS (zinc blende), CuFeS2 (copper pyrite), and PbS (galena) are concentrated by this method.

Electromagnetic Separation Method

• Applied when either the ore or impurity is magnetic.
• The powdered ore is dropped on a conveyor belt moving between two rollers, one of which is an electromagnet.
• Magnetic particles are attracted to the magnet and fall with slight deflection; non-magnetic particles fall undeflected.
• Separate heaps are formed for the magnetic and non-magnetic particles.
• The magnetic impurity wolframite is separated from tin stone (cassiterite, SnO2) this way.

Leaching (Chemical Method)

• Chemical ore concentration method dissolving water-insoluble ore in water using a suitable reagent.
• After filtration, the ore is recovered by heating or reacting with a suitable reagent,.
• Bauxite (Al2O3.2H2O) is concentrated by leaching with NaOH solution, forming soluble meta aluminate then heated to precipitate Al(OH)2, which is then calcined to get concentrated ore.

Calcination and Roasting

• Heating of ores converts them into respective oxides, carried out in a reverberatory furnace.
• Calcination:
  • Heating concentrated ore strongly below its melting point in absence or limited supply of air.
  • Mainly applied for ores containing oxygen like oxides, hydroxides, hydrated oxides, carbonates, etc.
  • Moisture and volatile organic matter is removed.
  • Water of hydration is driven away.
  • Ores are decomposed into their oxides.
  • The mass becomes porous.
• Roasting:
  • Heating concentrated ore strongly below its melting point in excess of air to oxidize the ore.
  • Mainly applied for sulfide ores.
  • Moisture and volatile organic matter is removed.
  • Impurities of sulfur, phosphorus, arsenic, antimony, etc., are removed as their volatile oxides.
  • Sulfide ores are converted to their respective oxides.
  • The mass becomes porous.

Reduction of Ore and Recovery of Metal

• The ore is reduced to metal using a suitable reducing agent, method applications depend on ore nature and metal extraction.
• Smelting (Carbon Reduction):
  • Reduction of oxide ore into metal by heating with coke (carbon) at high temperatures in a furnace.
  • Carbon (C) or carbon monoxide (CO) act as reducing agents.
• Refractory Impurities: Oxide ores contain high melting impurities such as SiO2, FeO, MnO.
• Flux : Chemical compound (usually oxide) added to the ore during smelting to convert refractory impurities into easily fusible compounds
• Slag: Easily fusible compound formed by combination of flux and refractory impurities.
• Borax can be acidic, and CaO and MgO can be basic depending upon the nature of impurities.

Aluminothermic or Thermite Process

• Certain metal oxides (chromium, titanium, manganese) can't be reduced by carbon and require aluminum.
• The ore is mixed with Al-powder and a little BaO2 in a crucible and, then ignited.
• Burning magnesium initiates reduction, and the exothermic reaction maintains heat for further reduction; the metal is obtained in liquid form below Al2O3.

Electrolytic Reduction

• Method applied for reactive metals (Na, K, Mg, Ca, Al) that require electrolytic reduction of their molten ores between suitable electrodes for extraction.
• Sodium extracted by electrolysis of molten sodium chloride between graphite anode and iron cathode (Down's process).

Metal Precipitation

• Extraction of less reactive metals like silver and gold via hydrometallurgy.
• The ore is reacted with a suitable reagent and dissolved in water, followed by precipitation using a more electropositive metal like zinc (Zn).
• Silver is extracted from argentite (Ag2S) by reacting with sodium cyanide (NaCN) followed by precipitation with zinc.

Purification/Refining of Metals

• The metal obtained by reduction of ore may contain impurities depending on whether it was processed via electrolytic reduction.
• Impurities include other metals, unreduced oxides or sulphides, dissolved non-metals (S, P, As), and residual flux/slag. - Purification methods differ depending on nature of the metal and impurities.
  • Distillation: Volatile or low-boiling metals like zinc, mercury, and cadmium are heated above boiling points in a retort, leaving high-boiling impurities behind.
  • Liquation: Impure metal is melted and allowed to flow from furnace hearth and the metal flows out so non-fusible impurities stay behind; purifies tin, lead.
  • Poling: Melting and stirring with green wood which release gaseous hydrocarbons to reduce remaining oxide or sulphide in metal; for example, copper and tin are purified this way.
  • Electrolytic refining: Blocks of impure metal are made the anode and strips of pure metal are used as the cathode; electrodes are placed in salt aqueous solution for purification.
  • Zone refining: For impurities in the metal:
    • Impurities are melted and heated in a tubular furnace
    • Heater moves and impurities are crystallized
    • Crystallized metal is pure, works with silicon and germanium

Multiple Choice Questions (MCQs) & Answers

• Haematite is an ore concentrated by gravity separation
• In alloy formation, melting point increases
• Flux removes SiO2 impurities from Haematite ore
• Froth flotation is based on Preferential wetting of ore
• Rock salt cannot be converted easily into oxide by roasting
• Smelting uses CO as the reducing agent in haematite
• Sodium uses an electrometallurgical method
• Hydrometallurgy method is used with Gold extracting by leaching
• Formation of allotropes are not properties of metal
• Pyrometallurgy is a aluminothermic product
• Reverberatory furnace for calcination
• High value of metal in market is not a criteria for mineral to become ore
• Poling metal purification where A metal contains its own oxide remain unreduced after the extraction
• Bronze is non-ferrous allloy
• P2O5 is probably when Ca0 is flux
• Gravity separation works by Ores containing impurities with lower density than ore
• Tin Stone is concentrated via magnetic separation
• Roasting is used to convert zinc
• Ca0 is a basic flux