Calcium hydroxide (hydrated lime) refers to a powdery product obtained by reacting quicklime with (controlled) quantitative water, generally containing less than 1% free water.
At temperature below 350℃: CaO+H2O →Ca(OH):+276(kcal /kg CaO)
In the 1980s, high specific surface area calcium hydroxide was mainly used to remove acidic gases from waste gas. Obviously, increasing the surface area of calcium hydroxide is conducive to improving efficiency. Therefore, people began to study and develop high specific surface area calcium hydroxide, which is widely used in the synthesis of medicine and food additives, the synthesis of high-tech biomaterials HA, the synthesis of feed additives VC phosphate, food konjac, calcium synthesis, and the synthesis of calcium cyclohexane acid, calcium lactate, calcium citrate, cola additives and other high-end organic chemicals.
Surface area determination method: (1) BET method to measure specific surface area: (2) Measure total pore volume and pore size distribution; (3) Measure particle size and distribution; (4) Electron microscope to observe particle morphology.
There are currently two methods for producing high specific surface area calcium hydroxide: one is to obtain calcium hydroxide with a specific surface area of up to 30m2/g from lime milk by drying and grinding (referred to as wet method); the other is to obtain high specific surface area calcium hydroxide by adopting a variety of measures (referred to as dry method), such as: (1) hydration with water-alcohol solution; (2) sucrose aqueous solution; (3) addition of sulfonated lignin; (4) amine derivatives, etc.
The hydration process parameters will also affect the size of the surface area, such as water temperature, degree of quicklime calcination, quicklime feed particle size, quicklime specific surface area, material retention time in the hydrators and its maximum temperature, etc., see Table 1 and Table 2 for details.
Table 1. Effects of lime calcination on the specific surface area of hydrated lime
| Soft-burnt lime | Hard-burnt lime | |
| Quicklime surface area(m2/g) | 1.18 | 0.55 |
| Hydrated lime surface area(m2/g) | 24 | 14.6 |
Table 2. Effects of hydration process on the specific surface area of hydrated lime
| Hydration process | Specific surface area (m2/g) |
| Clean water at 5oC | 6.67 |
| sucrose aqueous solution | 37-46.3 |
| alcohol solution | 36-45.6 |
Applications of high specific surface area calcium hydroxide
Calcium hydroxide has a wide range of applications. It is necessary to design the preparation process accordingly according to the application occasion, that is, to “tailor” and produce “special calcium hydroxide” to achieve good use effects. For example, for medicinal use, high-purity calcium hydroxide is required (the content of harmful heavy metals such as lead, arsenic, and mercury must meet the pharmacopoeia indicators); for flue gas desulphurization, high specific surface area calcium hydroxide is used to achieve high efficiency.
Main application areas:
