Drying research needs

The water content in the studied material is approximately 90%. For the present research work the black liquor were dried up to 100% content of solids. This drying stage needs to be gradual and carefully controlled in order to reach an homogeneous distribution of the inorganic compounds inside the solid matrix. After drying, the solids were ground, sieved under a particle size of 53 pm mesh and kept in a fiirnace at 105 C. 

Lab-, pilot-, and plant-scale experiments all play important roles in drying research. Lab-scale experiments are often necessary to study product characteristics and physical properties pilot-scale experiments are often used in proof-of-concept process tests and to generate larger quantities of sample material and plant-scale experiments are often needed to diagnose processing problems and to start or change a full-scale process. 

This study of methods to determine the moisture content of humic substances has yielded no absolute values for moisture content. The loss on drying shows no end point for water loss and the potential interferences of the Karl Fischer titration prevent definition of absolute values. Certainly, additional research needs to be done in this area. For example, techniques such as NMR and IR might be utilized to define and correlate the moisture status of these substances. In many cases it is sufficient to have a reference point to bring these substances to for comparison purposes. Based on Figure 1, loss on drying at 60°C should be the most consistent reference point, however, the interlaboratory study results showed very poor agreement. Based on this limited study we conclude that the Karl Fischer method gives more consistent results on these samples. 

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