Preliminary Chemistry

Preliminary ChemistryModule 3 - WaterDefine the terms mineral and oreOnly very few metals such as gold and platinum are found in native or uncombined form in nature. Most metals occur in natural compounds called minerals.A mineral is a pure, naturally occurring crystalline compound that occurs in the Earths crust.Define the terms mineral and oreThe most common minerals from which we obtain metals use oxides and sulfides, eg. Fe2O3, CuFeS2Ores contain minerals and waste (gangue). Ores contain metals that can make a profit.A deposit of minerals considered to be worth mining for extraction of one or more metals is called an oreGeneral process of metal extractionMine the ore -> concentrate the ore (froth floatation) -> extract metal by reduction -> purify the metals and/or make alloysChalcopyrite (CuFeS2) is the ore we use to extract copper.Extraction of copperStep 0 figuring out, surveying, sampling, doing gravimetric analysis to find how much copper is in the ore is it going to give us a profit if we mine it?Step 1 Mining, crushing and grindingThe mined ore (containing a minimum of 0.5% copper by weight) is placed in a crusher and converted to smaller pebbles. The pebbles are then ground in a grounding mill to liberate the mineral crystals from the rockExtraction of copperStep 2 concentrationFroth floatation can concentrate the ore to about 15 30% Cu by massOil covers minerals, helps air bubbles take the mineral to surface as oil is hydrophobic to waterGangue absorbs water. Detergent helps make bubbles. Air is blown through mixtureGangue has lower affinity for water hence sinks to the bottom of the vesselMiscible = can dissolve in one anotherImmiscible = cannot dissolve in one anotherExtraction of copperStep 3 Roasting and smeltingRoasting chemically separates copper and iron impurity into separate compounds.Smelting is the process in which a mixture is heated to a sufficiently high temperature in order to produce molten material which is conductive to metal ion reduction.

Extraction of copperRoasting: 2CuFeS2(s) + 3O2(g) -> 2CuS(s) + 2FeO(s) + 2SO2(g)Copper (I) sulfide and iron (II) oxide is smelted with silica (SiO2) at 1400C:Top layer: FeO(s) + SiO2 -> FeSiO3(l) [slag is discarded] Bottom layer: 2CuS(s) + O2(g) -> Cu2S(l) + SO2(g)Overall equation of roasting & smelting:2CuFeS2(s) + 2SiO2(s) + 4O2(g) -> Cu2S(l) + 2FeSiO3(l) + 3SO2(g)

Extraction of copperThe iron silicate (slag) and copper (I) sulfide products are drained through separate openings in the bottom of the furnace. This process allows iron to be effectively removed from chalcopyrite.The copper (I) sulfide liquid is then heated in a converter furnace. This converts it to an oxide, then facilitates the reduction to copper metal.Overall:Cu2S(l) + O2(g) -> 2Cu(l) + SO2(g)Extraction of copperWhile most SO2 escapes quickly, some do not leave the cooling copper until it is almost solid, giving a blistery appearanceThe blister copper is about 98% pure. To obtain ~100% copper, it must be purified by electrolysisEnvironmental concernsMining can cause significant environmental damageErosion in open cut minesInstability in land and earthLiberation of SO2 into the atmosphere can lead to acid rainWaterways more acidic kills fish eggsAcidifies soil crops may not growEroding marble (CaCO3) statues of historical valueEnvironmental concernsSO2 is a respiratory irritant at low concentrations 1ppmWorsens air qualityPeople with asthma will have breathing difficultiesEnergy considerationsLarge amounts of energy (heat or electricity) are required to extract metals. We need energy to break chemical bonds in the minerals and to facilitate reductionEnergy is also needed to:Mine the ore to drive machinery and explosivesConcentrate the oreMaintain the high temperatures needed for roasting and extraction reactionsPurify the raw metal and/or form alloysCost of productionCost of extraction: more reactive metals require higher energy inputs and are thus more likely to attract higher costsLocation of the ore: if the ore is located in a high population zone, the mining procedure can be more difficult. This may increase cost of productionIf the ore is located in a remote place, greater expense is required to transport raw materials to the refinery plantsWorldwide demandLinking metal extraction to reactivityMost metals occur in nature within minerals. To extract a metal from a mineral, a large input of energy is requiredReactive metals form stronger bonds with other elements (eg. Oxygen or sulfur) and their ions are harder to reduce. This means more energy is required to extract reactive metals from their ores than less reactive metalsSo why are more metals available now?Before 1800, only 10 metals were in use. These were either native metals (Au, Ag, Pt) or those extracted by heating with carbon (Cu, Sn, Fe, Pb, Zn, Hg, Bi)Lower cost generation and wide scale distribution of electricity have driven advances in extraction processesMany reactive metals can only be extracted by electrolysis eg. Aluminium from bauxite200 years ago, the lack of such technology and the scarcity of some metals meant only limited amounts could be extracted and usedWhy are ores non-renewable?Ores are deposits of naturally occurring minerals which were formed during the evolution of the universe and planets by the accretion of matter. There is no way of replacing these ores within our lifetimes.Ores are thus considered to be non-renewable resourcesAdvantages of recyclingLess energy is used in recycling metals than in extracting metals from ore, so recycled metals may be cheaperNon renewable sources of metals (ores) are conservedLess waste disposalHow is aluminium recycling done?Used aluminium is collected from homes, shopping centres, factoriesIt is then transported to a central processing plantThe metal is separated from impuritiesRe-smelt the metal into stock ingots and transport them to product manufacturersExtraction of aluminiumBauxite is separated from its impurities, mainly Fe2O3 and SiO2, by heating with NaOH solution. The dissolved mineral is filtered and precipitated to obtain Al2O3 (alumina)2Al(OH)3(s) -> Al2O3(s) + 3H2O(l)The Al2O3 is mixed with cryolite (Na3AlF6) so it can be smelted at 1000C and reduced to aluminium by electrolysis.2Al2O3(l) + 3C -> 4Al(l) + 3CO2(g)Concentration1. Solute, solvent, solutionSolute the component of a solution that the substance that is present in the lesser amount; the substance that gets dissolved by anotherSolvent the component of a solution that is present in the greater amount, the substance that dissolves the otherSolution a homogeneous mixture of 2 or more substancesSolute + solvent = solutionConcentration2. Concentration, saturated solution, solubilityConcentration amount of solute that is present in a given amount of solvent or solutionSaturation solution a solution which contains the maximum amount of solute in a given quantity of solvent at a particular temperature (no more solute can be dissolved)Eg. At 25C, the maximum amount of NaCl that can dissolve in 100mL of water is 36g. So if a solution contains 36g of NaCl in 100mL of water, then it is a saturated solution. 36g/100mL = 36% w/vSolubility the maximum amount of solute that can be dissolved in a given quantity of solvent at a particular temperature. That is, solubility = the concentration of the saturated solution at a particular temperatureConcentration3. Measures of concentrationMass of solute per unit volume of solvent (w/v)Weight for volume (technically mass)Eg. g/mL, g/100mL, g/LVolume of solute per unit of solution (v/v)Eg. mL/100mLUseful for liquid solute in liquid solventsEg. 5mL of ethanol in 100mL water

ConcentrationMass of solute per unit mass of solution (w/w)Eg. g/100g, ppm (parts per million), ppb (parts per billion)Useful for solid solutes in solid solvents (eg. Alloys)1ppm by mass = 1g/1000000gPpm by volume = 1mL/1000000mLPercentage by mass or volume% w/v (g/100mL), % v/v (mL/100mL), % w/w (g/100g)