Calcium oxide is the chemical combination of calcium and oxygen subsequently forming a product that is rich in its characteristics and has an excellent set of properties that enable it to perform various tasks. It is also known as quicklime as well as burnt lime. The uses of calcium oxide in our daily life are extended enough that they can be categorized into several branches due to the top characteristics that it holds. All of these are great, playing a role in enhancing the lifestyle of humans by contributing through all the means that are possibly accessible.
A broadly utilized chemical compound, calcium oxide (CaO) is usually known as burnt lime or quicklime. At room temperature, it is crystalline, alkaline, caustic, and white solid. Calcium-containing inorganic materials are connoted by 'lime', in which hydroxides, oxides, and carbonates of iron, aluminum, magnesium, silicon, and carbon predominate. In comparison, specifically, quicklime implements to calcium oxide's single chemical compound. Free lime is the calcium oxide that doesn't react in building products while processing for instance cement. In comparison, quicklime is cheap. Quicklime and calcium oxide (chemical derivatives) are significant commodity chemicals.
A high surface tension, medium viscosity, and a high to intermediate contraction and expansion rate are possessed by the calcium oxide. At ceramic temperatures, calcium oxide is not volatile. Colour is moderately affected by calcium oxide, but when it is in large quantity, then it has a bleaching effect on the iron oxide. Its existence is also in tomato reds or khaki colors.
Preparation of Calcium Oxide
Calcium carbonate (mineral calcite; CaCO3) is contained by materials like seashells and limestone, and the thermal decomposition of materials like these can produce calcium oxide in a lime kiln.
Calcination is the process that is utilized for preparing burnt lime. In this process, at high temperatures, the reactants are thermally decomposed while keeping the temperature less than the melting point.
1070-1270 C is the range of temperature for calcination of calcium carbonate. Usually, these reactions take place in a rotary kiln and carbon dioxide and burnt lime are the products and results of those reactions. The formed carbon dioxide is removed instantly so the reaction can be preceded until the process completes following Le-Chatelier’s principle.
CaCO3 → CaO + CO2
In the forward direction, a reaction like this in nature is exothermic and reversible.
Lime Water Formula
Lime water’s chemical name is calcium hydroxide and its chemical formula is Ca(OH)2. On the addition of water to lime, the production of calcium hydroxide Ca(OH)2 takes place according to the following reaction.
CaO + H2O → Ca (OH)2
It is a very strong and exothermic reaction and it occurs vigorously with the production of steam clouds.
What is the Difference between Quicklime and Lime Water?
CaO is quicklime or lime’s chemical formula. Calcium oxide is lime’s chemical name. However, Ca (OH)2 is limewater’s chemical formula and calcium hydroxide is this substance’s chemical name.
Characteristics of Calcium Oxide
Having 2600 C as its melting point, quick lime can withstand high temperatures. It is an amorphous white solid and a very stable one. Slaked lime is formed by it in water’s presence which is known as the slaking of lime.
CaO+H2O → Ca (OH)2
It is a basic oxide in nature that produces salts on making a contact with an acid. It crystallizes in a cubic crystal lattice. 40 joules per mole Kelvin is calcium oxide’s standard molar entropy. When it is heated to more than 2500 C of temperatures, an intense glow is emitted by it.
CaO+H2SO4 → CaSO4+H2O
Benefits of Calcium Oxide
It has a huge amount of usages for insecticides and medical purposes. Its applications are found in producing high-grade steel, paper, and cement. In laboratories, lime is utilized for precipitation reaction, dehydration, etc. as a reagent. When producing caustic soda, it is a significant ingredient as it is the cheapest alkali available. As the constituent of teeth, shells, and bones, calcium is important for the life of animals. Calcium carbonate is the most common of calcium compounds and potter utilizes it for glazes as calcium oxide's source.
Extraction of Calcium Oxide Particles from Eggshell Waste
For waste management and economic development, waste material's bioconversion into a valuable material is extremely important. These waste materials can be eggshells from the poultry industry. The classification of eggshell waste is done in agricultural and industrial wastes too. Using these wastes to form valuable materials for instance CCNPs, adsorbents, feed supplements, and fertilizers will give a solution for eggshell's disposal and for lessening pollution in the environment.
India, the USA, and China are the leading producer of eggs among other countries in the world. They contribute about 80 million metric tonnes almost. According to literature from 2017, 95 billion eggs per shell is the share from India, 109 billion eggs per shell are the share from the USA, and 458 billion eggs per shell is China's share. 78 million metric tonnes was the approximate global egg production in 2018 and this egg production resulted in the production of eggshells of 8.58 million metric tonnes which are wasted as a waste whereas at some places in the world, those same eggshells are utilized for fillers, and as landfills, etc.
As compared to the egg's total weight, the eggshell weight is 10-11 percent of that total weight. During processing, there is the generation of 250,000 tons of eggshell waste, annually. Every year in U.S landfills only, almost 150,000 tons of chicken eggshells are disposed of. 5 percent of organic materials like sulfated polysaccharides, type X collagen, and other proteins, and 95% CaCO3 as calcite is contained by the eggshell.
For waste eggshells, the methods of disposal are like the following, 26.3 percent in municipal dumps, 21.1 percent as ingredients to feed an animal, 26.6 percent as fertilizer, and 15.8 percent of the waste is utilized in other ways. Synthesis of microsized aragonite calcium carbonate particles i.e of 10-30 μm was reported in 2020 by Habte et al. by the method of carbonation along with calcination at high temperature from eggshell waste.
Recovering carbonate/Calcium Oxide from Waste Calcium Sulfide
One of the significant waste of various industries is calcium sulfide (CaS) and it is based on coal. This waste material is formed in large quantities, for instance, CaS of 67 tons/day is produced on gasificationof 3% sulfur coal of 1000 tons/day while a limestone-based adsorbent is being used for the desulfurization of hot coal gas. Being rich in sulfur is this waste's main problem that's why it can't be landfilled as there can be potential H2S gas evolution and sulfur's leaching in the soil.
H2S and CaCO3 were synthesized from waste CaS according to the reports from Brooks and Lynn (1997). In CaS, calcium sulfide reacts with H2S to produce a complex either with other alkanolamines or methyl diethanolamine (MDEA), and calcium sulfide is dissolved. Then in the next level, Ca (HS)2 forms a reaction with CO2 complexed with MDEA as it is very soluble. Uniformly sized and pure crystalline CaCO3 are precipitated by these and they produce MDEA-complexed hydrogen sulfide.
Calcium oxide is a significant inorganic compound utilized in numerous industries as an alkalization agent, a toxic waste remediation agent, and an adsorbent. Although, harmful impurities are possessed by LiMCaO and they have a very high heat of hydration. However, scallop shells are comparatively a CaO readily available source and they are also utilized in paving and plastering materials, and as a food additive. Still, most of the scallop shells are industrial waste, and they join each other in Japan’s harvesting district’s shores, resulting in serious problems like soil pollution and offensive tastes because of heavy metals and harmful materials leaching from the shells.
Heated scallop shell powder
Potent microbicidal activity is displayed by the well-known heated scallop shell powder (SSP). For instance, when SSP is heated to more than 1000 degrees Celsius, then the ground displays wide microbicidal action against biofilms, fungi, heat-resistant bacterial spores, bacteria, and numerous viruses. This material acts as an additive for prolonging the food product’s shelf life. On hydration with water, there is an easy conversion of CaO to Ca (OH)2. A base is generated by CaO hydration and it is one of the mechanisms for heated-SSP's disinfection action.
For instance, as compared to the disinfectant activity of NaOH or Ca(OH)2 solutions at the same pH, CaO hydration reaction’s disinfection activity towards both coliform bacteria (CF) and total viable cells (TC) was higher. We apply BiSCaO suspension (0.2 wt%) to cleanse contaminated pigskin and wooden pieces for eliminating both CF and TC. A higher disinfection activity was possessed by the BiSCaO suspension solution as compared to NaClO and HOCl in both CF and TC. Also, in order to disinfect BiSCaO, more than 10-fold higher concentrations are needed by chlorhexidine gluconate and povidone-iodine. Therefore, a great potential is possessed by BiSCaO for applications in the food industry and medicine.
Calcium oxide hydration:
A strong base is generated by CaO hydration and it is the main way for BiCaO dispersion’s deodorization and microbicidal activities. BiSCaO’s CaO content is way more, suggesting that higher deodorizing and microbicidal activities are showed by BiSCaO dispersion because of the higher pH as compared to SSP-Ca(OH)2. Although, according to the studies, at the same pH, higher activity was displayed by BiSCaO-6 as compared to NaOH solution, suggesting that only alkalinity is not what causes BiSCaO’s deodorizing and microbicidal properties.
Active radical species:
When CaO or MgO generates active radical species, those species force an increase in the stronger disinfection activity.
Like CaO, MgO is also an alkaline earth metal oxide, and its antibacterial activity was investigated by Krishnamoorthy et al. According to those investigations, MgO’s antibacterial activity depends on whether there are oxygen vacancies or defects at the particle's surface. Mg(OH)2’s surface layer is formed by MgO as it is easily hydrated, forming surface-bound electron-hole pairs. To understand CaO’s mechanism through which it exerts its microbicidal effects, there need to be further studies on it.
Important Safety Tips
Some things should be kept in mind while using Calcium Oxides. The reaction is usually vigorous between water and quicklime. Intense irritation can be caused by quicklime especially when it makes a contact with eyes or wet skin or when it is inhaled. Inhalation causes many effects, some of them are labored breathing, coughing, or sneezing. Also, abdominal pain, vomiting, and nausea burns with nasal septum's perforation can be caused. Enough heat can be released when quicklime causes a reaction with water for igniting the combustible materials.
Uses of calcium oxide
Quicklime’s major usage is in the process of basic oxygen steelmaking(BOS). It is utilized in about 65-110 pounds or 30-59 kg per ton of steel. Fe2O3, Al2O3, SiO2, and acidic oxides are neutralized by the quicklime for forming a basic molten slag.
With ca. 0.6–1.0 g/cm3 of densities, aerated concrete blocks are produced by using ground quicklime. Clay-containing soil's load-carrying capacity can be significantly increased by the hydrated lime and quicklime, and they do that by causing a reaction with finely divided alumina and finely divided silica for producing aluminates and silicates and they contain cementing characteristics. In other processes, quicklime is used in small amounts; for instance, the formation of organic chemicals, calcium aluminate cement, and glass.
Heat: Quicklime forms calcium hydroxide and is hydrated through the following equation to release thermal energy.
CaO (s) + H2O (l) ⇌ Ca(OH)2 (aq) (ΔHr = −63.7 kJ/mol of CaO)
The solid puff up as a result of an exothermic reaction as it hydrates. It is then heated to redness for reversing the reaction of hydration so that water can be removed so hydrate can be reconverted into quicklime. Calcium hydroxide and 3.54 MJ of energy are given when almost 6.8 pounds or 3.1 kilograms of quicklime combines with one liter of water. One can use this process for providing heat's convenient portable source, as for the instant warming of food in a self-heating can, heating water, and cooking, with no open flames. This method of heating is utilized by various companies which sell cooking kits. It possesses the E number E529. It's a food additive to the FAO as a leavener, a flour treatment agent, and an acidity regulator.
Light: An intense glow is emitted by the quicklime when it is heated to 4,350 degrees Farhenheit or 2,400 °C. Such kind of illumination is called the limelight and was utilized widely in theatrical productions before electric lighting was invented.
Cement: The main ingredient is used in the process of making cement, and is calcium oxide. As a broadly available and cheap alkali. Total quicklime production of almost 50% is changed to calcium hydroxide before usage. Drinking water is treated by using both hydrated- and quick-lime.
Petroleum industry: A mix of phenolphthalein and calcium oxide is contained by the water detection pastes. When the water in the fuel storage tank reacts with the paste, then the CaO forms a reaction with water for producing calcium hydroxide. Phenolphthalein is turned into a vivid purplish-pink color by calcium hydroxide as it possesses a high enough pH, and that transformation indicates water’s presence.
Paper: At kraft pulp mills, calcium oxide is utilized in the chemical recovery for regenerating the sodium hydroxide from the sodium carbonate.
Plaster: According to archeological evidence, limestone-based plaster was used by Pre-Pottery Neolithic B humans for flooring and other usages. There was some usage of the Lime-ash floor until the late 19th century.
Chemical or power production: A process known as flue-gas desulfurization is done for removing sulfur dioxide from the exhaust steams by using solid sprays or slurries of calcium oxide.
Mining: Rock can be broken when quicklime's exothermic characteristics are exploited by the compressed lime cartridges. The rock is drilled with a shot hole like usual and then within the shot hole, quicklime's sealed cartridge is placed and tamped. The cartridge is injected with an amount of water resulting in the release of steam, which can break the rock apart when it is joined with the residual hydrated solid's greater volume. However, if the rock is specifically hard then this won't work.
Disposal of corpses: It is used to be a belief that corpses’ decomposition can be accelerated by the quicklime. Preservation can be promoted on quicklime’s application. Decomposition’s stench can be eradicated by the aid of quicklime, which can result in people having this erroneous conclusion.
Calcium oxide has many significant usages in our daily life and some of them are listed and explained here:
1. Production of Heat
The following equation is used by the raw lime to produce heat energy by forming calcium hydroxide and hydrate.
CaO (s) + H2O (l) = Ca (OH) 2 (aq) (ΔHr = -63.7 kJ / mol CaO)
Calcium hydroxide and 3.54 MJ of energy are provided when 6.8 pounds or 3.1 kg of lime joins with one liter of water. One can use this process for giving an appropriate portable heat source, for instance, to immediately heat food.
2. Production of Light
Severe light is emitted by this lime when it is heated to 4350 degrees Fahrenheit or 2400 degrees celsius. Before electric lighting got invented, this lighting was called as limelight and it was utilized broadly in theater production.
3. Ingredient for Cement and as Alkaline
The process of making Cement has calcium oxide as its main ingredient. In the synthesis of biodiesel, it is also utilized as an alkaline.
4. For detection of water in the Petroleum Industry
A mixture of phenolphthalein and calcium oxide is contained by the water-detecting paste. The water in the fuel storage tank should make contact with this paste. Calcium hydroxide is formed on the reaction of CaP with water. Calcium hydroxide can easily transform phenolphthalein to pink-clear purplish as it has a high enough pH, therefore showing water’s presence.
5. As Plaster
According to archaeological evidence, lime-based plaster was used by Neolithic B Pre-Pottery (pottery sticks) for flooring and other usages. There was some usage of the ash-lime floor until the late 19th century.
6. Shrimp Culture Industry
There has been popular usage of lime as an alkaline substance in the industry of shrimp or tiger shrimp culture for anticipating the pond water's decline in pH because of rain. In the rainy season, the Tohor lime is usually sown on the shrimp pond's edge.
7. As Weapon
David Hume, a philosopher, and historian wrote in his English history book that in the early time of Henry III's reign, the French fleet was destroyed by the British Navy by blinding enemy fleets with the chalk. Greek fire has components and raw chalk is considered to be one. Lime will ignite the fuel after it increases its temperature to more than 150 degrees celsius in contact with water.
8. Production of Bitan Egg
Bitan eggs can also be made by utilizing the Tohor chalk with its basic characteristics. The typical Chinese foods, thousand-year eggs, the black egg, or bait eggs are made from ducks or chicken eggs preserved in rice husks, lime, salt, ash, and clay, for weeks or months, and the method of processing determines whether its weeks or months. The color of the eggs changes because of the alkaline material's presence as they raise the egg's pH to more than 9 or 9.
Although, some of the fat contents and complex proteins in the egg are destroyed by this chemical process, causing them to have no taste but a strong smell. At times, there are shades in the eggs, for instance, the white part having pine branches.
Calcium oxide is one of the most used products in daily life as it enhances the chances of ease, comfort, and safety for all human beings. Its availability and productivity have highly increased over the past years and are continuing to grow as the best results can be seen through its consistent use.