Calcium Hydroxide, Slaked Lime, Hydrated Lime: A Chemical by Many Names

Calcium hydroxide, also known as slaked lime or hydrated lime, is a chemical compound with the chemical formula Ca(OH)2. It is a white powder that is produced by mixing calcium oxide (quicklime) with water. Calcium hydroxide has a variety of uses, including as a flocculant in water treatment, as an ingredient in cement and plaster, as a pH regulator in agriculture and food production, and in the production of paper and textiles.

Calcium Hydroxide is fairly simple to make. First you must obtain Calcium Oxide. Calcium oxide, also known as quicklime, is obtained by heating limestone (calcium carbonate) in a lime kiln at a high temperature (around 900-1000°C) to drive off carbon dioxide. After that, the calcium oxide is then mixed with water in a process called “slaking”. The chemical reaction between calcium oxide and water generates a large amount of heat and the mixture produces calcium hydroxide, which is a white, powdery substance.

The chemical equation for this reaction is:

CaO + H2O → Ca(OH)2

After this high heat reaction, the mixture of calcium hydroxide and water is allowed to settle and the solids are separated from the liquid by filtration or sedimentation. Once the solid calcium hydroxide is separated, it is then dried to remove any remaining water and the resulting product is a fine, white powder.

Calcium Hydroxide has many uses over many different applications. In agriculture, Calcium hydroxide is commonly used as a soil conditioner and fertilizer to neutralize acidic soils and supply calcium to plants. In construction it is used as a component of mortar and cement, as well as a filler and coating material. Calcium hydroxide can also be used in water treatment to neutralize acidic water and to remove impurities. It can also be used further in the chemical industry to aid the production of calcium-based chemicals such as calcium stearate and calcium hypochlorite. It is also frequently used for the treatment of acid mine drainage and other forms of acidic wastewater.

While Calcium Hydroxide is GRAS (Generally Recognized As Safe), there are a few mild dangers when working with Calcium Hydroxide. It is highly alkaline and can cause severe irritation or burns if it comes into contact with skin or eyes. Appropriate personal protective equipment, such as gloves and goggles, should be worn when handling Calcium Hydroxide. Dust from Calcium Hydroxide can cause irritation to the respiratory tract if inhaled. Workers should avoid breathing in the dust and should wear respiratory protection when working with large quantities. Calcium hydroxide is not flammable, but it can react with acids to release heat and generate hydrogen gas, which is highly flammable. This can create a fire or explosion hazard in certain circumstances. While this last danger isn’t related to humans, Calcium hydroxide can be harmful to aquatic life if it is released into waterways. Appropriate measures should be taken to prevent spills and to contain and clean up any releases.

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