Research on lime slaking has been done on a limited basis in recent years. Most of this research has been done under auspices of the National Lime Association. The information presented in this paper builds upon the research done by others and the author’s years of hands-on experience in lime slaking.
Because limestone is a naturally occurring mineral its chemical composition and physical characteristics vary not only from area to area but within veins of limestone in the same area. This variation in raw material results in variation of quality of the end product, which is calcium hydroxide.
The use of lime in its various forms has been steadily on the rise with no end in site. Today lime is the most important chemical used throughout the world for pollution control. It is, therefore, imperative that knowledge of handling and processing lime be well understood by all those who use this chemical.
LIME MANUFACTURING AND LIME SLAKING PROCESS
Limestone or calcium carbonate (CaCO3) exists as a natural stone throughout the world. Limestone in its natural form is very slow reacting; therefore, it has a limited use. The most significant use of pulverized limestone is in agriculture in a finely ground and dry form or in flue gas desulphurization in slurry form. The use of lime in carbonate form is beyond the scope of this paper. We will concentrate on lime as calcium oxide and calcium hydroxide.
In most pollution control applications lime is used as calcium hydroxide. To manufacture calcium hydroxide the limestone calcium carbonate must be converted to calcium oxide and the calcium oxide then converted to calcium hydroxide.
THE equipment USED FOR THE SLAKING PROCESS
It is not the intent of this paper to evaluate the slaking equipment described below. The intent is to show the types of equipment available for slaking process. There are basically four types of lime slakers available on the market. They are:
A. Slurry Detention Slakers
B. Paste Slakers
C. ball mill Slakers
D. Batch Slakers
A slaker must mix the correct amount of quick lime (CaO) and water, hydrate the quicklime, and separate the impurities and grit from resultant calcium hydroxide slurry.