Ultra-fine Milks of Lime

Two techniques are used commercially to produce ultra-fine milks of lime, namely slaking at high shear rates and milling conventional milks. 

Ultra-fine milks of lime may be produced by pumping a conventional milk of lime through the mill at a suitable rate. The milk may be recycled if a single pass does not give the required size reduction. 

The chemical reactivities of ultra-fine milks of lime can be measured using a con-ductimetric method [22.1]. A quantity of milk sufficient to give a concentration equivalent to (say) half of the saturation concentration is added, with stirring, to a standard volume of de-ionised water. The rate of increase in the conductivity of the resulting mix is a measure of the rate of solution of the milk of lime. 

Ultra-fine milks of lime can have solution rates, which are measured in seconds, and which are more than 10 times greater than those of standard milks of lime. 

The milk of lime should be grit-free and should have as high a surface area as is practicable. Traditionally this has been produced by slaking a low carbonate quicklime under conditions favouring the production of finely divided calcium hydroxide (see chapter 22). More recently, ultra-fine milks of lime (see section 22.8) have proved to be particularly effective lubricant carriers. 

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