The production of lime from Limestone The process of the production of quicklime , also identified as calcium oxide is achieved through the decomposition of naturally occuring limestone products (calcium carbonate, CaCO3) , to produce quicklime (CaO) and carbon dioxide (CO2).The process of the production of lime from limestone was a method used by civilisations such as Egyptians when building the pyramid of Cheros, the Greek civilisation when painting murals and the Chinese Dynasty who used Lime to stabilise soil in order to build the great wall of china.There is no exact inventor or invention date but the earliest noted use of lime was around 14,000 BC in the Lascaux caves in France.If the conditions of the process of producing lime from limestone such temperature, concentration and pressure are monitored then the maximum yield of quicklime will be achieved. CaCO3(s) → CaO(s) + CO2(g) Process / Steps The production of lime is typically comprised of four different steps.As limestone occurs naturally as it is a sedimentary rock , typically the first step is to collect the Limestone.This is done through underground mines and quarries. Secondly, as it comes naturally it be will mixed with other impurities as it is found in substances such as chalk and marble therefore it must go through steps of screen preparation where the limestone is chemically washed and sieved.This Brings the limestone to near purity and to the next step, calcination.Limestone calcination is the process of heating pure limestone at intensely high temperature (900 Degrees C +, usually towards the 1300’s Degrees C) in a large rotary or vertical shaft kilns to produce the product of Calcium oxide (Quicklime) and Carbon dioxide (CO2) as seen in figure (1.1).A optional process would be to hydrate the lime which would create slaked lime which can be used for mortar, plaster and cement for construction. Lime Production: Le Chatelier’s Principle and the Factors that cause a shift in Equilibrium Le chatelier's principle states that if disturbance (Temperature, pressure, concentration and catalyst ) is applied to a system the equilibrium will shift to counteract this disturbance. Concentration Kc = [CO2]1 The concentration of solids remains constant (Kp = pCO2 atm or Pa), meaning that the equilibrium is solely impacted by the change of carbon dioxide as seen in (figure (1.2)) (lime production is carbon intensive) or heat (typically, 900 oC or 1000oC in a lime kiln). Furthermore, according to the collision theory, when increasing the concentration of reactants (calcium carbonate), there are more molecules likely to collide, forming a reaction. Temperature: Since the forward reaction is endothermic, 178 kJ of heat energy as seen in (figure (1.3)) (enthalpy value ) is absorbed for every mole of calcium oxide formed. Therefore, it is evident that CaO formation is favoured by high temperature as the reaction fails unless temp is at least 900 oC (at 1000oC in a limekiln the equilibrium position is more likely to favour the forward reaction). Hence, Kp will increase with increase in temperature. Furthermore, as the temperature is intensely high, the activation needed to decompose calcium carbonate into carbon dioxide and lime is low as the kinetic energy is being increased (heating up the system), overcoming the high activation energy and shifting the equilibrium to the right hand side of the equation. This is because as stated by LCP, an increase in temperature is counteracted by the movement of the equilibrium to the right (forward reaction will absorb the heat) to minimise the increase in temperature. It is vital to note that increasing the temperature does not make increase the speed of the reaction but also its direction (to the right).The fact that the entropy of the chemical process is 168.18 J/K, the process of Lime production is increasing in entropy and therefore more randomness.Hence this chemical process favours the forward reaction at T > 1173 K. Pressure In a ventilated lime kiln as seen in (figure (1.5)) at normal atmospheric pressure( 1 atm) , the pressure of carbon dioxide is decreased and hence, the chances of a reverse reaction. Decreasing the pressure will favor the increase in the moles of gas in lime production and this leads to the formation of more CO2 and ultimately more CaO. Furthermore, according to the collision theory, this will decrease the likelihood of collisions occurring between carbon dioxide and calcium oxide, reversing the reaction to form limestone. One mole of gas is formed in the process. Since there are no gaseous reactants, there is a net increase in the moles of gas, decreasing the pressure and favouring the production of more carbon dioxide molecules. As seen in (figure (1.4)) This will encourage a shift in equilibrium to the right hand side (products), increasing the yield of lime.Due to an increase in gaseous particles this chemical process is increasing in entropy as any chemical equation with a increase in gas particles will be have an increase in entropy.This is seen through the equation where there are no gases on the reactants side and when the reaction occurs there is an increase in gaseous particles, in this case being CO2. Partial Pressure In this reaction, there is a decrease in the partial pressure of carbon dioxide and thus, there is a decrease in the likelihood of the system shifting to the reverse reaction. As the kiln is ventilated (not a closed system) to allow the escape of air and carbon dioxide, a true equilibrium is never established because and the system favours the forward reaction. The equilibrium quotient (Q<K) For this specific reaction, the equilibrium constant is substantially bigger than 1 (K>1), specifically K= 1.7568809808x1023 . . This can aid in predicting the equilibrium shift, in this case it will be favour the right hand side (the forward reaction), producing more lime and carbon dioxide. This is because the ratio of products to reactants is less than when the system is at equilibrium, and since the products are lower, to reach equilibrium, the system will favor the forward reaction. This occurs in order to to use up the excess reactant to make more products. Removing a product An example of the yield obtained can be seen in scienceviews.com’s explanation of the yield of lime.It states that at optimal temperature (1010-1345 Degrees C) the yield receive from 100 kg of limestone would be 56 kg of quicklime and 44 kg of carbon dioxide.Therefore the percentage yield obtained from limestone would be split 56 (CaO) : 44 (CO2). Essentially, to maximise the production and yield of lime, it is essential that the reaction is manipulated and continuously monitored to favour the forward reaction, and avoid the reverse. Furthermore, if the industry is able to monitor the shift in equilibrium by flushing carbon dioxide from the mixture as it is released from the lime kiln. Ultimately, this drives the reaction to the right hand side, as elaborated by the figure above.As seen in ((figure 1.6)) The effects of monitoring the Process of the production of Lime from Limestone Positives Negatives ● ● ● ● ● ● In terms of Calcium Oxide only, when monitored correctly there are few hazards to the environment. Lime has a variety of uses, this is a huge positive as it can be used to boosted the economy by creating more products.Products such as steel are created, 45% of lime is used in the steel industry. 80 kg of lime is used to produce every 1000 metric tons of iron through the process of removing Slag from Iron.Aluminum can be created through the use of Lime as lime removes silicates from alumina.Lime also creates silicates that can be used to create glass which is so important to today's economy. The abundance of limestone allows for great economical gain as it can produced without fear of being a limiting reagent. Quarrying and mining boosts the economy immensely as it provides high paying jobs and raw materials. Providing jobs around the area of the quarry is a huge positive. Over 22 million tons of limestone is produced in the US every year, therefore we can see the importance to the economy. ● ● ● ● ● ● Acidity levels of 12 pH are dropped down to 7.5 - 8.5 pH in the case calcium oxide .This is negative to the environment as a decrease in pH can lead to more pollution in the environment. The process of the production of lime from limestone is immensely negative to the environment as the production CO2 must occur in order for the process to occur.Data provided by ScienceView.com outlines that 44% of Carbon Dioxide must be produced for 56% of limestone.Also, in order for the reaction to produce more lime the carbon dioxide must be let out following le chatelier's principle.The effect this has on the environment ranges from Air-Pollution to Climate change.This issue of Carbon dioxide emission is the most negative impact on the Earth's environment. Limestone mines and quarries are extremely negative to the environment due to the environment being permanently damaged due to the mining that occurs.This damage to the environment destroys animal habitats and homes.Also the noise created denies the chance of birds and other wildlife to inhabit the area. Socially the negative effects of Lime production is that the noise that quarries and mining areas collecting limestone create heavy amounts of noise that damages people's quality of life. Cement factories create huge amounts of dust that affects people's breathing and damages their quality of life.This is again a negative social impact. Many injuries have occured in the workplace for Lime production due to the fact that the lime Kilns are huge and contain heavy equipment.This is a huge social effect and ethical effect. The process of the production of lime from limestone is positive to an extent in the criteria of the economy, society and the environment.The Carbon dioxide emissions of this process is immensely negative due to the impacts result in air pollution and climate change . The production limestone creates 44% of carbon dioxide that must be let out in order for process to occur correctly.To add to this quarries and mines are extremely destructing to the environment not only due to the fact that they damage the area they are based in but also due to being extremely noisy.This in turn does not allow for animals, birds especially to live in that area. Also, the mines and quarries loud noise affects the quality of life for those who live around the area, this is a huge social negative.Due to the heavy machinery used in the collection of limestone and the production of lime man injuries and deaths occur.This is a huge social negative as injuries affect the quality of life of the injury and also the deaths are a massive ethical issue.However the Calcium oxide itself is not harmful when maintained correctly.Adding to this Calcium oxide is a huge benefit to the economy as it allows for products such as glass, steel and silicon to be created.Another huge positive is the abundance of the Limestone that is used in the process.Finally, the fact that the production of lime creates many jobs due to people in the area of the mines and quarries are able to work is a huge positive economically and socially.