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Main Factors of Lime Hydration Process

2023-06-06 11:07:22

There are many variables that could affect the lime hydration process, below are the major factors.

 Hydration temperature:
The temperature of water and quicklime will affect the hydration reaction speed. Generally, the hydration speed increases with the increase of the reaction temperature. The relationship is as follows:
K(T) =K(0)×1.035T
K(T): the reaction speed when the temperature is T;
K(0): the reaction speed when the temperature is T0;
T: T-T0
 Chemical composition of quicklime
High-purity quicklime accelerates the hydration reaction. The higher the purity of the quicklime, the lower the possibility that the pores of the quicklime will be blocked, and the chance that the surface of the quicklime will be coated with impurities (such as quartz, alumina, iron powder, etc.) that are dissolved during calcination will also reduce the chance that these impurities will hinder the contact between water and the quicklime . In addition, the high magnesium oxide content present in the quicklime powder will also have a negative impact on the reaction, because the higher magnesium content tends to cause over-burning of the lime.
 Activity of quicklime
The activity of quicklime depends on the size of the quicklime and magnesium oxide crystal particles, the specific surface area of the calcined quicklime powder and the porosity of the oxide.
These three characteristics are closely related, that is, the smaller the quicklime crystal particles, the larger the specific surface area of the quicklime, and the higher the porosity. The realization of these characteristics largely depends on the calcination temperature and the residence time of the quicklime in the kiln. The higher the calcination temperature, the longer the residence time of the quicklime in the kiln, and the slower the hydration speed of the quicklime will be.
The conversion of calcium oxide to calcium hydroxide is a liquid reaction. When Ca2+ and OH+ ions form supersaturation in the solution, calcium hydroxide precipitates out in the form of crystals.
The quicklime produced by light burning process has a large specific surface area and high porosity, so the solution concentration can quickly increase during the reaction and reach a supersaturated state quickly. During the crystallization process, the strong supersaturation state will inevitably lead to the rapid formation of single crystals.
On the contrary, if it is over-burned quicklime, the solution concentration will increase slowly, the supersaturated crystal precipitation rate will also be reduced significantly, thus the coarse-grained crystal formation rate will increase, and the sizes of hydrated lime will be coarser.
 Sizes of quicklime
The smaller the particle size of quicklime powder, the faster the hydration reaction speed. It’s notable that finer feeding sizes may react too quickly with water so that the generated heat can’t be removed soon enough, therefore cause sharp temperature increase that may overcook the particles, which consequently compromise hydration performance.
Based on our experience, the advised lime feeding size is to be controlled at 0-20mm. size distribution can be adjusted according to the product requirements and lime quality.
 Mixing system
The more intense the mixing and stirring of the oxide and water, the faster the reaction rate and the diffusion rate of calcium hydroxide particles.
 Water
From an industrial perspective, impurities in water have little effect on the hydration reaction of quicklime and water. If the sulfate and chloride content in the water is high, it will affect the hydration reaction.
Water temperature has influence on hydration speed, the higher the water temperature, the faster of reaction speed.
If there are unknown concerns, we recommend a preliminary laboratory test to compare the test results with the lime reaction results with distilled water.
In addition, if the concentration of impurities in the water is high, the water will corrode the pump and hydrator.


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