Limestone
Limestone is one of the
crystalline forms of Calcium Carbonate, CaCO3, an ionic compound
Ca2+CO32-
When it is heated strongly it breaks up in time to give Calcium Oxide
(Quicklime) and Carbon Dioxide
CaCO3(s) à CaO(s) + CO2(g)
This reaction is a Thermal
Decomposition
The Calcium Carbonate is in a sense reacting with itself.
We heated some Calcium Carbonate chips on a gauze strongly from above for about 40 minutes. They glowed red and then quite a bright white. This provided evidence that a reaction was taking place. Afterwards, we noticed that the marble had changed from being hard and quite shiny to dull and powdery. The solid was now mainly Calcium Oxide.
We cautiously added water drop by drop. An exothermic reaction occurred : the solid showed a large increase in volume and steam was produced. The calcium oxide had reacted with the water :
CaO(s) + H2O(l) à Ca(OH)2(s)
We remember that metal
oxides don't dissolve in water but those that do produce hydroxides.
Excess water will also produce calcium hydroxide solution, an alkali
These compounds have some old names :
CaCO3(s) MMMMMMMLimestone
CaO(s) MMMMMMiiMIQuicklime
Ca(OH)2(s) MMMiiMMISlaked lime
Ca(OH)2(aq) MMMiiiMILime water
Thermal Decomposition of calcium carbonate is performed industrially in a Lime Kiln. This is a sloping rotating cylinder down which roll pieces of calcium carbonate and up roars a flame.
Uses of Limestone (CaCO3, CaO)
Roadstone,
Raw material for blast furnace to make Na2CO3 to
make glass Quicklime (CaO).
Basic Oxygen Steel making process,
add H2O to get Ca(OH)2,
Neutralise Acidity in the soil,
Drinking water treatment.
The lumps of limestone from the quarry are crushed, and this process produces some sand, which is also used in glass making and after washing, some very fine solid particles. These are mixed with bauxite and sand, and this mixture is heated strongly to make Cement.
The socio-economic consequences of Limestone quarrying
The setting up of a new quarry improves the economy of the area by producing new jobs, and opportunities for a variety of companies to be expanded or set up. However, there are problems :
holes and scars, often in areas of astounding natural beauty.
The distraction and disruption of wildlife and wildlife habitats.
Pollution from exhaust gases, noise, dust, vibration from lorries and explosions. Spent quarries are generally landscaped, but the other problems are difficult to overcome.