The characteristics, applications and usage and storage regulations of calcium hydroxide
Calcium hydroxide, commonly known as slaked lime or hydrated lime, with the chemical formula Ca(OH)₂, is a widely used inorganic base. It appears as a white powder-like solid with significant hygroscopicity and is prone to deliquescence in the air. When calcium hydroxide is added to water, it naturally forms a two-layer structure. The clear aqueous solution on the upper layer is called clear lime water, while the turbid suspension on the lower layer is called lime milk or lime slurry. With its unique chemical properties, calcium hydroxide holds an important position and plays an indispensable role in numerous industries such as chemistry, medicine, food, industry and agriculture.
In the field of industrial wastewater treatment, calcium hydroxide demonstrates a powerful purification capacity. It can effectively neutralize acidic wastewater, capture metal ions in the wastewater through chemical reactions, remove fluoride ions at the same time, accelerate the sedimentation of impurities, and improve the dewatering property of sludge. In addition, it can also exert a bactericidal effect and promote the hydrolysis of organic matter, and is widely used in enterprises that generate a large amount of industrial wastewater, such as petrochemical and starch factories, to help the wastewater meet the treatment standards.
In agricultural production, calcium hydroxide serves as an effective aid for soil improvement. It helps reduce soil acidity, adjust pH levels, and enhance soil structure, creating a better growing environment for crops. When applied as a calcium fertilizer solution, it promotes plants’ uptake of essential nutrients such as nitrogen, phosphorus, and potassium, thereby increasing crop yield and quality.
Calcium hydroxide also plays a role in pest and disease control. Bordeaux mixture—prepared by combining lime milk (calcium hydroxide in water) with copper sulfate solution—effectively combats bacteria and pests. Additionally, applying lime slurry to tree trunks up to 80 cm above the ground in winter helps protect trees from pests and diseases, supporting their survival through the cold season.
In the construction industry, calcium hydroxide is an indispensable basic material. It is used in processes such as bricklaying, wall plastering, and making three-component soil, and can achieve excellent thermal insulation and heat preservation effects. Meanwhile, it is also an important raw material for cement production, which can be obtained by electrically calcining kaolin. In the papermaking industry, calcium hydroxide, as an important inorganic filler, can effectively improve the penetration and diffusion capabilities of paper products and enhance the quality of paper.
In the coatings industry, by taking advantage of the characteristics of calcium hydroxide such as its alkalinity, weak corrosiveness, stable performance and being unaffected by temperature, its application in coatings can endow them with excellent water resistance, moisture-proof and anti-mold functions. Adding an appropriate amount of calcium hydroxide to various types of paints can also adjust the color and gloss.
In the production of refractory materials, adding calcium hydroxide as an additive during the manufacturing process of silica bricks can enhance the strength and viscosity of the bricks and improve their refractory performance. In addition, calcium hydroxide is also used in the production of a variety of chemical products such as bleaching powder, bleaching powder essence, disinfectants, antacids, astringents, water softeners, depilators, buffers, neutralizers, and curing agents.
In the food industry, calcium hydroxide has become a commonly used food additive due to its strong activity and loose structure. Calcium hydroxide can react with carbon dioxide in the air to form calcium carbonate, which is insoluble in water. This property is fully utilized in the sugar industry: first, calcium hydroxide is used to neutralize the acidic substances in the syrup, and then carbon dioxide is introduced to react the remaining calcium hydroxide to form calcium carbonate precipitate. After filtration to remove the precipitate, the sour taste of the sugar can be effectively reduced and the quality of the sugar can be improved.
In the medical field, calcium hydroxide, due to its strong alkalinity, has anti-inflammatory effects and is widely used in dentistry. It can be used to repair damaged teeth and also participate in various dental treatment procedures such as pulp filling, root canal filling, and oral disinfection, providing a guarantee for oral health.
In the field of environmental protection, calcium hydroxide plays a crucial role in flue gas desulfurization. It can undergo neutralization reactions with sulfur dioxide, sulfur trioxide, and a small amount of fluoride ions, chloride ions and other acidic gases in the flue gas, reducing the sulfur content in the flue gas, making the emitted flue gas meet environmental protection standards, and reducing air pollution.
Although calcium hydroxide has a wide range of applications, it is necessary to strictly follow relevant precautions during its use to ensure safety. Firstly, closed operations must be carried out. Operators must strictly follow the operating procedures. It is recommended to wear a dust mask (full face mask), a one-piece rubber-coated anti-toxic suit, and rubber gloves to avoid generating dust. Contact with acidic substances is strictly prohibited. When handling, load and unload gently to prevent damage to packaging and containers.
At the same time, emergency handling equipment for leakage should be provided, as empty containers may still contain harmful substances. Secondly, stay away from acidic liquids. As calcium hydroxide is a strong base, it will undergo chemical reactions with acidic liquids, so contact with them should be avoided. Furthermore, it is necessary to isolate the leakage contamination. Warning signs should be set up around the calcium hydroxide storage area.
When handling the leaked substance, it is recommended that the handling personnel wear gas masks and chemical protective suits, and must not come into direct contact with the leaked substance. The leaked substance can be collected in a dry, clean and covered container with a clean shovel, or a small amount of sodium hydroxide can be added to the leaked substance and then a large amount of water can be added to adjust it to neutral and then discharged into the wastewater system.
It can also be directly rinsed with a large amount of water, and the diluted wash water can be discharged into the wastewater system. In the event of a large-scale leakage, the leaked substance should be collected, recycled or treated harmlessly before being discarded. In addition, it is necessary to pay attention to its irritability.
Calcium hydroxide dust or suspended droplets have a stimulating effect on mucous membranes. Inhaling them can cause sneezing and coughing. Its alkalinity can also saponify fat, absorb moisture from the skin, dissolve proteins, irritate and corrode tissues. Inhaling lime dust may also cause pneumonia. Therefore, protective measures should be taken during operation.
When storing calcium hydroxide, a cool and well-ventilated warehouse should be chosen, and the humidity inside the warehouse should not exceed 85%. Sealed packaging should be adopted to prevent moisture absorption. When storing, it should be kept separate from flammable or combustible materials, acids, edible chemicals, etc. Mixed storage is strictly prohibited to ensure storage safety.
